An Electrical System fault can be defined as a condition in the electrical system that causes failure of the electrical equipment in the circuit such as Generators, Transformers, Busbars, Cables and all other equipment in the system that operates at given voltage level.The fault is caused either by insulation failure or by conducting path failure.
- The failure of insulation results in a short circuit which is very harmful as they may damage some equipment of power system.
- Most of the fault in power system i.e transmission and distribution line is caused by overvoltage due to lightning or switching surge or by external conducting object falling in overhead line.
- Overvoltage due to lightning or switching surge cause flashover surface of insulator resulting in short circuit. Sometimes insulator gets puncture or break. Sometime certain foreign particle such as cement dust, or any type of foreign dust may cause layer in the insulator. Sometimes bird, tree etc fall on the transmission line or pole cause fault.
Types of Fault
Symmetrical Fault
- LLL or LLLG Fault
Unsymmetrical Fault
- LG Fault
- LLG Fault
- LL Fault
- Open Circuit Fault
SYMMETRICAL FAULT
- A three-phase fault is called symmetrical type of fault. In this fault, all the phase become short-circuited.
- There may be two situations. All the phase are a short circuit to ground or without in involving the ground.
- A three-phase short circuit is generally treated as a standard fault to determine the standard level fault.
UNSYMMETRICAL FAULT
- Single phase to ground, two-phase to the ground, phase to phase short circuit, one conductor open circuit and two conductor open circuit are involving in Unsymmetrical fault
- Single phase to ground (L-G), two-phase to ground (2L-G) and phase to phase short circuit(L-L) is also known as shunt fault where one conductor open circuit and two conductor open circuit are known as the series fault.
Single phase to ground (L-G) Fault:
- A short circuit between any phase of the conductor to the ground is called L-G fault.
- It may occur when the insulation become fail in line and ground conductor and touch with together.
Two-phase to ground (2L-G) Fault:
Phase to phase (L-L) Fault:
One conductor open or two conductors open circuit Fault:
- This type of fault caused by the break in conducting path. Such fault occurs when one or more conductors are the break due to any reason.
- Due to the opening of one or two-phase, unbalance current flow in the system, thereby heating rotating machine.
Effect of Fault
- Heavy short-circuit current may cause damage to equipment or any other element of the system due to over-heating and high mechanical force set up due to heavy current.
- Arcs associated with short circuit may cause the fire hazard. Such fires, resulting from arching, may destroy the faulty element of a system.
- There is also a possibility of the fire spreading to another part of the system.
- There may be the reduction in the supply voltage of the healthy feeders, resulting in loss of industrial load.
- A short-circuit may cause unbalance of supply voltage and current thereby heating in rotating machine.
- They may be the loss of system stability. Individual generator in power system may loss own synchronism, they result in complete shutdown of the system.
- The fault may cause interruption of supply to the consumer.
Fault Occurrence in Power System:
- Percentage distribution of fault in various elements of power system
- Overhead Line - 50%
- Underground Cable - 9%
- Transformer - 10%
- Generator 7%
- Switchgear - 12%
- Relay, CT, PT et - 12%
- Frequency occurrence of different type of fault on overhead lines
- LG Fault - 85%
- LL Fault - 8%
- LLG Fault - 5%
- LLL/LLLG Fault - 2%
- Overhead Line - 50%
- Underground Cable - 9%
- Transformer - 10%
- Generator 7%
- Switchgear - 12%
- Relay, CT, PT et - 12%
- LG Fault - 85%
- LL Fault - 8%
- LLG Fault - 5%
- LLL/LLLG Fault - 2%
🔽 Frequently Asked Questions (FAQs)
1. What is an electrical fault in a power system?
An electrical fault is an abnormal condition that disrupts the normal flow of current in the system. It often causes damage to equipment like transformers, generators, cables, and busbars. Most faults are due to insulation failure or conducting path breakdown.
2. What are the main causes of faults in power systems?
Faults can be caused by overvoltage (due to lightning or switching surges), insulation failure, external objects like birds or tree branches, pollution (dust, cement particles), or mechanical damage to conductors and insulators.
3. What is the difference between symmetrical and unsymmetrical faults?
A symmetrical fault affects all three phases equally, usually a 3-phase short circuit. Unsymmetrical faults involve one or two phases, such as single line-to-ground (L-G), line-to-line (L-L), or double line-to-ground (2L-G) faults, and are more common in practice.
4. What is a line-to-ground (L-G) fault?
An L-G fault occurs when one phase conductor comes in contact with the ground. This is the most common type of fault and is often caused by insulation breakdown or contact with grounded objects like trees or poles.
5. How does a two-phase to ground (2L-G) fault occur?
A 2L-G fault occurs when two phase conductors come into contact with the ground. It is more severe than an L-G fault and causes higher fault currents, leading to greater system stress and potential equipment damage.
6. What are series faults in power systems?
Series faults are caused by open circuits in one or more phases due to broken conductors or equipment failure. They result in unbalanced current flow, which can cause heating and damage to rotating machines.
7. What are the effects of electrical faults on a power system?
Faults can cause heavy short-circuit currents, equipment damage, voltage drop in healthy feeders, fire hazards due to arcing, system instability, generator desynchronization, and power interruptions to consumers.
8. Which components of a power system are most vulnerable to faults?
Transmission lines, transformers, and insulators are the most exposed and vulnerable to electrical faults. Environmental conditions and mechanical stress increase their likelihood of failure.
9. How frequently do different types of faults occur?
According to studies, single line-to-ground faults are the most frequent (about 70%), followed by line-to-line faults, double line-to-ground faults, and three-phase symmetrical faults which are rare but severe.
10. How can electrical faults be prevented or minimized?
Using protective relays, lightning arresters, proper insulation, regular maintenance, tree trimming near lines, and grounding systems can greatly reduce the occurrence and impact of electrical faults.