Transformer oils are poured into measuring and power transformers, oil switches and reactor equipment. In the reactor equipment, they serve as a medium for damping the arc.
The electrical insulating qualities that transformer oils possess depend on the dielectric losses. Dielectric strength of oils for transformers can greatly 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 figure should be -45 ° C or lower in the working fluid. For the heat to be removed with maximum efficiency, the liquid should have a minimum viscosity at a flash point, which for different brands should not be less than 150-95 ° C.
The most important parameter that transformer oils possess is the resistance to oxidation, or the property of maintaining a constant performance when working for a long time. Most of the used grades of transformer oils are stabilized by such additives against oxidation as ionol or agidol-1. Their action is based on the ability to react with the active peroxide radicals formed during the chain reaction of oxidation of hydrocarbons. Ionol-stabilized liquids for the transformer are most often oxidized with a pronounced induction period.
In the initial stage, oils that retain susceptibility to additives are oxidized very slowly, since all the oxidation sites appearing in the oil are inhibited by the inhibitor. When the additive is depleted, the oxidation rate approaches that with which the original oil is oxidized. The additive is the more effective the longer the induction oxidation cycle. The effect of the additive effect is determined by the hydrocarbon composition of the transformer oil and by the impurities of other non-hydrocarbon compounds that enhance the oxidation of the oil (nitrogenous bases, naphthenic acids, oxygen-containing oxidation products).
Transformer oils are designed to isolate parts and components of power transformers that are under stress, remove heat from parts that are heated during operation, and protect the insulation from moisture.
Transformer oil, the characteristics of which are completely determined by its content, in turn, depends to a large extent on the chemical composition of the feedstock and the cleaning methods used. In the brands of transformer oils used there are differences in chemical composition and performance characteristics, and they are designed for various purposes. For new oil transformers only completely fresh oils are required, which were not previously in use. Each batch of liquid used for pouring must have a manufacturer's certificate. Before filling transformer oil from the oil refinery into the power transformer, it is necessary to clean it of moisture, gases and mechanical impurities.
Moisture can be contained in transformer oil in various forms. It can be a precipitate, an emulsion and a solution. Transformer oil before refilling is completely cleaned of 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 electrical strength, although it contributes to an increase in the oxidability of the liquid for transformers and to a deterioration in the stability of its composition. In this connection, obtaining the values of the breakdown voltage and the loss tangent satisfying the norms can not serve as a criterion for complete purification.
An important parameter is the density of the transformer oil. You need to know it to calculate the mass of the product that came to the enterprise. The density of transformer oil allows us to know its hydrocarbon composition.
At a pressure equal to atmospheric pressure, up to 10% of the air in the dissolved state in the transformer oil may be present. If the power transformers are equipped with film and nitrogen protection, then before filling, the special oil must be degassed to achieve a residual gas content not exceeding 0.1% of the mass.
After the cleaning is done, there should not be any mechanical impurities in the oil.
Measurement of oil parameters
The parameters of the oils are checked by analyzing their electrical insulating and physicochemical characteristics:
- electric strength;
- loss tangent;
- measurement of moisture content;
- measurement of the gas content in the oil by means of an absorptiometer consists in determining the degree of change in the residual pressure in a certain container after it has been filled with samples of the test fluid;
- measurement of the quantitative composition of mechanical impurities by passing a sample dissolved in gasoline through a paper filter without ash.
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 the oxygen hydride.
Transformer oil tests
Before transformers are commissioned, a transformer oil test is performed.
For transformer equipment, all nominal voltages, oil tests from the on-load tap-changer tank are performed in full accordance with the manufacturer's management. Oil for equipment having a capacity of up to 630 kVA, which is installed in electrical networks, is permitted not to be subjected to testing.
Transformer oil is checked by customers in a certified laboratory that is certified for the right to test it.
This method of processing transformer oil consists in removing moisture and suspended particles under the influence of centrifugal forces. Thus only moisture is removed, which is in the form of an emulsion, and the particles are in a solid state. The specific mass of the particles during centrifugation should be greater than that of the transformer oil to be treated. This method purifies primarily the liquid for power transformers having a voltage of up to 35 kV, or pre-process it.
The method consists in passing oil through porous-type partitions that retard all impurities contained in it.
The method of cleaning transformer oil by means of adsorption is based on the absorption of water and other impurities by various adsorbents. In their quality, synthetic zeolites having a high absorption capacity are used, especially with respect to water particles. Cleaning of transformer oil with zeolites makes it possible to remove moisture from the composition, which is in the state of solution.
The basic element of the purification method was the degasser. Crude oil is first heated to a temperature of 50-60 ° C. After this, the oil is sprayed into the degasser at its first stage. Further it flows in a very thin stream along the surface of Raschig rings. The first stage is then evacuated by means of a vacuum pump. The separated water and gas vapors are pumped out through the air filter and the zeolite cartridge. From the capacity of the degasser of the first stage, the oil flows into the second stage by gravity, where it is finally dried and degassed. At the final stage, the transformer oil passes through a fine filter, fed into the transformer.
The spent transformer oil is regenerated at serial oil-regeneration plants using silica gel.
GK Transformer Oil
The specified marking technical fluid was obtained on the basis of the method of its production. Transformer oil GK is produced by hydrocracking technology. The raw material for its production is paraffinic sulfuric oil. This type of oil has high insulating properties and is recommended for use in a variety of high-voltage equipment. Transformer oil GK contains an additive ionol and possesses the best antioxidant properties.