What is Phase Imbalance?


Phase unbalance of a three-phase system exists when one or more of the line-to-line voltages in a three-phase system are mismatched. Three-phase power systems and equipment are intended to operate with phases (Lines) balanced.

Line-to-line voltages in a three-phase circuit typically vary by a few volts, but a difference that exceeds 1% can damage motors and equipment. The unbalanced voltages cause unbalanced current in the motor windings; unbalanced currents mean an increase of current to at least one winding raising that winding temperature. Increased temperature reduces motor or equipment life leading to premature failure.

Phase imbalance shown in voltage data from building monitoring system

Why it Matters

A phase unbalance may be caused by unstable utility supply, unbalanced transformer bank, unevenly distributed single-phase loads on the same power system, or unidentified single-phase to ground faults. Single phasing (phase loss) caused by utility supply faults, broken wires, failed fuses, damaged contacts, or malfunctioning overloads can also result in damaging unbalance conditions.

A building monitoring system is a cost-effective and easy to install solution to prevent costly damage from phase unbalance to your motors and equipment. A building monitoring system protects against premature equipment failure by monitoring for several common fault conditions including phase unbalance. Notifying operators to turn off equipment or motors in real-time has been proven to help correct phase imbalances before damage occurs.

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