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:

- I
_{sc}: Short circuit at transformer secondary side - I
_{sec}: 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.