Single Phase Voltage Monitoring Relay

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Tips: What is single phase voltage monitoring relay?

Relays can be used in motor-driven applications to measure and monitor parameters such as temperature, current or voltage to prevent damage to the motor and connected equipment in the event of a fault or abnormal operating condition. Voltage monitoring relays can detect not only undervoltage and overvoltage conditions, but also voltage-related problems such as phase imbalance, phase loss and phase sequence.

Single-phase voltage monitoring relays are available for single-phase AC or DC voltages. Their primary purpose is to protect the motor and connected equipment from under- or over-voltage conditions, although some are designed to ensure that the voltage remains within a predetermined bandwidth under both high and low voltage limits.

While different manufacturers use different operating principles (open or closed) to energize or de-energize the relay when the set point is exceeded, a simple example of an overvoltage monitoring relay is a relay that uses normally closed (NC) contacts. Here's how it works:

When the operating voltage is below the maximum voltage setting, the relay will de-energize and the contacts will remain in their default closed state. If the voltage exceeds the maximum voltage setting (sometimes called the pickup voltage), the relay energizes, the contacts open, and power is removed from the load. When the voltage drops below the maximum voltage setting including the hysteresis value (called dropout), the relay is de-energized again and the contacts close, restoring power to the load.