Research on key techniques for improving reliability of in-situ detection of no-load and load loss of oil-immersed transformer under low temperature environment

Oil-immersed transformers in cold areas such as northeast and northwest of China face a special problem of low temperature in actual operation. In recent years, the lowest temperature in Heilongjiang has reached about -52°C. No-load loss is the active power consumed when the secondary winding of the transformer opens the circuit and the primary winding applies the rated voltage with sinusoidal waveform of rated frequency. No-load loss means constant loss. It is independent of the current passing through, but is related to the voltage to which the component is subjected. There are many factors affecting the no-load performance of transformer, such as the material properties of silicon steel sheet, processing technology and equipment, the structure of iron core, etc. The magnetic parameters of silicon steel sheet are related to temperature; For a double-winding transformer, the short-circuit loss is the active power absorbed by the transformer when the rated current passes through one winding of the transformer, and the other winding is shorted. For a multi-winding transformer, the short-circuit loss is based on the specified pair of windings. Short circuit loss, also known as the copper loss of the transformer, also known as the load loss, is caused by the load current passing through the winding. Since the coil resistance is related to temperature, the load loss standard is defined based on different operating temperatures. In the transformer load loss, the winding resistance loss is proportional to the temperature, because the resistivity of copper will rise with the rise of temperature. The higher the resistivity, the higher the DC resistance loss, and the additional loss is inversely proportional to the temperature. This is because the resistivity of copper rises with the rise of temperature, the additional loss is caused by the eddy current in the conductor. The greater the resistance value in the conductor is, the smaller the eddy current is, so the additional loss is naturally smaller. The regulations require that the transformer empty load loss test should be carried out at an ambient temperature of 5°~40°. At present, the research on no-load loss and load loss of 66kV oil-immersed transformer under low temperature environment is still in the blank stage. The no-load loss and load loss of 66kV oil-immersed transformer at low temperature are studied in this paper. It can solve the problem that the field measurement results of 66kV oil-immersed transformer in low temperature environment do not match the current standard regulations, and the research field of empty load loss is blank.