What is an Electrical Fault? Definition, Types, Nature & Cause, its Effects and statistics.

Electrical Faults

Definition: Electrical Fault is defined as the abnormality of a current in the system due to which there is a failure of system equipment like generators, transformers, lines, and other small equipment.

In other words, the ‘fault’ simply means a ‘defect’. Short circuits and other abnormal conditions often occur on a power system. When there is a heavy current during the short circuit, the equipment is likely to cause damage to a piece of equipment, if there is no proper protective device installed to it.

Therefore, an automatic protective device is needed in order to isolate or cut the faulty elements as quickly as possible so that the healthy section of a system runs in normal condition.

Also read: What is Electromagnetic Relays? Working Principle & Types

Nature and Caused of Electrical faults

Some of the nature and causes of Faults in the electrical system can be due to:

  1. Insulation failure or conducting path failures.
  2. Overvoltage due to lightning or switching surges.
  3. Punctured or breaking of insulator.
  4. Certain foreign particles, such as fine cement dust or any dirt.
  5. Conducting objects falling on the overhead lines like tree branches.
  6. Poor quality of the system components or because of a faulty system design.

Causes of fault on overhead lines are direct lightning strokes, abnormal loading, storms, earthquake, etc. On the other hand, cables, transformers, generators and other equipment, the cause of faults is the failure of solid insulations due to aging, heat, moisture or overvoltage, mechanical damage, accidental contact with the earth, or earthed screens, flashover due to overvoltage, etc.

Types of fault

types of electrical faults

The types of electrical fault are:

  1. A three-phase fault: In this fault, all the three-phase may be short-circuited to the ground or it may be short-circuited without touching the ground.
  2. Single-phase to Ground (L-G) Fault: A short circuit between any one of the phases and the ground is called single-phase to ground fault.
  3. Two-phase to Ground (2L-G) Fault: A short circuit between any two of the phases and the ground is called a single-phase to ground fault.
  4. Phase to Phase Fault (L-L): A short circuit between any two phases is called single-phase to ground fault.
  5. Open-Circuited Phase: The fault that is caused by a break in the conducting part is called the open-circuited phase.

Must know: What is the Loading effect in Measurement? [with Examples]

Classification of faults

There are two broad classifications of faults:

  1. Symmetrical faults:- All three-phase fault in the system is called an asymmetrical fault.
  1. Unsymmetrical faults:- Unsymmetrical types of fault are Single-phase to Ground (L-G) Fault, Two-phase to Ground (2L-G) Fault, Phase to Phase Fault (L-L), Open-Circuited Phase.

Effects of Faults

A short circuit is the most common and dangerous type of fault, we will discuss its effect on a power system.

  1. Heavy short circuit current may cause damage to equipment due to overheating & high mechanical forces.
  2. Arc associating with short circuits may cause fire hazards.
  3. The voltage will reduce from healthy feeders, resulting in industrial loads.
  4. There will be unbalancing of supply voltages and currents, thereby heating the rotating machine.
  5. A short circuit can lead to the interruption of supply to consumers, thereby causing a loss of revenue.

Fault Statistics

Table 1: Percentage of faults in various elements in the power system.


% of Total Faults

Overhead Lines


Underground Cables








CTs, VTs, Relays, Control Equipment, etc.


Table 2: Percentage of fault that occurs in overhead lines

Types of Fault

Fault Symbol

% of Total Faults

Line to Ground



Line to Line



Double line to Ground






Note: High Grade, High speed, Reliable Proactive devices are essential requirements of a power system in order to minimize fault and abnormalities.


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