The Voltage Supervision Relay is an integral part of any protection system. The voltage supervision relay protections systems from under-voltage and over-voltage. Over voltage in a system can result in serious damage to insulation and equipment while under-voltage can cause motors to draw more current and reduce the speed of the motors, disturbing the process.
Besides protecting against over-voltage, the voltage supervision relay can also be used to detect earth faults as the phase to earth voltage is distorted when there is an earth fault in one of the phases. Voltage supervision relays can generate alarms when the voltage is low or high in only one phase. This is also known as phase asymmetry.
In motor circuits, the voltage supervision relay protects against single phasing. Single phasing can cause serious damage to motors.
A simple auxiliary relay can also be used to generate alarm for under-voltage. When the voltage drops, the relay can drop off thus generating an alarm or a shutdown.
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