Ac. Automatic Voltage Regulator (servo Motor Type)WHY NEED THEM: When your grid voltage down or up until ouside the normal use range, which will affect your device until to get damaged! Our regulator will help you to get stable voltage for normal home & industrial use.Three Phase SBW Series (Heavy Power): Common Control, up to 650KVAThree Phase SBW-F Series : Independent Control, up to 3500KVA