Seven aspects should be paid attention to in the wiring of current transformer

- Mar 02, 2020-

1) The wiring of current transformer shall follow the principle of series connection: the primary winding shall be connected in series with the circuit under test, and the secondary winding shall be connected in series with all instrument loads.
2) According to the measured current, choose 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 jumping into the secondary low voltage side once the insulation is damaged, causing personal and equipment accidents
3) The secondary side is absolutely not allowed to open. Once the primary side is open, all the current I1 on the primary side will become magnetizing current, which will cause the sudden increase of φ m and E2, resulting in the over saturation magnetization of the core, serious heating and even burning of the coil. At the same time, after the over saturation magnetization of the magnetic circuit, the error will increase. When the current transformer is in normal operation, the secondary side is close to short circuit. If it is suddenly open circuit, the excitation electromotive force will suddenly change from a small value to a large value, and the magnetic flux in the iron core will present a seriously saturated flat top wave. Therefore, the secondary side winding will induce a very high peak wave when the magnetic flux passes through zero, and its value can reach thousands or even tens of thousands of volts, which will endanger the safety of workers and instruments Insulation performance of.
In addition, the secondary side open circuit makes E2 reach several hundred volts, once touched, it will cause electric shock accident. Therefore, the secondary side of current transformer is equipped with short-circuit switch to prevent the primary side from opening. In the process of use, once the secondary side is open, the circuit load should be removed immediately, and then stop for processing. It can be reused only after everything has been handled.
4) In order to meet the needs of measuring instruments, relay protection, breaker failure judgment and fault recording devices, current transformers with 2-8 secondary winding are set in the circuits of generator, transformer, outgoing line, bus section breaker, bus link breaker, bypass breaker, etc. For large current grounding system, it is generally configured as three-phase; for small current grounding system, it is configured as two-phase or three-phase according to specific requirements
5) For the installation location of protective current transformer, the unprotected area of main protective device shall be eliminated as far as possible. For example, if there are two groups of current transformers, and the position allows, they should be set on both sides of the circuit breaker, so that the circuit breaker is in the cross protection range
6) In order to prevent busbar fault caused by bushing flashover of strut 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 shall be arranged on the outgoing side of the generator stator winding. In order to facilitate the analysis and internal fault detection before the generator is incorporated into the system, the current transformer used for measuring instrument should be installed at the neutral point side of the generator.