Short-circuit current at the transformer

Calculated on

Short-circuit current at the transformer

Inputs

Rated apparent power

kVA

Nominal voltage, low-voltage side

V

Short-circuit voltage uₖ

%

Result

Initial symmetrical short-circuit current I″k

kA

Rated current

A

Ratio I″k / Iᵣ

Formula

• Iᵣ = Sᵣ / (√3 · Uᵣ)
• I″k = Iᵣ / (uₖ / 100)

Assumptions and standards

• The calculation assumes an infinitely strong upstream source, neglecting its impedance, the real network limits the current further, so the result is on the safe side.
• Only the transformer is considered, not cables, busbars or motor contribution.
• The result is the RMS value I″k, which governs the rated breaking capacity of protective devices. The peak short-circuit current iₚ, the crest of the first half-cycle, governing the dynamic strength of busbars, follows from iₚ = κ · √2 · I″k with κ ≈ 1.8 and is therefore about 2.5 times as high.
• A binding design requires calculation to IEC 60909.

A guide, not a design to standard. We give no warranty for the correctness of the results, the applicable standards and case-by-case verification govern.

FISEKON GmbH – Fischer Elektrokonstruktion · https://fisekon.com