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Transformer Calculator

Select the parameters and enter their values. The calculator will instantly determine voltage, current, and other transformer-related terms.

I Want to Find:

Primary Voltage

V ▾

Primary Winding,Primary

V ▾

Primary Voltage:

Primary Voltage,Primary:

Primary Current:

Related

The transformer calculator allows you to compute the primary and secondary voltages and full-load currents (Amps) for both single-phase and three-phase transformers. It works for ideal and real transformers, determines transformer type from the turns ratio, and helps estimate EMF and transmission losses, including:

Eddy Current Loss
Total Iron Loss
Total Copper Loss
Hysteresis Loss

What Is a Transformer?

A transformer is an electrical device that transfers AC power from one circuit to another. It operates on Faraday’s Law of Electromagnetic Induction and can either step up or step down voltage levels.

Symbol:

Transformer Formulas:

The transformer calculator uses the following formulas to model its electrical behavior.

Voltage Equation:

\(V_p = \frac{N_p}{N_s} \times V_s\)

Where:

\(V_p\) = Voltage across the Primary Coil
\(V_s\) = Voltage across the Secondary Coil
\(N_p\) = Number of turns on the Primary Coil
\(N_s\) = Number of turns on the Secondary Coil

Current Equation:

\(I_s = I_p \times \frac{N_p}{N_s}\)

Full-Load Current:

Single-Phase:

\(Full\text{-}Load\ Current\ (Amps) = \frac{kVA \times 1000}{V}\)

Three-Phase:

\(Full\text{-}Load\ Current\ (Amps) = \frac{kVA \times 1000}{\sqrt{3} \times V}\)

Turns Ratio:

\(Turns\ Ratio = \frac{N_1}{N_2} = \frac{V_1}{V_2} = \frac{I_2}{I_1}\)

Example:

Consider a single-phase transformer rated at 56 kVA, with a primary voltage of 350 V and a secondary voltage of 120 V. Calculate the turns ratio and full-load currents for an ideal transformer.

Solution:

Turns ratio:

\(Turns\ Ratio = \frac{V_1}{V_2} = \frac{350}{120} \approx 2.917\)

Primary Full-Load Current:

\(I_p = \frac{56 \times 1000}{350} \approx 160 \text{ Amps}\)

Secondary Full-Load Current:

\(I_s = \frac{56 \times 1000}{120} \approx 466.67 \text{ Amps}\)

Related: Always consider calculating Voltage Drop and Amperage across circuits for accurate transformer analysis.

How To Size a Transformer?

To size a transformer, multiply the required load current by the secondary voltage:

VA = Secondary Voltage × Required Current

Note: Do not load a transformer above 80% of its KVA rating. To find the minimum KVA needed, divide the calculated VA by 0.8. Always confirm values with a licensed electrician or electrical engineer.