{"id":10523,"date":"2026-08-29T23:43:04","date_gmt":"2026-08-29T15:43:04","guid":{"rendered":"https:\/\/q8bbzjnpm5.wpdns.site\/?p=10523"},"modified":"2026-08-29T23:43:04","modified_gmt":"2026-08-29T15:43:04","slug":"transformer-ratio-the-regulating-valve-for-stable-operation-of-power-systems","status":"publish","type":"post","link":"https:\/\/subian-electric.com\/es\/news\/transformer-ratio-the-regulating-valve-for-stable-operation-of-power-systems\/","title":{"rendered":"Relaci\u00f3n del Transformador: La \u201cV\u00e1lvula Reguladora\u201d para la Operaci\u00f3n Estable de los Sistemas de Potencia"},"content":{"rendered":"

Un operador de subestaci\u00f3n mir\u00f3 su medidor electr\u00f3nico hoy cuando lleg\u00f3 una tormenta el\u00e9ctrica y cambi\u00f3 la l\u00ednea de 110 kV de potencia de 108 kV a 116 kV. A pesar de eso, el bus de 20 kV en el lado secundario mostr\u00f3 valores entre 19.9 y 20.1 kV al mismo tiempo. El instrumento que trabaja all\u00ed se llama cambiador de tomas bajo carga: la relaci\u00f3n de transformaci\u00f3n se corrige paso a paso.<\/p>\n

El art\u00edculo interpreta qu\u00e9 es la relaci\u00f3n de transformaci\u00f3n, c\u00f3mo se calcula, cu\u00e1l es la relaci\u00f3n entre la relaci\u00f3n de transformaci\u00f3n<\/strong> y la estabilidad de voltaje, c\u00f3mo los cambiadores de tomas hacen que la relaci\u00f3n de transformaci\u00f3n sea estable en ese mismo momento, y qu\u00e9 consecuencias se pueden obtener si hay un error en la relaci\u00f3n de transformaci\u00f3n. Se proporcionan ejemplos de c\u00e1lculos en el documento junto con referencias a las normas IEC 60076 y IEEE C57, rango t\u00edpico de tomas, el costo de los cambiadores de tomas, y otros.<\/p>\n

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\u00bfQu\u00e9 es la relaci\u00f3n de transformaci\u00f3n? (Definici\u00f3n y f\u00f3rmula)<\/h2>\n

La relaci\u00f3n de transformaci\u00f3n o relaci\u00f3n de vueltas define la relaci\u00f3n de vueltas del devanado primario al n\u00famero de vueltas del devanado secundario. Es igual a la relaci\u00f3n de voltaje primario a voltaje secundario y la relaci\u00f3n inversa de las corrientes primarias a secundarias en el caso te\u00f3rico.
\nN1\/N2 = V1\/V2 = I2\/I1.
\nLos transformadores reales no son ideales. En los transformadores reales, la reactancia de fuga y la resistencia del devanado dan lugar a ca\u00eddas de voltaje, haciendo que el voltaje real sea m\u00e1s bajo que el voltaje en vac\u00edo. La diferencia en el voltaje en porcentaje se llama regulaci\u00f3n de voltaje<\/strong> que est\u00e1 alrededor de 2%-6% dependiendo de las caracter\u00edsticas de los transformadores.
\nLa siguiente definici\u00f3n se utiliza de manera intercambiable en los contratos:<\/p>\n\n\n\n\n\n\n
Terminolog\u00eda de la relaci\u00f3n de transformaci\u00f3n<\/caption>\n
T\u00e9rmino<\/th>\nSignificado<\/th>\nEjemplo<\/th>\n<\/tr>\n
Relaci\u00f3n de vueltas<\/td>\nN1 \/ N2 (geometr\u00eda de devanado puro)<\/td>\n550 \/ 100 = 5.5<\/td>\n<\/tr>\n
Relaci\u00f3n de voltaje<\/td>\nV1 \/ V2 en vac\u00edo<\/td>\n110 kV \/ 20 kV = 5.5<\/td>\n<\/tr>\n
Regulaci\u00f3n<\/td>\nCa\u00edda de voltaje de vac\u00edo a carga completa<\/td>\n2.5%\u20136%<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

C\u00f3mo calcular la relaci\u00f3n de transformaci\u00f3n: ejemplos resueltos<\/h2>\n

Determinar la relaci\u00f3n es f\u00e1cil si se conoce el voltaje o el n\u00famero de vueltas.<\/p>\n

Por ejemplo:
\nUn transformador de voltaje de 110 kV\/20 kV tiene 110:20 con 2200 vueltas en el primario, lo que significa que hay 400 vueltas en el secundario.
\nEn el caso de un transformador de mayor voltaje, 18 kV \u2013 400 kV, la relaci\u00f3n se convierte en (400\/18 = 22.2).
\nUn transformador de distribuci\u00f3n generalmente tiene una relaci\u00f3n de voltaje de 11 kV\/0.4 kV, lo que significa que la relaci\u00f3n es 11\/0.4 = 27.5:1.
\nDebido a la construcci\u00f3n del autotransformador, que comparte una parte del sistema de devanado, tiene un menor n\u00famero de vueltas para la misma relaci\u00f3n de voltaje de 2:1.<\/p>\n

En el caso de transformadores que operan en un sistema trif\u00e1sico, se debe utilizar el voltaje l\u00ednea a l\u00ednea, mientras que el grupo vectorial (Dyn11, YNd11) es importante en t\u00e9rminos de determinar la relaci\u00f3n del desplazamiento de fase y la relaci\u00f3n de magnitud del sistema.<\/p>\n

Por qu\u00e9 la relaci\u00f3n es la v\u00e1lvula reguladora de la red.<\/h2>\n

Las fluctuaciones de voltaje en una l\u00ednea de transmisi\u00f3n ocurren debido a varios factores, a saber, modificaciones en la carga, fallos de generador, p\u00e9rdidas de potencia reactiva y distancia de la fuente. Sin ajuste al ratio, un alimentador puede experimentar fluctuaciones de voltaje de 5% a 10% a lo largo de un solo d\u00eda. El ratio del transformador act\u00faa como el medio pr\u00e1ctico para compensar las ventajas de la variabilidad del voltaje, ya que existe una relaci\u00f3n directa entre las vueltas y el voltaje de salida, con cualquier cambio que conduce a fluctuaciones correspondientes.
\nLos operadores del sistema deben mantener el voltaje dentro de los l\u00edmites legales establecidos por las regulaciones, que requieren mantener el voltaje en \u00b1 5% en el sector de distribuci\u00f3n y \u00b1 10% en el sector de transmisi\u00f3n. El m\u00e9todo m\u00e1s utilizado en este proceso es el OLTC, que ajusta el ratio del transformador. De hecho, el OLTC es tan ampliamente utilizado que tener un transformador sin OLTC necesita una justificaci\u00f3n por escrito.<\/p>\n

Cambiadores de tomas: El mecanismo que ajusta el ratio<\/h2>\n

Existen dos familias de cambiadores de tomas, y elegir entre ellas es principalmente una cuesti\u00f3n de ciclo de trabajo:<\/p>\n\n\n\n\n\n\n\n\n\n
Cambiadores de tomas fuera de circuito vs. bajo carga<\/caption>\n
Aspecto<\/th>\nFuera de circuito (DETC)<\/th>\nBajo carga (OLTC)<\/th>\n<\/tr>\n
Operaci\u00f3n<\/td>\nDesenergizado solamente<\/td>\nBajo carga, automatizado<\/td>\n<\/tr>\n
Rango t\u00edpico de tomas<\/td>\n\u00b12.5% a \u00b15%<\/td>\n\u00b110% a \u00b116%<\/td>\n<\/tr>\n
Pasos<\/td>\n3\u20135<\/td>\n13\u201317 (1.25%\u20132.5% cada uno)<\/td>\n<\/tr>\n
Capacidad de regulaci\u00f3n<\/td>\nSolo estacional<\/td>\nContinua, autom\u00e1tica (\u00b12% de mantenimiento)<\/td>\n<\/tr>\n
Prima de precio<\/td>\nL\u00ednea base<\/td>\n+$15,000\u2013$60,000 depending on rating<\/td>\n<\/tr>\n
Common on<\/td>\nDistribution transformers<\/td>\nPower transformers \u22655 MVA<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

While OLTCs are operating with electrical current, they use resistors or reactors and fast vacuum interrupters in order to minimize electrical arcing on the main contacts in the process of switching from fixed taps. A contemporary motor-controlled OLTC takes approximately 2 to 10 seconds to finish a cycle. It can be noted that the controller in this case uses voltage feedback from the secondary side of the transformer.<\/p>\n

Ratio Matching for Parallel Operation<\/h2>\n

When using two transformers to supply the same bus simultaneously, the ratios need to be adjusted to be closely matched. A difference in ratios of \u0394% generates a so-called circulating current (participating in the circuit even in idle condition).<\/p>\n

One advice is to make sure we keep the circulating current below 10% of the capacity of the smaller transformer.
\nThe effect of a 1% difference in ratio is usually a circulating current of 2%-5% of the capacity of two transformers with capacity of 20 MVA \/ 110 kV, which depends on impedance (normally 10%).
\nThe transformers should be operated in accordance with some basic conditions for this, namely: same group of vector, ratio must match, and impedance should not vary more than 10%, if at all.<\/p>\n

To account for this, operators need to change the tap position for each transformer to make those equal, and many of modern AVRs have a master-follower scheme for this purpose.<\/p>\n

Effects of Wrong Ratio: Circulating Current & Protection Issues<\/h2>\n

Relaying misoperation, due to relay rating, can lead to malfunctioning of protections with erroneous relay settings resulting in either protector operation without proper fault or failure to detect real internal defects because of 2%-5% errors.
\nVoltage changes can force the voltage along the creek into outside limits.
\nImbalance in load situation implies that a unit with a higher ratio consumes a considerable share of both active and reactive power leading to acceleration of its aging.
\nThat is why ratio check became one of the steps of commissioning according to IEC 60076-1 requirements stating that the voltage ratio on the main tapping must differ by no more than \u00b10.5% from design value and every tap must be verified against the nameplate data.<\/p>\n

Ratio Testing Methods & Standards<\/h2>\n

The standard field test is the turns-ratio test performed with a transformer turns ratio (TTR) meter:<\/p>\n\n\n\n\n\n\n
Ratio Testing Methods<\/caption>\n
Method<\/th>\nPrinciple<\/th>\nPrecisi\u00f3n<\/th>\nUso T\u00edpico<\/th>\n<\/tr>\n
TTR meter (TTR test)<\/td>\nCompares injected and induced voltage on each tap<\/td>\n\u00b10.1%<\/td>\nCommissioning, routine maintenance<\/td>\n<\/tr>\n
Voltage ratio check at no load<\/td>\nApply reduced voltage, measure both sides<\/td>\n\u00b10.3%<\/td>\nOn-site verification<\/td>\n<\/tr>\n
Capacitance ratio \/ low-voltage test<\/td>\nEquivalent ratio via capacitive coupling<\/td>\n\u00b10.5%<\/td>\nFactory type tests<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

Both factory tests and site tests originate from IEC 60076-1 and IEEE C57.12.90. The TTR test is considered a primary diagnostic test as the movement in the ratio between different tests done on the same unit oftentimes signifies a shorted turn in the winding, making yearly ratio tests an essential element of monitoring.<\/p>\n

Typical Ratios and Tap Ranges by Application<\/h2>\n\n\n\n\n\n\n\n\n
Typical Ratios & Tap Ranges Across Applications<\/caption>\n
Aplicaci\u00f3n<\/th>\nTypical Ratio<\/th>\nTap Range<\/th>\nTap Changer<\/th>\n<\/tr>\n
GSU at a power plant<\/td>\n18\/400 kV (22.2:1)<\/td>\n\u00b17.5% in 5 steps<\/td>\nOff-circuit, sometimes OLTC<\/td>\n<\/tr>\n
Transmission substation<\/td>\n220\/110 kV (2:1)<\/td>\n\u00b116% in 17 steps<\/td>\nOLTC<\/td>\n<\/tr>\n
Sub-transmission<\/td>\n110\/20 kV (5.5:1)<\/td>\n\u00b112% in 13 steps<\/td>\nOLTC<\/td>\n<\/tr>\n
Industrial power<\/td>\n33\/11 kV (3:1)<\/td>\n\u00b110% in 9 steps<\/td>\nOLTC or off-circuit<\/td>\n<\/tr>\n
Distribution<\/td>\n11\/0.4 kV (27.5:1)<\/td>\n\u00b12.5% off-circuit<\/td>\nOff-circuit<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

Distribution transformers require only periodic adjustments, so off-load taps in steps of \u00b12.5% and \u00b15% are adequate to account for seasonal load variation. By contrast, transmission and sub-transmission transformers areconfigured with OLTC because large groups of customers are directly affected by the action of the transmission voltage on them.<\/p>\n

Tap Changer & Transformer Price Impact<\/h2>\n

Tap-changer choice is a real line item in any transformer budget. Planning ranges:<\/p>\n\n\n\n\n\n\n
Price Impact of Tap Changer Selection<\/caption>\n
Transformador<\/th>\nWithout OLTC<\/th>\nWith OLTC<\/th>\nPremium<\/th>\n<\/tr>\n
5 MVA \/ 33 kV<\/td>\n$55,000\u2013$90,000<\/td>\n$75,000\u2013$130,000<\/td>\n+$15,000\u2013$40,000<\/td>\n<\/tr>\n
20 MVA \/ 110 kV<\/td>\n$150,000\u2013$260,000<\/td>\n$175,000\u2013$320,000<\/td>\n+$20,000\u2013$60,000<\/td>\n<\/tr>\n
50 MVA \/ 110 kV<\/td>\n$360,000\u2013$700,000<\/td>\n$400,000\u2013$800,000<\/td>\n+$25,000\u2013$90,000<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

The charges differ according to the type of specifications, the brand, and the area. The high expense involved in grid-tied units pays off in short time: the On-load tap changer (OLTC) can recover the cost quickly because it keeps the voltage regulated and diminishes the energy losses in feeders.<\/p>\n

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Brands & How Ratio Design Differs<\/h2>\n

Ratio mathematics remains the same irrespective of the originating company \u2014 physics is not up for negotiation; however, manufacturers distinguish themselves based on the type of tap-changer design, control, quality management, and pricing. Reliability benchmarks are set by the MR (Maschinenfabrik Reinhausen) and ABB tap changers as Asian companies increasingly make use of licensed or self-developed OLTC designs at cheaper rates.<\/p>\n\n\n\n\n\n\n\n\n
Transformer Brands & Tap-Change Capability<\/caption>\n
Marca<\/th>\nPa\u00eds<\/th>\nTap-Changer Strengths<\/th>\nIndicative Price (20 MVA\/110 kV, with OLTC)<\/th>\n<\/tr>\n
Hitachi Energy<\/td>\nSuiza\/Jap\u00f3n<\/td>\nProprietary OLTC, AVR integration<\/td>\n$450,000\u2013$700,000<\/td>\n<\/tr>\n
Siemens Energy<\/td>\nAlemania<\/td>\nMR OLTC options, digital control<\/td>\n$430,000\u2013$680,000<\/td>\n<\/tr>\n
Schneider Electric<\/td>\nFrancia<\/td>\nDistribution focus, MV units<\/td>\n$280,000\u2013$450,000<\/td>\n<\/tr>\n
TBEA<\/td>\nChina<\/td>\nIn-house OLTC, scale<\/td>\n$180,000\u2013$320,000<\/td>\n<\/tr>\n
Jiangsu Subian Electric Power<\/td>\nChina<\/td>\nCustom ratios & taps, MR or in-house OLTC<\/td>\n$160,000\u2013$300,000<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

The cost is determined by specification and area. In projects that require customized ratio and tap specifications \u2013 unique vector groups, special tap ranges, or particular brands of OLTC \u2013 Jiangsu Subian Electric Power is a reliable partner: it manufactures distribution and power transformers with capacity from 50 kva to 220 kV, provides quotes for individual tap configurations, and installs the required MR or similar on-load tap changers. Each unit is delivered with ratio test records on all taps under the IEC 60076-1 standard, and factory prices are usually 30%-50% lower than prices for European companies.<\/p>\n

Preguntas Frecuentes<\/h2>\n

How is transformer ratio calculated?<\/h3>\n

The transformer ratio is determined by the number of turns in the primary coil divided by the number of turns in the secondary coil (N1\/N2), which is equal to the no-load voltage ratio (V1\/V2). For example, the transformer applied at 110 kV\/20 kV will have a 5.5:1 ratio, while for the 11 kV\/0.4 kV transformer the ratio is 27.5:1. Because of the inverse relationship, it is evident that in a step-up transformer (ratio smaller than one; such as 0.045 for the transformer with 18\/400 kV voltage), the output voltage will be high while the output current is low.<\/p>\n

What is the tolerance on transformer ratio?<\/h3>\n

Per IEC 60076-1, the ratio at the principal tap must be within \u00b10.5% of the nameplate value, and the same tolerance applies at every tap position unless otherwise specified. Field TTR meters measure to \u00b10.1%, so a deviation beyond 0.5% on a commissioning test warrants investigation for shorted turns or a wrong connection.<\/p>\n

Why do transformers need tap changers for voltage regulation?<\/h3>\n

Due to fluctuations in line voltage based on load, generation, and distance from the source, without the ratio adjustment, the distribution feeder can fluctuate 5%\u201310% throughout the day. OLTC varies the ratio by 1.25%\u20132.5% in steps within a range of \u00b110% to \u00b116% to provide a secondary voltage of about \u00b12% automatically. This ensures the motors, electronics, and the customer equipment are safe from overvoltage and undervoltage.<\/p>\n

What happens if two transformers in parallel have different ratios?<\/h3>\n

An electric current circulates between the two units, even when there is no load coming from outside. In other words, a circulating current flows in a transformer even when it is on standby mode. When we take the case of 20 MVA\/110 kV units, even a 1%-ratio mismatch will cause a circulating current of around 2%-5% of full-load rated current. Moreover, if the mismatch increases, the circulating current will also increase accordingly. The action of operators, who equalize the ratio through the tap selection process, will prevent circulating currents from rising more than 10% of the rating of the small transformer.<\/p>\n

How much does an on-load tap changer add to transformer cost?<\/h3>\n

OLTC generally makes it possible to add between $15,000 and $60,000 to the cost of power transformers rated between 5 MVA and 50 MVA, with higher rated transformers costing more. The investment usually pays off due to better voltage control and lower losses of power as well as absence of equipment failures.<\/p>\n

Referencias<\/h2>\n