What is zero sequence current protection

A device that uses the zero-sequence current generated when grounding is used to initiate protection is called zero-sequence current protection. Special zero-sequence current transformers are used on cable lines to achieve grounding protection. Place the zero sequence current transformer on the grounded three-core cable and connect the current relay to the secondary coil of the transformer，During normal operation or when there is no ground fault, since the vector sum of the three-phase currents of the cable is zero, the current of the secondary coil of the zero sequence transformer is also zero (only a small unbalanced current), so the current relay does not operate. When a ground fault occurs, a large current will appear in the secondary coil of the zero sequence transformer, causing the current relay to operate to send a signal or remove the fault.