The correct use of Power Current Transformer

1. The wiring of the Power Current Transformer should follow the series principle: 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

2. According to the measured current, select the appropriate change, 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 the circuit is opened, the primary side current I1 will all become magnetizing current, causing a sudden increase in φm and E2, causing the core to be over-saturated and magnetized, causing serious heating and even burning the coil; at the same time, after the magnetic circuit is over-saturated and magnetized , Make the error increase. During normal operation of the Power Current Transformer, the secondary side is similar to a short circuit. If it is suddenly opened, the excitation electromotive force will suddenly change from a small value to a large value, and the magnetic flux in the iron core will show a severely saturated flat top. Therefore, the secondary winding will induce a very high peak wave when the magnetic passes through zero, and its value can reach thousands or even tens of thousands of volts, which endangers the safety of workers and the insulation performance of the instrument.

In addition, an open circuit on the primary side causes the secondary side voltage to reach several hundred volts, which will cause an electric shock if touched. Therefore, the secondary side of the Power Current Transformer is equipped with a short-circuit switch to prevent the primary side from opening. During use, once the secondary side is open, the circuit load should be removed immediately, and then stop for processing. It can be reused after everything is handled.

4. In order to meet the needs of measuring instruments, relay protection, circuit breaker failure judgment and fault filtering, etc., the generators, transformers, outlets, bus section circuit breakers, bus circuit breakers, bypass circuit breakers and other circuits are all set 2～8 Power Current Transformers with secondary winding. For large-current grounding systems, generally three-phase configuration; for low-current grounding systems, two-phase or three-phase configuration according to specific requirements

5. The installation location of the Power Current Transformer for protection should be set up as far as possible to eliminate the unprotected area of the main protection device. For example: if there are two sets of Power Current Transformer, and the location permits, they should be installed on both sides of the circuit breaker, so that the circuit breaker is in the cross protection range

6. In order to prevent the bushing flashover of the pillar-type Power Current Transformer from causing bus failure, the Power Current Transformer is usually arranged on the outlet or transformer side of the circuit breaker

7. In order to reduce the damage caused by the generator's internal failure, the Power Current Transformer for automatically adjusting the excitation device should be arranged on the outlet side of the generator stator winding. In order to facilitate analysis and find internal faults before the generator is incorporated into the system, the Power Current Transformer used for measuring instruments should be installed on the neutral side of the generator.