Solutions to the Current transformer core remanence problem.Transformer is the general term for current transformer and voltage transformer. It is used to convert high voltage and large current into low voltage and small current. It is used for measuring or protecting system.
In the case of a sudden drop in Current transformer core, the transformer core may generate remanence.Such as current transformer in the case of large current suddenly cut off the power supply, the secondary winding suddenly open circuit.There is residual magnetism in the iron core of the transformer, which reduces the magnetic permeability of the iron core and affects the performance of the transformer.All long-term transformers shall be demagnetized.Current transformer core must also demagnetize before checking.Demagnetization is the alternating excitation current through the primary or secondary windings to give the core an alternating magnetic field.Starting from 0, gradually increase the alternating magnetic field (excitation current) to make the core reach the saturation state, and then slowly reduce the excitation current to zero to eliminate the residual magnetism.
For the demagnetization of Current transformer core, the primary windings shall be opened and the secondary windings shall be connected with the power frequency Current, which shall be gradually increased from zero to a certain Current value (the Current value is related to the upper limit of the design measurement of the transformer and is generally about 20-50% of the rated Current).It can be judged that if the current suddenly and sharply increases, the iron core will enter the magnetic saturation stage.Then slowly reduce the current to zero and repeat 2-3 times.
Before disconnecting the power supply, the primary winding shall be short-connected before disconnecting the power supply, and the core demagnetization shall be completed.This method is called open circuit demagnetization.For some current transformers, the number of turns in the secondary winding is relatively large.If open circuit demagnetization method is used, open circuit winding may produce high voltage.Therefore, a larger resistance can be connected to the secondary winding.
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