Earth Bondhon
Creators
Rojony Khatun Author
Rojony Khatun
CalculatorToolsProjectExpert
Reviewers
Małgorzata Koperska, MD Steven Wooding
Last updated: September 30, 2025

Voltage Imbalance Calculator | % Unbalance & Seq. Method

🇺🇸
English
Default
🇪🇸
Español
Spanish
🇫🇷
Français
French
🇩🇪
Deutsch
German
V
V
V
V
V
%

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

InputActionOutput
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

ScenarioInputCalcResult
Balanced230,230,230 VVavg=230 → max dev 0%U=0, %VUF≈0
Small mag unbalance230,225,235 VVavg=230, max dev=5 → 5/230×100%U≈2.17%
Severe240,210,230 VVavg≈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.

Rojony Khatun

Rojony Khatun

CalculatorToolsProject

Rojony Khatun is the creator of a free online tools website designed to simplify everyday and engineering-related calculations for students, professionals, and hobbyists. The platform offers a wide variety of basic and advanced calculators across key categories, including Electrical Calculators, Electronic Calculators, and Time & Date Calculators, helping users solve problems quickly and accurately.