Voltage Imbalance Calculator
Calculate percent voltage imbalance (PVU) using both phase-deviation and negative-sequence methods. Includes formulas, examples, and troubleshooting tips.
negative sequence voltage calculator
Voltage imbalance is computed in two forms: percent unbalance and deviations calculated by determination of the maximum between (V a -voltage and V b -voltage and V c -voltage) /100%bar V; or sequence-based VUF:(Vneg)/(Vpos)100% using symmetrical components. Precise results should be obtained using RMS phase voltages, preferably VUF instead of the latter when standards and harmonics sensitivity is required.
Formula & Table Summary:
Phase-deviation: Vavg=(Va+Vb+Vc)/3; %U = max(|Va−Vavg|,|Vb−Vavg|,|Vc−Vavg|)/Vavg×100%
Sequence (VUF): Vpos=(Va+aVb+a²Vc)/3, Vneg=(Va+a²Vb+aVc)/3; %VUF=|Vneg|/|Vpos|×100%
Converter table
| Input | Action | Output |
|---|---|---|
| Va,Vb,Vc (RMS) | Compute Vavg and deviations | %U |
| Va∠θa,... (phasors) | Compute Vpos,Vneg | %VUF |
| Vab,Vbc,Vca (line) | Convert to phase then above | %U or %VUF |
voltage unbalance troubleshooting
Voltage imbalance (voltage unbalance) is the condition that exists when three three-phase line voltages are not equal in magnitude or phase. Two common measurements of it are (1) phase deviation or percent unbalance by deviations of the average phase voltage, and (2) sequence method by the ratio of negative-sequence voltage to positive-sequence voltage (Vn/Vp), sometimes expressed as VUF ( Voltage Unbalance Factor ). When a voltage imbalance occurs, the motor will heat, the torque will pulse, and the efficiency and nuisance trips will decrease. Calculate imbalance using phase or line voltages, select the correct procedure to use standards diagnostics, and find worked examples using this calculator. Add sampling as RMS values and make sure that units are the same. Normal acceptable imbalance is limited (e.,less than 12 percent; above that requires research.
calculate voltage unbalance percent
| Scenario | Input | Calc | Result |
|---|---|---|---|
| Balanced | 230,230,230 V | Vavg=230 → max dev 0 | %U=0, %VUF≈0 |
| Small mag unbalance | 230,225,235 V | Vavg=230, max dev=5 → 5/230×100 | %U≈2.17% |
| Severe | 240,210,230 V | Vavg≈226.67, max dev≈13.33 | %U≈5.9% |
