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% |
Frequently Asked Questions - Voltage Imbalance Calculator:
What is voltage imbalance?
Voltage imbalance (unbalance) describes unequal phase voltages in a three-phase system in magnitude and/or angle.
How is percent voltage unbalance (%U) calculated?
%U = max(|Va−Vavg|,|Vb−Vavg|,|Vc−Vavg|)/Vavg ×100%, using RMS phase voltages.
What is VUF?
Voltage Unbalance Factor (VUF) = |Vneg|/|Vpos| ×100%, from symmetrical components.
Which method is better, %U or VUF?
%U is simple and practical; VUF (sequence method) is preferred for standards, phasor/angle issues and harmonics-aware analysis.
What levels of imbalance are acceptable?
Typical targets are <1% for sensitive equipment; many utilities allow up to 2–3% but lower is better for motors.
How does imbalance affect motors?
It increases heating, reduces torque, causes vibration, and shortens motor life.
What data do I need to calculate VUF?
Phase phasors (complex RMS values) Va∠θa, Vb∠θb, Vc∠θc to compute positive and negative sequence components.
Can I use line-to-line voltages?
Yes if you convert to phase (line-to-neutral) voltages appropriately for the chosen connection type (wye/delta) before applying formulas.
Does voltage imbalance include harmonic effects?
Harmonics create sequence components too; VUF from phasors (using spectral components) captures harmonic-contributed negative sequence.
How often should I measure imbalance?
For diagnostics, measure under typical load. For continuous monitoring, sample RMS over time and report max, average, and trends.
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