Calculates the short circuit fault current of a 3-phase AC generator.

The generator short circuit fault current calculator uses a simplified method to calculate the fault current from the following parameters:

**Rated (Ur)**. The rated phase-to-phase voltage of the generator in V.**Rating (Sr).**The rating power of the generator in kVA.**Impedance (Zk)**. The short circuit impedance of the generator as a percentage. The short circuit impedance can be specified for the sub-transient, transient or steady state phase of the generator fault. For simplification the resistance can be ignored and only the reactance can be considered. Typical reactance values are shown below.

Phase | Equation | Typical reactance (%) | Typical time |

Sub-transient | 10 – 20% | 10ms | |

Transient | 15 – 25% | 250ms | |

Steady state | 200 – 350% | > 250ms |

The generator short circuit current is calculated as follows:

\(I_{fault-actual}= \dfrac{S_{r} \times 100}{\sqrt{3} \times U_{r} \times Z_{\%}}\)Where,

- \(I_{fault-actual}\) is the fault current in kA.
- \(S_{r}\) is the generator power rating in kVA.
- \(U_{r}\) is the generator rated voltage in V.
- \(Z_{\%}\) is the generator impedance in base percentage.

This is basically a combination of the steps in the per-unit calculation method:

**Step 1:** Calculate the per unit fault current:

Note that \(Z_{pu} = \dfrac {Z_{\%} }{100}\)

**Step 2:** Calculate the nominal base current:

\(I_{nominal-base}= \dfrac{S_r}{\sqrt{3} \times U_r}\)

**Step 3:** Calculate the actual fault current: