The secondary side of the current transformer must not be open during operation. Once the secondary side is open, it will burn out due to excessive iron loss and high temperature, or the voltage of the secondary winding will rise and the insulation will break down, which may cause high-voltage electric shock. Therefore, when changing the meter, such as changing the ammeter, active meter, reactive meter, etc., the current loop should be short-circuited before the metering meter is replaced. After the meter is adjusted, connect it to the secondary circuit first, then remove the short wiring and check whether the meter is normal. If sparks are found when the short wiring is removed, and the current transformer has been opened at this time, it should be re-shorted immediately, and the short wiring can be removed only when it is found that there is no open circuit in the meter circuit. When removing the short circuit of the current transformer, you should stand on the insulating pad. In addition, you should consider disabling the protection device of the current transformer loop. After the work is completed, the protection device can be put into operation. If the current transformer has a buzzing noise, check whether the internal iron core is loose, and the iron core bolts can be tightened. One end of the secondary side of the current transformer and the shell must be reliably grounded.