Minor project

Simulation and Protection of
Long Transmission Line
A Minor Project Report
Submitted in Partial Fulfillment of the Requirements for the Degree
of
BACHELOR OF TECHNOLOGY
IN
ELECTRICAL ENGINEERING
By
Vasav Shethna (13BEE110)
Tushar Shingala (13BEE111)
Under the Guidance of
Prof. Shankar Godwal
DEPARTMENT OF ELECTRICAL ENGINEERING
INSTITUTE OF TECHNOLOGY
NIRMA UNIVERSITY
Ahmedabad 382 481
November 2016

INSTITUTE OF TECHNOLOGY
NIRMA UNIVERSITY
DEPARTMENT OF ELECTRICAL
ENGINEERING
AHMEDABAD – 382481
CERTIFICATE
THIS IS TO CERTIFY THAT THE MINOR PROJECT REPORT ENTITLED “SIMULATION
AND PRTOECTION OF LONG TRANSMISSION LINE ” SUBMITTED BY
MR./MS. VASAV SHETHNA(13BEE110), TUSHAR
SHINGALA(13BEE111) TOWARDS THE PARTIAL FULFILLMENT OF THE
REQUIREMENTS FOR THE AWARD OF THE DEGREE IN
BACHELOR OF TECHNOLOGY (ELECTRICAL ENGINEERING) OF NIRMA
UNIVERSITY IS THE RECORD OF WORK CARRIED OUT BY HIM/HER UNDER MY/OUR
SUPERVISION AND GUIDANCE. THE WORK SUBMITTED HAS IN OUR OPINION REACHED A
LEVEL REQUIRED FOR BEING ACCEPTED FOR EXAMINATION.
DATE:
Prof. Shankar Godwal
(Guide)
Dr. P. N. Tekwani
HOD(EE)

ACKNOWLEDGEMENT
We would like to express our gratitude towards all the people who
have contributed their precious time and efforts to help us in the
survey of project literature, without whom it would not be possible
for us to understand and analyse the project.
We would like to thank Prof. Shankar Godwal of Department of
Electrical Engineering, our Project Supervisor, for his guidance,
support, motivation and encouragement throughout the period this
work was carried out. His readiness for consultation at all the times,
his educative comments, his concern and assistance have been
invaluable.
We are also grateful to Department of Electrical Engineering, for
providing the necessary facilities in the department.

ABSTRACT
Main component of Power System is the transmission line.
Transmission Line plays an important role and a medium to transfer
power from generating station to the distribution network that
ultimately reaches to the end user.
However, in transmission line there are a number of problems faced
in our day to day life such as power loss due to corona effect,
voltage drop due to line parameters such as resistance, inductance
and capacitance.
In this report MHO relay and Frequency Dependent model type
transmission line are modelled using PSCAD software. Simulation
of single line to ground fault is realized to study the performance of
mho relay.

List of circuit diagrams and graphs of various
results obtained by simulation
Fig 1.0 General Transmission Line
Fig 1.1 Short Transmission Line
Fig 1.2 End Condenser Method
Fig 1.3 Nominal T Method
Fig 1.4 Nominal π Method
Fig 1.5 Long Transmission Line
Fig 2.1 Circuit diagram of single generator single load system
Fig 2.2 Circuit diagram of power system under line to ground
fault without circuit breaker
Fig 2.3 Circuit diagram of power system under line to ground
fault with circuit breaker
Graph 2.1 Active power demanded by load
Graph 2.2 Reactive power demanded by load
Graph 2.3 Active power demanded by load during fault
Graph 2.4 Reactive power demanded by load during fault
Graph 2.5 Positive sequence voltage without circuit breaker
Graph 2.6 Negative sequence voltage without circuit breaker
Graph 2.7 Zero sequence voltage without circuit breaker
Graph 2.8 Positive sequence voltage with circuit breaker
Graph 2.9 Negative sequence voltage with circuit breaker
Graph 2.10 Zero sequence voltage with circuit breaker
Graph 2.11 Positive sequence current with circuit breaker
Graph 2.12 Negative sequence current with circuit breaker
Fig 3.0.0 Impedance Relay Characteristics
Fig 3.0.1 Reactance Relay Characteristics
Fig 3.0.2 Ohm Relay Characteristics
Fig 3.0.3 Mho Relay Characteristics
Fig 3.1 Circuit diagram of simple distance protection scheme
Fig 3.2 Diagram of Control Panel for various types of fault
Fig 3.3 Diagram of operation circuit
Fig 3.4 Diagram of Signal Processing Block
Fig 3.5 Diagram of Protection Scheme Block
Graph 3.1 Mho Diagram for LG fault and LL fault
Graph 3.2 Graph of Fault signal and Tripping Signal for fault at
50km
Graph 3.3 Graph of Fault signal and Tripping Signal for fault at
100km

Fig 4.1 Mho Relay Modelling Algorithm
Fig 4.2 Mho Relay Characteristics for three Zone Protection
Fig 4.3 Zone 1 Protection Scheme
Fig 4.6 Fault at 60km from Bus 1,Zone 1
Fig 4.7 Fault at 60km from Bus 1,Zone 1(From Reference
Paper)
Paper)
Paper)

List of Tables
Table 3.1 Line Voltage and their
respective maximum loading
Table 3.2 Line Voltage and their
respective equivalent spacing
Table 4.1 Settings of Zone Protection

CONTENTS
Acknowledgment (I)
Abstract (II)
List of various circuit diagram and graph of various
results obtained by simulation
(III)
List of Tables (IV)
Chapter 1 Introduction
1.1 Overview 1
1.2 Classification of Transmission Line 2
1.3 Generalised Constants of a Transmission Line 5
Chapter 2 Simulation Part
2.1 Simulation of total active and reactive power
demanded by load in single generator feeding a motor
type load
7
2.2 Simulation of identification of voltage sequence
components under line to ground (L-G) fault without
circuit breaker
9
2.3 Simulation of identification of voltage sequence
components with current sequence components under
line to ground (L-G) fault with circuit breaker
13
2.4 Programming to calculate generalised constants
for long transmission line
17
Chapter 3 Protection of Long Transmission Line 21
3.1 Simple Distance Protection Scheme 24
3.2 Fault Analysis 25
Chapter 4 Zones Of Protection 31
4.1 Mho Relay Model Algorithm 31
4.2 Zones of Protection 32
4.3 Taking Example of International Journal of
Advances in Engineering and validating simulation
results with the same.
32
Conclusion 39
References 40

1
Chapter 1 Introduction
1.1 Overview
Fig 1.0 General Transmission Line
The important parameters in any given transmission line are the determination
of voltage drop, line losses and efficiency of transmission. These parameters are
greatly influenced by line constants such as R(Resistance), L(Inductance) and
C(Capacitance) of the transmission line.
By studying these parameters we can know their effects on bus voltages and
power flow. They also help to understand the nature of power system.

2
1.2 Classification of Overhead Transmission line
Depending upon the manner according to which capacitance is taken into
account, the overhead transmission line can be classified as:
(i) Short Transmission Line:
When the length of transmission line is between 50 to 100 km and line voltage
is less than 20 kV, it is considered as short transmission line. In this case, the
effect of capacitance is neglected and only the effects of resistance and
inductance are taken into consideration.
Fig 1.1 Short Transmission line

3
(ii) Medium Transmission Line:
When the length of transmission line is between 100 to 150 km and line voltage
is between 20 kV to 100kV, it is considered as medium transmission line.
Depending upon the effect of capacitance taken into consideration it is further
classified as
(a) End Condenser Method
In this method, the effect of capacitance is taken as a lumped parameter at the
receiving side.
Fig 1.2 End Condenser Method
(b) Nominal T Method
In this method, the effect of capacitance is taken into consideration by taking it
as a parameter which is in the middle of transmission line.
Fig 1.3 Nominal T Method

4
(c) Nominal π Method
In this method, the effect of capacitance is divided into two, one at the sending
end and other one at the receiving end.
3
Fig 1.4 Nominal π Method
(iii) Long Transmission Line:
When the length of transmission line is more than 150 km and the voltage is
greater than 100kV, it is considered as long transmission line.
Fig 1.5 Long Transmission Line

5
1.3 Generalised Circuit Constants of a Transmission Line
Any transmission line can be expressed in terms of 4 terminals: 2 as input
terminals of voltage and current respectively, which can be considered as power
entering the network and other 2 as output terminals of voltage and current
respectively, considering power leaving the network.
⃗⃗⃗⃗ ⃗⃗⃗⃗ ⃗ ⃗⃗⃗
⃗⃗⃗ ⃗⃗⃗⃗ ⃗⃗ ⃗⃗⃗
Where, ⃗⃗⃗⃗
⃗⃗⃗
⃗⃗⃗⃗
⃗⃗⃗
⃗ ⃗⃗
For short transmission line
⃗
⃗⃗
For Nominal T Method
+ (⃗ /2)
⃗ (1 + ⃗
⃗
⃗⃗ + (⃗ /2)

6
For Nominal π Method
+ (⃗ /2)
⃗
⃗ (1 + ⃗
⃗⃗ + (⃗ /2)
For Long Transmission Line
√
⃗ √ √
√ √
⃗⃗ √

7
Chapter 2 Simulation Part
2.1 Simulation of total active and reactive power demanded by load in single
generator feeding a motor type load
Fig 2.1 Circuit diagram of single generator single load system
The above figure shows the circuit diagram of single generator feeding a single
load of resistor and inductor in nature.
The simulation is conducted in PSCAD (Power System Computer Aided
Design) software.
Various specifications:
Generating Voltage: 11 kV
Generator side Transformer: Y-∆ 11/230 kV
Transmission Line: 100 km
Load Side Transformer: ∆-Y 230/11 kV
Load: 50MW+16MVAR

8
Results:
The various graphs or results obtained by conducting this simulation is as
follows
Active power demanded by load:
The active power demanded by the load is 14.6 MW.
Reactive power demanded by load:
The reactive power demanded by the load is 5.6 MVAR.

9
2.2 Simulation of identification of voltage sequence components under line to
ground (L-G) fault without circuit breaker
Fig 2.2 Circuit diagram of power system under line to ground fault without
circuit breaker
Load: 50 MW+ 16MVAR
Fault occurring time: 0.1s

10
Results:
follows
Active Power demanded by load:
During normal condition the active power demanded by load is 13.5 MW.
But during the fault the active power goes to 0.21MW higher than normal
condition.
Reactive power demanded by load:

11
Positive Sequence Voltage:
Graph 2.5 Positive Sequence Voltage
Negative Sequence Voltage:
Graph 2.6 Negative Sequence Voltage

12
Zero Sequence Voltage:
Graph 2.7 Zero Sequence Voltage

13
2.3 Simulation of identification of voltage sequence components with current
sequence components under line to ground (L-G) fault with circuit breaker
Fig 2.3 Circuit diagram of power system under line to ground fault with circuit
breaker
Load: 50MW+16MVAR
Fault occurring time: 0.1s
Opening time of Circuit Breaker: 0.1s
Closing time of Circuit Breaker: 0.14s

14
Results:
follows
Positive Sequence Voltage:
Graph 2.8 Positive Sequence Voltage
We can say from the graph that when the fault occurs and circuit breaker
operates, at that time positive sequence voltage increases more than twice of
original value and when fault is cleared and circuit breaker closes, positive
sequence voltage again turns to normal value.

15
Graph 2.9 Negative Sequence Voltage
From the graph we can say that during fault negative sequence voltage increases
to many times and after clearing of fault it again turns to normal value.
Zero Sequence Voltage:
Graph 2.10 Zero Sequence Voltage

16
Positive Sequence Current:
Graph 2.11 Positive Sequence Current
From the graph we can say that during normal condition, normal current flows
through the system but during the fault the same becomes zero and again
becomes normal after fault has been cleared,
Graph 2.12 Negative Sequence Current

17
From the graph we can say that it behaves just in the opposite way of positive
sequence current. During fault its value becomes many times and after fault has
been cleared it again turns to normal value.
2.4 Programming to calculate generalised constants for long transmission line
For the following given data calculate ABCD parameters, current and sending
end voltage. Assume suitable data where ever necessary from given tables.
Line to line voltage kV Line loading kW km
11 24×103
33 200×103
66 600×103
110 11×106
132 20×106
166 35×106
230 90×106
Table 3.1 Line Voltage and their respective maximum loading
Line to line voltage kV Equivalent Spacing m
11 1.0
33 1.3
66 2.6
110 5.0
132 6.0
166 8.0
230 10.2
Table 3.2 Line Voltage and their respective equivalent spacing

18
At 132 kV, 85 MW of three phase power is to be supplied over a distance of
160 km at 0.9 power factor lagging.
Programming in MATLAB:
P=input('Power to be transmited in KW=');
Vr=input('Receiving end voltage in KV=');
PF=input('Power factor=');
Ir=P/(1.73*Vr*PF);
disp('Receiving end current in A = ');
disp(Ir);
L=input('Length of transmission in km=');
dia=input('diameter of conductor in CM :');
rad=dia/2;
d12=input('distance between 1 & 2 in CM :');
d=(d12*d23*d31);
deq=(d)^(1/3);
disp(deq);
e=log(deq/rad);
Li=(10^-7)*(0.5+(2*e))*L*1000;
disp('Inductance per km in H');
disp(Li);
R=input('Total line Resistance in ohm');
X=314*Li;
disp('Reactance of line in ohm = ');
disp(X);
Cap=((L/18)/e)*(10^-6);
y=314*Cap;
disp('Admittance of line in ohm = ');
disp(y);
Y=0-y*1i;
Z=R+1i*X;
disp('Impedance in ohm');
disp(Z);
A=(1+(Y*Z*0.5));
disp('A = ');
disp(A);
B=(Z+(Y*Z*Z*0.25));
disp('B = ');
disp(B);
a=real(A);
b=imag(A);
c=real(B);

19
d=imag(B);
Ma=((a*a)+(b*b))^0.5;
Mb=((c*c)+(d*d))^0.5;
alpha=atand(b/a);
beta=atand(d/c);
Vs=((Ma*Vr)+((Mb*Ir)/1000));
disp('Sending end Voltage in KV = ');
disp(Vs);
Output Result:
abcdparam
Power to be transmited in KW=85000
Receiving end voltage in KV=132
Power factor=0.9
Receiving end current in A =
413.5770
Length of transmission in km=160
diameter of conductor in CM :2.347
distance between 1 & 2 in CM :600
600.0000
Inductance per km in H
0.2076
Total line Resistance in ohm17.456
Reactance of line in ohm =
65.1808
Admittance of line in ohm =
4.4751e-04
Impedance in ohm

20
17.4560 +65.1808i
A =
1.0146 - 0.0039i
B =
17.7106 +65.6220i
Sending end Voltage in KV =
162.0370

21
Chapter 3 Protection of Long Transmission Line
3.0 Relay: A relay is a electrically operated switch. It is a device designed to
give tripping signal to circuit breaker in case of fault.
Types of distance relay:
(1) Impedence Relay:
It compares the local current and local voltage and operates if the ratio of
measured voltage to current is less than the set impedence K.
Fig 3.0.0 Impedance Relay Characteristics
(2) Reactance Relay:
It measures the reactance of the line to be protected and operates if measured
reactance is less than the set reactance K.

22
Fig 3.0.1 Reactance Relay Characteristics
(3) Ohm Relay:
It measures a particular component |Z| and angle ϴ of line impedance vector Z.
Fig 3.0.2 Ohm Relay Characteristics
(4) Mho Relay:
It measures component |Y| and angle ϴ of line admittance vector Y.

23
Fig 3.0.3 Mho Relay Characteristics

24
3.1 Simple Distance Protection Scheme
Fig 3.1 Circuit diagram of simple distance protection scheme
The above diagram shows a simple distance protection scheme for a long
transmission line whose length is 100 km. It comprises of a sending end side
part and a receiving side part. Here two breakers are in service, one being at
sending end and other being at receiving end.
Breaker 1 i.e. B1 (as shown in figure) is working on using relay operation while
working of breaker 2 i.e.B2 is a normal one.
Here relay used for operation of breaker 1 is Mho Relay.

25
3.2 Fault Analysis
Fig 3.2 Diagram of Control Panel for various types of fault
Case1:
In this case, line to ground fault has been stimulated. The fault is made to occur
at middle of transmission line i.e. at 50 km.
Fig 3.3 Diagram of operation circuit

26
Fig 3.4 Diagram of Signal Processing Block
Signal Processing Block consists of FFT block. This FFT block separates out
voltage magnitude, voltage phase angle, current magnitude and current phase
angles of all three phases.
These voltage magnitudes and phase angles are given to sequence components
block whose output gives magnitude and phase angle of positive, negative and
zero sequence components.

27
Fig 3.5 Diagram of Protection Scheme Block

28
Graph 3.1 Mho Diagram for LG fault and LL fault

29
From the above figure we can say that when LG fault will occur then at that
time some value will be seen in mho circle for LG fault while nothing is seen in
LLG fault.
As LG fault is detected, mho relay will give tripping signal to the circuit breaker
1and circuit breaker will operate.
Graph 3.2 Graph of Fault signal and Tripping Signal for fault at 50km
Case2:
In this second case, line to ground fault has been stimulated. The fault is made
to occur on transmission line at distance of 90 km.

30
Graph 3.3 Graph of Fault signal and Tripping Signal for fault at 90km
From graph 3.2 and 3.3 we can say that as the distance of fault increases and the
time taken for tripping of relay also increases.

31
Chapter 4 Zones of Protection
4.1 Mho Relay Model Algorithm
Fig 4.1 Mho Relay Modelling Algorithm
The above flowchart shows the working of mho relay in a transmission line.

32
4.2 Zones of Protection
Fig 4.2 Mho Relay Characteristics for three zones of protection
Zone 1: Covers 80% to 85% of length of protected line
Zone 2: Covers all protected line plus 50% of shortest next line
Zone 3: Covers all protected line plus 100% of second longest line plus 25% of
shortest next line.
4.3 Taking Example of International Journal of Advances in Engineering and
Technology, Jan 2014 (ISSN: 22311963) and validating simulation results with
the same.
Source Data
Voltage = 230kV
R = 9.186 Ω
L = 138 mH
Frequency = 50Hz
Transmission line data
Positive sequence impedance = 0.12312+j0.663 Ω/km
Zero sequence impedance = 0.08844+j0.2397 Ω/km
Frequency = 50Hz

33

34
Setting of Mho Relay
Zone 1 = 53.95 Ω (80 % of protected line between Bus1 and Bus 3).
Zone 2 = 101.16 Ω (100 % of protected line between Bus 1 and Bus 3 + 50 % of
the protected line between Bus 3 and bus 4).
Zone 3 = 151.75 Ω (100 % of protected line between Bus 1 and Bus 3 + 100 %
of the protected line between Bus 3and Bus 4 +25% of the protected line
between Bus 4 and Bus 2).
ZONE R X
1 4.92 Ω 26.52 Ω
2 9.23 Ω 49.74 Ω
3 13.85 Ω 74.60 Ω
Table 4.1Settings of Zone Protection

35
Simulation Results:
Single line to ground fault was set on the 230kV, 300 km transmission line
model at a distance of 60km, 20km and 12 km from the location of bus-1, bus-3
and bus-4. Simulation results are shown
Fig 4.6 Fault at 60 Km from Bus-1, Zone 1

36
Fig 4.7 Fault at 60 Km from Bus-1, Zone 1(From Reference Paper)

37

38

39
Conclusions:
From this project we can conclude that transmission line plays an important role
in power system, so its protection has to be done precisely and accurately. If
transmission line collapses then the entire power system is said to be failed.
Distance protection scheme is used for transmission line protection. In that Mho
relay with zone wise protection is useful.
Depending upon the zone of fault mho relay operates respectively and separates
the faulty part from the healthy part.

40
References:
• Principles of Power System by V. K. Mehta and Rohit Mehta
• Electrical Power System Design by M. V. Deshpande
• Modern Power System Analysis by D. P. Kothari and I. J. Nagrath
• Power System Protection by Bhuvanesh Oza
• http://www.engineering.uodiyala.edu.iq/uploads/depts/power/teacher%20
lectures/protection%204%20stage/Protective%20Relays.pdf
• International Journal of Advances in Engineering and Technology, Jan
2014(ISSN:22311963)
DISTANCE PROTECTION FOR LONG TRANSMISSION LINE
USING PSCAD by M.P.Thakre, V.S.Kale (Electrical Engineering
Department, V.N.I.T, Nagpur, M.S., India)
• http://www.gegridsolutions.com/multilin/notes/artsci/art02.pdf

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