Undervoltage protection is provided for A circuit bars,motors, generators, transformers, rectifiers, etc.. Such protection is given by means of undervoltage relay. Undervoltage relay are necessary for voltage control and reactive power control of network buses and load buses. These type of relays have inverse time characteristics and their operating time reduces twith the reduction in operating voltage. Undervoltage protection is provided for AC circuit bars,motors, generators, transformers, rectifiers, etc.. Such protection is given by means of undervoltage relay. Undervoltage relay are necessary for voltage control and reactive power control of network buses and load buses. These type of relays have inverse time characteristics and their operating time reduces twith the reduction in operating voltage.