impact of distributed generation on impedance relay for distribution network

8/10/2019 Impact of Distributed Generation on Impedance Relay for Distribution Network

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I here by declare that I have read this report and in my opinion

this report has fulfills the scope and quality for the award

of the degree of Bachelor of Engineering (Electrical).

Signature : .

Name of Supervisor : Dr. SAIFULNIZAM ABD KHALID

Date : ....


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IMPACT OF DISTRIBUTED GENERATION ON IMPEDANCE RELAY FORDISTRIBUTION NETWORK

GHAZI BIN MOHD YUSUF

A THESIS SUBMITTED IN FULFILLMENT OF THE

REQUIREMENT FOR THE AWARD OF THE DEGREE OF

BACHELOR OF ENGINEERING (ELECTERICAL ENGINEERING)

FACULTY OF ELECTRICAL ENGINEERING

UNIVERSITI TEKNOLOGI MALAYSIA

MEI 2011


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I declare that this thesis entitled Impact of Distributed Generation On Impedance

Relay For Distributed Generation is the result of my own research except as cited in

the references. The thesis has not been accepted for any degree and is notconcurrently submitted in candidature of any other degree.

Signature :

Name : Ghazi Bin Mohd Yusuf

Date :


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Specially dedicated to my beloved parents and friends

for their endless support and encouragement


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ACKNOWLEDGEMENTS

First of all, I would like to thank God for giving me His guidance, blessing

and strength to finish my project.

My sincere appreciation to my project supervisor, Dr. Saifulnizam Abd

Khalid for all his encouragement, guidance and support in completing the final year

project. Not forgetting all the lecturers who have taught me throughout the years

during my study in UTM. I thank you very much for all the knowledge that have

imparted.

I would also like to express my gratitude to my parents for all the sacrifices

and love they have showered on me. A million thanks to the rest of my family

members and closed friends for giving tremendous support in completing this

project.

Last but not least, my sincerest appreciation and words of thanks to all the lab

technicians and tutors for their invaluable contributions in this project.


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ABSTRACT

In every distribution network power system, there is a protection system that

separate the area that is faulty and to reduce the impact on nearest area which may be

faulty to. Today, with distributed generation in distributed network, electrical power

can be distributed to the consumers with effectively.

In this project, fault analysis simulation was simulated into two scenarios -

for distributed network without distributed generation, and with distributed

generation. It analyses the impact distributed generation to the network and to the

protection system. From fault analysis, fault current between two busbar with

distributed generation were compared with fault current between busbar without

distributed generation to see the impact to the impedance relay.

.


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ABSTRAK

Setiap rangkaian agihan dalam sistem kuasa terdapatnya sistem perlindungan

bagi mengasingkan kawasan yang mengalami kerosakan dan mengurangkan

kawasan sekitar dari berlakunya kerosakan. Dengan adanya penjana teragih di

rangkaian agihan Kini, tenaga elektrik dapat dihantar kepada pengguna dengan lebih

berkesan.

Dalam projek ini, simulasi analisis kerosakan dilakukan dalam dua situasi

untuk rangkaian agihan dengan tiada penjana teragih dan dengan penjana teragih.

Analisis dilakukan ke atas kesan kepada rangkaian dan kepada sistem perlindungan.

Untuk analisis kerosakan, arus kerosakan diantara dua busbar dengan penjana teragih

akan dibandingkan dengan arus kerosakan diantara dua busbar tanpa penjana teragih

untuk mengetahui kesannya terhadap geganti jarak.


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TABLE OF CONTENTS

CHAPTER TITLE PAGE

DECLARATION ii

DEDICATION iii

ACKNOWLEDGEMENT iv

ABSTRACT v

ABSTRAK vi

TABLE OF CONTENTS vii

LIST OF TABLES ix

LIST OF FIGURES x

LIST OF ABBREVIATIONS xi

LIST OF SYMBOLS xii

1 INTRODUCTION 1

1.1 Background of Study 1

1.2 Problem Statement 2

1.3 Project Objective 3

1.4 Project Scope 3

1.5 Thesis Outline 3

2 LITERATURE REVIEW 5

2.1 Introduction 5

2.2 Distributed generation 5

2.3 Impedance Relay 6

2.4 Current Transformer 10


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2.5 Voltage Transformer 10

2.6 Fault Current 11

3 METHODOLOGY 123.1 Introduction 12

3.2 Designing the Distribution

Network System Circuit 13

3.2.1 Three Phase Voltage Supply 13

3.2.2 Three Phase Faults 14

3.3 Designing the Distributed Generation 15

4 RESULT AND ANALYSIS 18

4.1 Introduction 18

4.2 Simulation results 18

4.2.1 Impact of Fault Current 19

4.2.2 Impact of Current Source Contribution 21

4.2.3 Impact of impedance Relay 22

4.3 Summary 26

5 CONCLUSIONS AND RECOMMENDATIONS 27

5.1 Conclusions 27

5.2 Recommendations 28

REFERENCES 29


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LIST OF TABLES

TABLE NO. TITLE PAGE

1.1 Fault current value at certain location without distributed 14

generation.

1.2 Fault current value at certain location with distributed 15

generation

1.3 Current contribution from the source with and without 15

distributed generation

1.4 Current value between two busbar without distributed 16

generation

1.5 Current value between two busbar with distributed 16

generation


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LIST OF FIGURES

FIGURE NO. TITLE PAGE

2.1 Operating characteristics of an impedance relay 6

obtained using a phase comparator

2.2 Impedance Z inside the operating zone of R-X 6

characteristic

2.3 Impedance Z outside the operating zone of R-X 7

characteristic

3.1 PSCAD Distribution system circuit 10

3.2 PSCAD Wind Turbine system circuit 11

3.3 Wind Source 12

3.4 Wind Turbine 12

3.5 Wind Turbine governor 12

3.6 Squirrel Cage Induction Machines 13

4.0 Fault current when fault occurs at F3 22



4.3 Current contribution from the source 23

4.4 Current in between busbar when fault occurs at F3 23

4.5 Current in between busbar when fault occurs at F2 234.6 Current in between busbar when fault occurs at F1 24

4.7 Current in between busbar when fault occurs at F2 and F3 24




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LIST OF ABBREVIATIONS

CT - Current Transformer

DG - Diastributed Generation

F1 - Fault at Busbar 1

F2 - Fault at Busbar 2

F3 - Fault at Busbar3

I01 - Current between Busbar 0 and 1



VT - Voltage Transformer


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LIST OF SYMBOLS

ZR - Relay Impedance

Z - Impedance

V - Voltage

I - Current

K - Transformation RatioSo - Phase Comparator

Sr - Phase Comparator for Relay

Is - Current Source


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CHAPTER 1

INTRODUCTION

1.1 Background of study

Electric supply is important to all the people in the world. Without it, people

cannot do anything and daily life will be difficult such as using candles to read, using

wood to make fire for cooking and much more. Today with the development of an

advance technology, many new things have been produced to make our life better,

including the provision of electricity. Houses and buildings now have been supplied

with electricity and with it everything can be easily.

To make electricity operates continuously system protection must be included

to the network either in generation, transmission or distribution network. It is

important to protect from faults through the isolation parts, keeps the power system

stable and allowing as much provision as possible to enable the network operates

effectively.


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Many of the system protection are using over current relay while some places

use distributed generation. There are many relays that can be used as system

protection such as impedance relay and differential relay. Impedance relay is

impossible to use and apply because it is too expensive and complicated to set andmaintain. If impedance relay is used, it a special trainee personal is needed to set and

to maintain.

1.2 Problem Statement

Local distributed generation and untraditional energy source like diesel,

wind, wave, tidal power and others are now challenging the structure of sub-

transmission and distribution network. When distributed generation is installed at

the distribution network, there will be some effect that will occur to the network and

to the protection system. Problem will arise when distributed generation result in low

in-feed compared to the capacity of feeding system transformer. During faults, short

circuit current may be low because of high short circuit impedance. When the short

circuit current is higher, it will be easily become less then the load current in the

supply source and over current protection cannot protect the network. Because of

this, other protection system has to be introduced to overcome the situation. Distance

relay is one of the protection system solutions that can be used [1].


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1.3 Project Objectives

For this project, there are some objectives that have to be achieved. First,

study the impact of distributed generation on impedance relay and study of

impedance relay. Next is to investigate the impact towards the distribution network

when distributed generation is inserted, and lastly is to obtain the impedance relay

characteristics at the distribution network to see the success of the impedance relay.

1.4 Project Scope

Several scopes had been outlined in order to achieve the objective of the

project. The scope of this project including using PSCAD software to modeling and

simulate the distribution network with and without distributed generation. Wind

turbine will be used as distributed generation at the end of the circuit and three phase

fault to ground will occurs at several busbar. Last but not least, a graph of current

value is obtained by using Microsoft excel 2007 to compare the current that flow

between busbar with and without DG to observe the relay operation.

1.5 Thesis Outline

This thesis is divided into five important chapters. In Chapter 1, it briefed

about the introduction on the background of the project, the project objectives and

scope. While Chapter 2 will explain the literature review of the project including

explanation of distributed generation, impedance relay, current transformer and

voltage transformer. In Chapter 3, the discussion will be on methodology and

software implementation using PSCAD. Then, Chapter 4 will discuss and analyses


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the results that is obtained from the simulation of the system. Last but not least,

Chapter 5 will conclude the project and provides recommendations for future work.


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CHAPTER 2

LITERATURE REVIEW

2.1 Introduction

This chapter includes the study of distributed generation, impedance relay,

current transformer, voltage transformer and fault current.

2.2 Distributed Generation (DG)

Distributed generation can be describe as an electrical power source that is

connected directly to the power network, sufficiently smaller than the controlling

generating plant and it is preferably at the customer side of the meter.

It can be divide into 4 levels. Micro DG (between 1W and 5kW), small DG

(between 5kW and 5MW), medium DG (between 5MW and 50MW) and the last one

is large DG (between 50MW and 300MW). To drive the DG, there are several

energy sources that can be used such as reciprocating engines, combustion turbines,

micro-turbines, wind turbines, fuel cells and photovoltaic [2].


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Using DG can give many advantage, helps to reduce losses in distribution

network, as a back-up generation, maintain stable operation on the grid, cogeneration

and provide higher power quality for electric equipment. This advantages is base on

grid support, environmental concerns, DG combined generation, heat capacity,power quality and system frequency [3].

2.3 Impedance Relay

Protection system is important to protect the network from disturbances that

may occur. Impedance relay is one of distance relay that can provide adequate

protection. This relay will monitor the impedance between the relay location and the

fault. During fault, the voltage will drop and the current will rise. The relay will

operate when the impedance falls within the relay setting and it does not take

account the phase and angle between voltage and current applied. The relay will

operate when

ZR >= V/I (2.1)

IZR>= V (2.2)

where

ZR = impedance relay setting

V = voltage

I = current


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Soand Srshould be assigned if the impedance relay wants to work as phase

comparator.

So= IZR (2.3)Sr = KV (2.4)

where

So = operation setting

Sr = restrain setting

Constant K is transformation ratios of the CTs and VTs. The corresponding

signals for phase comparator is

S1 = Sr+ So (2.5)

S2 = -Sr+ So (2.6)

where

S1= phase comparator 1

S2= phase comparator 2

Then, divide equation 2.5 and 2.6 with KI. The equation will be

S1 = Z + ZR/K (2.7)

S2= -Z + ZR/K (2.8)

where

Z = V/I (2.9)

I = Z/R (2.10)


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Angle different between S1 and S2 is and to get the , rhomboid OABC

must be constructed from diagonal of S1and S2. From Figure 2.1, is 90 when [Z] =

[ZR/K]. Therefore, the limit for relay to operate is inside the locus of point C. Figure

2.2 shows that the is less than 90. Meaning Z is less than Z R/K and vector for Z isinside the relay operation and will make the relay operate. For Figure 2.3, it shows

that the is greater than 90. Meaning Z is greater than ZR/K and vector for Z is

outside the relay operation. Therefore the relay will not operate. [4]

Figure 2.1 Operating characteristics of an impedance relay obtained using a

phase comparator

X

R

Limit ofoperating point

O

A

= 90

S2

Z

ZR/K

S1

B

CZ


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Figure 2.2 Impedance Z inside the operating zone of R-X characteristic

Figure 2.3 Impedance Z outside the operating zone of R-X characteristic

Operating

zone

X

R0

ZR/K

Z

S2

90

0

OperatingOperating

zone

A

C

B


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2.4 Current Transformer (CT)

Current transformer is used for measurement of electric current. When

current that runs through the network is too high and was applied to measuring

instrument, current transformer will produce a reduced current accurately

proportional to the current that flows in the network. Commonly CT is used in

metering and protective relay in high voltage electrical power industry. The accuracy

of the CT is directly related to a number of a certain factor including burden, rating

factor, load, temperature, physical configuration and the selected tap [5].

2.5 Voltage Transformer (VT)

Voltage transformer is a device to change the voltage of electricity flowing in

the circuit either to increase the voltage (stepping up) or decrease the voltage

(stepping down) [6]. It is used to operate protective relay and devices and other

application. The secondary voltage has a fixed relationship to the primary voltage.

So that a change in potential within the primary circuit is monitored accurately by

meters connected across the secondary terminals. There are some performance

specifications for VT that includes accuracy, operating temperature, primary and

secondary voltage range and burden and insulation voltage [7].


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2.6 Fault Current

Fault current or short circuit current can be described as current flow during a

short circuit. Fault current is generally very large and very hazardous and can cause

death [8].


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CHAPTER 3

METHODOLOGY

3.1 Introduction

PSCAD is one of the software that enables users to schematically construct a

circuit, run a simulation, analyze the results, and manage the data in a completely

integrated, graphical environment. This software also includes online plotting

functions, controls and meter, so that users can alter system parameters during a

simulation run, and view the results directly. [9]

In this project, PSCAD software is used to model and simulate a fault current

in a distribution network. The fault is applied at certain busbar to get the current flow

in between two busbars. The frequency used in the system is 50Hz, base MVA for

the power system is 100 MVA and the base line to line voltage is 11kV. The system

is injected with three lines to ground fault at different locations to get the value of

current flow.

The system designed can be divided into two sections, distribution network

circuit and distributed generation circuit.


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3.2 Designing the Distribution Network System Circuit

Figure 3.1 shows a single line diagram of the distribution system circuit

designed using PSCAD software. The system is a four-bus system with one end

being the power supply and another end is distributed generation. Each busbar has

balance load and between the busbar is the line impedance. A fault model is placed

at three different locations. Fault location is determined by a controller.

Figure 3.0 PSCAD Distribution system circuit

3.2.1 Three Phase Voltage Supply

Figure 3.1 show the Three Phase Voltage Source Model 3. It is used to

generate the voltage for the circuit and permits users to control the line-to-line RMS

voltage magnitude to be controlled. For this particular system, the line-to-line

voltage and phase angle is set to 11kV and 0 respectively.


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Below was the table for values used of the voltage source configuration.

Table 3.1: Values of voltage source configuration

Base MVA (3-phase) 100MVABase voltage (L-L, RMS) 11kV

Base frequency 50Hz

Figure 3.1 Three Phase Voltage Source Model 3

3.2.2 Three Phase Faults

Figure 3.2 show the Three Phase Fault. It is used to generate fault. It permits

the users to control the faults, line to line or line to neutral faults. For this particular

system, three phase to neutral is being set.

Figure 3.2 Three Phase Fault


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3.3 Designing the Distributed Generation

The distribution comes from wind turbine that is injected in the end of the

circuit. Figure 3.3 shows an example of wind turbine circuit that has been construct

for this project. The system consists of wind source mean, wind turbine MOD2 type,wind turbine governor MOD2 type, and wind generator.

Figure 3.3 PSCAD Wind Turbine system circuit

Figure 3.4 show the wind source component models with the wind speed

through the wind turbine. Input sign for external signal (ES) representing wind speed

and wind speed (Vw) are the output of the wind source and be connected to the

turbine. The external input ES can be used to input any type of wind variation and

the user has the option to enable or disable this input. In this project external wind

speed has been used [10].

Figure 3.4 Wind Source


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Figure 3.5 show the wind turbine model. Wind speed (Vw) and the

mechanical speed of the machine (w) connected to the turbine are the inputs. Beta is

the pitch angle of the turbine blades and is entered in degrees. Output torque (Tm)

and the output power (P) are based on the machine rating. Tmwill be connected tothe induction machines (IM) [10].

Figure 3.5 Wind turbine

Figure 3.6 show the wind turbine governer that models a pitch angle regulator

of a wind turbine. The inputs are the mechanical speed of the machines (Wm) and the

power output of the machines (Pg). In this project , Induction machines is used andWm will not be available. The output is pitch angle (beta) of the wind turbine

governor and be the input of the wind turbine [10].

Figure 3.6 Wind Turbine Governor


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Figure 3.7 show the squirrel cage induction machine. This machine can be

operated either via speed control or torque control modes. In speed control mode,

machine rotates at the speed specified at the input W. In this project, speed control is

being used. The T gained from the gain that will multiply a signal that is Tmby thefactor specified [10].

Figure 3.7 Squirrel Cage Induction Machines


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CHAPTER 4

RESULT AND ANALYSIS

4.1 Introduction

This chapter discusses the result that is obtained from the simulation of

adding distributed generation to the system by using PSCAD. The fault current will

be measured at busbar 1, 2, and 3 and current between the busbar I01, I12and I23 when

fault occurs at certain cases. The negative sign from the table can be ignored because

it shows the direction of the current flow at the line. There are two cases in this

project, first one is when fault occurs only at one busbar and the other case is when

fault occurs at two busbar at the same time.

4.2 Simulation Results

From the simulation result, there are several impacts that can be seen when

distributed generation was inserted to the system. Result from the simulation has

been tabulated and plotted using Microsoft excel.


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4.2.1 Impact of Fault Current

Table 4.0 and 4.1 shows the difference in fault current value that flow when

fault occurs at busbar 1, 2 and 3, with and without distributed generation. The fault

current is increasing when distributed generation was inserting at the end of the

system. Figure 4.0, 4.1 and 4.2 shows the graph different of fault current when fault

occurs at F1, F2and F3.

Table 4.0: Fault current at certain location without distributed generation

Fault location IF1 IF2 IF3

F3 0.0214 0.0128 345.655

F2 0.0179 593.736 0.005

F1 1281.92 0.0055 0.005

Table 4.1: Fault current at certain location with distributed generation

Fault location IF1 IF2 IF3

F3 0.0211 0.0097 576.974

F2 0.0152 1176.39 0.0141

F1 1551.82 0.0069 0.0141


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Figure 4.0 Fault current at F1




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4.2.2 Impact of Current Source Contribution

Current contribution from the source was another impact that can be seen

when inserting distributed generation at the end of the system. Table 4.2 below show

the current contribution from the source with and without distributed generation and

it shows that the current is decreasing when there was distributed generation. It

happened because the distributed generation is supplying the current to the load.

Figure 4.3 show the different in current contribution from the source.

Table 4.2: Current contribution from the source

Distributed generation Fault location Is

No No 613.198

Yes No 565.827

Figure 4.3 Current Contribution Source


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4.2.3 Impact of Impedance Relay

For the impedance relay, current flow between two busbar has been measured

from the simulation and been tabulated in tables 1.4 and 1.5. Table 1.4 is the current

flow when there was no distributed generation and will be as a the relay setting.

From the equation for impedance relay, impedance Z will be used to gauge and

understand the range of the operation. But in this project, current value that flowed in

between busbar will be used to compare whether it will be tripped or not and the

voltage is constant 11 kV.

From equation (2.9), the equation can be rearrange to equation (2.10). Relaywill operate when impedance (Z) is smaller than the impedance relay ZR. From

equation (2.10), when impedance (Z) is small, current (I) is high. Meaning when

current is bigger than the current setting, the relay will operate and if the current is

smaller than the setting, the relay is considered not operating. The current setting can

be obtained from the current flow in between two busbar without distributed

generation.

Figure 4.4 show when the fault occur at F3, current at I23with DG is higher

than without DG. It shows that the relay at that current flow will operate because the

current value is higher than the setting. It same does for the figure 4.5 and 4.6 that

fault occurs at F2 and F1 respectively. Relay at I12 and I23will operate when fault

occur at F2and Relay at I01, I12, I23will operate when fault occur at F1.


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When two fault occur at the same time at two busbar, the results as in figure

4.7, 4.8 and 4.9. When fault occurs at F2and F3, relay at I12will operate and relay at

I23is not functioning because there is no current that flow in that relay. Then, when

the fault occurs at F1 and F2, relay at I01 and I23 will operate and relay I12 is notfunctioning because there is no currant flow at the relay. Last but not least, when

fault occurs at F1and F3, relay at I01will operate and relay at another two place is not

operating because when there is DG, there is no current flow at I12and I23.

Table 4.3: Current value between two busbar without distributed generation

fault location I01 I12 I23

F3 530.306 406.205 345.655F2 688.408 593.741 0.0045

F1 1281.93 0.008 0.0035

F2 & F3 688.408 593.741 0

F1 & F2 1281.93 0 0.0045

F1 & F3 1281.93 0.0026 -0.0026

Table 4.4: Current value between two busbar with distributed generation

fault location I01 I12 I23F3 530.304 406.204 345.657

F2 688.407 593.742 -582.651

F1 1281.9 -269.891 -312.901

F2 & F3 688.407 593.742 0

F1 & F2 1281.9 0 -582.651

F1 & F3 1281.93 0 0


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Figure 4.4 Current between busbar when fault at F3




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Figure 4.7 Current between busbar when fault at F2and F3




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4.3 Summary

With a distributed generation, many impact can be seen at distributionnetwork and impedance relay. Fault current are increasing while current contribution

from the source are decreasing. It because of the power that comes from distributed

generation. For impedance relay, the relay setting was from fault current flow when

there is no distributed generation. Then, distributed generation was inserted to the

network. If the fault current is higher than the setting, the relay will operate and vice

versa.


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CHAPTER 5

CONCLUSIONS AND RECOMMENDATION

5.1 Conclusions

There is an impact when inserting distributed generation to the distribution

network system. The fault current occurs at the fault will increase due to source on a

network that comes from the distribution system and distributed generation or from

the loads. Current contribution from the source will also decrease due to the power

delivered by the distributed generation to the load.

For impedance relay, it can be used when inserting distributed generation

because the relay will function due to the current differences with and without

distributed generation.


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5.2 Recommendations

Studies on distributed generation on distribution network and impedance

relay can still be expanded. Listed below are several recommendations that can be

carried out in future research.

i) Insert more distributed generation to the network

ii) Consider other type of distribution generation

iii) Consider more busbar to be used

iv) Consider other type of fault

v)

Consider other type of distance relay


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REFFERENCES

[1] http://www.jacobson_elektro.com/Brochures_english/Impedance_relay-

in_Distribution_network_rev_01.pdf

[2] James A. Momoh, Electric Power Distribution, Automation, Protection and

Control, CRC press, 2008

[3] T.A.Short, Electric Power Distribution Handbook, CRC press,2003

[4] P.J. Freeman, Electric Power Transmission and Distribution, Harrap

London, 1977

[5] http//:www.wikipedia.Current_transformer.htm

[6] http//:www.globalspecevent.voltage_transformers.htm

[7] http//:www.windowstotheuniverse. Voltage Transformers in Electric

Circuits.html

[8] http://www.trane.com/commercial/library/vol273/fault.asp

[9] PSCAD Electromagnetic Transients. Users Guide. Version 4.

[10] PSCAD on-Line Help System Version 4.2

[11] http://www.electricenergyonline.com/?page=show_article&mag=22&article

[12] http://www.esbi.ie/news/pdf/White-Paper-Distribution-Network-
http://www.jacobson_elektro.com/Brochures_english/Impedance_relay-in_Distribution_network_rev_01.pdfhttp://www.jacobson_elektro.com/Brochures_english/Impedance_relay-in_Distribution_network_rev_01.pdfhttp://www.trane.com/commercial/library/vol273/fault.asphttp://www.esbi.ie/news/pdf/White-Paper-Distribution-Network-Protection.pdfhttp://www.esbi.ie/news/pdf/White-Paper-Distribution-Network-Protection.pdfhttp://www.trane.com/commercial/library/vol273/fault.asphttp://www.jacobson_elektro.com/Brochures_english/Impedance_relay-in_Distribution_network_rev_01.pdfhttp://www.jacobson_elektro.com/Brochures_english/Impedance_relay-in_Distribution_network_rev_01.pdf

impact of distributed generation on impedance relay for distribution network

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