Voltage Unbalance Calculator
Calculate voltage unbalance using the ANSI method and sequence components (VUF). Input phase magnitudes or phasors (Va, Vb, Vc) to get % unbalance, VUF, and step-by-step results.
Voltage unbalance calculator:
Input the three-phase voltages (magnitudes or phasors) to calculate the ANSI percentage voltage unbalance and Voltage Unbalance Factor (VUF). ANSI operates based on maximum deviation of average magnitude; VUF operates based on symmetrical components: VUF = |V₂| / |V₁|. Both solutions, and in between phasors and step-by-step equations, are presented.
Voltage unbalance Tools formula
Voltage Unbalance Calculator VUC is used to calculate the degree of unbalanced three-phase supply - one of the important parameters of power quality that can influence heating, vibration, efficiency, and protective relays in motors. Two of the most commonly employed measures are: ANSI percent unbalance (in terms of the deviation of the phase magnitudes of the phases of a load) and Voltage Unbalance Factor (VUF), which is based on symmetrical components (ratio of negative-sequence to positive-sequence phasor magnitudes).
It can take phase voltages (phase-to-neutral or phase-to-phase) either as a magnitude V, or a complex phasor V magnitude -angle. It calculates average phase voltage, ANSI percent unbalance, positive and negative sequence voltage (V₁ and V₂), VUF = |V₂|/|V₁| (as fraction or percent), and reports along the way (e.g, V₁ is close to zero). Quickly determine power quality, verify motor drive inputs, or generate maintenance and compliance reports with the calculator.
Work & Installation — Input to Output Summary
Input:
- Phase voltages as magnitudes only (|Va|, |Vb|, |Vc|) — typically phase-to-neutral; OR
- Phase voltages as phasors (Va = |Va|∠θa, Vb, Vc) — required to compute sequence components accurately.
- Option: Are inputs phase-to-phase (line) or phase-to-neutral? (If line, convert to phase equivalents if needed.)
- Units: volts (V); angles in degrees.
Processing:
- ANSI percent unbalance (magnitude method)
Average phase magnitude:
\( V_{avg} = \frac{|V_{a}|+|V_{b}|+|V_{c}|}{3} \)
Maximum absolute deviation: \( \Delta_{max} = Max(||V_{a}|-V_{avg}|,||V_{b}-V_{avg}|,||V_{c}|-V_{avg}|) \)
ANSI % unbalance:
\( \textrm{%Unb}_{ABSI}=\frac{\Delta_{max}}{V_{avg}} \times 100% \) - Symmetrical components → Voltage Unbalance Factor (VUF): Voltage Unbalance Factor (decimal): VUF = |v2|/|v1|. Present also as percentage: VUF% = VUF × 100%.
Output:
- ANSI % unbalance (≥0 %).
- VUF (decimal) and VUF% (|V2|/|V1| ×100).
- Sequence phasors: V0, V1, V2 (complex values and magnitudes/angles).
- Phase average, max deviation, intermediate calculations.
- Warnings if V1 ≈ 0 (division risk), or if inconsistent units/inputs.
Testing and Final Adjustments
Test cases to verify calculator:
- Balanced system — Va = 230∠0°, Vb = 230∠-120°, Vc = 230∠120°
Expected: ANSI % ≈ 0%, VUF ≈ 0 (|V2| ≈ 0). - Magnitude unbalance only — Va = 230∠0°, Vb = 220∠-120°, Vc = 240∠120°
ANSI % will be nonzero (compute with magnitudes). VUF will require angles — with these angles given, V2 nonzero. - Phase shift error — Va=230∠0°, Vb=230∠-115° (angle shifted), Vc=230∠125°
ANSI % may be small (magnitudes same), but VUF can be significant because of phase displacement. - Edge cases: zero voltage on a phase (Va=0) — calculator shows large unbalance, warns of potential division by near-zero V1 and suggests careful interpretation.
Frequently Asked Questions - Voltage Unbalance Calculator:
What is voltage unbalance?
Voltage unbalance is the inequality of magnitudes and/or phase angles among the three phase voltages in a three-phase system; it degrades motor performance and increases losses.
Which methods measure unbalance?
Common methods are ANSI percent unbalance (based on magnitude deviations) and Voltage Unbalance Factor (VUF) using symmetrical components (|V2|/|V1|).
How do I compute ANSI % unbalance?
Compute average magnitude V_avg, find maximum deviation Δ_max, then %Unb = (Δ_max / V_avg) × 100%.
What is VUF?
VUF (Voltage Unbalance Factor) = |V₂| / |V₁|, where V₁ and V₂ are positive- and negative-sequence phasors from symmetrical components.
Do I need phase angles to calculate VUF?
Yes — symmetrical components require phasors (magnitude and angle). Without angles VUF cannot be computed reliably.
Which unbalance metric should I use?
Use ANSI % for quick checks from magnitudes; use VUF (sequence method) for rigorous power-quality analysis and standards compliance.
What level of unbalance is acceptable?
Limits depend on equipment and standards; many guidelines consider VUF below 1% (or ANSI % below ~2%) acceptable, but check manufacturer and local standards.
Can unbalance damage motors?
Yes — unbalance causes increased heating, vibration, reduced torque, and shortened motor life.
How to reduce voltage unbalance?
Check and correct single-phase loading, balance transformer taps, inspect connections, and use phase-balancing equipment or reconfigure loads.
What units are used?
Voltages in volts (V); angles in degrees; ANSI % is percent; VUF often reported as a decimal or percent (×100).
