Understanding Voltage Regulation in Power Systems
The Voltage Regulation Calculator determines the percentage change in voltage from no-load to full-load conditions. Critical for transformers, transmission lines, and distribution systems to maintain stable voltage within ±5% per ANSI C84.1.
Definition
Voltage Regulation (%) = [(V_no-load - V_full-load) / V_full-load] × 100
Positive = voltage drop under load. Negative = voltage rise (e.g., capacitive loads).
Simple Method
Use when sending (no-load) and receiving (full-load) voltages are known:
%VR = (Vs - Vr) / Vr × 100
Detailed Method (Approximate)
%VR ≈ (I × (R × cosφ + X × sinφ)) / Vr × 100
Where:
- I = Load current
- R, X = Line resistance and reactance
- cosφ = Power factor
- sinφ = √(1 - cos²φ)
Acceptable Limits
| System | Max %VR |
|---|---|
| Util. Service Entrance | ±3% |
| Feeder | 3% |
| Branch Circuit | 3% |
| Total (Service to Outlet) | 5% |
Causes of Poor Regulation
- Long cable runs
- Undersized conductors
- Low power factor
- High inductive loads
Improvement Methods
- Use larger conductors
- Install capacitors for PF correction
- Add voltage regulators
- Balance loads
Examples
- Vs = 500V, Vr = 480V → 4.17% regulation
- 100 kVA, PF 0.8, R=0.5Ω, X=1.2Ω, Vr=480V → ~3.8%
Transformer Regulation
Check nameplate %Z and PF. Typical 1–3% for distribution transformers.
Conclusion
Keep voltage regulation under 5% for equipment longevity and efficiency. Use with Voltage Drop and Power Factor tools.