Filling of oil into power transformers is an important operation; the reliability of electrical equipment largely depends on it. This filling is usually performed using oil processing units.
Oil filling depends on the transformer voltage class. If the voltage is below 11 kV, oil can be filled without vacuum, with the temperature of the dielectric liquid above 10ºC. An oil purifier is connected to the transformer tank, and the oil is supplied at the rate of 1.5 – 3 tons per hour. The process continues until oil appears in stopper orifices. If the transformer is equipped with an expansion tank, the end of filling is signaled by the oil reaching the marks in the oil indicator. After that, the dielectric liquid is allowed to settle for 12 hours. The process is completed by opening stoppers to let out the air from under them.
If the transformer is designed for 150 – 500 kV and has not air tight protection, the oil is filled at 40-50ºС. Residual pressure in the transformer tank must not exceed 665 Pa. The oil is supplied into the transformer tank at 1.5-3 tons per hour after vacuumizing, but the vacuum pump is kept running. This is required to maintain the residual pressure.
Another important factor is the level of oil inside the transformer in operation. This can be measured using temporary oil indicators (transparent tubes), or by two vacuum meters. The latter method is more advanced.
Adding transformer oil to the level of the control marks may be performed by GlobeCore’s UVD units. This product can perform degassing, storage, transportation and filling of transformer oil into the transformer. The UVD unit is mobile, allowing to service electrical equipment rapidly.