How to demagnetize a current transformer

FAQ | Feb 22,2023

Demagnetization is through primary or secondary winding with alternating excitation current, to the core with alternating magnetic field. Gradually increase the alternating magnetic field (excitation current) from 0 to saturate the core, and then slowly reduce the excitation current to zero to eliminate remanence.
According to the electrical theory, the use of power transformer degaussing instrument from positive and negative through DC current, and gradually reduce, reduce the hysteresis loop of the core, to eliminate the purpose of remanence. Direct current, such as 5A, is fed into the high-voltage winding of the current transformer under test (it is sufficient for the three-phase current transformer to degausse only B-0 or A-C), whose degaussing current is no less than the test current of the high-voltage winding. Dc demagnetization ends when the current value is reduced by 5%-10% each time until the current is 0.5mA.
Or apply 50Hz ac voltage (such as generator) respectively to the low-voltage side of the current transformer (between ac,ab and bc), and ground the high-voltage neutral point. Depending on the capacity of the power supply, adjust the compensating capacitor C to reduce the current of the power supply. The test changed the low-voltage side to reflect the Va reading of the average voltmeter, and gradually increased the voltage to 50% of the rated voltage, and stayed for about 5 min. The voltage slowly dropped to “zero” and then slowly increased the voltage to 100% of the rated voltage until complete demagnetization.


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