Secondary Voltage of a Transformer Calculator

Transformer Secondary Voltage Calculator

Phase Type

Primary Connection

Secondary Connection

Primary Line Voltage

Primary Turns

Secondary Turns

Tap Adjustment %

Full Load Regulation %

Load Percentage %

External Voltage Drop

Rated kVA

Minimum Acceptable Voltage

Maximum Acceptable Voltage

Decimal Places

Example Data Table

Primary Voltage	Primary Turns	Secondary Turns	Tap %	Regulation %	Estimated Use
480 V	1000	250	0	3	120 V control transformer estimate
2400 V	2000	100	2.5	4	Low voltage distribution check
11000 V	5500	240	-2.5	5	Service transformer review

Formula Used

The ideal transformer relation is:

Vs / Vp = Ns / Np

So the secondary phase voltage is:

Vs = Vp × Ns ÷ Np

For three phase systems, the calculator converts line voltage to phase voltage before applying the winding ratio. It then converts the result back to secondary line voltage. Tap adjustment and load regulation are then applied.

Tap adjusted voltage = Ideal secondary voltage × (1 + tap % ÷ 100)

Loaded voltage = Tap adjusted voltage ÷ (1 + load drop % ÷ 100) − external drop

How to Use This Calculator

Enter the primary line voltage, primary turns, and secondary turns. Choose the phase type and winding connections. Add tap percentage if the transformer tap is not at nominal position. Enter regulation and load percentage when you want a loaded estimate. Add rated kVA if you also want estimated secondary current. Use voltage limits to check whether the result is within your required range.

Understanding Secondary Voltage

A transformer changes voltage by magnetic coupling between two windings. The secondary voltage depends mainly on the primary voltage and the turns ratio. If the secondary winding has fewer turns, the output voltage falls. If it has more turns, the output rises. This calculator expands that simple rule for practical planning.

Why Turns Ratio Matters

Turns ratio compares secondary turns with primary turns. A ratio below one means step down service. A ratio above one means step up service. The ideal output assumes no losses, no tap shift, and no load drop. Real equipment may deliver slightly different voltage because winding resistance, leakage reactance, and supply variation create change.

Using Line Connections

Three phase transformers need extra care. Wye and delta connections change the relationship between line voltage and phase voltage. The calculator first converts primary line voltage into phase voltage. It then applies the winding ratio. Finally, it converts the secondary phase value back to line voltage. This gives a useful line to line estimate for panels, motors, drives, and distribution work.

Tap and Regulation Effects

Tap settings adjust voltage before load is considered. A positive tap raises the calculated secondary output. A negative tap lowers it. Regulation describes how much voltage may sag under rated load. The load percentage lets you estimate partial load conditions. Added external drop can represent cable drop or known downstream loss. These options make the result more realistic than a basic ratio calculation.

Reading the Output

Review the ideal voltage first. Then review tap adjusted voltage. The loaded voltage shows the expected delivered value. The status line compares this value with your entered limits.

Planning Use

Use the result for early design checks, training, troubleshooting, and documentation. Compare the loaded voltage with equipment nameplate limits. Confirm whether the system is step up or step down. Review the volts per turn value to see winding stress trends. Check the secondary current only when rated kVA is known.

Safety Notes

This tool is an estimator. It cannot replace nameplate data, manufacturer tables, field tests, or code review. Transformers can store dangerous energy. Work should follow local electrical rules and lockout procedures. Use meters, protective equipment, and qualified supervision before touching live circuits.

FAQs

What is secondary voltage?

Secondary voltage is the voltage available at the transformer output winding. It depends on primary voltage, winding turns, connection style, tap setting, and load behavior.

What is the basic transformer voltage formula?

The basic formula is Vs / Vp = Ns / Np. Secondary voltage equals primary voltage multiplied by secondary turns, then divided by primary turns.

Does this calculator support three phase transformers?

Yes. It includes single phase, wye, and delta options. The tool converts line and phase voltage where needed before showing the secondary line value.

What does tap adjustment mean?

Tap adjustment changes the effective transformer voltage ratio. A positive tap raises the estimated output. A negative tap lowers the estimated output.

What is voltage regulation?

Voltage regulation estimates voltage change from no load to load. Higher regulation usually means more voltage sag as load increases.

Why enter rated kVA?

Rated kVA lets the calculator estimate secondary current. Without kVA, voltage can still be calculated, but current cannot be estimated reliably.

Can this replace nameplate data?

No. Always check the transformer nameplate, manufacturer data, and field measurements. This calculator is for estimates and planning support.

Why is my loaded voltage lower than ideal voltage?

Loaded voltage is lower because regulation and external drop are applied. Winding impedance, cable length, and load level can reduce delivered voltage.