The wiring of the current transformer shall be in series: that is, the primary winding shall be in series with the circuit under test, and the secondary winding shall be in series with all instrument loads.
According to the measured current, select the appropriate ratio, otherwise the error will increase.At the same time, one end of the secondary side must be grounded, in case the insulation is damaged, the high voltage of the primary side enters the secondary low voltage side, causing personal and equipment accidents.
The secondary side is absolutely not allowed to open circuit, because once the open circuit, the primary side current I1 all becomes the magnetization current, causing a sharp increase in φm and E2,Cause the over-saturation magnetization of the current transformer core material, the current transformer core material becomes hot and even burns out the coil;At the same time, the error increases after the over-saturation magnetization of the magnetic circuit.
When the ct is in normal operation, the secondary side is used in series with current coils of measuring instruments and relays. The impedance of current coils of measuring instruments and relays is very small, and the secondary side is close to short circuit.The value of CT secondary current is determined by the primary current, and the magnetic potential generated by the secondary current is to balance the magnetic potential of the primary current.
If the path is suddenly opened, the excitation electromotive force will change from a small value to a large value,the current transformer core material of the ct presents a flat-topped wave with severe saturation,therefore the secondary side winding will induce a very high peak wave when the magnet passes through zero, and its value 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 secondary side open circuit makes the secondary side voltage up to several hundred volts, once touched, it will cause electric shock accident.Therefore, the secondary side of the ct is equipped with short-circuit switches to prevent the secondary side from opening.In the process of use, once the secondary side open circuit should be immediately removed from the circuit load, and then power failure treatment.Don't use it until everything is in order.
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