Free calculator estimate Switchgear Short Circuit Rating with contribution from upstream transformer and downstream rotating motor load.
Transformer
Secondary Voltage
Impedance
%
Motor Lump Load
| Secondary Rating Current | ||
| Transformer SC contribution | ||
| Motor SC contribution | ||
| Switchgear SC Current |
Basis and Assumption for Switchgear Short Circuit Rating Calculator
The calculator is based on following assumption:
- Neglect power source at primary side of Transformer,
- All cable or bus duct impedance is consider zero,
- Motor load contribution is estimated as recommended by IEEE Std 141 (chapter 4.5.4.1),
- Voltage factor c as IEC 60909 is ignored.
Clearly, the result from calculator is conservative when all above parameters accounted (i.e. cable impedance will lower short circuit current).
Transformer Impedance
Typical impedance of transformer can be found as below table
| Rated Power (kVA) | Impedance (%) |
|---|---|
| 25 to 630 | 4 |
| 631 to 1250 | 5 |
| 1251 to 2500 | 6 |
| 2501 to 6300 | 7 |
Transformer Short Circuit Current
Transformer short circuit current is calculated with data from short circuit impedance:
where:
- Isc : Short circuit at transformer secondary side
- Isec : Rating current at transformer secondary side
- Z : Transformer short circuit impedance (% or pu)
For other related calculator, pls access Transformer Rating Current Calculator or Transformer Efficiency Calculator.