The role of zero sequence residual current transformer

- Jul 13, 2020-

The high-voltage incoming line is a three-phase three-wire system. Generally, the current of three-phase electricity is balanced. The zero-sequence transformer uses the principle of electromagnetic induction to measure the three-phase unbalanced current. If there is a one-way ground fault, the zero-sequence transformer measures the current reflected to Relay protection, so as to alarm or trip.

Principle: The basic principle of zero-sequence current protection is based on Kirchhoff's current law: the algebraic sum of the complex current flowing into any node in the circuit is equal to zero. When the line and electrical equipment are normal, the vector sum of each phase current is equal to zero. Therefore, the secondary winding of the zero sequence current transformer has no signal output, and the actuator does not operate. When the ground fault occurs, the vector sum of each phase current is not zero. The fault current causes magnetic flux in the ring core of the zero-sequence current transformer. The induced voltage on the secondary side of the zero-sequence current transformer causes the actuator to move and drive Trip device to switch the power supply network to achieve the purpose of ground fault protection.