A relay that has contacts that operate when the voltage drops below a set voltage. Undervoltage relays are used for protection against voltage drops, to detect short-circuit faults, etc.

Why do we need undervoltage protection?

Undervoltage protection is commonly used to protect motors from damage during abnormal conditions and to prevent breaker-fed motors from re-accelerating after a restoration of bus voltage. This protection method has the unfortunate consequence of introducing the possibility of a nuisance trip when VT's fail.

Where is under voltage relay used?

Under voltage relay is a relay that has contacts that operate when the voltage drops below a set voltage. These are used for protection against voltage drops, to detect short-circuit faults, etc. These are used in motors, alternators and in busbars.