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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