What is the principle of using Power Current Transformer?

1) The wiring of the Power Current Transformer should comply with the series rules: 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 external loads.

2) According to the size of the current to be measured, 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 incidents.

3) The secondary side must not be opened. Once the circuit is opened, the primary side current I1 will all become the magnetizing current, causing φm and E2 to increase sharply, resulting in excessive saturation magnetization of the iron core, severe heating and even burning of the coil; at the same time, after the magnetic circuit is excessively saturated and magnetized, Increase the error. In the normal operation of the Power Current Transformer, the secondary side is used in series with the current coils such as the measuring surface and the relay. The impedance of the current coils such as the measuring surface and the relay is very small, and the secondary side is similar to a short circuit. The size of the CT secondary current is determined by the primary current, and the magnetic potential generated by the secondary current balances the magnetic potential of the primary current. 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 appear a severely saturated flat-top wave, so the secondary winding will induce when the magnetic passes through zero. Very high peak waves, whose value can reach thousands or even tens of thousands of volts, endanger the safety of operators and the insulation function of the exterior.

In addition, an open circuit on the secondary side causes the secondary side voltage to reach several hundred volts. Once touched, an electric shock will occur. Therefore, the secondary side of the Power Current Transformer is equipped with a short-circuit switch to prevent the secondary side from opening. In the process of operation, once the secondary side is open, the circuit load should be removed immediately, and then the power failure should be dealt with. It can be used after all disposal.

4) In order to meet the requirements of measuring appearance, relay maintenance, 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.

5) The installation location of the Power Current Transformer for maintenance should be set up as far as possible to eliminate the non-maintenance area of the main maintenance device. For example: if there are two sets of Power Current Transformers and the directions are allowed, they should be installed on both sides of the circuit breaker so that the circuit breaker is in the range of interspersed maintenance.

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

7) In order to reduce the damage caused by the internal fault of the generator, the Power Current Transformer used to actively adjust the excitation device should be placed 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 to measure the appearance should be installed on the neutral side of the generator.