The calculation, without hidden assumptions
Check transformer secondary-voltage regulation two ways: directly from comparable no-load and loaded readings, or with the standard first-order R/X and power-factor approximation. Keep transformer internal regulation separate from feeder voltage drop.
How to use this calculator
Choose measured mode when you have comparable secondary-terminal readings.
For measured mode, keep primary voltage, tap position and measurement location consistent.
Choose equivalent-circuit mode when %R and %X are available from reliable transformer test data.
Enter load power factor, lagging or leading behavior and load percentage for the approximation.
Read the signed result: negative regulation can occur with sufficiently leading load and should not be silently clamped to zero.
Where people use it
- •Checking transformer acceptance or field-test secondary voltage change.
- •Estimating regulation from short-circuit/equivalent-circuit parameters.
- •Comparing lagging and leading power-factor effects.
- •Separating transformer internal regulation from downstream conductor voltage drop.
Example: 230 V no-load, 220 V loaded
Measured regulation = (230 − 220) ÷ 220 × 100 = 4.545%. With %R = 1.2, %X = 4.8 and PF 0.8 lagging, the first-order full-load estimate is 1.2×0.8 + 4.8×0.6 = 3.84%.
What the result does not assume
- •Measured-mode voltages must be comparable RMS quantities at the same secondary terminals and operating reference; do not mix line-line with line-neutral readings.
- •The R/X method is a first-order approximate transformer model. Exact phasor regulation and certified performance require the applicable test method and transformer data.
- •Nameplate %Z alone does not uniquely determine regulation because resistance/reactance split and load power factor matter.
- •Transformer regulation is not feeder or branch-circuit voltage drop; source variation, tap changers and downstream conductors are outside this calculation.
- •Different references may use a no-load-voltage denominator for a differently defined regulation convention. This owner explicitly uses loaded voltage for the direct measurement formula and shows that convention.
Frequently asked questions
What is transformer voltage regulation?+
It describes how secondary terminal voltage changes between defined no-load and loaded conditions while the primary reference is held constant.
Why does MAXScanner show the denominator?+
Regulation conventions can be ambiguous. This calculator explicitly uses loaded voltage in the direct formula so results are reproducible and the convention is visible.
Can transformer regulation be negative?+
Yes. A sufficiently leading capacitive load can make the approximate reactive term subtract enough to produce negative regulation, meaning loaded voltage can rise relative to the reference.
Is transformer %Z the same as voltage regulation?+
No. %Z is impedance magnitude. Regulation depends on its resistance/reactance components and load power factor, so identical %Z values can produce different regulation.
Is this the same as cable voltage drop?+
No. This calculator models the transformer itself. Use the dedicated voltage-drop calculator for conductor and feeder drop.
Can I use this result as a compliance certificate?+
No. Use applicable standards, manufacturer data and prescribed test conditions for contractual or compliance decisions.
Semantic next steps
Continue the calculation
These links move to a different input, formula or project stage rather than a keyword variation of this page.
Transformer kVA Calculator — Single & Three Phase Load Sizing
Calculate load kVA from voltage and current for single or balanced three-phase systems, then apply an explicit spare-capacity percentage.
OpenTransformer Turns Ratio Calculator — Voltage, Current & Apparent Power
Solve an ideal transformer from primary and secondary turns, primary voltage and current. Get turns ratio, secondary voltage/current, apparent power and step-up or step-down classification.
OpenPower Factor Correction Calculator — Required Capacitor kVAR
Calculate ideal capacitor reactive power needed to move a real-power load from an initial to a target displacement power factor.
OpenVoltage Drop Calculator — Forward & Reverse Electrical Solve
Calculate voltage drop and percentage drop, or reverse-solve maximum run, current or conductor area from explicit resistivity and circuit assumptions.
OpenTransformer Efficiency Calculator — Load, Core & Copper Losses
Calculate transformer efficiency at partial load from rated kVA, power factor, core loss and full-load copper loss, with maximum-efficiency loading and 25–100% scenarios.
OpenTransformer All-Day Efficiency Calculator — 24-Hour Load Profile
Calculate transformer all-day energy efficiency from a multi-period load profile, core loss and full-load copper loss, with kWh loss breakdown and duty-cycle diagnostics.
OpenOhm's Law Calculator — Volts, Amps, Ohms and Watts
Calculate voltage, current, resistance and power from any two positive electrical values using Ohm's Law and Watt's Law.
OpenReactance Calculator — Inductive XL, Capacitive XC & LC Resonance
Calculate inductive or capacitive reactance, reverse-solve frequency or component value, or find ideal LC resonant frequency with engineering-unit inputs and visible formulas.
OpenMore in this calculator collection
Browse nearby calculators in the same topic cluster so related pages reinforce each other instead of sitting as isolated URLs.
Free publisher widget
Put this calculator on your website
Give readers the live calculator without rebuilding the math. Copy the responsive embed in one click, or customize width, height, border and corner radius before publishing. The branded MAXScanner attribution stays visible.
Calculator embed HTML
Paste this code into your page. Focus the code box to select it manually.
Keep the result connected to the real job
MAXScanner keeps the formula and assumptions beside the result so you can verify the number before using it in a drawing, estimate, specification, worksheet or document. Where a supplier, manufacturer, drawing or applicable standard owns a requirement, that source remains authoritative.