In a voltage stabilizer, voltage correction from over and under voltage conditions is performed through two essential operations, namely boost and buck operations. These operations can be carried manually by switches or automatically through electronic circuitry. During under voltage condition, boost operation increases the voltage to a rated level while buck operation reduces the voltage level during over voltage condition.

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.

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