1) The wiring of current transformer shall comply with the principle of series connection: the primary winding resistance shall be connected in series with the circuit under test, while the secondary winding resistance shall be connected in series with all instrument loads
2) Select the appropriate transformation ratio according to the measured current, 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 low voltage side of the secondary side and causing equipment accidents once the insulation is damaged
3) Open circuit is not allowed on the secondary side, because once open circuit occurs, all the current I1 on the primary side becomes magnetizing current, causing φ The sudden increase of m and E2 causes the iron core to be supersaturated and magnetized, and the coil is severely burnt by heating; At the same time, the error increases after the magnetic circuit is supersaturated and magnetized. When the current transformer works normally, the secondary side is used in series with current coils such as measuring instruments and relays. The impedance of current coils such as measuring instruments and relays is very small, and the secondary side is close to short circuit. The size of 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 changes from a small value to a large value suddenly, and the magnetic flux in the iron core presents a seriously saturated flat top wave. Therefore, the secondary side winding will induce a very high peak wave when the magnetic field passes through zero, which can reach thousands or even tens of thousands of volts, endangering the safety of workers and the insulation performance of the instrument.
In addition, the open circuit on the secondary side makes the secondary side voltage reach hundreds of volts, which will cause electric shock once touched. Therefore, the secondary side of the current transformer is equipped with a short circuit switch to prevent open circuit on the secondary side. During use, once the secondary side is open circuit, the circuit load shall be removed immediately, and then the power shall be cut off again. It can be reused only after everything is handled.
4) In order to meet the needs of measuring instruments, relay protection, circuit breaker failure judgment, fault filtering and other devices, 2-8 secondary winding current transformers are set in generator, transformer, outgoing line, bus sectionalized circuit breaker, bus circuit breaker, bypass circuit breaker and other circuits.
5) The installation location of current transformer for protection shall be set to eliminate the unprotected area of main protection device as far as possible. For example, if there are two groups of current transformers and the position is allowed, they should be set at both sides of the circuit breaker to make the circuit breaker in the cross protection range
6) In order to prevent busbar fault caused by bushing flashover of pillar current transformer, current transformer is usually arranged at the outgoing line of circuit breaker or transformer side
7) In order to reduce the damage caused by internal fault of generator, the current transformer used for automatic regulation of excitation device shall be arranged at the outgoing line side of 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 measuring instruments should be installed at the neutral side of the generator.
