RV2 series relay adopt digital circuit processing system with singlechip as core part, They can be used in the circuit of AC 50/60Hz, Rated voltage 220V, 230V, 240V, 400V, 415V as over-voltage, under-voltage, phase failure, phase sequence, three phase unbalance protection. In the circuit of three phase four wire system, the relay which have no phase sequence protection function can be used to protect single phase or two phase circuit. The relay can be widely used in industry-control system, capacitor of power compensation, switch -boards, air-condition system, motor etc occasion.