Most of the faults in the power system are mainly due to:

Overhead lines are most exposed to environmental conditions, hence most power system faults occur due to overhead lines.

There are two types of faults:

Open Circuit Faults:

The open-circuit fault happens due to the failure of one or two conductors. These faults take place in series with the line so referred to as a series fault. Such types of faults have a
strong impact on the reliability of the system. The open-circuit fault is classified as:

• Open Conductor Fault
• Two conductors Open Fault
• Three conductors Open Fault

Short Circuit Faults:

The short-circuit fault is commonly divided into symmetrical and asymmetrical types.

Symmetrical faults: Symmetrical faults do not give rise to zero sequence or negative sequence components because they are perfectly balanced, symmetrical faults only have positive sequence values.

• Three Phase Line to Ground Fault: The 3-phase to ground faults are faults in which all the phases (A, B, and C) are shorted together and are grounded.
• Three Phase Line to Line Fault: The three-phase faults occur when A, B, and C phases are shorted together but the ground is not involved.

Unsymmetrical faults:  These faults lead to unequal currents with unequal phase shifts in a three-phase system

• Single Line to Ground Fault: This type of fault occurs when one of the phases (A, B or C) is shorted with the ground.
• Line to Line Fault: This type of fault occurs when one of the phases (A, B or C) is shorted with the ground.
• Double Line to Ground Fault: This type of fault occurs when two phases are shorted with the ground together.