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Motors: The Proactive Approach To Voltage Unbalance

Publication: 
Engineered Systems
Publication date: 
June 2016
Author: 
Tom Bishop, P.E., EASA Senior Technical Support Specialist

It’s impossible to balance line-to-line voltages perfectly in three-phase circuits, so they typically differ by a few volts or more. However, if voltage unbalance exceeds 1%, it can markedly decrease the performance and energy efficiency of three-phase motors while increasing the likelihood of premature failure. Avoiding these issues requires a proactive approach that includes installing adequate protective devices and periodically checking for voltage unbalance at the motor terminals.

The article covers:

  • What it is
  • Common causes
  • Effects of unbalanced voltage
  • Testing for unbalanced voltages and single-phasing
  • Ways to correct unbalanced voltages