Causes of residual current transformer short circuit burnout

- Jun 29, 2020-

Working principle of current transformer: the primary winding is connected in series in the circuit under test with very few turns; the secondary winding is connected to low-impedance loads such as ammeter and relay current coil, which is similar to short circuit. The primary current and secondary current depend on the load of the line under test, and are independent of the current transformer secondary load. When the current transformer is running, the secondary side cannot be open. Because the primary current becomes the excitation current, the magnetic flux and the secondary voltage will greatly exceed the normal value and endanger personal and equipment safety. Therefore, it is not allowed to connect the fuse in the secondary loop of the current transformer, and it is not allowed to disassemble the ammeter and relay without any bypass during operation.

Residual current transformers are inevitably burned out during use, and the main causes of burnout are also caused by the following points:

1. The residual current transformer is opened for a second time, which generates a high voltage and burns the residual current transformer.

2. The service life of the residual current transformer is too long. The insulation is aging, and breakdown or discharge occurs locally, resulting in overvoltage.

3. The contact surface of the residual current transformer once connected to the aluminum row is too oxidized, the contact resistance is too large, and the current transformer is burnt out due to heat.

4. The user is overloaded at certain times.