基于外部直流激励的电力变压器剩磁评估与试验验证

Remanence, which is inevitably generated in the transformer core after a DC resistance measurement, a transformation ratio measurement, or a maintenance test, makes the core saturated, causing the excitation inrush current and the mis-operation of the differential protection, which seriously affects the reliable operation of the transformer. Based on the mechanism of remanence generation, this paper proposes an external DC excitation method for the transformer remanence assessment. Firstly, a 3kV single-phase four-column transformer model remanence test platform was built in the laboratory. The remanence simulation and evaluation tests under the constant and unequal amplitude currents were carried out. The results show that in the equal-amplitute current method there is a higher accuracy, the maximum relative error of which is less than 4.5%. The average relative error of the saturation section is 4.13%, and those of the linear section and the knee section have similar values of less than 1.5%. While in the unequal amplitude current method, the average relative error of the linear segment, the knee segment and the saturation segment is 5.27%. Then, the remanence simulation, evaluation and no-load closing test verification on the 500kV single-phase transformer were carried out in a larger-capacity laboratory. The magnetizing inrush current reached 1276A during a random closing. By using the phase-selective closing strategy based on the residual magnetization evaluation value, the ratio of the peak value of the magnetizing inrush current to the rated current is reduced to less than 2%, which verifies the effectiveness of the method. The research results in this paper provide a useful reference for the on-site remanence assessment of the transformers and the suppression of inrush current during closing.