Free Tool

Electrical Transformer Current Calculator

Calculate the rated current of any transformer from its power and voltage in seconds — for single-phase and three-phase transformers, with the formula used shown.

Approximate Current

The result is approximate and represents the theoretical rated current. Always check the transformer nameplate and actual operating conditions (temperature, cooling mode, altitude) before making any engineering decision.

Equations Used

For a single-phase transformer:

I = S / V

For a three-phase transformer:

I = S / (√3 × VL)

where S is the apparent power in volt-amperes (VA) and V is the voltage in volts — the calculator automatically converts kVA, MVA, and kV.

Worked Example

A three-phase transformer rated at 1000 kVA, 13.8 kV:

I = 1,000,000 / (√3 × 13,800) ≈ 41.8 A

And the same transformer on its 400 V low-voltage side: I = 1,000,000 / (√3 × 400) ≈ 1443 A — note the inverse relationship between voltage and current.

Related Topics

How to Calculate Transformer Current Why Is Transformer Capacity Rated in Kilovolt-Amperes (kVA)? What Does the Turns Ratio Mean in Transformers? How to Read a Transformer Nameplate Transformer Interview Questions

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