1)The wiring of the current transformer should follow the series principle: the primary winding should be connected in series with the circuit under test, while the secondary winding should be connected in series with all loadded instruments.
2)Selecting appropriate transformation ratio according to the measured current, otherwise the error will be larger. At the same time, one side of the secondary winding must be grounded to prevent the high voltage of the primary winding from entering the low voltage side of the secondary winding once the insulation is damaged, causing personal and equipment accidents.
3)The circuit of secondary winding can not be opened absolutely,once its circuit is opened, the current of primary windingI1 will all transform into magnetizing current, causing αm and E2 to soar sharply, resulting in excessive saturation and magnetization of the iron core, serious heating and even burningthe coil; at the same time, the error will be larger after the magnetic circuit is excessively saturated and magnetized. When the current transformer is working properly, the secondary winding is used in series with measuring instrument and current coils such as relays. The impedance of measuring instrument and current coils such as relays is very small, and the secondary winding is merely in a short circuit. The intensity of secondary current of the CT is determined by the primary current. And the magnetic potential generated by the secondary current balances the magnetic potential of the primary current. If the circuit 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 present a severely saturated flat-top wave. Therefore, the secondary winding will induce a high peak wave when the magnetic passes through zero, with whose value can reach thousands or even tens of thousands of volts, harming the safety of workers and the insulation performance of the instrument.
In addition, the opened circuit of the secondary winding makes the voltage of the secondary side reach several hundreds of volts, which will cause an electric shock accident once touched. Therefore, the secondary winding of the current transformer is equipped with a short-circuit switch to prevent it from being opened. In the using process , once the secondary winding is opened, the circuit load should be removed immediately, and then should deal with it after the power failure. It can be reused after everything is done.
4)In order to meet the requirements of instruments measuring, relay protection, circuit breaker failure and fault filtering, etc. It should set 2 to 8 current transformers with secondary winding in all circuits in generators, voltage transformers, outgoing lines, bus sectional circuit breakers, bus circuit breakers, bypass circuit breakers, etc.
5)The installing site of the protection current transformer should be set in the aim of eliminating non-protection zone of the main protection device as far as possible. For example: if there are two sets of current transformers and the space is vacant, they should be located on both sides of the circuit breaker, so that the circuit breaker is within the scope of cross protection.
6)In order to prevent the busbar fault caused by the bushing flashover of the pillar-type current transformer, the current transformer is usually installed on the outgoing line of the circuit breakeror the side of transformer.
7)In order to reduce the damage caused by the internal fault of the generator, the current transformer used for automatic adjustment of the excitation device should be arranged on the outgoing side of the stator winding of the generator. In order to facilitate analysis and find internal faults before the generator is integrated into the system, the current transformer used for measuring instruments should be installed middle of generator.
