{"id":2409,"date":"2026-03-29T10:52:54","date_gmt":"2026-03-29T02:52:54","guid":{"rendered":"https:\/\/zmgs-global.com\/?p=2409"},"modified":"2026-04-08T10:53:31","modified_gmt":"2026-04-08T02:53:31","slug":"what-is-the-main-function-of-the-current-transformer","status":"publish","type":"post","link":"https:\/\/zmgs-global.com\/id\/what-is-the-main-function-of-the-current-transformer.html","title":{"rendered":"What is The Main Function of The Current Transformer?"},"content":{"rendered":"\t\t<div data-elementor-type=\"wp-post\" data-elementor-id=\"2409\" class=\"elementor elementor-2409\" data-elementor-post-type=\"post\">\n\t\t\t\t<div class=\"elementor-element elementor-element-4614db8 e-flex e-con-boxed e-con e-parent\" data-id=\"4614db8\" data-element_type=\"container\" data-e-type=\"container\">\n\t\t\t\t\t<div class=\"e-con-inner\">\n\t\t\t\t<div class=\"elementor-element elementor-element-02c74b4 elementor-widget elementor-widget-text-editor\" data-id=\"02c74b4\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t\t\t\t\t\t<div class=\"node-slot\" data-v-37d25bc6=\"\" data-node-index=\"5\" data-node-type=\"paragraph\"><div class=\"node-content\" data-v-37d25bc6=\"\"><p class=\"paragraph-node\" dir=\"auto\" data-v-4e2afdbc=\"\" data-v-37d25bc6=\"\"><span class=\"whitespace-pre-wrap break-words text-node\" data-v-4e2afdbc=\"\">Walk into any electrical substation or industrial facility and there\u2019s a good chance you\u2019ll find current transformers installed almost everywhere \u2014 on busbars, cable feeders, switchgear panels. They\u2019re not the most glamorous piece of equipment, but understanding what they actually do explains a lot about how modern power systems stay reliable and safe.<\/span><\/p><\/div><\/div><div class=\"node-slot\" data-v-37d25bc6=\"\" data-node-index=\"6\" data-node-type=\"paragraph\"><div class=\"node-content\" data-v-37d25bc6=\"\"><p class=\"paragraph-node\" dir=\"auto\" data-v-4e2afdbc=\"\" data-v-37d25bc6=\"\"><span class=\"whitespace-pre-wrap break-words text-node\" data-v-4e2afdbc=\"\">At its core, the main function of a <a href=\"https:\/\/zmgs-global.com\/products\/current-transformer\"><strong>current transformer<\/strong><\/a> is to reproduce a scaled-down version of the primary current in its secondary circuit. That sounds simple enough, but the implications of that function reach into metering, protection, monitoring, and control \u2014 pretty much every layer of how electrical systems are managed.<\/span><\/p><\/div><\/div>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-7417679 elementor-widget__width-initial elementor-widget elementor-widget-image\" data-id=\"7417679\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"image.default\">\n\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t<img fetchpriority=\"high\" decoding=\"async\" width=\"700\" height=\"700\" src=\"https:\/\/zmgs-global.com\/wp-content\/uploads\/2025\/09\/\u5fae\u4fe1\u56fe\u7247_2025-09-17_124925_892-e1775097943684.png\" class=\"attachment-full size-full wp-image-610\" alt=\"Zero Sequence Current Transformer\" \/>\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-a1110bd elementor-widget elementor-widget-heading\" data-id=\"a1110bd\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t\t<div id=\"ez-toc-container\" class=\"ez-toc-v2_0_82_2 counter-hierarchy ez-toc-counter ez-toc-grey ez-toc-container-direction\">\n<div class=\"ez-toc-title-container\">\n<p class=\"ez-toc-title\" style=\"cursor:inherit\">Table of Contents<\/p>\n<span class=\"ez-toc-title-toggle\"><\/span><\/div>\n<nav><ul class='ez-toc-list ez-toc-list-level-1 ' ><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-1\" href=\"https:\/\/zmgs-global.com\/id\/what-is-the-main-function-of-the-current-transformer.html\/#The_Core_Functions_of_a_Current_Transformer\" >The Core Functions of a Current Transformer<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-2\" href=\"https:\/\/zmgs-global.com\/id\/what-is-the-main-function-of-the-current-transformer.html\/#Accuracy_Classes_and_Their_Functions\" >Accuracy Classes and Their Functions<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-3\" href=\"https:\/\/zmgs-global.com\/id\/what-is-the-main-function-of-the-current-transformer.html\/#Where_Current_Transformers_Are_Typically_Installed\" >Where Current Transformers Are Typically Installed<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-4\" href=\"https:\/\/zmgs-global.com\/id\/what-is-the-main-function-of-the-current-transformer.html\/#Choosing_the_Right_CT_for_the_Job\" >Choosing the Right CT for the Job<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-5\" href=\"https:\/\/zmgs-global.com\/id\/what-is-the-main-function-of-the-current-transformer.html\/#FAQ\" >FAQ<\/a><\/li><\/ul><\/nav><\/div>\n<h2 class=\"elementor-heading-title elementor-size-default\"><span class=\"ez-toc-section\" id=\"The_Core_Functions_of_a_Current_Transformer\"><\/span>The Core Functions of a Current Transformer<span class=\"ez-toc-section-end\"><\/span><\/h2>\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-0a4926d elementor-widget elementor-widget-heading\" data-id=\"0a4926d\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t\t<h3 class=\"elementor-heading-title elementor-size-default\">Stepping Down Current for Safe Measurement<\/h3>\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-5ee5380 elementor-widget elementor-widget-text-editor\" data-id=\"5ee5380\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t\t\t\t\t\t<div class=\"node-slot\" data-v-37d25bc6=\"\" data-node-index=\"9\" data-node-type=\"paragraph\"><div class=\"node-content\" data-v-37d25bc6=\"\"><p class=\"paragraph-node\" dir=\"auto\" data-v-4e2afdbc=\"\" data-v-37d25bc6=\"\"><span class=\"whitespace-pre-wrap break-words text-node\" data-v-4e2afdbc=\"\">High-voltage, high-current conductors can carry thousands of amperes. No standard measuring instrument is designed to handle that directly. A current transformer reduces that current proportionally \u2014 a 2000:5 ratio CT, for instance, converts 2000A into 5A \u2014 so that ordinary meters, analyzers, and data loggers can connect safely without any direct contact with the high-current circuit.<\/span><\/p><\/div><\/div><div class=\"node-slot\" data-v-37d25bc6=\"\" data-node-index=\"10\" data-node-type=\"paragraph\"><div class=\"node-content\" data-v-37d25bc6=\"\"><p class=\"paragraph-node\" dir=\"auto\" data-v-4e2afdbc=\"\" data-v-37d25bc6=\"\"><span class=\"whitespace-pre-wrap break-words text-node\" data-v-4e2afdbc=\"\">This isolation is actually a dual benefit. It protects the instruments, and it protects the people working with them.<\/span><\/p><\/div><\/div>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-92311c7 elementor-widget elementor-widget-heading\" data-id=\"92311c7\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t\t<h3 class=\"elementor-heading-title elementor-size-default\">Enabling Accurate Energy Metering<\/h3>\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-6eaf457 elementor-widget elementor-widget-text-editor\" data-id=\"6eaf457\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t\t\t\t\t\t<div class=\"node-slot\" data-v-37d25bc6=\"\" data-node-index=\"12\" data-node-type=\"paragraph\"><div class=\"node-content\" data-v-37d25bc6=\"\"><p class=\"paragraph-node\" dir=\"auto\" data-v-4e2afdbc=\"\" data-v-37d25bc6=\"\"><span class=\"whitespace-pre-wrap break-words text-node\" data-v-4e2afdbc=\"\">Revenue metering is one of the most critical applications. Utilities depend on current transformers to feed accurate current signals into energy meters, which then calculate consumption in kilowatt-hours. Any error in the CT output translates directly into billing inaccuracies \u2014 which is why metering-class CTs are held to tight accuracy standards (Class 0.2 or 0.5 in most cases).<\/span><\/p><\/div><\/div><div class=\"node-slot\" data-v-37d25bc6=\"\" data-node-index=\"13\" data-node-type=\"paragraph\"><div class=\"node-content\" data-v-37d25bc6=\"\"><p class=\"paragraph-node\" dir=\"auto\" data-v-4e2afdbc=\"\" data-v-37d25bc6=\"\"><span class=\"whitespace-pre-wrap break-words text-node\" data-v-4e2afdbc=\"\">Large commercial and industrial facilities use the same principle internally, tracking energy use across different production lines or building zones. It\u2019s a practical way to identify waste and allocate costs.<\/span><\/p><\/div><\/div>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-314ca79 elementor-widget elementor-widget-heading\" data-id=\"314ca79\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t\t<h3 class=\"elementor-heading-title elementor-size-default\">Supporting Protective Relay Systems<\/h3>\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-ddf1800 elementor-widget elementor-widget-text-editor\" data-id=\"ddf1800\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t\t\t\t\t\t<div class=\"node-slot\" data-v-37d25bc6=\"\" data-node-index=\"15\" data-node-type=\"paragraph\"><div class=\"node-content\" data-v-37d25bc6=\"\"><p class=\"paragraph-node\" dir=\"auto\" data-v-4e2afdbc=\"\" data-v-37d25bc6=\"\"><span class=\"whitespace-pre-wrap break-words text-node\" data-v-4e2afdbc=\"\">Perhaps the most safety-critical function. Protection relays \u2014 overcurrent relays, differential relays, earth fault relays \u2014 all receive their current inputs from CTs. When a fault occurs, the CT needs to accurately reproduce the fault current so the relay can make the right decision: trip the breaker or hold.<\/span><\/p><\/div><\/div><div class=\"node-slot\" data-v-37d25bc6=\"\" data-node-index=\"16\" data-node-type=\"paragraph\"><div class=\"node-content\" data-v-37d25bc6=\"\"><p class=\"paragraph-node\" dir=\"auto\" data-v-4e2afdbc=\"\" data-v-37d25bc6=\"\"><span class=\"whitespace-pre-wrap break-words text-node\" data-v-4e2afdbc=\"\">Protection CTs are built differently from metering CTs. They\u2019re designed to stay linear even when current surges to 10, 20, or more times the rated value during a fault. A metering CT would saturate under those conditions and give the relay a distorted signal \u2014 potentially causing a delayed or missed trip.<\/span><\/p><\/div><\/div>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-5e16cf6 elementor-widget elementor-widget-heading\" data-id=\"5e16cf6\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t\t<h3 class=\"elementor-heading-title elementor-size-default\">Isolation Between High and Low Voltage Circuits<\/h3>\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-2469df3 elementor-widget elementor-widget-text-editor\" data-id=\"2469df3\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t\t\t\t\t\t<p>This function sometimes gets overlooked, but it matters. The current transformer provides galvanic isolation between the primary high-voltage circuit and the secondary instrumentation circuit. Secondary equipment \u2014 meters, relays, recorders \u2014 operates at low voltage and is physically separated from the dangerous primary side. That separation is what makes it practical to install sensitive electronics in the same panel as high-voltage equipment.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-9c2a3c3 elementor-widget__width-initial elementor-widget elementor-widget-image\" data-id=\"9c2a3c3\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"image.default\">\n\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t<img decoding=\"async\" width=\"750\" height=\"750\" src=\"https:\/\/zmgs-global.com\/wp-content\/uploads\/2025\/09\/lmzj1-0.66-e1775616450795.png\" class=\"attachment-full size-full wp-image-592\" alt=\"current transformer\" \/>\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-59f9d91 elementor-widget elementor-widget-heading\" data-id=\"59f9d91\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t\t<h2 class=\"elementor-heading-title elementor-size-default\"><span class=\"ez-toc-section\" id=\"Accuracy_Classes_and_Their_Functions\"><\/span>Accuracy Classes and Their Functions<span class=\"ez-toc-section-end\"><\/span><\/h2>\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-b2bd4c0 elementor-widget elementor-widget-text-editor\" data-id=\"b2bd4c0\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t\t\t\t\t\t<div class=\"node-slot\" data-v-37d25bc6=\"\" data-node-index=\"3\" data-node-type=\"paragraph\"><div class=\"node-content\" data-v-37d25bc6=\"\"><p class=\"paragraph-node\" dir=\"auto\" data-v-4e2afdbc=\"\" data-v-37d25bc6=\"\"><span class=\"whitespace-pre-wrap break-words text-node\" data-v-4e2afdbc=\"\">Different functions demand different accuracy levels, and the class system reflects that fairly clearly. At the high-precision end, Class 0.1 and 0.2 are reserved for revenue metering and laboratory-grade measurement \u2014 these carry the tightest limits on ratio error and phase displacement. Class 0.5 and 1 cover general industrial metering, where a small degree of error is acceptable for monitoring and cost-allocation purposes. Class 3 and 5 drop further in precision and are only suitable for approximate indication, the kind of rough reading where exact figures don\u2019t really matter.<\/span><\/p><\/div><\/div><div class=\"node-slot\" data-v-37d25bc6=\"\" data-node-index=\"4\" data-node-type=\"paragraph\"><div class=\"node-content\" data-v-37d25bc6=\"\"><p class=\"paragraph-node\" dir=\"auto\" data-v-4e2afdbc=\"\" data-v-37d25bc6=\"\"><span class=\"whitespace-pre-wrap break-words text-node\" data-v-4e2afdbc=\"\">On the protection side, the classification works differently. Class 5P and 10P are designed for overcurrent protection schemes, rated to maintain acceptable accuracy up to a defined multiple of the rated current \u2014 that multiple being the accuracy limit factor. Class X sits in a category of its own, specified not by error limits but by knee-point voltage and secondary resistance, making it the standard choice for differential protection applications where the CT\u2019s behavior under fault conditions needs to be tightly controlled.<\/span><\/p><\/div><\/div><div class=\"node-slot\" data-v-37d25bc6=\"\" data-node-index=\"5\" data-node-type=\"paragraph\"><div class=\"node-content\" data-v-37d25bc6=\"\"><p class=\"paragraph-node\" dir=\"auto\" data-v-4e2afdbc=\"\" data-v-37d25bc6=\"\"><span class=\"whitespace-pre-wrap break-words text-node\" data-v-4e2afdbc=\"\">Mixing up metering and protection classes is a common installation mistake \u2014 one that can compromise either billing accuracy or system protection, depending on which way the error goes.<\/span><\/p><\/div><\/div><div class=\"node-slot\" data-v-37d25bc6=\"\" data-node-index=\"6\" data-node-type=\"thematic_break\">\u00a0<\/div>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-aa4f06e elementor-widget elementor-widget-heading\" data-id=\"aa4f06e\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t\t<h2 class=\"elementor-heading-title elementor-size-default\"><span class=\"ez-toc-section\" id=\"Where_Current_Transformers_Are_Typically_Installed\"><\/span>Where Current Transformers Are Typically Installed<span class=\"ez-toc-section-end\"><\/span><\/h2>\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-58b812b elementor-widget elementor-widget-text-editor\" data-id=\"58b812b\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t\t\t\t\t\t<div class=\"node-slot\" data-v-37d25bc6=\"\" data-node-index=\"24\" data-node-type=\"paragraph\"><div class=\"node-content\" data-v-37d25bc6=\"\"><p class=\"paragraph-node\" dir=\"auto\" data-v-4e2afdbc=\"\" data-v-37d25bc6=\"\"><span class=\"whitespace-pre-wrap break-words text-node\" data-v-4e2afdbc=\"\">Current transformers show up in a wide range of locations across power systems:<\/span><\/p><\/div><\/div><div class=\"node-slot\" data-v-37d25bc6=\"\" data-node-index=\"25\" data-node-type=\"list\"><div class=\"node-content\" data-v-37d25bc6=\"\"><ul class=\"list-node list-disc\" data-v-79057d57=\"\" data-v-37d25bc6=\"\"><li class=\"list-item pl-1.5 my-2\" dir=\"auto\" data-v-7a618746=\"\" data-v-79057d57=\"\"><div class=\"markstream-vue markdown-renderer\" data-v-37d25bc6=\"\" data-v-7a618746=\"\"><div class=\"node-slot\" data-v-37d25bc6=\"\" data-node-index=\"0\" data-node-type=\"paragraph\"><div class=\"node-content\" data-v-37d25bc6=\"\"><p class=\"paragraph-node\" dir=\"auto\" data-v-4e2afdbc=\"\" data-v-37d25bc6=\"\"><span class=\"whitespace-pre-wrap break-words text-node\" data-v-4e2afdbc=\"\">High-voltage transmission substations<\/span><\/p><\/div><\/div><\/div><\/li><li class=\"list-item pl-1.5 my-2\" dir=\"auto\" data-v-7a618746=\"\" data-v-79057d57=\"\"><div class=\"markstream-vue markdown-renderer\" data-v-37d25bc6=\"\" data-v-7a618746=\"\"><div class=\"node-slot\" data-v-37d25bc6=\"\" data-node-index=\"0\" data-node-type=\"paragraph\"><div class=\"node-content\" data-v-37d25bc6=\"\"><p class=\"paragraph-node\" dir=\"auto\" data-v-4e2afdbc=\"\" data-v-37d25bc6=\"\"><span class=\"whitespace-pre-wrap break-words text-node\" data-v-4e2afdbc=\"\">Medium-voltage switchgear and ring main units<\/span><\/p><\/div><\/div><\/div><\/li><li class=\"list-item pl-1.5 my-2\" dir=\"auto\" data-v-7a618746=\"\" data-v-79057d57=\"\"><div class=\"markstream-vue markdown-renderer\" data-v-37d25bc6=\"\" data-v-7a618746=\"\"><div class=\"node-slot\" data-v-37d25bc6=\"\" data-node-index=\"0\" data-node-type=\"paragraph\"><div class=\"node-content\" data-v-37d25bc6=\"\"><p class=\"paragraph-node\" dir=\"auto\" data-v-4e2afdbc=\"\" data-v-37d25bc6=\"\"><span class=\"whitespace-pre-wrap break-words text-node\" data-v-4e2afdbc=\"\">Low-voltage distribution boards and motor control centers<\/span><\/p><\/div><\/div><\/div><\/li><li class=\"list-item pl-1.5 my-2\" dir=\"auto\" data-v-7a618746=\"\" data-v-79057d57=\"\"><div class=\"markstream-vue markdown-renderer\" data-v-37d25bc6=\"\" data-v-7a618746=\"\"><div class=\"node-slot\" data-v-37d25bc6=\"\" data-node-index=\"0\" data-node-type=\"paragraph\"><div class=\"node-content\" data-v-37d25bc6=\"\"><p class=\"paragraph-node\" dir=\"auto\" data-v-4e2afdbc=\"\" data-v-37d25bc6=\"\"><span class=\"whitespace-pre-wrap break-words text-node\" data-v-4e2afdbc=\"\">Revenue metering panels at utility connection points<\/span><\/p><\/div><\/div><\/div><\/li><li class=\"list-item pl-1.5 my-2\" dir=\"auto\" data-v-7a618746=\"\" data-v-79057d57=\"\"><div class=\"markstream-vue markdown-renderer\" data-v-37d25bc6=\"\" data-v-7a618746=\"\"><div class=\"node-slot\" data-v-37d25bc6=\"\" data-node-index=\"0\" data-node-type=\"paragraph\"><div class=\"node-content\" data-v-37d25bc6=\"\"><p class=\"paragraph-node\" dir=\"auto\" data-v-4e2afdbc=\"\" data-v-37d25bc6=\"\"><span class=\"whitespace-pre-wrap break-words text-node\" data-v-4e2afdbc=\"\">Industrial machinery with high-current drives or motors<\/span><\/p><\/div><\/div><\/div><\/li><\/ul><\/div><\/div><div class=\"node-slot\" data-v-37d25bc6=\"\" data-node-index=\"26\" data-node-type=\"paragraph\"><div class=\"node-content\" data-v-37d25bc6=\"\"><p class=\"paragraph-node\" dir=\"auto\" data-v-4e2afdbc=\"\" data-v-37d25bc6=\"\"><span class=\"whitespace-pre-wrap break-words text-node\" data-v-4e2afdbc=\"\">The physical form varies too \u2014 toroidal (ring-type) CTs for retrofitting onto existing cables, bar-type CTs for busbars, wound-type CTs for precision metering, and split-core CTs when the conductor can\u2019t be disconnected.<\/span><\/p><\/div><\/div>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-0648343 elementor-widget elementor-widget-heading\" data-id=\"0648343\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t\t<h2 class=\"elementor-heading-title elementor-size-default\"><span class=\"ez-toc-section\" id=\"Choosing_the_Right_CT_for_the_Job\"><\/span>Choosing the Right CT for the Job<span class=\"ez-toc-section-end\"><\/span><\/h2>\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-7c55cc6 elementor-widget elementor-widget-text-editor\" data-id=\"7c55cc6\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t\t\t\t\t\t<div class=\"node-slot\" data-v-37d25bc6=\"\" data-node-index=\"28\" data-node-type=\"paragraph\"><div class=\"node-content\" data-v-37d25bc6=\"\"><p class=\"paragraph-node\" dir=\"auto\" data-v-4e2afdbc=\"\" data-v-37d25bc6=\"\"><span class=\"whitespace-pre-wrap break-words text-node\" data-v-4e2afdbc=\"\">Getting the selection right involves a few key steps:<\/span><\/p><\/div><\/div><div class=\"node-slot\" data-v-37d25bc6=\"\" data-node-index=\"29\" data-node-type=\"list\"><div class=\"node-content\" data-v-37d25bc6=\"\"><ol class=\"list-node list-decimal\" data-v-79057d57=\"\" data-v-37d25bc6=\"\"><li class=\"list-item pl-1.5 my-2\" dir=\"auto\" value=\"1\" data-v-7a618746=\"\" data-v-79057d57=\"\"><div class=\"markstream-vue markdown-renderer\" data-v-37d25bc6=\"\" data-v-7a618746=\"\"><div class=\"node-slot\" data-v-37d25bc6=\"\" data-node-index=\"0\" data-node-type=\"paragraph\"><div class=\"node-content\" data-v-37d25bc6=\"\"><p class=\"paragraph-node\" dir=\"auto\" data-v-4e2afdbc=\"\" data-v-37d25bc6=\"\"><span class=\"whitespace-pre-wrap break-words text-node\" data-v-4e2afdbc=\"\">Determine the maximum primary current (including any expected overload)<\/span><\/p><\/div><\/div><\/div><\/li><li class=\"list-item pl-1.5 my-2\" dir=\"auto\" value=\"2\" data-v-7a618746=\"\" data-v-79057d57=\"\"><div class=\"markstream-vue markdown-renderer\" data-v-37d25bc6=\"\" data-v-7a618746=\"\"><div class=\"node-slot\" data-v-37d25bc6=\"\" data-node-index=\"0\" data-node-type=\"paragraph\"><div class=\"node-content\" data-v-37d25bc6=\"\"><p class=\"paragraph-node\" dir=\"auto\" data-v-4e2afdbc=\"\" data-v-37d25bc6=\"\"><span class=\"whitespace-pre-wrap break-words text-node\" data-v-4e2afdbc=\"\">Select the appropriate transformation ratio<\/span><\/p><\/div><\/div><\/div><\/li><li class=\"list-item pl-1.5 my-2\" dir=\"auto\" value=\"3\" data-v-7a618746=\"\" data-v-79057d57=\"\"><div class=\"markstream-vue markdown-renderer\" data-v-37d25bc6=\"\" data-v-7a618746=\"\"><div class=\"node-slot\" data-v-37d25bc6=\"\" data-node-index=\"0\" data-node-type=\"paragraph\"><div class=\"node-content\" data-v-37d25bc6=\"\"><p class=\"paragraph-node\" dir=\"auto\" data-v-4e2afdbc=\"\" data-v-37d25bc6=\"\"><span class=\"whitespace-pre-wrap break-words text-node\" data-v-4e2afdbc=\"\">Identify the required accuracy class based on the application<\/span><\/p><\/div><\/div><\/div><\/li><li class=\"list-item pl-1.5 my-2\" dir=\"auto\" value=\"4\" data-v-7a618746=\"\" data-v-79057d57=\"\"><div class=\"markstream-vue markdown-renderer\" data-v-37d25bc6=\"\" data-v-7a618746=\"\"><div class=\"node-slot\" data-v-37d25bc6=\"\" data-node-index=\"0\" data-node-type=\"paragraph\"><div class=\"node-content\" data-v-37d25bc6=\"\"><p class=\"paragraph-node\" dir=\"auto\" data-v-4e2afdbc=\"\" data-v-37d25bc6=\"\"><span class=\"whitespace-pre-wrap break-words text-node\" data-v-4e2afdbc=\"\">Calculate the burden (total VA load on the secondary circuit)<\/span><\/p><\/div><\/div><\/div><\/li><li class=\"list-item pl-1.5 my-2\" dir=\"auto\" value=\"5\" data-v-7a618746=\"\" data-v-79057d57=\"\"><div class=\"markstream-vue markdown-renderer\" data-v-37d25bc6=\"\" data-v-7a618746=\"\"><div class=\"node-slot\" data-v-37d25bc6=\"\" data-node-index=\"0\" data-node-type=\"paragraph\"><div class=\"node-content\" data-v-37d25bc6=\"\"><p class=\"paragraph-node\" dir=\"auto\" data-v-4e2afdbc=\"\" data-v-37d25bc6=\"\"><span class=\"whitespace-pre-wrap break-words text-node\" data-v-4e2afdbc=\"\">Confirm the CT\u2019s rated burden meets or exceeds the connected burden<\/span><\/p><\/div><\/div><\/div><\/li><\/ol><\/div><\/div><div class=\"node-slot\" data-v-37d25bc6=\"\" data-node-index=\"30\" data-node-type=\"paragraph\"><div class=\"node-content\" data-v-37d25bc6=\"\"><p class=\"paragraph-node\" dir=\"auto\" data-v-4e2afdbc=\"\" data-v-37d25bc6=\"\"><span class=\"whitespace-pre-wrap break-words text-node\" data-v-4e2afdbc=\"\">Undersizing the burden rating is a frequent oversight. When the actual burden exceeds the rated value, accuracy degrades \u2014 sometimes significantly. If you want to know more about current transformer, please read\u00a0<a href=\"https:\/\/zmgs-global.com\/what-is-the-current-transformer.html\"><strong>What is the current transformer<\/strong><\/a>.<\/span><\/p><\/div><\/div>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t<div class=\"elementor-element elementor-element-5f5b4c1e e-con-full e-flex e-con e-parent\" data-id=\"5f5b4c1e\" data-element_type=\"container\" data-e-type=\"container\">\n\t\t\t\t<div class=\"elementor-element elementor-element-311d2eb2 elementor-widget__width-inherit elementor-widget elementor-widget-heading\" data-id=\"311d2eb2\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t\t<h2 class=\"elementor-heading-title elementor-size-default\"><span class=\"ez-toc-section\" id=\"FAQ\"><\/span>FAQ<span class=\"ez-toc-section-end\"><\/span><\/h2>\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-38c1f22c elementor-widget elementor-widget-n-accordion\" data-id=\"38c1f22c\" data-element_type=\"widget\" data-e-type=\"widget\" data-settings=\"{&quot;default_state&quot;:&quot;expanded&quot;,&quot;max_items_expended&quot;:&quot;one&quot;,&quot;n_accordion_animation_duration&quot;:{&quot;unit&quot;:&quot;ms&quot;,&quot;size&quot;:400,&quot;sizes&quot;:[]}}\" data-widget_type=\"nested-accordion.default\">\n\t\t\t\t\t\t\t<div class=\"e-n-accordion\" aria-label=\"Accordion. Open links with Enter or Space, close with Escape, and navigate with Arrow Keys\">\n\t\t\t\t\t\t<details id=\"e-n-accordion-item-9520\" class=\"e-n-accordion-item\" open>\n\t\t\t\t<summary class=\"e-n-accordion-item-title\" data-accordion-index=\"1\" tabindex=\"0\" aria-expanded=\"true\" aria-controls=\"e-n-accordion-item-9520\" >\n\t\t\t\t\t<span class='e-n-accordion-item-title-header'><div class=\"e-n-accordion-item-title-text\"> Can one current transformer serve both metering and protection functions? <\/div><\/span>\n\t\t\t\t\t\t\t<span class='e-n-accordion-item-title-icon'>\n\t\t\t<span class='e-opened' ><svg aria-hidden=\"true\" class=\"e-font-icon-svg e-fas-minus\" viewBox=\"0 0 448 512\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\"><path d=\"M416 208H32c-17.67 0-32 14.33-32 32v32c0 17.67 14.33 32 32 32h384c17.67 0 32-14.33 32-32v-32c0-17.67-14.33-32-32-32z\"><\/path><\/svg><\/span>\n\t\t\t<span class='e-closed'><svg aria-hidden=\"true\" class=\"e-font-icon-svg e-fas-plus\" viewBox=\"0 0 448 512\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\"><path d=\"M416 208H272V64c0-17.67-14.33-32-32-32h-32c-17.67 0-32 14.33-32 32v144H32c-17.67 0-32 14.33-32 32v32c0 17.67 14.33 32 32 32h144v144c0 17.67 14.33 32 32 32h32c17.67 0 32-14.33 32-32V304h144c17.67 0 32-14.33 32-32v-32c0-17.67-14.33-32-32-32z\"><\/path><\/svg><\/span>\n\t\t<\/span>\n\n\t\t\t\t\t\t<\/summary>\n\t\t\t\t<div role=\"region\" aria-labelledby=\"e-n-accordion-item-9520\" class=\"elementor-element elementor-element-7da47c2d e-con-full e-flex e-con e-child\" data-id=\"7da47c2d\" data-element_type=\"container\" data-e-type=\"container\">\n\t\t\t\t<div class=\"elementor-element elementor-element-3962dc1 elementor-widget elementor-widget-text-editor\" data-id=\"3962dc1\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t\t\t\t\t\t<p>Some CTs are dual-rated with separate secondary windings \u2014 one for metering, one for protection. This is common in medium-voltage switchgear where space is limited. Each winding has its own accuracy class and burden rating.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/details>\n\t\t\t\t\t\t<details id=\"e-n-accordion-item-9521\" class=\"e-n-accordion-item\" >\n\t\t\t\t<summary class=\"e-n-accordion-item-title\" data-accordion-index=\"2\" tabindex=\"-1\" aria-expanded=\"false\" aria-controls=\"e-n-accordion-item-9521\" >\n\t\t\t\t\t<span class='e-n-accordion-item-title-header'><div class=\"e-n-accordion-item-title-text\"> Why does a CT secondary need to be kept closed? <\/div><\/span>\n\t\t\t\t\t\t\t<span class='e-n-accordion-item-title-icon'>\n\t\t\t<span class='e-opened' ><svg aria-hidden=\"true\" class=\"e-font-icon-svg e-fas-minus\" viewBox=\"0 0 448 512\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\"><path d=\"M416 208H32c-17.67 0-32 14.33-32 32v32c0 17.67 14.33 32 32 32h384c17.67 0 32-14.33 32-32v-32c0-17.67-14.33-32-32-32z\"><\/path><\/svg><\/span>\n\t\t\t<span class='e-closed'><svg aria-hidden=\"true\" class=\"e-font-icon-svg e-fas-plus\" viewBox=\"0 0 448 512\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\"><path d=\"M416 208H272V64c0-17.67-14.33-32-32-32h-32c-17.67 0-32 14.33-32 32v144H32c-17.67 0-32 14.33-32 32v32c0 17.67 14.33 32 32 32h144v144c0 17.67 14.33 32 32 32h32c17.67 0 32-14.33 32-32V304h144c17.67 0 32-14.33 32-32v-32c0-17.67-14.33-32-32-32z\"><\/path><\/svg><\/span>\n\t\t<\/span>\n\n\t\t\t\t\t\t<\/summary>\n\t\t\t\t<div role=\"region\" aria-labelledby=\"e-n-accordion-item-9521\" class=\"elementor-element elementor-element-78cb828a e-con-full e-flex e-con e-child\" data-id=\"78cb828a\" data-element_type=\"container\" data-e-type=\"container\">\n\t\t\t\t<div class=\"elementor-element elementor-element-7d4bfde elementor-widget elementor-widget-text-editor\" data-id=\"7d4bfde\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t\t\t\t\t\t<p>An open secondary while the primary is energized causes the core flux to rise uncontrolled, generating dangerously high voltages at the secondary terminals. It can damage the CT and create a serious shock hazard. Secondary terminals should always be shorted before removing any connected burden.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/details>\n\t\t\t\t\t\t<details id=\"e-n-accordion-item-9522\" class=\"e-n-accordion-item\" >\n\t\t\t\t<summary class=\"e-n-accordion-item-title\" data-accordion-index=\"3\" tabindex=\"-1\" aria-expanded=\"false\" aria-controls=\"e-n-accordion-item-9522\" >\n\t\t\t\t\t<span class='e-n-accordion-item-title-header'><div class=\"e-n-accordion-item-title-text\"> How often should current transformers be tested or calibrated? <\/div><\/span>\n\t\t\t\t\t\t\t<span class='e-n-accordion-item-title-icon'>\n\t\t\t<span class='e-opened' ><svg aria-hidden=\"true\" class=\"e-font-icon-svg e-fas-minus\" viewBox=\"0 0 448 512\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\"><path d=\"M416 208H32c-17.67 0-32 14.33-32 32v32c0 17.67 14.33 32 32 32h384c17.67 0 32-14.33 32-32v-32c0-17.67-14.33-32-32-32z\"><\/path><\/svg><\/span>\n\t\t\t<span class='e-closed'><svg aria-hidden=\"true\" class=\"e-font-icon-svg e-fas-plus\" viewBox=\"0 0 448 512\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\"><path d=\"M416 208H272V64c0-17.67-14.33-32-32-32h-32c-17.67 0-32 14.33-32 32v144H32c-17.67 0-32 14.33-32 32v32c0 17.67 14.33 32 32 32h144v144c0 17.67 14.33 32 32 32h32c17.67 0 32-14.33 32-32V304h144c17.67 0 32-14.33 32-32v-32c0-17.67-14.33-32-32-32z\"><\/path><\/svg><\/span>\n\t\t<\/span>\n\n\t\t\t\t\t\t<\/summary>\n\t\t\t\t<div role=\"region\" aria-labelledby=\"e-n-accordion-item-9522\" class=\"elementor-element elementor-element-641ee210 e-con-full e-flex e-con e-child\" data-id=\"641ee210\" data-element_type=\"container\" data-e-type=\"container\">\n\t\t\t\t<div class=\"elementor-element elementor-element-d39fc6c elementor-widget elementor-widget-text-editor\" data-id=\"d39fc6c\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t\t\t\t\t\t<p>For revenue metering applications, periodic calibration is often required by regulation \u2014 typically every few years depending on the jurisdiction. Protection CTs are usually tested during commissioning and as part of scheduled maintenance on the associated protection scheme.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/details>\n\t\t\t\t\t<\/div>\n\t\t\t\t\t<script type=\"application\/ld+json\">{\"@context\":\"https:\\\/\\\/schema.org\",\"@type\":\"FAQPage\",\"mainEntity\":[{\"@type\":\"Question\",\"name\":\"Can one current transformer serve both metering and protection functions?\",\"acceptedAnswer\":{\"@type\":\"Answer\",\"text\":\"Some CTs are dual-rated with separate secondary windings \\u2014 one for metering, one for protection. This is common in medium-voltage switchgear where space is limited. Each winding has its own accuracy class and burden rating.\"}},{\"@type\":\"Question\",\"name\":\"Why does a CT secondary need to be kept closed?\",\"acceptedAnswer\":{\"@type\":\"Answer\",\"text\":\"An open secondary while the primary is energized causes the core flux to rise uncontrolled, generating dangerously high voltages at the secondary terminals. It can damage the CT and create a serious shock hazard. Secondary terminals should always be shorted before removing any connected burden.\"}},{\"@type\":\"Question\",\"name\":\"How often should current transformers be tested or calibrated?\",\"acceptedAnswer\":{\"@type\":\"Answer\",\"text\":\"For revenue metering applications, periodic calibration is often required by regulation \\u2014 typically every few years depending on the jurisdiction. Protection CTs are usually tested during commissioning and as part of scheduled maintenance on the associated protection scheme.\"}}]}<\/script>\n\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t","protected":false},"excerpt":{"rendered":"Walk into any electrical substation or industrial facility and there\u2019s a good chance you\u2019ll find current transformers installed almost everywhere \u2014 on busbars, cable feeders, switchgear panels. They\u2019re not the most glamorous piece of equipment, but understanding what they actually do explains a lot about how modern power systems stay reliable and safe. At its [&hellip;]","protected":false},"author":8,"featured_media":598,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[47],"tags":[],"class_list":["post-2409","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-knowledge"],"acf":[],"_links":{"self":[{"href":"https:\/\/zmgs-global.com\/id\/wp-json\/wp\/v2\/posts\/2409","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/zmgs-global.com\/id\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/zmgs-global.com\/id\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/zmgs-global.com\/id\/wp-json\/wp\/v2\/users\/8"}],"replies":[{"embeddable":true,"href":"https:\/\/zmgs-global.com\/id\/wp-json\/wp\/v2\/comments?post=2409"}],"version-history":[{"count":0,"href":"https:\/\/zmgs-global.com\/id\/wp-json\/wp\/v2\/posts\/2409\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/zmgs-global.com\/id\/wp-json\/wp\/v2\/media\/598"}],"wp:attachment":[{"href":"https:\/\/zmgs-global.com\/id\/wp-json\/wp\/v2\/media?parent=2409"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/zmgs-global.com\/id\/wp-json\/wp\/v2\/categories?post=2409"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/zmgs-global.com\/id\/wp-json\/wp\/v2\/tags?post=2409"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}