Power and energy

Transformer full-load current calculator

Calculate nominal primary and secondary line current from transformer kVA, voltages, phase arrangement and loading.

Calculate

Transformer nameplate and loading
kVA
%
100% represents the entered nameplate kVA.
V
V

Worked example

Secondary line current, each line

 A

Primary line current, each line
 A
Apparent power at the entered loading
100 kVA
Voltage ratio, primary to secondary
27.5 :1

Three-phase, line-to-line voltages. The entered loading is within the nameplate kVA; permissible duty remains manufacturer-specific.

Underlined figures are rounded. Select one to copy its full value.

Method and assumptions

Formula

1φ: I = kVA × 1000 ÷ V; 3φ: I = kVA × 1000 ÷ (√3 × VLL)

Rated kVA is apparent power, so power factor and efficiency are not used to calculate nominal winding current from the nameplate rating.

Limits of this result

  • This calculates nominal line current from apparent-power loading; it does not model losses, inrush, harmonics or unbalance.
  • Voltage taps, vector group, cooling, impedance, protection and loading duty remain transformer-specific.
  • Do not use this result alone to size or protect a transformer or conductor.

Technical sources

  1. What is the formula to determine the kVA on a transformer?Schneider Electric · modified 2025-12-15

Put the value to work

Read the related engineering guidance, or carry this task into System Builder to identify the signal path and EpiSensor products.

On this page