Voltage Imbalance and Derating Factor in Polyphase Motors

The efficiency of an electrical polyphase motor decreases with increased voltage imbalance.

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Electrical motors are designed to operate with high efficiency within some variation in the electric power supplied.

  • voltage variation should not exceed +/- 10%
  • frequency variation should not exceed +/- 5%
  • combined arithmetic sum of voltage and frequency variation should not exceed 10%
  • voltage imbalance between phases should not exceed 1%
Voltage Imbalance % Derating factor
0 1.00
0.5 1.00
1.5 0.97
2.0 0.95
2.5 0.93
3.0 0.89
3.5 0.85
4.0 0.82
4.5 0.78
5.0 0.76

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Related Topics

  • Electrical - Amps and electrical wiring, AWG - wire gauge, electrical formulas, motors and units

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