Types of faults in Power System

A fault occurs when two or more conductors come in contact with each other. these faults may be due to Sudden failure of equipment

• Accidental damage
• Short Circuit
• Insulation failure

The faults in 3-Phase Power System are classified into two main categories

• Symmetrical Faults   
• Unsymmetrical fault

Symmetrical Faults   

The fault which gives rise to symmetrical fault currents (i.e. equal fault currents with 120 displacement) is called a Symmetrical fault. The most common example of symmetrical fault is when all three conductors of three phase line come together simultaneously into a short circuit condition, more clear picture is shown in figure.

Unsymmetrical faults

Those faults which give rise to unsymmetrical currents (i.e. unequal line currents with unequal displacement) are called unsymmetrical faults. The unsymmetrical faults may take one of the following forms:

     a)       Single line to ground fault        b) Line-to-Line fault      c) Double line-to-ground fault

The majority of faults on power system are of unsymmetrical nature; the mist common is short circuit form one line to ground fault. more clear picture is shown in figure.