Conservator Tank of Transformer : Construction & Its Working

We know that transformer is the most essential electrical device used in different areas like power plants, industries, etc. There are different types of transformers available based on its application, its classification is done. But to provide long service life to the transformer, there are different kinds of accessories are used by connecting to it. The transformer accessories are breather, conservator tank (cylindrical tank), and explosion vent. A cylindrical tank accessory plays a key role in the transformer. It is arranged over the main tank’s roof so that sufficient space can be provided to expand the transformer oil. Once the temperature increases, then the oil volume can also be increased. So it acts as a reservoir for expanded oil in the transformer oil. This article discusses an overview of what is a conservator tank, construction, working, and its types.

What is a Conservator Tank?

Definition: A conservator tank can be defined as, a tank that is placed on the transformer’s roof to provide sufficient space for oil expansion in the transformer. The main function of the conservator tank of a transformer is, once the transformer is loaded and the ambient temperature rises, then the volume of the transformer oil will increase. So it works like a reservoir for insulating the transformer oil.

Conservator Tank
Conservator Tank

Construction of Conservator Tank

The shape of the conservator tank in the transformer is cylindrical where both the ends of the oil container are closed. One side of the container is provided with a large cover for cleaning and maintaining the tank.

The pipe of the conservator comes from the main tank of the transformer. It is placed in the conservator tank at the bottom part. The head of this pipe in the tank has a cap so that oil mud can be prevented and residue to come into the main tank from the conservator tank.

Conservator Tank Construction
Conservator Tank Construction

Generally, the fixing pipe of the silica gel breather goes into the conservator tank from the top. When this pipe goes from the base, then it should be projected well on top of the oil level in the tank. This arrangement ensures that transformer oil does not flow into a silica gel breather even at the maximum operating level.


The working of the conservator tank is, once the transformer insulating oil increases because of the ambient temperature and load, then the vacant space on top of the oil level in the conservator is incompletely occupied through the extended oil. As a result, the equivalent amount of air in that gap is pushed away using a breather. Once the transformer load reduces, then the transformer is turned off similarly, once the ambient temperature reduces, the transformer oil contracts. This mainly occurs due to the outside air because it enters the tank through a silica gel breather.


Oil Level

Maintaining the transformer oil level within the conservator tank is not important but there must be some amount of oil for proper operation. So the oil tank should not overflow or empty in the process because, in low load conditions, the empty tank must be avoided whereas, in full load condition, the overload must be avoided. Here, the level of transformer oil mainly depends on the temperature of oil, solar radiation, transformer loading, ambient temperature, etc. The design of this tank mainly depends on the change in the transformer oil level. According to the International Electrotechnical Commission (IEC), conservator tank design must use the temperature which ranges from -25°C to +110°C.

Different Types

There are two types of conservator tanks of a transformer which include the following.

  • Atmoseal Type Conservator
  • Diaphragm Sealed Conservator

Atmoseal Type Conservator

In atmoseal conservator, it includes an air cell that is made with NBR material. This material can be connected to the conservator reservoir. The silica gel breather can be connected at the summit of the air cell. The level of oil will be increased in the transformer and reduces based on reflating & deflate of the air cell

Once the air cell deflates then the air in the air cell comes out through a breather and alternatively if this cell inflates then the outside air enters into the tank using a breather. This arrangement stops straight contact of oil through air, so it reduces the oil’s aging effect. The gap available the outside of the cell within the tank can be filled completely with the air
Air vents are present on the summit of the tank for emitting accumulated air at the outside of the air cell. The force inside the air cell should be maintained at 1.0 PSI.

Diaphragm Sealed Conservator

This kind of sealed conservator works like a barrier between the air in the atmosphere as well as the transformer. In this case, the transformer’s conservator tank can be designed with two hemispherical halves. The arrangement of the diaphragm within the tank can be done between the two bolts & halves.

Once the transformer oil increases then it pushes above the diaphragm. So the diaphragm arrangement indicates the oil level. Whenever the level of oil reduces within conservator, then diaphragm will deflect & the atmospheric air can fill the empty place. This air can be sucked throughout the silica gel breather. This can be connected to the center of the conservator tank in the transformer.

This kind of conservator tank has one benefit compare with the air cell type conservator. If gas is forced to a high level, then it gets dissolves within the transformer oil. In a specific period of time, the quantity of gas in the transformer oil achieves the saturation point.

At this period, the transformer load will drop suddenly otherwise the ambient temperature drops, transformer oil supersaturated & the bubbles from the gas will be evolved. If the pump is attached to the cooling circuit, then it helps in generating gas bubbles to cause the failure of insulation in the area of strong fields.

Thus, this is all about an overview of the conservator tank and the arrangement of this tank can be done over the main tank of a transformer. The main function of this tank is to provide an extra place for heated oil because it enlarges through a rise in temperature. Consequently, oxidation cannot occur within the main tank as well as there is no mud formation in the transformer oil tank. Here is a question for you, what are the advantages of Conservator Tank of Transformer?