Servo - Controlled Automatic AC Voltage Stabilizers of 'PCS' make are of 'Electro - Mechanical (EMS) type. The purpose of voltage stabilizer is to receive a fluctuating AC voltage of large amplitude & deliver an almost constant voltage, which remains within a very narrow band (± 1%) of the nominal voltage - quality of the AC voltage remains unchanged. The voltage variations, which have become a common phenomenon in current power supply system, cause havoc in modern complicated & sophisticated equipments. The voltage stabilizers are meant to take care of this problem & protect the equipments. They ensure longer life of the equipments & also drastically cut down electricity consumption of equipments leading to continuous reduction in electricity bills. Thus, they play an important role in energy conservation which is need of the day.