Principles of using current transformers

- Mar 20, 2021-

1) The wiring of the current transformer should follow the series principle: that is, the primary winding should be connected in series with the circuit under test, and the secondary winding should be connected in series with all instrument loads and current transformers.

2) According to the measured current, select the appropriate transformation ratio, otherwise the error will increase. At the same time, one end of the secondary side must be grounded to prevent the primary side high voltage from entering the secondary low voltage side once the insulation is damaged, causing personal and equipment accidents.

3) No open circuit on the secondary side is allowed. Once open, the primary current I1 will all become the magnetizing current, causing a sudden increase in φm and E2, causing the iron core to be oversaturated and magnetized, causing serious heating and even burning.

4) In order to meet the needs of measuring instruments, relay protection, circuit breaker failure judgment and fault filtering, etc., the generator, transformer, outgoing line, bus section circuit breaker, bus circuit breaker, bypass circuit breaker and other circuits are all set 2 to 8 secondary winding current transformers.

5) The installation location of the current transformer for protection should be set as far as possible to eliminate the unprotected area of the main protection device.

6) In order to prevent the bushing flashover of the pillar current transformer from causing a bus failure, the current transformer is usually arranged on the outgoing line or transformer side of the circuit breaker.

7) In order to reduce the damage caused by the internal fault of the generator, the current transformer used for the automatic adjustment of the excitation device should be arranged on the outlet side of the generator stator winding.