1B variac type servo three phase stabilizer is installed in the building structure to protects the equipment against short circuit, line losses and overload. Constant voltage can be achieved with this stabilizer. We design and develop this device to be used efficiently and keep the owners at peace. The problem of voltage variations in the mains power supply, can be solved by the device we are offering. The components that make this device are solid state sensing circuit, double wound step up Transformer, motor and SVT Auto -Transformer. The front panel of the device has neon indicator, HI/LO indicator, voltmeter, output adj., auto-manual switch and incr/decr. switch.