NJYB3 relay is used to provide overvoltage, undervoltage, phase failure, phase sequence and threephase unbalance control in three-phase three-wire 380V circuits and three-phase four-wire 220V circuits with a frequency of AC 50Hz. For example, it is used for power control systems, air conditioning systems and motors. This relay is a voltage protection relay. After detecting the voltage signal, the relay processes the input signal, judges if there is an overvoltage, undervoltage, phase failure, error-phase or unbalance and controls the operation accurately and stably by means of the built-in microprocessor