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Purpose of fault analysis; fault types

Short answer

Purpose: determine maximum fault current/MVA for breaker selection, relay coordination, equipment withstand, reactor sizing, and stability analysis. Types: symmetrical (3-phase), unsymmetrical (L-G, L-L, L-L-G), and series (open conductor) faults.

What is the purpose of fault analysis in electric power system? What types of fault occur in a power system network?

Fault analysis is the calculation of the currents and voltages in a power network during abnormal (fault) conditions such as short circuits and open conductors.

Purpose of fault analysis

  • To find the maximum fault current and fault MVA so circuit breakers and fuses of the right breaking capacity can be chosen.
  • To find minimum and maximum fault currents for setting and coordinating protective relays.
  • To check that bus bars, cables, CTs and other equipment can withstand the thermal and mechanical stresses.
  • To size current-limiting reactors and neutral grounding impedances.
  • To provide fault conditions for transient stability studies.

Types of faults

1. Symmetrical (balanced) fault

  • Three-phase fault (L-L-L) or three-phase to ground fault (L-L-L-G). All phases remain balanced; about 2–5% of faults, but usually the most severe. Analysed with the per phase (positive sequence) network.

2. Unsymmetrical (shunt) faults — analysed with symmetrical components:

FaultApprox. occurrence
Single line to ground (L-G)70–80%
Line to line (L-L)15–20%
Double line to ground (L-L-G)10%

3. Series (open conductor) faults

  • One conductor open or two conductors open (e.g. broken conductor, blown fuse in one phase, single-pole breaker operation). They cause unbalance but not heavy current.

Faults can also be classed as temporary (e.g. flashover due to lightning, cleared by reclosing) or permanent (e.g. broken conductor, insulator failure).

✓ Answer checked by Claude Sonnet 5.5

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