The current transformer plays a role in current transformation and electrical isolation. For the convenience of secondary instrument measurement, it is necessary to convert it into a relatively uniform current to avoid the danger of directly measuring the current transformer circuit. The detection methods for current transformers are as follows:

1. Appearance inspection of current transformers

Before current transformer detection, it is necessary to check whether the external insulation of the transformer is damaged, whether the primary and secondary markings are clear and complete, whether each terminal is damaged or missing, whether the wiring method is clear, and whether there are other serious defects in the loose internal structural components. If there is no problem with the appearance, record the nameplate information of the transformer: model, manufacturer, grade, transformation ratio, secondary load, etc

2. Insulation Resistance Test

Use a 2500V insulation resistance meter to measure the insulation resistance values between each winding and between the winding and ground.

3. Power frequency voltage test

The insulation resistance of the current transformer should meet the requirement that "under normal use conditions, the insulation resistance of the low transformer primary winding to the secondary winding and ground terminal should not be less than 40M @". The insulation resistance between the primary winding of the high-voltage transformer and the secondary winding and the grounding terminal should be specified in the product technical conditions. The insulation resistance between the secondary winding of the low-voltage transformer and the grounding terminal of the high-voltage transformer shall not be less than 20M @ The power frequency induced withstand voltage of current transformers should meet the following requirements. The power frequency test voltage between the secondary winding of the low-voltage current transformer and the grounding terminal of the high-voltage current transformer should meet the following requirements (1) The frequency of the test power supply should be between 45-62Hz, and the voltage waveform distortion factor should not exceed 5%. The current when the high-voltage output terminal of the test transformer is short circuited should not be less than 0.5A When applying power frequency test voltage to the transformer, the voltage should be gradually increased to the specified value and maintained for 1 minute. Sudden connection and disconnection of the test power supply should be avoided during the test. The recommended method for measuring the test voltage is to directly measure it at the high-voltage output terminal of the test transformer During the test process, there should be no destructive discharge phenomena such as breakdown or flashover. The power frequency withstand voltage test method between the primary winding of the high-voltage transformer and the secondary winding and the grounding terminal should be carried out in accordance with the method specified in GB811.2-GB811.6. Winding turn to turn insulation strength test: ① The secondary winding should be open circuit, and one end of it should be grounded together with the shell. Apply the rated primary current at the rated frequency to the primary winding and continue for 1 minute. If the voltage at the secondary winding end exceeds 3 5kV (peak), then the primary current value should be reduced to make the secondary winding terminal voltage equal to 3.5kV (peak) Open the primary winding and ground one end together with the casing. Apply the rated secondary current at the rated frequency to the secondary winding for 1 minute. If the secondary winding terminal voltage exceeds 3.5kV (peak) under this secondary current. Then the secondary current value should be reduced so that the voltage at the secondary winding end is equal to 3.5kV (peak)