VOLTAGE SAGS MITIGATION TECHNIQUES ANALYSIS
NORSHAFINASH BINTI SAUDIN
A project report submitted in partial fulfillment of the
requirements for the award of the degree of Master of Engineering
(Electrical Power)
Faculty of Electrical Engineering Universiti Teknologi
Malaysia
JUNE 2007
I hereby declare that I have read this thesis and in my opinion
this thesis is sufficient in terms of scope and quality for the
award of the degree of Master of Engineering (Electrical Power)
Signature Name Date
: : :
... Dr. Ahmad Safawi Bin Mokhtar 18 June 2007
ii
I declare that this thesis entitled Voltage Sags Mitigation
Techniques Analysis is the result of my own research except as
cited in the references. The thesis has not been accepted for any
degree and is not concurrently submitted in candidature of any
other degree.
Signature Name Date
: : :
. Norshafinash Binti Saudin 18 June 2007
iii
To my beloved husband
iv
ACKNOWLEDGEMENT
I would like to express my gratitude to Allah S.W.T. for giving
me the opportunity to complete this Masters Project. I am deeply
indebted to individuals who, directly or indirectly, are
responsible for this project.
I am most grateful to the most kindheartedness supervisor Dr
Ahmad Safawi bin Mokhtar for his guidance in this project and to
panel of seminar presentation, PM. Dr. Mohd Wazir bin Mustafa and
PM. Md. Shah Majid, with their superior guidance, information and
ideas for this project become abundance.
My admiration falls upon En. Saudin bin Mat, my father, and
especially to my mother, Pn. Siah binti Taharin for them to bear
with me my absence in the family. Your encouragement, pray and
support are very much appreciated.
I would also like to express my sincere thanks to my entire
friend for their support and ideas during the development of the
project.
And last but not the least, to my husband, thanks.
v
ABSTRACT
For some decades, power quality did not cause any problem,
because it had no effect on most of the loads connected to the
electric distribution system. When an induction motor is subjected
to voltage sag, the motor still operates but with a lower output
until the sag ends. With the increased use of sophisticated
electronics, high efficiency variable speed drive, and power
electronic controller, power quality has become an increasing
concern to utilities and customers. Voltage sags is the most common
type of power quality disturbance in the distribution system. It
can be caused by fault in the electrical network or by the starting
of a large induction motor. Although the electric utilities have
made a substantial amount of investment to improve the reliability
of the network, they cannot control the external factor that causes
the fault, such as lightning or accumulation of salt at a
transmission tower located near to sea. This project intends to
investigate mitigation technique that is suitable for different
type of voltage sags source with different type of loads. The
simulation will be using PSCAD/EMTDC software. The mitigation
techniques that will be studied are such as Dynamic Voltage
Restorer (DVR), Distribution Static Compensator (DSTATCOM) and
Solid State Transfer Switch (SSTS). All the mitigation techniques
will be tested on different type of faults. The analysis will focus
on the effectiveness of these techniques in mitigating the voltage
sags. The study will also investigate the effects of using the
techniques to phase shift. At the end of the project it is expected
that a few suggestions can be made on the suitability of the
techniques.
vi
ABSTRAK
Beberapa dekad yang lalu, kualiti kuasa tidak menjadi
permasalahan kerana ia tidak memberi kesan yang sangat nyata kepada
beban yang bersambung dengan sistem pengagihan. Apabila motor
aruhan mengalami voltan lendut, motor tersebut masih berfungsi
tetapi dengan keluaran yang lebih rendah sehingga kejatuhan voltan
tamat. Walau bagaimanapun, dengan peningkatan penggunaan peralatan
elektronik yang maju, pemacu pelbagai halaju berkecekapan tinggi,
dan pengawal elektronik kuasa, kualiti kuasa mula menjadi perhatian
kepada utiliti dan pelanggan. Di mana, voltan lendut adalah
gangguan kualiti kuasa yang seringkali terjadi terhadap sistem
pengagihan yang disebabkan oleh kerosakan pada rangkaian elektrik
dan pemulaan yang besar untuk motor aruhan. Walaupun utiliti telah
membuat pelaburan untuk memperbaiki keboleharapan rangkaian, faktor
luaran yang menyebabkan kerosakan masih tidak dapat dikawal,
contohnya kilat dan pengumpulan garam pada menara penghantaraan
yang terletak berhampiran dengan laut. Oleh itu, projek ini
bertujuan mengkaji kesesuaian teknik mitigasi untuk pelbagai punca
voltan lendut pada beban yang berbeza di mana perisian PSCAD/EMTDC
digunakan sebagai bantuan untuk simulasi. Teknik - teknik mitigasi
yang dikaji adalah seperti Dynamic Voltage Restorer (DVR),
Distribution Static Compensator (DSTATCOM), dan Solid State
Transfer Switch (SSTS). Teknik - teknik ini akan diuji dengan
pelbagai kerosakan yang menyebabkan voltan lendut. Tumpuan akan
diberikan kepada keberkesanan teknik-teknik tersebut untuk
mengatasi voltan lendut dan kesannya terhadap anjakan fasa. Di
akhir projek ini, beberapa cadangan akan diutarakan berkenaan
kesesuaian teknik - teknik tersebut digunakan untuk mengatasai
voltan lendut.
vii
TABLE OF CONTENTS
CHAPTER
TITLE
PAGE
DECLARATION DEDICATION ACKNOWLEDGEMENT ABSTRACT ABSTRAK TABLE OF
CONTENTS LIST OF TABLES LIST OF FIGURES LIST OF ABBREVIATIONS LIST
OF APPENDICES
ii iii iv v vi vii xi xii xv xvi
I
INTRODUCTION
1
1.1 1.2 1.3 1.4
Introduction Problem Statement Project Objectives Project
Scope
1 3 6 6
viii
II
VOLTAGE SAGS
7
2.1 2.2 2.3
Introduction Definition of Voltage Sags Standards Associated
with Voltage Sags 2.3.1 IEEE Standard 2.3.2 Industry Standard
2.3.2.1 SEMI 2.3.2.2 CBEMA (ITI) Curve
7 8 9 10 12 12 14 15 15 17 18
2.4
General Causes and Effects of Voltage Sags 2.4.1 Voltage Sags
due to Faults 2.4.2 Voltage Sags due to Motor Starting 2.4.3
Voltage Sags due to Transformer Energizing
III
PSCAD/EMTDC SOFTWARE
19
3.1 3.2 3.3 3.4
Introduction Characteristics of Software Example of Circuit
Conclusion
19 20 22 25
ix
IV
VOLTAGE SAG MITIGATION TECHNIQUES
26
4.1 4.2
Introduction Dynamic Voltage Restorer (DVR) 4.2.1 Principles of
DVR Operation
26 28 28 30
4.3
Distribution Static Compensator (DSTATCOM) 4.2.1 Basic
Configuration and Function of DSTATCOM
31 34 35
4.4
Solid State Transfer Switch (SSTS) 4.4.1 Basic Configuration and
Function of SSTS
V
MITIGATION TECNIQUES REALIZATION
39
5.1 5.2 5.3 5.4 5.5
Sinusoidal PWM-Based Control Scheme Test System Dynamic Voltage
Restorer Distribution Static Compensator Solid State Transfer
Switch
39 42 43 45 47
x
VI
SIMULATIONS AND RESULTS
49
6.1 6.2
Test case Single line to ground fault 6.2.1 Phase A to ground
6.2.2 Phase B to ground 6.2.3 Phase C to ground
49 50 50 56 59 62 62 67 70 73
6.3
Double lines to ground fault 6.3.1 Phase A and B to ground 6.3.2
Phase A and C to ground 6.3.3 Phase B and C to ground
6.4
Conclusion
VII
CONCLUSION
74
7.1 7.2
Conclusion Suggestion
74 77
REFERENCES Appendices A-C
78 81-85
xi
LIST OF TABLES
TABLE NO.
TITLE
PAGE
1.1 6.1 6.2 6.3 6.4 6.5 6.6
Cause of TNB network disruption. (a) Test results for line A to
the ground fault. (b) Recovery result. (a) Test results for line B
to the ground fault. (b) Recovery result. (a) Test results for line
C to the ground fault. (b) Recovery result. (a) Test results for
line AB to the ground fault. (b) Recovery result. (a) Test results
for line AC to the ground fault. (b) Recovery result. (a) Test
results for line BC to the ground fault. (b) Recovery result.
4 5 8 1 6 9 2
xii
LIST OF FIGURES
FIGURE NO.
TITLE
PAGE
1.1
Demarcation of the various power quality issues defined by IEEE
Std. 1159-1995 2 9
2.1 2.2
Depiction of voltage sag Immunity curve for semiconductor
manufacturing equipment according to SEMI F47
13 14 16 17 18 23 24
2.3 2.4 2.5 2.6 3.1 3.2 4.1
Revised CBEMA curve, ITIC curve, 1996 Voltage sag due to a
cleared line-ground fault Voltage sag due to motor starting Voltage
sag due to transformer energizing DVR with main components in PSCAD
The Wye-Connected DVR in PSCAD Different protection options for
improving performance during power quality variation.
27
4.2
Principle of DVR with a response time of less than one
millisecond 29
4.3
Schematic diagram of the DSTATCOM as a custom power controller
30 32 33
4.4 4.5
Building blocks of DSTATCOM Operation modes of a DSTATCOM
xiii 4.6 4.7 4.8 Schematic representations of the SSTS as a
custom power device. 34 Solid State Transfer Switch systems
Thyristors of the SSTS conducting in the positive and negative half
cycle of the preferred source. 4.9 Thyristors on the alternate
supply are turned ON on sensing a disturbance on the preferred
source. 5.1 Control scheme for the test system implemented in
PSCAD/EMTDC to carry out the DSTATCOM and DVR simulations. 5.2 5.3
5.4 5.5 The test system implemented in PSCAD/EMTDC One line diagram
of the DVR test system Schematic diagram of the DVR Schematic
diagram of the test system with DVR connected to the system. 5.6
5.7 One line diagram of the DSTATCOM test system. Schematic diagram
of the test system with DSTATCOM connected to the system. 5.8 5.9
5.10 One line diagram of the SSTS test system. SSTS switches
implemented in PSCAD/EMTDC Schematic diagram of the test system
with SSTS connected to the system. 6.1 (a) Phase shift for line A
to the ground fault (b) Rms voltage drop 6.2 (a) Corrected phase
with DVR (b) Compensated voltage sag with DVR 6.3 (a) Corrected
phase using DSTATCOM (b) Compensated voltage sag using DSTATCOM 6.4
(a) Corrected phase using SSTS (b) Compensated voltage sag using
SSTS 6.5 Phase shift of line B to the ground fault. 54 56 53 51 50
48 46 47 48 44 45 40 42 43 44 38 37 35
xiv
6.6
(a) Phase correction using DVR (b) Phase correction using
DSTATCOM; line B to the ground fault. 57 59
6.7 6.8
Phase shift of line B to the ground fault. (a) Phase correction
using DVR (b) Phase correction using DSTATCOM; line C to the ground
fault.
60
6.9
(a) Phase shift for line A and B to the ground fault (b) Rms
voltage drop 63
6.10
(a) Phase correction using DVR, (b) Phase correction using
DSTATCOM; line A and B to the ground fault. 64
6.11
(a) Compensated voltage sag using DVR (b) Compensated voltage
sag using DSTATCOM; Line A and B to the ground fault. 65 67
6.12 6.13
Phase shift for line A and C to the ground fault (a) Phase
correction using DVR, (b) Phase correction using DSTATCOM; line A
and C to the ground fault.
68 70
6.14 6.15
Phase shift for line B and C to the ground fault. (a) Phase
correction using DVR, (b) Phase correction using DSTATCOM; line B
and C to the ground fault.
71
xv
LIST OF ABBREVIATIONS
CBEMA
-
Computer Business Equipment Manufacturers Association
Distribution Static Compensator Dynamic Voltage Restorer
Electromagnetic Transient Program with DC Analysis Electronic
Restart Modules Hertz International Electrotechnical Commission
Institute of Electrical and Electronics Engineers Information
Technology Industry Council kilovolt megavolt ampere mega volt amps
reactive megawatt per unit point of common coupling Power System
Aided Design Pulse Width Modulation root mean square Semiconductor
Equipment and Materials International Solid State Transfer Switch
Tenaga Nasional Berhad transient recovery voltage
DSTATCOM DVR EMTDC ERM Hz IEC IEEE ITIC kV MVA MVAR MW p.u. PCC
PSCAD PWM RMS SEMI SSTS TNB TRV -
xvi
LIST OF APPENDICES
APPENDIX
TITLE
PAGE
A B C
Data generated by PSCAD/EMTDC for DSTATCOM Data generated by
PSCAD/EMTDC for DVR Data generated by PSCAD/EMTDC for SSTS
81 83 85
CHAPTER I
INTRODUCTION
1.1
Introduction
Both electric utilities and end users of electrical power are
becoming increasingly concerned about the quality of electric
power. The term power quality has become one of the most prolific
buzzword in the power industry since the late 1980s [1]. The issue
in electricity power sector delivery is not confined to only energy
efficiency and environment but more importantly on quality and
continuity of supply or power quality and supply quality.
Electrical Power quality is the degree of any deviation from the
nominal values of the voltage magnitude and frequency. Power
quality may also be defined as the degree to which both the
utilization and delivery of electric power affects the performance
of electrical equipment [2]. From a customer perspective, a power
quality problem is defined as any power problem manifested in
voltage, current, or frequency deviations that result in power
failure or disoperation of customer of equipment [3].
2 Power quality problems concerning frequency deviation are the
presence of harmonics and other departures from the intended
frequency of the alternating supply voltage. On the other hand,
power quality problems concerning voltage magnitude deviations can
be in the form of voltage fluctuations, especially those causing
flicker. Other voltage problems are the voltage sags, short
interruptions and transient over voltages. Transient over voltage
has some of the characteristics of high-frequency phenomena. In a
three-phase system unbalanced voltages also is a power quality
problem [2]. Among them, two power quality problems have been
identified to be of major concern to the customers are voltage sags
and harmonics, but this project will be focusing on voltage
sags.
Figures 1.1 describe the demarcation of the various power
quality issues defined by IEEE Std. 1159-1995. [4]
Figure 1.1
Demarcation of the various power quality issues defined by IEEE
Std. 1159-1995[4]
3
Three factors that are driving interest and serious concerns in
power quality are [1]:
i.
Increased load sensitivity and production automation. The focus
on power quality is therefore more of voltage quality as the
momentary drop in voltage disrupts automated manufacturing
processes.
ii.
Automation and efficiency relies on digital components which
requires dc supply. As public utilities supply ac power, dc power
supplies powered by ac are needed by the dc loads.
iii.
As more dc power supply are needed the converters that convert
ac to dc cause harmonics to be injected into the system and hence
reduce wave form quality
1.2
Problem Statement
With the increased use of sophisticated electronics, high
efficiency variable speed drive, and power electronic controller,
power quality has become an increasing concern to utilities and
customers. Voltage sags is the most common type of power quality
disturbance in the distribution system. It can be caused by fault
in the electrical network or by the starting of a large induction
motor. Although the electric utilities have made a substantial
amount of investment to improve the reliability of the network,
they cannot control the external factor that causes the fault, such
as lightning or accumulation of salt at a transmission tower
located near to sea.
4 Meanwhile during short circuits, bus voltages throughout the
supply network are depressed, severities of which are dependent of
the distance from each bus to point where the short circuit occurs.
After clearance of the fault by the protective system the voltages
return to their new steady state values. Part of the circuit that
is cleared will suffer supply disruption or blackout. Thus in
general a short circuit will cause voltage sags throughout the
system but cause blackout to a small portion of the network
[1].
A comprehensive study on the cost of losses due to power quality
problem has not been carried out yet. However, it has been reported
that a petrochemical based industries customer in the Tenaga
Nasional Berhad, Malaysia system can lose up to RM164,000
(US$43,000) per incident related to power quality problem due to
voltage sag. Another semiconductor-based industry in the Klang
Valley has estimated the loss of RM5million for the year 2000.
Other types of industries such the cement and garment industries in
Malaysia have also reported huge losses due power quality problems.
One cement plant has reported an average loss of RM300, 000 per
incident [2].
5
Table 1.1
Cause of TNB network disruption [2]
In general, voltage sags can causes:
i. ii. iii. iv. v. vi. vii. viii. ix. x.
Motor load to stall/stop Digital devices to reset causing loss
of data Equipment damage and/or failure Materials Spoilage Lost
production due to downtime Additional costs Product reworks Product
quality impacts Impacts on customer relations such as late delivery
and lost of sales Cost of investigations into problem
Therefore, this project intends to investigate mitigation
technique that is suitable for different type of voltage sags
source with different type of loads.
6 1.3 Project Objectives
The objectives of this project are:
i.
To investigate suitable mitigation techniques for different type
of voltage sags source that connected to linear and non-linear
load.
ii. iii.
To simulate and analyze the techniques using PSCAD/EMTDC
software. To observe the effect on the characteristic of voltage
sag such as the magnitude and phase shift for each techniques.
iv.
To make a few suggestions on the suitability of such techniques
used for both type of loads.
1.4
Project Scope
The scopes for the project are:
i.
Mitigation techniques that will be studied a. Dynamic Voltage
Restorer (DVR), b. Distribution Static Compensator (D-STATCOM), c.
Solid State Transfers Switch (SSTS), and
ii. iii.
All techniques will be tested on different type of loads.
Analysis will focus on effectiveness of each techniques in
mitigating the voltage sags
CHAPTER II
VOLTAGE SAGS
2.1
Introduction
Voltage sags are huge problems for many industries, and it is
probably the most pressing power quality problem today. Voltage
sags may cause tripping and large torque peaks in electrical
machines. Tripping is caused by under voltage protection or over
current protection. These two protections operate independently.
Large torque peaks may cause damage to the shaft or equipment
connected to the shaft. Some common reason for voltage sags are
lightning strikes in power lines, equipment failures, accidental
contact power lines, and electrical machine starts. Despite being a
short duration between 10 milliseconds to 1 second event during
which a reduction in the RMS voltage magnitude takes place, a small
reduction in the system voltage can cause serious consequences
[5].
8 2.2 Definition of Voltage Sags
The definition of voltage sags is often set based on two
parameters, magnitude or depth and duration. However, these
parameters are interpreted differently by various sources. Other
important parameters that describe voltage sags are:
i. ii.
the point-on-wave where the voltage sags occurs, and how the
phase angle changes during the voltage sag. A phase angle jump
during a fault is due to the change of the X/R-ratio. The phase
angle jump is a problem especially for power electronics using
phase or zero-crossing switching.
The voltage sags as defined by IEEE Standard 1159, IEEE
Recommended Practice for Monitoring Electric Power Quality, is a
decrease in RMS voltage or current at the power frequency for
durations from 0.5 cycles to 1 minute, reported as the remaining
voltage. Typical values are between 0.1 p.u. and 0.9 p.u., and
typical fault clearing times range from three to thirty cycles
depending on the fault current magnitude and the type of over
current detection and interruption [4].
Terminology used to describe the magnitude of voltage sag is
often confusing. The recommended terminology according to IEEE Std.
1159 is the sag to 20%, which means that line voltage is reduced to
20% of normal value. Another definition as given in IEEE Std. 1159,
3.1.73 is A variation of the RMS value of the voltage from nominal
voltage for a time greater than 0.5 cycles of the power frequency
but less than or equal to 1 minute. Usually further described using
a modifier indicating the magnitude of a voltage variation (e.g.
sag, swell, or interruption) and possibly a modifier indicating the
duration of the variation (e.g., instantaneous, momentary, or
temporary). Figure 2.1 shows the rectangular depiction of the
voltage sag.
9
Figure 2.1
Depiction of voltage sag
2.3
Standards Associated with Voltage Sags
Standards associated with voltage sags are intended to be used
as reference documents describing single components and systems in
a power system. Both the manufacturers and the buyers use these
standards to meet better power quality requirements. Manufactures
develop products meeting the requirements of a standard, and buyers
demand from the manufactures that the product comply with the
standard [2].
The most common standards dealing with power quality are the
ones issued by IEEE, IEC, CBEMA, and SEMI. A brief description of
each of the standards is provided in next subtopic.
10 2.3.1 IEEE Standard
The Technical Committees of the IEEE societies and the Standards
Coordinating Committees of IEEE Standards Board develop IEEE
standards. The IEEE standards associated with voltage sags are
given below [4].
IEEE 446-1995, IEEE recommended practice for emergency and
standby power systems for industrial and commercial applications
range of sensibility loads
The standard discusses the effect of voltage sags on sensitive
equipment, motor starting, etc. It shows principles and examples on
how systems shall be designed to avoid voltage sags and other power
quality problems when backup system operates.
IEEE 493-1990, Recommended practice for the design of reliable
industrial and commercial power systems
The standard proposes different techniques to predict voltage
sag characteristics, magnitude, duration and frequency. There are
mainly three areas of interest for voltage sags. The different
areas can be summarized as follows [4]:
i.
Calculating voltage sag magnitude by calculating voltage drop at
critical load with knowledge of the network impedance, fault
impedance and location of fault.
ii.
By studying protection equipment and fault clearing time it is
possible to estimate the duration of the voltage sag.
11 iii. Based on reliable data for the neighborhood and
knowledge of the system parameters an estimation of frequency of
occurrence can be made.
IEEE 1100-1999, IEEE recommended practice for powering and
grounding electronic equipment
This standard presents different monitoring criteria for voltage
sags and has a chapter explaining the basics of voltage sags. It
also explains the background and application of the CBEMA (ITI)
curves. It is in some parts very similar to Std. 1159 but not as
specific in defining different types of disturbances.
IEEE 1159-1995, IEEE recommended practice for monitoring
electric power quality
The purpose of this standard is to describe how to interpret and
monitor electromagnetic phenomena properly. It provides unique
definitions for each type of disturbance.
IEEE 1250-1995, IEEE guide for service to equipment sensitive to
momentary voltage disturbances
This standard describes the effect of voltage sags on computers
and sensitive equipment using solid-state power conversion. The
primary purpose is to help identify potential problems. It also
aims to suggest methods for voltage sag sensitive devices to
operate safely during disturbances. It tries to categorize the
voltage-related problems that can be fixed by the utility and those
which have to be addressed by the user or
12 equipment designer. The second goal is to help designers of
equipment to better understand the environment in which their
devices will operate. The standard explains different causes of
sags, lists of examples of sensitive loads, and offers solutions to
the problems [4].
2.3.2 Industry Standard
2.3.2.1 SEMI
The SEMI International Standards Program is a service offered by
Semiconductor Equipment and Materials International (SEMI). Its
purpose is to provide the semiconductor and flat panel display
industries with standards and recommendations to improve
productivity and business. SEMI standards are written documents in
the form of specifications, guides, test methods, terminology, and
practices. The standards are voluntary technical agreements between
equipment manufacturer and end-user. The standards ensure
compatibility and interoperability of goods and services.
Considering voltage sags, two standards address the problem for the
equipment [6].
SEMI F47-0200, Specification for semiconductor processing
equipment voltage sag immunity
The standard addresses specifications for semiconductor
processing equipment voltage sag immunity. It only specifies
voltage sags with duration from 50ms up to 1s. It
13 is also limited to phase-to-phase and phase-to-neutral
voltage incidents, and presents a voltage-duration graph, shown in
Figure 2.2. SEMI F42-0999, Test method for semiconductor processing
equipment voltage sag immunity
This standard defines a test methodology used to determine the
susceptibility of semiconductor processing equipment and how to
qualify it against the specifications. It further describes test
apparatus, test set-up, test procedure to determine the
susceptibility of semiconductor processing equipment, and finally
how to report and interpret the results [6].
Figure 2.2
Immunity curve for semiconductor manufacturing equipment
according to SEMI F47 [6]
14 2.3.2.2 CBEMA (ITI) Curve
Information Technology Industry (ITI, formally known as the
Computer & Business Equipment Manufactures Association, CBEMA)
is an organization with members in the IT industry. Within the
organization, the Technical Committee 3 (TC3) has published the ITI
(CBEMA) curve application note [7]. The note describes an AC input
voltage that typically can be tolerated by most information
technology equipment. The note is not intended to be a design
specification (although it is often used by many designers for that
purpose), but a description of behavior for most IT equipment. The
curve assumes a nominal voltage of 120VAC RMS and 60Hz and is
intended for singlephase information technology equipment [IEEE
1100 1999].
The voltage-time curve in Figure 2.3 describes the border of an
area. Above the border the equipment shall work properly and below
it shall shutdown in a controlled way.
Figure 2.3
Revised CBEMA curve, ITIC curve, 1996 [7]
15 This chapter has described the term voltage sags and provided
a foundation for the following chapters. The definitions provided
by IEEE standards are the ones that are used universally. The
characterization of voltage sags has also been discussed. This
complies with the industry concerns related to the problem of power
quality.
2.4
General Causes and Effects of Voltage Sags
There are various causes of voltage sags in a power system.
Voltage sags can caused by faults (more than 70% are weather
related such as lightning) on the transmission or distribution
system or by switching of loads with large amounts of initial
starting or inrush current such as motors, transformers, and large
dc power supply [3].
2.4.1 Voltage Sags due to Faults
Voltage sags due to faults can be critical to the operation of a
power plant, and hence, are of major concern. Depending on the
nature of the fault such as symmetrical or unsymmetrical, the
magnitudes of voltage sags can be equal in each phase or unequal
respectively.
For a fault in the transmission system, customers do not
experience interruption, since transmission systems are looped or
networked. Figure 2.4 shows voltage sag on all three phases due to
a cleared line-ground fault.
16
Figure 2.4
Voltage sag due to a cleared line-ground fault
Factors affecting the sag magnitude due to faults at a certain
point in the system are:
i. ii. iii. iv. v.
Distance to the fault Fault impedance Type of fault Pre-sag
voltage level System configuration a. System impedance b.
Transformer connections
The type of protective device used determines sag duration.
17 2.4.2 Voltage Sags due to Motor Starting
Since induction motors are balanced 3 phase loads, voltage sags
due to their starting are symmetrical. Each phase draws
approximately the same in-rush current. The magnitude of voltage
sag depends on:
i. ii.
Characteristics of the induction motor Strength of the system at
the point where motor is connected.
Figure 2.5 represents the shape of the voltage sag on the three
phases (A, B, and C) due to voltage sags.
Figure 2.5
Voltage sag due to motor starting
18 2.4.3 Voltage Sags due to Transformer Energizing
The causes for voltage sags due to transformer energizing
are:
i.
Normal system operation, which includes manual energizing of a
transformer.
ii.
Reclosing actions
Figure 2.6
Voltage sag due to transformer energizing
The voltage sags are unsymmetrical in nature, often depicted as
a sudden drop in system voltage followed by a slow recovery. The
main reason for transformer energizing is the over-fluxing of the
transformer core which leads to saturation. Sometimes, for long
duration voltage sags, more transformers are driven into
saturation. This is called Sympathetic Interaction. Figure 2.6 show
the voltage sag due to transformer energizing.
CHAPTER III
PSCAD/EMTDC SOFTWARE
3.1
Introduction
In this project, all the mitigation technique, PSCAD/EMTDC
software will be used to simulate and analyze the techniques. Power
System Aided Design (PSCAD) was first conceptualized in 1988 and
began its evolution as a tool to generate data files for the
Electromagnetic Transient Program with DC Analysis (EMTDC)
simulation program. In its early form, Version was largely
experimental. Nevertheless, it represented a great leap forward in
speed and productivity, since users of EMTDC could now draw their
systems, rather than creating text listings. PSCAD was first
introduced as a commercial product as Version 2 targeted for UNIX
platform in 1994. Version 3 comes in 1994 bringing new usability by
fully integrating the drafting and runtime systems of its
predecessors. This integration produced an intuitive environment
for both design and simulation [15].
20 PSCAD Version 4 represents the latest developments in power
system simulation software. With much of the simulation engine
being fully mature form many years, the new challenges lie in the
advancement of the design tools for the user. Version 4 retains the
strong simulation models of it predecessors, while bringing the
table an updated and fresh new look and feel to its windowing and
plotting
3.2
Characteristics of Software
PSCAD is a powerful and flexible graphical user interface to the
worldrenowned, EMTDC solution engine. PSCAD enables the user to
schematically construct a circuit, run a simulation, analyze the
results, and manage the data in a completely integrated, graphical
environment. Online plotting function, controls and meters are also
included, so that the user can alter system parameters during a
simulation run, and view the results directly [15].
PSCAD comes complete 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
utilizing an intuitively Design Editor.
21
The following are some common models found in systems studied
using PSCAD:
i. ii. iii.
Resistors, inductors, capacitors Mutually coupled windings, such
as transformers Frequency dependent transmission lines and cables
(including the most accurate time domain line model in the
world)
iv. v. vi. vii. viii. ix. x. xi. xii. xiii.
Current and voltage sources Switches and breakers Protection and
relaying Diodes, thyristors and GTOs Analog and digital control
functions AC and DC machines, exciters, governors, stabilizers and
initial models Meters and measuring functions Generic DC and AC
controls HVDC, SVC and other FACTS controllers Wind source, turbine
and governors
PSCAD Version 4 has some major features that have been included
prior to its predecessors for users convenience in modeling and
analysis of custom power system, such as:
i.
Windowing Interface PSCAD V4 boasts a completely new windowing
interface, which includes full MFC (Microsoft Foundation Class)
compatibility, docking window support and a new integrated design
editor.
22 ii. Drawing Interface the drawing interface has been enhanced
to provide uniform messaging and core support, as well as a full
double-buffered display. iii. On-Line Plotting Tools the online
plotting facilities in PSCAD V4 have been completely redesigned and
are now more powerful. The new advanced graphs come complete with
full features, including: full zoom and panning support, marker
control, Polymeter and XY plotting capabilities. iv. Off-Line
Plotting Facilities with the inclusion of Livewire, the best data
visualization and analysis software package available today, PSCAD
output come to life. v. Single-Line Diagram Input PSCAD now
includes the ability to construct a circuits in a convenient and
space saving single-line format. This new feature includes fully
adaptive three-phase electrical components in the Master Library
can be adjusted easily to display a single-line equivalent view.
vi. MATLAB/SIMULINK Interface now interface PSCAD to both MATLAB
and/or SIMULINK files.
3.3
Example of Circuit
A typical DVR built in PSCAD and installed into a simple power
system to protect a sensitive load in a large radial distribution
system [4] is presented in Figure 3.1. The coupling transformer
with either a delta or wye connection on the DVR side is installed
on the line in front of the protected load. Filters can be
installed at the coupling transformer to block high frequency
harmonics caused by DC to AC conversion to reduce distortion in the
output. The DC voltage source is an external source supplying
23 DC voltage to the inverter to convert to AC voltage. The
optimization of the DC source can be determined during simulation
with various scenarios of control schemes, DVR configurations,
performance requirements, and voltage sags experienced at the point
DVR is installed.
Figure 3.1
DVR with main components in PSCAD
The inverter is a six-pulse gate turn off (GTO) thyristor
controlled bridge. Currents will follow in different directions at
outputs depending on the control scheme, eventually supplying AC
output power to the critical load during power disturbances. The
control of this bridge is indeed the control of thyristor firing
angles. Time to open
24 and close gates will be determined by the control system.
There are several methods for controlling the inverter. To model a
DVR protecting a sensitive load against only balanced voltage sags,
a simple method of using the measurement of three-phase rms output
voltage for controlling signals can be applied. Amplitude
modulation (AM) is then used. In addition, to provide appropriate
firing angles to thyristor gates the switching control using pulse
width modulation (PWM) technique and interpolation firing is
employed.
Figure 3.2
The Wye-Connected DVR in PSCAD
25 In Figure 3.2 the transformer is wye-connected with a common
connection to the midpoint of the DC source. This allows that
current will pump into each phase through each pair of GTO and then
return without affecting the other two phases. It is noted that to
maintain an equal injecting voltage to each phase, the same value
of DC voltage at each half of the source would be required.
3.4
Conclusion
PSCAD Version 4 is a powerful tools to simulate and analysis
custom power systems. With all the benefits, designing a systems is
as simple as using a drawing board and a pencil in our hands. Many
new models have been added to the PSCAD Master Library since the
last release of PSCAD V3 thus improving capability of designing.
Navigating the software is now has been made easy with the
multi-window tab feature and toolbars. Common components were made
available and easy to drag-and-drop it to the drawing board.
All those features were shadowed over with the limitation due to
its commercial value. It has been described in the manual as
Dimension Limits. Those limits are divided into two major groups
which are Edition Specific Limits and Compiler Specific Limits. As
for this project those limitations be of less interest because only
one subsystem that will be analysis for each mitigation
technique.
CHAPTER IV
VOLTAGE SAG MITIGATION TECHNIQUES
4.1
Introduction
Different power quality problems would require different
solution. It would be very costly to decide on mitigate measure
that do not or partially solve the problem. These costs include
lost productivity, labor costs for clean up and restart, damaged
product, reduced product quality, delays in delivery and reduced
customer satisfaction.
Voltage sag can be classified in power quality problem. Hence,
when a customer or installation suffers from voltage sag, there is
a number of mitigation methods are available to solve the problem.
These responsibilities are divided to three parts that involves
utility, customer and equipment manufacturer. Figure 4.1 shows the
different protection options for improving performance during power
quality variation [1].
27
Figure 4.1
Different protection options for improving performance during
power quality variation. [1]
This project intends to investigate mitigation technique that is
suitable for different type of voltage sags source with different
type of loads. The simulation will be using PSCAD/EMTDC software.
The mitigation techniques that will be studied such as using
dynamic voltage restorer (DVR), distribution static compensator
(DSTATCOM), and solid state transfer switch (SSTS).
28 4.2 Dynamic Voltage Restorer (DVR)
Voltage magnitude is one of the major factors that determine the
quality of power supply. Loads at distribution level are usually
subject to frequent voltage sags due to various reasons. Voltage
sags are highly undesirable for some sensitive loads, especially in
high-tech industries. It is a challenging task to correct the
voltage sag so that the desired load voltage magnitude can be
maintained during the voltage disturbances [8].
The effect of voltage sag can be very expensive for the customer
because it may lead to production downtime and damage. Voltage sag
can be mitigated by voltage and power injections into the
distribution system using power electronics based devices, which
are also known as custom power device [9]. Different approaches
have been proposed to limit the cost causes by voltage sag. One
approach to address the voltage sag problem is dynamic voltage
restorer (DVR). It can be used to correct the voltage sag at
distribution level.
4.4.1 Principles of DVR Operation
A DVR is a solid state power electronics switching device
consisting of either GTO or IGBT, a capacitor bank as an energy
storage device and injection transformers. It is connected in
series between a distribution system and a load that shown in
Figure 4.2. The basic idea of the DVR is to inject a controlled
voltage generated by a forced commuted converter in a series to the
bus voltage by means of an injecting transformer. A DC capacitor
bank which acts as an energy storage device, provides a regulated
dc
29 voltage source. A DC to Ac inverter regulates this voltage by
sinusoidal PWM technique.
During normal operating condition, the DVR injects only a small
voltage to compensate for the voltage drop of the injection
transformer and device losses. However, when voltage sag occurs in
the distribution system, the DVR control system calculates and
synthesizes the voltage required to maintain output voltage to the
load by injecting a controlled voltage with a certain magnitude and
phase angle into the distribution system to the critical load
[9].
Figure 4.2
Principle of DVR with a response time of less than one
millisecond
Note that the DVR capable of generating or absorbing reactive
power but the active power injection of the device must be provided
by an external energy source or energy storage system. The response
time of DVD is very short and is limited by the power electronics
devices and the voltage sag detection time. The expected response
time is about 25 milliseconds, and which is much less than some of
the traditional methods of voltage correction such as tap-changing
transformers [8].
30 4.3 Distribution Static Compensator (DSTATCOM)
In its most basic function, the DSTATCOM configuration consist
of a two level voltage source converter (VSC), a dc energy storage
device, a coupling transformer connected in shunt with the ac
system, and associated control circuit [10, 11] as shown in Figure
4.3. More sophisticated configurations use multipulse and/or
multilevel configurations as discussed in [12]. The VSC converts
the dc voltage across the storage device into a set of three phase
ac output voltages. These voltages are in phase and coupled with
the ac system through the reactance of the coupling transformer.
Suitable adjustment of the phase and magnitude of the DSTATCOM
output voltages allows effective control of active and reactive
power exchanges between the DSTATCOM and the ac system.
Figure 4.3
Schematic diagram of the DSTATCOM as a custom power
controller
31 The VSC connected in shunt with the ac system provides a
multifunctional topology which can be used for up to three quite
distinct purposes [13]:
i. ii. iii.
Voltage regulation and compensation of reactive power;
Correction of power factor; Elimination of current harmonics.
The design approach of the control system determines the
priorities and functions developed in each case. In this case,
DSTATCOM is used to regulate voltage at the point of connection.
The control is based on sinusoidal PWM and only requires the
measurement of the rms voltage at the load point.
4.4.1 Basic Configuration and Function of DSTATCOM
The DSTATCOM is a three phase and shunt connected power
electronics based device. It is connected near the load at the
distribution systems. The major components of the DSTATCOM are
shown in Figure 4.4 below. It consists of a dc capacitor, three
phase inverter module such as IGBT or thyristor, ac filter,
coupling transformer and a control strategy. The basic electronic
block of the DSTATCOM is the voltage sourced converter that
converts an input dc voltage into three phase output voltage at
fundamental frequency.
32
Figure 4.4
Building blocks of DSTATCOM
Referring to Figure 4.4, the controller of the DSTATCOM is used
to operate the inverter in such a way that the phase angle between
the inverter voltage and the line voltage is dynamically adjusted
so that the DSTATCOM generates or absorbs the desired VAR at the
point of connection. The phase of the output voltage of the
thyristor based converter, Vi, is controlled in the same way as the
distribution system voltage, Vs. Figure 4.5 shows the three basic
operation modes of the DSTATCOM output current, I, which varies
depending upon Vi.
For instance, if Vi is equal to Vs, the reactive power is zero
and the DSTATCOM does not generate or absorb reactive power. When
Vi is greater than Vs, the DSTATCOM sees an inductive reactance
connected at its terminal. Hence, the system sees the DSTATCOM as a
capacitive reactance. The current, I, flows through the transformer
reactance from the DSTATCOM to the ac system, and the device
generates capacitive reactive power. Furthermore, if Vs is greater
than Vi, the system sees and inductive reactance connected at its
terminal and the DSTATCOM sees the system as a capacitive
reactance, then the current flows from the ac system to the
DSTATCOM, resulting in the device absorbing inductive reactive
power.
33
Figure 4.5
Operation modes of a DSTATCOM
34 4.4 Solid State Transfer Switch (SSTS)
The SSTS can be used very effectively to protect sensitive loads
against voltage sags, swells and other electrical disturbance [14].
The SSTS ensures continuous high quality power supply to sensitive
loads by transferring, within a time scale of milliseconds, the
load from a faulted bus to a healthy one.
The basic configuration of this device consists of two three
phase solid state switches, one for main feeder and one for the
backup feeder. These switches have an arrangement of back-to-back
connected thyristors, as illustrated in Figure 4.6
Figure 4.6
Schematic representations of the SSTS as a custom power
device.
35 Each time a fault condition is detected in the main feeder,
the control system swaps the firing signals to the thyristor in
both switches, in example, Switch 1 in the main feeder is
deactivated and Switch 2 in the backup feeder is activated. The
control system measures the peak value of the voltage waveform at
every half cycle and checks whether or not it is within a
prespecified range. If it is outside limits, an abnormal condition
is detected and the firing signals of the thyristors are changed to
transfer the load to the healthy feeder.
4.4.1 Basic Configuration and Function of SSTS
The SSTS as shown in Figure 4.7 is a high speed, open transition
switch which enables the transfer of electrical loads from one ac
power source to another within a few milliseconds.
Figure 4.7
Solid State Transfer Switch system
36 The open-transition property of the SSTS means that the
switch break contact with one source before it makes contact with
the other source. The advantage of this transfer scheme over the
closed-transition mechanical switch is that the electrical sources
are never cross-connected unintentionally. The cross connection of
independent ac sources, with the alternate source switching on to a
faulted system is discouraged by electric utilities.
The solid state transfer switch consists of two three phase ac
thyristor switches. The thyristor, operating in its two modes,
forms the key component of the SSTS. In the ON-state mode, low
impedance forward conduction of current takes place. In the
OFFstate mode, an open circuit with almost infinite impedance
occurs in the thyristor.
The basic ON-state and OFF-state properties of the thyristor are
used to form an intelligent switch which can choose between two
upstream power sources providing the better quality of supply
available to the electrical load downstream. The basic
configuration is based on anti-parallel thyristor group on
preferred and alternate sides of the switch. A thyristor allows
conduction only in forward direction. Figure 4.8 illustrate how the
thyristors of transfer switch 1 can conduct either in the positive
or the negative half cycle of the ac sinusoid and the supply path
is indicated by the bold line.
37
Figure 4.8
Thyristors of the SSTS conducting in the positive and negative
half cycle of the preferred source.
During normal operation, thyristors associated with the
preferred source are in the ON-state normally closed (NC) position,
while those associated with the alternate source are in the
OFF-state normally open (NO) position.
Current sensing circuits constantly monitor the states of the
preferred and alternate sources and feed the information to the
monitoring high speed controller. Upon detecting the loss of the
preferred source or voltage that is not within the preset range,
the controller blocks the firing impulse signals to the gate-driven
thyristors of transfer switch 1 and instructs the thyristors of
transfer switch 2 to turn ON with a fail-safe interlocking
mechanism. Power then flows via the path as indicated by the bold
line in Figure 4.9.
38
Figure 4.9
Thyristors on the alternate supply are turned ON on a sensing a
disturbance on the preferred source.
The mechanical bypass equipment provides conventional transfer
switch functionality when the SSTS is in a thermal overload
condition or is out of service for testing or maintenance.
CHAPTER V
MITIGATION TECNIQUES REALIZATION
5.1
Sinusoidal PWM-Based Control Scheme
In order to mitigate the simulated voltage sags in the test
system of each mitigation technique, also to mitigate voltage sags
in practical application, a sinusoidal PWM-based control scheme is
implemented, with reference to the DSTATCOM. The control scheme for
the DVR follows the same principle. The aim of the control scheme
is to maintain a constant voltage magnitude at the point where
sensitive load is connected, under the system disturbance.
The control system only measures the rms voltage at load point
[10], in example, no reactive power measurements is required [17].
The VSC switching strategy is based on a sinusoidal PWM technique
which offers simplicity and good response. Since custom power is a
relatively low-power application, PWM methods offer a more flexible
option than the fundamental frequency switching (FFS) methods
favored in FACTS applications. Besides, high switching frequencies
can be used to improve the efficiency
40 of the converter, without incurring significant switching
losses. Figure 5.1 shows the DSTATCOM controller scheme implemented
in PSCAD/EMTDC. The DSTATCOM control system exerts voltage angle
control as follows: an error signal is obtained by comparing the
reference voltage with the rms voltage measured at the load point.
The PI controller processes the error signal and generates the
required angle to drive the error to zero, in example, the load rms
voltage is brought back to the reference voltage. In the PWM
generators, the sinusoidal signal, vcontrol, is phase modulated by
means of the angle or delta as nominated in the Figure 5.1. The
modulated signal, vcontrol, is compared against a triangular signal
(carrier) in order to generate the switching signals of the VSC
valves.
Figure 5.1
Control scheme for the test system implemented in PSCAD/EMTDC to
carry out the DSTATCOM and DVR simulations.
41 The main parameters of the sinusoidal PWM scheme are the
amplitude modulation index, ma, of signal vcontrol, and the
frequency modulation index, mf, of the triangular signal. The
vcontrol in the Figure 5.1 are nominated as CtrlA, CtrlB and CtrlC.
The amplitude index ma is kept fixed at 1 pu, in order to obtain
the highest fundamental voltage component at the controller output
[13, 18]. The switching frequency mf is set at 450 Hz, mf = 9. It
should be noted that, an assumption of balanced network and
operating conditions are made.
The modulating angle or delta is applied to the PWM generators
in phase A, whereas the angles for phase B and C are shifted by 240
or -120 and 120 respectively. It can be seen in Figure 5.1 that the
control implementation is kept very simple by using only voltage
measurements as feedback variable in the control scheme. The speed
of response and robustness of the control scheme are clearly shown
in the test results.
42 5.2 Test System
Figure 5.2
The test system implemented in PSCAD/EMTDC
Figure 5.2 depict the test system implemented in PSCAD/EMTDC to
carry out the simulations for the aforementioned mitigation
techniques. The test system comprises of a 230 kilovolt, 50 Hertz
transmission system, represented in Thevenin equivalent, feeding
into the primary side of a 2-winding transformer. The load is
connected to the 11 kilovolt secondary side of the transformer.
Another 3-winding transformer will be used to replace the 2-winding
transformer to accommodate the implantation of the two-level
DSTATCOM and it will be connected in the tertiary winding of the
transformer to provide instantaneous voltage support at the load
point. The transformer employ a leakage reactance of 10% or 0.1 per
unit with a unity turns ratio and no booster capabilities
exist.
43 5.3 Dynamic Voltage Restorer
The DVR is a powerful controller that is commonly used for
voltage sags mitigation at the point of connection. The DVR employs
the same block as the DSTATCOM, but in this application the
coupling transformer is connected in series with the ac system, as
illustrated in Figure 5.3. The VSC generates a three-phase ac
output voltage which is controllable in phase and magnitude. These
voltages are injected into the ac system in order to maintain the
load voltage at the desired voltage reference. The main features of
the DVR control scheme have been explained in section 5.1.
Figure 5.3
One line diagram of the DVR test system
The DVR that have been used to test the system in section 5.1 is
shown in Figure 5.4. The DVR is basically the same as DSTATCOM but
instead of using a capacitor, DVR employs 5 kilovolt dc storage
supply. The DVR is then connected in series using transformers in
delta to the lines. Figure 5.5 will show the full test system to
realize the effectiveness of the DVR control.
44
Figure 5.4
Schematic diagram of the DVR
Figure 5.5
Schematic diagram of the test system with DVR connected to the
system.
45 5.4 Distribution Static Compensator
The test system employed to carry out the simulations concerning
the DSTATCOM actuation is shown in Figure 2.9, which is the same
system presented in [16]. A two-level DSTATCOM is connected to the
11 kV tertiary winding to provide instantaneous voltage support at
the load point. A 750 F capacitor on the dc side provides the
DSTATCOM energy storage capabilities.
The transformer of the test system has been changed to a
3-winding transformer to accommodate DSTATCOM. The purpose of
including the transformer is to protect and provide isolation
between the IGBT legs. This prevents the dc storage capacitor from
being shorted through switches in different IGBT. Figure 5.6 shows
the build of the DSTATCOM in PSCAD/EMTDC which is the two-level
voltage source converter and the realization of the test system
being employed shown in Figure 5.7.
Figure 5.6
One line diagram of the DSTATCOM test system.
46
Figure 5.7
Schematic diagram of the test system with DSTATCOM connected to
the system.
47 5.5 Solid State Transfer Switch
In the test to carry out the SSTS simulations, the system
comprises with two identical feeders from section 5.1 and a
sensitive load connected to the bus bar. Figure 5.8 shows the
system that is employed.
Figure 5.8
One line diagram of the SSTS test system.
Simulations were carried out to assess the effectiveness of the
simple control scheme that has been employed in the system proposed
earlier. Figure 5.9 shows the SSTS system that being employed for
the test in PSCAD/EMTDC. It comprises of two sets of switches which
is switch group 1 and switch group 2 that alternately turns ON and
OFF corresponds to the fault detector signals. The full system
application to test the SSTS is shown in Figure 5.10.
48
Figure 5.9
SSTS switches implemented in PSCAD/EMTDC
Figure 5.10
Schematic diagram of the test system with SSTS connected to the
system.
CHAPTER VI
SIMULATIONS AND RESULTS
6.1
Test case
This section contains the results of the simulations to assess
the capability of each technique to mitigate various fault sources.
In order to make a fair assessment, the simulations only use one
test system as proposed in section 5.1. The test were divide into
the most common faults which are
6.1.1 Single line to ground fault, and 6.1.2 Double line to
ground fault
The most common fault is the single line to ground faults which
covers 70% of total faults. There are many situations that can make
the occurrence of single line to ground faults possible. The low
impedance faults are referred to as bolted faults indicating that
the faulted conductors are effectively bolted together to create a
line to
50 line faults which cover 10% of the total faults or double
line to fault for the total of 15%. A much more common effect is
where the fault has some finite impedance. When a line falls on
sandy soil or there is a significant distance for an arc to jump,
then the characteristic may have a constant voltage characteristic.
The remaining 5% of the faults are three phase faults.
6.2
Single line to ground fault
6.2.1 Phase A to ground
Using the faults generator, Figure 6.1a clearly shows a phase
shift of line A after the fault has been applied. The angle of the
line shifted as much as 88.44 from the reference angle for line A
of -1.94. For the rms value of the line, we can refer to Figure
6.1b which clearly shows the voltage sag. The value of the rms has
been normalized and for the phase A to the ground fault, the rms
drops to 0.685 or nearly 31% from the reference value
51
(a)
(b) Figure 6.1 (a) Phase shift for line A to the ground fault
(b) Rms voltage drop
The simulations have two parts which have been run separately.
This first part involves simulating the test system on different
fault as mention above. The second part involves simulating the
mitigation techniques with the test system so that each of the
technique can be assessed on their performance in mitigating
voltage sags.
52
(a)
(b) Figure 6.2 (a) Corrected phase with DVR (b) Compensated
voltage sag with DVR
The first technique that has been used is the DVR. Figure 6.2a
shows the capability of the technique to balance the phase shift
while Figure 6.2b shows how the technique compensates the voltage
drop. DVR recover almost 96% of the reference voltage.
53 The second technique that has been used in mitigating the
voltage sags and phase shift is the DSTATCOM. Figure 6.3a shows the
phase balance of the system and Figure 6.3b shows the recovery of
the voltage sags. DSTATCOM manage to recover nearly 94% of the
voltage with respect to the reference voltage.
(a)
(b) Figure 6.3 (a) Corrected phase using DSTATCOM (b)
Compensated voltage sag using DSTATCOM
54 The third technique that has been used is SSTS. In SSTS,
whenever the fault detector control scheme detects a faulty line,
it changes the firing angle of the switches that are connected to
the line thus change the feed from the main feeder to the
alternative or backup feed. Figure 6.4a and Figure 6.4b clearly
shows that no interruption can be noticed since the backup feeder
is healthy.
(a)
(b) Figure 6.4 (a) Corrected phase using SSTS (b) Compensated
voltage sag using SSTS
55 Since SSTS switch the faulty feeder with the healthy one
whenever faults occur, as long as the back up feeder is healthy,
the result produced by this technique will always be the same.
Hence, the result of the SSTS will be omitted hereafter with the
assumption that the backup feeder is always healthy.
Table 6.1
(a) Test results for line A to the ground fault. (b) Recovery
resultTEST 1: PHASE A TO GROUND PHASE() VRMS(pu) C 118.06 98.32
142.4 118.11 min 0.685 0.923 0.948 0.989 max 0.991 0.963 1.011
0.989
TECHNIQUES A FAULT DVR DSTATCOM SSTS -90.38 0.75 1.28 -1.89 B
-121.94 -98.93 -147.87 -121.89
(a)TEST 1: PHASE A TO GROUND RECOVERY PHASE() TECHNIQUES A DVR
DSTATCOM SSTS 89.63 89.1 88.49 B 23.01 25.93 0.05 C 19.74 24.34
0.05 GAIN 95.85 93.77 100 VRMS(%)
(b)
56 From table 6.1a and 6.1b, we can see that SSTS has the best
recovery rate since it doesnt involve compensating technique either
to absorb or inject power to the system. The rms value of the
system is always constant. It is different than the other two
techniques which require them to inject or absorb power to and from
the system. DVR has better recovery in mitigating the voltage sag
than DSTATCOM but poor in correcting the phase of the lines. DVR
recover 2% better in comparison with DSTATCOM.
6.2.2 Phase B to ground
For test 2, the faults generator still emulates a single line to
ground fault of line B. it is applied from 25 milliseconds to 35
milliseconds. The rms value of the faulty system is as the same as
Figure 6.1b. The only difference is in the phase of the system.
Figure 6.5 show the shifted phase of the system when the fault
occurs.
Figure 6.5
Phase shift of line B to the ground fault.
57 It can be noticed that phase B has been shifted 90 to 150 for
the duration of the fault. Figure 6.6a shows the result from DVR
mitigation and Figure 6.6b shows the result for DSTATCOM for phase
correction. Each technique recovers the same value of the rms as
when it mitigates the phase A to the ground fault.
(a)
(b) Figure 6.6 (a) Phase correction using DVR (b) Phase
correction using DSTATCOM; line B to the ground fault.
58 From the figure above, it can be observed that other line
phases were also affected when both techniques try to correct the
lines phase. The effect can be clearly noted in Figure 6.6a where
the phase of line A and C are shifted even though those lines were
not in fault. This condition as well happen when DSTATCOM try to
correct the phases. The result of the test is shown in Table 6.2(a)
whereas Table 6.2(b) will show the recoveries that have been
achieved by those three techniques.
Table 6.2
(a) Test results for line B to the ground fault. (b) Recovery
resultTEST 2: PHASE B TO GROUND PHASE() RMS(pu) C 118.06 140 96.72
118.11 min 0.686 0.923 0.942 0.989 max 0.991 0.963 1.016 0.989
TECHNIQUES A FAULT DVR DSTATCOM SSTS -1.94 -21 15.83 -1.89 B
149.64 -118.56 -122.37 -121.89
(a)TEST 2: PHASE B TO GROUND RECOVERY PHASE() TECHNIQUES A DVR
DSTATCOM SSTS 19.06 13.89 0.05 B 31.08 27.27 27.75 C 21.94 21.34
0.05 GAIN 95.85 92.72 100 VRMS(%)
(b)
59 DVR manage to recover 95.85% of the rms voltage with respect
to the reference value and DSTATCOM recover 3% less of DVR. For
SSTS, the recovery rate is always 100% since the backup feeder is
healthy.
6.2.3 Phase C to ground
Test 3 involves line C of the system. This test is practically
the same as previous test which only involves 1 line of the system.
The results of the rms voltage is the same as Figure 6.1(b), but
the phase of line C is shifted as much as 90 and can be seen in
Figure 6.7.
Figure 6.7
Phase shift of line B to the ground fault.
60 Mitigation of the fault outcome is the same product as the
preceding test which DVR and DSTATCOM compensate the rms voltage
similarly. Figure 6.8(a) and Figure 6.8(b) shows the phase
difference for the mitigation technique accordingly.
(a)
(b) Figure 6.8 (a) Phase correction using DVR (b) Phase
correction using DSTATCOM; line C to the ground fault.
61 The numerical result will be shown in Table 6.3(a) whereas
the recovery will be shown in Table 6.3(b). The phase of line C has
been corrected but at the same time, other lines were also
affected. This is true for both of the technique but not for SSTS
which is the same as Figure 6.4(a) and Figure 6.4(b).
Table 6.3
(a) Test results for line C to the ground fault. (b) Recovery
result.TEST 3: PHASE C TO GROUND PHASE() RMS(pu) C 29.69 117.42
128.67 118.11 min 0.686 0.923 0.914 0.989 max 0.991 0.963 1.011
0.989
TECHNIQUES A FAULT DVR DSTATCOM SSTS -1.94 19.69 -22.83 -1.89 B
-121.94 -139.45 -101.83 -121.89
(a)TEST 3: PHASE C TO GROUND RECOVERY PHASE() TECHNIQUES A DVR
DSTATCOM SSTS 17.75 20.89 0.05 B 17.51 20.11 0.05 C 87.73 98.98
88.42 GAIN 95.85 90.41 100 VRMS(%)
(b)
From the table, line A and line B should have stay fixed on 0
and -120 respectively but after DVR and DSTATCOM try to correct the
phase of line C, the phase of those lines were shifted to 20 and
-149 for DVR and -23 and -102 for DSTATCOM. This could be due to
the control scheme that is too simple. In the mean
62 time, the rms voltage compensation for both DVR and DSTATCOM
are still above 90% in respect to the reference voltage. DVR still
maintain 5% from the overall voltage. This is true for the entire
tests that have been carried out before, while SSTS results are
overwhelming with no ripple or overshoot.
6.3
Double lines to ground fault
The next line of test is double line to the ground fault. As an
overall, those techniques except SSTS suffer terrible loss when its
try to mitigate double line to the ground fault. This fault only
covers 15% of overall fault that occurs practically, but it pose
much more danger to the loads that draw supply from the lines.
6.3.1 Phase A and B to ground
The first test to come is line A and line B to the ground fault.
The effect of this fault is depicted in Figure 6.8(a) which shows
the phase fault and Figure 6.8(b) that shows the rms voltage of the
test system during the fault.
63
(a)
Figure 6.9
(b) (a) Phase shift for line A and B to the ground fault (b) Rms
voltage drop
For this test, the phase A and B has been shifted 90 to -90 and
150 respectively. The voltage drop is doubled from previous test
set to 0.366 per unit with respect to the reference voltage. Figure
6.10(a) shows the result of the DVR try to correct the shifted
phases for the fault and Figure 6.10(b) shows for the DSTATCOM.
64
(a)
(b) Figure 6.10 (a) Phase correction using DVR (b) Phase
correction using DSTATCOM; line A and B to the ground fault.
As we can see from the figure, DVR continue to correct the
phases of the faulted lines steadily with almost the same value at
the time DVR is correcting the single line to ground fault. The
same abnormality happens with the line that doesnt need any
correction and in this case, it is line C. The phase of line C is
shifted nearly 10. However, DSTATCOM capability of correcting the
phase of single line to the ground fault has not been continual for
the double line to the ground fault. For lines A and B to the
ground fault, DSTATCOM is able to correct the phase of line B but
this is not occurred to line A. The phase is shifted about 140 and
rest at 50.
65
Even though the voltage sag is double from the previous value,
DVR manage to compensate the voltage drop and recovered nearly 90%
with respect to the reference voltage. DSTATCOM only manage to
recover 78%. This is due to the inability of DSTATCOM to mitigate
double line to the ground fault with only using simple control
scheme that has been introduced in section 5.1. It is clearly shown
in Figure 6.11(a) and 6.11(b) for DVR and DSTATCOM
respectively.
(a)
(b) Figure 6.11 (a) Compensated voltage sag using DVR (b)
Compensated voltage sag using DSTATCOM; Line A and B to the ground
fault.
66
The value of voltage sag that have been recovered for other
double lines to the ground fault, such as line A and C to the
ground fault and line B and C to the ground fault, is the same as
the result shown in Figure 6.11. Hence, those results are omitted
hereafter.
Table 6.4(a) will show the full result of line A and B to the
ground fault while Table 6.4(b) shows the recovered voltage sag and
corrected phase for those lines.
Table 6.4
(a) Test results for line A and B to the ground fault. (b)
Recovery result.TEST 4: PHASE AB TO GROUND PHASE() VRMS(pu) C
118.06 110.331 117.25 118.11 min 0.366 0.858 0.777 0.989 max 0.991
0.963 0.991 0.989
TECHNIQUES A FAULT DVR DSTATCOM SSTS -90.38 -0.78 49.61 -1.89 B
149.66 -110.6 -123.36 -121.89
(a)TEST 4: PHASE AB TO GROUND RECOVERY PHASE() TECHNIQUES A DVR
DSTATCOM SSTS 89.6 40.77 88.49 B 39.06 26.3 27.77 C 7.729 0.81 0.05
GAIN 89.1 78.41 100 VRMS(%)
(b)
67 6.3.2 Phase A and C to ground
The next test case is line A and C to the ground fault. As
mention before, the result of voltage sag that is mitigated is the
same as the result for section 6.3.1. DVR and DSTATCOM recover the
same value as its try to mitigate test case 4. Therefore, the
results of voltage sag mitigation of this section are omitted.
Figure 6.12
Phase shift for line A and C to the ground fault
Figure 6.12 shows the phases that are in fault. The phase of
line A is shifted 90 to rest at -90 while the phase of line C is
also shifted 90 and stays at 30 during the fault. The result of the
corrected phase will be shown in Figure 6.13(a) and 6.13(b) for DVR
and DSTATCOM respectively.
68
(a)
(b) Figure 6.13 (a) Phase correction using DVR (b) Phase
correction using DSTATCOM; line A and C to the ground fault.
The result in Figure 6.13(b) clearly shows the improper phase
correction of line C which definitely affect the result of DSTATCOM
voltage mitigation while in Figure 6.13(a), DVR also cannot correct
the phase accurately. The full test result is shown in Table 6.5(a)
while Table 6.5(b) shows the recovery result.
69 Table 6.5 (a) Test results for line A and C to the ground
fault. (b) Recovery result.TEST 5: PHASE AC TO GROUND PHASE()
TECHNIQUES A FAULT DVR DSTATCOM SSTS -90.38 -19.82 2.86 -1.89 B
-121.93 -119.38 -128.98 -121.89 C 29.65 139.3 178.72 118.11 min
0.365 0.858 0.769 0.989 max 0.991 0.963 0.995 0.989 VRMS(pu)
(a)TEST 5: PHASE AC TO GROUND RECOVERY PHASE() TECHNIQUES A DVR
DSTATCOM SSTS 70.56 87.52 88.49 B 2.55 7.05 0.04 C 109.65 149.07
88.46 GAIN 89.1 77.29 100 VRMS(%)
(b)
70 6.3.3 Phase B and C to ground
The last test case is line B and C to the ground fault. In this
case, phase B is shifted 90 to end at 150 and phase C is also
shifted 90 and stays at 30 respectively. This can be seen in Figure
6.14 as it shows the phase shift of the faulty lines.
Figure 6.14
Phase shift for line B and C to the ground fault.
The phase of line A is unaffected by the fault of other lines
throughout the fault period. However, the phase of the line is
affected and shifted 30 for the moment of mitigation using DVR.
This affect is obviously depicted in Figure 6.15(a).
71
(a)
(b) Figure 6.15 (a) Phase correction using DVR (b) Phase
correction using DSTATCOM; line B and C to the ground fault.
As typically happened for DSTATCOM, one of the faulty lines in
Figure 6.15(b) is not corrected appropriately and this time, it is
line B. The phase of the line at the time of mitigation is -60 as
it suppose to be at -120. The full result of the test is shown in
Table 6.6(a) and the recovery result is shown in Table 6.6(b).
72 Table 6.6 (a) Test results for line B and C to the ground
fault. (b) Recovery result.TEST 6: PHASE BC TO GROUND PHASE()
TECHNIQUES A FAULT DVR DSTATCOM SSTS -1.93 30.73 -6.26 -1.89 B
149.65 -135.93 -61.6 -121.89 C 29.68 147.93 126.03 118.11 min 0.365
0.858 0.768 0.989 max 0.991 0.963 0.991 0.989 VRMS(pu)
(a)TEST 6: PHASE BC TO GROUND RECOVERY PHASE() TECHNIQUES A DVR
DSTATCOM SSTS 28.8 4.33 0.04 B 13.72 88.05 27.76 C 118.25 96.35
88.43 GAIN 89.1 77.5 100 VRMS(%)
(b)
73
6.4
Conclusion
In mitigating single line to the ground fault, DVR and DSTATCOM
that has been introduced in section 5 are able to compensate the
voltage sag without any difficulty. The problem lies in correcting
the phase of the system. Even though the phase of the faulty line
has been corrected, the rest of the lines that are not in fault is
also affected and shifted a few degrees. This affect can be seen
happened to DVR when it mitigates the test system. In general, the
capability of the techniques to mitigate single line to the ground
fault are uncontested especially SSTS as it pose the best
result.
While mitigating double lines to the ground fault, the same
problems occurred to the DVR where the phase of the healthy line is
unwontedly shifted a few degrees, but the performance of DVR in
mitigating voltage sag remain the same as it mitigates single line
to the ground fault. For DSTATCOM, a new problem occurred while
DSTATCOM is mitigating double line to the ground fault. One of the
faulty lines is not corrected appropriately and this brings an
upsetting effect in mitigating the voltage sag of the system. Once
again, SSTS that has been introduced in section 5 remain as the
best mitigation technique. This is due to the nature of the SSTS
where it doesnt try to compensate or correct the faulty line;
instead, SSTS switch the faulty feeder to the alternative feeder.
The result is always and remains constant if and only if the backup
or alternative feeder is being kept healthy.
CHAPTER VII
CONCLUSION
7.1
Conclusion
Nowadays, reliability and quality of electric power is one of
the most discuss topics in power industry. There are numerous types
of power quality issues and power problems and each of them might
have varying and diverse causes. The types of power quality
problems that a customer may encounter classified depending on how
the voltage waveform is being distorted. There are transients,
short duration variations (sags, swells, and interruption), long
duration variations (sustained interruptions, under voltages, over
voltages), voltage imbalance, waveform distortion (dc offset,
harmonics, interharmonics, notching, and noise), voltage
fluctuations and power frequency variations. Among them, two power
quality problems have been identified to be of major concern to the
customers are voltage sags and harmonics, but this project is
focusing on voltage sags.
75 Voltage sags are huge problems for many industries, and it is
probably the most pressing power quality problem today. Voltage
sags may cause tripping and large torque peaks in electrical
machines. Generally, voltage sags are short duration reductions in
rms voltage caused by faults in the electric supply system and the
starting of large loads, such as motors. Voltage sags are also
generally created on the electric system when faults occur due to
lightning, which are accidental shorting of the phases by trees,
animals, birds, human error such as digging underground lines or
automobiles hitting electric poles, and failure of electrical
equipment. Sags also may be produced when large motor loads are
started, or due to operation of certain types of electrical
equipment such as welders, arc furnaces, smelters, etc.
Therefore, this project intends to investigate mitigation
technique that is suitable for different type of voltage sags
source. The simulation will be using PSCAD/EMTDC software and the
mitigation techniques that using such as dynamic voltage restorer
(DVR), distribution static compensator (DSTATCOM), and solid state
transfer switch (SSTS).
Dynamic voltage restorers (DVR) are used to protect sensitive
loads from the effects of voltage sags on the distribution feeder.
In all cases it is necessary for the DVR control system to not only
detect the start and end of a voltage sag but also to determine the
sag depth and any associated phase shift. The DVR, which is placed
in series with a sensitive load, must be able to respond quickly to
voltage sag if end users of sensitive equipment are to experience
no voltage sags.
The distribution static compensator (DSTATCOM) offers an
alternative to conventional series shunt compensation. In the
traditional power transmission system, controllable devices are
restricted to the slow mechanisms such as transformer tap changers
and switched capacitor. In the late 1980s, thanks to the major
developments
76 in the semiconductor technology, it became possible to apply
power electronics in the control of DSTATCOM. Based on the
simulation, theres a room for improvement. DSTATCOM is a device
that promises a prominent feature in power system in mitigating
power quality related problems in the future.
Solid state transfer switch (SSTS) is not the most cost
effective but in many cases, it is a practical mitigating technique
to apply especially for sensitive loads. These solutions involve
fixing the two identical power source components in order to
increase the ride-through of the entire system. SSTS solutions are
attractive since they in theory do not require add on power
conditioning equipment, but instead involve using another source
components. Furthermore, semiconductor tool suppliers are more
comfortable with this approach since it does not require the
addition of unfamiliar technologies.
As conclusion, voltage sag is unwanted phenomenon which
unavoidable but can be reduced using all techniques, but not
limited to the techniques that have been discussed. There is no one
mitigation technique that will suitable with every application, and
whilst the power supply utilities strive to supply improved power
quality, it is up to the applications engineer to minimize power
quality problems. It means, power quality problem cannot be
eliminated but we can reduce and try to avoid this problem form
occur. The best way to avoid power quality problem is by ensuring
that all equipment to be installed in the industrial plants are
compatible with power quality in the power system. This can be
achieved by procuring equipment with proper technical
specifications that incorporate power quality performance of its
operating electrical environment.
77
7.2
Suggestion
Mitigating voltage sag requires a lot of intensive research
especially in developing custom power device to help distribution
system to achieve desired power quality as been insisted by many
customer or end-user. There are still rooms of improvement that can
be achieved further, for the technique that have been included in
this thesis and other techniques that are available.
The DVR and DSTATCOM that has been used earlier, employs a two-
level voltage source converter or VSC in both technique. Additional
research of other multilevel and multipulse VSC can be implemented
in the future to exploit the simplicity of the pulse width
modulation or PWM based control scheme to further enhance both DVR
and DSTATCOM. Another control scheme can also be proposed to take
the advantage of the two-level VSC that has been employed
previously to support more control over voltage sags that were
caused by double line to ground, line to line faults and three
phase fault that cover 25 percent of the total faults.
78
REFERENCES
[1]
Roger C. Dugan, Mark F. McGranaghan and H. Wayne Beaty,
TK1001.D84 (1996) Electrical Power Systems Quality, Mc Graw-Hill.
Pages 1-8 and 39-80.
[2]
Prof. Khalid Mohd Nor (2006), Lecture Notes MEP 1542 Special
Topic In Power Engineering, session 2005/2006-II.
[3]
Tenaga National Berhad (1996), A Guidebook on Power
QualityMonitoring, Analysis & Mitigations, pages 1-61
[4]
IEEE Standards Board (1995), IEEE Std. 1159-1995, IEEE
Recommended Practice for Monitoring Electric Power Quality. IEEE
Inc. New York.
[5]
IEEE Industry Applications Magazine, Before and During Voltage
sags, available at http://www.ieee.org/ias
[6]
SEMI
F47-0200
voltage
sag
immunity
curve,
available
at
http://www.semi.org
[7]
ITI (CBEMA) curve application note, Available at
http://.www.itic.org/technical/iticurv.pdf.
79
[8]
M. H. Haque, (2001) "Compensation of Distribution System Voltage
Sag by DVR and D-STATCOM", IEEE Porto Power Tech Conference
2001
[9]
M A Hannan and A Mohamed, (2002) Modeling and Analysis of a
24Pulse Dynamic Voltage Restorer in a Distribution System, Student
Conference on Research and Development PROCEEDINGS, Shah Alam,
Malaysia.
[10]
A. Hernandez, K. E. Chong, G. Gallegos, and E. Acha The
implementatio of a solid state voltage source in PSCAD/EMTDC, IEEE
Power Eng. Rev., pp. 61-62, Dec 1998.
[11]
L. Xu, Anaya-Lara, V. G. Agelidis, and E. Acha Development of
custom power devices for power quality enhancement, in Proc. 9th
ICHQP 2000, Orlando, FL, Oct. 2000, pp. 775-783.
[12]
Y. Chen and B. T. Ooi, STATCOM based on multimodules of
multilevel converters under multiple regulation feedback control,
IEEE Trans. Power Electron., vol. 14, pp. 959-965, Sept. 1999.
[13]
E. Acha, V. G. Agelidis, O. Anaya-Lara, and T. J. E. Miller,
Electronic Control in Electrical Power Systems, London, U.K.,
Butterworth-Heinemann, 2001.
[14]
K. Chan, A. Kara, and G. Kieboom, Power quality improvement with
solid state transfer switches, in Proc. 8th ICHQP 1998, Athens,
Greece, Oct. 1998, pp. 210-215
[15]
PSCAD Electromagnetic Transients Users Guide, The Professionals
Tool for Power System Simulation
80 [16] O. Anaya-Lara, E. Acha, Modelling and analysis of custom
power systems by PSCAD/EMTDC, IEEE Trans., Power Delivery, Vol.
PWDR-17 (1), pp. 266-272, 2002.
[17]
I. T. Fernando, W. T. Kwasnicki, and A. M. Gole. Modeling of
conventional and advanced static var compensators in
electromagnetic transients simulation program. Available at
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[18]
N. Mohan, T. M. Underland, and W. P. Robbins, Power electronics:
Converters, Application and Design, New York, Wiley, 1995.
81 APPENDIX A Data generated by PSCAD/EMTDC for
DSTATCOM!=======================================================================
! Generated by : PSCAD v4.1.0 ! ! Warning: The content of this file
is automatically generated. ! Do not modify, as any changes made
here will be lost!
!=======================================================================
!--------------------------------------! Local Node Voltages
!--------------------------------------VOLTAGES: 1 0.0 // NT_1 2
0.0 // NT_2 3 0.0 // NT_6 4 0.0 // NT_7 5 0.0 // NT_8 6 0.0 //
NT_12 7 0.0 // NT_13 8 0.0 // NT_14 9 0.0 // NT_15 10 0.0 // NT_16
11 0.0 // NT_17 12 0.0 // NT_18 13 0.0 // NT_19 14 0.0 // NT_20 15
0.0 // NT_21 16 0.0 // NT_22 17 0.0 // NT_23 18 0.0 // NT_24
!--------------------------------------! Local Branch Data
!--------------------------------------BRANCHES: 1 2 RE 0.0 6 9 RS
1000000.0 6 1 RS 1000000.0 1 6 RS 1000000.0 2 6 RS 1000000.0 6 2 RS
1000000.0 7 1 RS 1000000.0 1 7 RS 1000000.0 2 7 RS 1000000.0 7 2 RS
1000000.0 8 1 RS 1000000.0 1 8 RS 1000000.0 2 8 RS 1000000.0 8 2 RS
1000000.0 7 10 RS 1000000.0 0 12 RE 0.0 0 13 RE 0.0 0 14 RE 0.0 8
11 RS 1000000.0 16 18 RS 1000000.0 15 18 RS 1000000.0 17 18 RS
1000000.0 16 17 RS 1000000.0 17 15 RS 1000000.0 15 16 RS 1000000.0
17 0 RL 12.1 0.1926 15 0 RL 12.1 0.1926 16 0 RL 12.1 0.1926
// // // // // // // // // // // // // // // // // // // // //
// // // // // // //
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
NT_1 NT_12 NT_12 NT_1 NT_2 NT_12 NT_13 NT_1 NT_2 NT_13 NT_14
NT_1 NT_2 NT_14 NT_13 GND GND GND NT_14 NT_22 NT_21 NT_23 NT_22
NT_23 NT_21 NT_23 NT_21 NT_22
NT_2 NT_15 NT_1 NT_12 NT_12 NT_2 NT_1 NT_13 NT_13 NT_2 NT_1
NT_14 NT_14 NT_2 NT_16 NT_18 NT_19 NT_20 NT_17 NT_24 NT_24 NT_24
NT_23 NT_21 NT_22 GND GND GND
8214 13 12 1 5 4 3 2 RL RL RL C 0.1 0.1 0.1 0.758 0.758 0.758
750.0 // // // // 1 1 1 1 NT_20 NT_19 NT_18 NT_1 NT_8 NT_7 NT_6
NT_2
!--------------------------------------! Local Transformer Data
!--------------------------------------TRANSFORMERS: ! 3 Phase, 3
Winding Transformer: !* Name: T1 Tmva: 100.0 MVA, Freq: 50.0 Hz,
V1: 230.0 kV, V3: 11.0 kV !* Imag1: 0.02 p.u., Imag2: 0.02 p.u.,
Imag3: 0.02 p.u., (p.u.) !* Sat: 0 , -3 / Number of windings... 3 0
7.91831796746 / 11 0 -82.7824151144 3461.8100866 / 17 0
-82.7824151144 -1730.9050433 3461.8100866 / 888 / 4 0 / 10 0 / 15 0
/ 888 / 5 0 / 9 0 / 16 0 / !
V2: 11.0 kV, Xl: 0.1, 0.1, 0.1
DATADSD:
DATADSO:
ENDPAGE
83 APPENDIX B Data generated by PSCAD/EMTDC for
DVR!=======================================================================
! Generated by : PSCAD v4.1.0 ! ! Warning: The content of this file
is automatically generated. ! Do not modify, as any changes made
here will be lost!
!=======================================================================
!--------------------------------------! Local Node Voltages
!--------------------------------------VOLTAGES: 1 0.0 // NT_1 2
0.0 // NT_2 3 0.0 // NT_3 4 0.0 // NT_4 5 0.0 // NT_5 6 0.0 // NT_6
7 0.0 // NT_7 8 0.0 // NT_10 9 0.0 // NT_11 10 0.0 // NT_13 11 0.0
// NT_17 12 0.0 // NT_18 13 0.0 // NT_19 14 0.0 // NT_20 15 0.0 //
NT_21 16 0.0 // NT_22 17 0.0 // NT_23
!--------------------------------------! Local Branch Data
!--------------------------------------BRANCHES: 5 1 RS 1000000.0 5
3 RS 1000000.0 2 0 RS 1000000.0 3 0 RS 1000000.0 1 0 RS 1000000.0 5
2 RS 1000000.0 5 0 RS 1.0 0 17 RE 0.0 0 16 RE 0.0 3 5 RS 1000000.0
2 5 RS 1000000.0 1 5 RS 1000000.0 0 3 RS 1000000.0 0 2 RS 1000000.0
0 1 RS 1000000.0 11 6 RS 1000000.0 6 7 RS 1000000.0 7 11 RS
1000000.0 11 0 RS 1000000.0 6 0 RS 1000000.0 7 0 RS 1000000.0 0 15
RE 0.0 15 10 RL 0.1 0.758 13 0 RL 0.1 0.1926 12 0 RL 0.1 0.1926 16
8 RL 0.1 0.758 17 9 RL 0.1 0.758 14 0 RL 0.1 0.1926
// // // // // // // // // // // // // // // // // // // // //
// // // // // // //
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
NT_5 NT_5 NT_2 NT_3 NT_1 NT_5 NT_5 GND GND NT_3 NT_2 NT_1 GND
GND GND NT_17 NT_6 NT_7 NT_17 NT_6 NT_7 GND NT_21 NT_19 NT_18 NT_22
NT_23 NT_20
NT_1 NT_3 GND GND GND NT_2 GND NT_23 NT_22 NT_5 NT_5 NT_5 NT_3
NT_2 NT_1 NT_6 NT_7 NT_17 GND GND GND NT_21 NT_13 GND GND NT_10
NT_11 GND
84
!--------------------------------------! Local Transformer Data
!--------------------------------------TRANSFORMERS: ! 3 Phase, 2
Winding Transformer !* Name: T32 Tmva: 100.0 MVA, Freq: 50.0 Hz,
V1: 230.0 kV, !* Imag1: 0.02 p.u., Imag2: 0.02 p.u., Xl: 0.1 p.u.
!* Sat: 0 , -2 / Number of windings... 10 0 5.9387384756 / 11 0
-124.173622672 2596.35756495 / 888 / 8 0 / 6 0 / 888 / 9 0 / 7 0 /
! ! Single Phase Transformer: 100.0 MVA, 11.0 kV : 230.0 kV -2 /
Number of windings... 14 11 2596.35756495 / 4 1 -124.173622672
5.9387384756 / ! ! Single Phase Transformer: 100.0 MVA, 11.0 kV :
230.0 kV -2 / Number of windings... 12 6 2596.35756495 / 4 2
-124.173622672 5.9387384756 / ! ! Single Phase Transformer: 100.0
MVA, 11.0 kV : 230.0 kV -2 / Number of windings... 13 7
2596.35756495 / 4 3 -124.173622672 5.9387384756 / !
V2: 11.0 kV
DATADSD:
DATADSO:
ENDPAGE
85 APPENDIX C Data generated by PSCAD/EMTDC for
SSTS!=======================================================================
! Generated by : PSCAD v4.1.0 ! ! Warning: The content of this file
is automatically generated. ! Do not modify, as any changes made
here will be lost!
!=======================================================================
!--------------------------------------! Local Node Voltages
!--------------------------------------VOLTAGES: 1 0.0 // NT_1 2
0.0 // NT_2 3 0.0 // NT_3 4 0.0 // NT_7 5 0.0 // NT_8 6 0.0 // NT_9
7 0.0 // NT_10 8 0.0 // NT_11 9 0.0 // NT_12
!--------------------------------------! Local Branch Data
!--------------------------------------BRANCHES: 0 9 RE 0.0 0 8 RE
0.0 0 7 RE 0.0 3 2 RS 1000000.0 2 1 RS 1000000.0 1 3 RS 1000000.0 3
0 RS 1000000.0 2 0 RS 1000000.0 1 0 RS 1000000.0 7 3 RL 0.1 0.758 5
0 R 20.0 4 0 R 20.0 6 0 R 20.0 8 2 RL 0.1 0.758 9 1 RL 0.1
0.758
// // // // // // // // // // // // // // //
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
GND GND GND NT_3 NT_2 NT_1 NT_3 NT_2 NT_1 NT_10 NT_8 NT_7 NT_9
NT_11 NT_12
NT_12 NT_11 NT_10 NT_2 NT_1 NT_3 GND GND GND NT_3 GND GND GND
NT_2 NT_1
!--------------------------------------! Local Transformer Data
!--------------------------------------TRANSFORMERS: ! 3 Phase, 2
Winding Transformer !* Name: T32 Tmva: 100.0 MVA, Freq: 50.0 Hz,
V1: 230.0 kV, !* Imag1: 0.02 p.u., Imag2: 0.02 p.u., Xl: 0.1 p.u.
!* Sat: 0 , 2 / Number of windings... 3 0 0.0 84.1929648956 / 6 0
0.0 4.02259344016 0.0 0.192577481141 / 888 / 2 0 / 4 0 / 888 / 1 0
/ 5 0 / !
V2: 11.0 kV
86DATADSD:
DATADSO:
ENDPAGE