Transformer oil insulates energized parts and components of power transformers, acts as a coolant and protects solid insulation from moisture. Beside transformers, oil is used in switches, high voltage capacitors and power cables. In switches oil acts as an arc extinguisher.

In the process of transformer operation, the oil accumulates various contaminants, which adversely affect the oil’s functions. To restore them, the oil must be purified from foreign substances (water, gases and solid particles). Let’s look into the methods of transformer oil purification methods depending on the substance to be removed from the oil.

Centrifugal purification is a method for water removal. It comes down to separation of materials under centrifugal force. The main advantage of this method is the relatively high rate of water removal. However, there are several drawbacks: low degree of purification, complexity and the necessity for constant presence of controlling personnel.

Anothe method for water removal is adsorption purification. The biggest advantage of this method is its simplicity. The drawbacks are the dependency of purification rate on the sorbent used, the need to dispose of sorbent with potential environmental risks, high quality requirement to input oil and low processing capacity.

The difference of water and oil boiling temperatures is the essence of thermovacuum drying. The oil to be purified goes into a special chamber with low pressure. In such conditions water evaporates at room temperatures. The method allows for high efficiency of purification, it is rather reliable and requires no complex adjustments. The main drawback is the relatively low rate of water removal.

The above methods may also be used for removal of gases, solids and acids from transformer oil. E.g. thermovacuum purification is also good at degassing. Centrifugal purification can also remove solid particles. Single and multiple use filters with high degree of purification are also used for the same purpose. Such filters must be replaced from time to time. Acidity of the oil is decreased by adsorption.