It is an electrical appliance which is designed to deliver a constant voltage to a load at its output terminals regardless of the changes in the input or incoming supply voltage. It protects the equipment or machine against over voltage, under voltage, and other voltage surges.

It is also called as automatic voltage regulator (AVR). Voltage stabilizers are preferred for costly and precious electrical equipments to protect them from harmful low/high voltage fluctuations. Some of these equipments are air conditioners, offset printing machines, laboratory equipments, industrial machines, and medical apparatus.

Generally, each and every electrical equipment or device is designed for a wide range of input voltage. Depending on the sensitivity, the working range of the equipments are limited to a specific values, for instance, some equipments can tolerate ± 10 percent of the rated voltage while others ± 5 percent or less.

The voltage fluctuations (rise or dip of the magnitude of rated voltage) are quite common in many areas, especially at terminated lines. The most common reasons for voltage fluctuations are lighting, electrical faults, faulty wiring and periodic turning off the device. These fluctuations create mishap to the electrical equipments or appliances.

Long time over voltage will result

• Permanent damage to the equipment
• Insulation damage to the windings
• Unwanted interruption in the load
• Increased losses in cables and associated equipments
• De-rating life of the appliance

Long time under voltage will result

• Malfunctioning of the equipment
• Longer working periods (as in case of resistive heaters)
• Reduced performance of the equipment
• Drawing large currents which further lead to overheating
• Computational errors
• Reduced speed of motors

So the voltage stability and accuracy decide the correct operation of the equipment. Voltage stabilizers therefore ensure that the voltage fluctuations at the incoming power supply does not affect the load or electrical appliance.