The use of current transformers mainly pay attention to seven aspects

- Sep 11, 2020-

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, while the secondary winding should be connected in series with all instrument loads.

2) Select the appropriate change according to the measured current size, 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 open, the primary side current I1 all becomes the magnetizing current, causing φm and E2 to increase rapidly, causing the iron core to become 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. When the current transformer is in normal operation, 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. The magnetic flux in the iron core presents 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. The safety of personnel and the insulation performance of instruments are in danger.

The other two = secondary side open circuit makes E2 reach several hundred volts-once touched, it will cause electric shock accident. Therefore, the secondary side of the current transformer is equipped with a short-circuit switch to prevent open circuit on the primary side. When K0 is in use, the secondary side should be open once. Remove the circuit load and then stop processing. -Cut and handle before reuse.

4) In order to meet the needs of measuring instrument relay protection, circuit breaker failure judgment and fault recorder, etc., the generator, transformer, outgoing line, bus section circuit breaker, bus tie circuit breaker, bypass circuit breaker and other circuits are all set Current transformer with 28 secondary windings. For large current grounding systems-generally three-phase configuration; for small current grounding systems according to specific requirements according to two-phase or three-phase configuration

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. For example, if there are two sets of current transformers and their location allows, 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 busbar fault caused by the bushing flashover of the pillar current transformer, 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 to automatically adjust 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 current transformer used for the measuring instrument should be installed on the neutral side of the generator.