{"id":2907,"date":"2026-02-02T06:21:16","date_gmt":"2026-02-02T06:21:16","guid":{"rendered":"https:\/\/xbrele.com\/?p=2907"},"modified":"2026-10-14T12:57:42","modified_gmt":"2026-10-14T12:57:42","slug":"ct-accuracy-classes-metering-protection-guide","status":"publish","type":"post","link":"https:\/\/xbrele.com\/es\/ct-accuracy-classes-metering-protection-guide\/","title":{"rendered":"Explicaci\u00f3n de las clases de precisi\u00f3n de los transformadores de corriente (0,2\/0,5, 5P\/10P): Medici\u00f3n vs Protecci\u00f3n"},"content":{"rendered":"<p class=\"xbrele-article-updated\"><small>\u00daltima actualizaci\u00f3n: <time datetime=\"2026-10-14\">October 14, 2026<\/time>.<\/small><\/p>\n\n\n\n<p>Current transformers supply measuring instruments and protection relays with scaled current signals. Metering classes describe measurement accuracy over a specified load-current range; protection classes describe performance under the fault conditions covered by their designation. A metering-class label alone does not establish suitability for protection, and a protection-class label alone does not establish revenue-metering accuracy.<\/p>\n\n\n\n<p>Esta gu\u00eda desglosa las designaciones de clase de precisi\u00f3n de la norma IEC 61869-2, explica las diferencias t\u00e9cnicas entre las clases de medici\u00f3n (0,1, 0,2, 0,5) y las clases de protecci\u00f3n (5P, 10P), y ofrece orientaciones pr\u00e1cticas de selecci\u00f3n para aplicaciones de media tensi\u00f3n.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"what-are-ct-accuracy-classes\">\u00bfQu\u00e9 son las clases de precisi\u00f3n de TC?<\/h2>\n\n\n\n<p>A CT accuracy class defines permissible errors under specified current, burden, frequency and test conditions. For a metering CT, the class number identifies the rated-current ratio-error limit; other test currents have their own limits. In a 5P or 10P designation, the number identifies the composite-error limit at the rated accuracy-limit primary current, not the ratio-error limit at normal load.<\/p>\n\n\n\n<p>Existen dos sistemas de clasificaci\u00f3n distintos. Las clases de medici\u00f3n (0,1, 0,2, 0,5, 1,0) optimizan la precisi\u00f3n en corrientes de funcionamiento normales, normalmente de 5% a 120% de la corriente nominal. Las clases de protecci\u00f3n (5P, 10P) dan prioridad al rendimiento en condiciones de fallo, manteniendo la precisi\u00f3n a m\u00faltiplos de corriente muy superiores al funcionamiento normal.<\/p>\n\n\n\n<p>Metering and protection impose different design requirements. A CT may contain separate metering and protection cores, and some designs carry more than one accuracy designation. Select each core using its declared ratings and the connected equipment requirements; neither core size nor material alone proves its accuracy class.<\/p>\n\n\n\n<figure class=\"wp-block-embed is-type-video is-provider-youtube wp-block-embed-youtube wp-embed-aspect-16-9 wp-has-aspect-ratio\"><div class=\"wp-block-embed__wrapper\">\n<iframe title=\"Explicaci\u00f3n de las clases de precisi\u00f3n de TC: Medici\u00f3n 0,2\/0,5 vs Protecci\u00f3n 5P\/10P\" width=\"1290\" height=\"726\" src=\"https:\/\/www.youtube.com\/embed\/PVXlrxYOFzA?feature=oembed\" frameborder=\"0\" allow=\"accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share\" referrerpolicy=\"strict-origin-when-cross-origin\" allowfullscreen><\/iframe>\n<\/div><\/figure>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"how-current-transformers-introduce-measurement-errors\">C\u00f3mo introducen errores de medici\u00f3n los transformadores de corriente<\/h2>\n\n\n\n<p>Part of the primary ampere-turns supplies the core excitation rather than the secondary load. The resulting exciting current, together with the secondary circuit impedance, produces ratio error and phase displacement.<\/p>\n\n\n\n<p><strong>Error de relaci\u00f3n (\u03b5)<\/strong> is the difference between the primary current inferred from the rated ratio and the actual primary current, expressed as a percentage of the actual primary current. With a rated ratio of 1000\/5 A, a secondary reading of 4.98 A at 1000 A primary gives (200 \u00d7 4.98 \u2212 1000) \/ 1000 \u00d7 100 = \u22120.4%. The error varies with current and burden.<\/p>\n\n\n\n<p><strong>Desplazamiento de fase (\u03b4)<\/strong>&nbsp;mide la diferencia angular entre los fasores de corriente primario y secundario, expresada en minutos de arco. La transformaci\u00f3n ideal produce un desfase cero; los TC reales presentan peque\u00f1os desplazamientos debidos a los requisitos de la corriente magnetizante.<\/p>\n\n\n\n<p>Core material, geometry, turns and excitation characteristics all influence CT performance. Rated output is stated in VA at the rated secondary current. Check the manufacturer\u2019s declared burden range and burden power factor as well as the VA rating: a very small connected burden is not automatically within the metering accuracy guarantee.<\/p>\n\n\n\n<p>The limits apply at the current and burden conditions specified for the class. At rated primary current, Class 0.2 has ratio-error and phase-displacement limits of \u00b10.2% and \u00b110 minutes. For protection classes, the rated-current ratio-error limits are \u00b11% for 5P and \u00b13% for 10P; their respective composite-error limits at the rated accuracy-limit current are 5% and 10%.<\/p>\n\n\n\n\n\n<h2 class=\"wp-block-heading\" id=\"metering-ct-accuracy-classes-0.1-0.2-0.5-and-extended-s-classes\">Clases de precisi\u00f3n del TC de medici\u00f3n: 0,1, 0,2, 0,5 y clases \u201cS\u201d ampliadas<\/h2>\n\n\n\n<p>Metering classes specify ratio-error and phase-displacement limits at several test currents. The table lists the limits at 100% rated current and the covered current range. It does not mean that the rated-current error limit applies unchanged over that entire range; use the full class table and the CT\u2019s declared burden conditions for selection.<\/p>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><thead><tr><th>Clase<\/th><th>Error de relaci\u00f3n en 100% In<\/th><th>Phase displacement at 100% In<\/th><th>Specified current range<\/th><th>Aplicaci\u00f3n t\u00edpica<\/th><\/tr><\/thead><tbody><tr><td>0.1<\/td><td>\u00b10,1%<\/td><td>\u00b15 min<\/td><td>5-120%<\/td><td>Normas de referencia de laboratorio<\/td><\/tr><tr><td>0.2<\/td><td>\u00b10,2%<\/td><td>\u00b110 min<\/td><td>5-120%<\/td><td>Medici\u00f3n de los ingresos de transmisi\u00f3n<\/td><\/tr><tr><td>0.2S<\/td><td>\u00b10,2%<\/td><td>\u00b110 min<\/td><td>1-120%<\/td><td>Medici\u00f3n de la carga variable<\/td><\/tr><tr><td>0.5<\/td><td>\u00b10,5%<\/td><td>\u00b130 min<\/td><td>5-120%<\/td><td>Medici\u00f3n de subestaciones de distribuci\u00f3n<\/td><\/tr><tr><td>0.5S<\/td><td>\u00b10,5%<\/td><td>\u00b130 min<\/td><td>1-120%<\/td><td>Medici\u00f3n de ingresos industriales<\/td><\/tr><tr><td>1.0<\/td><td>\u00b11,0%<\/td><td>\u00b160 min<\/td><td>5-120%<\/td><td>Instrumentos indicadores<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<p>The \u201cS\u201d suffix identifies metering classes with additional low-current requirements. Classes 0.2S and 0.5S include a 1% rated-current test point, whereas the ordinary classes listed above start at 5%. Error limits differ by test point. Select a class and ratio that cover the expected minimum load and the applicable metering requirements.<\/p>\n\n\n\n<p>For variable-load facilities, compare the expected minimum primary current with the CT rating before choosing between 0.2 and 0.2S. Billing value alone does not define the required class. Include the meter, voltage measurement and wiring in the overall measurement-accuracy assessment.<\/p>\n\n\n\n<p><strong>Instrument security factor (FS)<\/strong> describes the overcurrent behavior specified for a metering core at rated burden. FS5 and FS10 are common declared ratings, but the accuracy class alone does not prescribe a universal saturation multiple. Reducing the connected burden can increase the current at which the core saturates. Verify FS and the meter\u2019s withstand capability rather than assuming every metering CT saturates at 2\u20135 times rated current.<\/p>\n\n\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<blockquote class=\"wp-block-quote is-layout-flow wp-block-quote-is-layout-flow\">\n<p><strong>Metering CT selection checks<\/strong><\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Compare the expected minimum load with the class test points and the CT ratio.<\/li>\n\n\n\n<li>Verify the complete connected burden is within the CT\u2019s declared metering accuracy range.<\/li>\n\n\n\n<li>Obtain the selected meter\u2019s actual input burden; verify accuracy at the resulting total burden.<\/li>\n\n\n\n<li>Solicite certificados de pruebas en f\u00e1brica que muestren los errores reales medidos, no s\u00f3lo la conformidad de clase.<\/li>\n<\/ul>\n<\/blockquote>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"protection-ct-accuracy-classes-decoding-5p-and-10p-designations\">Clases de precisi\u00f3n de TC de protecci\u00f3n: Decodificaci\u00f3n de las designaciones 5P y 10P<\/h2>\n\n\n\n<p>Las clases de protecci\u00f3n siguen un sistema de notaci\u00f3n diferente que refleja su funci\u00f3n principal: la medici\u00f3n precisa de la corriente de defecto. La designaci\u00f3n \u201c5P20\u201d codifica tres par\u00e1metros esenciales para la coordinaci\u00f3n de rel\u00e9s.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\" id=\"nomenclature-breakdown\"><strong>Desglose de la nomenclatura:<\/strong><\/h3>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>5<\/strong>\u00a0= L\u00edmite de error compuesto (5% m\u00e1ximo)<\/li>\n\n\n\n<li><strong>P<\/strong>\u00a0= Designaci\u00f3n de la clase de protecci\u00f3n<\/li>\n\n\n\n<li><strong>20<\/strong> = rated accuracy limit factor at rated burden; the specified composite-error limit is checked at 20 times rated primary current<\/li>\n<\/ul>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><thead><tr><th>Clase<\/th><th>Error compuesto en el ALF<\/th><th>Valores comunes del ALF<\/th><th>Aplicaci\u00f3n t\u00edpica<\/th><\/tr><\/thead><tbody><tr><td>5P<\/td><td>\u22645%<\/td><td>10, 15, 20, 30<\/td><td>Overcurrent protection; verify each relay application<\/td><\/tr><tr><td>10P<\/td><td>\u226410%<\/td><td>10, 15, 20<\/td><td>Overcurrent protection where the scheme accepts 10P<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<p>El <strong>accuracy limit factor (ALF)<\/strong> is the rated accuracy-limit primary current divided by the rated primary current. A 1000\/5 A, 5P20 CT has a rated accuracy-limit current of 20,000 A at its rated burden. This is a defined steady-state error test condition, not a sharp physical saturation threshold or a guarantee of transient performance.<\/p>\n\n\n\n<p>For a 5P20 CT, the composite error must not exceed 5% at 20 times rated primary current under the specified test conditions and rated burden. Composite error includes waveform distortion and is not a signed \u00b15% ratio-error band. DC offset, remanent flux and the required operating time can impose additional CT requirements.<\/p>\n\n\n\n<p><strong>Initial steady-state screening:<\/strong> if the scheme requires class accuracy at the maximum symmetrical through-fault current, compare the effective ALF at the actual burden with that fault-current multiple.<\/p>\n\n\n\n<p>Required effective ALF \u2265 Maximum symmetrical through-fault current \u00f7 CT rated primary current<\/p>\n\n\n\n<p>For a 12.5 kA symmetrical fault and a 500\/5 A CT, the fault-current multiple is 12,500 \/ 500 = 25.<\/p>\n\n\n\n<p>At rated burden, 5P20 alone does not demonstrate the above 25-times screening requirement; a 5P30 rating would cover that steady-state multiple. Final selection still requires the relay manufacturer\u2019s criteria, actual secondary burden, fault duration and transient assessment. Some protection functions tolerate partial CT saturation, so this screening rule is not a universal relay-sizing formula.<\/p>\n\n\n\n<p>Protection CT selection also involves excitation characteristics, secondary winding resistance and short-time thermal and dynamic ratings. A 5P or 10P designation does not replace these checks. For differential or transient duties, the relay manufacturer may specify PX, PR or a transient class, or give a calculation for an acceptable P-class CT.<\/p>\n\n\n\n\n\n<h2 class=\"wp-block-heading\" id=\"metering-vs-protection-ct-side-by-side-comparison\">TC de medici\u00f3n frente a TC de protecci\u00f3n: comparaci\u00f3n por pares<\/h2>\n\n\n\n<p>The following comparison summarizes the different performance specifications. Individual CTs can have additional ratings beyond the class names shown.<\/p>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><thead><tr><th>Par\u00e1metro<\/th><th>TC de medici\u00f3n<\/th><th>Protecci\u00f3n CT<\/th><\/tr><\/thead><tbody><tr><td><strong>Funci\u00f3n principal<\/strong><\/td><td>Facturaci\u00f3n de ingresos, control de la energ\u00eda<\/td><td>Detecci\u00f3n de aver\u00edas, funcionamiento del rel\u00e9<\/td><\/tr><tr><td><strong>Rango de precisi\u00f3n<\/strong><\/td><td>1-120% de nominal (clase S)<\/td><td>Rated error limit at ALF \u00d7 rated current and rated burden<\/td><\/tr><tr><td><strong>Especificaci\u00f3n de errores<\/strong><\/td><td>Error de relaci\u00f3n + desplazamiento de fase<\/td><td>Rated-current ratio error and composite error at ALF<\/td><\/tr><tr><td><strong>Comportamiento de saturaci\u00f3n<\/strong><\/td><td>Specified by FS and burden; not by metering class alone<\/td><td>Specified accuracy-limit and transient characteristics<\/td><\/tr><tr><td><strong>Dise\u00f1o del n\u00facleo<\/strong><\/td><td>Design depends on accuracy, burden and FS<\/td><td>Design depends on burden, fault and transient duty<\/td><\/tr><tr><td><strong>Clases t\u00edpicas<\/strong><\/td><td>0,2, 0,2S, 0,5, 0,5S, 1,0<\/td><td>5P10, 5P20, 10P10, 10P15<\/td><\/tr><tr><td><strong>Dispositivos conectados<\/strong><\/td><td>contadores de kWh, analizadores de potencia<\/td><td>Rel\u00e9s de protecci\u00f3n, registradores de aver\u00edas<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<p>A saturated CT produces a distorted secondary waveform. Depending on the relay function and settings, this can delay operation or affect differential stability. The magnitude and timing of the effect must be assessed for the actual protection scheme; they cannot be inferred from the metering class alone.<\/p>\n\n\n\n<p>Separate cores allow the metering burden and protection burden to be specified and tested independently when both functions are needed.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"burden-effects-and-practical-selection-considerations\">Efectos de la carga y consideraciones pr\u00e1cticas sobre la selecci\u00f3n<\/h2>\n\n\n\n<p>Connected burden affects the voltage the CT must develop and therefore its accuracy and saturation behavior. Include the relay or meter input and the complete secondary wiring circuit. Keep the metering burden within its declared accuracy range, and calculate protection performance at the actual burden.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\" id=\"burden-components-include\"><strong>Los componentes de la carga incluyen:<\/strong><\/h3>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Instrument burden: use the selected meter, relay or transducer input data.<\/li>\n\n\n\n<li>Carga del cable: resistencia del cable secundario (importante en tramos largos)<\/li>\n\n\n\n<li>Connection burden: include terminals and test switches using their actual resistance.<\/li>\n<\/ul>\n\n\n\n<p><strong>Lead burden calculation for a separate outgoing and return pair:<\/strong><br>Lead VA = I<sub>secondary<\/sub>\u00b2 \u00d7 R<sub>loop<\/sub> = I<sub>secondary<\/sub>\u00b2 \u00d7 2 \u00d7 R<sub>one-way<\/sub><\/p>\n\n\n\n<p>Example: a 50 m one-way run with a measured or calculated one-way resistance of 0.35 \u03a9 has a 0.70 \u03a9 loop. At 5 A, its burden is 25 \u00d7 0.70 = 17.5 VA; at 1 A, it is 0.70 VA. Use the cable resistance at the design temperature and the actual return-circuit arrangement.<\/p>\n\n\n\n<p>Esto explica por qu\u00e9 los secundarios de 1 A son adecuados para largas tiradas de cable: la carga se reduce en 25\u00d7 en comparaci\u00f3n con los secundarios de 5 A para un cable id\u00e9ntico.<\/p>\n\n\n\n<p><strong>Lista de control de la selecci\u00f3n:<\/strong><\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Obtain maximum and minimum fault currents and the relay operating-time requirements.<\/li>\n\n\n\n<li>\u00a0Suma de la carga total, incluida la resistencia del plomo<\/li>\n\n\n\n<li>Verify the declared burden conditions for metering and the effective ALF for protection.<\/li>\n\n\n\n<li>Include credible future fault levels and transient duty using the relay manufacturer\u2019s calculation method.<\/li>\n\n\n\n<li>Choose the metering class and ratio to cover the actual load range and project requirements.<\/li>\n<\/ul>\n\n\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<blockquote class=\"wp-block-quote is-layout-flow wp-block-quote-is-layout-flow\">\n<p><strong>Protection CT specification checks<\/strong><\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>For auto-reclosing, assess remanence, fault duration and the required operating cycle.<\/li>\n\n\n\n<li>For differential protection, follow the selected relay\u2019s CT ratio and saturation requirements.<\/li>\n\n\n\n<li>Use the relay\u2019s actual input burden and the complete wiring burden when calculating effective ALF.<\/li>\n\n\n\n<li>Request excitation curves and secondary winding resistance when required by the protection calculation.<\/li>\n<\/ul>\n<\/blockquote>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"dual-core-cts-and-switchgear-integration\">TC de doble n\u00facleo e integraci\u00f3n de aparamenta<\/h2>\n\n\n\n<p>La mayor\u00eda de las instalaciones de media tensi\u00f3n requieren tanto la medici\u00f3n como la protecci\u00f3n de cada alimentador. Los TC de doble n\u00facleo (o multin\u00facleo) solucionan este problema incorporando n\u00facleos magn\u00e9ticos separados bobinados en el mismo conductor primario.<\/p>\n\n\n\n<p>Illustrative dual-core specification, subject to the actual meter, relay and wiring calculations:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>N\u00facleo 1: clase 0,5S, carga 10 VA (medici\u00f3n de ingresos)<\/li>\n\n\n\n<li>N\u00facleo 2: 5P20, carga de 30 VA (rel\u00e9s de protecci\u00f3n)<\/li>\n<\/ul>\n\n\n\n<p>Specify and verify the accuracy and burden of each core separately. Confirm metering FS, protection performance, insulation level and the assembly\u2019s thermal and dynamic withstand ratings. Separate cores do not remove the need to coordinate the complete secondary circuits.<\/p>\n\n\n\n<p>Integraci\u00f3n con <a href=\"https:\/\/xbrele.com\/es\/vacuum-circuit-breaker\/\">Interruptores de vac\u00edo de media tensi\u00f3n<\/a> requires a common system fault study. ALF is a dimensionless ratio and cannot be compared directly with a breaker breaking-current rating in kA. Evaluate the CT against the maximum through-fault current, its primary rating, actual burden and relay requirements. Separately verify the CT short-time\/dynamic withstand ratings and the breaker interrupting duty. Ask the <a href=\"https:\/\/xbrele.com\/es\/switchgear-parts\/\">fabricantes de componentes<\/a> for the data needed to complete those checks.<\/p>\n\n\n\n<p>Cuando especifique TC para instalaciones nuevas, facilite lo siguiente a su proveedor:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Nivel m\u00e1ximo de fallo del sistema (kA)<\/li>\n\n\n\n<li>Rango de corriente de carga (m\u00ednimo a m\u00e1ximo)<\/li>\n\n\n\n<li>Distancia del cable a los paneles de medici\u00f3n\/rel\u00e9<\/li>\n\n\n\n<li>Modelos espec\u00edficos de contadores y rel\u00e9s con datos de carga<\/li>\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"common-ct-specification-errors-and-how-to-avoid-them\">Errores comunes en la especificaci\u00f3n del TC y c\u00f3mo evitarlos<\/h2>\n\n\n\n<p>Review the following specification errors before purchasing or replacing a CT.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\" id=\"error-1-using-metering-ct-for-protection\"><strong>Error 1: Utilizaci\u00f3n del TC de medida para la protecci\u00f3n<\/strong><\/h3>\n\n\n\n<p>A metering class alone does not verify fault-current performance. <strong>Soluci\u00f3n:<\/strong> select a core with the protection characteristics required by the relay scheme and verify its performance at the actual burden, through-fault current and required operating time.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\" id=\"error-2-ignoring-lead-burden-in-total-burden-calculation\"><strong>Error 2: Ignorar la carga de plomo en el c\u00e1lculo de la carga total<\/strong><\/h3>\n\n\n\n<p>Long secondary circuits can add substantial burden, particularly at 5 A. <strong>Soluci\u00f3n:<\/strong> calculate the complete loop resistance at the design temperature. Compare 1 A and 5 A options using the actual cable and compatible relay inputs; cable length alone is not a universal selection threshold.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\" id=\"error-3-mismatched-cts-in-differential-protection\"><strong>Error 3: TI no coincidentes en la protecci\u00f3n diferencial<\/strong><\/h3>\n\n\n\n<p>Different saturation behavior can produce unwanted differential current during an external fault. <strong>Soluci\u00f3n:<\/strong> use the relay manufacturer\u2019s ratio-compensation, excitation, winding-resistance and stability requirements. Transformer differential schemes may use different primary CT ratios; identical ratios and knee-point voltages are not a universal requirement.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\" id=\"error-4-overlooking-remanent-flux-in-auto-reclose-schemes\"><strong>Error 4: Pasar por alto el flujo remanente en los esquemas de autocierre<\/strong><\/h3>\n\n\n\n<p>Remanent flux can change CT saturation during a subsequent fault or reclosing sequence. <strong>Soluci\u00f3n:<\/strong> assess the specified operating cycle, system time constant and relay requirements. Select suitable remanence or transient performance where required; a blanket 50% ALF increase is not a verified substitute.<\/p>\n\n\n\n<p>Comprensi\u00f3n <a href=\"https:\/\/xbrele.com\/es\/vacuum-circuit-breaker-ratings\/\">Clasificaciones de los interruptores autom\u00e1ticos de vac\u00edo<\/a> helps establish the switching duty. CT accuracy selection is a separate calculation based on the actual through-fault duty and protection scheme, while CT thermal\/dynamic withstand must also cover the clearing duty.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"frequently-asked-questions\">Preguntas frecuentes<\/h2>\n\n\n\n<h3 class=\"wp-block-heading\" id=\"what-does-5p20-mean-on-a-current-transformer-nameplate\"><strong>\u00bfQu\u00e9 significa 5P20 en la placa de caracter\u00edsticas de un transformador de corriente?<\/strong><\/h3>\n\n\n\n<p>5P20 specifies a protection CT with a composite-error limit of 5% at a rated accuracy-limit current of 20 times rated primary current, at rated burden and the specified test conditions. For a 400\/5 A CT this test current is 8,000 A. It does not identify an exact saturation threshold or guarantee performance for every transient waveform.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\" id=\"can-a-0-5-class-metering-ct-feed-protection-relays\"><strong>\u00bfPuede un TC de medida de clase 0,5 alimentar rel\u00e9s de protecci\u00f3n?<\/strong><\/h3>\n\n\n\n<p>Do not assume that a Class 0.5 metering core is suitable for protection. Its class establishes metering accuracy under specified conditions, not the fault-current performance required by a relay. Use a core whose declared protection characteristics have been checked against the particular relay scheme.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\" id=\"when-should-i-specify-0-2s-instead-of-standard-0-2-class\"><strong>\u00bfCu\u00e1ndo debo especificar 0,2S en lugar de la clase est\u00e1ndar 0,2?<\/strong><\/h3>\n\n\n\n<p>Consider 0.2S when accurate measurement is required at low load, especially between 1% and 5% of rated CT current. The required class also depends on the utility or project metering specification. Check the limits at each current test point and the declared burden range; 0.2S does not mean \u00b10.2% at every current.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\" id=\"how-does-burden-affect-protection-ct-performance\"><strong>\u00bfC\u00f3mo afecta la carga al rendimiento del TC de protecci\u00f3n?<\/strong><\/h3>\n\n\n\n<p>A lower external burden generally increases the effective ALF of a P-class CT, but winding resistance must be included. For mainly resistive burdens, ALF<sub>actual<\/sub> \u2248 ALF<sub>clasificado<\/sub> \u00d7 (R<sub>ct<\/sub> + R<sub>rated burden<\/sub>) \/ (R<sub>ct<\/sub> + R<sub>actual burden<\/sub>). Therefore, halving external burden does not generally double ALF. Use manufacturer data for the actual circuit and transient duty.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\" id=\"what-is-knee-point-voltage-and-why-does-it-matter\"><strong>\u00bfQu\u00e9 es la tensi\u00f3n en el punto de inflexi\u00f3n y por qu\u00e9 es importante?<\/strong><\/h3>\n\n\n\n<p>Knee-point voltage characterizes the bend in the secondary excitation curve. The IEC convention uses the point at which a 10% voltage increase produces a 50% increase in exciting current. It is particularly relevant when specifying PX-type CTs. Apply the relay manufacturer\u2019s knee-point, excitation-current and winding-resistance requirements; a simple voltage comparison does not establish suitability for every protection scheme.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"how-do-iec-and-ieee-ct-accuracy-standards-differ\"><strong>\u00bfEn qu\u00e9 se diferencian las normas IEC e IEEE sobre precisi\u00f3n de TC?<\/strong><\/h2>\n\n\n\n<p>IEC 61869-2 includes metering classes such as 0.2 and 0.5 and protection classes such as 5P, 10P and PX. IEEE C57.13 uses a different set of designations, including voltage-based relaying classes such as C100 and C200. The test conditions and burden definitions differ. Specify the standard required by the project and compare the full ratings rather than treating the class names as direct equivalents.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\" id=\"what-accuracy-class-suits-capacitor-bank-switching-applications\"><strong>\u00bfQu\u00e9 clase de precisi\u00f3n se adapta a las aplicaciones de conmutaci\u00f3n de bater\u00edas de condensadores?<\/strong><\/h3>\n\n\n\n<p>A capacitor bank can need phase overcurrent, earth-fault and sensitive unbalance protection, each with different measurement duties. Select CT ratio, accuracy, burden and transient performance from the bank configuration, expected unbalance level and relay instructions. A universal 5P10 or 0.5 recommendation cannot establish suitability for all capacitor banks.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<p><em>Para obtener asistencia sobre especificaciones de TC adaptadas a sus requisitos de conmutaci\u00f3n, p\u00f3ngase en contacto con el equipo de ingenier\u00eda de XBRELE a trav\u00e9s de <a href=\"https:\/\/xbrele.com\/es\/contact\/\">la p\u00e1gina de contacto t\u00e9cnico<\/a>. Ofrecemos soluciones integradas que combinan&nbsp;<a href=\"https:\/\/xbrele.com\/es\/what-is-a-vacuum-interrupter\/\">tecnolog\u00eda de interrupci\u00f3n en vac\u00edo<\/a>&nbsp;con transformadores de medida adecuadamente coordinados para un funcionamiento fiable de la medici\u00f3n y la protecci\u00f3n, incluyendo <a href=\"https:\/\/xbrele.com\/es\/transformer-protection-vcb-inrush-coordination-mistakes\/\">controles de coordinaci\u00f3n de rel\u00e9s<\/a> para alimentadores de transformadores.<\/em><\/p>\n\n\n\n<p><strong>Technical references:<\/strong> <a href=\"https:\/\/webstore.iec.ch\/en\/publication\/6050\" target=\"_blank\" rel=\"noopener\">IEC 61869-2:2012 \u2014 inductive current transformers<\/a>; <a href=\"https:\/\/library.e.abb.com\/public\/194811e319ce2bb7c2256f9e00324a2f\/applicationCT_accuracylimitfactorENa.pdf\" target=\"_blank\" rel=\"noopener\">ABB \u2014 calculation of actual accuracy limit factor<\/a>; <a href=\"https:\/\/library.e.abb.com\/public\/eb71e99b34df40fac2256f230034b639\/applicationCTreqENa.pdf\" target=\"_blank\" rel=\"noopener\">ABB \u2014 CT requirements for non-directional overcurrent protection<\/a>; <a href=\"https:\/\/techdoc.relays.protection-control.abb\/r\/615-series-Technical-Manual\/5.0-FP1-IEC\/en-US\/Current-transformer-requirements-for-transformer-differential-protection?contentId=IOsDImuRMieCseqaGT6Irw\" target=\"_blank\" rel=\"noopener\">ABB \u2014 transformer differential CT requirements<\/a>. The ABB application notes explain calculation methods; final selection must use the applicable project standard and the selected relay\u2019s current instructions.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>","protected":false},"excerpt":{"rendered":"<p>Understand CT accuracy classes 0.2S, 0.5S, 5P and 10P, including rated burden, effective ALF and checks for metering and protection applications.<\/p>","protected":false},"author":3,"featured_media":4294,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_gspb_post_css":"\/* XBRELE: keep the image-free article hero readable. *\/\nbody.postid-2907 #main > .hero-section[data-type=\"type-2\"] {\n  background-color: var(--theme-palette-color-4, #080c0e);\n  --theme-text-color: #e6eef1;\n}\nbody.postid-2907 #main > .hero-section[data-type=\"type-2\"] .page-description {\n  color: var(--theme-text-color);\n}\n","footnotes":""},"categories":[27],"tags":[],"class_list":["post-2907","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-switchgear-parts-knowledge"],"blocksy_meta":[],"_links":{"self":[{"href":"https:\/\/xbrele.com\/es\/wp-json\/wp\/v2\/posts\/2907","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/xbrele.com\/es\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/xbrele.com\/es\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/xbrele.com\/es\/wp-json\/wp\/v2\/users\/3"}],"replies":[{"embeddable":true,"href":"https:\/\/xbrele.com\/es\/wp-json\/wp\/v2\/comments?post=2907"}],"version-history":[{"count":5,"href":"https:\/\/xbrele.com\/es\/wp-json\/wp\/v2\/posts\/2907\/revisions"}],"predecessor-version":[{"id":4291,"href":"https:\/\/xbrele.com\/es\/wp-json\/wp\/v2\/posts\/2907\/revisions\/4291"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/xbrele.com\/es\/wp-json\/wp\/v2\/media\/4294"}],"wp:attachment":[{"href":"https:\/\/xbrele.com\/es\/wp-json\/wp\/v2\/media?parent=2907"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/xbrele.com\/es\/wp-json\/wp\/v2\/categories?post=2907"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/xbrele.com\/es\/wp-json\/wp\/v2\/tags?post=2907"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}