Demagnetization method of current transformer

After the polarity of the current transformer is checked by the DC method, or when the power supply is cut off under the AC current and the secondary winding is accidentally opened, the iron core may generate residual magnetism, which will affect the error characteristics of the transformer. Therefore, before the error test, the current Each iron core of the transformer is demagnetized, and the demagnetization of the iron core can adopt any method in the open circuit demagnetization method and the closed circuit demagnetization method.
1. Open circuit demagnetization method
When the secondary (or primary) winding of the current transformer is open-circuited, pass power frequency current to the primary winding (or primary winding) of the demagnetized core to increase the current from zero to 10% of the rated current, and then uniformly and slowly current drops to zero. Repeat this process 2 to 3 times, and the applied current decreases gradually to make the current transformer magnetized. If at 10% rated current, the peak voltage induced at both ends of the open-circuit winding exceeds 75% of the specified value during the inter-turn insulation test, demagnetization should be performed at a smaller current value. Generally, it is advisable to pass current through the primary winding of the current transformer. For current transformers with multiple secondary windings, the non-demagnetizing secondary windings should be opened.
2. Closed circuit demagnetization method
Connect a resistance equivalent to 10 to 20 times the rated load on the secondary winding, pass a power frequency current through the primary winding, the current increases from zero to 1.2 times the rated current, and then decreases to zero evenly and slowly to demagnetize the current transformer . When demagnetizing a current transformer with multiple secondary windings, when one of the secondary windings is connected to a large load, the remaining secondary windings should be open.