• The Importance of Short Circuit Knowledge

• Types and Examples of Faults

• Fault Parameters

• The Per-Unit (PU) System

• KVA or MVA Method Fault Calculation & Coordination

• Symmetrical Components

• Sequence Impedances of Network Components

  • Generators and Motors

  • Transformers

  • Lines

• Asymmetrical Three Phase Fault Analysis

  • Phase to Ground

  • Phase to Phase

  • Double Phase to Ground

  • Three Phase

  • Short Circuit Calculations

  • Real Time Fault Recorder Analysis

The fault analysis of a power system is required in order to provide information for the selection of switch-gear, setting of relays and stability of system operation. These faults, may involve all three phases in a symmetrical manner, or may be asymmetrical where usually only one or two phases may be involved.  Faults may also be caused by short-circuits to earth or between live conductors, or by broken conductors. Sometimes simultaneous faults may occur involving both short-circuit and broken conductors. Balanced three phase faults may be analysed using an equivalent single phase circuit. With asymmetrical three phase faults, the use of symmetrical components helps to reduce the complexity of the calculations.

Network Components (Generators, Transformers & Lines) may be represented by their equivalent circuits for each of the three symmetrical components. Generators may be represented by the star-connected equivalent with possibly a neutral to earth connection using sub-transient, transient or steady state internal impedances. Transformers also may be represented by simple equivalent circuits for each of the three symmetrical components but winding configurations will determine the nature of zero-sequence components and their subsequent equivalent circuit.

Asymmetrical fault analysis is made easy with the use of symmetrical components. Each fault type has a predetermined equivalent circuit for each component. Due to the symmetry of components simple single phase analysis is now possible for each circuit. The desired result is now a simple vector sum of all components. Fault results are now predictable including the flow of ground or zero sequence currents in a system including their path through all three phase transformer configurations. Equipment ratings are now possible including the settings of protection relays.