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Formula & Calculator

Voltage Regulation

Measures how much a source's voltage changes between no-load and full-load conditions.

Written by the Vorzep Team

Power SystemsTransformers

Voltage Regulation Calculator VR = (VNL − VFL) / VFL × 100%

VR = (VNL − VFL) / VFL × 100%
VR = voltage regulation (%)  ·  VNL = no‑load voltage (V)  ·  VFL = full‑load voltage (V)
⟹ Solve ⟷ VR, VNL, VFL
V
V
%
Please fix the errors above.
Solve for:
Presets:
Voltage Regulation —
—
VNL: — VFL: — VR: —
✓ Copied!
Voltage Regulation —
Excellent (< 2%) Good (2–6%) Poor (> 6%)
VR = (VNL − VFL) / VFL × 100%  ·  Lower VR indicates better voltage regulation (more stable voltage).

Variables

SymbolQuantityUnit
VRVoltage regulation (percentage)%
V_NLNo-load voltage (output voltage with zero load current)V
V_FLFull-load voltage (output voltage at rated load current)V

What it means

Voltage regulation (VR) is a measure of the change in output voltage of a power supply or generator from no‑load to full‑load, expressed as a percentage of the full‑load voltage. The formula is VR = (V_no‑load − V_full‑load) / V_full‑load * 100%. A lower VR indicates a more stable supply, which is important for sensitive equipment. Voltage regulation is a key specification for voltage regulators, transformers, and generators. It accounts for the internal resistance of the source and the drop across leads. In power systems, good regulation ensures that loads receive voltages within acceptable limits. Example: A supply has no‑load voltage 120V and full‑load voltage 114V. VR = (120−114)/114 * 100 = 6/114*100 ≈ 5.26%. This indicates a 5.26% drop under load.

Worked example

Voltage Regulation – Practical Example

Real‑World
Scenario: A small generator produces 120 V at no load and 115 V at full load. Calculate the voltage regulation.
ParameterValue
VNL120 V
VFL115 V
FormulaVR = (VNL − VFL) / VFL × 100%
1Difference: 120 – 115 = 5 V
2Divide by full‑load: 5 / 115 = 0.04348
3Convert to %: 0.04348 × 100 = 4.35%
Final Design VR = 4.35% ✓ Acceptable regulation
Why: Lower regulation means better voltage stability – 4.35% is typical for good generators.

Common mistakes

  • No‑load voltage: The output voltage when no load is connected (or minimum load).
  • Full‑load voltage: The output voltage at rated load.
  • Regulation: A lower percentage indicates better voltage stability.
  • Sign: Typically V_NL > V_FL (positive regulation).
  • Power factor: Voltage regulation depends on load power factor.

Applications

Voltage regulation (VR) measures the change in output voltage from no‑load to full‑load as a percentage of the full‑load voltage. It indicates how well a power supply or transformer maintains its output voltage under varying load. A lower VR means a more stable supply. Engineers use this parameter to design regulated power supplies, to specify transformers, and to assess the quality of distribution networks. By calculating VR, they can ensure that the voltage delivered to equipment remains within acceptable limits. This formula is essential for power quality and reliability. Understanding voltage regulation helps in troubleshooting voltage fluctuations.

  • Transformer and generator voltage stability analysis
  • Design of voltage‑regulated power supplies
  • Power quality assessment in distribution systems
  • Sizing of automatic voltage regulators (AVR)
  • Educational understanding of load regulation