Ankit Alwariya

1. Submitted To:
Mr. Rajnish Mitter
Asst. Professor
Submitted By:
Ankit Kumar
17ELDEE010
A
Power Point Presentation
On
Fault Analysis & Sequence Network
Subject : Power System Protection

2. Content
 What is Fault
 Type of Fault
 Open Circuit Fault
 Short Circuit Fault
 Symmetrical Fault
 Unsymmetrical Fault
 Sequence Network
 Positive Sequence Network
 Negative Sequence Network
 Zero Sequence Network

3. • The fault is the abnormal condition of the electrical system
which damages the electrical equipment and disturbs the
normal flow of the electric current.
• The fault reduces the insulation strength between phase
conductors and earth. It also reduces the impedance
(property of circuit to oppose the flow of current) between
the conductors and earth due to which the heavy short circuit
current flows through the system and damage the power
system equipment.
What is Fault

4. The fault in the power system is mainly categorised into two
types they are:-
i. Open Circuit Fault
ii. Short Circuit Fault

5. 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:-
1. Open Conductor Fault
2. Two conductors Open Fault
3. Three conductors Open Fault

7. 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 two parts:
1. Symmetrical fault.
2. Unsymmetrical fault.

8. The faults which involve all the three phases is
known as the symmetrical fault. Such types of fault
remain balanced even after the fault. The symmetrical
faults mainly occur at the terminal of the generators. The
fault on 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 three types :-
1. Line-to-line-to-line fault.
2. Three-phase line-to-ground-fault.
Symmetrical Fault

9. 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.
Line-to-line-to-line fault

10. The three-phase line to ground fault includes all the three
phase of the system. It is very rarely occurs in the power
system. It occurs due to a breakdown of insulation between all
the phases as well as to the earth. The chance of such type of
fault is hardly 2 % to 3 % in power system.
Three Line to Ground Fault

11. 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 the one or two phases such
as L- G, L – L, L – L – G fault. The 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

12. Single line-to-ground fault
It is also called a single phase to ground fault . It mainly
occurs due to insulation breakdown between one of the
phase and earth. Single-line-to-fault is most frequently
occurs in the power system. Their chances of appearance
in the power system are 70%.

13. In 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%.

14. 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 %.
Double Line – to – Ground Fault

15. The sequence impedance network is defined as a
balance equivalent network for the balance power system
under an imagined working condition so that only single
sequence component of voltage and current is present in the
system.
Sequence impedances and sequence networks are the
fault analysing and calculating parameters in power system
networks.
Every power system have three sequence network. They are:
1. Positive Sequence Networks.
2. Negative Sequence Networks.
3. Zero Sequence Networks.

16. The positive network is considered in the analysis of
symmetrical fault. The positive sequence network is the same
as that of the sequence reactance or impedance network.

17. The negative sequence network is similar to the positive
sequence network only difference is that the negative
sequence network is of opposite sign to that of the positive
sequence impedance.

18. The zero sequence network will be internally free of the
internal fault point and the flow of current being caused by the
voltage at the fault point.

19. Thank You…