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Electromagnetic wave hazards and degaussing methods of power transformers

Due to the inherent hysteresis phenomenon of ferromagnetic materials, residual magnetism will remain in the iron core after operations such as voltage ratio and DC resistance measurements. Due to residual magnetism, when the transformer is put into operation, the residual magnetism of the iron core will saturate the transformer core for half a cycle, generating lots of harmonics in the excitation current. This increases the transformer's reactive power consumption and may also cause the relay protector to malfunction. , causing certain economic losses.

Therefore, we must perform degaussing work before the transformer is put into operation to ensure safe and normal operation.

Degaussing methods include

1. DC method: According to electrical theory, the XHXC105 degaussing instrument passes DC in both forward and reverse directions, gradually decreasing it to reduce the core's hysteresis loop and eliminate residual magnetism. Direct current, for example, 5A, is passed through the high-voltage winding of the transformer under test (for a three-phase transformer, it is enough to demagnetize only B-0 or A-C). The degaussing current is not less than the test current of the high-voltage winding. Each time the current value decreases by 5%~10% until the current reaches 0.5mA, and DC demagnetization is completed.

2. AC method: Apply 50Hz AC voltage (such as a generator) to the low-voltage side of the transformer under test (between AC, AB, and BC), and the high-voltage neutral point is grounded. Adjust the compensation capacitor C to reduce the power supply current depending on the power supply capacity. The subject changes to the low-voltage side based on the reading of the average voltmeter Va. Gradually increase the voltage to 50% of the rated voltage and stay for about 5 minutes to slowly reduce the voltage to "0" and slowly increase the voltage to 100% rated voltage until complete demagnetization.


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