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.
1. Type of 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);
A short circuit between any two phase and earth is called as the double
line to ground fault.
Phase to phase (L-L) fault; A short circuit between to line
is called 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.
2. Effect of Fault
Effect of fault in power system is following
- 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.
3. Fault Occurrence
Percentage distribution of fault in various elements of
power system
Frequency occurrence of different type of fault on overhead
lines
