The following assumptions are usually made in fault analysis in three phase transmission lines.
- All sources are balanced and equal in magnitude & phase.
- Sources represented by the Thevenin’s voltage prior to fault at the fault point.
- Large systems may be represented by an infinite bus-bars.
- Transformers are on nominal tap position.
- Resistances are negligible compared to reactances.
- Transmission lines are assumed fully transposed and all 3 phases have same Z.
- Loads currents are negligible compared to fault currents.
- Line charging currents can be completely neglected.