Transformer Short-Circuit Current
Estimate secondary symmetrical short-circuit current, short-circuit capacity, and peak current from transformer rating, secondary voltage, and impedance voltage for switchgear breaking checks.
Key points
Transformer Short-Circuit Current: Estimate secondary symmetrical short-circuit current, short-circuit capacity, and peak current from transformer rating, secondary voltage, and impedance voltage for switchgear breaking checks. Formula: I_sc = S/(√3·U·u_k) ｜ S_sc = S/u_k ｜ i_p ≈ √2·I_sc·(1+e^(−π/(X/R))). Enter parameters on the DD-CAT IDE online tool page to get results instantly, with a calculation-model diagram that updates with the inputs. The estimate is a bolted three-phase fault at the transformer secondary, ignoring source impedance, line impedance, and motor contribution; actual values are usually lower. Short-circuit capacity S_sc = S/u_k, and the current multiple is about 1/u_k; lower impedance voltage means higher fault current.
Inputs
I_sc = S/(√3·U·u_k) ｜ S_sc = S/u_k ｜ i_p ≈ √2·I_sc·(1+e^(−π/(X/R)))Calculation model (updates with parameters)
| Transformer rated current I_n | 1.443 kA | Secondary侧额定线current |
| Short-circuit capacity S_sc | 25 MVA | S/u_k = 1 MVA/4.0% |
| Symmetrical short-circuit current I_sc | 36.08 kA | Secondary端子三相短路，忽略系统阻抗andmotor反馈 |
| Short-circuit current multiple | 25.0 × I_n | ≈等于 1/u_k |
| Peak short-circuit current i_p | 88.3 kA | 按 X/R=10.0 估算，含直流分量 |
| Breaker breaking check | 未填分断能Force | 填 icb 可自动校核 |
| 1 s thermal-equivalent current | 36.08 kA | 按 1s Equivalent，实际按厂家 I²t and保护Time校核 |
Engineering notes
- The estimate is a bolted three-phase fault at the transformer secondary, ignoring source impedance, line impedance, and motor contribution; actual values are usually lower.
- Short-circuit capacity S_sc = S/u_k, and the current multiple is about 1/u_k; lower impedance voltage means higher fault current.
- Switchgear, breakers, and busbars must be checked for peak (dynamic) and I²t (thermal) withstand, not just rated current.
FAQ
- What is Transformer Short-Circuit Current for?
- Estimate secondary symmetrical short-circuit current, short-circuit capacity, and peak current from transformer rating, secondary voltage, and impedance voltage for switchgear breaking checks.
- What is the formula for Transformer Short-Circuit Current?
- Core formula: I_sc = S/(√3·U·u_k) ｜ S_sc = S/u_k ｜ i_p ≈ √2·I_sc·(1+e^(−π/(X/R))). The tool returns results instantly using this formula and the selected parameters.
- What engineering notes should I keep in mind when using Transformer Short-Circuit Current?
- The estimate is a bolted three-phase fault at the transformer secondary, ignoring source impedance, line impedance, and motor contribution; actual values are usually lower. Short-circuit capacity S_sc = S/u_k, and the current multiple is about 1/u_k; lower impedance voltage means higher fault current. Switchgear, breakers, and busbars must be checked for peak (dynamic) and I²t (thermal) withstand, not just rated current.