Simplified, regeneration is the process of restoring used, aged and contaminated oil. The process let oil pass through a special bleaching earth filter, where the filter removes contaminants by adsorption. Bleaching earth is the mixture of naturally occurring minerals. In the old days it has been expensive and cumbersome because bleaching earth could only be used once. With modern technology, the bleaching earth is reactivated and used over and over again with the same effect.


The regeneration plant is fully automated consists of bleaching earth columns, degassing, command and control for the operator. Normally the oil is pumped from the bottom valve, passed bleaching earth columns and a vacuum chamber for degassing, various filter, mechanical treatment and returned in the expansion tank. When the efficiency of the bleaching earth begins to sink, the reactivation of bleaching earth is started. Through a controlled combustion at about 600 degrees C the bleaching earth is reactivated and ready for a new cleaning cycle. The exhaust gases from the combustion is refined by a catalyst. The oil should normally pass through bleaching earth columns 8-12 times. Inhibitor is added after regeneration for protection against oxidation.

Power supply

The regenereration plant requires normally 63 A, 400 V.

Operating conditions, interruptions

For most transformers hoses can be connected without interruption is required. Best results are achieved with the transformer in service when you can take advantage of the transformer heat loss and get more moisture out of the insulation. The temperature is kept between 60-70 degrees C.

Security leakage system

The plant is fully automated and equipped with safety devices that immediately close the pneumatic valves on the units and the transformer when fault occurs. An alarm system sends an SMS message to the mobile phone operator in case of any problems. All normal protection such as transformer guards are in full operation during the cleaning process.

Operator and staffing

The plant is normally handled by one person, usually staffed during daytime when regeneration is underway.

So, what do the regeneration procedure actually do?

The exhaust system which functions as a normal high vacuum filter remove gases, water and particles. Bleaching earth resolves acid value, Tan-Delta, interfacial tension and color. Bleaching earth does not affect viscosity, flash point, pour point ie it does not alter the oil characteristics from the origin.


Takes place after the customers wishes, but always after completion of regeneration in order to get a confirmation that a satisfactory result is achieved.


The operators who carry out the regeneration has been training in ESA and are familiar with the work of the high-voltage installations.


PCB-contaminated oil will not be treated due to contagion to other customers sites.

Advantages of regeneration versus oil change:

- No operation interuption.
- Use of existing resources.
- Cheaper.
- Cleaning of the transformer's internal parts
- No costs for disposal of oil.
- No environmental impact by the transportation of new oil.