Transformer oils: characteristics, properties, features of the application


transformer oilsThe insulating qualities that transformer oils possess depend on dielectric loss. Dielectric strength of oils for transformers can significantly reduce water and a variety of fibers. Consequently, these substances in its composition should not be. An important parameter is the pour point. To maintain mobility in the cold, this indicator for the working fluid should be - 45 ° C and below. In order for heat to be removed with maximum efficiency, the liquid must have a minimum viscosity at flash point, which for various grades should not be less than 150-95 ° C.

The most important parameter that transformer oils possess is oxidation resistance, or the ability to maintain consistency of performance when operating for a long time.Most of the used varieties of transformer oils are stabilized by anti-oxidation additives such as ionol or agidol-1. Their action is based on the ability to react with active peroxide radicals formed during the passage of a chain reaction of oxidation of hydrocarbons. Ionol-stabilized liquids for a transformer are most often oxidized with a pronounced induction period.

transformer oilIn the initial stage, oils that retain susceptibility to additives are oxidized very slowly, since all the oxidation sites that appear in the oil are suppressed by the inhibitor. When the additive is depleted, the oxidation rate approaches that with which the original oil is oxidized. The addition is the more effective the longer the induction oxidation cycle. The effect of the additive is determined by the hydrocarbon composition of transformer oil and impurities of other compounds of non-hydrocarbon origin, which increase oil oxidation (these are nitrogenous bases, naphthenic acids, oxygen-containing oxidation products).

Transformer oils are designed to isolate parts and assemblies of power transformers,which are under stress, remove heat from parts exposed to heat during their operation, and protect the insulation from moisture.


transformer oil densityTransformer oil, the characteristics of which are completely determined by its content, in turn, largely depends on the chemical composition of the feedstock and the purification methods used. In the used brands of transformer oils there are differences in the chemical composition and performance characteristics, and they are intended for various purposes. For new oil transformers, only completely fresh oils are required that have not been in operation before. Each batch of liquid that is used for filling must have a certificate of the manufacturer. Before pouring transformer oil coming from the refinery into the power transformer, it is necessary to clean it from moisture, gases and mechanical impurities.

Moisture can be contained in transformer oil in various forms. It may be sediment, emulsion and solution. Transformer oil before pouring is completely cleaned from moisture contained in the oil in the emulsion state and in the form of sludge.As a solution, moisture does not significantly affect the loss tangent and dielectric strength, although it contributes to an increase in the oxidizability of a liquid for transformers and a deterioration in the stability of its composition. In this regard, obtaining the values ​​of the breakdown voltage and the loss tangent that satisfy the norms cannot serve as a criterion for complete cleaning.

transformer oil testAn important parameter is the density of transformer oil. It is necessary to know it in order to calculate the mass of the product received by the enterprise. The density of transformer oil allows you to find out its hydrocarbon composition.

When the pressure value is equal to atmospheric, in a dissolved state in the oil of the transformer can be up to 10% of air. If the power transformers are equipped with film and nitrogen protection, before pouring the special oil must undergo degassing in order to achieve a residual gas content not exceeding 0.1% of the mass.

After cleaning is done, there should be no mechanical impurities in the oil.

Oil measurement

used transformer oilChecking the parameters of oils is carried out by analyzing their electrical insulation and physico-chemical characteristics:

  • electrical strength;
  • loss tangent;
  • moisture content measurement;
  • measuring the gas content in the oil by means of an absorptiometer consists in determining the degree of change in the residual pressure in a tank after the samples of the test liquid are filled in;
  • measurement of the quantitative composition of mechanical impurities by passing a sample dissolved in gasoline through an ash-free filter paper.

The method for determining the moisture content of the oil is based on the fact that hydrogen evolution occurs during the reaction of moisture in the oil with oxygen hydride.

Tests of transformer oil

transformer oil characteristicsBefore commissioning transformers, a test of transformer oil is performed.

For transformer equipment, all rated voltages of the oil test from the RPN tank are made in full accordance with the management of the manufacturing company. Oil for equipment having a capacity of up to 630 kVA, which is installed in electrical networks, is allowed not to be tested.

Transformer oil is tested by customers in a certified laboratory that is certified to test it.


transformer oil cleaningThis method of processing transformer oil is to remove moisture and suspended particles under the influence of centrifugal forces. This only removes moisture, which is in the form of an emulsion, and particles in the solid state. The specific gravity of the particles during centrifugation must be greater than that of the transformer oil being treated. In this way, liquid is preferably purified for power transformers having a voltage of up to 35 kV, or it is pretreated.


The method consists in passing oil through partitions of the porous type, which detain all impurities contained in it.

Adsorption treatment

The method of purification of transformer oil by adsorption is based on the absorption of water and other impurities by various adsorbents. Synthetic zeolites having a high absorption capacity, especially in relation to water particles, are used in their quality. Purification of transformer oil with zeolites makes it possible to remove moisture in the solution state from its composition.

Vacuum processing

The basic element of the cleaning method has become a degasser.The crude oil is first heated to a temperature of 50-60 ° C. After that, the oil is sprayed in the degasser at its first stage. Further, it flows in the thinnest trickle along the surface of the Raschig rings. In this case, the first stage is subjected to vacuuming by means of a vacuum pump. Allocated water and gas vapors are pumped out through an air filter and a zeolite cartridge. From the tank of the first stage degasser, the oil passes by gravity to the second stage, where it is finally dried and degassed. At the final stage, the transformer oil passes through the fine filter, being fed into the transformer.

Waste oil

Used transformer oil is regenerated on serial oil recovery units using silica gel.

Transformer oil GK

The specified marking technical fluid received on the basis of the method of its production. Transformer oil GC receive technology hydrocracking. The raw material for its manufacture are paraffin sulfur oils. This type of oil has high insulating properties and is recommended for use in various high-voltage equipment. GK transformer oil contains an ionol additive and has the best antioxidant properties.

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