OLTC representa el Cambiador de Tomacorriente Bajo Carga. Aunque eso puede ser suficiente información para una pregunta, la abreviatura normalmente no aparecerá por sí sola. En su lugar, la encontrará en la hoja de datos del transformador, especificación de la licitación o cotización del proveedor. Por lo tanto, en lugar de preguntar qué significa, es mejor preguntar sobre el funcionamiento de este dispositivo, sobre su necesidad y posible precio.
Por lo tanto, veamos el asunto completo en detalle: interpretación del término, qué sucede dentro del tanque, casos de aplicación de OLTC, cómo OLTC se diferencia de los cambiadores de tomacorriente utilizados en la mayoría de los transformadores de distribución estándar, qué números representan y los principales productores de los dispositivos también.
Un OLTC es un Cambiador de Tomacorriente Bajo Carga, que es un mecanismo que opera cambiando la posición del tomacorriente de un transformador mientras aún está funcionando. Un OLTC es un aspecto importante de un transformador ya que ayuda a mantener su voltaje mientras el transformador está en funcionamiento. Por otro lado, un transformador común utiliza OCTC, que es un tipo de cambiador de tomacorriente donde los ajustes no se pueden realizar a menos que el transformador esté apagado. Un OLTC puede aumentar el precio del transformador en aproximadamente 10-30%. El costo del OLTC varía de $3,000-$30,000, dependiendo de la clase de voltaje y tipo, incluidos los transformadores de distribución que cuestan alrededor de $2,000-$8,000 y los transformadores de transmisión que cuestan alrededor de $15,000-$60,000. La empresa europea Maschinenfabrik Reinhausen (MR) es el principal fabricante en esta área, junto con empresas como Hitachi Energy, Siemens Energy, ABB, etc.
Lo que OLTC significa, palabra por palabra
Las tres palabras de la descripción deben entenderse literalmente, lo que significa que el nombre completo es más que una simple pregunta trivial.
- Bajo carga significa que el transformador no se apaga y continúa suministrando cargas mientras ocurre el cambio de tomacorriente. Sin interrupciones, sin desconexiones, sin necesidad de enviar un equipo al sitio. Este es el propósito principal del dispositivo y la razón por la que cuesta lo que cuesta.
- Tomacorriente se refiere a la conexión realizada en el devanado de alta tensión. El cambio de tomacorriente permite cambiar el número de vueltas en el circuito, lo que afectará la relación de vueltas y, en consecuencia, el voltaje de salida. La idea es similar a la idea de enlaces de tomacorriente fijos en un transformador de distribución ordinario, con la única diferencia de que un OLTC está diseñado para permitir el cambio rápido durante el flujo de corriente.
- Cambiador es la unidad donde se encuentran todas las partes del mecanismo: la unidad de motor, el eje vertical, el interruptor selector y los desviadores, junto con el cubículo de control para establecer el proceso de cambio de tomacorriente. Los diseños modernos a menudo dependen del uso del desviador con interruptores de vacío en lugar de los contactos sumergidos en aceite, lo que es responsable de las recientes mejoras en precios y mantenimiento.
A menudo se encontrará con el término “dispositivo de cambio de toma bajo carga” o “equipo de cambio de toma bajo carga”, “transformador OLTC” utilizado como sinónimo del transformador equipado con uno. Significa lo mismo. En los antiguos documentos británicos y de la Commonwealth, a menudo se escribe como “cambiador de toma bajo carga”, y en América del Norte a veces se refiere como LTC (cambiador de toma de carga).
Lo que un OLTC hace físicamente dentro de un transformador
El controlador monitorea la tensión secundaria y cuando sale de una banda muerta —por ejemplo, si se desvía más de 1.25% de la tensión requerida— activa el motor. El interruptor de derivación opera, se produce un breve flujo de corriente a través de algún resistor o reactor de transición, y el selector de toma se mueve a otra toma. El derivador se aferra a su nueva posición.
La razón de la impedancia de transición es el problema de ingeniería completo. No se puede simplemente abrir la toma bajo carga, por lo que el derivador crea un puente controlado momentáneo con la ayuda del resistor o reactor que permite que la corriente pase.
El resto de la configuración está compuesto por el selector de toma, que es el dispositivo de hacer antes de romper que no lleva corriente por sí mismo; motor, engranajes; indicador de posición y interruptores de límite, así como un sistema de control automático, que conecta todos los demás dispositivos al relé de tensión, SCADA y comandos remotos.
El OLTC ordinario en el transformador de potencia trabaja con 8 o más +/- 1.25 %, por lo que tiene 17 números de posición y un grado de ajuste de tensión de aproximadamente +/- 10 %. Sin embargo, también se pueden hacer algunas otras configuraciones como 9 con +/- 1.67 % o 16 con +/- 0.625 %. El precio depende tanto del tamaño del procedimiento de paso, ya que impacta en los conductores utilizados, como de la vista del transformador de toma que debe estar conectada al elemento de conmutación.
Dónde se sitúa el OLTC en la familia de transformadores
Necesitamos aclarar la posición del dispositivo mencionado, ya que el término “transformador OLTC” es ambiguo.
El término OLTC no se refiere a un tipo de transformador, sino más bien a un dispositivo que se adjunta a los transformadores y se puede encontrar en transformadores de potencia, transformadores de subestación de gran tamaño, transformadores rectificadores y transformadores de desplazamiento de fase. No se integrará en un transformador de poste pequeño o un transformador de tipo seco simplemente porque no sería económicamente viable instalar el OLTC en tales transformadores.
El principio general es que cuanto más grande es el transformador y más varía la carga, más justificado está el OLTC. Un transformador de 40 MVA conectado a una subestación donde la carga varía de 30% a 100% sería un uso adecuado de un OLTC, pero un transformador de 1,000 kVA que suministra energía a una instalación donde el consumo de energía es constante no necesitaría el OLTC.
Si desea una visión más amplia de cómo se clasifican estas unidades —por función, por refrigeración, por aplicación— esa taxonomía se establece en esta visión general de cómo se clasifican los transformadores de potencia y qué hace cada tipo en la red., y es un marco útil antes de que vayas a comprar uno específico.
OLTC vs. OCTC vs. DETC: ¿Qué es realmente diferente?
Aquí es donde vive la mayor confusión, y vale la pena una tabla.
| Dispositivo | Forma completa | Operado | Donde lo verás |
|---|---|---|---|
| OLTC | Cambiador de tomas bajo carga | Mientras está energizado y bajo carga, automáticamente o de forma remota | Transformadores de potencia, transformadores de transmisión y grandes transformadores de subestación |
| OCTC | Cambiador de tomas fuera de circuito | Solo con el transformador desenergizado | Transformadores de distribución, unidades montadas en postes, la mayoría de los transformadores de tipo seco |
| DETC | Cambiador de tomas desenergizado | Solo con el transformador desenergizado | El mismo hardware que un OCTC; DETC es el término norteamericano |
OCTC y DETC son similares aunque la diferencia entre estos y OLTC está lejos de ser simple. La intuición detrás de un OCTC es que consiste solo en interruptores que solo alteran su posición cuando un sistema se enciende por primera vez o cuando hay un cambio estacional en el perfil de voltaje. Por lo tanto, el dispositivo debe ser apagado y cerrado de manera segura de antemano.
En contraste, un OLTC realiza esta operación de manera continua. Reacciona a los cambios de voltaje en cuestión de segundos. El sistema de control puede ser bastante simple, que solo consiste en un regulador de voltaje con un retraso de tiempo, o puede ser más complejo, adaptativo, teniendo en cuenta el factor de potencia, la corriente circulante de los transformadores conectados en paralelo o señales SCADA del sistema de control.
El aspecto práctico de esta diferencia es el aspecto de diseño. Debido a que el OCTC rara vez cambia y nunca está bajo carga operativa, no hay necesidad de características como impedancia de transición, control de arco o accionamiento de motor.
Los principales tipos de OLTC
No todos los cambiadores de tomas bajo carga son iguales, por lo que es importante estar al tanto de las diferencias al seleccionarlos o reemplazarlos.
- Tipo resistor. El interruptor de derivación se conecta a través de un resistor de transición para el proceso de conmutación. Rápido, compacto y el diseño más popular en Europa y Asia tanto para distribución como para transmisión.
- Tipo reactancia. Utiliza un autotransformador como medida preventiva. Dominaba el mercado estadounidense en el pasado, pero es más lento y puede manejar altas corrientes sin pérdidas causadas por la conmutación. Aún se utiliza con frecuencia en aplicaciones más antiguas y grandes.
- Derivador aislado en aceite. El interruptor de derivación funciona en su propio compartimento de aceite. Es una tecnología antigua, confiable, pero el aceite necesita ser reemplazado periódicamente después de cada operación debido a la degradación.
- Vacuum diverter. The sealed vacuum interrupters perform the current transfer process. It provides protection from current breaks because it is performed in no oil, thus providing longer operational periods but at a little higher price. It is widely used nowadays in the bulk prices.
- In-tank vs. separate compartment. In-tank technology shares the oil with the transformer, while separate compartment keeps diverter oil in isolation to prevent contamination. For heavily loaded transformers separate implementation should be chosen despite higher costs.
- Reversing vs. coarse/fine. The reversing mechanism has a smaller design and can provide a wide range of tap changing in one section; whereas coarse/fine implementation gives a wider range but requires more winding.
The choice of the right model should depend on its working frequency, required breaking current, and availability of maintenance access.There’s a longer treatment of the trade-offs in this transformer tap changer selection guide if you’re at the point of comparing specific configurations rather than just understanding the categories.
Where OLTC Transformers Are Used
Voltage control is required constantly.
- Transmission substations where high voltage (220 or 110 kV) is changed to low voltage in order to deliver electricity to an everchanging load.
- Long rural feeders where voltage drop is big and demand varies according to the season or irrigation regime.
- Transformation stations for renewable generation since output of solar and wind plants fluctuates much quicker than that of traditional load, so the voltage needs to be kept within narrow limits.
- Traction and railway transformers due to constant variation of the load during train movement.
- Electric arc and rectifier transformers since big current load fluctuations happen all the time and result in continuous need for adjustment of voltage.
- Phase shifting transformers where electric parameters are managed using transformers with changing tappings.
An example from manufacturing will clarify this issue much better. A unit like this SZ11 31,500 kVA 35/10.5 kV oil-immersed on-load voltage regulating transformer is built specifically for the case where a 35 kV incoming supply has to deliver a stable 10.5 kV to a distribution network whose load varies throughout the day. That’s an OLTC application in one component and one sentence.
What an OLTC Costs
The price varies widely among various manufacturers in terms of rating, voltage class, and current, but the general frame of costs remains stable enough to perform assessments.
| Artículo | Typical range (USD) | Notas |
|---|---|---|
| OCTC / DETC (off-circuit) | $500–$3,000 | The baseline. No motor drive, no transition impedance |
| Distribution-level OLTC (≤33 kV) | $2,000–$8,000 | Oil-insulated diverter, typically 9 to 17 positions |
| Transmission-level OLTC (≥110 kV) | $15,000–$60,000 | Vacuum types sit at the upper end |
| Resistor or vacuum type, mid-range | $6,000–$35,000 | Driven mainly by current rating and step count |
| OLTC as a share of transformer price | +10–30% | Compared with +2–5% for an OCTC |
| OLTC increment on a 10 MVA transformer | $10,000–$25,000 | Depends heavily on whether vacuum or oil diverter |
The first point to discuss concerning the table is that the cost of the changer is not all included in the price of an OLTC transformer. Apart from the changer, an OLTC transformer has to be equipped with a tap winding, its leads, a motor with a control unit, and so on, so if we evaluate the gap in terms of price per kVA, then it is observed that the OLTC as compared to the OCTC transformer costs much more.
The lubricant or oil for the oil lantern should not be considered as an irrelevant item as it requires frequent checks of the oil and sometimes its replacement. Thus, with every 50,000 to 100,000 operations, it has to be replaced every three or five years (depending on the load). The vacuum type of transformers extends this interval, which is why they allow to achieve savings in the cost over its lifespan.
To give an example of the costs, OLTC transformers of capacity 20 MVA and voltage of 110 kV typically cost 430,000-700,000 EUR from major European manufacturers, below 450, 000 EUR from Schneider, and below 320,000 EUR from Chinese manufacturers.
Brands and Manufacturers Worth Knowing
There are two very distinct categories of producers, and their customers generally must decide which one to go for.
Specialists. The Maschinenfabrik Reinhausen company is regarded as the market leader of the entire industry. If, in the call for tender, the specification reads “OLTC by MR or equal”, it signifies what exact product is intended. This manufacturer’s product portfolio includes everything from oil diverter products designed for the distribution voltag to vacuum devices suitable for the highest voltage classes, and their devices are widely imitated. Moreover, Reinhausen is engaged in licensing and supplying transformers to other manufacturers, which is why you can find tax changers of this manufacturer among transformers offered under various labels.
Integrated producers. Companies like Hitachi Energy, Siemens Energy and Alstom manufacture transformers and supply tap changing devices as one package. Hitachi Energy is particularly well known for this. This experience allows it to produce transformers along with tap-changing devices that comprise the product list offered. What is the key advantage of this approach? It is the single supplier who is responsible for the single warranty — a crucial benefit for the project with high uncertainty related to the interfaces.
Chinese and regional manufacturers. Due to their attractive price, TBEA, Subin and some other companies became successful in producing OLTC transformers. Due to their affordability these transformers can be applied in various projects implemented throughout Southeast Asia, Africa, Middle East and Latin America. The competition became fiercer with respect to medium voltage transformers, while the long-established specialists still retain the competitive edge in high voltage products and service network.
The primary consideration when making your decision should be the place where transformers will be delivered to and serviced. Companies that have well-developed infrastructures and capable personnel for maintenance usually opt for products manufactured by specialists. General contractors working at time-constrained projects usually prefer to purchase integrated products. Either way, the brand comparison exercise is the same one you’d run for any transformer purchase, and the frameworks in this buying guide for oil-immersed transformers with brand recommendations apply directly to OLTC-fitted units.
How to Specify One Without Regrets
If you’re developing a specification, the following parameters will determine whether you’ll get a practical device or merely an expensive ornament:
- Voltage regulation range and step size. Start with considering how much the supply voltage will fluctuate. A variation with a 10% accuracy range and a fluctuation of about 1.25% is what is needed in the majority of cases. Transmission and renewable connections may require higher accuracy or wider range.
- Number of operations per year. This number will determine whether to choose oil or vacuum, and whether to use tank installation or separate compartment. If a transformer is rated for 300,000 operations but is expected to run 20 cycles a day, it’ll mean regular servicing.
- Through-current through diverter. Voltage regulation is about breaking current load not only voltage. When it comes to this matter, oversizing is inexpensive compared to replacing contacts since it costs much less.
- Control philosophy. Will you have a stand-alone voltage regulation with a dead zone and time delay or coordinated control with parallel transformers and SCADA? The latter requires ensuring that control cubicles in both variants function properly and switching gears regulates current effectively.
- Parallel operation. In order to run two transformers in parallel, running both at the same tap position is necessary, and hence the need for either master-slave control or controlling circulating current in advance.
- Maintenance access. Having a separate tank might be costlier but make diverter service possible without draining the main tank. On a remote site, this might be the only deciding factor.
- Proof of compliance with the standards. You need to check documents in compliance with IEC 60214-1. Be not satisfied with copies of certificates and ask data on type test.
There is a longer walkthrough of these choices in this guide on how to select the on-load tap changer for a main power transformer, including how step size interacts with the tap winding and how the operating duty class should be matched to the project. If you’re specifying for the first time, start there rather than with the price list.
Preguntas Frecuentes
What is OLTC and OCTC?
OLTC stands for On-Load Tap Changer, while OCTC stands for Off-Circuit Tap Changer. The difference between the two is that OLTC operates while the transformer is energized and in operation; it will use motorized drive, a selector switch, and a diverter switch that works under transition resistance, which ensures that the current is not broken. An OCTC can operate only when the transformer is turned off and safe; thus, it will work using the link that is made at commissioning. OLTC is installed in transformers that ensure the continuous control of voltage in the system; whereas OCTC is installed in distribution transformers since it is more cost-efficient.
What are the types of OLTC?
The first distinction is in terms of the method of switching from one state to another with use of transition resistors in the case of the resistor type, which is commonly used in Europe, Asia, and the hybrid type using an autotransformer. Furthermore, the division is based on the switching medium and thus to oil insulated switching systems with the switching contacts located in the oil and taking special care of it, while there is the vacuum type of systems in case of which the switching is made by using enclosed vacuum interruptions and no routine maintenance is necessary. Construction-wise, the systems are divided into either in-tank or separate-compartment units, and depending on the design there might be linear, reversing and coarse/fine taps.
What is the difference between RTCC and OLTC?
The OLTC is the actual switching apparatus and the RTCC represents the layer of controls that tells it what to do. The RTCC or Remote Tap Changer Control (also known as Remote Tap Changer Controller) is an electronic relay or controller that receives the secondary voltage, compares it with the desired value and dead-band, implements a time delay on the operation in order to ignore temporary voltage drops, and produces “raise” or “lower” commands for the motor assembly. Some RTCCs carry out the operation of coordination of transformers in parallel, line-drop compensation as well as SCADA communication. So RTCC is not an alternative to OLTC — it is the unit that provides automatic function of the OLTC. You can use OLTC without a sophisticated RTCC — a simple voltage relay will suffice, but it is impossible to have automatic operation without both devices.
What does OLTC mean?
On-Load Tap Changer is referred to as OLTC. In electrical engineering, the term “on-load” emphasizes that the equipment is functioning while the transformer is energizing and transmitting current. This deviates from the term “off-circuit” or “de-energized” since those terms indicate that the transformer has to be turned off first and be isolated from other components. The tap changer is the equipment used for selecting the point of connection of the winding. It changes the connection point in order to modify the number of turns, which also in turn enables voltage modification. Consequently, OLTC is translated into “a device that makes taps changes while the transformer is under load.” The equivalent acronym used in North America is LTC (load tap changer).
Can an OLTC be retrofitted to an existing transformer?
In a technical sense retrofitting is possible, but for a practical application it does not really make sense. Retrofitting can be described as an operation involving opening up the tank to replace the wire and insulate the leads, installing a driving motor and a separate compartment to actually rerun the control circuit. What is more, the costs involved in retrofitting may exceed a big part of the price of a transformer of the same rating and it also means giving up all the state of affairs concerning factory type tests. In situations when voltage control during operation is really needed but the transformer can only provide OCTC, some of the options include installing a separate regulator, using the booster transformer or changing the transformer with a new one at the end of its technical lifespan.
Referencias
- IEC 60214-1 — Tap-changers, Part 1: Performance requirements and test methods — the governing standard for on-load and off-circuit tap changers
- Fábrica de Máquinas Reinhausen (MR) — manufacturer information and technical literature on on-load tap changers
- Hitachi Energy — Transformers — integrated transformer and tap changer solutions
- Siemens Energy — industry context on equipment design and environmental regulation
- Departamento de Energía de EE. UU. — grid equipment, transformer supply and reliability reporting
- National Electrical Manufacturers Association (NEMA) — electrical equipment standards and industry data
Conclusión
OLTC denotes the On-Load Tap Changer. If the reader only recalls one sentence from this text, then that should be this one: it is the device that allows a transformer to self-correct its output voltage while current is still flowing; this is an outstanding feature compared to simple tap links of a standard distribution transformer.
The practical facts one needs to keep in mind while having a specification dialogue are as follows: expect to have ±8 up to ±16 steps with the step being between 0.625% and 1.67%; the price of the changer would range between $3,000 and $30,000 and would make the transformer cost by about 10%-30% more expensive; expect to see that while oil-insulated diverters would require servicing every few years, vacuum ones would serve for much longer; the standard you should be held to should be IEC 60214-1; and the name of MR Reinhausen will always be used as a benchmark.
The question of whether or not you need an OLTC boils down to one question. Is the voltage at the supply point fluctuating enough and often enough that you cannot regulate it by other means? In case the load profile is steady and the supply is stable, it is better to use an OCTC and spend money elsewhere.