Transformer Voltage Regulation

VR = (Vnl − Vfl) / Vfl

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Result
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Formula

VR = (Vno-load − Vfull-load) / Vfull-load × 100%

Description

Voltage regulation measures how much a transformer’s secondary voltage sags between no load and full load, expressed as a fraction of the full-load voltage. The drop is caused by the winding resistance and leakage reactance carrying the load current. A lower regulation percentage means a stiffer, better-regulated supply. Ideal transformers have zero regulation; real ones are typically a few percent.

Variables

  • VR — Voltage regulation (fraction or %)
  • Vnl — Secondary voltage at no load (V)
  • Vfl — Secondary voltage at full load (V)

Practical Notes

Good distribution transformers achieve 1–3% regulation; small mains transformers may be 5–10%. Poor regulation forces the design to use a higher no-load voltage so the loaded output stays in spec.

Related Concepts

All Magnetics & Transformers formulas →
Transformer EMF Equation Transformer VA Rating Transformer Voltage Regulation Transformer Current Ratio Transformer Copper Loss Transformer Iron (Core) Loss Transformer Turns-per-Volt Transformer Impedance Matching

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