Name: Abdelrahman Ashraf
ID: 9587
PME406
Types of faults in power system
Eng. Youssef asaker
Types of Faults in Power System
The fault in the power system is defined as the defect in the power system
due to which the current is distracted from the intended path. The fault
creates an abnormal condition which reduces the insulation strength
between the conductors. The reduction in insulation causes excessive
damage to the system. The fault in the power system is mainly
categorized into two types they are.
1. Open Circuit Fault
2. Short Circuit Fault.
The different types of power system faults are shown below in the image.
The faults in the power system may occur because of the number of
natural disturbances like lightning, high-speed winds, earthquakes, etc. It
may also occur because of some accidents like falling off a tree, vehicle
colliding, with supporting structure, aero plane crashing, etc.
1. Open Circuit Fault
The open circuit fault mainly occurs because of the failure of one or two
conductors. The open circuit fault takes place in series with the line, and
because of this, it is also called the series fault. Such types of faults affect
the reliability of the system. The open circuit fault is categorised as
• Open Conductor Fault
• Two conductors Open Fault
• Three conductors Open Fault.
The open circuit fault is shown in the figure below.
2. Short-Circuit Fault
In this type of fault, the conductors of the different phases come into
contact with each other with a power line, power transformer or any other
circuit element due to which the large current flow in one or two phases of
the system. The short-circuit fault is divided into the symmetrical and
unsymmetrical fault.
Symmetrical Fault
The faults which involve all the three phases are known as the
symmetrical fault. Such types of faults remain balanced even after the
fault. The symmetrical faults mainly occur at the terminal of the
generators. The fault in the system may arise on account of the resistance
of the arc between the conductors or due to the lower footing resistance.
The symmetrical fault is sub-categorized into line-to-line-to-line fault and
three-phase line-to-ground-fault.
a. Line – Line – Line Fault –
Such types of faults are balanced, i.e., the system remains
symmetrical even after the fault. The L – L – L fault occurs rarely, but
it is the most severe type of fault which involves the largest current.
This large current is used for determining the rating of the circuit
breaker.
b. L – L – L – G (Three-phase line to the ground fault)
c. – The three-phase line to ground fault includes all the three phase of
the system. The L – L – L – G fault occurs between the three phases
and the ground of the system. The probability of occurrence of such
type of fault is nearly 2 to 3 percent.
Unsymmetrical Fault
The fault gives rise to unsymmetrical current, i.e., current differing in
magnitude and phases in the three phases of the power system are known
as the unsymmetrical fault. It is also defined as the fault which involves
one or two phases such as L- G, L – L, L – L – G fault. Unsymmetrical
makes the system unbalanced. It is mainly classified into three types. They
are.
1. Single Line-to-ground (L – G) Fault
2. Line-to-Line Fault (L – L)
3. Double Line-to-ground (L – L – G) Fault
Unsymmetrical faults are the most common types of faults that occur in
the power system.
Single Line-to-Line Ground –
The single line of ground fault occurs when one conductor falls to the
ground or contacts the neutral conductor. 70 – 80 percent of the fault in
the power system is the single line-to-ground fault.
Line – to – Line Fault –
A line-to-line fault occurs when two conductors are short circuited.
The major cause of this type of fault is the heavy wind. The heavy wind
swinging the line conductors which may touch together and hence
cause short-circuit. The percentage of such type of faults is
approximately 15 – 20%.
Double Line – to – line Ground Fault
In double line-to-ground fault, the two lines come in contact with each
other along with the ground. The probability of such types of faults is
nearly 10 %.
The symmetrical and unsymmetrical fault mainly occurs in the terminal of
the generator, and the open circuit and short circuit fault occur on
the transmission line.
