Phase-monitoring relay prevents motor burnout

3rd June 2006

Finder Plc

ES Admin

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Finder has introduced the 72.31 three-phase monitoring relay, which is used for detecting a loss of phase or incorrect phase rotation when using three-phase supplies. This compact relay is ideally suited for the protection of motors in plant and machinery, and helps to satisfy the mandatory requirement of ensuring the correct rotation of motors in transportable equipment.

The 72.31 allows OEMs, panel builders and installers of control systems to ensure that motors do not become permanently damaged due to phase loss, and also to avoid potential hazards or damage due to incorrect rotation of the motors. The relay features positive safety logic, which triggers the contact to open if an error is detected so that the system will fail to a safe condition. The wide supply voltage specification allows a single unit to be used across the full three-phase supply voltage range of 208V to 480V AC.

The relay provides reliable monitoring of phase loss, even under conditions where the lost phase may be “regenerated” by the action of the rotating motor. This phenomenon is not uncommon, and many monitoring relay units that are currently available may falsely detect this phase regeneration and thus fail to disconnect the supply, which can cause damage to the motor. The 72.31 can discriminate phase regeneration up to 80% of the line voltage.

Featuring a SPDT output contact rated at 6A (maximum peak 15A), the 72.31 monitoring relay is enclosed in a compact housing measuring 84mm high x 56.5mm deep x 17.5mm wide. The narrow profile offers considerable saving in panel space.