Protective relays Overvoltage

Undervoltage and overvoltage relays are often used on the generators to protect against prolonged overload, seen as undervoltage and excessive stress on insulation, seen as overvoltage. These relays are usually chosen with adjustable definite time delays. 

To protect the system from prolonged high voltage it is the usual practice to install an overvoltage relay (59) in each of the generator circuit breakers or at their common busbar. The relay settings are usually set to operate at 115%, with a time delay between 0.5 and 10.0 seconds. 

Overvoltage Protection. Devices such as overvoltage relays provide a reduction in the level of apphed voltage or a maintained interruption of power to the motor circuit when excessive voltage levels are experienced. High induced voltages may occur as a result of the interruption of inductive motor control circuits. 

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