Electrical Current Transformer, precautions for use When Electrical Current Transformer is running, no open circuit on the secondary side is allowed. 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 Electrical Current Transformer, and it is also not allowed to remove the ammeter, relay and other equipment without bypassing during operation. The impedance of the series coil of the measuring instrument and the protection circuit is very small, and the working state of the Electrical Current Transformer is close to a short circuit. Electrical Current Transformer converts the large current on the primary side into a small current on the secondary side for measurement, and the secondary side cannot be open.