CINXE.COM

<!DOCTYPE html> <html class="client-nojs vector-feature-language-in-header-enabled vector-feature-language-in-main-page-header-disabled vector-feature-sticky-header-disabled vector-feature-page-tools-pinned-disabled vector-feature-toc-pinned-clientpref-1 vector-feature-main-menu-pinned-disabled vector-feature-limited-width-clientpref-1 vector-feature-limited-width-content-enabled vector-feature-custom-font-size-clientpref-1 vector-feature-appearance-pinned-clientpref-1 vector-feature-night-mode-enabled skin-theme-clientpref-day vector-toc-available" lang="en" dir="ltr"> <head> <meta charset="UTF-8"> <title>Utility frequency - Wikipedia</title> <script>(function(){var className="client-js vector-feature-language-in-header-enabled vector-feature-language-in-main-page-header-disabled vector-feature-sticky-header-disabled vector-feature-page-tools-pinned-disabled vector-feature-toc-pinned-clientpref-1 vector-feature-main-menu-pinned-disabled vector-feature-limited-width-clientpref-1 vector-feature-limited-width-content-enabled vector-feature-custom-font-size-clientpref-1 vector-feature-appearance-pinned-clientpref-1 vector-feature-night-mode-enabled skin-theme-clientpref-day vector-toc-available";var cookie=document.cookie.match(/(?:^|; )enwikimwclientpreferences=([^;]+)/);if(cookie){cookie[1].split('%2C').forEach(function(pref){className=className.replace(new RegExp('(^| )'+pref.replace(/-clientpref-\w+$|[^\w-]+/g,'')+'-clientpref-\\w+( |$)'),'$1'+pref+'$2');});}document.documentElement.className=className;}());RLCONF={"wgBreakFrames":false,"wgSeparatorTransformTable":["",""],"wgDigitTransformTable":["",""],"wgDefaultDateFormat":"dmy", "wgMonthNames":["","January","February","March","April","May","June","July","August","September","October","November","December"],"wgRequestId":"968c0318-7cc5-45d3-8af4-3e28cbe6717e","wgCanonicalNamespace":"","wgCanonicalSpecialPageName":false,"wgNamespaceNumber":0,"wgPageName":"Utility_frequency","wgTitle":"Utility frequency","wgCurRevisionId":1252869788,"wgRevisionId":1252869788,"wgArticleId":488815,"wgIsArticle":true,"wgIsRedirect":false,"wgAction":"view","wgUserName":null,"wgUserGroups":["*"],"wgCategories":["CS1 Spanish-language sources (es)","Articles containing explicitly cited English-language text","CS1: long volume value","CS1 German-language sources (de)","Articles with short description","Short description is different from Wikidata","All articles with unsourced statements","Articles with unsourced statements from September 2017","All pages needing factual verification","Wikipedia articles needing factual verification from March 2017", "Articles with unsourced statements from April 2024","Electric power"],"wgPageViewLanguage":"en","wgPageContentLanguage":"en","wgPageContentModel":"wikitext","wgRelevantPageName":"Utility_frequency","wgRelevantArticleId":488815,"wgIsProbablyEditable":true,"wgRelevantPageIsProbablyEditable":true,"wgRestrictionEdit":[],"wgRestrictionMove":[],"wgNoticeProject":"wikipedia","wgCiteReferencePreviewsActive":false,"wgFlaggedRevsParams":{"tags":{"status":{"levels":1}}},"wgMediaViewerOnClick":true,"wgMediaViewerEnabledByDefault":true,"wgPopupsFlags":0,"wgVisualEditor":{"pageLanguageCode":"en","pageLanguageDir":"ltr","pageVariantFallbacks":"en"},"wgMFDisplayWikibaseDescriptions":{"search":true,"watchlist":true,"tagline":false,"nearby":true},"wgWMESchemaEditAttemptStepOversample":false,"wgWMEPageLength":50000,"wgRelatedArticlesCompat":[],"wgCentralAuthMobileDomain":false,"wgEditSubmitButtonLabelPublish":true,"wgULSPosition":"interlanguage","wgULSisCompactLinksEnabled":false, "wgVector2022LanguageInHeader":true,"wgULSisLanguageSelectorEmpty":false,"wgWikibaseItemId":"Q1361387","wgCheckUserClientHintsHeadersJsApi":["brands","architecture","bitness","fullVersionList","mobile","model","platform","platformVersion"],"GEHomepageSuggestedEditsEnableTopics":true,"wgGETopicsMatchModeEnabled":false,"wgGEStructuredTaskRejectionReasonTextInputEnabled":false,"wgGELevelingUpEnabledForUser":false};RLSTATE={"ext.globalCssJs.user.styles":"ready","site.styles":"ready","user.styles":"ready","ext.globalCssJs.user":"ready","user":"ready","user.options":"loading","ext.cite.styles":"ready","ext.math.styles":"ready","ext.tmh.player.styles":"ready","skins.vector.search.codex.styles":"ready","skins.vector.styles":"ready","skins.vector.icons":"ready","jquery.makeCollapsible.styles":"ready","ext.wikimediamessages.styles":"ready","ext.visualEditor.desktopArticleTarget.noscript":"ready","ext.uls.interlanguage":"ready","wikibase.client.init":"ready","ext.wikimediaBadges":"ready"}; RLPAGEMODULES=["ext.cite.ux-enhancements","mediawiki.page.media","ext.tmh.player","ext.scribunto.logs","site","mediawiki.page.ready","jquery.makeCollapsible","mediawiki.toc","skins.vector.js","ext.centralNotice.geoIP","ext.centralNotice.startUp","ext.gadget.ReferenceTooltips","ext.gadget.switcher","ext.urlShortener.toolbar","ext.centralauth.centralautologin","mmv.bootstrap","ext.popups","ext.visualEditor.desktopArticleTarget.init","ext.visualEditor.targetLoader","ext.echo.centralauth","ext.eventLogging","ext.wikimediaEvents","ext.navigationTiming","ext.uls.interface","ext.cx.eventlogging.campaigns","ext.cx.uls.quick.actions","wikibase.client.vector-2022","ext.checkUser.clientHints","ext.quicksurveys.init","ext.growthExperiments.SuggestedEditSession","wikibase.sidebar.tracking"];</script> <script>(RLQ=window.RLQ||[]).push(function(){mw.loader.impl(function(){return["user.options@12s5i",function($,jQuery,require,module){mw.user.tokens.set({"patrolToken":"+\\","watchToken":"+\\","csrfToken":"+\\"}); }];});});</script> <link rel="stylesheet" href="/w/load.php?lang=en&modules=ext.cite.styles%7Cext.math.styles%7Cext.tmh.player.styles%7Cext.uls.interlanguage%7Cext.visualEditor.desktopArticleTarget.noscript%7Cext.wikimediaBadges%7Cext.wikimediamessages.styles%7Cjquery.makeCollapsible.styles%7Cskins.vector.icons%2Cstyles%7Cskins.vector.search.codex.styles%7Cwikibase.client.init&only=styles&skin=vector-2022"> <script async="" src="/w/load.php?lang=en&modules=startup&only=scripts&raw=1&skin=vector-2022"></script> <meta name="ResourceLoaderDynamicStyles" content=""> <link rel="stylesheet" href="/w/load.php?lang=en&modules=site.styles&only=styles&skin=vector-2022"> <meta name="generator" content="MediaWiki 1.44.0-wmf.4"> <meta name="referrer" content="origin"> <meta name="referrer" content="origin-when-cross-origin"> <meta name="robots" content="max-image-preview:standard"> <meta name="format-detection" content="telephone=no"> <meta property="og:image" content="https://upload.wikimedia.org/wikipedia/commons/thumb/b/bf/50Hz60Hz.svg/1200px-50Hz60Hz.svg.png"> <meta property="og:image:width" content="1200"> <meta property="og:image:height" content="688"> <meta property="og:image" content="https://upload.wikimedia.org/wikipedia/commons/thumb/b/bf/50Hz60Hz.svg/800px-50Hz60Hz.svg.png"> <meta property="og:image:width" content="800"> <meta property="og:image:height" content="459"> <meta property="og:image" content="https://upload.wikimedia.org/wikipedia/commons/thumb/b/bf/50Hz60Hz.svg/640px-50Hz60Hz.svg.png"> <meta property="og:image:width" content="640"> <meta property="og:image:height" content="367"> <meta name="viewport" content="width=1120"> <meta property="og:title" content="Utility frequency - Wikipedia"> <meta property="og:type" content="website"> <link rel="preconnect" href="//upload.wikimedia.org"> <link rel="alternate" media="only screen and (max-width: 640px)" href="//en.m.wikipedia.org/wiki/Utility_frequency"> <link rel="alternate" type="application/x-wiki" title="Edit this page" href="/w/index.php?title=Utility_frequency&action=edit"> <link rel="apple-touch-icon" href="/static/apple-touch/wikipedia.png"> <link rel="icon" href="/static/favicon/wikipedia.ico"> <link rel="search" type="application/opensearchdescription+xml" href="/w/rest.php/v1/search" title="Wikipedia (en)"> <link rel="EditURI" type="application/rsd+xml" href="//en.wikipedia.org/w/api.php?action=rsd"> <link rel="canonical" href="https://en.wikipedia.org/wiki/Utility_frequency"> <link rel="license" href="https://creativecommons.org/licenses/by-sa/4.0/deed.en"> <link rel="alternate" type="application/atom+xml" title="Wikipedia Atom feed" href="/w/index.php?title=Special:RecentChanges&feed=atom"> <link rel="dns-prefetch" href="//meta.wikimedia.org" /> <link rel="dns-prefetch" href="//login.wikimedia.org"> </head> <body class="skin--responsive skin-vector skin-vector-search-vue mediawiki ltr sitedir-ltr mw-hide-empty-elt ns-0 ns-subject mw-editable page-Utility_frequency rootpage-Utility_frequency skin-vector-2022 action-view"><a class="mw-jump-link" href="#bodyContent">Jump to content</a> <div class="vector-header-container"> <header class="vector-header mw-header"> <div class="vector-header-start"> <nav class="vector-main-menu-landmark" aria-label="Site"> <div id="vector-main-menu-dropdown" class="vector-dropdown vector-main-menu-dropdown vector-button-flush-left vector-button-flush-right" > <input type="checkbox" id="vector-main-menu-dropdown-checkbox" role="button" aria-haspopup="true" data-event-name="ui.dropdown-vector-main-menu-dropdown" class="vector-dropdown-checkbox " aria-label="Main menu" > <label id="vector-main-menu-dropdown-label" for="vector-main-menu-dropdown-checkbox" class="vector-dropdown-label cdx-button cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--weight-quiet cdx-button--icon-only " aria-hidden="true" ><span class="vector-icon mw-ui-icon-menu mw-ui-icon-wikimedia-menu"></span> <span class="vector-dropdown-label-text">Main menu</span> </label> <div class="vector-dropdown-content"> <div id="vector-main-menu-unpinned-container" class="vector-unpinned-container"> <div id="vector-main-menu" class="vector-main-menu vector-pinnable-element"> <div class="vector-pinnable-header vector-main-menu-pinnable-header vector-pinnable-header-unpinned" data-feature-name="main-menu-pinned" data-pinnable-element-id="vector-main-menu" data-pinned-container-id="vector-main-menu-pinned-container" data-unpinned-container-id="vector-main-menu-unpinned-container" > <div class="vector-pinnable-header-label">Main menu</div> <button class="vector-pinnable-header-toggle-button vector-pinnable-header-pin-button" data-event-name="pinnable-header.vector-main-menu.pin">move to sidebar</button> <button class="vector-pinnable-header-toggle-button vector-pinnable-header-unpin-button" data-event-name="pinnable-header.vector-main-menu.unpin">hide</button> </div> <div id="p-navigation" class="vector-menu mw-portlet mw-portlet-navigation" > <div class="vector-menu-heading"> Navigation </div> <div class="vector-menu-content"> <ul class="vector-menu-content-list"> <li id="n-mainpage-description" class="mw-list-item"><a href="/wiki/Main_Page" title="Visit the main page [z]" accesskey="z"><span>Main page</span></a></li><li id="n-contents" class="mw-list-item"><a href="/wiki/Wikipedia:Contents" title="Guides to browsing Wikipedia"><span>Contents</span></a></li><li id="n-currentevents" class="mw-list-item"><a href="/wiki/Portal:Current_events" title="Articles related to current events"><span>Current events</span></a></li><li id="n-randompage" class="mw-list-item"><a href="/wiki/Special:Random" title="Visit a randomly selected article [x]" accesskey="x"><span>Random article</span></a></li><li id="n-aboutsite" class="mw-list-item"><a href="/wiki/Wikipedia:About" title="Learn about Wikipedia and how it works"><span>About Wikipedia</span></a></li><li id="n-contactpage" class="mw-list-item"><a href="//en.wikipedia.org/wiki/Wikipedia:Contact_us" title="How to contact Wikipedia"><span>Contact us</span></a></li> </ul> </div> </div> <div id="p-interaction" class="vector-menu mw-portlet mw-portlet-interaction" > <div class="vector-menu-heading"> Contribute </div> <div class="vector-menu-content"> <ul class="vector-menu-content-list"> <li id="n-help" class="mw-list-item"><a href="/wiki/Help:Contents" title="Guidance on how to use and edit Wikipedia"><span>Help</span></a></li><li id="n-introduction" class="mw-list-item"><a href="/wiki/Help:Introduction" title="Learn how to edit Wikipedia"><span>Learn to edit</span></a></li><li id="n-portal" class="mw-list-item"><a href="/wiki/Wikipedia:Community_portal" title="The hub for editors"><span>Community portal</span></a></li><li id="n-recentchanges" class="mw-list-item"><a href="/wiki/Special:RecentChanges" title="A list of recent changes to Wikipedia [r]" accesskey="r"><span>Recent changes</span></a></li><li id="n-upload" class="mw-list-item"><a href="/wiki/Wikipedia:File_upload_wizard" title="Add images or other media for use on Wikipedia"><span>Upload file</span></a></li> </ul> </div> </div> </div> </div> </div> </div> </nav> <a href="/wiki/Main_Page" class="mw-logo"> <img class="mw-logo-icon" src="/static/images/icons/wikipedia.png" alt="" aria-hidden="true" height="50" width="50"> <span class="mw-logo-container skin-invert"> <img class="mw-logo-wordmark" alt="Wikipedia" src="/static/images/mobile/copyright/wikipedia-wordmark-en.svg" style="width: 7.5em; height: 1.125em;"> <img class="mw-logo-tagline" alt="The Free Encyclopedia" src="/static/images/mobile/copyright/wikipedia-tagline-en.svg" width="117" height="13" style="width: 7.3125em; height: 0.8125em;"> </span> </a> </div> <div class="vector-header-end"> <div id="p-search" role="search" class="vector-search-box-vue vector-search-box-collapses vector-search-box-show-thumbnail vector-search-box-auto-expand-width vector-search-box"> <a href="/wiki/Special:Search" class="cdx-button cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--weight-quiet cdx-button--icon-only search-toggle" title="Search Wikipedia [f]" accesskey="f"><span class="vector-icon mw-ui-icon-search mw-ui-icon-wikimedia-search"></span> <span>Search</span> </a> <div class="vector-typeahead-search-container"> <div class="cdx-typeahead-search cdx-typeahead-search--show-thumbnail cdx-typeahead-search--auto-expand-width"> <form action="/w/index.php" id="searchform" class="cdx-search-input cdx-search-input--has-end-button"> <div id="simpleSearch" class="cdx-search-input__input-wrapper" data-search-loc="header-moved"> <div class="cdx-text-input cdx-text-input--has-start-icon"> <input class="cdx-text-input__input" type="search" name="search" placeholder="Search Wikipedia" aria-label="Search Wikipedia" autocapitalize="sentences" title="Search Wikipedia [f]" accesskey="f" id="searchInput" > <span class="cdx-text-input__icon cdx-text-input__start-icon"></span> </div> <input type="hidden" name="title" value="Special:Search"> </div> <button class="cdx-button cdx-search-input__end-button">Search</button> </form> </div> </div> </div> <nav class="vector-user-links vector-user-links-wide" aria-label="Personal tools"> <div class="vector-user-links-main"> <div id="p-vector-user-menu-preferences" class="vector-menu mw-portlet emptyPortlet" > <div class="vector-menu-content"> <ul class="vector-menu-content-list"> </ul> </div> </div> <div id="p-vector-user-menu-userpage" class="vector-menu mw-portlet emptyPortlet" > <div class="vector-menu-content"> <ul class="vector-menu-content-list"> </ul> </div> </div> <nav class="vector-appearance-landmark" aria-label="Appearance"> <div id="vector-appearance-dropdown" class="vector-dropdown " title="Change the appearance of the page's font size, width, and color" > <input type="checkbox" id="vector-appearance-dropdown-checkbox" role="button" aria-haspopup="true" data-event-name="ui.dropdown-vector-appearance-dropdown" class="vector-dropdown-checkbox " aria-label="Appearance" > <label id="vector-appearance-dropdown-label" for="vector-appearance-dropdown-checkbox" class="vector-dropdown-label cdx-button cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--weight-quiet cdx-button--icon-only " aria-hidden="true" ><span class="vector-icon mw-ui-icon-appearance mw-ui-icon-wikimedia-appearance"></span> <span class="vector-dropdown-label-text">Appearance</span> </label> <div class="vector-dropdown-content"> <div id="vector-appearance-unpinned-container" class="vector-unpinned-container"> </div> </div> </div> </nav> <div id="p-vector-user-menu-notifications" class="vector-menu mw-portlet emptyPortlet" > <div class="vector-menu-content"> <ul class="vector-menu-content-list"> </ul> </div> </div> <div id="p-vector-user-menu-overflow" class="vector-menu mw-portlet" > <div class="vector-menu-content"> <ul class="vector-menu-content-list"> <li id="pt-sitesupport-2" class="user-links-collapsible-item mw-list-item user-links-collapsible-item"><a data-mw="interface" href="https://donate.wikimedia.org/wiki/Special:FundraiserRedirector?utm_source=donate&utm_medium=sidebar&utm_campaign=C13_en.wikipedia.org&uselang=en" class=""><span>Donate</span></a> </li> <li id="pt-createaccount-2" class="user-links-collapsible-item mw-list-item user-links-collapsible-item"><a data-mw="interface" href="/w/index.php?title=Special:CreateAccount&returnto=Utility+frequency" title="You are encouraged to create an account and log in; however, it is not mandatory" class=""><span>Create account</span></a> </li> <li id="pt-login-2" class="user-links-collapsible-item mw-list-item user-links-collapsible-item"><a data-mw="interface" href="/w/index.php?title=Special:UserLogin&returnto=Utility+frequency" title="You're encouraged to log in; however, it's not mandatory. [o]" accesskey="o" class=""><span>Log in</span></a> </li> </ul> </div> </div> </div> <div id="vector-user-links-dropdown" class="vector-dropdown vector-user-menu vector-button-flush-right vector-user-menu-logged-out" title="Log in and more options" > <input type="checkbox" id="vector-user-links-dropdown-checkbox" role="button" aria-haspopup="true" data-event-name="ui.dropdown-vector-user-links-dropdown" class="vector-dropdown-checkbox " aria-label="Personal tools" > <label id="vector-user-links-dropdown-label" for="vector-user-links-dropdown-checkbox" class="vector-dropdown-label cdx-button cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--weight-quiet cdx-button--icon-only " aria-hidden="true" ><span class="vector-icon mw-ui-icon-ellipsis mw-ui-icon-wikimedia-ellipsis"></span> <span class="vector-dropdown-label-text">Personal tools</span> </label> <div class="vector-dropdown-content"> <div id="p-personal" class="vector-menu mw-portlet mw-portlet-personal user-links-collapsible-item" title="User menu" > <div class="vector-menu-content"> <ul class="vector-menu-content-list"> <li id="pt-sitesupport" class="user-links-collapsible-item mw-list-item"><a href="https://donate.wikimedia.org/wiki/Special:FundraiserRedirector?utm_source=donate&utm_medium=sidebar&utm_campaign=C13_en.wikipedia.org&uselang=en"><span>Donate</span></a></li><li id="pt-createaccount" class="user-links-collapsible-item mw-list-item"><a href="/w/index.php?title=Special:CreateAccount&returnto=Utility+frequency" title="You are encouraged to create an account and log in; however, it is not mandatory"><span class="vector-icon mw-ui-icon-userAdd mw-ui-icon-wikimedia-userAdd"></span> <span>Create account</span></a></li><li id="pt-login" class="user-links-collapsible-item mw-list-item"><a href="/w/index.php?title=Special:UserLogin&returnto=Utility+frequency" title="You're encouraged to log in; however, it's not mandatory. [o]" accesskey="o"><span class="vector-icon mw-ui-icon-logIn mw-ui-icon-wikimedia-logIn"></span> <span>Log in</span></a></li> </ul> </div> </div> <div id="p-user-menu-anon-editor" class="vector-menu mw-portlet mw-portlet-user-menu-anon-editor" > <div class="vector-menu-heading"> Pages for logged out editors <a href="/wiki/Help:Introduction" aria-label="Learn more about editing"><span>learn more</span></a> </div> <div class="vector-menu-content"> <ul class="vector-menu-content-list"> <li id="pt-anoncontribs" class="mw-list-item"><a href="/wiki/Special:MyContributions" title="A list of edits made from this IP address [y]" accesskey="y"><span>Contributions</span></a></li><li id="pt-anontalk" class="mw-list-item"><a href="/wiki/Special:MyTalk" title="Discussion about edits from this IP address [n]" accesskey="n"><span>Talk</span></a></li> </ul> </div> </div> </div> </div> </nav> </div> </header> </div> <div class="mw-page-container"> <div class="mw-page-container-inner"> <div class="vector-sitenotice-container"> <div id="siteNotice"></div> </div> <div class="vector-column-start"> <div class="vector-main-menu-container"> <div id="mw-navigation"> <nav id="mw-panel" class="vector-main-menu-landmark" aria-label="Site"> <div id="vector-main-menu-pinned-container" class="vector-pinned-container"> </div> </nav> </div> </div> <div class="vector-sticky-pinned-container"> <nav id="mw-panel-toc" aria-label="Contents" data-event-name="ui.sidebar-toc" class="mw-table-of-contents-container vector-toc-landmark"> <div id="vector-toc-pinned-container" class="vector-pinned-container"> <div id="vector-toc" class="vector-toc vector-pinnable-element"> <div class="vector-pinnable-header vector-toc-pinnable-header vector-pinnable-header-pinned" data-feature-name="toc-pinned" data-pinnable-element-id="vector-toc" > <h2 class="vector-pinnable-header-label">Contents</h2> <button class="vector-pinnable-header-toggle-button vector-pinnable-header-pin-button" data-event-name="pinnable-header.vector-toc.pin">move to sidebar</button> <button class="vector-pinnable-header-toggle-button vector-pinnable-header-unpin-button" data-event-name="pinnable-header.vector-toc.unpin">hide</button> </div> <ul class="vector-toc-contents" id="mw-panel-toc-list"> <li id="toc-mw-content-text" class="vector-toc-list-item vector-toc-level-1"> <a href="#" class="vector-toc-link"> <div class="vector-toc-text">(Top)</div> </a> </li> <li id="toc-Electric_clocks" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Electric_clocks"> <div class="vector-toc-text"> <span class="vector-toc-numb">1</span> <span>Electric clocks</span> </div> </a> <ul id="toc-Electric_clocks-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Operating_factors" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Operating_factors"> <div class="vector-toc-text"> <span class="vector-toc-numb">2</span> <span>Operating factors</span> </div> </a> <button aria-controls="toc-Operating_factors-sublist" class="cdx-button cdx-button--weight-quiet cdx-button--icon-only vector-toc-toggle"> <span class="vector-icon mw-ui-icon-wikimedia-expand"></span> <span>Toggle Operating factors subsection</span> </button> <ul id="toc-Operating_factors-sublist" class="vector-toc-list"> <li id="toc-Lighting" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Lighting"> <div class="vector-toc-text"> <span class="vector-toc-numb">2.1</span> <span>Lighting</span> </div> </a> <ul id="toc-Lighting-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Rotating_machines" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Rotating_machines"> <div class="vector-toc-text"> <span class="vector-toc-numb">2.2</span> <span>Rotating machines</span> </div> </a> <ul id="toc-Rotating_machines-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Transmission_and_transformers" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Transmission_and_transformers"> <div class="vector-toc-text"> <span class="vector-toc-numb">2.3</span> <span>Transmission and transformers</span> </div> </a> <ul id="toc-Transmission_and_transformers-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-System_interconnection" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#System_interconnection"> <div class="vector-toc-text"> <span class="vector-toc-numb">2.4</span> <span>System interconnection</span> </div> </a> <ul id="toc-System_interconnection-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-History" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#History"> <div class="vector-toc-text"> <span class="vector-toc-numb">3</span> <span>History</span> </div> </a> <button aria-controls="toc-History-sublist" class="cdx-button cdx-button--weight-quiet cdx-button--icon-only vector-toc-toggle"> <span class="vector-icon mw-ui-icon-wikimedia-expand"></span> <span>Toggle History subsection</span> </button> <ul id="toc-History-sublist" class="vector-toc-list"> <li id="toc-25_Hz_origins" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#25_Hz_origins"> <div class="vector-toc-text"> <span class="vector-toc-numb">3.1</span> <span>25 Hz origins</span> </div> </a> <ul id="toc-25_Hz_origins-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-40_Hz_origins" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#40_Hz_origins"> <div class="vector-toc-text"> <span class="vector-toc-numb">3.2</span> <span>40 Hz origins</span> </div> </a> <ul id="toc-40_Hz_origins-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Standardization" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Standardization"> <div class="vector-toc-text"> <span class="vector-toc-numb">3.3</span> <span>Standardization</span> </div> </a> <ul id="toc-Standardization-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-Railways" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Railways"> <div class="vector-toc-text"> <span class="vector-toc-numb">4</span> <span>Railways</span> </div> </a> <ul id="toc-Railways-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-400_Hz" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#400_Hz"> <div class="vector-toc-text"> <span class="vector-toc-numb">5</span> <span>400 Hz</span> </div> </a> <ul id="toc-400_Hz-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Stability" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Stability"> <div class="vector-toc-text"> <span class="vector-toc-numb">6</span> <span>Stability</span> </div> </a> <button aria-controls="toc-Stability-sublist" class="cdx-button cdx-button--weight-quiet cdx-button--icon-only vector-toc-toggle"> <span class="vector-icon mw-ui-icon-wikimedia-expand"></span> <span>Toggle Stability subsection</span> </button> <ul id="toc-Stability-sublist" class="vector-toc-list"> <li id="toc-Time_error_correction_(TEC)" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Time_error_correction_(TEC)"> <div class="vector-toc-text"> <span class="vector-toc-numb">6.1</span> <span>Time error correction (TEC)</span> </div> </a> <ul id="toc-Time_error_correction_(TEC)-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-US_regulations" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#US_regulations"> <div class="vector-toc-text"> <span class="vector-toc-numb">6.2</span> <span>US regulations</span> </div> </a> <ul id="toc-US_regulations-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Frequency_and_load" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Frequency_and_load"> <div class="vector-toc-text"> <span class="vector-toc-numb">6.3</span> <span>Frequency and load</span> </div> </a> <ul id="toc-Frequency_and_load-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Load-frequency_control" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Load-frequency_control"> <div class="vector-toc-text"> <span class="vector-toc-numb">6.4</span> <span>Load-frequency control</span> </div> </a> <ul id="toc-Load-frequency_control-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Rate_of_change_of_frequency" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Rate_of_change_of_frequency"> <div class="vector-toc-text"> <span class="vector-toc-numb">6.5</span> <span>Rate of change of frequency</span> </div> </a> <ul id="toc-Rate_of_change_of_frequency-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-Audible_noise_and_interference" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Audible_noise_and_interference"> <div class="vector-toc-text"> <span class="vector-toc-numb">7</span> <span>Audible noise and interference</span> </div> </a> <ul id="toc-Audible_noise_and_interference-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-See_also" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#See_also"> <div class="vector-toc-text"> <span class="vector-toc-numb">8</span> <span>See also</span> </div> </a> <ul id="toc-See_also-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Further_reading" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Further_reading"> <div class="vector-toc-text"> <span class="vector-toc-numb">9</span> <span>Further reading</span> </div> </a> <ul id="toc-Further_reading-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-References" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#References"> <div class="vector-toc-text"> <span class="vector-toc-numb">10</span> <span>References</span> </div> </a> <ul id="toc-References-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Sources" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Sources"> <div class="vector-toc-text"> <span class="vector-toc-numb">11</span> <span>Sources</span> </div> </a> <ul id="toc-Sources-sublist" class="vector-toc-list"> </ul> </li> </ul> </div> </div> </nav> </div> </div> <div class="mw-content-container"> <main id="content" class="mw-body"> <header class="mw-body-header vector-page-titlebar"> <nav aria-label="Contents" class="vector-toc-landmark"> <div id="vector-page-titlebar-toc" class="vector-dropdown vector-page-titlebar-toc vector-button-flush-left" > <input type="checkbox" id="vector-page-titlebar-toc-checkbox" role="button" aria-haspopup="true" data-event-name="ui.dropdown-vector-page-titlebar-toc" class="vector-dropdown-checkbox " aria-label="Toggle the table of contents" > <label id="vector-page-titlebar-toc-label" for="vector-page-titlebar-toc-checkbox" class="vector-dropdown-label cdx-button cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--weight-quiet cdx-button--icon-only " aria-hidden="true" ><span class="vector-icon mw-ui-icon-listBullet mw-ui-icon-wikimedia-listBullet"></span> <span class="vector-dropdown-label-text">Toggle the table of contents</span> </label> <div class="vector-dropdown-content"> <div id="vector-page-titlebar-toc-unpinned-container" class="vector-unpinned-container"> </div> </div> </div> </nav> <h1 id="firstHeading" class="firstHeading mw-first-heading"><span class="mw-page-title-main">Utility frequency</span></h1> <div id="p-lang-btn" class="vector-dropdown mw-portlet mw-portlet-lang" > <input type="checkbox" id="p-lang-btn-checkbox" role="button" aria-haspopup="true" data-event-name="ui.dropdown-p-lang-btn" class="vector-dropdown-checkbox mw-interlanguage-selector" aria-label="Go to an article in another language. Available in 12 languages" > <label id="p-lang-btn-label" for="p-lang-btn-checkbox" class="vector-dropdown-label cdx-button cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--weight-quiet cdx-button--action-progressive mw-portlet-lang-heading-12" aria-hidden="true" ><span class="vector-icon mw-ui-icon-language-progressive mw-ui-icon-wikimedia-language-progressive"></span> <span class="vector-dropdown-label-text">12 languages</span> </label> <div class="vector-dropdown-content"> <div class="vector-menu-content"> <ul class="vector-menu-content-list"> <li class="interlanguage-link interwiki-ca mw-list-item"><a href="https://ca.wikipedia.org/wiki/Freq%C3%BC%C3%A8ncia_de_xarxa" title="Freqüència de xarxa – Catalan" lang="ca" hreflang="ca" data-title="Freqüència de xarxa" data-language-autonym="Català" data-language-local-name="Catalan" class="interlanguage-link-target"><span>Català</span></a></li><li class="interlanguage-link interwiki-de mw-list-item"><a href="https://de.wikipedia.org/wiki/Netzfrequenz" title="Netzfrequenz – German" lang="de" hreflang="de" data-title="Netzfrequenz" data-language-autonym="Deutsch" data-language-local-name="German" class="interlanguage-link-target"><span>Deutsch</span></a></li><li class="interlanguage-link interwiki-et mw-list-item"><a href="https://et.wikipedia.org/wiki/V%C3%B5rgusagedus" title="Võrgusagedus – Estonian" lang="et" hreflang="et" data-title="Võrgusagedus" data-language-autonym="Eesti" data-language-local-name="Estonian" class="interlanguage-link-target"><span>Eesti</span></a></li><li class="interlanguage-link interwiki-es mw-list-item"><a href="https://es.wikipedia.org/wiki/Frecuencia_de_red" title="Frecuencia de red – Spanish" lang="es" hreflang="es" data-title="Frecuencia de red" data-language-autonym="Español" data-language-local-name="Spanish" class="interlanguage-link-target"><span>Español</span></a></li><li class="interlanguage-link interwiki-fa mw-list-item"><a href="https://fa.wikipedia.org/wiki/%D9%81%D8%B1%DA%A9%D8%A7%D9%86%D8%B3_%D8%B4%D8%A8%DA%A9%D9%87%E2%80%8C%D9%87%D8%A7%DB%8C_%D8%A8%D8%B1%D9%82" title="فرکانس شبکه‌های برق – Persian" lang="fa" hreflang="fa" data-title="فرکانس شبکه‌های برق" data-language-autonym="فارسی" data-language-local-name="Persian" class="interlanguage-link-target"><span>فارسی</span></a></li><li class="interlanguage-link interwiki-fr mw-list-item"><a href="https://fr.wikipedia.org/wiki/Fr%C3%A9quences_des_courants_industriels" title="Fréquences des courants industriels – French" lang="fr" hreflang="fr" data-title="Fréquences des courants industriels" data-language-autonym="Français" data-language-local-name="French" class="interlanguage-link-target"><span>Français</span></a></li><li class="interlanguage-link interwiki-ja mw-list-item"><a href="https://ja.wikipedia.org/wiki/%E5%95%86%E7%94%A8%E9%9B%BB%E6%BA%90%E5%91%A8%E6%B3%A2%E6%95%B0" title="商用電源周波数 – Japanese" lang="ja" hreflang="ja" data-title="商用電源周波数" data-language-autonym="日本語" data-language-local-name="Japanese" class="interlanguage-link-target"><span>日本語</span></a></li><li class="interlanguage-link interwiki-pl mw-list-item"><a href="https://pl.wikipedia.org/wiki/Cz%C4%99stotliwo%C5%9B%C4%87_napi%C4%99cia" title="Częstotliwość napięcia – Polish" lang="pl" hreflang="pl" data-title="Częstotliwość napięcia" data-language-autonym="Polski" data-language-local-name="Polish" class="interlanguage-link-target"><span>Polski</span></a></li><li class="interlanguage-link interwiki-pt mw-list-item"><a href="https://pt.wikipedia.org/wiki/Frequ%C3%AAncia_el%C3%A9trica" title="Frequência elétrica – Portuguese" lang="pt" hreflang="pt" data-title="Frequência elétrica" data-language-autonym="Português" data-language-local-name="Portuguese" class="interlanguage-link-target"><span>Português</span></a></li><li class="interlanguage-link interwiki-simple mw-list-item"><a href="https://simple.wikipedia.org/wiki/Utility_frequency" title="Utility frequency – Simple English" lang="en-simple" hreflang="en-simple" data-title="Utility frequency" data-language-autonym="Simple English" data-language-local-name="Simple English" class="interlanguage-link-target"><span>Simple English</span></a></li><li class="interlanguage-link interwiki-uk mw-list-item"><a href="https://uk.wikipedia.org/wiki/%D0%A7%D0%B0%D1%81%D1%82%D0%BE%D1%82%D0%B0_%D0%B7%D0%BC%D1%96%D0%BD%D0%BD%D0%BE%D0%B3%D0%BE_%D1%81%D1%82%D1%80%D1%83%D0%BC%D1%83" title="Частота змінного струму – Ukrainian" lang="uk" hreflang="uk" data-title="Частота змінного струму" data-language-autonym="Українська" data-language-local-name="Ukrainian" class="interlanguage-link-target"><span>Українська</span></a></li><li class="interlanguage-link interwiki-zh mw-list-item"><a href="https://zh.wikipedia.org/wiki/%E5%B7%A5%E9%A2%91" title="工频 – Chinese" lang="zh" hreflang="zh" data-title="工频" data-language-autonym="中文" data-language-local-name="Chinese" class="interlanguage-link-target"><span>中文</span></a></li> </ul> <div class="after-portlet after-portlet-lang"><span class="wb-langlinks-edit wb-langlinks-link"><a href="https://www.wikidata.org/wiki/Special:EntityPage/Q1361387#sitelinks-wikipedia" title="Edit interlanguage links" class="wbc-editpage">Edit links</a></span></div> </div> </div> </div> </header> <div class="vector-page-toolbar"> <div class="vector-page-toolbar-container"> <div id="left-navigation"> <nav aria-label="Namespaces"> <div id="p-associated-pages" class="vector-menu vector-menu-tabs mw-portlet mw-portlet-associated-pages" > <div class="vector-menu-content"> <ul class="vector-menu-content-list"> <li id="ca-nstab-main" class="selected vector-tab-noicon mw-list-item"><a href="/wiki/Utility_frequency" title="View the content page [c]" accesskey="c"><span>Article</span></a></li><li id="ca-talk" class="vector-tab-noicon mw-list-item"><a href="/wiki/Talk:Utility_frequency" rel="discussion" title="Discuss improvements to the content page [t]" accesskey="t"><span>Talk</span></a></li> </ul> </div> </div> <div id="vector-variants-dropdown" class="vector-dropdown emptyPortlet" > <input type="checkbox" id="vector-variants-dropdown-checkbox" role="button" aria-haspopup="true" data-event-name="ui.dropdown-vector-variants-dropdown" class="vector-dropdown-checkbox " aria-label="Change language variant" > <label id="vector-variants-dropdown-label" for="vector-variants-dropdown-checkbox" class="vector-dropdown-label cdx-button cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--weight-quiet" aria-hidden="true" ><span class="vector-dropdown-label-text">English</span> </label> <div class="vector-dropdown-content"> <div id="p-variants" class="vector-menu mw-portlet mw-portlet-variants emptyPortlet" > <div class="vector-menu-content"> <ul class="vector-menu-content-list"> </ul> </div> </div> </div> </div> </nav> </div> <div id="right-navigation" class="vector-collapsible"> <nav aria-label="Views"> <div id="p-views" class="vector-menu vector-menu-tabs mw-portlet mw-portlet-views" > <div class="vector-menu-content"> <ul class="vector-menu-content-list"> <li id="ca-view" class="selected vector-tab-noicon mw-list-item"><a href="/wiki/Utility_frequency"><span>Read</span></a></li><li id="ca-edit" class="vector-tab-noicon mw-list-item"><a href="/w/index.php?title=Utility_frequency&action=edit" title="Edit this page [e]" accesskey="e"><span>Edit</span></a></li><li id="ca-history" class="vector-tab-noicon mw-list-item"><a href="/w/index.php?title=Utility_frequency&action=history" title="Past revisions of this page [h]" accesskey="h"><span>View history</span></a></li> </ul> </div> </div> </nav> <nav class="vector-page-tools-landmark" aria-label="Page tools"> <div id="vector-page-tools-dropdown" class="vector-dropdown vector-page-tools-dropdown" > <input type="checkbox" id="vector-page-tools-dropdown-checkbox" role="button" aria-haspopup="true" data-event-name="ui.dropdown-vector-page-tools-dropdown" class="vector-dropdown-checkbox " aria-label="Tools" > <label id="vector-page-tools-dropdown-label" for="vector-page-tools-dropdown-checkbox" class="vector-dropdown-label cdx-button cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--weight-quiet" aria-hidden="true" ><span class="vector-dropdown-label-text">Tools</span> </label> <div class="vector-dropdown-content"> <div id="vector-page-tools-unpinned-container" class="vector-unpinned-container"> <div id="vector-page-tools" class="vector-page-tools vector-pinnable-element"> <div class="vector-pinnable-header vector-page-tools-pinnable-header vector-pinnable-header-unpinned" data-feature-name="page-tools-pinned" data-pinnable-element-id="vector-page-tools" data-pinned-container-id="vector-page-tools-pinned-container" data-unpinned-container-id="vector-page-tools-unpinned-container" > <div class="vector-pinnable-header-label">Tools</div> <button class="vector-pinnable-header-toggle-button vector-pinnable-header-pin-button" data-event-name="pinnable-header.vector-page-tools.pin">move to sidebar</button> <button class="vector-pinnable-header-toggle-button vector-pinnable-header-unpin-button" data-event-name="pinnable-header.vector-page-tools.unpin">hide</button> </div> <div id="p-cactions" class="vector-menu mw-portlet mw-portlet-cactions emptyPortlet vector-has-collapsible-items" title="More options" > <div class="vector-menu-heading"> Actions </div> <div class="vector-menu-content"> <ul class="vector-menu-content-list"> <li id="ca-more-view" class="selected vector-more-collapsible-item mw-list-item"><a href="/wiki/Utility_frequency"><span>Read</span></a></li><li id="ca-more-edit" class="vector-more-collapsible-item mw-list-item"><a href="/w/index.php?title=Utility_frequency&action=edit" title="Edit this page [e]" accesskey="e"><span>Edit</span></a></li><li id="ca-more-history" class="vector-more-collapsible-item mw-list-item"><a href="/w/index.php?title=Utility_frequency&action=history"><span>View history</span></a></li> </ul> </div> </div> <div id="p-tb" class="vector-menu mw-portlet mw-portlet-tb" > <div class="vector-menu-heading"> General </div> <div class="vector-menu-content"> <ul class="vector-menu-content-list"> <li id="t-whatlinkshere" class="mw-list-item"><a href="/wiki/Special:WhatLinksHere/Utility_frequency" title="List of all English Wikipedia pages containing links to this page [j]" accesskey="j"><span>What links here</span></a></li><li id="t-recentchangeslinked" class="mw-list-item"><a href="/wiki/Special:RecentChangesLinked/Utility_frequency" rel="nofollow" title="Recent changes in pages linked from this page [k]" accesskey="k"><span>Related changes</span></a></li><li id="t-upload" class="mw-list-item"><a href="/wiki/Wikipedia:File_Upload_Wizard" title="Upload files [u]" accesskey="u"><span>Upload file</span></a></li><li id="t-specialpages" class="mw-list-item"><a href="/wiki/Special:SpecialPages" title="A list of all special pages [q]" accesskey="q"><span>Special pages</span></a></li><li id="t-permalink" class="mw-list-item"><a href="/w/index.php?title=Utility_frequency&oldid=1252869788" title="Permanent link to this revision of this page"><span>Permanent link</span></a></li><li id="t-info" class="mw-list-item"><a href="/w/index.php?title=Utility_frequency&action=info" title="More information about this page"><span>Page information</span></a></li><li id="t-cite" class="mw-list-item"><a href="/w/index.php?title=Special:CiteThisPage&page=Utility_frequency&id=1252869788&wpFormIdentifier=titleform" title="Information on how to cite this page"><span>Cite this page</span></a></li><li id="t-urlshortener" class="mw-list-item"><a href="/w/index.php?title=Special:UrlShortener&url=https%3A%2F%2Fen.wikipedia.org%2Fwiki%2FUtility_frequency"><span>Get shortened URL</span></a></li><li id="t-urlshortener-qrcode" class="mw-list-item"><a href="/w/index.php?title=Special:QrCode&url=https%3A%2F%2Fen.wikipedia.org%2Fwiki%2FUtility_frequency"><span>Download QR code</span></a></li> </ul> </div> </div> <div id="p-coll-print_export" class="vector-menu mw-portlet mw-portlet-coll-print_export" > <div class="vector-menu-heading"> Print/export </div> <div class="vector-menu-content"> <ul class="vector-menu-content-list"> <li id="coll-download-as-rl" class="mw-list-item"><a href="/w/index.php?title=Special:DownloadAsPdf&page=Utility_frequency&action=show-download-screen" title="Download this page as a PDF file"><span>Download as PDF</span></a></li><li id="t-print" class="mw-list-item"><a href="/w/index.php?title=Utility_frequency&printable=yes" title="Printable version of this page [p]" accesskey="p"><span>Printable version</span></a></li> </ul> </div> </div> <div id="p-wikibase-otherprojects" class="vector-menu mw-portlet mw-portlet-wikibase-otherprojects" > <div class="vector-menu-heading"> In other projects </div> <div class="vector-menu-content"> <ul class="vector-menu-content-list"> <li id="t-wikibase" class="wb-otherproject-link wb-otherproject-wikibase-dataitem mw-list-item"><a href="https://www.wikidata.org/wiki/Special:EntityPage/Q1361387" title="Structured data on this page hosted by Wikidata [g]" accesskey="g"><span>Wikidata item</span></a></li> </ul> </div> </div> </div> </div> </div> </div> </nav> </div> </div> </div> <div class="vector-column-end"> <div class="vector-sticky-pinned-container"> <nav class="vector-page-tools-landmark" aria-label="Page tools"> <div id="vector-page-tools-pinned-container" class="vector-pinned-container"> </div> </nav> <nav class="vector-appearance-landmark" aria-label="Appearance"> <div id="vector-appearance-pinned-container" class="vector-pinned-container"> <div id="vector-appearance" class="vector-appearance vector-pinnable-element"> <div class="vector-pinnable-header vector-appearance-pinnable-header vector-pinnable-header-pinned" data-feature-name="appearance-pinned" data-pinnable-element-id="vector-appearance" data-pinned-container-id="vector-appearance-pinned-container" data-unpinned-container-id="vector-appearance-unpinned-container" > <div class="vector-pinnable-header-label">Appearance</div> <button class="vector-pinnable-header-toggle-button vector-pinnable-header-pin-button" data-event-name="pinnable-header.vector-appearance.pin">move to sidebar</button> <button class="vector-pinnable-header-toggle-button vector-pinnable-header-unpin-button" data-event-name="pinnable-header.vector-appearance.unpin">hide</button> </div> </div> </div> </nav> </div> </div> <div id="bodyContent" class="vector-body" aria-labelledby="firstHeading" data-mw-ve-target-container> <div class="vector-body-before-content"> <div class="mw-indicators"> </div> <div id="siteSub" class="noprint">From Wikipedia, the free encyclopedia</div> </div> <div id="contentSub"><div id="mw-content-subtitle"></div></div> <div id="mw-content-text" class="mw-body-content"><div class="mw-content-ltr mw-parser-output" lang="en" dir="ltr"><div class="shortdescription nomobile noexcerpt noprint searchaux" style="display:none">Frequency used on standard electricity grid in a given area</div> <style data-mw-deduplicate="TemplateStyles:r1236090951">.mw-parser-output .hatnote{font-style:italic}.mw-parser-output div.hatnote{padding-left:1.6em;margin-bottom:0.5em}.mw-parser-output .hatnote i{font-style:normal}.mw-parser-output .hatnote+link+.hatnote{margin-top:-0.5em}@media print{body.ns-0 .mw-parser-output .hatnote{display:none!important}}</style><div role="note" class="hatnote navigation-not-searchable">"60 cycles" redirects here. For the 1965 Canadian film, see <a href="/wiki/60_Cycles" title="60 Cycles">60 Cycles</a>.</div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"><div role="note" class="hatnote navigation-not-searchable">"ROCOF" redirects here. For the rate of occurrence of failures, see <a href="/wiki/Failure_rate" title="Failure rate">Failure rate</a>.</div> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:50Hz60Hz.svg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/b/bf/50Hz60Hz.svg/290px-50Hz60Hz.svg.png" decoding="async" width="290" height="166" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/b/bf/50Hz60Hz.svg/435px-50Hz60Hz.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/b/bf/50Hz60Hz.svg/580px-50Hz60Hz.svg.png 2x" data-file-width="750" data-file-height="430" /></a><figcaption>The waveform of 230 V and 50 Hz compared with 120 V and 60 Hz</figcaption></figure> <p>The <b>utility frequency</b>, <b>(power) line frequency</b> (<a href="/wiki/American_English" title="American English">American English</a>) or <b>mains frequency</b> (<a href="/wiki/British_English" title="British English">British English</a>) is the nominal <a href="/wiki/Frequency" title="Frequency">frequency</a> of the oscillations of <a href="/wiki/Alternating_current" title="Alternating current">alternating current</a> (AC) in a <a href="/wiki/Wide_area_synchronous_grid" title="Wide area synchronous grid">wide area synchronous grid</a> transmitted from a <a href="/wiki/Power_station" title="Power station">power station</a> to the <a href="/wiki/End-user" class="mw-redirect" title="End-user">end-user</a>. In large parts of the world this is 50 <a href="/wiki/Hertz" title="Hertz">Hz</a>, although in the <a href="/wiki/Americas" title="Americas">Americas</a> and parts of <a href="/wiki/Asia" title="Asia">Asia</a> it is typically 60 Hz. Current usage by country or region is given in the list of <a href="/wiki/Mains_electricity_by_country" title="Mains electricity by country">mains electricity by country</a>. </p><p>During the development of commercial electric power systems in the late-19th and early-20th centuries, many different frequencies (and voltages) had been used. Large investment in equipment at one frequency made standardization a slow process. However, as of the turn of the 21st century, places that now use the 50 Hz frequency tend to use 220–240 <a href="/wiki/Voltage" title="Voltage">V</a>, and those that now use 60 Hz tend to use 100–127 V. Both frequencies coexist today (Japan uses both) with no great technical reason to prefer one over the other<sup id="cite_ref-1" class="reference"><a href="#cite_note-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup> and no apparent desire for complete worldwide standardization. </p> <meta property="mw:PageProp/toc" /> <div class="mw-heading mw-heading2"><h2 id="Electric_clocks">Electric clocks</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Utility_frequency&action=edit&section=1" title="Edit section: Electric clocks"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"><div role="note" class="hatnote navigation-not-searchable">Main article: <a href="/wiki/Time_error_correction_(TEC)" class="mw-redirect" title="Time error correction (TEC)">Time error correction (TEC)</a></div> <p>In practice, the exact frequency of the grid varies around the nominal frequency, reducing when the grid is heavily loaded, and speeding up when lightly loaded. However, most utilities will adjust generation onto the grid over the course of the day to ensure a constant number of cycles occur.<sup id="cite_ref-2" class="reference"><a href="#cite_note-2"><span class="cite-bracket">[</span>2<span class="cite-bracket">]</span></a></sup> This is used by some clocks to accurately maintain their time. </p> <div class="mw-heading mw-heading2"><h2 id="Operating_factors">Operating factors</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Utility_frequency&action=edit&section=2" title="Edit section: Operating factors"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Several factors influence the choice of frequency in an AC system.<sup id="cite_ref-LAMME18_3-0" class="reference"><a href="#cite_note-LAMME18-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup> Lighting, motors, transformers, generators, and transmission lines all have characteristics which depend on the power frequency. All of these factors interact and make selection of a power frequency a matter of considerable importance. The best frequency is a compromise among competing requirements. </p><p>In the late 19th century, designers would pick a relatively high frequency for systems featuring <a href="/wiki/Transformer" title="Transformer">transformers</a> and <a href="/wiki/Arc_lamp" title="Arc lamp">arc lights</a>, so as to economize on transformer materials and to reduce visible flickering of the lamps, but would pick a lower frequency for systems with long transmission lines or feeding primarily motor loads or <a href="/wiki/Rotary_converter" title="Rotary converter">rotary converters</a> for producing <a href="/wiki/Direct_current" title="Direct current">direct current</a>. When large central generating stations became practical, the choice of frequency was made based on the nature of the intended load. Eventually improvements in machine design allowed a single frequency to be used both for lighting and motor loads. A unified system improved the economics of electricity production, since system load was more uniform during the course of a day. </p> <div class="mw-heading mw-heading3"><h3 id="Lighting">Lighting</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Utility_frequency&action=edit&section=3" title="Edit section: Lighting"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>The first applications of commercial electric power were <a href="/wiki/Incandescent_light_bulb" title="Incandescent light bulb">incandescent lighting</a> and <a href="/wiki/Commutator_(electric)" title="Commutator (electric)">commutator</a>-type <a href="/wiki/Electric_motor" title="Electric motor">electric motors</a>. Both devices operate well on DC, but DC could not be easily changed in voltage, and was generally only produced at the required utilization voltage. </p><p>If an incandescent lamp is operated on a low-frequency current, the filament cools on each half-cycle of the alternating current, leading to perceptible change in brightness and <i>flicker</i> of the lamps; the effect is more pronounced with <a href="/wiki/Arc_lamp" title="Arc lamp">arc lamps</a>, and the later <a href="/wiki/Mercury-vapor_lamp" title="Mercury-vapor lamp">mercury-vapor lamps</a> and <a href="/wiki/Fluorescent_lamp" title="Fluorescent lamp">fluorescent lamps</a>. Open arc lamps made an audible buzz on alternating current, leading to experiments with high-frequency alternators to raise the sound above the range of human hearing.<sup class="noprint Inline-Template Template-Fact" style="white-space:nowrap;">[<i><a href="/wiki/Wikipedia:Citation_needed" title="Wikipedia:Citation needed"><span title="This claim needs references to reliable sources. (September 2017)">citation needed</span></a></i>]</sup> </p> <div class="mw-heading mw-heading3"><h3 id="Rotating_machines">Rotating machines</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Utility_frequency&action=edit&section=4" title="Edit section: Rotating machines"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p><a href="/wiki/Commutator_(electric)" title="Commutator (electric)">Commutator</a>-type motors do not operate well on high-frequency AC, because the rapid changes of current are opposed by the <a href="/wiki/Inductance" title="Inductance">inductance</a> of the motor field. Though commutator-type <a href="/wiki/Electric_motor#Universal_AC/DC_motor" title="Electric motor"><i>universal</i></a> motors are common in AC household appliances and power tools, they are small motors, less than 1 kW. The <a href="/wiki/Induction_motor" title="Induction motor">induction motor</a> was found to work well on frequencies around 50 to 60 Hz, but with the materials available in the 1890s would not work well at a frequency of, say, 133 Hz. There is a fixed relationship between the number of magnetic poles in the induction motor field, the frequency of the alternating current, and the rotation speed; so, a given standard speed limits the choice of frequency (and the reverse). Once AC <a href="/wiki/Electric_motor" title="Electric motor">electric motors</a> became common, it was important to standardize frequency for compatibility with the customer's equipment. </p><p>Generators operated by slow-speed reciprocating engines will produce lower frequencies, for a given number of poles, than those operated by, for example, a high-speed steam <a href="/wiki/Turbine" title="Turbine">turbine</a>. For very slow prime mover speeds, it would be costly to build a generator with enough poles to provide a high AC frequency. As well, synchronizing two generators to the same speed was found to be easier at lower speeds. While belt drives were common as a way to increase speed of slow engines, in very large ratings (thousands of kilowatts) these were expensive, inefficient, and unreliable. After about 1906, generators driven directly by <a href="/wiki/Steam_turbine" title="Steam turbine">steam turbines</a> favored higher frequencies. The steadier rotation speed of high-speed machines allowed for satisfactory operation of <a href="/wiki/Commutator_(electric)" title="Commutator (electric)">commutators</a> in rotary converters.<sup id="cite_ref-LAMME18_3-1" class="reference"><a href="#cite_note-LAMME18-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup> The synchronous speed N in RPM is calculated using the formula, </p> <dl><dd><span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle N={\frac {120f}{P}}\,}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mi>N</mi> <mo>=</mo> <mrow class="MJX-TeXAtom-ORD"> <mfrac> <mrow> <mn>120</mn> <mi>f</mi> </mrow> <mi>P</mi> </mfrac> </mrow> <mspace width="thinmathspace" /> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle N={\frac {120f}{P}}\,}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/445d3e441661c67ba57ebbe60c341e8003527f5f" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -1.838ex; width:11.151ex; height:5.343ex;" alt="{\displaystyle N={\frac {120f}{P}}\,}"></span></dd></dl> <p>where f is the frequency in <a href="/wiki/Hertz" title="Hertz">hertz</a> and P is the number of poles. </p> <table class="wikitable"> <caption>Synchronous speeds of AC motors for some current and historical utility frequencies </caption> <tbody><tr> <th>Poles </th> <th>RPM at 133<style data-mw-deduplicate="TemplateStyles:r1154941027">.mw-parser-output .frac{white-space:nowrap}.mw-parser-output .frac .num,.mw-parser-output .frac .den{font-size:80%;line-height:0;vertical-align:super}.mw-parser-output .frac .den{vertical-align:sub}.mw-parser-output .sr-only{border:0;clip:rect(0,0,0,0);clip-path:polygon(0px 0px,0px 0px,0px 0px);height:1px;margin:-1px;overflow:hidden;padding:0;position:absolute;width:1px}</style><span class="frac"><span class="num">1</span>⁄<span class="den">3</span></span> Hz</th> <th>RPM at 60 Hz</th> <th>RPM at 50 Hz</th> <th>RPM at 40 Hz</th> <th>RPM at 25 Hz</th> <th>RPM at 16<link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1154941027"><span class="frac"><span class="num">2</span>⁄<span class="den">3</span></span> Hz </th></tr> <tr> <td>2</td> <td>8,000</td> <td>3,600</td> <td>3,000</td> <td>2,400</td> <td>1,500</td> <td>1,000 </td></tr> <tr> <td>4</td> <td>4,000</td> <td>1,800</td> <td>1,500</td> <td>1,200</td> <td>750</td> <td>500 </td></tr> <tr> <td>6</td> <td>2,666.7</td> <td>1,200</td> <td>1,000</td> <td>800</td> <td>500</td> <td>333.3 </td></tr> <tr> <td>8</td> <td>2,000</td> <td>900</td> <td>750</td> <td>600</td> <td>375</td> <td>250 </td></tr> <tr> <td>10</td> <td>1,600</td> <td>720</td> <td>600</td> <td>480</td> <td>300</td> <td>200 </td></tr> <tr> <td>12</td> <td>1,333.3</td> <td>600</td> <td>500</td> <td>400</td> <td>250</td> <td>166.7 </td></tr> <tr> <td>14</td> <td>1142.9</td> <td>514.3</td> <td>428.6</td> <td>342.8</td> <td>214.3</td> <td>142.9 </td></tr> <tr> <td>16</td> <td>1,000</td> <td>450</td> <td>375</td> <td>300</td> <td>187.5</td> <td>125 </td></tr> <tr> <td>18</td> <td>888.9</td> <td>400</td> <td>333<link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1154941027"><span class="frac"><span class="num">1</span>⁄<span class="den">3</span></span></td> <td>266<link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1154941027"><span class="frac"><span class="num">2</span>⁄<span class="den">3</span></span></td> <td>166<link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1154941027"><span class="frac"><span class="num">2</span>⁄<span class="den">3</span></span></td> <td>111.1 </td></tr> <tr> <td>20</td> <td>800</td> <td>360</td> <td>300</td> <td>240</td> <td>150</td> <td>100 </td></tr> </tbody></table> <p>Direct-current power was not entirely displaced by alternating current and was useful in railway and electrochemical processes. Prior to the development of <a href="/wiki/Mercury-arc_valve" title="Mercury-arc valve">mercury arc valve</a> <a href="/wiki/Rectifier" title="Rectifier">rectifiers</a>, rotary converters were used to produce DC power from AC. Like other commutator-type machines, these worked better with lower frequencies. </p> <div class="mw-heading mw-heading3"><h3 id="Transmission_and_transformers">Transmission and transformers</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Utility_frequency&action=edit&section=5" title="Edit section: Transmission and transformers"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>With AC, <a href="/wiki/Transformer" title="Transformer">transformers</a> can be used to step down high transmission voltages to lower customer utilization voltage. The transformer is effectively a voltage conversion device with no moving parts and requiring little maintenance. The use of AC eliminated the need for spinning DC voltage conversion motor-generators that require regular maintenance and monitoring. </p><p>Since, for a given power level, the dimensions of a transformer are roughly inversely proportional to frequency, a system with many transformers would be more economical at a higher frequency. </p><p><a href="/wiki/Electric_power_transmission" title="Electric power transmission">Electric power transmission</a> over long lines favors lower frequencies. The effects of the distributed capacitance and inductance of the line are less at low frequency. </p> <div class="mw-heading mw-heading3"><h3 id="System_interconnection">System interconnection</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Utility_frequency&action=edit&section=6" title="Edit section: System interconnection"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"><div role="note" class="hatnote navigation-not-searchable">Main article: <a href="/wiki/Synchronization_(alternating_current)" title="Synchronization (alternating current)">Synchronization (alternating current)</a></div> <p>Generators can only be interconnected to operate in parallel if they are of the same frequency and wave-shape. By standardizing the frequency used, generators in a geographic area can be interconnected in a <a href="/wiki/Power_transmission" title="Power transmission">grid</a>, providing reliability and cost savings. </p> <div class="mw-heading mw-heading2"><h2 id="History">History</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Utility_frequency&action=edit&section=7" title="Edit section: History"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"><div role="note" class="hatnote navigation-not-searchable">See also: <a href="/wiki/War_of_the_currents" title="War of the currents">War of the currents</a></div> <figure class="mw-default-size mw-halign-right" typeof="mw:File/Thumb"><a href="/wiki/File:Power_Grid_of_Japan.svg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/0/0c/Power_Grid_of_Japan.svg/220px-Power_Grid_of_Japan.svg.png" decoding="async" width="220" height="231" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/0/0c/Power_Grid_of_Japan.svg/330px-Power_Grid_of_Japan.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/0/0c/Power_Grid_of_Japan.svg/440px-Power_Grid_of_Japan.svg.png 2x" data-file-width="2480" data-file-height="2600" /></a><figcaption>Japan's utility frequencies are <span class="nowrap">50 Hz</span> and <span class="nowrap">60 Hz</span></figcaption></figure> <p>Many different power frequencies were used in the 19th century.<sup id="cite_ref-4" class="reference"><a href="#cite_note-4"><span class="cite-bracket">[</span>4<span class="cite-bracket">]</span></a></sup> </p><p>Very early isolated AC generating schemes used arbitrary frequencies based on convenience for <a href="/wiki/Steam_engine" title="Steam engine">steam engine</a>, <a href="/wiki/Water_turbine" title="Water turbine">water turbine</a>, and <a href="/wiki/Electric_generator" title="Electric generator">electrical generator</a> design. Frequencies between <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1154941027"><span class="frac">16<span class="sr-only">+</span><span class="num">2</span>⁄<span class="den">3</span></span> Hz and <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1154941027"><span class="frac">133<span class="sr-only">+</span><span class="num">1</span>⁄<span class="den">3</span></span> Hz were used on different systems. For example, the city of Coventry, England, in 1895 had a unique 87 Hz single-phase distribution system that was in use until 1906.<sup id="cite_ref-5" class="reference"><a href="#cite_note-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup> The proliferation of frequencies grew out of the rapid development of electrical machines in the period 1880 through 1900. </p><p>In the early incandescent lighting period, single-phase AC was common and typical generators were 8-pole machines operated at 2,000 RPM, giving a frequency of 133 hertz. </p><p>Though many theories exist, and quite a few entertaining <a href="/wiki/Urban_legends_and_myths" class="mw-redirect" title="Urban legends and myths">urban legends</a>, there is little certitude in the details of the history of 60 Hz vs. 50 Hz. </p><p>The German company <a href="/wiki/AEG_(German_company)" title="AEG (German company)">AEG</a> (descended from a company founded by Edison in Germany) built the first German generating facility to run at 50 Hz. At the time, AEG had a virtual <a href="/wiki/Monopoly" title="Monopoly">monopoly</a> and their standard spread to the rest of Europe. After observing flicker of lamps operated by the 40 Hz power transmitted by the <a href="/wiki/International_Electrotechnical_Exhibition" title="International Electrotechnical Exhibition">Lauffen-Frankfurt link</a> in 1891, AEG raised their standard frequency to 50 Hz in 1891.<sup id="cite_ref-OWEN97_6-0" class="reference"><a href="#cite_note-OWEN97-6"><span class="cite-bracket">[</span>6<span class="cite-bracket">]</span></a></sup> </p><p><a href="/wiki/Westinghouse_Electric_Corporation" title="Westinghouse Electric Corporation">Westinghouse Electric</a> decided to standardize on a higher frequency to permit operation of both electric lighting and induction motors on the same generating system. Although 50 Hz was suitable for both, in 1890 Westinghouse considered that existing arc-lighting equipment operated slightly better on 60 Hz, and so that frequency was chosen.<sup id="cite_ref-OWEN97_6-1" class="reference"><a href="#cite_note-OWEN97-6"><span class="cite-bracket">[</span>6<span class="cite-bracket">]</span></a></sup> The operation of Tesla's induction motor, licensed by Westinghouse in 1888, required a lower frequency than the 133 Hz common for lighting systems at that time.<sup class="noprint Inline-Template" style="white-space:nowrap;">[<i><a href="/wiki/Wikipedia:Verifiability" title="Wikipedia:Verifiability"><span title="The material near this tag needs to be fact-checked with the cited source(s). (March 2017)">verification needed</span></a></i>]</sup> In 1893 General Electric Corporation, which was affiliated with AEG in Germany, built a generating project at <a href="/wiki/Mill_Creek_(San_Bernardino_County)" title="Mill Creek (San Bernardino County)">Mill Creek</a> to bring electricity to <a href="/wiki/Redlands,_California" title="Redlands, California">Redlands, California</a> using 50 Hz, but changed to 60 Hz a year later to maintain market share with the Westinghouse standard. </p> <div class="mw-heading mw-heading3"><h3 id="25_Hz_origins">25 Hz origins</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Utility_frequency&action=edit&section=8" title="Edit section: 25 Hz origins"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>The first generators at the <a href="/wiki/Adams_Power_Plant_Transformer_House" title="Adams Power Plant Transformer House">Niagara Falls project</a>, built by Westinghouse in 1895, were 25 Hz, because the turbine speed had already been set before <a href="/wiki/Alternating_current" title="Alternating current">alternating current</a> power transmission had been definitively selected. Westinghouse would have selected a low frequency of 30 Hz to drive motor loads, but the turbines for the project had already been specified at 250 RPM. The machines could have been made to deliver <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1154941027"><span class="frac">16<span class="sr-only">+</span><span class="num">2</span>⁄<span class="den">3</span></span> Hz power suitable for heavy commutator-type motors, but the Westinghouse company objected that this would be undesirable for lighting and suggested <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1154941027"><span class="frac">33<span class="sr-only">+</span><span class="num">1</span>⁄<span class="den">3</span></span> Hz. Eventually a compromise of 25 Hz, with 12-pole 250 RPM generators, was chosen.<sup id="cite_ref-LAMME18_3-2" class="reference"><a href="#cite_note-LAMME18-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup> Because the Niagara project was so influential on electric power systems design, 25 Hz prevailed as the North American standard for low-frequency AC. </p> <div class="mw-heading mw-heading3"><h3 id="40_Hz_origins">40 Hz origins</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Utility_frequency&action=edit&section=9" title="Edit section: 40 Hz origins"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>A <a href="/wiki/General_Electric" title="General Electric">General Electric</a> study concluded that 40 Hz would have been a good compromise between lighting, motor, and transmission needs, given the materials and equipment available in the first quarter of the 20th century. Several 40 Hz systems were built. The <a href="/wiki/International_Electrotechnical_Exhibition" title="International Electrotechnical Exhibition">Lauffen-Frankfurt demonstration</a> used 40 Hz to transmit power 175 km in 1891. A large interconnected 40 Hz network existed in north-east England (the <a href="/wiki/North_Eastern_Electric_Supply_Company" title="North Eastern Electric Supply Company">Newcastle-upon-Tyne Electric Supply Company</a>, NESCO) until the advent of the <a href="/wiki/National_Grid_(Great_Britain)" title="National Grid (Great Britain)">National Grid (UK)</a> in the late 1920s, and projects in Italy used 42 Hz.<sup id="cite_ref-7" class="reference"><a href="#cite_note-7"><span class="cite-bracket">[</span>7<span class="cite-bracket">]</span></a></sup> The oldest continuously operating commercial <a href="/wiki/Hydroelectricity" title="Hydroelectricity">hydroelectric</a> power station in the United States, <a href="/wiki/Mechanicville_Hydroelectric_Plant" title="Mechanicville Hydroelectric Plant">Mechanicville Hydroelectric Plant</a>, still produces electric power at 40 Hz and supplies power to the local 60 Hz transmission system through <a href="/wiki/Frequency_changer" title="Frequency changer">frequency changers</a>. Industrial plants and mines in North America and Australia sometimes were built with 40 Hz electrical systems which were maintained until too uneconomic to continue. Although frequencies near 40 Hz found much commercial use, these were bypassed by standardized frequencies of 25, 50 and 60 Hz preferred by higher volume equipment manufacturers. </p><p>The <a href="/wiki/Ganz_Works" title="Ganz Works">Ganz Company</a> of Hungary had standardized on 5000 alternations per minute (41<link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1154941027"><span class="frac"><span class="num">2</span>⁄<span class="den">3</span></span> Hz) for their products, so Ganz clients had 41<link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1154941027"><span class="frac"><span class="num">2</span>⁄<span class="den">3</span></span> Hz systems that in some cases ran for many years.<sup id="cite_ref-Neidhofer11_8-0" class="reference"><a href="#cite_note-Neidhofer11-8"><span class="cite-bracket">[</span>8<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading3"><h3 id="Standardization">Standardization</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Utility_frequency&action=edit&section=10" title="Edit section: Standardization"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>In the early days of electrification, so many frequencies were used that no single value prevailed (London in 1918 had ten different frequencies). As the 20th century continued, more power was produced at 60 Hz (North America) or 50 Hz (Europe and most of Asia). <a href="/wiki/Standardization" title="Standardization">Standardization</a> allowed international trade in electrical equipment. Much later, the use of standard frequencies allowed interconnection of power grids. It was not until after World War II – with the advent of affordable electrical consumer goods – that more uniform standards were enacted. </p><p>In the United Kingdom, a standard frequency of 50 Hz was declared as early as 1904, but significant development continued at other frequencies.<sup id="cite_ref-9" class="reference"><a href="#cite_note-9"><span class="cite-bracket">[</span>9<span class="cite-bracket">]</span></a></sup> The implementation of the <a href="/wiki/National_Grid_(Great_Britain)" title="National Grid (Great Britain)">National Grid</a> starting in 1926 compelled the standardization of frequencies among the many interconnected electrical service providers. The 50 Hz standard was completely established only after <a href="/wiki/World_War_II" title="World War II">World War II</a>. </p><p>By about 1900, European manufacturers had mostly standardized on 50 Hz for new installations. The German <a href="/wiki/VDE_e.V." title="VDE e.V.">Verband der Elektrotechnik</a> (VDE), in the first standard for electrical machines and transformers in 1902, recommended 25 Hz and 50 Hz as standard frequencies. VDE did not see much application of 25 Hz, and dropped it from the 1914 edition of the standard. Remnant installations at other frequencies persisted until well after the Second World War.<sup id="cite_ref-Neidhofer11_8-1" class="reference"><a href="#cite_note-Neidhofer11-8"><span class="cite-bracket">[</span>8<span class="cite-bracket">]</span></a></sup> </p><p>Because of the cost of conversion, some parts of the distribution system may continue to operate on original frequencies even after a new frequency is chosen. 25 Hz power was used in <a href="/wiki/Ontario" title="Ontario">Ontario</a>, <a href="/wiki/Quebec" title="Quebec">Quebec</a>, the northern United States, and for <a href="/wiki/Railway_electrification" title="Railway electrification">railway electrification</a>. In the 1950s, many 25 Hz systems, from the generators right through to household appliances, were converted and standardized. Until 2006, some 25 Hz generators were still in existence at the <a href="/wiki/Sir_Adam_Beck_Hydroelectric_Generating_Stations" title="Sir Adam Beck Hydroelectric Generating Stations">Sir Adam Beck 1</a> (these were retrofitted to 60 Hz) and the <a href="/wiki/Rankine_Generating_Station" title="Rankine Generating Station">Rankine generating stations</a> (until its 2006 closure) near <a href="/wiki/Niagara_Falls" title="Niagara Falls">Niagara Falls</a> to provide power for large industrial customers who did not want to replace existing equipment; and some 25 Hz motors and a 25 Hz power station exist in New Orleans for floodwater pumps.<sup id="cite_ref-10" class="reference"><a href="#cite_note-10"><span class="cite-bracket">[</span>10<span class="cite-bracket">]</span></a></sup> The <a href="/wiki/15_kV_AC_railway_electrification" title="15 kV AC railway electrification">15 kV AC</a> rail networks, used in <a href="/wiki/Germany" title="Germany">Germany</a>, <a href="/wiki/Austria" title="Austria">Austria</a>, <a href="/wiki/Switzerland" title="Switzerland">Switzerland</a>, <a href="/wiki/Sweden" title="Sweden">Sweden</a>, and <a href="/wiki/Norway" title="Norway">Norway</a>, still operate at <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1154941027"><span class="frac">16<span class="sr-only">+</span><span class="num">2</span>⁄<span class="den">3</span></span> Hz or 16.7 Hz. </p><p>In some cases, where most load was to be railway or motor loads, it was considered economic to generate power at 25 Hz and install <a href="/wiki/Rotary_converter" title="Rotary converter">rotary converters</a> for 60 Hz distribution.<sup id="cite_ref-11" class="reference"><a href="#cite_note-11"><span class="cite-bracket">[</span>11<span class="cite-bracket">]</span></a></sup> Converters for production of DC from alternating current were available in larger sizes and were more efficient at 25 Hz compared with 60 Hz. Remnant fragments of older systems may be tied to the standard frequency system via a rotary converter or <a href="/wiki/HVDC_converter_station" title="HVDC converter station">static inverter</a> frequency changer. These allow energy to be interchanged between two power networks at different frequencies, but the systems are large, costly, and waste some energy in operation. </p><p>Rotating-machine frequency changers used to convert between 25 Hz and 60 Hz systems were awkward to design; a 60 Hz machine with 24 poles would turn at the same speed as a 25 Hz machine with 10 poles, making the machines large, slow-speed, and expensive. A ratio of 60/30 would have simplified these designs, but the installed base at 25 Hz was too large to be economically opposed. </p><p>In the United States, <a href="/wiki/Southern_California_Edison" title="Southern California Edison">Southern California Edison</a> had standardized on 50 Hz.<sup id="cite_ref-12" class="reference"><a href="#cite_note-12"><span class="cite-bracket">[</span>12<span class="cite-bracket">]</span></a></sup> Much of Southern California operated on 50 Hz and did not completely change frequency of their generators and customer equipment to 60 Hz until around 1948. Some projects by the Au Sable Electric Company used 30 Hz at transmission voltages up to 110,000 volts in 1914.<sup id="cite_ref-13" class="reference"><a href="#cite_note-13"><span class="cite-bracket">[</span>13<span class="cite-bracket">]</span></a></sup> </p><p>Initially in Brazil, electric machinery were imported from Europe and United States, implying the country had both 50 Hz and 60 Hz standards according to each region. In 1938, the federal government made a law, <i>Decreto-Lei 852</i>, intended to bring the whole country under 50 Hz within eight years. The law did not work, and in the early 1960s it was decided that Brazil would be unified under 60 Hz standard, because most developed and industrialized areas used 60 Hz; and a new law <i>Lei 4.454</i> was declared in 1964. Brazil underwent a frequency conversion program to 60 Hz that was not completed until 1978.<sup id="cite_ref-14" class="reference"><a href="#cite_note-14"><span class="cite-bracket">[</span>14<span class="cite-bracket">]</span></a></sup> </p><p>In Mexico, areas operating on 50 Hz grid were converted during the 1970s, uniting the country under 60 Hz.<sup id="cite_ref-15" class="reference"><a href="#cite_note-15"><span class="cite-bracket">[</span>15<span class="cite-bracket">]</span></a></sup> </p><p>In Japan, the western part of the country (Nagoya and west) uses 60 Hz and the eastern part (Tokyo and east) uses 50 Hz. This originates in the first purchases of generators from AEG in 1895, installed for Tokyo, and General Electric in 1896, installed in Osaka. The boundary between the two regions contains four back-to-back <a href="/wiki/High-voltage_direct_current" title="High-voltage direct current">HVDC</a> substations which convert the frequency; these are <a href="/wiki/Shin-Shinano_Frequency_Converter" title="Shin-Shinano Frequency Converter">Shin Shinano</a>, <a href="/wiki/Sakuma_Dam#HVDC_Back-to-Back_Station" title="Sakuma Dam">Sakuma Dam</a>, <a href="/wiki/Minami-Fukumitsu_Frequency_Converter" title="Minami-Fukumitsu Frequency Converter">Minami-Fukumitsu</a>, and the <a href="/wiki/Higashi-Shimizu_Frequency_Converter" title="Higashi-Shimizu Frequency Converter">Higashi-Shimizu Frequency Converter</a>. </p><p><b>Utility frequencies in North America in 1897</b><sup id="cite_ref-16" class="reference"><a href="#cite_note-16"><span class="cite-bracket">[</span>16<span class="cite-bracket">]</span></a></sup> </p> <table class="wikitable"> <tbody><tr> <th>Hz</th> <th>Description </th></tr> <tr> <td>140</td> <td>Wood arc-lighting dynamo </td></tr> <tr> <td>133</td> <td>Stanley-Kelly Company </td></tr> <tr> <td>125</td> <td>General Electric single-phase </td></tr> <tr> <td>66.7</td> <td>Stanley-Kelly Company </td></tr> <tr> <td>62.5</td> <td>General Electric "<a href="/wiki/Three-phase_electric_power#Alternatives_to_three-phase" title="Three-phase electric power">monocyclic</a>" </td></tr> <tr> <td>60</td> <td>Many manufacturers, becoming "increasingly common" in 1897 </td></tr> <tr> <td>58.3</td> <td>General Electric Lachine Rapids </td></tr> <tr> <td>40</td> <td>General Electric </td></tr> <tr> <td>33</td> <td>General Electric at Portland Oregon for rotary converters </td></tr> <tr> <td>27</td> <td>Crocker-Wheeler for <a href="/wiki/Calcium_carbide" title="Calcium carbide">calcium carbide</a> furnaces </td></tr> <tr> <td>25</td> <td>Westinghouse Niagara Falls 2-phase—for operating motors </td></tr></tbody></table> <p><b>Utility frequencies in Europe to 1900</b><sup id="cite_ref-Neidhofer11_8-2" class="reference"><a href="#cite_note-Neidhofer11-8"><span class="cite-bracket">[</span>8<span class="cite-bracket">]</span></a></sup> </p> <table class="wikitable"> <tbody><tr> <th>Hz</th> <th>Description </th></tr> <tr> <td>133</td> <td>Single-phase lighting systems, UK and Europe </td></tr> <tr> <td>125</td> <td>Single-phase lighting system, UK and Europe </td></tr> <tr> <td>83.3</td> <td>Single phase, Ferranti UK, <a href="/wiki/Deptford_Power_Station" title="Deptford Power Station">Deptford Power Station</a>, London </td></tr> <tr> <td>70</td> <td>Single-phase lighting, Germany 1891 </td></tr> <tr> <td>65.3</td> <td><a href="/wiki/Brown,_Boveri_%26_Cie" title="Brown, Boveri & Cie">BBC</a> Bellinzona </td></tr> <tr> <td>60</td> <td>Single phase lighting, Germany, 1891, 1893 </td></tr> <tr> <td>50</td> <td>AEG, Oerlikon, and other manufacturers, eventual standard </td></tr> <tr> <td>48</td> <td><a href="/wiki/Brown,_Boveri_%26_Cie" title="Brown, Boveri & Cie">BBC</a> Kilwangen generating station, </td></tr> <tr> <td>46</td> <td>Rome, Geneva 1900 </td></tr> <tr> <td>45<link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1154941027"><span class="frac"><span class="num">1</span>⁄<span class="den">3</span></span></td> <td>Municipal power station, Frankfurt am Main, 1893 </td></tr> <tr> <td>42</td> <td>Ganz customers, also Germany 1898 </td></tr> <tr> <td>41<link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1154941027"><span class="frac"><span class="num">2</span>⁄<span class="den">3</span></span></td> <td>Ganz Company, Hungary </td></tr> <tr> <td>40</td> <td>Lauffen am Neckar, hydroelectric, 1891, to 1925 </td></tr> <tr> <td>38.6</td> <td><a href="/wiki/Brown,_Boveri_%26_Cie" title="Brown, Boveri & Cie">BBC</a> Arlen </td></tr> <tr> <td>33<link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1154941027"><span class="frac"><span class="num">1</span>⁄<span class="den">3</span></span></td> <td>St. James and Soho Electric Light Co. London </td></tr> <tr> <td>25</td> <td>Single phase lighting, Germany 1897 </td></tr></tbody></table> <p>Even by the middle of the 20th century, utility frequencies were still not entirely standardized at the now-common 50 Hz or 60 Hz. In 1946, a reference manual for designers of radio equipment<sup id="cite_ref-17" class="reference"><a href="#cite_note-17"><span class="cite-bracket">[</span>17<span class="cite-bracket">]</span></a></sup> listed the following now obsolete frequencies as in use. Many of these regions also had 50-cycle, 60-cycle, or direct current supplies. </p><p><b>Frequencies in use in 1946 (as well as 50 Hz and 60 Hz)</b> </p> <table class="wikitable"> <tbody><tr> <th>Hz</th> <th>Region </th></tr> <tr> <td>25</td> <td>Canada (Southern Ontario), Panama Canal Zone(*), France, Germany, Sweden, UK, China, Hawaii, India, Manchuria </td></tr> <tr> <td>33<link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1154941027"><span class="frac"><span class="num">1</span>⁄<span class="den">3</span></span></td> <td>Lots Road Power station, Chelsea, London (for London Underground and Trolley busses after conversion to DC) </td></tr> <tr> <td>40</td> <td>Jamaica, Belgium, Switzerland, UK, Federated Malay States, Egypt, Western Australia(*) </td></tr> <tr> <td>42</td> <td>Czechoslovakia, Hungary, Italy, Monaco(*), Portugal, Romania, Yugoslavia, Libya (Tripoli) </td></tr> <tr> <td>43</td> <td>Argentina </td></tr> <tr> <td>45</td> <td>Italy, Libya (Tripoli) </td></tr> <tr> <td>76</td> <td>Gibraltar(*) </td></tr> <tr> <td>100</td> <td>Malta(*), <a href="/wiki/East_Africa_Protectorate" title="East Africa Protectorate">British East Africa</a> </td></tr> </tbody></table> <p>Where regions are marked (*), this is the only utility frequency shown for that region. </p> <div class="mw-heading mw-heading2"><h2 id="Railways">Railways</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Utility_frequency&action=edit&section=11" title="Edit section: Railways"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"><div role="note" class="hatnote navigation-not-searchable">Main article: <a href="/wiki/List_of_railway_electrification_systems" title="List of railway electrification systems">List of railway electrification systems</a></div> <p>Other power frequencies are still used. Germany, Austria, Switzerland, Sweden, and Norway use <a href="/wiki/Traction_power_network" title="Traction power network">traction power networks</a> for railways, distributing single-phase AC at <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1154941027"><span class="frac">16<span class="sr-only">+</span><span class="num">2</span>⁄<span class="den">3</span></span> Hz or 16.7 Hz.<sup id="cite_ref-18" class="reference"><a href="#cite_note-18"><span class="cite-bracket">[</span>18<span class="cite-bracket">]</span></a></sup> A frequency of 25 Hz is used for the Austrian <a href="/wiki/Mariazell_Railway" title="Mariazell Railway">Mariazell Railway</a>, as well as <a href="/wiki/Amtrak%27s_25_Hz_traction_power_system" title="Amtrak's 25 Hz traction power system">Amtrak</a> and <a href="/wiki/SEPTA%27s_25_Hz_traction_power_system" title="SEPTA's 25 Hz traction power system">SEPTA</a>'s traction power systems in the United States. Other AC railway systems are energized at the local commercial power frequency, 50 Hz or 60 Hz. </p><p>Traction power may be derived from commercial power supplies by frequency converters, or in some cases may be produced by dedicated <a href="/wiki/Traction_powerstation" title="Traction powerstation">traction powerstations</a>. In the 19th century, frequencies as low as 8 Hz were contemplated for operation of electric railways with commutator motors.<sup id="cite_ref-LAMME18_3-3" class="reference"><a href="#cite_note-LAMME18-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup> Some outlets in trains carry the correct voltage, but using the original train network frequency like <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1154941027"><span class="frac">16<span class="sr-only">+</span><span class="num">2</span>⁄<span class="den">3</span></span> Hz or 16.7 Hz. </p> <div class="mw-heading mw-heading2"><h2 id="400_Hz">400 Hz</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Utility_frequency&action=edit&section=12" title="Edit section: 400 Hz"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Power frequencies as high as 400 Hz are used in aircraft, spacecraft, submarines, server rooms for <a href="/wiki/Power_supply_unit_(computer)" title="Power supply unit (computer)">computer power</a>,<sup id="cite_ref-19" class="reference"><a href="#cite_note-19"><span class="cite-bracket">[</span>19<span class="cite-bracket">]</span></a></sup> military equipment, and hand-held machine tools. Such high frequencies cannot be economically transmitted long distances; the increased frequency greatly increases series impedance due to the inductance of transmission lines, making power transmission difficult. Consequently, 400 Hz power systems are usually confined to a building or vehicle. </p><p><a href="/wiki/Transformer" title="Transformer">Transformers</a>, for example, can be made smaller because the magnetic core can be much smaller for the same power level. Induction motors turn at a speed proportional to frequency, so a high-frequency power supply allows more power to be obtained for the same motor volume and mass. Transformers and motors for 400 Hz are much smaller and lighter than at 50 or 60 Hz, which is an advantage in aircraft and ships. A United States military standard <a href="/wiki/MIL-STD-704" title="MIL-STD-704">MIL-STD-704</a> exists for aircraft use of 400 Hz power. </p> <div class="mw-heading mw-heading2"><h2 id="Stability">Stability</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Utility_frequency&action=edit&section=13" title="Edit section: Stability"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <div class="mw-heading mw-heading3"><h3 id="Time_error_correction_(TEC)"><span id="Time_error_correction_.28TEC.29"></span>Time error correction (TEC)</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Utility_frequency&action=edit&section=14" title="Edit section: Time error correction (TEC)"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p><span class="anchor" id="Long-term_stability_and_clock_synchronization"></span> </p> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:TEC_availability.png" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/7/7b/TEC_availability.png/220px-TEC_availability.png" decoding="async" width="220" height="108" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/7/7b/TEC_availability.png/330px-TEC_availability.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/7/7b/TEC_availability.png/440px-TEC_availability.png 2x" data-file-width="1175" data-file-height="579" /></a><figcaption>TEC availability</figcaption></figure> <p>Regulation of power system frequency for timekeeping accuracy was not commonplace until after 1916 with <a href="/wiki/Henry_E._Warren" title="Henry E. Warren">Henry Warren</a>'s invention of the <a href="/wiki/File:Warren_master_clock.png" title="File:Warren master clock.png">Warren Power Station Master Clock</a> and self-starting synchronous motor. <a href="/wiki/Nikola_Tesla" title="Nikola Tesla">Nikola Tesla</a> demonstrated the concept of clocks synchronized by line frequency at the <a href="/wiki/World%27s_Columbian_Exposition" title="World's Columbian Exposition">1893 Chicago Worlds fair</a>. The <a href="/wiki/Hammond_organ" title="Hammond organ">Hammond Organ</a> also depends on a synchronous AC clock motor to maintain the correct speed of its internal "tone wheel" generator, thus keeping all notes pitch-perfect. </p><p>Today, AC power network operators regulate the daily average frequency so that clocks stay within a few seconds of the correct time. In practice the nominal frequency is raised or lowered by a specific percentage to maintain synchronization. Over the course of a day, the average frequency is maintained at a nominal value within a few hundred parts per million.<sup id="cite_ref-20" class="reference"><a href="#cite_note-20"><span class="cite-bracket">[</span>20<span class="cite-bracket">]</span></a></sup> In the <a href="/wiki/Synchronous_grid_of_Continental_Europe" title="Synchronous grid of Continental Europe">synchronous grid of Continental Europe</a>, the deviation between network phase time and <a href="/wiki/Coordinated_Universal_Time" title="Coordinated Universal Time">UTC</a> (based on <a href="/wiki/International_Atomic_Time" title="International Atomic Time">International Atomic Time</a>) is calculated at 08:00 each day in a control center in <a href="/wiki/Switzerland" title="Switzerland">Switzerland</a>. The target frequency is then adjusted by up to ±0.01 Hz (±0.02%) from 50 Hz as needed, to ensure a long-term frequency average of exactly 50 Hz × 60 <a href="/wiki/Second" title="Second">s</a>/<a href="/wiki/Minute" title="Minute">min</a> × 60 min/<a href="/wiki/Hour" title="Hour">h</a> × 24 h/<a href="/wiki/Day" title="Day">d</a> = <span class="nowrap"><span data-sort-value="7006432000000000000♠"></span>4<span style="margin-left:.25em;">320</span><span style="margin-left:.25em;">000</span></span> cycles per day.<sup id="cite_ref-21" class="reference"><a href="#cite_note-21"><span class="cite-bracket">[</span>21<span class="cite-bracket">]</span></a></sup> In <a href="/wiki/North_American_Electric_Reliability_Corporation" title="North American Electric Reliability Corporation">North America</a>, whenever the error exceeds 10 seconds for the <a href="/wiki/Eastern_Interconnection" title="Eastern Interconnection">Eastern Interconnection</a>, 3 seconds for the <a href="/wiki/Texas_Interconnection" title="Texas Interconnection">Texas Interconnection</a>, or 2 seconds for the <a href="/wiki/Western_Interconnection" title="Western Interconnection">Western Interconnection</a>, a correction of ±0.02 Hz (0.033%) is applied. Time error corrections start and end either on the hour or on the half-hour.<sup id="cite_ref-22" class="reference"><a href="#cite_note-22"><span class="cite-bracket">[</span>22<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-23" class="reference"><a href="#cite_note-23"><span class="cite-bracket">[</span>23<span class="cite-bracket">]</span></a></sup> </p><p>Real-time frequency meters for power generation in the United Kingdom are available online – an official one for the National Grid, and an unofficial one maintained by Dynamic Demand.<sup id="cite_ref-24" class="reference"><a href="#cite_note-24"><span class="cite-bracket">[</span>24<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-25" class="reference"><a href="#cite_note-25"><span class="cite-bracket">[</span>25<span class="cite-bracket">]</span></a></sup> Real-time frequency data of the synchronous grid of Continental Europe is available on websites such as <span class="url"><a rel="nofollow" class="external text" href="https://www.mainsfrequency.com/">www<wbr />.mainsfrequency<wbr />.com</a></span>. The <a href="/wiki/FNET" title="FNET">Frequency Monitoring Network (FNET)</a> at the <a href="/wiki/University_of_Tennessee" title="University of Tennessee">University of Tennessee</a> measures the frequency of the interconnections within the North American power grid, as well as in several other parts of the world. These measurements are displayed on the FNET website.<sup id="cite_ref-26" class="reference"><a href="#cite_note-26"><span class="cite-bracket">[</span>26<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading3"><h3 id="US_regulations">US regulations</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Utility_frequency&action=edit&section=15" title="Edit section: US regulations"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>In the United States, the <a href="/wiki/Federal_Energy_Regulatory_Commission" title="Federal Energy Regulatory Commission">Federal Energy Regulatory Commission</a> made time error correction mandatory in 2009.<sup id="cite_ref-27" class="reference"><a href="#cite_note-27"><span class="cite-bracket">[</span>27<span class="cite-bracket">]</span></a></sup> In 2011, The <a href="/wiki/North_American_Electric_Reliability_Corporation" title="North American Electric Reliability Corporation">North American Electric Reliability Corporation</a> (NERC) discussed a proposed experiment that would relax frequency regulation requirements<sup id="cite_ref-28" class="reference"><a href="#cite_note-28"><span class="cite-bracket">[</span>28<span class="cite-bracket">]</span></a></sup> for electrical grids which would reduce the long-term accuracy of clocks and other devices that use the 60 Hz grid frequency as a time base.<sup id="cite_ref-29" class="reference"><a href="#cite_note-29"><span class="cite-bracket">[</span>29<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading3"><h3 id="Frequency_and_load">Frequency and load</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Utility_frequency&action=edit&section=16" title="Edit section: Frequency and load"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p><a href="/wiki/Wide-area_synchronous_grid" class="mw-redirect" title="Wide-area synchronous grid">Modern alternating-current grids</a> use precise frequency control as an <a href="/wiki/Out-of-band_data" title="Out-of-band data">out-of-band signal</a> to coordinate generators connected the network. The practice arose because the frequency of a mechanical <a href="/wiki/Electric_generator" title="Electric generator">generator</a> varies with the input <a href="/wiki/Force" title="Force">force</a> and output <a href="/wiki/Electrical_load" title="Electrical load">load</a> experienced. Excess load withdraws <a href="/wiki/Rotational_kinetic_energy" class="mw-redirect" title="Rotational kinetic energy">rotational energy</a> from the generator shaft, reducing the <a href="/wiki/Frequency" title="Frequency">frequency</a> of the generated current; excess force deposits rotational energy, increasing frequency. <a href="/wiki/Automatic_generation_control" title="Automatic generation control">Automatic generation control</a> (AGC) maintains scheduled frequency and interchange power flows by adjusting the generator <a href="/wiki/Governor_(machine)" class="mw-redirect" title="Governor (machine)">governor</a> to counteract frequency changes, typically within several <a href="/wiki/SI_prefixes" class="mw-redirect" title="SI prefixes">decaseconds</a>.<sup id="cite_ref-30" class="reference"><a href="#cite_note-30"><span class="cite-bracket">[</span>30<span class="cite-bracket">]</span></a></sup> </p><p><a href="/wiki/Flywheel" title="Flywheel">Flywheel</a> physics does not apply to <a href="/wiki/Inverter" class="mw-redirect" title="Inverter">inverter</a>-connected <a href="/wiki/Solar_farm" class="mw-redirect" title="Solar farm">solar farms</a> or other <a href="/wiki/Direct_current" title="Direct current">DC</a>-linked power supplies. However, such <a href="/wiki/Power_plant" class="mw-redirect" title="Power plant">power plants</a> or storage systems can be <a href="/wiki/Microprocessor_control" class="mw-redirect" title="Microprocessor control">programmed</a> to follow the frequency signal.<sup id="cite_ref-31" class="reference"><a href="#cite_note-31"><span class="cite-bracket">[</span>31<span class="cite-bracket">]</span></a></sup> Indeed, a 2017 trial for <a href="/wiki/CAISO" class="mw-redirect" title="CAISO">CAISO</a> discovered that solar plants could respond to the signal faster than traditional generators, because they did not need to <a href="/wiki/Angular_acceleration" title="Angular acceleration">accelerate a rotating</a> mass.<sup id="cite_ref-32" class="reference"><a href="#cite_note-32"><span class="cite-bracket">[</span>32<span class="cite-bracket">]</span></a></sup> </p><p>Small, temporary frequency changes are an unavoidable consequence of changing demand, but dramatic, rapid frequency shifts often signal that a distribution network is near capacity limits. Exceptional examples have occurred before major <a href="/wiki/Power_outage" title="Power outage">outages</a>. During a severe failure of generators or transmission lines, the ensuing load-generation imbalance will induce variation in local power system frequencies. Loss of an <a href="/wiki/Transmission_line" title="Transmission line">interconnection</a> causes system frequency to increase (due to excess generation) upstream of the loss, but may cause a collapse in frequency or <a href="/wiki/Voltage" title="Voltage">voltage</a> (due to excess load) downstream of the loss.<sup class="noprint Inline-Template Template-Fact" style="white-space:nowrap;">[<i><a href="/wiki/Wikipedia:Citation_needed" title="Wikipedia:Citation needed"><span title="This claim needs references to reliable sources. (April 2024)">citation needed</span></a></i>]</sup> Consequently many power system <a href="/wiki/Protective_relay" title="Protective relay">protective relays</a> automatically trigger on severe underfrequency (typically <span class="avoidwrap" style="display:inline-block;">0.5–2 Hz</span> too low, depending on the system's disturbance tolerance and the severity of protection measures). These initiate <a href="/wiki/Load_shedding" class="mw-redirect" title="Load shedding">load shedding</a> or <a href="/wiki/Circuit_breaker" title="Circuit breaker">trip</a> interconnection lines to <a href="/wiki/Islanding" title="Islanding">preserve the operation of at least part of the network</a>.<sup id="cite_ref-33" class="reference"><a href="#cite_note-33"><span class="cite-bracket">[</span>33<span class="cite-bracket">]</span></a></sup> </p><p>Smaller power systems, not extensively interconnected with many generators and loads, will not maintain frequency with the same degree of accuracy. Where system frequency is not tightly regulated during heavy load periods, system operators may allow system frequency to rise during periods of light load to maintain a daily average frequency of acceptable accuracy.<sup id="cite_ref-34" class="reference"><a href="#cite_note-34"><span class="cite-bracket">[</span>34<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-35" class="reference"><a href="#cite_note-35"><span class="cite-bracket">[</span>35<span class="cite-bracket">]</span></a></sup> Portable generators, not connected to a utility system, need not tightly regulate their frequency because typical loads are insensitive to small frequency deviations. </p> <div class="mw-heading mw-heading3"><h3 id="Load-frequency_control">Load-frequency control</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Utility_frequency&action=edit&section=17" title="Edit section: Load-frequency control"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Load-frequency control (LFC) is a type of <a href="/wiki/PID_controller#Integral_term" class="mw-redirect" title="PID controller">integral control</a> that restores the system frequency while respecting <a href="/wiki/Contract" title="Contract">contracts</a> for power provision or consumption to surrounding areas. The automatic generation scheme described in <a href="#Frequency_and_load">§ Frequency and load</a> establishes a <a href="/wiki/Damping" title="Damping">damping</a> that minimizes the magnitude of average frequency error, <span class="texhtml"><span style="text-decoration:overline;">Δ<i>f</i></span></span>, where <span class="texhtml mvar" style="font-style:italic;">f</span> is frequency, <span class="texhtml">Δ</span> refers to the difference between measured and desired values, and <a href="/wiki/Overline" title="Overline">overlines</a> indicate time averages. </p><p>LFC incorporates power transfer between different areas, known as "net <a href="/wiki/Balancing_authority" title="Balancing authority">tie-line</a> power", into the minimized quantity. For a particular <b>frequency bias</b> constant <span class="texhtml mvar" style="font-style:italic;">B</span>, the <span class="anchor" id="Area_control_error"></span><b>area control error</b> (ACE) associated with LFC at any moment in time is simply <span class="mwe-math-element"><span class="mwe-math-mathml-display mwe-math-mathml-a11y" style="display: none;"><math display="block" xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle \Delta (P_{T}-Bf){\text{,}}}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mi mathvariant="normal">Δ</mi> <mo stretchy="false">(</mo> <msub> <mi>P</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>T</mi> </mrow> </msub> <mo>−</mo> <mi>B</mi> <mi>f</mi> <mo stretchy="false">)</mo> <mrow class="MJX-TeXAtom-ORD"> <mtext>,</mtext> </mrow> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle \Delta (P_{T}-Bf){\text{,}}}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/db4248cec67c11e77b94950db4ba44c2bda6c126" class="mwe-math-fallback-image-display mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.838ex; width:13.157ex; height:2.843ex;" alt="{\displaystyle \Delta (P_{T}-Bf){\text{,}}}"></span> where <span class="texhtml"><i>P<sub>T</sub></i></span> refers to tie-line power.<sup id="cite_ref-36" class="reference"><a href="#cite_note-36"><span class="cite-bracket">[</span>36<span class="cite-bracket">]</span></a></sup> This instantaneous error is then <a href="/wiki/Numeric_integration" class="mw-redirect" title="Numeric integration">numerically integrated</a> to give the time <a href="/wiki/Average" title="Average">average</a>, and governors adjusted to counteract its value.<sup id="cite_ref-37" class="reference"><a href="#cite_note-37"><span class="cite-bracket">[</span>37<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-38" class="reference"><a href="#cite_note-38"><span class="cite-bracket">[</span>38<span class="cite-bracket">]</span></a></sup> The coefficient <span class="texhtml mvar" style="font-style:italic;">B</span> traditionally has a negative value, so that when the frequency is lower than the target, area power production should increase; its magnitude is usually <a href="/wiki/On_the_order_of" class="mw-redirect" title="On the order of">on the order of</a> <a href="/wiki/Megawatt" class="mw-redirect" title="Megawatt">MW</a>/<a href="/wiki/Decihertz" class="mw-redirect" title="Decihertz">dHz</a>.<sup id="cite_ref-FOOTNOTENERC202120_39-0" class="reference"><a href="#cite_note-FOOTNOTENERC202120-39"><span class="cite-bracket">[</span>39<span class="cite-bracket">]</span></a></sup> </p><p>Tie-line bias LFC was known since 1930s, but was rarely used until the <a href="/wiki/Post-war_period" class="mw-redirect" title="Post-war period">post-war period</a>. In the 1950s, <a href="/wiki/Nathan_Cohn" title="Nathan Cohn">Nathan Cohn</a> popularized the practice in a series of articles, arguing that load-frequency control minimized the adjustment necessary for changes in load.<sup id="cite_ref-FOOTNOTEBratton19714–5_40-0" class="reference"><a href="#cite_note-FOOTNOTEBratton19714–5-40"><span class="cite-bracket">[</span>40<span class="cite-bracket">]</span></a></sup> In particular, Cohn supposed that all regions of the grid shared a common <a href="/wiki/Linearization" title="Linearization">linear regime</a>, with location-invariant<sup id="cite_ref-41" class="reference"><a href="#cite_note-41"><span class="cite-bracket">[</span>41<span class="cite-bracket">]</span></a></sup> frequency change per additional loading (<span class="texhtml"><style data-mw-deduplicate="TemplateStyles:r1214402035">.mw-parser-output .sfrac{white-space:nowrap}.mw-parser-output .sfrac.tion,.mw-parser-output .sfrac .tion{display:inline-block;vertical-align:-0.5em;font-size:85%;text-align:center}.mw-parser-output .sfrac .num{display:block;line-height:1em;margin:0.0em 0.1em;border-bottom:1px solid}.mw-parser-output .sfrac .den{display:block;line-height:1em;margin:0.1em 0.1em}.mw-parser-output .sr-only{border:0;clip:rect(0,0,0,0);clip-path:polygon(0px 0px,0px 0px,0px 0px);height:1px;margin:-1px;overflow:hidden;padding:0;position:absolute;width:1px}</style><span class="sfrac">⁠<span class="tion"><span class="num">d<i>f</i></span><span class="sr-only">/</span><span class="den">d<i>L</i></span></span>⁠</span></span>). If the utility selected <span class="mwe-math-element"><span class="mwe-math-mathml-display mwe-math-mathml-a11y" style="display: none;"><math display="block" xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle B={\frac {1}{2}}{\frac {dL}{df}}{\text{,}}}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mi>B</mi> <mo>=</mo> <mrow class="MJX-TeXAtom-ORD"> <mfrac> <mn>1</mn> <mn>2</mn> </mfrac> </mrow> <mrow class="MJX-TeXAtom-ORD"> <mfrac> <mrow> <mi>d</mi> <mi>L</mi> </mrow> <mrow> <mi>d</mi> <mi>f</mi> </mrow> </mfrac> </mrow> <mrow class="MJX-TeXAtom-ORD"> <mtext>,</mtext> </mrow> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle B={\frac {1}{2}}{\frac {dL}{df}}{\text{,}}}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/aade126765c0c55af2b5c316a6c6c6923166ac56" class="mwe-math-fallback-image-display mw-invert skin-invert" aria-hidden="true" style="vertical-align: -2.338ex; width:11.143ex; height:5.843ex;" alt="{\displaystyle B={\frac {1}{2}}{\frac {dL}{df}}{\text{,}}}"></span> and one region experienced a temporary <a href="/wiki/Short_circuit" title="Short circuit">fault</a> or other generation-load mismatch, then adjacent generators would observe a decrease in frequency but a counterbalancing increase in outward tieline power flow, giving no ACE. They would thus make no governor adjustments in the (presumed) brief period before the failed region recovered.<sup id="cite_ref-FOOTNOTEBratton197148–49_42-0" class="reference"><a href="#cite_note-FOOTNOTEBratton197148–49-42"><span class="cite-bracket">[</span>42<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading3"><h3 id="Rate_of_change_of_frequency">Rate of change of frequency</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Utility_frequency&action=edit&section=18" title="Edit section: Rate of change of frequency"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Rate of change of frequency (also <b>RoCoF</b>) is simply a time <a href="/wiki/Derivative" title="Derivative">derivative</a> of the utility frequency (<span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle {df}/{dt}}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mrow class="MJX-TeXAtom-ORD"> <mi>d</mi> <mi>f</mi> </mrow> <mrow class="MJX-TeXAtom-ORD"> <mo>/</mo> </mrow> <mrow class="MJX-TeXAtom-ORD"> <mi>d</mi> <mi>t</mi> </mrow> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle {df}/{dt}}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/9bbda26c211e123ac071a5e9947da812b82e17d5" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.838ex; width:5.712ex; height:2.843ex;" alt="{\displaystyle {df}/{dt}}"></span>), usually measured in Hz per second, Hz/s. The importance of this parameter increases when the traditional <a href="/wiki/Alternator" title="Alternator">synchronous generators</a> are replaced by the <a href="/wiki/Variable_renewable_energy" title="Variable renewable energy">variable renewable energy</a> (VRE) <a href="/wiki/Inverter-based_resource" title="Inverter-based resource">inverter-based resources</a> (IBR). The design of a synchronous generator inherently provides the <a href="/wiki/Inertial_response" title="Inertial response">inertial response</a> that limits the RoCoF. Since the IBRs are not electromechanically coupled into the power grid, a system with high VRE penetration might exhibit large RoCoF values that can cause problems with the operation of the system due to stress placed onto the remaining synchronous generators, triggering of the protection devices and <a href="/wiki/Demand_response" title="Demand response">load shedding</a>.<sup id="cite_ref-FOOTNOTEENTSO-E20173–4_43-0" class="reference"><a href="#cite_note-FOOTNOTEENTSO-E20173–4-43"><span class="cite-bracket">[</span>43<span class="cite-bracket">]</span></a></sup> </p><p>As of 2017, regulations for some grids required the power plants to tolerate RoCoF of 1–4 Hz/s, the upper limit being a very high value, an order of magnitude higher than the design target of a typical older gas turbine generator.<sup id="cite_ref-FOOTNOTEMillerLewBarnes20173-17_44-0" class="reference"><a href="#cite_note-FOOTNOTEMillerLewBarnes20173-17-44"><span class="cite-bracket">[</span>44<span class="cite-bracket">]</span></a></sup> Testing high-power (multiple <a href="/wiki/Watt" title="Watt">MW</a>) equipment for RoCoF tolerance is hard, as a typical test setup is powered off the grid, and the frequency thus cannot be arbitrarily varied. In the US, the <i>controllable grid interface</i> at the <a href="/wiki/National_Renewable_Energy_Laboratory" title="National Renewable Energy Laboratory">National Renewable Energy Laboratory</a> is the only facility that allows testing of multi-MW units<sup id="cite_ref-FOOTNOTEMillerLewBarnes20172-16_45-0" class="reference"><a href="#cite_note-FOOTNOTEMillerLewBarnes20172-16-45"><span class="cite-bracket">[</span>45<span class="cite-bracket">]</span></a></sup> (up to 7 <a href="/wiki/Volt-ampere" title="Volt-ampere">MVA</a>).<sup id="cite_ref-46" class="reference"><a href="#cite_note-46"><span class="cite-bracket">[</span>46<span class="cite-bracket">]</span></a></sup> Testing of large thermal units is not possible.<sup id="cite_ref-FOOTNOTEMillerLewBarnes20172-16_45-1" class="reference"><a href="#cite_note-FOOTNOTEMillerLewBarnes20172-16-45"><span class="cite-bracket">[</span>45<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading2"><h2 id="Audible_noise_and_interference">Audible noise and interference</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Utility_frequency&action=edit&section=19" title="Edit section: Audible noise and interference"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>AC-powered appliances can give off a characteristic hum, often called "<a href="/wiki/Mains_hum" title="Mains hum">mains hum</a>", at the multiples of the frequencies of AC power that they use (see <a href="/wiki/Magnetostriction" title="Magnetostriction">Magnetostriction</a>). It is usually produced by motor and transformer core laminations vibrating in time with the magnetic field. This hum can also appear in audio systems, where the power supply filter or signal shielding of an amplifier is not adequate. </p> <figure class="mw-default-size" typeof="mw:File/Thumb"><span><audio id="mwe_player_0" controls="" preload="none" data-mw-tmh="" class="mw-file-element" width="220" style="width:220px;" data-durationhint="6" data-mwtitle="50Hz_hum_square.ogg" data-mwprovider="wikimediacommons" resource="/wiki/File:50Hz_hum_square.ogg"><source src="//upload.wikimedia.org/wikipedia/commons/b/b7/50Hz_hum_square.ogg" type="audio/ogg; codecs="vorbis"" data-width="0" data-height="0" /><source src="//upload.wikimedia.org/wikipedia/commons/transcoded/b/b7/50Hz_hum_square.ogg/50Hz_hum_square.ogg.mp3" type="audio/mpeg" data-transcodekey="mp3" data-width="0" data-height="0" /></audio></span><figcaption>50 Hz power hum</figcaption></figure> <figure class="mw-default-size" typeof="mw:File/Thumb"><span><audio id="mwe_player_1" controls="" preload="none" data-mw-tmh="" class="mw-file-element" width="220" style="width:220px;" data-durationhint="6" data-mwtitle="60Hz_hum_square.ogg" data-mwprovider="wikimediacommons" resource="/wiki/File:60Hz_hum_square.ogg"><source src="//upload.wikimedia.org/wikipedia/commons/7/72/60Hz_hum_square.ogg" type="audio/ogg; codecs="vorbis"" data-width="0" data-height="0" /><source src="//upload.wikimedia.org/wikipedia/commons/transcoded/7/72/60Hz_hum_square.ogg/60Hz_hum_square.ogg.mp3" type="audio/mpeg" data-transcodekey="mp3" data-width="0" data-height="0" /></audio></span><figcaption>60 Hz power hum</figcaption></figure> <figure class="mw-default-size" typeof="mw:File/Thumb"><span><audio id="mwe_player_2" controls="" preload="none" data-mw-tmh="" class="mw-file-element" width="220" style="width:220px;" data-durationhint="6" data-mwtitle="400Hz_hum_square.ogg" data-mwprovider="wikimediacommons" resource="/wiki/File:400Hz_hum_square.ogg"><source src="//upload.wikimedia.org/wikipedia/commons/b/b4/400Hz_hum_square.ogg" type="audio/ogg; codecs="vorbis"" data-width="0" data-height="0" /><source src="//upload.wikimedia.org/wikipedia/commons/transcoded/b/b4/400Hz_hum_square.ogg/400Hz_hum_square.ogg.mp3" type="audio/mpeg" data-transcodekey="mp3" data-width="0" data-height="0" /></audio></span><figcaption>400 Hz power hum</figcaption></figure> <p>Most countries chose their <a href="/wiki/Television" title="Television">television</a> <a href="/wiki/Analog_television#Vertical_synchronization" title="Analog television">vertical synchronization</a> rate to be the same as the local mains supply frequency. This helped to prevent power line hum and magnetic interference from causing visible beat frequencies in the displayed picture of early analogue TV receivers particularly from the mains transformer. Although some distortion of the picture was present, it went mostly un-noticed because it was stationary. The elimination of transformers by the use of <a href="/wiki/AC/DC_receiver_design" title="AC/DC receiver design">AC/DC receivers</a>, and other changes to set design helped minimise the effect and some countries now use a vertical rate that is an approximation to the supply frequency (most notably 60 Hz areas). </p> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"><div role="note" class="hatnote navigation-not-searchable">Main article: <a href="/wiki/Electrical_network_frequency_analysis" title="Electrical network frequency analysis">Electrical network frequency analysis</a></div> <p>Another use of this side effect is as a forensic tool. When a recording is made that captures audio near an AC appliance or socket, the hum is also incidentally recorded. The peaks of the hum repeat every AC cycle (every 20 ms for 50 Hz AC, or every 16.67 ms for 60 Hz AC). The exact frequency of the hum should match the frequency of a forensic recording of the hum at the exact date and time that the recording is alleged to have been made. Discontinuities in the frequency match or no match at all will betray the authenticity of the recording.<sup id="cite_ref-47" class="reference"><a href="#cite_note-47"><span class="cite-bracket">[</span>47<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading2"><h2 id="See_also">See also</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Utility_frequency&action=edit&section=20" title="Edit section: See also"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <ul><li><a href="/wiki/Mains_electricity" title="Mains electricity">Mains electricity</a></li> <li><a href="/wiki/Maximum_demand_indicator" title="Maximum demand indicator">Maximum demand indicator</a></li> <li><a href="/wiki/Network_analyzer_(AC_power)" title="Network analyzer (AC power)">Network analyzer (AC power)</a></li> <li><a href="/wiki/Telechron" title="Telechron">Telechron</a></li></ul> <div class="mw-heading mw-heading2"><h2 id="Further_reading">Further reading</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Utility_frequency&action=edit&section=21" title="Edit section: Further reading"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <ul><li>Furfari, F.A., <i>The Evolution of Power-Line Frequencies <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1154941027"><span class="frac">133<span class="sr-only">+</span><span class="num">1</span>⁄<span class="den">3</span></span> to 25 Hz</i>, Industry Applications Magazine, IEEE, Sep/Oct 2000, Volume 6, Issue 5, Pages 12–14, <style data-mw-deduplicate="TemplateStyles:r1238218222">.mw-parser-output cite.citation{font-style:inherit;word-wrap:break-word}.mw-parser-output .citation q{quotes:"\"""\"""'""'"}.mw-parser-output .citation:target{background-color:rgba(0,127,255,0.133)}.mw-parser-output .id-lock-free.id-lock-free a{background:url("//upload.wikimedia.org/wikipedia/commons/6/65/Lock-green.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-limited.id-lock-limited a,.mw-parser-output .id-lock-registration.id-lock-registration a{background:url("//upload.wikimedia.org/wikipedia/commons/d/d6/Lock-gray-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-subscription.id-lock-subscription a{background:url("//upload.wikimedia.org/wikipedia/commons/a/aa/Lock-red-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .cs1-ws-icon a{background:url("//upload.wikimedia.org/wikipedia/commons/4/4c/Wikisource-logo.svg")right 0.1em center/12px no-repeat}body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-free a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-limited a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-registration a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-subscription a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .cs1-ws-icon a{background-size:contain;padding:0 1em 0 0}.mw-parser-output .cs1-code{color:inherit;background:inherit;border:none;padding:inherit}.mw-parser-output .cs1-hidden-error{display:none;color:var(--color-error,#d33)}.mw-parser-output .cs1-visible-error{color:var(--color-error,#d33)}.mw-parser-output .cs1-maint{display:none;color:#085;margin-left:0.3em}.mw-parser-output .cs1-kern-left{padding-left:0.2em}.mw-parser-output .cs1-kern-right{padding-right:0.2em}.mw-parser-output .citation .mw-selflink{font-weight:inherit}@media screen{.mw-parser-output .cs1-format{font-size:95%}html.skin-theme-clientpref-night .mw-parser-output .cs1-maint{color:#18911f}}@media screen and (prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .cs1-maint{color:#18911f}}</style><a href="/wiki/ISSN_(identifier)" class="mw-redirect" title="ISSN (identifier)">ISSN</a> <a rel="nofollow" class="external text" href="https://www.worldcat.org/search?fq=x0:jrnl&q=n2:1077-2618">1077-2618</a>.</li> <li>Rushmore, D.B., <i>Frequency</i>, AIEE Transactions, Volume 31, 1912, pages 955–983, and discussion on pages 974–978.</li> <li>Blalock, Thomas J., <i>Electrification of a Major Steel Mill – Part II Development of the 25 Hz System</i>, Industry Applications Magazine, IEEE, Sep/Oct 2005, Pages 9–12, <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><a href="/wiki/ISSN_(identifier)" class="mw-redirect" title="ISSN (identifier)">ISSN</a> <a rel="nofollow" class="external text" href="https://www.worldcat.org/search?fq=x0:jrnl&q=n2:1077-2618">1077-2618</a>.</li></ul> <div class="mw-heading mw-heading2"><h2 id="References">References</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Utility_frequency&action=edit&section=22" title="Edit section: References"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <style data-mw-deduplicate="TemplateStyles:r1239543626">.mw-parser-output .reflist{margin-bottom:0.5em;list-style-type:decimal}@media screen{.mw-parser-output .reflist{font-size:90%}}.mw-parser-output .reflist .references{font-size:100%;margin-bottom:0;list-style-type:inherit}.mw-parser-output .reflist-columns-2{column-width:30em}.mw-parser-output .reflist-columns-3{column-width:25em}.mw-parser-output .reflist-columns{margin-top:0.3em}.mw-parser-output .reflist-columns ol{margin-top:0}.mw-parser-output .reflist-columns li{page-break-inside:avoid;break-inside:avoid-column}.mw-parser-output .reflist-upper-alpha{list-style-type:upper-alpha}.mw-parser-output .reflist-upper-roman{list-style-type:upper-roman}.mw-parser-output .reflist-lower-alpha{list-style-type:lower-alpha}.mw-parser-output .reflist-lower-greek{list-style-type:lower-greek}.mw-parser-output .reflist-lower-roman{list-style-type:lower-roman}</style><div class="reflist reflist-columns references-column-width" style="column-width: 30em;"> <ol class="references"> <li id="cite_note-1"><span class="mw-cite-backlink"><b><a href="#cite_ref-1">^</a></b></span> <span class="reference-text">A.C. Monteith, C.F. Wagner (ed), <i>Electrical Transmission and Distribution Reference Book 4th Edition</i>, Westinghouse Electric Corporation 1950, page 6</span> </li> <li id="cite_note-2"><span class="mw-cite-backlink"><b><a href="#cite_ref-2">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFWald2011" class="citation web cs1">Wald, Matthew L. (2011-01-07). <a rel="nofollow" class="external text" href="https://green.blogs.nytimes.com/2011/01/07/hold-that-megawatt/">"Hold That Megawatt!"</a>. <i>Green Blog</i><span class="reference-accessdate">. Retrieved <span class="nowrap">2020-10-16</span></span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=Green+Blog&rft.atitle=Hold+That+Megawatt%21&rft.date=2011-01-07&rft.aulast=Wald&rft.aufirst=Matthew+L.&rft_id=https%3A%2F%2Fgreen.blogs.nytimes.com%2F2011%2F01%2F07%2Fhold-that-megawatt%2F&rfr_id=info%3Asid%2Fen.wikipedia.org%3AUtility+frequency" class="Z3988"></span></span> </li> <li id="cite_note-LAMME18-3"><span class="mw-cite-backlink">^ <a href="#cite_ref-LAMME18_3-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-LAMME18_3-1"><sup><i><b>b</b></i></sup></a> <a href="#cite_ref-LAMME18_3-2"><sup><i><b>c</b></i></sup></a> <a href="#cite_ref-LAMME18_3-3"><sup><i><b>d</b></i></sup></a></span> <span class="reference-text">B. G. Lamme, <i>The Technical Story of the Frequencies</i>, Transactions AIEE January 1918, reprinted in the Baltimore Amateur Radio Club newsletter <i>The Modulator</i> January -March 2007</span> </li> <li id="cite_note-4"><span class="mw-cite-backlink"><b><a href="#cite_ref-4">^</a></b></span> <span class="reference-text">Fractional <a href="/wiki/Hertz" title="Hertz">Hz</a> frequencies originated in the 19th century practice that gave frequencies in terms of alternations per minute, instead of alternations (cycles) per second. For example, a machine which produced 8,000 alternations per minute is operating at <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1154941027"><span class="frac">133<span class="sr-only">+</span><span class="num">1</span>⁄<span class="den">3</span></span> cycles per second.</span> </li> <li id="cite_note-5"><span class="mw-cite-backlink"><b><a href="#cite_ref-5">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFGordon_Woodward" class="citation web cs1">Gordon Woodward. <a rel="nofollow" class="external text" href="https://web.archive.org/web/20071031063316/http://www.iee.org/OnComms/pn/History/HistoryWk_Single_&_2_phase.pdf">"City of Coventry Single and Two Phase Generation and Distribution"</a> <span class="cs1-format">(PDF)</span>. Archived from <a rel="nofollow" class="external text" href="http://www.iee.org/OnComms/pn/History/HistoryWk_Single_&_2_phase.pdf">the original</a> <span class="cs1-format">(PDF)</span> on 2007-10-31.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=City+of+Coventry+Single+and+Two+Phase+Generation+and+Distribution&rft.au=Gordon+Woodward&rft_id=http%3A%2F%2Fwww.iee.org%2FOnComms%2Fpn%2FHistory%2FHistoryWk_Single_%26_2_phase.pdf&rfr_id=info%3Asid%2Fen.wikipedia.org%3AUtility+frequency" class="Z3988"></span></span> </li> <li id="cite_note-OWEN97-6"><span class="mw-cite-backlink">^ <a href="#cite_ref-OWEN97_6-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-OWEN97_6-1"><sup><i><b>b</b></i></sup></a></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFOwen1997" class="citation journal cs1">Owen, Edward (1997-11-01). "The Origins of 60-Hz as a Power Frequency". <i>Industry Applications Magazine</i>. <b>3</b> (6). IEEE: 8, 10, 12–14. <a href="/wiki/Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.1109%2F2943.628099">10.1109/2943.628099</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=Industry+Applications+Magazine&rft.atitle=The+Origins+of+60-Hz+as+a+Power+Frequency&rft.volume=3&rft.issue=6&rft.pages=8%2C+10%2C+12-14&rft.date=1997-11-01&rft_id=info%3Adoi%2F10.1109%2F2943.628099&rft.aulast=Owen&rft.aufirst=Edward&rfr_id=info%3Asid%2Fen.wikipedia.org%3AUtility+frequency" class="Z3988"></span></span> </li> <li id="cite_note-7"><span class="mw-cite-backlink"><b><a href="#cite_ref-7">^</a></b></span> <span class="reference-text"><a href="/wiki/Thomas_P._Hughes" title="Thomas P. Hughes">Thomas P. Hughes</a>, <i>Networks of Power: Electrification in Western Society 1880–1930</i>, The Johns Hopkins University Press, Baltimore 1983 <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/0-8018-2873-2" title="Special:BookSources/0-8018-2873-2">0-8018-2873-2</a> pgs. 282–283</span> </li> <li id="cite_note-Neidhofer11-8"><span class="mw-cite-backlink">^ <a href="#cite_ref-Neidhofer11_8-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-Neidhofer11_8-1"><sup><i><b>b</b></i></sup></a> <a href="#cite_ref-Neidhofer11_8-2"><sup><i><b>c</b></i></sup></a></span> <span class="reference-text">Gerhard Neidhofer <i>50-Hz frequency: how the standard emerged from a European jungle</i>, <i>IEEE Power and Energy Magazine</i>, July/August 2011 pp. 66–81</span> </li> <li id="cite_note-9"><span class="mw-cite-backlink"><b><a href="#cite_ref-9">^</a></b></span> <span class="reference-text">The Electricity Council, <i>Electricity Supply in the United Kingdom: A Chronology from the beginnings of the industry to 31 December 1985 Fourth Edition</i>, <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/0-85188-105-X" title="Special:BookSources/0-85188-105-X">0-85188-105-X</a>, page 41</span> </li> <li id="cite_note-10"><span class="mw-cite-backlink"><b><a href="#cite_ref-10">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://web.archive.org/web/20050923233630/http://www.dotd.louisiana.gov/press/pressrelease.asp?nRelease=513">"News in DOTD"</a>. Louisiana Department of Transportation and Development. September 5, 2005. Archived from <a rel="nofollow" class="external text" href="http://www.dotd.louisiana.gov/press/pressrelease.asp?nRelease=513">the original</a> on September 23, 2005.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=News+in+DOTD&rft.pub=Louisiana+Department+of+Transportation+and+Development&rft.date=2005-09-05&rft_id=http%3A%2F%2Fwww.dotd.louisiana.gov%2Fpress%2Fpressrelease.asp%3FnRelease%3D513&rfr_id=info%3Asid%2Fen.wikipedia.org%3AUtility+frequency" class="Z3988"></span></span> </li> <li id="cite_note-11"><span class="mw-cite-backlink"><b><a href="#cite_ref-11">^</a></b></span> <span class="reference-text">Samuel Insull, <i>Central-Station Electric Service</i>, private printing, Chicago 1915, available on the Internet Archive, page 72</span> </li> <li id="cite_note-12"><span class="mw-cite-backlink"><b><a href="#cite_ref-12">^</a></b></span> <span class="reference-text">Central Station Engineers of the Westinghouse Electric Corporation, <i> Electrical Transmission and Distribution Reference Book</i>, 4th Ed., Westinghouse Electric Corporation, East Pittsburgh Pennsylvania, 1950, no ISBN</span> </li> <li id="cite_note-13"><span class="mw-cite-backlink"><b><a href="#cite_ref-13">^</a></b></span> <span class="reference-text">Hughes as above</span> </li> <li id="cite_note-14"><span class="mw-cite-backlink"><b><a href="#cite_ref-14">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFAtitude_Editorial" class="citation web cs1">Atitude Editorial. <a rel="nofollow" class="external text" href="http://www.osetoreletrico.com.br/web/component/content/article/58-artigos-e-materias-relacionadas/244-padroes-brasileiros.html">"Padrões brasileiros"</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=Padr%C3%B5es+brasileiros&rft.au=Atitude+Editorial&rft_id=http%3A%2F%2Fwww.osetoreletrico.com.br%2Fweb%2Fcomponent%2Fcontent%2Farticle%2F58-artigos-e-materias-relacionadas%2F244-padroes-brasileiros.html&rfr_id=info%3Asid%2Fen.wikipedia.org%3AUtility+frequency" class="Z3988"></span></span> </li> <li id="cite_note-15"><span class="mw-cite-backlink"><b><a href="#cite_ref-15">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation web cs1 cs1-prop-foreign-lang-source"><a rel="nofollow" class="external text" href="https://web.archive.org/web/20091213122845/http://www.cfe.gob.mx/es/LaEmpresa/queescfe/CFEylaelectricidadenM%C3%A9xico/">"Historia"</a> (in Spanish). Archived from <a rel="nofollow" class="external text" href="http://www.cfe.gob.mx/es/LaEmpresa/queescfe/CFEylaelectricidadenMéxico/">the original</a> on 2009-12-13.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=Historia&rft_id=http%3A%2F%2Fwww.cfe.gob.mx%2Fes%2FLaEmpresa%2Fqueescfe%2FCFEylaelectricidadenM%C3%A9xico%2F&rfr_id=info%3Asid%2Fen.wikipedia.org%3AUtility+frequency" class="Z3988"></span></span> </li> <li id="cite_note-16"><span class="mw-cite-backlink"><b><a href="#cite_ref-16">^</a></b></span> <span class="reference-text">Edwin J. Houston and Arthur Kennelly, <i>Recent Types of Dynamo-Electric Machinery</i>, copyright American Technical Book Company 1897, published by P.F. Collier and Sons New York, 1902</span> </li> <li id="cite_note-17"><span class="mw-cite-backlink"><b><a href="#cite_ref-17">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFH.T._Kohlhaas1946" class="citation book cs1">H.T. Kohlhaas, ed. (1946). <a rel="nofollow" class="external text" href="http://www.tubebooks.org/books/ftr_ref_data.pdf"><i>Reference Data for Radio Engineers</i></a> <span class="cs1-format">(PDF)</span> (2nd ed.). New York: Federal Telephone and Radio Corporation. p. 26.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Reference+Data+for+Radio+Engineers&rft.place=New+York&rft.pages=26&rft.edition=2nd&rft.pub=Federal+Telephone+and+Radio+Corporation&rft.date=1946&rft_id=http%3A%2F%2Fwww.tubebooks.org%2Fbooks%2Fftr_ref_data.pdf&rfr_id=info%3Asid%2Fen.wikipedia.org%3AUtility+frequency" class="Z3988"></span></span> </li> <li id="cite_note-18"><span class="mw-cite-backlink"><b><a href="#cite_ref-18">^</a></b></span> <span class="reference-text"> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFC._Linder2002" class="citation cs2 cs1-prop-long-vol cs1-prop-foreign-lang-source">C. Linder (2002), "Umstellung der Sollfrequenz im zentralen Bahnstromnetz von 16 2/3 Hz auf 16,70 Hz (English: <span lang="en">Switching the frequency in train electric power supply network from 16 2/3 Hz to 16,70 Hz</span>)", <i>Elektrische Bahnen</i> (in German), vol. Book 12, Munich: Oldenbourg-Industrieverlag, <a href="/wiki/ISSN_(identifier)" class="mw-redirect" title="ISSN (identifier)">ISSN</a> <a rel="nofollow" class="external text" href="https://search.worldcat.org/issn/0013-5437">0013-5437</a></cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=Elektrische+Bahnen&rft.atitle=Umstellung+der+Sollfrequenz+im+zentralen+Bahnstromnetz+von+16+2%2F3+Hz+auf+16%2C70+Hz+%28English%3A+%3Cspan+lang%3D%22en%22%3ESwitching+the+frequency+in+train+electric+power+supply+network+from+16+2%2F3+Hz+to+16%2C70+Hz%3C%2Fspan%3ECategory%3AArticles+containing+explicitly+cited+English-language+text%29&rft.volume=Book+12&rft.date=2002&rft.issn=0013-5437&rft.au=C.+Linder&rfr_id=info%3Asid%2Fen.wikipedia.org%3AUtility+frequency" class="Z3988"></span></span> </li> <li id="cite_note-19"><span class="mw-cite-backlink"><b><a href="#cite_ref-19">^</a></b></span> <span class="reference-text">Formerly, <a href="/wiki/IBM" title="IBM">IBM</a> <a href="/wiki/Mainframe_computer" title="Mainframe computer">mainframe computer</a> systems also used 415 Hz power systems within a computer room. Robert B. Hickey, <i>Electrical engineer's portable handbook</i>, page 401</span> </li> <li id="cite_note-20"><span class="mw-cite-backlink"><b><a href="#cite_ref-20">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFFinkBeaty1978" class="citation book cs1"><a href="/wiki/Donald_G._Fink" title="Donald G. Fink">Fink, Donald G.</a>; Beaty, H. Wayne (1978). <i>Standard Handbook for Electrical Engineers</i> (Eleventh ed.). New York: McGraw-Hill. pp. 16–15, 16–16. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/978-0-07-020974-9" title="Special:BookSources/978-0-07-020974-9"><bdi>978-0-07-020974-9</bdi></a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Standard+Handbook+for+Electrical+Engineers&rft.place=New+York&rft.pages=16-15%2C+16-16&rft.edition=Eleventh&rft.pub=McGraw-Hill&rft.date=1978&rft.isbn=978-0-07-020974-9&rft.aulast=Fink&rft.aufirst=Donald+G.&rft.au=Beaty%2C+H.+Wayne&rfr_id=info%3Asid%2Fen.wikipedia.org%3AUtility+frequency" class="Z3988"></span></span> </li> <li id="cite_note-21"><span class="mw-cite-backlink"><b><a href="#cite_ref-21">^</a></b></span> <span class="reference-text"><a rel="nofollow" class="external text" href="https://www.entsoe.eu/fileadmin/user_upload/_library/publications/entsoe/Operation_Handbook/Policy_1_final.pdf">Entsoe Load Frequency Control and Performance, chapter D</a>.</span> </li> <li id="cite_note-22"><span class="mw-cite-backlink"><b><a href="#cite_ref-22">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="http://www.naesb.org/pdf2/weq_bklet_011505_tec_mc.pdf">"Manual Time Error Correction"</a> <span class="cs1-format">(PDF)</span>. <i>naesb.org</i><span class="reference-accessdate">. Retrieved <span class="nowrap">4 April</span> 2018</span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=naesb.org&rft.atitle=Manual+Time+Error+Correction&rft_id=http%3A%2F%2Fwww.naesb.org%2Fpdf2%2Fweq_bklet_011505_tec_mc.pdf&rfr_id=info%3Asid%2Fen.wikipedia.org%3AUtility+frequency" class="Z3988"></span></span> </li> <li id="cite_note-23"><span class="mw-cite-backlink"><b><a href="#cite_ref-23">^</a></b></span> <span class="reference-text"><a rel="nofollow" class="external text" href="http://www.nerc.com/files/BAL-004-0.pdf">Time Error Correction</a>.</span> </li> <li id="cite_note-24"><span class="mw-cite-backlink"><b><a href="#cite_ref-24">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://extranet.nationalgrid.com/Realtime/Home/Frequency60Mins">"National Grid: Real Time Frequency Data – Last 60 Minutes"</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=National+Grid%3A+Real+Time+Frequency+Data+%E2%80%93+Last+60+Minutes&rft_id=https%3A%2F%2Fextranet.nationalgrid.com%2FRealtime%2FHome%2FFrequency60Mins&rfr_id=info%3Asid%2Fen.wikipedia.org%3AUtility+frequency" class="Z3988"></span></span> </li> <li id="cite_note-25"><span class="mw-cite-backlink"><b><a href="#cite_ref-25">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://www.dynamicdemand.co.uk/grid.htm">"Dynamic Demand"</a>. <i>www.dynamicdemand.co.uk</i>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=www.dynamicdemand.co.uk&rft.atitle=Dynamic+Demand&rft_id=https%3A%2F%2Fwww.dynamicdemand.co.uk%2Fgrid.htm&rfr_id=info%3Asid%2Fen.wikipedia.org%3AUtility+frequency" class="Z3988"></span></span> </li> <li id="cite_note-26"><span class="mw-cite-backlink"><b><a href="#cite_ref-26">^</a></b></span> <span class="reference-text"><span class="url"><a rel="nofollow" class="external text" href="http://fnetpublic.utk.edu/">fnetpublic<wbr />.utk<wbr />.edu</a></span></span> </li> <li id="cite_note-27"><span class="mw-cite-backlink"><b><a href="#cite_ref-27">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://web.archive.org/web/20161221015250/https://ferc.gov/whats-new/comm-meet/2009/052109/E-14.pdf">"Western Electricity Coordinating Council Regional Reliability Standard Regarding Automatic Time Error Correction"</a> <span class="cs1-format">(PDF)</span>. <a href="/wiki/Federal_Energy_Regulatory_Commission" title="Federal Energy Regulatory Commission">Federal Energy Regulatory Commission</a>. May 21, 2009. Archived from <a rel="nofollow" class="external text" href="https://www.ferc.gov/whats-new/comm-meet/2009/052109/E-14.pdf">the original</a> <span class="cs1-format">(PDF)</span> on December 21, 2016<span class="reference-accessdate">. Retrieved <span class="nowrap">June 23,</span> 2016</span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=Western+Electricity+Coordinating+Council+Regional+Reliability+Standard+Regarding+Automatic+Time+Error+Correction&rft.pub=Federal+Energy+Regulatory+Commission&rft.date=2009-05-21&rft_id=http%3A%2F%2Fwww.ferc.gov%2Fwhats-new%2Fcomm-meet%2F2009%2F052109%2FE-14.pdf&rfr_id=info%3Asid%2Fen.wikipedia.org%3AUtility+frequency" class="Z3988"></span></span> </li> <li id="cite_note-28"><span class="mw-cite-backlink"><b><a href="#cite_ref-28">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="http://www.nerc.com/pa/Stand/Project%2020101422%20Phase%202%20of%20BARC%20%20BAL004%20DL/BAL-004-0_White_Paper_Clean_09242015.pdf">"Time error correction and reliability (draft)"</a> <span class="cs1-format">(PDF)</span>. <a href="/wiki/North_American_Electric_Reliability_Corporation" title="North American Electric Reliability Corporation">North American Electric Reliability Corporation</a><span class="reference-accessdate">. Retrieved <span class="nowrap">June 23,</span> 2016</span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=Time+error+correction+and+reliability+%28draft%29&rft.pub=North+American+Electric+Reliability+Corporation&rft_id=http%3A%2F%2Fwww.nerc.com%2Fpa%2FStand%2FProject%252020101422%2520Phase%25202%2520of%2520BARC%2520%2520BAL004%2520DL%2FBAL-004-0_White_Paper_Clean_09242015.pdf&rfr_id=info%3Asid%2Fen.wikipedia.org%3AUtility+frequency" class="Z3988"></span></span> </li> <li id="cite_note-29"><span class="mw-cite-backlink"><b><a href="#cite_ref-29">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://web.archive.org/web/20200804173352/http://www.nbcnews.com/id/43532031">"Power-grid experiment could confuse clocks – Technology & science – Innovation – NBC News"</a>. <i>NBC News</i>. 25 June 2011. Archived from <a rel="nofollow" class="external text" href="http://www.nbcnews.com/id/43532031">the original</a> on August 4, 2020.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=NBC+News&rft.atitle=Power-grid+experiment+could+confuse+clocks+%E2%80%93+Technology+%26+science+%E2%80%93+Innovation+%E2%80%93+NBC+News&rft.date=2011-06-25&rft_id=http%3A%2F%2Fwww.nbcnews.com%2Fid%2F43532031&rfr_id=info%3Asid%2Fen.wikipedia.org%3AUtility+frequency" class="Z3988"></span></span> </li> <li id="cite_note-30"><span class="mw-cite-backlink"><b><a href="#cite_ref-30">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFGraingerStevenson1994" class="citation book cs1">Grainger, John J.; Stevenson, William D. (1994). <a rel="nofollow" class="external text" href="https://archive.org/details/powersystemanaly0000grai/page/562/"><i>Power system analysis</i></a> (International Student ed.). Tata-McGraw Hill. pp. 562–565.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Power+system+analysis&rft.pages=562-565&rft.edition=International+Student&rft.pub=Tata-McGraw+Hill&rft.date=1994&rft.aulast=Grainger&rft.aufirst=John+J.&rft.au=Stevenson%2C+William+D.&rft_id=https%3A%2F%2Farchive.org%2Fdetails%2Fpowersystemanaly0000grai%2Fpage%2F562%2F&rfr_id=info%3Asid%2Fen.wikipedia.org%3AUtility+frequency" class="Z3988"></span></span> </li> <li id="cite_note-31"><span class="mw-cite-backlink"><b><a href="#cite_ref-31">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFLombardo2016" class="citation web cs1">Lombardo, Tom (6 May 2016). <a rel="nofollow" class="external text" href="https://www.engineering.com/story/battery-storage-a-clean-alternative-for-frequency-regulation">"Battery Storage: A Clean Alternative for Frequency Regulation"</a>. <i>Engineering.com</i>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=Engineering.com&rft.atitle=Battery+Storage%3A+A+Clean+Alternative+for+Frequency+Regulation&rft.date=2016-05-06&rft.aulast=Lombardo&rft.aufirst=Tom&rft_id=https%3A%2F%2Fwww.engineering.com%2Fstory%2Fbattery-storage-a-clean-alternative-for-frequency-regulation&rfr_id=info%3Asid%2Fen.wikipedia.org%3AUtility+frequency" class="Z3988"></span></span> </li> <li id="cite_note-32"><span class="mw-cite-backlink"><b><a href="#cite_ref-32">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFSt._John2017" class="citation news cs1">St. John, Jeff (19 January 2017). <a rel="nofollow" class="external text" href="https://www.greentechmedia.com/articles/read/PV-Plants-Can-Rival-Frequency-Response-Services-From-Natural-Gas-Peakers">"First Solar Proves That PV Plants Can Rival Frequency Response Services From Natural Gas Peakers"</a>. Grid Optimization. <i>gtm</i>. <a href="/wiki/Wood_Mackenzie" title="Wood Mackenzie">Wood Mackenzie</a><span class="reference-accessdate">. Retrieved <span class="nowrap">20 January</span> 2017</span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=gtm&rft.atitle=First+Solar+Proves+That+PV+Plants+Can+Rival+Frequency+Response+Services+From+Natural+Gas+Peakers&rft.date=2017-01-19&rft.aulast=St.+John&rft.aufirst=Jeff&rft_id=https%3A%2F%2Fwww.greentechmedia.com%2Farticles%2Fread%2FPV-Plants-Can-Rival-Frequency-Response-Services-From-Natural-Gas-Peakers&rfr_id=info%3Asid%2Fen.wikipedia.org%3AUtility+frequency" class="Z3988"></span></span> </li> <li id="cite_note-33"><span class="mw-cite-backlink"><b><a href="#cite_ref-33">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFBaylissHardy2022" class="citation book cs1">Bayliss, Colin; Hardy, Brian (14 October 2022). <a rel="nofollow" class="external text" href="https://archive.org/details/transmission-and-distribution-electrical-engineering-fourth-edition/page/343/"><i>Transmission and Distribution Electrical Engineering</i></a> (4th ed.). Newnos. pp. 344–345.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Transmission+and+Distribution+Electrical+Engineering&rft.pages=344-345&rft.edition=4th&rft.pub=Newnos&rft.date=2022-10-14&rft.aulast=Bayliss&rft.aufirst=Colin&rft.au=Hardy%2C+Brian&rft_id=https%3A%2F%2Farchive.org%2Fdetails%2Ftransmission-and-distribution-electrical-engineering-fourth-edition%2Fpage%2F343%2F&rfr_id=info%3Asid%2Fen.wikipedia.org%3AUtility+frequency" class="Z3988"></span></span> </li> <li id="cite_note-34"><span class="mw-cite-backlink"><b><a href="#cite_ref-34">^</a></b></span> <span class="reference-text">Donald G. Fink and H. Wayne Beaty, <i>Standard Handbook for Electrical Engineers, Eleventh Edition</i>, McGraw-Hill, New York, 1978, <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/0-07-020974-X" title="Special:BookSources/0-07-020974-X">0-07-020974-X</a>, pp. 16‑15–16‑21</span> </li> <li id="cite_note-35"><span class="mw-cite-backlink"><b><a href="#cite_ref-35">^</a></b></span> <span class="reference-text"><a href="/wiki/Edward_Kimbark" title="Edward Kimbark">Edward Wilson Kimbark</a>, <i>Power System Stability</i>, vol. 1, John Wiley and Sons, New York, 1948 pg. 189</span> </li> <li id="cite_note-36"><span class="mw-cite-backlink"><b><a href="#cite_ref-36">^</a></b></span> <span class="reference-text"><a href="#CITEREFNERC2021">NERC 2021</a>, p. 11 or <a href="#CITEREFBratton1971">Bratton 1971</a>, pp. 48–49. Note that an older notation instead uses <span class="texhtml mvar" style="font-style:italic;">B</span> for the <a href="/wiki/Opposite_(arithmetic)" class="mw-redirect" title="Opposite (arithmetic)">opposite</a> of the frequency bias as defined here, and sometimes a <a href="/wiki/Unit_conversion" class="mw-redirect" title="Unit conversion">unit conversion</a> factor of <span class="texhtml">10</span> is included in the area control formula.</span> </li> <li id="cite_note-37"><span class="mw-cite-backlink"><b><a href="#cite_ref-37">^</a></b></span> <span class="reference-text">Glover, Duncan J. et al. <i>Power System Analysis and Design.</i> 5th Edition. Cengage Learning. 2012. pp. 663–664.</span> </li> <li id="cite_note-38"><span class="mw-cite-backlink"><b><a href="#cite_ref-38">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFSterling1978" class="citation book cs1">Sterling, M. J. H. (1978). <a rel="nofollow" class="external text" href="https://archive.org/details/powersystemcontr0000ster/page/193/"><i>Power System Control</i></a>. IEE Control Engineering. Stevenage: Peter Peregrinus. pp. 193–198. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/0-906048-01-X" title="Special:BookSources/0-906048-01-X"><bdi>0-906048-01-X</bdi></a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Power+System+Control&rft.place=Stevenage&rft.series=IEE+Control+Engineering&rft.pages=193-198&rft.pub=Peter+Peregrinus&rft.date=1978&rft.isbn=0-906048-01-X&rft.aulast=Sterling&rft.aufirst=M.+J.+H.&rft_id=https%3A%2F%2Farchive.org%2Fdetails%2Fpowersystemcontr0000ster%2Fpage%2F193%2F&rfr_id=info%3Asid%2Fen.wikipedia.org%3AUtility+frequency" class="Z3988"></span></span> </li> <li id="cite_note-FOOTNOTENERC202120-39"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTENERC202120_39-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFNERC2021">NERC 2021</a>, p. 20.</span> </li> <li id="cite_note-FOOTNOTEBratton19714–5-40"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTEBratton19714–5_40-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFBratton1971">Bratton 1971</a>, pp. 4–5.</span> </li> <li id="cite_note-41"><span class="mw-cite-backlink"><b><a href="#cite_ref-41">^</a></b></span> <span class="reference-text">Mathematically, the derivative can vary with location as long as each generation control system has only one neighbor generating plant. That is only possible on a grid with the unrealistically few one or two generators.</span> </li> <li id="cite_note-FOOTNOTEBratton197148–49-42"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTEBratton197148–49_42-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFBratton1971">Bratton 1971</a>, pp. 48–49.</span> </li> <li id="cite_note-FOOTNOTEENTSO-E20173–4-43"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTEENTSO-E20173–4_43-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFENTSO-E2017">ENTSO-E 2017</a>, pp. 3–4.</span> </li> <li id="cite_note-FOOTNOTEMillerLewBarnes20173-17-44"><span class="mw-cite-backlink"><b><a href="#cite_ref-FOOTNOTEMillerLewBarnes20173-17_44-0">^</a></b></span> <span class="reference-text"><a href="#CITEREFMillerLewBarnes2017">Miller, Lew & Barnes 2017</a>, p. 3-17.</span> </li> <li id="cite_note-FOOTNOTEMillerLewBarnes20172-16-45"><span class="mw-cite-backlink">^ <a href="#cite_ref-FOOTNOTEMillerLewBarnes20172-16_45-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-FOOTNOTEMillerLewBarnes20172-16_45-1"><sup><i><b>b</b></i></sup></a></span> <span class="reference-text"><a href="#CITEREFMillerLewBarnes2017">Miller, Lew & Barnes 2017</a>, p. 2-16.</span> </li> <li id="cite_note-46"><span class="mw-cite-backlink"><b><a href="#cite_ref-46">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFNREL" class="citation web cs1">NREL. <a rel="nofollow" class="external text" href="https://www.nrel.gov/grid/controllable-grid-interface.html">"Controllable Grid Interface"</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=Controllable+Grid+Interface&rft.au=NREL&rft_id=https%3A%2F%2Fwww.nrel.gov%2Fgrid%2Fcontrollable-grid-interface.html&rfr_id=info%3Asid%2Fen.wikipedia.org%3AUtility+frequency" class="Z3988"></span></span> </li> <li id="cite_note-47"><span class="mw-cite-backlink"><b><a href="#cite_ref-47">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation news cs1"><a rel="nofollow" class="external text" href="https://www.bbc.co.uk/news/science-environment-20629671">"The hum that helps to fight crime"</a>. <i>BBC News</i>. 12 December 2012.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=BBC+News&rft.atitle=The+hum+that+helps+to+fight+crime&rft.date=2012-12-12&rft_id=https%3A%2F%2Fwww.bbc.co.uk%2Fnews%2Fscience-environment-20629671&rfr_id=info%3Asid%2Fen.wikipedia.org%3AUtility+frequency" class="Z3988"></span></span> </li> </ol></div> <div class="mw-heading mw-heading2"><h2 id="Sources">Sources</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Utility_frequency&action=edit&section=23" title="Edit section: Sources"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <ul><li><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFENTSO-E2017" class="citation book cs1">ENTSO-E (29 March 2017). <a rel="nofollow" class="external text" href="https://docstore.entsoe.eu/Documents/Network%20codes%20documents/Implementation/CNC/IGD-RoCoF_withstand_capability.pdf"><i>Rate of Change of Frequency (ROCOF) withstand capability</i></a> <span class="cs1-format">(PDF)</span>. <a href="/wiki/European_Network_of_Transmission_System_Operators_for_Electricity" title="European Network of Transmission System Operators for Electricity">European Network of Transmission System Operators for Electricity</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Rate+of+Change+of+Frequency+%28ROCOF%29+withstand+capability&rft.pub=European+Network+of+Transmission+System+Operators+for+Electricity&rft.date=2017-03-29&rft.au=ENTSO-E&rft_id=https%3A%2F%2Fdocstore.entsoe.eu%2FDocuments%2FNetwork%2520codes%2520documents%2FImplementation%2FCNC%2FIGD-RoCoF_withstand_capability.pdf&rfr_id=info%3Asid%2Fen.wikipedia.org%3AUtility+frequency" class="Z3988"></span></li> <li><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFMillerLewBarnes2017" class="citation book cs1">Miller, Nicholas; Lew, Debra; Barnes, Steven (April 9, 2017). <a rel="nofollow" class="external text" href="https://www.aemo.com.au/-/media/Files/Electricity/NEM/Security_and_Reliability/Reports/2017/20170904-GE-RoCoF-Advisory"><i>Advisory on Equipment Limits associated with High RoCoF</i></a>. General Electric International, Inc.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Advisory+on+Equipment+Limits+associated+with+High+RoCoF&rft.pub=General+Electric+International%2C+Inc&rft.date=2017-04-09&rft.aulast=Miller&rft.aufirst=Nicholas&rft.au=Lew%2C+Debra&rft.au=Barnes%2C+Steven&rft_id=https%3A%2F%2Fwww.aemo.com.au%2F-%2Fmedia%2FFiles%2FElectricity%2FNEM%2FSecurity_and_Reliability%2FReports%2F2017%2F20170904-GE-RoCoF-Advisory&rfr_id=info%3Asid%2Fen.wikipedia.org%3AUtility+frequency" class="Z3988"></span></li> <li><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFNERC2021" class="citation book cs1">NERC (May 11, 2021). <a rel="nofollow" class="external text" href="https://www.nerc.com/comm/OC/ReferenceDocumentsDL/Reference_Document_NERC_Balancing_and_Frequency_Control.pdf"><i>Balancing and Frequency Control</i></a> <span class="cs1-format">(PDF)</span>. <a href="/wiki/North_American_Electric_Reliability_Corporation" title="North American Electric Reliability Corporation">North American Electric Reliability Corporation</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Balancing+and+Frequency+Control&rft.pub=North+American+Electric+Reliability+Corporation&rft.date=2021-05-11&rft.au=NERC&rft_id=https%3A%2F%2Fwww.nerc.com%2Fcomm%2FOC%2FReferenceDocumentsDL%2FReference_Document_NERC_Balancing_and_Frequency_Control.pdf&rfr_id=info%3Asid%2Fen.wikipedia.org%3AUtility+frequency" class="Z3988"></span></li> <li><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFBratton1971" class="citation thesis cs1">Bratton, Timothy Lee (May 1971). <a rel="nofollow" class="external text" href="https://scholarship.rice.edu/bitstream/handle/1911/89670/RICE0701.pdf?sequence=1"><i>On the load-frequency control problem</i></a> <span class="cs1-format">(PDF)</span> (MSc thesis). Houston, Texas: <a href="/wiki/Rice_University" title="Rice University">Rice University</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Adissertation&rft.title=On+the+load-frequency+control+problem&rft.degree=MSc&rft.inst=Rice+University&rft.date=1971-05&rft.aulast=Bratton&rft.aufirst=Timothy+Lee&rft_id=https%3A%2F%2Fscholarship.rice.edu%2Fbitstream%2Fhandle%2F1911%2F89670%2FRICE0701.pdf%3Fsequence%3D1&rfr_id=info%3Asid%2Fen.wikipedia.org%3AUtility+frequency" class="Z3988"></span></li></ul> <div class="navbox-styles"><style data-mw-deduplicate="TemplateStyles:r1129693374">.mw-parser-output .hlist dl,.mw-parser-output .hlist ol,.mw-parser-output .hlist ul{margin:0;padding:0}.mw-parser-output .hlist dd,.mw-parser-output .hlist dt,.mw-parser-output .hlist li{margin:0;display:inline}.mw-parser-output .hlist.inline,.mw-parser-output .hlist.inline dl,.mw-parser-output .hlist.inline ol,.mw-parser-output .hlist.inline ul,.mw-parser-output .hlist dl dl,.mw-parser-output .hlist dl ol,.mw-parser-output .hlist dl ul,.mw-parser-output .hlist ol dl,.mw-parser-output .hlist ol ol,.mw-parser-output .hlist ol ul,.mw-parser-output .hlist ul dl,.mw-parser-output .hlist ul ol,.mw-parser-output .hlist ul ul{display:inline}.mw-parser-output .hlist .mw-empty-li{display:none}.mw-parser-output .hlist dt::after{content:": "}.mw-parser-output .hlist dd::after,.mw-parser-output .hlist li::after{content:" · ";font-weight:bold}.mw-parser-output .hlist dd:last-child::after,.mw-parser-output .hlist dt:last-child::after,.mw-parser-output .hlist li:last-child::after{content:none}.mw-parser-output .hlist dd dd:first-child::before,.mw-parser-output .hlist dd dt:first-child::before,.mw-parser-output .hlist dd li:first-child::before,.mw-parser-output .hlist dt dd:first-child::before,.mw-parser-output .hlist dt dt:first-child::before,.mw-parser-output .hlist dt li:first-child::before,.mw-parser-output .hlist li dd:first-child::before,.mw-parser-output .hlist li dt:first-child::before,.mw-parser-output .hlist li li:first-child::before{content:" (";font-weight:normal}.mw-parser-output .hlist dd dd:last-child::after,.mw-parser-output .hlist dd dt:last-child::after,.mw-parser-output .hlist dd li:last-child::after,.mw-parser-output .hlist dt dd:last-child::after,.mw-parser-output .hlist dt dt:last-child::after,.mw-parser-output .hlist dt li:last-child::after,.mw-parser-output .hlist li dd:last-child::after,.mw-parser-output .hlist li dt:last-child::after,.mw-parser-output .hlist li li:last-child::after{content:")";font-weight:normal}.mw-parser-output .hlist ol{counter-reset:listitem}.mw-parser-output .hlist ol>li{counter-increment:listitem}.mw-parser-output .hlist ol>li::before{content:" "counter(listitem)"\a0 "}.mw-parser-output .hlist dd ol>li:first-child::before,.mw-parser-output .hlist dt ol>li:first-child::before,.mw-parser-output .hlist li ol>li:first-child::before{content:" ("counter(listitem)"\a0 "}</style><style data-mw-deduplicate="TemplateStyles:r1236075235">.mw-parser-output .navbox{box-sizing:border-box;border:1px solid #a2a9b1;width:100%;clear:both;font-size:88%;text-align:center;padding:1px;margin:1em auto 0}.mw-parser-output .navbox .navbox{margin-top:0}.mw-parser-output .navbox+.navbox,.mw-parser-output .navbox+.navbox-styles+.navbox{margin-top:-1px}.mw-parser-output .navbox-inner,.mw-parser-output .navbox-subgroup{width:100%}.mw-parser-output .navbox-group,.mw-parser-output .navbox-title,.mw-parser-output .navbox-abovebelow{padding:0.25em 1em;line-height:1.5em;text-align:center}.mw-parser-output .navbox-group{white-space:nowrap;text-align:right}.mw-parser-output .navbox,.mw-parser-output .navbox-subgroup{background-color:#fdfdfd}.mw-parser-output .navbox-list{line-height:1.5em;border-color:#fdfdfd}.mw-parser-output .navbox-list-with-group{text-align:left;border-left-width:2px;border-left-style:solid}.mw-parser-output tr+tr>.navbox-abovebelow,.mw-parser-output tr+tr>.navbox-group,.mw-parser-output tr+tr>.navbox-image,.mw-parser-output tr+tr>.navbox-list{border-top:2px solid #fdfdfd}.mw-parser-output .navbox-title{background-color:#ccf}.mw-parser-output .navbox-abovebelow,.mw-parser-output .navbox-group,.mw-parser-output .navbox-subgroup .navbox-title{background-color:#ddf}.mw-parser-output .navbox-subgroup .navbox-group,.mw-parser-output .navbox-subgroup .navbox-abovebelow{background-color:#e6e6ff}.mw-parser-output .navbox-even{background-color:#f7f7f7}.mw-parser-output .navbox-odd{background-color:transparent}.mw-parser-output .navbox .hlist td dl,.mw-parser-output .navbox .hlist td ol,.mw-parser-output .navbox .hlist td ul,.mw-parser-output .navbox td.hlist dl,.mw-parser-output .navbox td.hlist ol,.mw-parser-output .navbox td.hlist ul{padding:0.125em 0}.mw-parser-output .navbox .navbar{display:block;font-size:100%}.mw-parser-output .navbox-title .navbar{float:left;text-align:left;margin-right:0.5em}body.skin--responsive .mw-parser-output .navbox-image img{max-width:none!important}@media print{body.ns-0 .mw-parser-output .navbox{display:none!important}}</style></div><div role="navigation" class="navbox" aria-labelledby="Electricity_delivery" style="padding:3px"><table class="nowraplinks hlist mw-collapsible autocollapse navbox-inner" style="border-spacing:0;background:transparent;color:inherit"><tbody><tr><th scope="col" class="navbox-title" colspan="3"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1129693374"><style data-mw-deduplicate="TemplateStyles:r1239400231">.mw-parser-output .navbar{display:inline;font-size:88%;font-weight:normal}.mw-parser-output .navbar-collapse{float:left;text-align:left}.mw-parser-output .navbar-boxtext{word-spacing:0}.mw-parser-output .navbar ul{display:inline-block;white-space:nowrap;line-height:inherit}.mw-parser-output .navbar-brackets::before{margin-right:-0.125em;content:"[ "}.mw-parser-output .navbar-brackets::after{margin-left:-0.125em;content:" ]"}.mw-parser-output .navbar li{word-spacing:-0.125em}.mw-parser-output .navbar a>span,.mw-parser-output .navbar a>abbr{text-decoration:inherit}.mw-parser-output .navbar-mini abbr{font-variant:small-caps;border-bottom:none;text-decoration:none;cursor:inherit}.mw-parser-output .navbar-ct-full{font-size:114%;margin:0 7em}.mw-parser-output .navbar-ct-mini{font-size:114%;margin:0 4em}html.skin-theme-clientpref-night .mw-parser-output .navbar li a abbr{color:var(--color-base)!important}@media(prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .navbar li a abbr{color:var(--color-base)!important}}@media print{.mw-parser-output .navbar{display:none!important}}</style><div class="navbar plainlinks hlist navbar-mini"><ul><li class="nv-view"><a href="/wiki/Template:Electricity_delivery" title="Template:Electricity delivery"><abbr title="View this template">v</abbr></a></li><li class="nv-talk"><a href="/wiki/Template_talk:Electricity_delivery" title="Template talk:Electricity delivery"><abbr title="Discuss this template">t</abbr></a></li><li class="nv-edit"><a href="/wiki/Special:EditPage/Template:Electricity_delivery" title="Special:EditPage/Template:Electricity delivery"><abbr title="Edit this template">e</abbr></a></li></ul></div><div id="Electricity_delivery" style="font-size:114%;margin:0 4em"><a href="/wiki/Electricity_delivery" title="Electricity delivery">Electricity delivery</a></div></th></tr><tr><th scope="row" class="navbox-group" style="width:1%">Concepts</th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Automatic_generation_control" title="Automatic generation control">Automatic generation control</a></li> <li><a href="/wiki/Backfeeding" title="Backfeeding">Backfeeding</a></li> <li><a href="/wiki/Base_load" title="Base load">Base load</a></li> <li><a href="/wiki/Demand_factor" title="Demand factor">Demand factor</a></li> <li><a href="/wiki/Droop_speed_control" title="Droop speed control">Droop speed control</a></li> <li><a href="/wiki/Electric_power" title="Electric power">Electric power</a></li> <li><a href="/wiki/Electric_power_quality" title="Electric power quality">Electric power quality</a></li> <li><a href="/wiki/Electrical_fault" title="Electrical fault">Electrical fault</a></li> <li><a href="/wiki/Energy_demand_management" title="Energy demand management">Energy demand management</a></li> <li><a href="/wiki/Energy_return_on_investment" title="Energy return on investment">Energy return on investment</a></li> <li><a href="/wiki/Grid_code" title="Grid code">Grid code</a></li> <li><a href="/wiki/Grid_energy_storage" title="Grid energy storage">Grid energy storage</a></li> <li><a href="/wiki/Grid_strength" class="mw-redirect" title="Grid strength">Grid strength</a></li> <li><a href="/wiki/Home_energy_storage" title="Home energy storage">Home energy storage</a></li> <li><a href="/wiki/Load-following_power_plant" title="Load-following power plant">Load-following</a></li> <li><a href="/wiki/Merit_order" title="Merit order">Merit order</a></li> <li><a href="/wiki/Nameplate_capacity" title="Nameplate capacity">Nameplate capacity</a></li> <li><a href="/wiki/Peak_demand" title="Peak demand">Peak demand</a></li> <li><a href="/wiki/Power_factor" title="Power factor">Power factor</a></li> <li><a href="/wiki/Power-flow_study" title="Power-flow study">Power-flow study</a></li> <li><a href="/wiki/Repowering" title="Repowering">Repowering</a></li> <li><a class="mw-selflink selflink">Utility frequency</a></li> <li><a href="/wiki/Variable_renewable_energy" title="Variable renewable energy">Variability</a></li> <li><a href="/wiki/Vehicle-to-grid" title="Vehicle-to-grid">Vehicle-to-grid</a></li></ul> </div></td><td class="noviewer navbox-image" rowspan="8" style="width:1px;padding:0 0 0 2px"><div><span typeof="mw:File"><a href="/wiki/File:Abspannportal.jpg" class="mw-file-description" title="Portal pylons of Kriftel substation near Frankfurt"><img alt="Portal pylons of Kriftel substation near Frankfurt" src="//upload.wikimedia.org/wikipedia/commons/thumb/e/e2/Abspannportal.jpg/120px-Abspannportal.jpg" decoding="async" width="120" height="90" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/e/e2/Abspannportal.jpg/180px-Abspannportal.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/e/e2/Abspannportal.jpg/240px-Abspannportal.jpg 2x" data-file-width="2048" data-file-height="1536" /></a></span></div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Sources</th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><th scope="row" class="navbox-group" style="width:7em"><a href="/wiki/Non-renewable_resource" title="Non-renewable resource">Non-renewable</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Fossil_fuel_power_station" title="Fossil fuel power station">Fossil fuel power station</a> <ul><li><a href="/wiki/Coal" title="Coal">Coal</a></li> <li><a href="/wiki/Natural_gas" title="Natural gas">Natural gas</a></li> <li><a href="/wiki/Oil_shale" title="Oil shale">Oil shale</a></li> <li><a href="/wiki/Petroleum" title="Petroleum">Petroleum</a></li></ul></li> <li><a href="/wiki/Nuclear_power" title="Nuclear power">Nuclear</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:7em"><a href="/wiki/Renewable_energy" title="Renewable energy">Renewable</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Biofuel" title="Biofuel">Biofuel</a></li> <li><a href="/wiki/Biogas" title="Biogas">Biogas</a></li> <li><a href="/wiki/Biomass" title="Biomass">Biomass</a></li> <li><a href="/wiki/Geothermal_power" title="Geothermal power">Geothermal</a></li> <li><a href="/wiki/Hydroelectricity" title="Hydroelectricity">Hydro</a></li> <li><a href="/wiki/Marine_energy" title="Marine energy">Marine</a> <ul><li><a href="/wiki/Marine_current_power" title="Marine current power">Current</a></li> <li><a href="/wiki/Osmotic_power" title="Osmotic power">Osmotic</a></li> <li><a href="/wiki/Ocean_thermal_energy_conversion" title="Ocean thermal energy conversion">Thermal</a></li> <li><a href="/wiki/Tidal_power" title="Tidal power">Tidal</a></li> <li><a href="/wiki/Wave_power" title="Wave power">Wave</a></li></ul></li> <li><a href="/wiki/Solar_power" title="Solar power">Solar</a></li> <li><a href="/wiki/Sustainable_biofuel" title="Sustainable biofuel">Sustainable biofuel</a></li> <li><a href="/wiki/Wind_power" title="Wind power">Wind</a></li></ul> </div></td></tr></tbody></table><div></div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Category:Power_station_technology" title="Category:Power station technology">Generation</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/AC_power" title="AC power">AC power</a></li> <li><a href="/wiki/Cogeneration" title="Cogeneration">Cogeneration</a></li> <li><a href="/wiki/Combined_cycle_power_plant" title="Combined cycle power plant">Combined cycle</a></li> <li><a href="/wiki/Cooling_tower" title="Cooling tower">Cooling tower</a></li> <li><a href="/wiki/Induction_generator" title="Induction generator">Induction generator</a></li> <li><a href="/wiki/Micro_combined_heat_and_power" title="Micro combined heat and power">Micro CHP</a></li> <li><a href="/wiki/Microgeneration" title="Microgeneration">Microgeneration</a></li> <li><a href="/wiki/Rankine_cycle" title="Rankine cycle">Rankine cycle</a></li> <li><a href="/wiki/Three-phase_electric_power" title="Three-phase electric power">Three-phase electric power</a></li> <li><a href="/wiki/Virtual_power_plant" title="Virtual power plant">Virtual power plant</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><div style="display: inline-block; line-height: 1.2em; padding: .1em 0;"><a href="/wiki/Electric_power_transmission" title="Electric power transmission">Transmission</a><br />and <a href="/wiki/Electric_power_distribution" title="Electric power distribution">distribution</a></div></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Demand_response" title="Demand response">Demand response</a></li> <li><a href="/wiki/Distributed_generation" title="Distributed generation">Distributed generation</a></li> <li><a href="/wiki/Dynamic_demand_(electric_power)" title="Dynamic demand (electric power)">Dynamic demand</a></li> <li><a href="/wiki/Electric_power_distribution" title="Electric power distribution">Electric power distribution</a></li> <li><a href="/wiki/Electric_power_system" title="Electric power system">Electric power system</a></li> <li><a href="/wiki/Electric_power_transmission" title="Electric power transmission">Electric power transmission</a></li> <li><a href="/wiki/Electrical_busbar_system" title="Electrical busbar system">Electrical busbar system</a></li> <li><a href="/wiki/Electrical_grid" title="Electrical grid">Electrical grid</a></li> <li><a href="/wiki/Electrical_substation" class="mw-redirect" title="Electrical substation">Electrical substation</a></li> <li><a href="/wiki/Electricity_retailing" title="Electricity retailing">Electricity retailing</a></li> <li><a href="/wiki/High-voltage_direct_current" title="High-voltage direct current">High-voltage direct current</a></li> <li><a href="/wiki/High-voltage_shore_connection" title="High-voltage shore connection">High-voltage shore connection</a></li> <li><a href="/wiki/Interconnector" title="Interconnector">Interconnector</a></li> <li><a href="/wiki/Load_management" title="Load management">Load management</a></li> <li><a href="/wiki/Mains_electricity_by_country" title="Mains electricity by country">Mains electricity by country</a></li> <li><a href="/wiki/Overhead_power_line" title="Overhead power line">Overhead power line</a></li> <li><a href="/wiki/Power_station" title="Power station">Power station</a></li> <li><a href="/wiki/Pumped-storage_hydroelectricity" title="Pumped-storage hydroelectricity">Pumped hydro</a></li> <li><a href="/wiki/Single-wire_earth_return" title="Single-wire earth return">Single-wire earth return</a></li> <li><a href="/wiki/Smart_grid" title="Smart grid">Smart grid</a></li> <li><a href="/wiki/Super_grid" title="Super grid">Super grid</a></li> <li><a href="/wiki/Transformer" title="Transformer">Transformer</a></li> <li><a href="/wiki/Transmission_system_operator" title="Transmission system operator">Transmission system operator</a> (TSO)</li> <li><a href="/wiki/Transmission_tower" title="Transmission tower">Transmission tower</a></li> <li><a href="/wiki/Utility_pole" title="Utility pole">Utility pole</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Failure modes</th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Black_start" title="Black start">Black start</a></li> <li><a href="/wiki/Brownout_(electricity)" title="Brownout (electricity)">Brownout</a></li> <li><a href="/wiki/Cascading_failure" title="Cascading failure">Cascading failure</a></li> <li><a href="/wiki/Power_outage" title="Power outage">Power outage</a> <ul><li><a href="/wiki/Rolling_blackout" title="Rolling blackout">Rolling blackout</a></li></ul></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><div style="display: inline-block; line-height: 1.2em; padding: .1em 0;">Protective<br />devices</div></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Arc-fault_circuit_interrupter" title="Arc-fault circuit interrupter">Arc-fault circuit interrupter</a></li> <li><a href="/wiki/Circuit_breaker" title="Circuit breaker">Circuit breaker</a> <ul><li><a href="/wiki/Earth-leakage_circuit_breaker" title="Earth-leakage circuit breaker">Earth-leakage</a></li> <li><a href="/wiki/Sulfur_hexafluoride_circuit_breaker" title="Sulfur hexafluoride circuit breaker">Sulfur hexafluoride</a></li></ul></li> <li><a href="/wiki/Generator_interlock_kit" title="Generator interlock kit">Generator interlock kit</a></li> <li><a href="/wiki/Numerical_relay" title="Numerical relay">Numerical relay</a></li> <li><a href="/wiki/Power_system_protection" title="Power system protection">Power system protection</a></li> <li><a href="/wiki/Protective_relay" title="Protective relay">Protective relay</a></li> <li><a href="/wiki/Residual-current_device" title="Residual-current device">Residual-current device</a> (GFI)</li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><div style="display: inline-block; line-height: 1.2em; padding: .1em 0;">Economics<br />and policies</div></th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Availability_factor" title="Availability factor">Availability factor</a></li> <li><a href="/wiki/Capacity_factor" title="Capacity factor">Capacity factor</a></li> <li><a href="/wiki/Carbon_offsets_and_credits" title="Carbon offsets and credits">Carbon offsets and credits</a></li> <li><a href="/wiki/Cost_of_electricity_by_source" title="Cost of electricity by source">Cost of electricity by source</a></li> <li><a href="/wiki/Energy_subsidy" title="Energy subsidy">Energy subsidies</a></li> <li><a href="/wiki/Environmental_tax" title="Environmental tax">Environmental tax</a></li> <li><a href="/wiki/Feed-in_tariff" title="Feed-in tariff">Feed-in tariff</a></li> <li><a href="/wiki/Fossil_fuel_phase-out" title="Fossil fuel phase-out">Fossil fuel phase-out</a></li> <li><a href="/wiki/Load_factor_(electrical)" title="Load factor (electrical)">Load factor</a></li> <li><a href="/wiki/Net_metering" title="Net metering">Net metering</a></li> <li><a href="/wiki/Pigouvian_tax" title="Pigouvian tax">Pigouvian tax</a></li> <li><a href="/wiki/Renewable_Energy_Certificate_(United_States)" title="Renewable Energy Certificate (United States)">Renewable Energy Certificates</a></li> <li><a href="/wiki/Renewable_energy_commercialization" title="Renewable energy commercialization">Renewable energy commercialization</a></li> <li><a href="/wiki/Renewable_Energy_Payments" title="Renewable Energy Payments">Renewable Energy Payments</a></li> <li><a href="/wiki/Spark_spread" title="Spark spread">Spark/Dark/Quark/Bark spread</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><div style="display: inline-block; line-height: 1.2em; padding: .1em 0;">Statistics and<br />production</div></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Electric_energy_consumption" title="Electric energy consumption">Electric energy consumption</a></li> <li><a href="/wiki/List_of_electricity_sectors" title="List of electricity sectors">List of electricity sectors</a></li></ul> </div></td></tr><tr><td class="navbox-abovebelow" colspan="3"><div> <ul><li><span class="noviewer" typeof="mw:File"><span title="Category"><img alt="" src="//upload.wikimedia.org/wikipedia/en/thumb/9/96/Symbol_category_class.svg/16px-Symbol_category_class.svg.png" decoding="async" width="16" height="16" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/en/thumb/9/96/Symbol_category_class.svg/23px-Symbol_category_class.svg.png 1.5x, //upload.wikimedia.org/wikipedia/en/thumb/9/96/Symbol_category_class.svg/31px-Symbol_category_class.svg.png 2x" data-file-width="180" data-file-height="185" /></span></span> <a href="/wiki/Category:Electric_power_distribution" title="Category:Electric power distribution">Category</a></li></ul> </div></td></tr></tbody></table></div> <div class="navbox-styles"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1129693374"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236075235"></div><div role="navigation" class="navbox" aria-labelledby="Electric_clock_technology" style="padding:3px"><table class="nowraplinks mw-collapsible autocollapse navbox-inner" style="border-spacing:0;background:transparent;color:inherit"><tbody><tr><th scope="col" class="navbox-title" colspan="2"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1129693374"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1239400231"><div class="navbar plainlinks hlist navbar-mini"><ul><li class="nv-view"><a href="/wiki/Template:Electric_clock_technology" title="Template:Electric clock technology"><abbr title="View this template">v</abbr></a></li><li class="nv-talk"><a href="/w/index.php?title=Template_talk:Electric_clock_technology&action=edit&redlink=1" class="new" title="Template talk:Electric clock technology (page does not exist)"><abbr title="Discuss this template">t</abbr></a></li><li class="nv-edit"><a href="/wiki/Special:EditPage/Template:Electric_clock_technology" title="Special:EditPage/Template:Electric clock technology"><abbr title="Edit this template">e</abbr></a></li></ul></div><div id="Electric_clock_technology" style="font-size:114%;margin:0 4em"><a href="/wiki/Electric_clock" title="Electric clock">Electric clock technology</a></div></th></tr><tr><th scope="row" class="navbox-group" style="width:1%">Powerline synchronized</th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Telechron#Henry_Warren:_the_Synchronous_Motor_and_the_Master_Clock" title="Telechron">Synchronous Motor and the Master Clock</a></li> <li><a class="mw-selflink selflink">Utility frequency</a></li> <li><a href="/wiki/Synchronous_motor" title="Synchronous motor">Synchronous motor</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Electronic</th><td class="navbox-list-with-group navbox-list navbox-even hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Quartz_clock" title="Quartz clock">Quartz clock</a></li> <li><a href="/wiki/Atomic_clock" title="Atomic clock">Atomic clock</a></li> <li><a href="/wiki/Radio_clock" title="Radio clock">Radio clock</a></li></ul> </div></td></tr></tbody></table></div>    </div><noscript><img src="https://login.wikimedia.org/wiki/Special:CentralAutoLogin/start?type=1x1" alt="" width="1" height="1" style="border: none; position: absolute;"></noscript> <div class="printfooter" data-nosnippet="">Retrieved from "<a dir="ltr" href="https://en.wikipedia.org/w/index.php?title=Utility_frequency&oldid=1252869788">https://en.wikipedia.org/w/index.php?title=Utility_frequency&oldid=1252869788</a>"</div></div> <div id="catlinks" class="catlinks" data-mw="interface"><div id="mw-normal-catlinks" class="mw-normal-catlinks"><a href="/wiki/Help:Category" title="Help:Category">Category</a>: <ul><li><a href="/wiki/Category:Electric_power" title="Category:Electric power">Electric power</a></li></ul></div><div id="mw-hidden-catlinks" class="mw-hidden-catlinks mw-hidden-cats-hidden">Hidden categories: <ul><li><a href="/wiki/Category:CS1_Spanish-language_sources_(es)" title="Category:CS1 Spanish-language sources (es)">CS1 Spanish-language sources (es)</a></li><li><a href="/wiki/Category:Articles_containing_explicitly_cited_English-language_text" title="Category:Articles containing explicitly cited English-language text">Articles containing explicitly cited English-language text</a></li><li><a href="/wiki/Category:CS1:_long_volume_value" title="Category:CS1: long volume value">CS1: long volume value</a></li><li><a href="/wiki/Category:CS1_German-language_sources_(de)" title="Category:CS1 German-language sources (de)">CS1 German-language sources (de)</a></li><li><a href="/wiki/Category:Articles_with_short_description" title="Category:Articles with short description">Articles with short description</a></li><li><a href="/wiki/Category:Short_description_is_different_from_Wikidata" title="Category:Short description is different from Wikidata">Short description is different from Wikidata</a></li><li><a href="/wiki/Category:All_articles_with_unsourced_statements" title="Category:All articles with unsourced statements">All articles with unsourced statements</a></li><li><a href="/wiki/Category:Articles_with_unsourced_statements_from_September_2017" title="Category:Articles with unsourced statements from September 2017">Articles with unsourced statements from September 2017</a></li><li><a href="/wiki/Category:All_pages_needing_factual_verification" title="Category:All pages needing factual verification">All pages needing factual verification</a></li><li><a href="/wiki/Category:Wikipedia_articles_needing_factual_verification_from_March_2017" title="Category:Wikipedia articles needing factual verification from March 2017">Wikipedia articles needing factual verification from March 2017</a></li><li><a href="/wiki/Category:Articles_with_unsourced_statements_from_April_2024" title="Category:Articles with unsourced statements from April 2024">Articles with unsourced statements from April 2024</a></li></ul></div></div> </div> </main> </div> <div class="mw-footer-container"> <footer id="footer" class="mw-footer" > <ul id="footer-info"> <li id="footer-info-lastmod"> This page was last edited on 23 October 2024, at 08:08<span class="anonymous-show"> (UTC)</span>.</li> <li id="footer-info-copyright">Text is available under the <a href="/wiki/Wikipedia:Text_of_the_Creative_Commons_Attribution-ShareAlike_4.0_International_License" title="Wikipedia:Text of the Creative Commons Attribution-ShareAlike 4.0 International License">Creative Commons Attribution-ShareAlike 4.0 License</a>; additional terms may apply. By using this site, you agree to the <a href="https://foundation.wikimedia.org/wiki/Special:MyLanguage/Policy:Terms_of_Use" class="extiw" title="foundation:Special:MyLanguage/Policy:Terms of Use">Terms of Use</a> and <a href="https://foundation.wikimedia.org/wiki/Special:MyLanguage/Policy:Privacy_policy" class="extiw" title="foundation:Special:MyLanguage/Policy:Privacy policy">Privacy Policy</a>. Wikipedia® is a registered trademark of the <a rel="nofollow" class="external text" href="https://wikimediafoundation.org/">Wikimedia Foundation, Inc.</a>, a non-profit organization.</li> </ul> <ul id="footer-places"> <li id="footer-places-privacy"><a href="https://foundation.wikimedia.org/wiki/Special:MyLanguage/Policy:Privacy_policy">Privacy policy</a></li> <li id="footer-places-about"><a href="/wiki/Wikipedia:About">About Wikipedia</a></li> <li id="footer-places-disclaimers"><a href="/wiki/Wikipedia:General_disclaimer">Disclaimers</a></li> <li id="footer-places-contact"><a href="//en.wikipedia.org/wiki/Wikipedia:Contact_us">Contact Wikipedia</a></li> <li id="footer-places-wm-codeofconduct"><a href="https://foundation.wikimedia.org/wiki/Special:MyLanguage/Policy:Universal_Code_of_Conduct">Code of Conduct</a></li> <li id="footer-places-developers"><a href="https://developer.wikimedia.org">Developers</a></li> <li id="footer-places-statslink"><a href="https://stats.wikimedia.org/#/en.wikipedia.org">Statistics</a></li> <li id="footer-places-cookiestatement"><a href="https://foundation.wikimedia.org/wiki/Special:MyLanguage/Policy:Cookie_statement">Cookie statement</a></li> <li id="footer-places-mobileview"><a href="//en.m.wikipedia.org/w/index.php?title=Utility_frequency&mobileaction=toggle_view_mobile" class="noprint stopMobileRedirectToggle">Mobile view</a></li> </ul> <ul id="footer-icons" class="noprint"> <li id="footer-copyrightico"><a href="https://wikimediafoundation.org/" class="cdx-button cdx-button--fake-button cdx-button--size-large cdx-button--fake-button--enabled"><img src="/static/images/footer/wikimedia-button.svg" width="84" height="29" alt="Wikimedia Foundation" loading="lazy"></a></li> <li id="footer-poweredbyico"><a href="https://www.mediawiki.org/" class="cdx-button cdx-button--fake-button cdx-button--size-large cdx-button--fake-button--enabled"><img src="/w/resources/assets/poweredby_mediawiki.svg" alt="Powered by MediaWiki" width="88" height="31" loading="lazy"></a></li> </ul> </footer> </div> </div> </div> <div class="vector-settings" id="p-dock-bottom"> <ul></ul> </div><script>(RLQ=window.RLQ||[]).push(function(){mw.config.set({"wgHostname":"mw-web.codfw.main-694cf4987f-5mrbp","wgBackendResponseTime":159,"wgPageParseReport":{"limitreport":{"cputime":"0.685","walltime":"0.903","ppvisitednodes":{"value":4932,"limit":1000000},"postexpandincludesize":{"value":97375,"limit":2097152},"templateargumentsize":{"value":6444,"limit":2097152},"expansiondepth":{"value":16,"limit":100},"expensivefunctioncount":{"value":13,"limit":500},"unstrip-depth":{"value":1,"limit":20},"unstrip-size":{"value":138608,"limit":5000000},"entityaccesscount":{"value":0,"limit":400},"timingprofile":["100.00% 714.496 1 -total"," 36.99% 264.321 1 Template:Reflist"," 12.71% 90.808 1 Template:Citation"," 12.59% 89.945 3 Template:Navbox"," 12.12% 86.571 1 Template:Electricity_delivery"," 11.98% 85.571 1 Template:Langx"," 11.05% 78.925 13 Template:Cite_web"," 9.22% 65.864 1 Template:Short_description"," 6.50% 46.419 7 Template:Sfn"," 6.06% 43.280 2 Template:ISSN"]},"scribunto":{"limitreport-timeusage":{"value":"0.399","limit":"10.000"},"limitreport-memusage":{"value":17118413,"limit":52428800},"limitreport-logs":"anchor_id_list = table#1 {\n [\"Area_control_error\"] = 1,\n [\"CITEREFAtitude_Editorial\"] = 1,\n [\"CITEREFBaylissHardy2022\"] = 1,\n [\"CITEREFBratton1971\"] = 1,\n [\"CITEREFC._Linder2002\"] = 1,\n [\"CITEREFENTSO-E2017\"] = 1,\n [\"CITEREFFinkBeaty1978\"] = 1,\n [\"CITEREFGordon_Woodward\"] = 1,\n [\"CITEREFGraingerStevenson1994\"] = 1,\n [\"CITEREFH.T._Kohlhaas1946\"] = 1,\n [\"CITEREFLombardo2016\"] = 1,\n [\"CITEREFMillerLewBarnes2017\"] = 1,\n [\"CITEREFNERC2021\"] = 1,\n [\"CITEREFNREL\"] = 1,\n [\"CITEREFOwen1997\"] = 1,\n [\"CITEREFSt._John2017\"] = 1,\n [\"CITEREFSterling1978\"] = 1,\n [\"CITEREFWald2011\"] = 1,\n [\"Long-term_stability_and_clock_synchronization\"] = 1,\n}\ntemplate_list = table#1 {\n [\"Anchor\"] = 2,\n [\"Awrap\"] = 1,\n [\"Citation\"] = 1,\n [\"Citation needed\"] = 1,\n [\"Cite book\"] = 8,\n [\"Cite journal\"] = 1,\n [\"Cite news\"] = 2,\n [\"Cite thesis\"] = 1,\n [\"Cite web\"] = 13,\n [\"Cn\"] = 1,\n [\"Electric clock technology\"] = 1,\n [\"Electricity delivery\"] = 1,\n [\"Frac\"] = 20,\n [\"Harvnb\"] = 2,\n [\"ISBN\"] = 3,\n [\"ISSN\"] = 2,\n [\"Langx\"] = 1,\n [\"Main\"] = 4,\n [\"Math\"] = 5,\n [\"Mvar\"] = 4,\n [\"Nbh\"] = 2,\n [\"Nowrap\"] = 2,\n [\"Overline\"] = 1,\n [\"Redirect\"] = 2,\n [\"Reflist\"] = 1,\n [\"See also\"] = 1,\n [\"Sfn\"] = 7,\n [\"Sfrac\"] = 1,\n [\"Short description\"] = 1,\n [\"Slink\"] = 1,\n [\"URL\"] = 2,\n [\"Val\"] = 1,\n [\"Verify source\"] = 1,\n}\narticle_whitelist = table#1 {\n}\n"},"cachereport":{"origin":"mw-web.codfw.main-6b7f745dd4-4ldpq","timestamp":"20241125143710","ttl":2592000,"transientcontent":false}}});});</script> <script type="application/ld+json">{"@context":"https:\/\/schema.org","@type":"Article","name":"Utility frequency","url":"https:\/\/en.wikipedia.org\/wiki\/Utility_frequency","sameAs":"http:\/\/www.wikidata.org\/entity\/Q1361387","mainEntity":"http:\/\/www.wikidata.org\/entity\/Q1361387","author":{"@type":"Organization","name":"Contributors to Wikimedia projects"},"publisher":{"@type":"Organization","name":"Wikimedia Foundation, Inc.","logo":{"@type":"ImageObject","url":"https:\/\/www.wikimedia.org\/static\/images\/wmf-hor-googpub.png"}},"datePublished":"2004-02-25T20:43:04Z","dateModified":"2024-10-23T08:08:40Z","image":"https:\/\/upload.wikimedia.org\/wikipedia\/commons\/b\/bf\/50Hz60Hz.svg","headline":"AC frequency used on a given area's electricity grid"}</script> </body> </html>