Due to the inherent hysteresis of the ferromagnetic material, residual magnetism remains in the core after the voltage ratio and DC resistance measurement of the power transformer. Due to the existence of residual magnetism, when the transformer is put into operation, the core remanence makes the transformer core half-cycle saturated, and a large amount of harmonics are generated in the excitation current, which not only increases the reactive power consumption of the transformer, but also may cause the relay protector to malfunction. , causing certain economic losses. Therefore, we must do degaussing before the transformer is put into operation to ensure the safe and normal operation of the transformer.
Degaussing method
1 DC method: According to the electrician theory, the XHXC105 degaussing device is to input DC current in the forward and reverse directions, and gradually reduce and reduce the hysteresis loop of the core to achieve the purpose of eliminating residual magnetism. In the high voltage winding of the transformer under test (three-phase transformer is only sufficient for B-0 or AC degaussing), a direct current, for example 5A, is applied, and the degaussing current is not less than the test current of the high voltage winding. Each time the current value is reduced by 5% to 10% until the current is 0.5 mA, the DC demagnetization ends.
2 AC method: Apply 50Hz AC voltage (such as generator) to the low voltage side (ac, ab and bc) of the transformer under test, and ground the high voltage neutral point. Depending on the power supply capacity, adjust the compensation capacitor C to reduce the power supply current. The tester changes the low-voltage side to reflect the reading of the average voltmeter Va, gradually increases the voltage to 50% of the rated voltage, and stays for about 5 minutes, slowly lowering the voltage. Go to “Zero†and slowly increase the voltage to 100% of the rated voltage until it is completely demagnetized.
Method of judging complete demagnetization
1 During the voltage rise and fall, the value of the excitation current at the same voltage is the same;
2 The waveform of the excitation current is symmetrical up and down, and there is no even harmonic component.
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