When detecting standby signal, microcomputer gives structure to relay switch to cut off the current, then standby power is eliminated so as to realize energy saving.

Introduction was made to the composition and working principle of a power-off time delay relay which adopts CMOS digital circuit, digital dial disc for switch setting and without auxiliary power.

The proposed method can be used both on-line and off-line in the relay parallel setting and coordination of a large-scale power system.