The complex transformer voltage lockout overcurrent protection

Composite voltage actuation element is composed of a filtration-type negative-sequence voltage relay and a low-voltage relays. Low-voltage relay negative sequence  electric transformer through the normally closed contacts connected to phase voltage, in order to ensure symmetrical three-phase short-circuit protection device when operated reliably, and can improve the low-voltage relays for three-phase short-circuit sensitivity. Because in the beginning phase short circuit occurs  mcb circuit breaker  negative sequence voltage will be short, so that the negative sequence voltage relay certain action, pending the negative sequence voltage disappears, the negative sequence voltage relay returns, low voltage relay and circuit breakers  to the alternating voltage. Subject the low voltage relay returns require bus residual voltage transformer must be greater than the return voltage relay. Since the three-phase short-circuit, three-phase voltages are lower, so the low-voltage relay is still in the operating state, this time to protect the work of which is equivalent to low-voltage startup overcurrent protection.