ClueLuma

Three-phase voltage unbalance (VU) calculator

Maximum line-voltage deviation from the average screens a motor supply for imbalance.

VU=100×max⁡(∣V1−V1+V2+V33∣, ∣V2−V1+V2+V33∣, ∣V3−V1+V2+V33∣)×3V1+V2+V3\mathrm{VU} = \frac{100 \times \max\left(\left|V_{1} - \frac{V_{1} + V_{2} + V_{3}}{3}\right|,\ \left|V_{2} - \frac{V_{1} + V_{2} + V_{3}}{3}\right|,\ \left|V_{3} - \frac{V_{1} + V_{2} + V_{3}}{3}\right|\right) \times 3}{V_{1} + V_{2} + V_{3}}

Calculator

Enter the values you know and leave one box empty. Calculate finds the empty one, the result or any input.

V
V
V
%

Worked example

Given

  • V1V_{1} = 472 V
  • V2V_{2} = 480 V
  • V3V_{3} = 488 V
VU=100×max⁡(∣472−472+480+4883∣, ∣480−472+480+4883∣, ∣488−472+480+4883∣)×3472+480+488≈1.667\mathrm{VU} = \frac{100 \times \max\left(\left|472 - \frac{472 + 480 + 488}{3}\right|,\ \left|480 - \frac{472 + 480 + 488}{3}\right|,\ \left|488 - \frac{472 + 480 + 488}{3}\right|\right) \times 3}{472 + 480 + 488} \approx 1.667

Symbols and units

SymbolMeaningUnit
VU\mathrm{VU}voltage unbalance%
V1V_{1}first line voltageV
V2V_{2}second line voltageV
V3V_{3}third line voltageV

Related calculators

Results are estimates for study and screening. Check the inputs, units and assumptions before you use them for design, billing or contract decisions.