Engineering CalculationTransformer Full Load Current & kVA Calculator (with fault level)
Get primary and secondary full load current from the transformer kVA, the LV fault level from its percent impedance, and a complete sizing check.
Open the calculator →Formula
IFL = (kVA × 1000) / (√3 × V)
ISC ≈ IFL × 100 / Z% (infinite source, at transformer terminals)
Worked example
1000 kVA, 11 kV / 433 V, impedance 5 %
LV current = 1,000,000 / (1.732 × 433) = 1,333 A; HV current = 52.5 A
LV fault level ≈ 1,333 × 100 / 5 = 26.7 kA
Where engineers use it
- Selecting ACB and HT breaker ratings
- Busbar and LT panel fault rating
- Transformer loading checks
How to use
- Click Open the calculator. It runs free in your browser, on desktop or phone.
- Enter your values. Units and typical ranges are shown next to each input.
- Read the result and the step-by-step working, then print or add it to your Project BOQ.
Questions
Why is the real fault current lower?
Source impedance and cable impedance reduce it. The Short-circuit Level tool adds those for a board downstream.