Oil treatment and transformer repair

The insulating oil contained in the electrical equipment in use is subject to a phenomenon of degradation caused mainly by the normal conditions of use. This degradation gradually reduces the dielectric (insulating) properties of the liquid by increasing the probability of damage.

The physical treatment of the oil, much more advantageous than its replacement, eliminates the contaminating substances, present in the insulating liquid, in the image:

Some water
Solid particles
Gases .

The oil treatment operation reduces these substances to the range indicated by industry standards and guidelines (IEC, CENELEC, CIGRE, etc.).

Our brand Micafluid type VOP90 9000l / h machine, sucks the transformer oil, decontaminate and reinject it into the transformer. This operation is done in closed cycle and can last hours and sometimes several days. Whenever the oil circulates in our treatment plant, it is:


This process ends when the indicators displayed "on-line" on the screen of the machine reach acceptable values.

Replacing the oil

When the state of degradation of the oil is very advanced or the treatment is not economically suitable, it is recommended to replace the oil. This operation takes place in several phases and presents many problems: logistic, functional, environmental etc ...

This is why it is better to entrust this task to a competent professional.

First of all, you have to be very careful about the transformer emptying activity which involves emptying the tank, while scrupulously respecting the operational protocols of the machine manufacturer or the customer.
2. Treatment and filling

The treatment is done in two stages. First, fill the flexible tank (Tarpaulin) from the oil futs. A breakdown voltage test is made on a sample of new oil from the tank. The oil is treated in the tank, at the end of which another breakdown voltage test is performed on a treated oil sample.

In the case of large transformers, it is necessary to make a vacuum operation in the transformer, before filling to dehumidify as much as possible the internal parts of the transformer and the oil.

After these preliminary operations, the filling of the transformer is carried out (under vacuum) and is followed immediately afterwards with the treatment operation as mentioned above. A breakdown voltage test of the transformer oil is performed before and after oil treatment.

The main phases are as follows:

Transport, installation and connection of treatment equipment
Initial analytical checks
Emptying the transformer
Transformer filling
Treatment of new oil
Verification of levels
Replacement of desiccant
Analytical checks at the end of the intervention
Disposal and transport of treatment units and tanks


This operation applies to equipment filled with insulating oils, with a high moisture content, especially in the magnetic circuit and the paper that coats the winding coils.

For this purpose a dew point measurement in the transformer is required.

Drying is a physical process that removes or reduces the moisture content present mainly in the insulating cellulosic paper, and the transformer magnetic circuit. Thanks to continuous high-temperature circulation of oil in a closed circuit, we obtain:

the gradual extraction of water,
dehumidification of solid insulation (kraft paper),
degassing and vacuum filtration of the oil.


The repair restores the transformer to its original state.

The most frequent repairs are:

Joint replacement
Replacement of terminals
Replacement of different accessories
Rehabilitation of transformers