Current transformer: Precautions for use When the current transformer is running, the secondary side is not allowed to open. Because once the circuit is opened, the primary side current becomes the excitation current, so that the magnetic flux and the secondary side voltage greatly exceed the normal value and endanger the safety of people and equipment. Therefore, it is not allowed to connect a fuse in the secondary circuit of the current transformer, and it is also not allowed to remove the ammeter, relay and other equipment without bypass during operation. Therefore, it often has all the current of the line flowing, and the number of turns of the secondary winding is relatively large. It is connected in series with the measuring instrument and the protection circuit. When the current transformer is working, its secondary circuit is always closed, so the measurement The impedance of the series coil of the instrument and the protection circuit is very small, and the working state of the current transformer is close to short circuit. The current transformer converts the large current on the primary side into the small current on the secondary side for measurement, and the secondary side cannot be opened.