What is voltage regulation of a line?

Voltage regulation (VR%) measures how much the receiving-end voltage changes between no-load and full-load conditions, expressed as a percentage of the full-load voltage. A lower VR% indicates a stiffer, better-regulated line.

What is the voltage regulation formula?

VR% = ((Vs − Vr) / Vr) × 100, where Vs is the sending-end voltage and Vr is the receiving-end (full-load) voltage. Both must be in the same units (V or kV).

What is an acceptable voltage regulation percentage?

For distribution systems, VR% is typically kept below 5%. Transmission lines may tolerate up to 10%. Values above 10% usually indicate undersized conductors or excessive line length.

Does phase (single vs. three-phase) affect the VR calculation?

The VR% formula is the same for both. For three-phase systems, use line-to-line voltages (or consistently use line-to-neutral voltages) — just be consistent between Vs and Vr.

Why can voltage regulation be negative?

Negative VR% occurs when the receiving-end voltage exceeds the sending-end voltage. This can happen with leading power-factor (capacitive) loads due to the Ferranti effect on lightly loaded long lines.

Voltage Regulation Line Calculator

Name: Voltage Regulation Line Calculator
Availability: InStock
Author: Nham Vu

Enter sending-end and receiving-end voltages to calculate the voltage regulation percentage of a power line.

Line Voltages

System Type

Single-phase Three-phase (line-to-line)

Sending-End Voltage (Vs)

Receiving-End Voltage — Full Load (Vr)

Quick Examples

Results

Enter voltages and click Calculate

Formula Reference

VR% = (Vs − Vr) / Vr × 100

Standard voltage regulation formula. Vs = sending-end voltage, Vr = receiving-end full-load voltage.

Typical Limits

≤ 5% — Distribution feeders (typical utility standard)
5–10% — Marginal; consider conductor upgrade
> 10% — Poor; voltage regulators or capacitors needed

Sign Convention

Positive VR% means voltage drops along the line (inductive/resistive load). Negative VR% indicates a voltage rise — possible with capacitive loads or lightly loaded long lines (Ferranti effect).

Summary

Enter sending-end and receiving-end voltages to calculate the voltage regulation percentage of a power line.

How it works

Enter the sending-end voltage at the source side of the line.
Enter the receiving-end voltage at the load side under full load.
The calculator applies VR% = ((Vs − Vr) / Vr) × 100.
Results include VR%, voltage drop, and a qualitative rating.

Use cases

Check if a distribution feeder meets utility voltage regulation standards.
Compare voltage regulation for different conductor sizes or line lengths.
Verify transformer tap settings keep VR within acceptable limits.
Analyze transmission line performance under varying load conditions.
Size voltage regulators or capacitor banks to correct poor VR.

Frequently Asked Questions

Last updated: 2026-06-11 · Reviewed by Nham Vu