Electrical fault

 Fault - A fault in a electrical equipment it's defined as a defect in the electrical circuit due to which current is diverted from the intended path. 

Short circuit fault 

* Resistance zero 

* current infinite 

Open circuit 

* Resistance infinite 

* Current zero 

Main kind of fault 

The most common and dangerous fault that occur in a power  system is the short circuit or short fault, they occur as a result of breakdown in the insulation of current carrying phase conductor relative to earth or in the insulation between phases. 

In three phase AC power circuit the short circuit fault can be classified as two part 

1) unsymmetrical fault 

2) symmetrical fault 

* unsymmetrical fault 

a) Single phase to ground fault [LG] - due to breakdown of insulation  between one of the phase and earth 

The occurrence of this fault is 70%

This is the least severe fault 

b)  Phase to phase or line to line fault [LL fault ] - due to breakdown of insulation between either of the two phase 

The chance of occurring this fault is 15%

c)  Two phase to ground fault [LLG fault] - due to breakdown of insulation between two phase and the earth 

The chance of occurring this fault is 10%

 Symmetrical fault 

a)  All the three phase short circuit / phase to phase to phase [LLL fault ] - due to breakdown of insulation between the all three phases .

The chance of occurring this fault is 2 to 3%

This is the most severe fault 

b)  All three phase to ground fault [LLLG fault ] - due to breakdown of insulation between all the three phase to a ground 

The chance of occurring this fault is 2 to 3 %

LG   }-- unsymmetrical fault 

LL    } -- unsymmetrical fault 

LLG ] -- unsymmetrical fault 

LLL } --- symmetrical fault 

LLLG }--- symmetrical fault