MAXScanner calculator widget

Transformer Fault Current Calculator — kA from kVA & %Z

Editable live calculator

Change any input — the result updates immediately

No hidden assumptions. Inputs, units and the working stay visible so you can check the calculation.

Transformer phase Transformer rating (kVA) Use the transformer nameplate apparent-power rating.Secondary voltage (V) Three-phase: line-to-line RMS voltage. Single-phase: voltage across the modeled secondary.Nameplate impedance (%) Enter percent, e.g. 5.75 for 5.75%.

Calculated result

27.824 kA

Rated current: 1,391.21 A

Fault-current multiplier: 20×

Transformer-limited fault level: 20 MVA

Equivalent transformer impedance: 8.611 mΩ

Show the working

1. Rated current = 1,000×1000 ÷ (√3×415) = 1,391.205 A.
2. Per-unit impedance = 5 ÷ 100 = 0.05.
3. Terminal fault current = 1,391.205 ÷ 0.05 = 27,824.11 A = 27.824 kA.
4. Fault level = 1,000 kVA × 100 ÷ 5 = 20 MVA.

Transformer-terminal infinite-bus estimate only. It excludes utility/source impedance, conductor and bus impedance, motor contribution, grounding/zero-sequence networks, X/R asymmetry and arc-flash energy. Use the actual nameplate %Z and a proper short-circuit study for equipment ratings.

More actions

Shared links reopen these inputs. Recent and saved calculations stay in this browser unless you clear site data.