How to check current transformer

FAQ | Feb 20,2023

1, polarity damage inspection basis:
The primary winding marks of the current transformer are P1 and P2, and the secondary winding marks are S1 and S2. If P1 and S1 are the same end, then this sign is called reduced polarity. The primary current comes in from P1 and the secondary current comes out from S1. Polarity check is simple. In addition to checking on the transformer calibrator, you can also use the DC check method.
2, whether the demagnetizing inspection basis:
When the current of the CT drops suddenly, the core of the CT may generate residual magnetism. For example, the current transformer suddenly cuts off the power supply and the secondary winding suddenly opens. There is residual magnetism in the core of the transformer, which reduces the permeability of the core and affects the performance of the transformer. The transformer should be demagnetized after long-term use. The transformer should also be demagnetized before testing.
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.
3. Check the accuracy of current transformer measurement:
The error test of the transformer is generally compared between the transformer under test and the standard transformer. The secondary current difference between the two transformers is the error of the transformer under test. This test method is called comparative method.
The standard transformer is required to be two levels higher than the transformer under test, so the error of the standard transformer can be ignored. If the standard transformer is only one grade higher than the transformer under test, the error of the test result should be considered plus the error of the standard transformer.

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