The basic principle of residual (zero sequence) current protection is based on Kirchhoff's current law. The algebraic sum of the complex currents flowing into any node in the circuit is equal to zero. Under normal conditions of circuits and electrical equipment, the vector sum of various currents is equal to zero. Therefore, the secondary winding of the residual (zero sequence) current standard transformer has no signal output and the actuator does not operate. When a ground fault occurs, the vector sum of each phase current is not zero. The fault current generates magnetic flux in the ring core of the current transformer, and the secondary side induced voltage of the zero-sequence current standard transformer causes the actuator to operate and drive tripping. device to switch the power supply network to achieve the purpose of grounding protection.

Usage: You can install a current transformer on each of the three-phase lines, or let the three-phase conductors pass through the residual (zero sequence) current transformer together. You can also install a residual (zero sequence) current transformer on the neutral line N. , use it to detect the current vector sum of the three phases.

The residual current refers to the vector sum of the instantaneous values of the current passing through the main circuit of the residual current action protection device (zero sequence transformer), expressed in its effective value. For a single-phase line, the residual current is the relative ground leakage current; for a three-phase line , the residual current is the vector sum of the instantaneous values of each phase current, represented by its effective value. The residual current transformer can automatically disconnect the circuit when the residual current in the protected circuit exceeds the set value under specified conditions. A relay protection device that sends an alarm signal.