1) The wiring of the current transformer should comply with the principle of series connection: that is, the primary winding resistance should be connected in series with the tested circuit, while the secondary winding resistance should be connected in series with all instrument loads
2) According to the size of 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 high voltage of the primary side from entering the secondary low voltage side once the insulation is damaged, resulting in personal and equipment accidents
3) The secondary side is absolutely not allowed to open the circuit, because once the open circuit is opened, the current I1 on the primary side becomes the magnetizing current, which causes a sudden increase in φm and E2, resulting in oversaturation and magnetization of the core, serious heating and even burning of the coil; At the same time, the error increases after the magnetic circuit is oversaturated and magnetized. When the current transformer is working normally, the secondary side is used in series with the current coils such as measuring instruments and relays, and the impedance of the current coils such as measuring instruments and relays is very small, and the secondary side is approximately short circuit. The magnitude of the secondary current of CT is determined by the primary current, and the magnetic potential generated by the secondary current is balanced by the magnetic potential of the primary current. If it is suddenly opened, the excitation electromotive force suddenly changes from a very small value to a very large value, and the magnetic flux in the iron core presents a seriously saturated flat-top wave, so the secondary side winding will induce a very high spire wave when the magnetic pass through zero, and its value can reach thousands or even tens of thousands of volts, endangering the safety of the staff and the insulation performance of the instrument.
In addition, the secondary side open circuit makes the secondary side voltage reach several hundred volts, and once touched, it will cause an electric shock accident. Therefore, the secondary side of the current transformer is equipped with a short-circuit switch to prevent the secondary side from being opened. In the process of use, once the secondary side is opened, the circuit load should be removed immediately, and then the power should be cut off. Everything can be reused after it has been processed.
4) In order to meet the needs of measuring instruments, relay protection, circuit breaker failure judgment and fault filtering devices, 2-8 secondary winding current transformers are set up in generators, transformers, outgoing wires, bus segmented circuit breakers, bus circuit breakers, bypass circuit breakers and other circuits.
5) For the installation site of the current transformer for protection, it should be set up according to the non-protection zone that eliminates the main protection device as much as possible. For example, if there are two sets of current transformers, and the position allows, they should be located on both sides of the circuit breaker so that the circuit breaker is in the cross protection range
6) In order to prevent bus failure caused by flashover of the bushing of the pillar type 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 in the event of an 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 the analysis and detection of internal faults before the generator is integrated into the system, the current transformer used for the measuring instrument should be installed on the neutral side of the generator.
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