Un planificador de servicios públicos está sopesando dos ofertas para un transformador de potencia con una capacidad nominal de 20 MVA y niveles de voltaje de 66/11 kV. Ambos fabricantes han ofrecido la misma capacidad de potencia con pérdidas idénticas y aproximadamente el mismo precio, pero la principal diferencia radica en sus sistemas de aceite. Un fabricante ha diseñado el transformador basado en un tanque conservador de aceite externo convencional con respiradero de gel de sílice, mientras que el otro fabricante ha diseñado un tanque de expansión corrugado sin conservador. El planificador entiende que el tipo de sistema de aceite elegido afecta no solo al sistema de preservación de aceite en sí, sino que también impacta en el programa de mantenimiento, el nivel de riesgo de incendio y el precio; típicamente, el costo de la unidad con conservador será un 5-10% más que el precio de una unidad sellada, pero la primera opción permite gestionar el aceite de acuerdo con regulaciones simplificadas durante muchos años.
La guía proporciona información sobre para qué sirve un conservador, qué diferentes diseños existen en el mercado, cómo calcular su tamaño y cómo elegir los que mejor se adapten al sistema de preservación de aceite del transformador aislado por aceite.
¿Qué es un conservador de transformador?
Un conservador puede definirse como un tanque auxiliar cilíndrico o rectangular colocado en la parte superior del tanque principal del transformador, interconectado con el tanque principal a través de una tubería. Posee el volumen de aceite en reserva para fluctuar en nivel de acuerdo con la variación de temperatura (carga). Cuando el aceite se expande debido al calentamiento, puede llenarse en el conservador para que no se genere presión en el tanque principal. El aceite fluye entre el conservador y el tanque principal sin crear un vacío adicional mientras trabaja. El conservador permanece abierto al aire atmosférico a través de un respiradero (o está sellado con una membrana), lo que es una razón adicional importante por la cual debe estar posicionado en la parte superior del tanque principal.
En ausencia de un conservador, un tanque completamente sellado significaría que la presión interna aumenta a medida que el aceite se expande, y en caso de enfriamiento, aparece un vacío en el interior, lo que genera tensiones en la construcción del tanque y conclusiones.
Tres características conducen a estos resultados.
El aceite se expande dependiendo de la temperatura. El aceite mineral se expande aproximadamente 0.071% por cada grado Celsius de temperatura. Usando un tanque de 10,000 litros de capacidad sometido a un cambio de temperatura de 50°C, y teniendo en cuenta que el volumen de aceite y la presión aumentarían en 350 litros, queda claro que el tanque rígido sellado puede romperse o empujar el aceite a través del orificio de respiración.
El tanque principal debe estar siempre lleno. Si el aceite en el tanque principal baja, su devanado superior queda descubierto y permite que la humedad entre en el aislamiento en el espacio de gas. Con la ayuda del conservador, el aceite llena fácilmente el tanque principal.
La presión en el espacio de gas debe ser gestionada. El diseño del conservador permite tener un pequeño espacio de gas sobre el aceite que es controlado por el respiradero. Si el diseño es sin el conservador, el espacio de gas crecería y disminuiría con la carga creciente, y como resultado, el aire sería movido dentro y fuera del tanque.
Así, se hace posible fabricar el sistema de preservación de aceite “de respiración libre”.
Comparación de Diseños de Conservador
| Diseño | Cómo Funciona | Reserva Típica de Volumen de Aceite | Costo Relativo |
|---|---|---|---|
| Conservador cilíndrico externo | Tambor separado sobre el tanque, respiradero en la parte superior, tubería de aceite por debajo | 8-15% del volumen del tanque | Línea base |
| Conservador de membrana / bolsa | Bolsa de goma o membrana separa el aceite del aire; espacio de gas sellado | 8-15% | +10-20% sobre el conservador simple |
| Diseño de pared de tanque corrugado | Sin conservador separado; la pared flexible y corrugada del tanque absorbe la expansión | Integrado | Similar al conservador simple |
| Tanque sellado / con gas cubierto | Tanque fijo con cojín de nitrógeno o membrana; sin respiradero | Ninguno (espacio de gas) | +5-15% |
El conservador externo con un respiradero sigue siendo el diseño más común del mundo porque es simple, barato de construir y fácil de inspeccionar. El conservador de membrana añade una bolsa de goma que separa completamente el aceite del aire exterior, por lo que el aceite nunca ve oxígeno ni humedad de la respiración, a costa de una bolsa que debe ser revisada por daños. El diseño del tanque corrugado elimina el recipiente separado y es popular en transformadores de distribución donde el espacio y la simplicidad importan más que la conveniencia de mantenimiento.
Dimensionando Correctamente el Conservador
El conservador debe tener suficiente capacidad para tener en cuenta el volumen de aceite que se expande entre la temperatura mínima durante la operación y la temperatura máxima permitida del aceite superior. Se deben seguir cada uno de los pasos: Determinar el rango de temperatura. En condiciones normales templadas, el aceite se comporta desde -10 grados en un arranque en frío hasta 90 grados mientras está bajo carga, lo que corresponde a un cambio de temperatura de 100 K. En caso de regiones cálidas, use datos reales en su lugar. Calcule el volumen de aceite que se expandirá, lo que requeriría multiplicar el volumen de aceite por el coeficiente de expansión, aproximadamente 0.0007 por K multiplicado por el grado de cambio de temperatura. Así, por ejemplo, el volumen de aceite alcanza 10,000 kg a 100K, lo que sería igual a aproximadamente 700 litros. Se debe tener en cuenta el espacio de reserva para el indicador de nivel de aceite. El conservador debe indicar el nivel de aceite todo el tiempo desde la marca máxima mientras está caliente y la marca mínima mientras está frío, sugiriendo así 20 a 30% más aceite que el volumen preciso de aceite, que se considera aproximadamente 8 a 15% del volumen total de aceite del tanque. Calcular todo incorrectamente costará mucho dinero. Si el conservador es pequeño, el aceite se filtrará hacia afuera a través del respiradero, lo que llevará a manchas de aceite en el tanque y aire húmedo siendo absorbido; mientras que si el conservador es sobredimensionado, tendrá materiales y aceite en exceso. Para dimensionar rápidamente, comenzamos con el volumen total de aceite en el transformador, aquí hay valores de referencia de ingeniería de muestra para el conservador para un cambio de temperatura de 100 k:
| Clasificación del transformador | Volumen Total de Aceite Típico | Volumen de Trabajo del Conservador (10-12%) | Volumen del Tanque del Conservador (con reserva de medidor) |
|---|---|---|---|
| 100 kVA distribución | 300-400 L | 35-50 L | 60-80 L |
| 1 MVA distribución | 1,500-2,000 L | 150-240 L | 250-350 L |
| 10 MVA potencia | 8,000-12,000 L | 800-1,400 L | 1,200-2,000 L |
| 40 MVA potencia | 25,000-35,000 L | 2,500-4,200 L | 3,500-6,000 L |
Accesorios y Protección del Conservador
| Accessory | Purpose | Typical Specification |
|---|---|---|
| Silica gel breather | Dehumidify air entering the conservator | 1-15 kg desiccant, color-change indicator |
| Oil level gauge (magnetic) | Show oil level at a glance | Float + pointer, dial marked Min/Max |
| Buchholz (gas) relay | Detect gas and oil surge at the conservator pipe | DN50-DN100, two float switches |
| Membrane / air cell | Separate oil from atmosphere in sealed designs | Rubber bag, replaceable |
| Conservator heater (optional) | Prevent condensation in cold climates | Thermostatic, weatherproof |
On a conservator-equipped transformer, the Buchholz relay is mounted in the pipe between the main tank and the conservator — its correct, standard location. The breather is fitted to the conservator’s top, and the oil gauge to the end cap. All of these accessories are tested as part of the transformer’s routine test in a properly managed factory.
Conservator vs. Corrugated Tank vs. Sealed Designs
| Característica | External Conservator | Corrugated Tank | Sealed / Gas-Blanketed |
|---|---|---|---|
| Oil-to-air contact | Controlled via breather | Controlled via breather | None (sealed) |
| Acceso para mantenimiento | Excellent; easy to inspect and top up | Good; level via gauge | Limited; oil sampling only |
| Transformer cost impact | +5 to +10% | +3 to +8% | +5 to +15% |
| Typical application | Most power and distribution transformers | Distribution, space-constrained sites | Where moisture ingress must be minimized |
| Riesgo de incendio | Similar; oil volume is the driver | Similar | Slightly lower oxygen exposure |
For transformers above 5 MVA, the external conservator is the overwhelmingly common choice because it makes oil management, level inspection, and gas relay maintenance straightforward. Corrugated tanks dominate the 100-2,500 kVA distribution class where price and footprint matter more than maintenance convenience. Sealed designs appear where the oil must never see air — but they complicate top-up and inspection, so they are the exception rather than the rule.
Which Design for Which Transformer
- Distribution transformers (50-2,500 kVA): external conservator or corrugated tank, both with breather; conservator simplifies seasonal checks.
- Power transformers (5-100 MVA): external conservator with breather, Buchholz relay, magnetic oil gauge; membrane conservator where low moisture uptake is specified.
- Generator step-up and network transformers: membrane or sealed conservator to meet stringent oil quality guarantees.
- Cold-climate installations: conservator with heater and adequate sizing for the low-temperature end of the range.
- Compact substations and skid packages: corrugated tank or membrane conservator to save height and space.
Comparación de marcas y precios
| Marca | Origen | Conservator Offering | Approx. Price Range (standalone) |
|---|---|---|---|
| ABB | Switzerland/Sweden | Full range of conservator and sealed designs | $1,200-$9,000 |
| Siemens | Alemania | Conservator-equipped power transformers | $1,500-$10,000 |
| Hitachi Energy | Suiza | Membrane conservator options for large units | $1,500-$12,000 |
| Schneider Electric | Francia | Distribution transformer conservators | $800-$5,000 |
| Specialist accessory makers (Comem, etc.) | Italy / China | Conservator tanks, bags, level gauges | $500-$6,000 |
| Jiangsu Subian Electric Power | China | Conservator and corrugated designs, full accessory set | $600-$6,000 |
European leaders such as ABB, Siemens, Hitachi Energy, and Schneider Electric build conservator designs as part of complete transformer packages, and specialist accessory makers supply standalone conservators and level gauges worldwide. On the transformer itself, the conservator is usually included in the base price, so the real comparison is between complete packages. Manufacturers like Jiangsu Subian Electric Power offer both external conservator and corrugated-tank designs, with the breather, Buchholz relay, and magnetic oil gauge included and tested as a set — the whole assembly appears on the routine test certificate. Subian’s pricing for a conservator-equipped transformer lands roughly 40-60% below equivalent European-brand quotes, which is why they are a common choice for utilities and OEMs in Asia, Africa, and Latin America. When comparing quotes, always confirm that the conservator, accessories, and their testing are itemized rather than hidden in the tank price.
Tips on Choosing the Appropriate Conservator
First of all, make decisions about your oil preservation methods. Will you be choosing free-breathing with a breather, membrane-sealed or fully sealed conservator? Your choice determines the design of the conservator.
Next step is to consider the size relative to temperature. Please use the actual lows and highs for your site; the 8-15% rule assumes a 100 K range meaning a bigger tank is needed in colder climates.
Now check the accessories. Your conservator should have a breather, an oil gauge, and a Buchholz relay in the positions required by the protection scheme.
Another step is to check the access to maintenance. In case your site is not manned, it is preferable to purchase a conservator with a level gauge that can be read from a distance or a design that does not need checking the oil level.
Consider footprint. Should you use a corrugated design for containerized substations or external conservators?
You also need to request the records on how the accessories were tested.
Operation and Maintenance
The maintenance requirements of a conservator are simple but particular:
Each week, check the oil level gauge of the conservator for discrepancy against a standard temperature corrected level chart; any deviation from the level chart indicates the occurrence of an oil leak, or infiltration of moisture into the oil.
Replace or recharge the silica gel located in the breather after every 3-6 months, or as soon as the color of the silica gel changes indicating saturation.
Annually carry out a function test on the Buchholz relay placed in the conservator pipe so as to confirm that this component works properly.
Each time there is an outage, inspect the membrane which may be laid inside the conservator for existence of holes or hardening and confirm the presence of a sufficient space between the bag and the conservator wall.
At the sample point of the conservator, sample the oil for water and dissolved gases, for the oil in the conservator is regarded to be the indicator of the whole oiling system.
Ignoring the gauge of the conservator is one of the main causes of the equipment cooling failure in practice; the steady oil leak lowers the level of oil, and as the relay reacts on the major gas generation, the operator finds out that the tank has not been filled for months. Despite the fact that the conservator costs only 100 dollars, it could have indicated the fact about the low oil level long time ago.
Preguntas Frecuentes
How much does a transformer conservator cost?
As a standalone component, a conservator tank costs $800-$8,000 depending on volume and material, plus $50-$1,200 for the breather, oil gauge, and relay. On a complete transformer, the conservator design adds roughly 5-10% to the total price versus a sealed tank. For a 1 MVA distribution unit, the conservator package typically adds $500-$2,000 to the quote.
What size conservator do I need?
Size it to absorb the full oil expansion between your site’s minimum and maximum oil temperatures. The engineering rule is 8-15% of the main tank oil volume, with 10-12% the common default for a 100 K swing. Cold climates need the larger end; tropical sites with tight temperature bands can use the smaller end.
What is the difference between a conservator and an oil expansion tank?
They are the same thing in different words. The conservator (also called an oil conservator, expansion tank, or oil preservation tank) is the small vessel mounted above the main tank that accommodates thermal expansion of the oil and keeps the tank full. The term “conservator” is the standard in transformer engineering, while “expansion tank” is the more general engineering term.
Can a transformer work without a conservator?
Yes — corrugated-tank, membrane, and fully sealed designs all operate without a separate external conservator. But every oil-immersed transformer needs some form of oil preservation. The corrugated tank uses the flexible wall, the sealed tank uses a nitrogen cushion or membrane, and only the conservator gives you a visible oil level and easy maintenance access. For transformers above 5 MVA, a conservator is strongly preferred in practice.
Why is my conservator oil level gauge dropping?
Check it against the temperature-corrected level chart first — a drop during a cold night is normal. If the level drifts below the charted value for the current temperature, there is either an oil leak (check welds, gaskets, and the sample valve) or moisture ingress consuming the oil space. Treat a genuine level drop as a priority finding: a low conservator level can eventually expose the top of the winding and trigger a Buchholz trip.
Referencias
- IEC 60076-1 — Power Transformers, General Requirements — The master standard covering oil preservation systems, conservators, and accessories.
- IEEE C57.12.00 — General Requirements for Liquid-Immersed Transformers — North American requirements for oil preservation equipment.
- IEEE C57.106 — Guide for Acceptance and Maintenance of Insulating Mineral Oil — Oil moisture and quality limits the conservator protects.
- Hitachi Energy — Transformer Products — Reference for conservator and sealed transformer design options.
- ABB Transformers — Industry reference for oil preservation system documentation.
- Transformers Magazine — Practical articles on conservator maintenance and oil system design.
Conclusión
The conservator acts as the calm core of the transformer’s oil preservation system. It absorbs heat expansion, provides oil-filled tank protection, serves as the support for the breather as well as for the gas relay, and facilitates monitoring by the maintenance personnel by having a visible and measurable oil system. Depending on whether the design of the conservator you prefer relies on solid form for the sake of compactness, or if you want to use an external conservator for the sake of utility, or if you need the membrane solution for the sake of oil purity, it still has to be chosen wisely rather than inherited from a template engineering specification.
Make sure to size the conservator according to the real temperatures at your site (8-15% of the tank volume).
Make sure to use the oil gauge, breather, and Buchholz relay as a set.
Check the level gauge against the temperature chart weekly.
List the conservator and accessories in every quotation.
For conservator-equipped oil-immersed transformers built to IEC 60076-1 with complete accessory testing, contact Jiangsu Subian Electric Power at www.subian-electric.com and request an itemized quotation with your kVA, voltage, and site temperature data.