Relay

 

SETTING OF DISTANCE RELAY ON POWER TRANSMISSION LINE USING PSCAD

SHAKIRA AZEEHAN BINTI AZLI

A report submitted in partial fulfilment of the requirements for award of degree of Bachelor of Engineering (Electrical)

Faculty of Electrical Engineering University Teknologi Malaysia

APRIL 2010

ii   

iii   

Dedicated to my beloved father PM Dr Azli Bin Sulaiman Mother Noor Sharidah Binti Alias Siblings Hizaz Shahiela Izzat Fahmi Adib Fikri Amelia Adrina and My Entire friend in SEE programme For their encouragement              

iv   

ACKNOWLEDGEMENT

“Praise is to Allah S.W.T, the Most Merciful and the Most Compassionate. Peace is upon him, Muhammad, the messenger of God”.

I wish to express my sincere appreciation to my project supervisor, Dr Ahmad Safawi Bin Mokhtar for all his guidance, encouragement and support in completing the final year project.

I would also like to express my gratitude to all the lectures who have taught me throughout the years of studying in UTM, thank you for all the knowledge that has been provided.

My gratitude is also extending to my fellow colleagues for sharing their ideas and discussions. Last but not least, I would like to thanks my family for their motivation and moral support.

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ABSTRACT

The role of protective relays in a power system is to detect systems abnormalities and to execute appropriates commands to isolate swiftly only at the faulty component from healthy system. One of the protective relays is the distance relay. High current flows through the network when fault occur. So, the distance relay will detect the over current by measuring the impedance on the transmission line and send the tripping signal to the circuit breaker to break the power line. This project focuses on determining the optimum setting of distance relay and also the performance of the distance relay when single line-to-ground fault occur in the system. In this project, the setting can be determined by using PSCAD software. The system consist of two source, five faults and two 100Km transmission line which are protected by distance relays. The modelling and analysis of the test system with corresponding relay circuits are done solely using PSCAD. From the simulation, it can be observed that the fault voltage and current characteristics are consistent with those from the theoretical concept. The optimum setting is also obtained from the analysis.

vi   

ABSTRAK

Peranan geganti perlindungan dalam system kuasa adalah untuk mengesan ketidakseimbangan sistem dan melaksanakan arahan yang sewajarnya untuk mengasingkan bahagian rosak sahaja daripada sistem yang normal.

Salah satu

daripada komponen sistem perlindungan ialah geganti jarak. Apabila kerosakan berlaku, arus yang tinggi akan mengalir melalui rangkaian. Oleh itu geganti jarak akan mengesan lebihan arus dengan mengukur galangan pada talian penghantaran dan akan menghantar isyarat putus kepada pemutus litar untuk memutuskan talian kuasa. Projek ini difokuskan untuk menentukan pengesatan optimum geganti jarak dan analisis penilaian prestasi geganti jarak beroperasi pada kerosakan satu talian ke bumi. Dalam projek ini, pengesatan optimum geganti jarak dapat ditentukan dengan menggunakan perisian PSCAD. Sistem ini mempunyai dua penjana, lima kerosakan dan dua talian penghantaran 100Km panjang yang dilindungi dengan geganti jarak. Rekaan dan ujian analisa pada sistem dengan litar geganti dijalankan sepenuhnya dengan PSCAD. Daripada keputusan, ia boleh dilihat bahawa sifat kerosakan voltan dan arus mematuhi sifat-sifat dalam teori. Pengesatan optimum juga diperolehi daripada analisis ini.

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TABLE OF CONTENTS

CHAPTER

1

TITLE

PAGE

DECLARATION

ii

DEDICATION

iii

ACKNOWLEDGEMENT

iv

ABSTRACT

v

ABSTRAK

vi

TABLE OF CONTENTS

vii

LIST OF TABLE

xi

LIST OF FIGURES

xii

LIST OF SYMBOLS AND ABBREVIATION

xiv

INTRODUCTION

1.1

Background

1

1.2

Problem of Statement

2

1.3

Objectives

2

1.4

Scope of the Project

3

viii   

1.5

2

Thesis Outline

3

LITERATURE REVIEW

2.1

Faults on Power System

4

2.2

Single Line-to-Ground Fault

5

2.3

Principles of Distance Relay

9

2.4

Distance Protection Scheme

9

3

METHODOLOGY

3.1

PSCAD Software

11

3.2

Process of Analysis

12

3.3

Circuit Construction

12

3.4

Components

14

3.4.1 Source

14

3.4.1.1 Configuration

15

3.4.1.2 Parameters

15

3.4.2 Multimeter

16

3.4.3 Transmission Line

17

3.4.3.1 Parameters

17

3.4.4 Circuit Breaker

18

3.4.5 Fault Component

19

3.4.6 Online Frequency Scanner

20

3.4.7 Sequence Filter

20

ix   

3.4.8 Line to Ground Impedance Component

21

3.4.9 Parameters

21

3.4.9.1 Main Data

22

3.4.9.2 Initializing

23

3.4.10 MHO Circle 3.4.10.1 Parameters 3.5 Run Simulation

4

23 24 24

RESULTS AND DISCUSSION

4.1

Introduction

25

4.2

No Fault Condition

26

4.3

Fault at Location 1

28

4.4

Fault at Location 2

31

4.5

Fault at Location 3

35

5

CONCLUSION AND RECOMMENDATION

5.1

Conclusion

38

5.2

Recommendation

39

x   

REFERENCES

40

APPENDIX A

41

APPENDIX B

43

APPENDIX C

45

APPENDIX D

46

xi   

LIST OF TABLES

NO. TABLE

TITLE

PAGE

3.1

Configuration of Voltage Source

17

xii   

LIST OF FIGURES

NO. FIGURE

TITLE

PAGE

2.1

The Condition of Each Types of Faults

5

2.2

Single Line-to-Ground Fault

6

2.3

Connection of Sequence Network for L-G fault

8

2.4

3-Zone Distance Protection Scheme

10

3.1

Project Flow

12

3.2

Main Circuit

13

3.3

Relay Circuit

13

3.4

Three Phase Voltage Source

14

3.5

Multimeter

16

3.6

Transmission Line

17

3.7

Parameters of Bergeron Model

18

3.8

Circuit Breaker

18

3.9

Three Phase Fault

19

3.10

Online Fast Fourier Transform

20

3.11

Sequence Filter

20

3.12

Line to Ground Impedance

21

3.13

MHO Circle Component

23

4.1

Waveform at No Fault Condition

27

xiii   

4.2

Fault at Location 1

28

4.3

Waveform of Breaker 1 when Fault at Location 1

29

4.4

Waveform of Breaker 2 when Fault at Location 1

30

4.5

Fault at Location 2

31

4.6

Waveform of Breaker 1 when Fault at Location 2

33

4.7

Waveform of Breaker 2 when Fault at Location 2

34

4.8

Fault at Location 3

35

4.9

Waveform of Breaker 1 when Fault at Location 3

36

4.10

Waveform of Breaker 2 when Fault at Location 2

37

A1

Main Circuit Connection

41

A2

Output Channel Connections

42

B1

Relay Circuit Connection

43

B2

Sequence Module for Current

44

B3

Sequence Module for Voltage

44

C1

Breaker Control Circuit

45

D1

Waveform of fault at Location 4 for Relay 1

46

D2

Waveform of fault at Location 4 for Relay 2

47

D3

Waveform of fault at Location 5 for Relay 1

48

D4

Waveform of fault at Location 5 for Relay 2

49

xiv   

LIST OF LIST OF ABBREAVIATIONS AND SYMBOLS

Ea - Voltage Source Ia - Current phase a Ib - Current phase b Ic - Current phase c If - Fault current I0 - Zero sequence current I1 - Positive sequence current I2 - Negative sequence current Va - Voltage phase a Vb - Voltage phase b Vc - Voltage phase c V0 - Zero sequence voltage V1 - Positive sequence voltage V2 - Negative sequence voltage

CHAPTER 1

INTRODUCTION

1.1 Background

Electrical energy is the most popular form of energy because it can be transported easily at high efficiency and reasonable cost [1]. Modern power engineering consists of three main subsystems, which is the generation, transmission and distribution. In order to provide electrical energy to consumers in usable form, a transmission and distribution system must satisfy some basic requirements. Thus, the system must [2]: 1. Provide, at all times, the power that consumers need. 2. Maintain a stable, nominal voltage that does not vary by more than +10%. 3. Maintain a stable frequency that does not vary by more than +0.1 Hz. 4. Supply energy at an acceptable price. 5. Meet standards of safety. 6. Respect environmental standards

The electrical power is distributed to a multiplicity of consumers for different applications. In the process of distributing or transmitting the power, faults

2 sometimes occur due to the physical accidents or insulation breakdowns [3]. Power system protection deals with the protection from faults through the isolation of faulted parts from the rest of the electrical network. The objective of a protection scheme is to keep the power system stable by isolating only the components that are under faults, whilst leaving as much of the network as possible in operation.

Protective relay system detects abnormal condition such as fault in electric circuit and the circuit breakers will operates automatically to isolate the fault that occurs in the system as fast as possible. Distance relays are generally used for phasefault primary and back-up protection on transmission lines. Distance relay meet the requirements of reliability and speed needed to protect the circuit.

1.1 Problem Statement

All faults that occur on a power system circuit must be cleared quickly otherwise it may result in disconnection of customers, loss of stability in the system and damage to the equipment. Therefore, in order to minimize the damage, suitable and reliable protection system should be installed on all of the circuit and equipments. In this project, distance relay is used to detect the fault that occurs.

1.2 Objective

i.

To study the principle and application of Distance Relay in Power System.

ii.

To optimize the performance and the effect of Distance Protection System.

iii.

To obtain the optimum settings of the Distance Relay in a transmission system.

3 1.3 Scope of the Project

The scopes of the project are as the following:

i.

The study on the characteristic, operation and performances of Distance Relay.

ii.

The modeling and simulation of Distance Protection System using PSCAD.

iii.

The use of Single Line-to-Ground fault on the system.

1.4 Thesis Outline

This thesis is divided into five chapters. For the first chapter, the introduction of the project study is covered, followed by the literature review in the second chapter. The third chapter is the methodology of the study that covers the software used for the simulation and its related library tools. The result and discussion is in the fourth chapter. Last but not least, the last chapter provides the conclusion of the study and the recommendation for future analysis.

CHAPTER 2

LITERATURE REVIEW

2.1 Faults on Power System

Power system fault is a condition or abnormality of a system which involves the electrical failure of the equipment such as generator, transformer, busbar, overhead line and cable. The type of fault can be categorized into two types which is symmetrical fault and asymmetrical fault. Fault occur as single line to ground faults, line to line faults, double line to ground faults or three phase fault. Each fault has its own characteristic and condition that make the fault happen. Since any unsymmetrical fault causes unbalance currents flow in the system, the method of symmetrical component is very useful in an analysis to determine the currents and voltages in all parts of the system after the occurrence of the fault [3]. Figure 2.1 shows the network condition when the faults occur.

5   

Figure 2.1: The condition of each types of fault

There are many factors that cause the fault to occur in the transmission line. For instance, the single line-to-earth fault often occurs because of the physical contact due to lightning. Line-to-line fault will occur by ionization of air or when line comes into physical contact due to broken insulator. Others examples of condition that will make the fault occur at the transmission line are [1]:-

a) Lightning strikes on bus bar b) Collapse of transmission line c) Accidental short circuit by snake, kite and bird d) Tree or bamboo touching line e) Human mistakes.

2.2 Single Line-to-Ground Fault

The single line to ground fault can occur in any of the three phases. However, it is sufficient to analyze only one of the cases. Looking at the symmetry

6   

of the symmetrical component matrix, it is seen that the simplest way to analyze would be the phase a which is the single line-to-ground fault as shown in Figure 2.2.

Figure 2.2: Single Line-to-Ground Fault

Assuming the generator is initially on no load, the boundary condition at the fault point is: V

ZI

I

I

0

1.1

By substituting for Ib = Ic =0, the symmetrical components of the currents is given as: I I I

1 1 1 1 a 3 1 a

I 0 0

1 a a

1.2

The observation from the equation (1.2) is:

I

I

I

I

(1.3)

7   

The symmetrical voltage components of voltage are given as:

V V V

0 E 0

Z 0 0

0 Z 0

0 0 Z

I I I

Z

Z

1.4

The phase a voltage is:

V

V

V

V

E

Z I

(1.5)

The fault current, If can be found by substituting the equations (1.1), (1.3) and (1.5) as follows: 3Z I

I

E

I

3I

Z

Z I

Z

(1.6)

3E Z

Z

Z

3Z

The equation can be obtained from the equivalent circuit as shown in Figure 2.3 which shows the connection of sequence network for a single-line-to ground fault.

8   

Figure 2.3: Connection of Sequence Networks for L-G fault

2.3 Principles of distance relays

Distance relay is used on power system network because the relay meets the requirement of reliability and speed needed to protect the circuit. Distance relays are preferred to overcurrent relays because they are not nearly so much affected by changes in short-circuit-current magnitude as overcurrent relays are and hence, they are much less affected by changes in generating capacity and in system configuration. This is because distance relays achieve selectivity on the basis of impedance rather than current.

Distance relay respond to a ratio of the voltage and current at the relay location. The ratio has the dimensions of impedance between the relay location and the fault point is proportional to the distance of the fault [3]. Such a relay is described as a distance relay and is designed to operate only faults occurring between the relay location and the selected point, thus giving discrimination for faults that may occur between different line sections.

9   

2.4 Distance protection scheme

One of the most critical issues in power system protection is the speed with which a fault can be cleared quickly to prevent from abnormalities of a system. Distance relays are classified according to polar characteristics, the number of inputs and the method by which the comparison is made.

The common types compare two input quantities are compared are essentially either amplitude or phase comparators. Modern static distance relays, based on single-phase measurement, use phase comparators to produce the required relay characteristic.    

Due to uncertainty in impedance measurements, when protecting a transmission line with non-pilot distance protection schemes, it is necessary to rely on stepped zones of protection.

This technique protects any given section of

transmission line with multiple zones.

The usual practice in applying distance protection is to install three sets of distance relays at each relaying point, creating the 3-zone distance protection scheme as shown in Figure 2.4. The zone 1 relays have the shortest reach and the fastest operating speed, while zone 2 and zone 3 relays have successively longer reaches and slower speeds. Zone 2 acts as a back-up for zone 1 and zone 3 acts as a back-up for zone 1 and 2.

A common arrangement is to make zone 1 and 2 polarised mho and zone 3 offset mho [3]. The first zone tripping which is instantaneous is normally set to 80% of the protected line detected by zone 1 unit should be cleared immediately without the need to wait for other device to operate. The zone 2 will cover the remaining 20% portion of the protected section.

10   

Figure 2.4: 3-Zone distance protection scheme

CHAPTER 3

METHODOLOGY

3.1 PSCAD SOFTWARE

Power System CAD which is known as PSCAD is a powerful and flexible graphical user interface to the world-renowned, EMTDC solution engine. PSCAD enables user to schematically construct a circuit, run a simulation, analyze the results and manage the data in a completely integrated graphical environment. Online plotting functions, controls and meters are also included so that user can alter system parameters during a simulation run and view the results directly.

PSCAD comes with a library of pre-programmed and tested models, ranging from simple passive elements and control functions to more complex models, such as electric machines, FACTS devices, transmission lines and cables. If a particular model does not exist, PSCAD provides the flexibility of building custom models, either by assembling them graphically using existing models or by utilising an intuitively designed Design Editor.

12 3.2 PROCESS OF ANALYSIS

In order to do the research, several steps have to be taken to obtain the result of the simulation. The process of the research is shown in Figure 3.1 below.

Figure 3.1: Project Flow

3.3 CIRCUIT CONSTRUCTION

In order to do the simulation, the major step that has to be done is the circuit construction. This is the process where circuit is designed and build up by using the PSCAD software. By using the PSCAD software, components are selected from the master library.

13 The master library consists of different types of components such as the sources, input and output devices, transmission lines and cables. Each component has the editing feature that enables user to alter the input depends on the appropriate parameter of the component. Figure 3.2 and Figure 3.3 shows the two circuits that were constructed in this project, which is the main circuit and relay circuit.

Figure 3.2: Main Circuit

Figure 3.3: Relay Circuit

14 The relay circuit shown in Figure 3.3 is constructed by using line-to-ground impedance, MHO circle component, comparator and gates. Each of the components is connected together and connects to the circuit breaker in the main circuit. The relay circuit is used to detect the fault that occurs in the system. Thus, the relay circuit will give a signal to the breaker so that the breaker will trip the system.

3.4 COMPONENTS

Components are either network components such as resistors, inductors, capacitors, switches, ac machines, transformers or power electronic devices and it can also be measurement, control, monitoring functions, signal processing and outputs. A component is essentially a graphical representation of a device model, and is the basic building block of circuits created in PSCAD. Component is usually designed to perform a specific function, and can exist as either electrical, control, documentary or simply decorative in type.

3.4 1 SOURCE

Figure 3.4: Three Phase Voltage Source

15 The three phase voltage source models which is shown in Figure 3.4 is a 3phase AC voltage source, where users may specify the positive sequence and zero sequence source impedances or select an ideal source.

3.4.1.1 CONFIGURATION

The parameters of the voltage source which consist of voltage, base MVA, frequency and voltage input time constant that is used in this simulation is shown in Table 3.1.

Table 3.1: Configuration of Voltage Source PARAMETERS

VALUE

Base Voltage (L-L)

230 KV

Base MVA ( 3-PHASE )

100 MVA

Base Frequency

50 Hz

Voltage Input Time Constant

0.01 Second

3.4.1.2 PARAMETERS

The positive sequence impedance is calculated based on the equation shown and the parameters used are as stated in Table 3.1. The positive sequence impedance is important in the setting of the distance protection relay because it is used to set the radius of the circle.

16

Based on the calculation, the value of the positive sequence impedance used in this project is 53.16 ⎳ 84.3º Ω.

3.4.2 MULTIMETER

Figure 3.5: Multimeter

The

Multimeter

performs

virtually

all

possible

system

quantity

measurements, all contained within a single, compact component. The Multimeter which is shown in Figure 3.5 is inserted in series within the circuit either 3-phase, single-line or 1-phase.

17 3.4.3 TRANSMISSION LINE

Figure 3.6: Transmission Line

As shown in Figure 3.6, the transmission line that is used in this project is the Bergeron Model, where the impedance or admittance data can be entered directly to define the transmission corridor.

The Bergeron model represents the L and C

elements of a PI section in a distributed manner.

It is accurate on at the specified frequency and is suitable for studies where the specified frequency load-flow is most important such as in the relay studies. In this project, the transmission line is set to a distance of 100 Km for both of the transmission line.

3.4.3.1 PARAMETERS

The parameters that is used in the Bergeron Model is shown in Figure 3.7 where it is copied to the transmission line format in PSCAD system.

18

Figure 3.7: Parameters of Bergeron Model

3.4.4 CIRCUIT BREAKER

Figure 3.8: Circuit Breaker

19 The component shown in Figure 3.8 simulates of single-phase circuit breaker operation. The ON (closed) and OFF (open) resistance of the breaker is specified along with its initial state. This component is controlled through a named input signal where the breaker logic is: •

0 = ON (closed)

•

1 = OFF (open)

3.4.5 FAULT COMPONENT

Figure 3.9: Three Phase Fault

The fault component is used for generating the fault condition. The three phase fault component which is shown in Figure 3.9 puts a combination of phase to phase and phase to ground faults to allow any combination of faults to be selected, even during multiple runs.

20 3.4.6 ONLINE FREQUENCY SCANNER

Figure 3.10: Online Fast Fourier Transform (FFT)

Figure 3.10 shows an online Fast Fourier Transform (FFT), which determines the harmonic magnitude and phase of the input signal as a function of time. The input signals first sampled before it is decomposed into harmonic constituents. Options are provided to use one, two or three inputs. In the case of three inputs, the component provides output in the form of sequence components.

3.4.7 SEQUENCE FILTER

Figure 3.11: Sequence Filter

21 The component shown in Figure 3.11 is a sequence filter which calculates the magnitudes and phase angles of sequence components when the magnitudes and phase angles of the phase quantities are given by the FFT component.

3.4.8 LINE TO GROUND IMPEDANCE COMPONENT

Figure 3.12: Line to Ground Impedance Component

The component shown in Figure 3.12 computes the line-to-ground impedance as seen by a ground impedance relay and the output impedance is in rectangular format (R and X).

3.4.9 PARAMETERS

The line-to-ground impedance consist of several parameters that needs to be calculated. The important parameter that is used in this component is the constant for ground impedance, K.

22 3.4.9.1 MAIN DATA

When the distance of the transmission line is set to 100Km, the constant for ground impedance is calculated as below:

Z1 = (0.36294X10-4 + J0.5031X10-3)(100km) = 50.44 ∟ 85.87º Ω

Z0 = (0.37958X10-3 +J0.13277X10-2)(100km) = 138.089 ∟ 74.05º Ω

Therefore: K =( Z0 - Z1 ) / Z1 = 1.771 ∟ -18.48º

The constant for ground impedance is used in the setting of the line to ground impedance component to prevent from overreach and underreach. Without the constant, the relay will cause underreach or overreach in the system. Thus, the optimum setting of the relay could not be obtained.

23 3.4.9.2 INITIALIZING

•

Initializing Time = 0.02 Second

•

Output R during initialization = 1 x 106Ω

•

Output X during initialization = 1 x 106Ω

3.4.10 MHO CIRCLE

Figure 3.13: MHO Circle Component

The Mho Circle component is classified as an ‘Impedance Zone Element’, which checks whether or not a point described by inputs R and X, lies inside a specified region on the impedance plane. R and X represent the resistive and reactive parts of the monitored impedance. The component produces an output '1' if the point defined by R and X is inside the specified region, otherwise the output will be '0'.

24 3.4.10.1 PARAMETER

•

Radius of the circle = 50 Ω

•

Z coordinate of the centre = 25

•

Theta coordinate of the centre = 1.49766[rad]

The Z coordinate of the centre is calculated based on the equation below: Z = Z1 / 2 = 50 / 2 = 25

3.5 RUN SIMULATION

To run the project, simply click on the Run button in the Main Toolbar. When this button is pressed, PSCAD will go through several stages of processing the circuit before starting the simulation. The simulation will run if no error occur in the circuit that was constructed. If an error occur, the warning will appear and correction has to be done. The output of the simulation can be seen based on the graphs and also the measurement of current, voltage and power.

CHAPTER 4

RESULTS AND DISCUSSION

4.1 Introduction

The final accomplishments and results of the project shall be explained in this chapter.

This chapter discusses on the result, analysis and problems that are

encountered throughout the completion of the project. After the development and completion of the simulation, it will then be evaluated in order to ensure whether it had met the outlined objectives successfully. By the methodology as discussed in the previous chapter, this project has made remarkable result and achievement.

Based on the project that had been done, the results are obtained when Single Line- to-Ground fault occurs at five different locations in the transmission line circuit. The performance of the distance relay can be seen when the circuit breaker trips during fault condition. This section will discuss on the performance of the distance relay at no fault condition and when the Single Line-to-Ground fault occur at different locations. The discussion will only focus on the phase a fault which is the blue line in the output waveform that can be seen in Figure 4.1 which indicates the Single Line-to-Ground fault.

26 4.2: No Fault Condition

At no fault condition, there are no faults that occur in the circuit. Since there is no fault in the system, the shape of the voltage and current waveform remains stable for Relay 1 and Relay 2. From Figure 4.1(a), it can be seen that no voltage drop occur and the value remains the same as the supply voltage which is 230KV.

Similar to the voltage, the current waveform is also stable and constant. Since the unit measurement for the current is in kilo ampere (kA), the value of the current is too small until it seems like there is no current at the transmission line which is shown in figure 4.1(b).

The distance relay does not detect any fault in the transmission line, so the circuit breaker behaves in a normal condition where it is in a CLOSE condition. Since there is no detection of fault in the transmission line, no tripping signals were sent to the breaker and it has been proved by the relay output signal in Figure 4.1(c) where the outputs are in’0’ condition at all time.

27

(a)

(b)

(c)

Figure 4.1: Waveform at No Fault Condition (a) Voltage Waveform (b) Current Waveform (c) Breaker Signal

28 4.3: Fault at location 1

Fault Point

Figure 4.2: Fault at Location 1

As shown in Figure 4.3(c) and Figure 4.4(c), when single line-to-ground fault is applied at location 1 at t = 0.2 s and duration of 0.1 s, both of the circuit breaker is not affected. It can be seen that the breaker does not trip and the signal is still in ‘0’ condition.

Since the fault occurred at 0.2 second, the voltage of phase a at breaker 1 which is equal to zero because the fault that occurs is bolted fault. The voltage which is at phase b and phase c has also been affected, where both of the voltage magnitudes decrease a little bit.

From the waveform of the fault current in figure 4.3(b) and Figure 4.4(b), the existing current at the transmission line is only the phase a current. The other phase b and phase c current are equal to zero when the fault occur. By comparing with the theoretical, when single line-to-ground fault occur, the value of Ib=Ic=0.

29

(a)

(b)

(c)

Figure 4.3: Waveform of Breaker 1 When Fault at Location 1 (a) Voltage Waveform (b) Current Waveform (c) Breaker Signal

30

(a)

(b)

(c)

Figure 4.4: Waveform of Breaker 2 When Fault at Location 1 (a) Voltage Waveform (b) Current Waveform (c) Breaker Signal

31 4.4 Fault at Location 2

Fault Point

Figure 4.5: Fault at Location 2

When single line-to-ground fault occur at location 2, the distance relay will send a tripping signal to circuit breaker 1. The breaker breaks the circuit at 0.22s after fault occur at 0.2s, so the voltage at transmission line becomes zero. But, when the fault clears, the breaker will reclose back at 0.3s and transient voltage occur in few microseconds.

From the voltage waveform shown in Figure 4.6(a), voltage at phase b and phase c is not stable. It is cleared and goes back to the normal condition at 0.35s. This is known as the post-fault. For phase a, voltage becomes zero which means that there is no voltage at phase a when single line-to-ground fault occur.

Figure 4.6(b) shows current waveform when single line-to-ground fault occurs at location 2. The existing current at the transmission line is only the phase a current and the other phases current are equal to zero when the fault occur.

Figure 4.7(c) shows the signal of the circuit breaker for relay 2. The signal is in ‘0’ condition even though fault occurs at location 2. This is due to the voltage and current value that flows through the circuit when fault occurs. The fault current that

32 flows from source 2 is lower than the fault current that flows from source 1. The fault voltages at source 2 are higher than the fault voltage at source 1. The values are difference because of the total impedance of the transmission line between the fault location and sources. So, the mho circle characteristic does not detect any fault because of the total value of impedance is higher than inside the specified region.

33

(a)

(b)

(c)

Figure 4.6: Waveform of Breaker 1 When Fault at Location 2 (a) Voltage Waveform (b) Current Waveform (c) Breaker Signal

34

(a)

(b)

(c)

Figure 4.7: Waveform of Breaker 2 When Fault at Location 2 (a) Voltage Waveform (b) Current Waveform (c) Breaker Signal

35 4.5 Fault at Location 3

Fault Point

Figure 4.8: Fault at Location 3

When fault occurs at location 3, relay 1 and relay 2 does not detect the fault. This is because the fault that occurs is out of the protection zone. As discussed earlier in Chapter 2, distance relay protects the system if fault occurs at about 85% of the distance of the transmission line.

Since the fault occur at 100Km of the

transmission line, both of the relay cannot detect the fault and the breaker signal is in ‘0’ condition.

The voltage waveform for both of the relay is the same. The output can be seen from the waveform in Figure 4.9 and Figure 4.10. The voltage for phase a decrease more then voltage of phase b and phase c at 0.2s, which is during the fault that occur in the transmission line. The current at breaker 2 increase really high compared to the current at breaker 1, this is due to the fault that occur is near the breaker 2.

36

(a)

(b)

(c) Figure 4.9: Waveform of Breaker 1 When Fault Occur at Location 3 (a) Voltage Waveform (b) Current Waveform (c) Breaker Signal

37

(a)

(b)

(c)

Figure 4.10: Waveform of Breaker 2 when Fault occur at Location 3 (a) Voltage Waveform (b) Current Waveform (c) Breaker Signal

CHAPTER 5

CONCLUSION AND RECOMMENDATION

5.1 Conclusion

This project involved the usage of PSCAD simulation. To understand the theories for this project, it is important to understand the concept of distance relay type mho characteristic and the output waveform. PSCAD software is very useful in terms of obtaining the waveform of the current and voltage fault. It gives similar result with the theoretical concept. By referring to the waveform are enough to determine the type of fault without doing the calculation. It makes the user can know the fault in very short time.

The optimum setting of the distance relay is when the relay does not overreach or underreach and the relay only operates in its protection zone as required. The automatically tripping of circuit breaker by using relay system will protect the generator, transformer and other electrical equipments that is connected to the network.

39 5.2 Recommendation

For further analysis, simulation can be done by considering:

i.

Other types of faults that can occur in transmission line such as the double lineto-ground fault, line-to-line fault and three-phase fault.

ii.

Other types of distance relay such as the Apple Characteristic and Lens Characteristic.

iii.

Other types of system such as the parallel transmission line circuit.

40

REFERENCES

1. Hadi Saadat “Power System Analysis” Mc Graw Hill, 2004. 2. Theodore Wildi “Electrical Machines, Drives, And Power Systems” Pearson Prentice Hall, 2006. 3. Abdullah Asuhaimi Mohd Zin, Md Shah Majid & Faridah Mohd Taha “ Power System Engineering” Fakulti Kejuruteraan Elektrik, 2009. 4. M.Sanaye-Pasand and H. Seyedi “Simulation, Analysis and Setting of Distance Relays on Double Circuit Transmission Line” Faculty of Engineering, University of Tehran, Iran. 5. G.E Alexander and J.G Andrichak “Ground Distance Relaying: Problems and Principles” General Electric Company Malvern, PA, 1991. 6. G.E Alexander and J.G Andrichak “Ground Distance Fundamentals” General Electric Company Malvern, PA, 1991. 7. M.I. Gilany, O.P. Malik and G.S. Hope “A Digital Protection Technique For Parallel Transmission Lines Using A Single Relay at Each End”, Transaction On Power Delivery, Vol 7 No1, January 1992.

APPENDIX A

MAIN CIRCUIT

Figure A1: Main Circuit Connection

OUTPUT CHANNELS

Figure A2: Output Channel Connections

43 APPENDIX B

REALY CIRCUIT

Figure B1: Realy Circuit Connection

44

Figure B2: Sequence module for current

Figure B3: Sequence module for voltage

45 APPENDIX C

BREAKER CONTROL

Figure C1: Breaker Control Circuit

46 APPENDIX D

1. Fault at location 4

Figure D1: Waveform of fault at location 4 for relay 1

47

Figure D2: Waveform of fault at location 4 for relay 2

48 2. Fault at location 5

Figure D3: Waveform of fault at location 5 for relay 1

49

Figure D4: Waveform of fault at location 5 for relay 2