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Motors: The proactive approach to voltage unbalance

  • June 2016
  • Number of views: 2332
  • Article rating: No rating
Trade press article — Engineered Systems

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.

The impact of voltage variation on motor performance

  • February 2014
  • Number of views: 1277
  • Article rating: No rating

The three-phase squirrel cage induction motor is a very robust machine that can operate over a wide range of voltage conditions; it is the workhorse of the industry. However, for optimum performance and life expectancy, the voltage supply should be a balanced three-phase, sine-wave voltage, and its magnitude should be as close to the nominal voltage stated on the motor nameplate as practical. 

Any deviations from these conditions may cause a depreciation in the motor performance and expected life, and increase energy costs. Benchmarking the service entry voltage and the motor performance may be a useful tool to assist in knowing when reasonable limits have been exceeded and that corrective action needs to be taken. 

The following detrimental conditions may alone or in combination exist at various times or continuously: 

  1. Voltage variation (+/- nominal)
  2. Voltage Unbalance
  3. Transient voltage (surges)
  4. Voltage waveform distortion (harmonics)

Unbalanced voltages and electric motors

  • December 2007
  • Number of views: 844
  • Article rating: No rating

Unbalanced voltages are unequal line-to-line voltage values on 3-phase circuits that can exist anywhere in a power distribution system. Unbalanced voltages can cause serious problems,particularly for motors and other inductive devices. Perfectly voltage-balanced circuits are not possible in the real world. Typically, the circuit line-to-line voltages may differ by a few volts or more. It's when voltages differ by more than 1% that problems tend to occur.

Getting The Most From Your Electric Motors

Getting The Most From Your Electric Motors - coverThis 40-page booklet provides great advice for obtaining the longest, most efficient and cost-effective operation from general and definite purpose electric motors.

This booklet covers topics such as:

  • Installation, startup and baseline information
  • Operational monitoring and maintenance
  • Motor and baseline installation data
  • How to read a motor nameplate
  • Motor storage recommendations



EASA/AEMT Rewind Study

EASA Rewind Study cover

The Effect of Repair/Rewinding on Premium Efficiency/IE3 Motors
Tests prove Premium Efficiency/IE3 Motors can be rewound without degrading efficiency.


ANSI/EASA AR100-2020

ANSI/EASA AR100-2015 cover

Recommended Practice for the Repair of Rotating Electrical Apparatus
This is a must-have guide to the repair of rotating electrical machines. Its purpose is to establish recommended practices in each step of the rotating electrical apparatus rewinding and rebuilding processes.



EASA Technical Manual

EASA Technical Manual cover

Revised May 2021
The EASA Technical Manual is the association's definitive and most complete publication. It's available FREE to members in an online format. Members can also download PDFs of the entire manual or individual sections.