Development of Digital Power and Machines Labs

COLLEGE OF ENGINEERING, DESIGN, ART AND
TECHNOLOGY (CEDAT)
SCHOOL OF ENGINEERING
DEPARTMENT OF ELECTRICAL AND COMPUTER ENGINEERING
Bachelor of Science in Electrical Engineering
DEVELOPMENT OF COMPUTER BASED POWER AND
MACHINES LABS
A Dissertation
Submitted in Partial Fulfillment of the Requirements for the award of the Degree of Bachelor of
Science in Electrical Engineering of Makerere University
SEMWOGERERE DAVID
08/U/464
MAY 2012

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DECLARATION
I DAVID SEMWOGERERE, declare that the information presented in this document is an
original composition, and has never been presented anywhere for academic purposes
Signed……………………………………
DAVID SEMWOGERERE
Date:………………………………………..
We, the supervisors, have approved this report. It meets the examiners’ requirements for the
Bachelor of Science in Electrical Engineering Degree of Makerere University.
Supervisor Co-Supervisor
MR. COSMAS MWIKIRIZE DR.JULIUS BUTIME
Department of Electrical Engineering Department of Electrical Engineering
Makerere University Makerere University
Signature………………………. Signature…………………………
Date:……………………………. Date:……………………………..

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DEDICATION
To my loving father Mr. Katende Herbert, who has seen me through
school up to this far.

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ACKNOWLEDGEMENTS
This report would not have been possible if it wasn’t for the many people who were willing to
selflessly share their time, knowledge and learning opportunities.
Mr. Cosmas Mwikirize who sacrificed his time and advice from the whole time we developed
the concept up to the final day of presentation.
Richard Seruwagi my project partner with whom we worked long hours at the lab in order to
develop the power and machines lab concept.
Moses Kamanyire from ABB, who introduced us to the Siemens LOGO PLC modules and the
LOGOSoft! Comfort software.
Lydia from Real Power Company, who helped in showing the functionalities of complete
Siemens PLC systems.
David Semwogerere

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TABLE OF CONTENTS
DECLARATION............................................................................................................................ i
DEDICATION............................................................................................................................... ii
ACKNOWLEDGEMENTS ........................................................................................................ iii
LIST OF FIGURES ................................................................................................................... viii
LIST OF TABLES ........................................................................................................................ x
LIST OF ACRONYMS ............................................................................................................... xi
ABSTRACT................................................................................................................................ xiii
1 Chapter One: INTRODUCTION......................................................................................... 1
1.1 Background .....................................................................................................................1
1.1.1 PLC Temperature Control of Speed Drives of Induction Machines..........................1
1.1.2 Power System Planning (Load Flow Studies and Transient Studies) .......................3
1.2 Problem Statement......................................................................................................3
1.3 Objectives .....................................................................................................................4
1.3.1 General Objective .....................................................................................................4
1.3.2 Specific Objectives ...................................................................................................4
1.4 Justification..................................................................................................................4
1.5 Scope...............................................................................................................................5
1.6 Ethical Consideration ..................................................................................................5
1.7 Report Outline ..............................................................................................................6

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1.8 Summary of Methodology ..........................................................................................7
2 Chapter Two: LITERATURE REVIEW ............................................................................ 8
2.1 Introduction..................................................................................................................8
2.2 Motivation......................................................................................................................8
2.3 Software tools in Laboratory Courses....................................................................9
2.4 Computer Based Power Labs.....................................................................................11
2.4.1 iLabs.........................................................................................................................11
2.4.2 Programmable Logic Controllers (PLC)..................................................................11
2.4.3 LOGO! Soft Comfort:.............................................................................................13
2.4.4 Supervisory Control And Data Acquisition (SCADA)...........................................14
2.5 Induction Motors .......................................................................................................14
2.5.1 Types of Induction Motors......................................................................................14
2.5.2 Life Span of an Electric Motor ...............................................................................17
2.5.3 Problem with High Temperatures...........................................................................17
2.5.4 Induction Motor Protection.....................................................................................18
2.5.5 Thermal Effects.......................................................................................................18
2.5.6 Temperature Control using PLC .............................................................................19
2.5.7 RTD Element Types............................................................................................... 20
2.5.8 Electrical Drives..................................................................................................... 22
2.6 Power Systems Planning........................................................................................... 23
2.6.1 Transient and Stability Studies .............................................................................. 24
2.6.2 Power Flow Analysis ............................................................................................. 32

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3 Chapter Three: METHODOLOGY .................................................................................. 38
3.1 Introduction............................................................................................................... 38
3.2 Overall System Description.................................................................................... 38
3.3 Requirements and Design Specification .............................................................. 39
3.3.1 Functional Requirements ....................................................................................... 39
3.3.2 Non-Functional Requirements ............................................................................... 40
3.4 Machines Lab Design .................................................................................................41
3.5 Power Lab Features .................................................................................................. 55
4 Chapter Four: PRESENTATION AND DISCUSSION OF RESULTS ......................... 57
4.1 Transient Stability Studies.................................................................................... 57
4.2 Load Flow Studies ..................................................................................................... 58
5 Chapter Five: CONCLUSIONS AND RECOMMENDATIONS.................................... 64
5.1 Summary...................................................................................................................... 64
5.2 Research Contribution ............................................................................................. 64
5.3 Conclusions.................................................................................................................. 64
5.4 Recommendations...................................................................................................... 65
5.5 Challenges ................................................................................................................... 65
REFERENCES............................................................................................................................ 66
APPENDIX.................................................................................................................................. 69
Appendix I: Gauss flow chart ...........................................................................................69
Appendix II: Matlab script for transient Stability.................................................... 70
Appendix III: Matlab Script for radial power system............................................... 72

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Appendix IV: Matlab Script for load flow in ring power system ............................. 74

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LIST OF FIGURES
Figure 2-1: Lab Preparation Setup.................................................................................................. 9
Figure 2-2: Basic PLC Block Diagram......................................................................................... 12
Figure 2-3: Program Blocks.......................................................................................................... 13
Figure 2-4: Squirrel Cage Induction Motor .................................................................................. 15
Figure 2-5: Wound Rotor Induction Motor. ................................................................................. 16
Figure 2-6: Schematic Diagram of PT Temperature Sensor......................................................... 20
Figure 2-7: Block Diagram of a Power System............................................................................ 24
Figure 2-8: Flow of Power in a Synchronous Generator .............................................................. 26
Figure 2-9: Plot of δ vs t ............................................................................................................... 28
Figure 2-10: Plot of P vs δ ............................................................................................................ 29
Figure 2-11: Power Flow Diagram ............................................................................................... 36
Figure 3-1: PLC diagram for Motor Temperature Control........................................................... 43
Figure 3-2: Program Blocks in Siemens LOGO!Soft Comfort .................................................... 44
Figure 3-3: Analog Amplifier Dialog Box.................................................................................... 45
Figure 3-4: Analog Comparator Dialog Box ................................................................................ 45
Figure 3-5: Network Input Dialog Box......................................................................................... 46
Figure 3-6: PLC Module Connection to Computer ...................................................................... 47
Figure 3-7: Siemens 0BA7 PLC Module...................................................................................... 48
Figure 3-8: PLC Module Power Connection ................................................................................ 49
Figure 3-9: RT100 Temperature Sensor ....................................................................................... 49
Figure 3-10: Stator Core and Wire................................................................................................ 50
Figure 3-11: RT100 Temperature Sensor Connection to PLC ..................................................... 51
Figure 3-12: PLC Connection to Contactor .................................................................................. 52
Figure 3-13: PLC Ethernet Connection ........................................................................................ 52
Figure 3-14: PLC Networking ...................................................................................................... 53
Figure 3-15: Addressing PLC Devices ......................................................................................... 54
Figure 3-16: Summary of Power Lab Program Structure ............................................................. 55
Figure 4-1: Radial Power System ................................................................................................. 57
Figure 4-2: Transient Stability Front Panel .................................................................................. 58

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Figure 4-3: Radial Power System ................................................................................................. 59
Figure 4-4: Radial Load Flow Front Panel ................................................................................... 60
Figure 4-5: Mesh Power System................................................................................................... 60
Figure 4-6: Ring Power System Load Flow Panel........................................................................ 61
Figure 4-7: Lab Running in Internet Explorer .............................................................................. 63

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LIST OF TABLES
Table 1: Summary of Methodology................................................................................................ 7
Table 2: Requirements .................................................................................................................. 41
Table 3: Temperature Sensor Characteristics ............................................................................... 51
Table 4: Induction motor specifications........................................................................................ 55

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LIST OF ACRONYMS
AC Alternating Current
ADC Analog to Digital Converter
ASD Adjustable Speed drives
AIM Analog Inputs Module
AOM Analog Outputs Module
CPU Central Processor Unit
DC Direct Current
DDE Directional Derivative Estimation
DIM Discrete Input Module
DOM Discrete Output Module
FLC Full Load Current
FORTRAN Formula Translator
HMI Human Machine Interface
IEC International Electrical Commission
ILAB Internet Laboratories
IM Induction Motor
I/O Input/Output
IP Internet Protocol
KCL Kirchoff’s Current Law

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LRC Locked Rotor Current
LRT Locked Rotor Test
MATLAB Matrix Laboratory
PC Personal Computer
PIC Programmable Integrated Circuit
PLC Programmable Logic Controllers
PRT Platinum Resistance Temperature
RTE Run time Engine
RTU Remote Terminal Unit
SCADA Supervisory Control and Data Acquisition
SPRT Sequential Probability Ratio Test
SQL Structured Query Language
TCP Transmission Control Protocol
VSD Variable Speed Drive

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ABSTRACT
Although principles of power systems and machines can be taught using conventional laboratory
tools that involve hardware, there is an increasing usage of computer systems to carry out labs in
these disciplines due to the various advantages associated with them. This research therefore set
out to show the development of power and machines labs with the objective of enabling students
to carry out power and electrical machines studies using computer based platforms.
To achieve the project objectives, the functional and non-functional requirements were first
established and the hardware together with associated software for the lab design determined.
The developed lab involves computer based PLC system for controlling an induction motor and a
simulation of load flow and fault analysis as well as studies on predesigned circuits.
With this lab in place, the students can be introduced to PLC programming for electrical
machines which is essential in today’s automated industry; as well as facilitate studies in power
systems planning.

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1 Chapter One: INTRODUCTION
Background1.1
Computer based learning platforms are continuously finding application in universities as
a way of supplementing physical laboratories to carry out lab experiments. Today, lab
experiments in electronics and circuit theory simulation experiments are widely carried
out using software program such as Simulink, LabVIEW and Matlab. An example of
such computer based learning platforms is ‘iLabs’, an online laboratories platform used
to support several courses at Makerere University. In this project, we extend this concept
to the development of computer based ‘power and machines’ labs. The labs consist of
two parts:
1) Development of PLC temperature control system for speed drives of Induction
machines.
2) Computer simulation of Power system Planning (load flow studies and transient
studies)
1.1.1 PLC Temperature Control of Speed Drives of Induction Machines
Monitoring and control of Induction machines is a fast emerging technology for the
detection of initial faults in induction machines. It has thus helped in avoiding unexpected
failure of industrial processes due to temperature rises before damage can be caused to
the motor winding. Monitoring techniques can be classified as the conventional and the
digital techniques.
Classical monitoring techniques for three-phase induction machines have generally been
provided by some combination of mechanical and electrical monitoring equipment.
Mechanical forms of motor sensing are limited in ability to detect electrical faults, such
as stator insulation failures due to high temperatures. It’s very basic in that it involves
mechanical dynamic parts and doesn’t enable visualization of the parameters measured.
In addition, the mechanical parts of the equipment can cause problems in the course of

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operation and can reduce the life and efficiency of a system. Some of the components
used in the classical methods include, timers, contactors, voltage, and current relays.
Advanced Computer based programmable integrated circuit protection and monitoring
methods were later introduced, which eliminated most of the mechanical components.
However, the computer-based protection method required an analog-to-digital conversion
(ADC) card. Today, the most widely used technology in the control circuits of industrial
automation systems for induction machines of programmable logic controller (PLC). The
PLC systems are equipped with special I/O units appropriate for direct usage in industrial
automation systems. The input components, such as temperature sensors, can be directly
connected to the input. The driver components of the control circuit such as contactors
and solenoid valves can directly be connected to the output.
Many factories and plants have therefore resorted to the use of PLC in automation
processes to diminish production cost and to increase quality and reliability. In
universities, similar projects have been implemented before with major focus on the
provision of motor protection from faults and high winding temperatures; as well as
speed control. Most of these projects however were based on classical monitoring and
protection techniques such as Programmable Integrated Circuit (PIC) controllers and
rarely any using Programmable Logic Control. Some of these projects were under titles
such as:
1) Fault Detection and Protection of Induction Motors Using Sensors by Ramazan
Bayindir, Ibrahim Sefa, IIhami Colak, Askin Bektas 3rd September 2008
2) Speed Control of 3-Phase Induction Motor Using PIC18 Microcontrollers by
Padmaraja Yedamale Microchip Technology
With a PLC based system however, the voltages, the currents, the speed, and the
temperature values of the motor, and the problems occurring in the system, are monitored
and warning messages can be shown on the computer screen unlike in the above projects.
In this study therefore, which involves induction machine drives and their temperature
control, a new protection and monitoring method based on a programmable logic

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controller (PLC) has been introduced. In this method, all contactors, timers, relays, and
the conversion card are eliminated.
This project also shows how the PLC-based protection method developed costs less,
provides higher accuracy as well as a safe and more visual environment compared with
the classical, and the PIC-based protection systems. The PLC-based temperature
protection system developed costs less, provides higher accuracy as well as safe and
visual environment compared with the classical, the computer, and the PIC-based
protection systems.
1.1.2 Power SystemPlanning (Load Flow Studies and Transient Studies)
Power systems load flow and transient study projects have been implemented before
using various tools in universities such as IIT Bombay India. Most of the previous
studies however were using conventional programming languages such as Visual Basic,
C++ and FORTRAN which are rather complex to learn and difficult to trouble shoot in
case of failure. In Makerere University, according to our knowledge, no experiments
have yet been done with respect to power systems planning and we hope that this will
change with the introduction of the Computer based power labs concept.
Problem Statement1.2
In an effort to enhance and aid the existing power systems and machines knowledge
platforms for the electrical engineering students, we set out to design for the
implementation of a Computer based power and machines labs. As far as power systems
and machines studies are concerned, the lab is a pioneering project in the College, upon
which the university can base to enhance the learning of electrical engineering students.
Unlike the conventional machines and power lab existing at the faculty which has costly
equipment, this computer based lab is cheaper and has more advantages such as:
i. It’s simple to set up
ii. It provides mobility of equipment
iii. It incorporates the latest technology that is applicable in industries
iv. Contribution to future research

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v. It poses less safety threats
Objectives1.3
1.3.1 General Objective
To develop power and machines labs that give students an opportunity to carry
out power and electrical machines studies using a computer based platform.
1.3.2 Specific Objectives
1. Design a system for the study of the induction motor temperature
protection system using a PLC.
2. Develop a system for undertaking power studies through simulation of
load flow and transients in power systems.
Justification1.4
Power systems and machines are some of the core component course units in the
electrical engineering course. Without a platform with which to continuously gain access
to practical knowledge in the contents of these course units, an electrical engineering
student is deprived of the opportunities to experiment and learn further, what they learn
in class.
Although the College has power and machines labs, not so many students get access to
these labs in their entire stay at the university. This has probably been due to the time that
is involved in setting up a lab experiment and the general fact that this lab is a master’s
student’s power laboratory. The Computer based power and machines lab will give the
students two options:
1. Simulation of a power system with respect to load flow and response to transients
Although, there has been a ‘Power Systems Theory’ course unit in the second
year of the Electrical Engineering course, most of the power course units that
follow haven’t been as practical as would be expected. Some of the following

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course units include Power Systems Engineering I, Power Systems Engineering II
as well as Power Systems Protection and Co-ordination. The lab will thus provide
a practical insight into the load flow and transient studies that are done in Power
Systems I, Power Systems Protection and Coordination as well as Network
Theory II.
2. PLC control of speed drives of induction machines and temperature monitoring
and control. Machine automation is increasing as more sophisticated systems are
installed in industries for both machine control and monitoring. This part of the
lab is meant to cater for the Machines I and Machines II course units. Although
the students have knowledge in machines, they need to get exposure in the new
systems that are used in induction machine control and monitoring. The lab
however focuses and puts more emphasis on induction machine control and
temperature monitoring using Programmable Logic Control (PLC) technology.
Scope1.5
Although the power systems and machines subjects are broad, more emphasis was put on
the following topics:
1) Transient and load flow studies in power systems.
2) Motor temperature control using Programmable Logic Controllers.
Ethical Consideration1.6
This research was conducted in accordance with Makerere codes and policies for
research. Attention was paid to avoidance of forms of misconduct including; deliberate
fabrication of data (falsification, obfuscation and making bare assertions), plagiarism,
misappropriation of data and suppression of research results. Care was taken while using
outcomes of other related research by giving appropriate citation to formulae, tables and
relationships used. The research aimed at generating results geared at adding value to the
body of knowledge considering that scientific research is built on the foundation of trust.

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Report Outline1.7
The report consists of four chapters. Chapter 1: Introduction, Chapter 2: Literature
Review, Chapter 3: Requirements and design specification, Chapter 4: Analysis of
Results and Outputs, Chapter 5: Conclusions and Recommendations.
Chapter 1: Introduction
The background about the project and the justification is given; as well as the general and
specific objectives for the project.
Chapter 2: Literature Review
This contains the motivation and theory on different topics concerning the project such as
induction motors, temperature sensor, Power systems analysis and more.
Chapter 3: Requirements and Design Specification
This gives the design of the power and machines labs. It also contains functional and non-
functional requirements. It also contains simulation results from the project.
Chapter 4: Analysis of Results and Outputs
This chapter is dedicated to the analysis of the project results generated after the
simulation and implementation.
Chapter 5: Conclusions and Recommendations
This gives a summary of the project, conclusions, recommendations as well as the
challenges met during the project.

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Summary of Methodology1.8
In order to achieve the identified objectives, the research methodology was bench marked
against a set of milestones. Each milestone was achieved through a set of activities and
work packages as illustrated in the table below.
Table 1: Summary of Methodology
MILESTONES WORK PACKAGES DELIVERABLES
Requirements
Analysis
1. Overall outlook of the lab
2. PLC programming hardware and
software analysis.
3. Power system analysis tools
Functional and Non-
functional requirements
development
Design
Specification
1. Development of program flow
charts
2. Power system configuration
development
3. Hardware specification for the
power lab
Siemens program and PLC
model selection
Matlab code for load flow
and transient studies
Modeling and
Simulation
1. PLC program block diagram and
simulation test runs
2. Matlab code development and
running
Analysis of results and
output

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2 Chapter Two: LITERATURE REVIEW
2.1 Introduction
This section gives an in depth look at how motor control came to be applied and power
management studies with regards to load flow and transient studies.
2.2 Motivation
Today, more universities are starting the application of virtual learning platforms that
enable students to carry out experiments to study different physical phenomenon. These
virtual platforms are computer based and enable students to model laboratories that
enable them to carry out an experiment without necessarily having physical equipment or
apparatus. Although no physical apparatus is involved, these laboratories have enabled
modeling of physical experiments / phenomenon with high levels of accuracy. This has
not only enhanced learning but has proven powerful in research applications as well. This
is further coupled with the advantage that these systems are cheaper than actual
laboratories to set up in the long run necessitates that computer based laboratories.
In Makerere University, such platforms have been applied; called the ilabs and have been
very influential in electronics as well as circuit theory experiments. In the same retrospect
however, other course units/ fields of study can also benefit from this technology and
hence the project aims at doing so in Power systems and Electrical machines. The project
aims at the development of computer based Power and Machines labs that will involve
the computer simulation of power systems planning and motor temperature control using
Programmable Logic Controllers.

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2.3 Software tools in Laboratory Courses
There are various categories of educational software that can be used in Laboratory
Courses, grouped by the specific task, which they are focused on:
Multimedia Presentations and Tutorials: These tools provide a theory background to
the student, enhanced by the use of different media such as sound, video, text and
hypertext (topic linked documents), pictures and animations. These presentations aim at
providing the students with a realistic description of the topic and enhance greatly their
interest.
Problem Solving and Self-examination Systems: They give the opportunity to the
students to evaluate the quality and amount of acquired knowledge relative to the subject
studied, and unveil their weaknesses and misunderstandings.
Laboratory Preparation Software: This class of educational software provides
information about the structure of a laboratory exercise, gives the theoretical background,
analyzes the physical models underlining the equipment used, discusses the tasks which
the student has to accomplish and provides tools or guidelines to collect the data, helps
them come to conclusions and explain their observations.
Figure 2-1: Lab Preparation Setup
Laboratory Work Support System: This is perhaps the most interesting case, since it
involves deep integration of software system and the laboratory equipment. The objective

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is to automate the execution of the laboratory work. An example of such system, relating
to an Electrical machines Laboratory, is shown in the above figure. This improves the
classical way to:
a) Perform engineering laboratory work, which presents the following
disadvantages: A lot of time is spent by the students for preparatory activities like
wiring and by the supervisor for checking the wiring.
b) Long manual measurements result in shifting attraction away from the lab
objective.
c) Measuring instruments are protected against accidental damage.
d) Lab reports, containing measurement analysis, are prepared by the students after
leaving the laboratory. Consequently, there is no possibility for checking or
repeating measurements that could have contributed to deeper understanding of
the subject.
e) Group work in labs, results in not effective participation of all students during the
laboratory work.
Modeling and Simulation: This type of educational software makes use of computer
models in order to simulate the behavior of the system or process under study,
substituting the laboratory equipment. This way, it is possible to repeat an experiment
many times, comparing the findings with the model-based values. We can expect that
complete laboratory-educational software can cover most of the above functionality,
maximizing the interaction with the student and enhancing various phases of the
educational process. The automation of the experimental bench through introduction of a
combination of the above systems, improves the quality of education, offering important
advantages such as:
a) The students devote their time to fruitful discussion and useful observations,
having the possibility to analyze directly the measurements, repeat some of them,
compare with theoretical simulation results.
b) The students are concentrated on understanding fundamental concepts and not
performing tedious wiring and measurements.

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c) The students can be introduced to interrelated disciplines, such as from electrical
machines to power electronics, automation and control, data acquisition and many
more.
d) Drilling can be enabled at any time without supplementary effort by the
educational staff.
e) Minimization of failures due to wrong wiring.
f) Minimization of the effort needed by the laboratory support staff.
g) New possibilities on continuous education, distance-learning, collaboration with
industries and training of industrial personnel etc.
2.4 Computer BasedPowerLabs
2.4.1 iLabs
Computer based labs were first introduced into the university in 2008 as a means of
enabling the university students to learn more about physical processes without using
physical equipment. The labs involve using LabVIEW software to control real hardware
in electronic or digital circuits, through a web-based interface. These labs are however
limited to a few course units such as Circuit Theory, Electronic Circuits, Analogue
Electronics and Communication Systems. Despite Power System Engineering and
Electrical Machines being the some of the core components of the electrical engineering
course, there haven’t been any computer based platforms for the electrical engineering
students to do any practical experiments in these course units. This project therefore aims
at designing and implementing laboratories that can be accessed over a computer
network.
2.4.2 Programmable Logic Controllers (PLC)
PLC is a microprocessor-based control system, designed for automation processes in
industrial environments. It uses a programmable memory for the internal storage of user-
orientated instructions for implementing specific functions such as arithmetic, counting,
logic, sequencing, and timing. A PLC can be programmed to sense, activate, and control

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industrial equipment and, therefore, incorporates a number of I/O points, which allow
electrical signals to be interfaced. Input devices and output devices of the process are
connected to the PLC and the control program is entered into the PLC memory.
Figure 2-2: Basic PLC Block Diagram
This refers to intelligent equipment that can enable control of physical processes or
actions or electrical equipment using computer software and data conversion modules. A
typical PLC system consists of the following items:
i. Monitor or Human Machine Interface
ii. PLC module
iii. Data acquisition cards
iv. ADC and DAC cards
v. Data cables.
This controller is implemented on a PLC modular system. The PLC architecture refers to
its internal hardware and software. As a microprocessor-based system, the PLC system
hardware is designed and built up with the following modules:
i. central processor unit (CPU)
ii. discrete output module (DOM)
iii. discrete input module (DIM)
iv. analog outputs module (AOM)
v. analog inputs module (AIM)

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vi. power supply
In this system, current and voltage are controlled by the temperature speed of the
induction motor.
2.4.3 LOGO! Soft Comfort:
This is a Siemens PLC programming software used to design the PLC program. The PLC
programming is done by combining different logic blocks as may be necessary. Some of
the block examples include analog and digital inputs, outputs, counters, as well as logic
functions such as OR and AND. These blocks when combined enable the PLC to operate
and give outputs depending on the circuit program. After programming the PLC circuit
diagram in LOGO! Soft Comfort, the program downloaded onto the PLC logic module
card using a Siemens data cable. Note that the downloaded program can be used in other
LOGO! by inserting this program card.
Figure 2-3: Program Blocks
Steps involved:
1) Develop the circuit program on the computer as shown above.
2) Simulate the circuit program on the computer and verify the functions. Here
comments can be added and then saved on the computer.
3) The circuit program is downloaded to LOGO!

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2.4.4 Supervisory Control And Data Acquisition (SCADA)
Supervisory Control And Data Acquisition is a computer system used to control process
operations. It is through SCADA that an operator is able to control field parameters
through the PLC system as it sends commands and gathers information from the field
instruments.
How SCADA works
SCADA works hand in hand with the PLC system. As an example, a PLC may control
the flow of cooling water through part of an industrial process, but the SCADA system
allows operators to change the set points for the flow, and enable alarm conditions, such
as loss of flow and high temperature, to be displayed and recorded. The feedback control
loop passes through the RTU or PLC, while the SCADA system monitors the overall
performance of the loop.
The key use of SCADA is to monitor an entire system in real time. This is facilitated by
data acquisitions including meter reading, checking statuses of sensors and other
monitoring functions; that are communicated at regular intervals depending on the
system. Besides the data being used by the RTU, it is also displayed to a human that is
able to interface with the system to override settings or make changes whenever
necessary.
2.5 Induction Motors
Induction motors are the most important ac machines as they are used intensively in
industry as an actuator. Low cost, high reliability, low inertia and high transient torque
capacity are among the advantages of these motors.
2.5.1 Types of Induction Motors
Based on the construction of the rotor, induction motors are broadly classified in two
categories; squirrel cage motors and slip ring motors. The stator construction is the same
in both motors.

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Squirrel Cage Motor
Almost 90% of induction motors are squirrel cage motors. This is because the squirrel
cage motor has a simple and rugged construction. The rotor consists of a cylindrical
laminated core with axially placed parallel slots for carrying the conductors. Each slot
carries a copper, aluminum, or alloy bar. If the slots are semi-closed, then these bars are
inserted from the ends. These rotor bars are permanently short-circuited at both ends by
means of the end rings, as shown in the figure below.
Figure 2-4: Squirrel Cage Induction Motor
From the figure, the motor assembly resembles the look of a squirrel cage, which gives
the motor its name. The rotor slots are not exactly parallel to the shaft. Instead, they are
given a skew for two main reasons:
i. To make the motor run quietly by reducing the magnetic hum.
ii. To help reduce the locking tendency of the rotor. Rotor teeth tend to remain
locked under the stator teeth due to direct magnetic attraction between the
two. This happens if the number of stator teeth is equal to the number of rotor
teeth.
Wound Rotor (Slip Ring Motors)
A wound rotor induction motor has a stator like the squirrel cage induction motor, but a
rotor with insulated windings brought out via slip rings and brushes. The windings on the
rotor are terminated to three insulated slip rings mounted on the shaft with brushes resting
on them. This allows an introduction of an external resistor to the rotor winding. The

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external resistor can be used to boost the starting torque of the motor and change the
speed-torque characteristic. When running under normal conditions, the slip rings are
short circuited, using an external metal collar, which is pushed along the shaft to connect
the rings. So, in normal conditions, the slip ring motor functions like a squirrel cage
motor.
However, no power is applied to the slip rings. Their sole purpose is to allow resistance
to be placed in series with the rotor windings while starting. This resistance is shorted out
once the motor is started to make the rotor look electrically like the squirrel cage
counterpart.
Figure 2-5: Wound Rotor Induction Motor.
The reason why a resistance is put in series with the rotor is because squirrel cage
induction motors draw 500% to over 1000% of full load current (FLC) during starting.
While this is not a severe problem for small motors, it is for large (10's of kW) motors.
Placing resistance in series with the rotor windings not only decreases start current,
locked rotor current (LRC), but also increases the starting torque, locked rotor torque
(LRT).

17
2.5.2 Life Span of an Electric Motor
The life of an electric motor is determined by two major factors:
a) Mechanical Life:
This is the life of the mechanical parts such as bearings, shaft, fan and the frame and
depends on the environment (dust, moisture, chemicals, etc.), vibration and
lubrication. The mechanical life can be extended by means of regular inspection and
maintenance.
b) Electrical Life:
This is the life of the electrical parts such as the stator winding and insulation, rotor
winding and the cable terminations in the motor connection box. Assuming that the
cable terminations are properly done and regularly checked, the electrical life may be
extended by ensuring that the windings and insulation are not subjected to excessive
temperatures which are usually the consequence of overloading or single phasing
(loss of one-phase). The purpose of good motor protection is to continuously monitor
the current flowing into the motor to detect overloading or fault conditions and to
automatically disconnect the motor when an abnormal situation arises. This
protection, when correctly applied, extends the useful life of the motor by preventing
insulation damage through overheating.
2.5.3 Problem with High Temperatures
These high temperatures result in the deterioration of the insulation materials through
hardening and cracking, eventually leading to electrical breakdown or faults. In many
cases, the motor can be repaired by rewinding the stator but this is expensive with a
longer downtime. The larger the motor, the higher the cost of repair.
There are several types of insulation materials commonly used on motors. In the IEC
specifications for motors, the insulation materials are classified by the temperature rise
above maximum ambient temperature that the materials can continuously withstand

18
without permanent damage. For example, specified temperature rises for commonly used
insulation classes are:
Class B: 80 °C above maximum ambient of 40 °C
(i.e. maximum continuous temperature of 120 °C)
Class F: 100 °C above maximum ambient of 40 °C
(i.e. maximum continuous temperature of 140 °C)
2.5.4 Induction Motor Protection
Protection of an induction motor (IM) against possible problems, such as overvoltage,
overcurrent, overload, over temperature, and under-voltage, occurring in the course of its
operation is very important. In this section we highlight how high temperatures can
result into motor failure or damage and hoe they can be protected using PLCs.
2.5.5 Thermal Effects
Many resources show that the majority of motor failures are caused by stator insulation
breakdown. Overheating is one of the major causes of the stator winding insulation
degradation in small induction machines. In most cases, it is necessary to monitor rotor
bars and stator windings to make sure that their temperature remains below the allowable
limits. The insulation life time in years can be approximated by
k
where k is 7.15x104, a is 0.08 and Ɵ is insulation temperature in 'C.
If motor temperature increases from 100°C to 105°C, insulation life decreases from 24 to
16 years. In order to extend the insulation life time, it is critical to monitor the stator
winding and rotor temperature and protect the motor under thermal overloading
conditions. Motor stall, jam, overload, unbalanced operation are some example of
thermal stress on induction motors. Moreover, motor heating can also be increased in
situations where the cooling ability of the motor is accidentally reduced.

19
2.5.6 Temperature Control using PLC
There a basically three ways by which thermal variations in a motor can be measured.
1) Thermal modeling provides a flexible and accurate way for motor temperature
estimation; however, it cannot respond to the changes in the motor thermal
characteristics.
2) The stator temperature can also be estimated based on the stator resistance
measurement. It is reported that, this method can provide temperature estimation
that is capable of responding to the changes in the thermal characteristics of the
motor. The limitation of this method is its disability to measure rotor resistance
directly.
3) Another more accurate method of temperature measurement however deals with
the direct measurement of motor heating using temperature sensors installed in
stator windings and rotor parts. In this method, temperature monitoring of
stationary parts is relatively easy, but difficult for the rotating parts. Therefore, we
only focus on the stationary parts for simplicity and economic reasons in this
study.
In this report, design and implementation of a temperature measuring system suitable for
three-phase induction motors is described. Temperature rise in rotor bars and stator
windings are monitored under various conditions. It is shown that the system is capable
for thermal monitoring of the test motor under various supply and load conditions. The
system mainly consists of stationary parts. In this design, an analog temperature sensor is
installed on the stator windings and not the rotor. The temperature produces a current 4-
20mA in the temperature sensor that is converted into a digital value on the PLC and also
actuates the PLC to produce the required function for motor control.
Temperature sensor
Platinum resistance thermometers (PTs) is the most common type of resistance
temperature sensor used in industry and was the temperature sensor element that was
chosen is the PT100. PT100 offer excellent accuracy over a wide temperature range
(from -200 to +800 °C). Standard Sensors are available from many manufacturers with

20
various accuracy specifications and numerous packaging options to suit most
applications. Unlike thermocouples, it is not necessary to use special cables to connect to
the sensor. It has a specified resistance of 100.00 ohms at 0°C and is made of Platinum
which has an accurately defined resistance vs. temperature characteristic.
Figure 2-6: Schematic Diagram of PT Temperature Sensor
The data from the thermal sensors on the stator is digitized using electronic parts such as
ADC and PLC module, and transmitted via cable from the sensor to the PLC module. A
data acquisition system is employed for capturing data from electronic parts to PC for
further analysis and monitoring purposes.
2.5.7 RTD Element Types
There are three main categories of RTD sensors; Thin Film, Wire-Wound, and Coiled
Elements.
a) Carbon Resistor Elements are widely available and are very inexpensive. They
have very reproducible results at low temperatures. They are the most reliable
form at extremely low temperatures. They generally do not suffer from significant
hysteresis or strain gauge effects.
b) Strain Free Elements a wire coil minimally supported within a sealed housing
filled with an inert gas. These sensors are used up to 961.78 °C and are used in the
SPRT’s that define ITS-90. They consisted of platinum wire loosely coiled over a
support structure so the element is free to expand and contract with temperature,
but it is very susceptible to shock and vibration as the loops of platinum can sway
back and forth causing deformation.
c) Thin Film Elements have a sensing element that is formed by depositing a very
thin layer of resistive material, normal platinum, on a ceramic substrate. This

21
layer is usually just 10 to 100 angstroms (1 to 10 nanometers) thick. This film is
then coated with an epoxy or glass that helps protect the deposited film and also
acts as a strain relief for the external lead-wires. Disadvantages of this type are
that they are not as stable as their wire wound or coiled counterparts.
d) Wire-wound Elements can have greater accuracy, especially for wide temperature
ranges. The coil diameter provides a compromise between mechanical stability
and allowing expansion of the wire to minimize strain and consequential drift.
The sensing wire is wrapped around an insulating mandrel or core. The winding
core can be round or flat, but must be an electrical insulator.
e) Coiled elements have largely replaced wire-wound elements in industry. This
design has a wire coil which can expand freely over temperature, held in place by
some mechanical support which lets the coil keep its shape. This strain free design
allows the sensing wire to expand and contract freely.
Advantages of PT100
i. The PT100 is the preferred sensor for all industrial applications from -200°C
to 800°C. It is accurate, relatively inexpensive and easy to use. Its output
change with temperature is relatively large compared to thermocouples, which
means lower drift errors on the electronics.
ii. For the majority of applications PT100 probes may be replaced with no
recalibration of instruments.
iii. Because its resistance bears an absolute relationship to temperature (unlike a
thermocouple whose output depends on the difference between the hot
junction and cold junction) no special compensating circuit needs to be
provided in the electronics.
Disadvantages of the PT100
i. Most people regard the major disadvantages of the PT100 sensor over other
industrial sensors, such as thermocouples, as response time and physical
strength.

22
ii. Modern PT100 sensors are now so small and light that the response time no
longer depends on the sensor itself. The response time of a PT100 in a
stainless steel sheath will be almost identical to that of an insulated
thermocouple in an identical sheath because the thermal characteristics of the
sheath are the major contributing factor.
iii. The physical strength of a thermocouple is still superior but a Pt100 sensor
properly packed in aluminium oxide in a stainless steel sheath should
withstand everything short of a direct blow from a hammer.
2.5.8 Electrical Drives
Electrical Drives are used to control power flow to the induction motor using power
electronics. In this section we shall focus on Variable Speed Drives (VSD) also referred
to as Adjustable Speed Drives (ASD’s).
AC Adjustable Speed Drives (ASD’s) have become very popular variable speed control
devices used in industrial, commercial and some residential applications. These devices
have been available for about 20 years and have a wide range of applications ranging
from single motor driven pumps, fans and compressors, to highly sophisticated multi-
drive machines. They operate by varying the frequency of the AC voltage supplied to the
motor using solid state electronic devices. ASD’s allow precise speed control of a
standard induction motor and can result in significant energy savings and improved
process control in many applications. Adjustable Speed Drives have a number of
advantages and disadvantages though, and one of these is motor heating.
Disadvantage - Motor Heating at Low Speed Operation
ASD’s used to run constant torque loads at slow speeds, have a high potential for motor
heating.
i. No matter what speed the motor runs, the current draw to the motor will be the
same with a constant torque load.
ii. At low speeds, the cooling fan on the motor produces less cooling air.

23
iii. If the motor produces the same amount of heat at low speed due to the constant
torque load and there is less cooling air, the motor will overheat.
As a rule of thumb therefore, you can generally take a fully loaded Class B insulation
motor down to 50 percent speed on constant torque loads without overheating. You can
generally take a fully loaded Class F insulation motor down to approximately 20 percent
speed without overheating the motor.
2.6 PowerSystems Planning.
A power system consists of generation, transmission and distribution of power from the
source to the final consumer. With ever increasing power demand, the nature and
complexity of power systems is constantly increasing and thus necessitating the need for
powers system analysis tools. With good power systems analysis, we can better predict
how much power to generate depending on the power consumption at different times.
Hence power systems analysis is used in load shedding and power rationing.

24
Figure 2-7: Block Diagram of a Power System
2.6.1 Transient and Stability Studies
The stability of a power system implies its ability to return to normal or stable operation
after having been subjected to some form of disturbance. Instability means a condition
where there’s loss of synchronism of synchronous machines or falls out of step. At that
point therefore there’s loss of equilibrium in the system. There are three types of stability
and these include; steady state, dynamic and transient stability.
Steady state stability relates to the response of a synchronous machine to a gradually
increasing load. It is basically concerned with the determination of the upper limit of
machine loadings before losing synchronism, provided the loading is increased gradually.
Stability involves the response to small disturbances that occur on the system.

25
Dynamic stability involves the response to small disturbances that occur on the system,
producing oscillations. The system is said to be dynamically stable if these oscillations do
not acquire more than certain amplitude and die out quickly. If these oscillations
continuously grow in amplitude, the system is dynamically unstable. Transient stability
involves the response to large disturbances, which may cause large changes in rotor
speeds, power angles and power transfers. It’s a fast phenomenon and occurs within a
few seconds.
Factors that Determine the Stability of a Power System
The parameters affecting system stability include:
i. How heavily the generator is loaded
ii. The generator output during fault. This depends on the fault location and type
iii. The fault-clearing time
iv. The post fault transmission system reactance
v. The generator reactance. A lower reactance increases peak power and reduces
initial rotor angle.
vi. The generator inertia. The higher the inertia, the slower the rate of change in
angle. This reduces the kinetic energy gained during fault; i.e., area A1 on the
stability curve is reduced.
vii. The generator internal voltage magnitude (E). This depends on the field
excitation.
viii. Synchronous machine parameters
ix. The infinite bus voltage magnitude
x. Transmission line parameters
xi. Circuit breaker & relay characteristics
xii. System layout
xiii. Excitation system and governor characteristics
xiv. Neutral grounding

26
The Swing Equation
Consider a synchronous generator developing an electromagnetic torque Te and a
corresponding electromagnetic power P while operating at the synchronous speed ωs
Figure 2-8: Flow of Power in a Synchronous Generator
If the input torque provided by the prime mover, at the generator shaft is Ti, then under
steady state conditions ie without any disturbance
Here we have neglected any retarding torque due rotational losses. Therefore we have
thus
If there is a departure from steady state e.g change in load or a fault, then the input power
is not equal to the electromagnetic power, (neglecting armature resistance) i.e
Therefore the left side of the equation is not zero and an accelerating torque comes into
play. If is the accelerating power then

27
Where M has been defined as above, D is the damping coefficient and ϴe is the electrical
angular position of the rotor with respect to a synchronously rotating frame of reference.
Let
Where is the power angle of the synchronous machine. Neglecting damping (i.e D=0)
and on substituting, we get
but
and
Where H is the inertia constant and G is the MVA rating of the machine. Diving through
by G, we get
( )
Where
Or ( )
This is known as the swing equation

28
The Equal Area Criterion
From above, we have seen that a solution to the swing equation for ( ) leads to the
determination of the stability of a single machine operating as part of a large power
system. However it does not necessarily investigate the system stability. It thus
necessitates the use of a direct approach called the equal area criterion.
Consider the equation,
As is shown in the figure below in an unstable system, increases indefinitely with
time and the machine loses synchronism. In a stable system, undergoes oscillations
which eventually die out due to damping.
Figure 2-9: Plot of δ vs t

29
From above, it’s clear that for a system to be stable, it must be that at some
instant
On multiplying the previous equation by and integrating with respect to time, we get
( ) ∫
The stability criterion implies that
∫
This condition requires that for stability, the area under the graph of accelerating power
versus must be zero for some value of , i.e the positive (accelerating) area under
the graph must be equal to the negative (decelerating) area. This criterion is therefore
known as the equal – area criterion for stability and is shown in the figure below.
Figure 2-10: Plot of P vs δ
Hence for stability,
Area A1 = Area A2

30
Numerical Methods of Solving Stability Equations
The transient stability analysis requires the solution of a system of coupled non-linear
differential equations. In general, no analytical solution of these equations exists.
However, techniques are available to obtain approximate solution of such differential
equations by numerical methods and one must therefore resort to numerical computation
techniques commonly known as digital simulation. Some of the commonly used
numerical techniques for the solution of the swing equation are:
a) Point by point method
b) Euler's method
c) Euler's modified method
d) Runge-Kutta method, etc.
a) Point by Point Method:
Point by point solution, also known as step-by-step solution is the most widely used way
of solving the swing equation. The following two steps are carried out alternately.
1. First, compute the angular position , and angular speed at the end of the time
interval using the formal solution of the swing equation from the knowledge of
the assumed value of the accelerating power and the values of and at the
beginning of the interval.
2. Then compute the accelerating power of each machine from the knowledge of the
angular position at the end of the interval as computed in step 1.
b) Runge-Kutta Method:
The R-K methods approximate the Taylor series solution; however, unlike the formal
Taylor series solution, the R-K methods do not require explicit evaluation of derivatives
higher than the first. The effects of higher derivatives are included by several evaluations
of the first derivative. Depending on the number of terms effectively retained in the
Taylor series, we have R-K methods of different orders.

31
Second-order R-K method:
Referring to the above differential equation, the second order R-K formula for the value
of x at t = t0b+ ∆t is
x 1 = x 0 +∆ x = x 0 + (k1 + k2)/2
where
k1 = f(x 0, t0) ∆t
k2 = f(x 0 + k1, t0 + ∆t) ∆t
This method is equivalent to considering first and second derivative terms in the Taylor
series; error is on the order of ∆t.
A general formula giving the value of x for (n + 1) step is
xn+1 = xn + (k1 + k2)/2
where
k1 = f(x n, tn) ∆t
k2 = f(x n + k1, tn + ∆t) ∆t
Fourth-order R-K method:
The general formula giving the value of x for the (n + 1) step is
xn+1 = xn + (k1 + 2k2 + 2k3 + k4)/6
where
k1 = f(x n, tn) ∆t
k2 = f(x n + k1/2, tn + ∆t/2) ∆t
k3 = f(x n + k2/2, tn + ∆t/2) ∆t
k4 = f(x n + k3, tn + ∆t) ∆t
The physical interpretation of the above solution is as follows:
k1 = (slope at the beginning of time step) ∆t
k2 = (first approximation to slope at mid-step) ∆t
k3 = (second approximation to slope at mid-step) ∆t
k4 = (slope at the end of step) ∆t
∆x = (k1 + 2k2 + 2k3 + k4)/6
Thus ∆x is the incremental value of x given by the weighted average of estimates based
on slopes at the beginning, midpoint, and end of the time step. This method is equivalent

32
to considering up to fourth derivative terms in the Taylor series expansion; it has an error
on the order of
c) Euler’s Method
This least accurate low-stability method has been widely used in the past, because of its
simple implementation. The basic application is as follows:
Starting at point ( ), is computed and is obtained as
where h is the integration step length.
Then the equation is solved to obtain yn. Although there is no interface error, the scheme
is inefficient. Euler's method demands very small step lengths unless the power system
model is very simple and non-stiff. Thus, while only a single evaluation of x is made per
step, the network has to be solved a very large number of times for the entire solution,
which consumes perhaps eighty percent or more of the total computation time.
2.6.2 Power Flow Analysis
Under this section, the importance of power flow analysis to power utilities will be
discussed. In a large integrated power network, it is important that the following are taken
into consideration:
a) Power system is not run above name plate rating
b) Voltage levels at various buses are within given tolerances to ensure correct
reactive power requirements and acceptable losses among other things.
c) Assessment of whether fault conditions at a given part of the network will
lead to wide scale power outages.
Consequently, power flow analysis, also known as load flow analysis is carried out to
determine currents, voltages, active power and reactive Volt-amperes at various points in
a power system operating under normal steady state or static conditions. Load flows are
particularly essential for the day to day operations of utilities where re-distribution of
power flows is necessary due to removal of lines or generation plants for maintenance.

33
Secondly, flow studies are important in power system planning where future expansions
(such as new loads, generating stations or lines) must be considered in light of existing
capacities. The load-flow calculation is the most common network analysis tool for
examining the undisturbed and disturbed network within the scope of operational and
strategic planning.
Methods used for Load Flow Analysis
Load flow studies are used to ensure that electrical power transfer from generators to
consumers through the grid system is stable, reliable and economic. Conventional
techniques for solving the load flow problem are iterative. There are a number of
different iterative techniques used in load floe, some of which include
a) Gauss method
b) Gauss-Siedel method
c) Newton-Raphson method
d) Fuzzy Logic
e) Fast Decoupled method
a) Gauss Iterative Method:
This is the simple iterative technique for solving the load flow problem, by successive
estimation of the node voltages. For a general network with N nodes, the KCL equation
in terms of node voltages may be written as shown below:
where
[ ]
is the bus admittance matrix and & are the N-element node voltage and current
matrices respectively.
From the admittance matrix, the first subscript on each element indicates the node at
which the current is being expressed and the second subscript indicates the node whose

34
voltage is responsible for a particular component of the current. Thus, the current
entering a node is given by the equation
∑
In general therefore, for a power system consisting of N buses, the voltage at the bus
is given by the equation
( ) ∑
Where: (diagonal elements) = sum of all admittances connected to bus-bar
(off-diagonal elements) = - (sum of admittances measured between bus-bars
and
Also,
[∑ ]
Expressing , and in polar form
∑ ( )
b) Newton Raphson Method
The Newton Raphson method differs from the Gauss-Siedel method in that new iterative
updates of the required bus-bar voltages are based upon the rate of change of the solution.
Power-flow solutions by Newton-Raphson are based on the non-linear power flow
equation obtained in the Gauss-Siedel method above.
Since the swing bus variables and are already known, the Jacobian matrix derived
has the form

35
[ ]
where
[ ] , [ ]
[ ] , [ ]
In general, the Newton-Raphson technique is outlined as follows, starting with
( ) [
( )
( )
] at the iteration
1) Use the Gauss equation to get
( ) [
( )
( )
] [
( )
( )
]
2) Compute the Jacobian matrix as given above
3) Use Gauss elimination and back substitution to solve
[ ] [
( )
( )
] [
( )
( )
]
4) Compute ( ) [
( )
( )
] [
( )
( )
] [
( )
( )
]
Thus starting with initial value ( ) the procedure continues until convergence is
obtained or until the number of iterations exceeds a specified maximum.

36
Categorization of Buses
As already stated, power flows involve the computation of voltage magnitude and phase
angle at each bus in a power system under steady-state conditions. Furthermore, real and
reactive power flows in equipment such as transmission lines and transformers as well as
equipment losses are computed.
As shown in the figure above, the following four variables are associated with each bus k:
voltage magnitude , phase angle , net real power and reactive power . At each
bus, two of these variables are specified as input data, and the other two unknowns to be
computed by power flow programs.
Each bus k is categorized into one of the following three bus types:
i. Swing bus, also known as slack bus:
This is the reference bus for which is known. The power flow analysis
computes real and reactive power.
To other buses
Bus k
𝑃𝑘 𝑄 𝑘
.
𝑉𝑘 𝑉𝑘 𝛿 𝑘
𝑃 𝐺𝑘
𝑃𝐿𝑘𝑄 𝐺𝑘
.
𝑄𝐿𝑘
.Gen Load
Figure 2-11: Power Flow Diagram

37
ii. Load bus:
Most buses in a typical power flow analysis are load buses and real and reactive
power values are known; thus the load flow computes the voltage magnitude and
phase angle
iii. Voltage controlled bus:
Examples are buses to which generators, capacitors or tap-changing transformers
are connected. The power flow program computes and since and .

38
3 Chapter Three: METHODOLOGY
3.1 Introduction
In this chapter, a brief description and implementation of the computer based power and
machines labs is given and its interaction with the users is defined. The functional and
non-functional requirements are presented and the rationale for the requirements given.
The design specification for the hardware and software are outlined following the
identified specifications.
3.2 Overall System Description
The computer based power and machines labs consists of two major parts
a) PLC temperature control of an induction motor.
b) Power system planning, with studies in load flow and transient studies.
The PLC part of the lab requires one to learn PLC programming using Siemens
‘LOGO!Soft comfort’ software to program PLC modules. Since the program is based on
temperature, the system is actuated by the temperature sensor signals that come from the
stator winding of the motor. In this particular program, the system continuously monitors
the winding temperature and the temperature is read from the PLC display. However,
when the temperature reaches 50°C, the PLC safely turns off power supply to the motor
thus safely turning it off and protecting it from any damage.
The Power systems lab was based on the Gauss Siedel iteration method to develop
programs for both transient studies and load flow studies. A radial power system was
used to carry out transient studies in the case a fault happens on any part of the radial
system. Load flow studies can be carried out on two radial and mesh power systems and
the lab enables simulation of the power flow under different fault, supply and load.

39
3.3 Requirements and DesignSpecification
3.3.1 Functional Requirements
In this section we shall specify what the computer based lab is required to do in as far as
the motor and temperature control is concerned as well as the Power Systems lab.
a) Motor Speed
The motor should have a maximum set safe speed at which it should be operated. This
will depend on the ratings of the particular motor which is under study. The rigidity of
the motor support should also be put into consideration when choosing this speed.
b) Temperature Range
This refers to the safe winding temperature range beyond which the PLC will trigger the
contactor and the motor will come to a halt. e.g beyond 50ᵒC.
c) Power consumption
The power consumption of the power and machines lab should not be considerable. This
however still depends on the 3 phase induction motor rating.
d) Accuracy
This implies that the degree of discrepancy of the practical lab results should not be too
large. This is so, since the lab is not meant to completely replace the conventional
physical power and machines lab but rather so make things more improved as earlier
highlighted in the previous chapter.
e) Current and Voltage requirements of the PLC
The PLC can be voltage or current actuated system. A selection therefore has to be made
from 0-5V or 4-20mA actuation. This also depends on the distance and cabling
requirements involved.

40
3.3.2 Non-Functional Requirements
a) Usability
Usability is described as the extent to which the system can be used with effectiveness,
efficiency and satisfaction in a specified context of use. The term is further characterized
by easiness and speed of learning of system use, efficiency to use, easiness to remember
system use after certain period of time, reduced number of user errors and easy recovery
from them, subjective satisfaction of users.
To make the system much simpler to use, the following have to be put into consideration
1) Use of simple and natural language
2) Minimization of required memory load from the user
3) Consistency in terminology and symbols used throughout the interface and
conformance with the domain norms and standards
4) Degree and quality of system feedback
5) Provision of clearly marked exits and undo
6) Provision of shortcuts for experienced users
7) Informative error messages.
8) Prevention of errors
b) Safety
The lab should be safe for anyone using it to carry out an experiment and the equipment
should not expose any nearby people to any danger such as from electrical shocks and
moving parts.
c) Reliability
This refers to the ability of the power and machines lab to perform its required functions
under stated conditions for a specified period of time

41
d) Performance
This is a measure of the lab’s ability to meet the learning objectives of the system under
study e.g load flow of a power system
Table 2: Requirements
Hardware Requirements Software Requirements Output
1. Siemens LOGO!
0BA7 PLC
2. Computer
3. Temperature sensor
4. Drive
5. Signal Conditioning
Circuit
6. Induction Motor
1) Siemens LOGO!Soft
Comfort V7.0
2) MATLAB, Simulink
Others(optional)
i. MP Lab /
WPLSoft
ii. Cadence
a) Design for
Prototype model
b) Simulation
3.4 Machines Lab Design
With emphasis on induction motor temperature control using PLC via a speed drive.
PLC- Programmable Logic Controller that is the basis of industrial machine automation
Features of the PLC System
A basic PLC system consists of the following
1. PLC module
2. Control program
3. Data inputs
4. Data outputs
Operational Description
1) Temperature sensor measures winding temperature.

42
2) The PLC takes analogue temperature readings from the Temperature sensor
via ADC.
3) Checks if the temperature reading is less than 50°C and if not, it switches the
motor off via a contactor or VSD.
4) Motor can also be switched off using a local or remote computer.
Equipment Layout
Below is the list of the equipment that male up the computer based lab
i. Computer
ii. HMI
iii. A.C Motor
iv. Siemens LOGO 0BA7 PLC module
v. Temperature sensor (PT100 - analogue)
vi. Analogue-Digital Converter
vii. Power and Signal Cables
viii. Contactor (24V) or AC/DC relay (240V output)
They relate to each other in the manner illustrated in the diagram below

43
Figure 3-1: PLC diagram for Motor Temperature Control
a) Computer:
The PLC programming language, Siemens LOGOSoft! Comfort is installed on the
computer. Free LOGOSoft Comfort downloads are available on the Siemens website;
although one needs a registered version to be able to download the finished program
designs to the PLC. Once the software installation has been done, the desired PLC
programs can be constructed, which in this case was a motor temperature monitoring and
switching system. The programming involves combination of program blocks which do
various functions, examples of these include;
i. Inputs and Outputs i.e Digital, Analogue and Network
Basic Functions such as AND, NOR, OR
i. Special Functions such as Timers, Counters, Relays
ii. Data Logging Function, for recording process output and input data

44
Figure3-2:ProgramBlocksinSiemensLOGO!SoftComfort

45
Program Description
AI1 is where the program flow starts and it represents the analog input from the
temperature sensor into the PLC module.
B002 is an analogue amplifier for the analogue temperature values from the sensor with
offset at -50 and its parameters are shown in the dialogue box below.
Figure 3-3: Analog Amplifier Dialog Box
B003 is an analogue comparator and is used to compare two temperature inputs in case
there’s a value against which the motor temperature has to be measured in order to trigger
the protective system. Since this wasn’t important for this program, the second input was
looped using an analogue flag AM1 shown in the program.
Figure 3-4: Analog Comparator Dialog Box

46
Q1 is the digital output that is used to actuate the motor contactor depending on the
temperature value i.e if temperature reaches 70°C.
L1 is the data logging command block which enables the PLC to record results.
B006 is a message text block that enables the temperature output to be displayed.
BOO5 is an AND block that combines inputs from Q1 and L1, B007 as shown.
I1 represents a local digital input that acts as a switch to the motor through the contactor,
and is independent of the temperature value.
NI1 is a network input that allows remote devices such as computers, other PLCs and
HMIs on the PLC network to interact with the PLC module.
Figure 3-5: Network Input Dialog Box
Q2 represents that arbitrary output from either I1 or NI1.
B007 and B009 are OR blocks that allow only one input to be received from more than
one possible outputs.
Q3 represents the final output from either Q1 or Q2 that is used to switch off the motor
from the contactor.

47
Therefore the motor will automatically switch itself off if the temperature reaches 70°C
but can also be actuated using the remoter terminal network inputs and the local switch
input.
The finished program can be simulated by pressing F3 in order to check for any errors
and make appropriate changes. Once the programming is over, the program is
downloaded onto the PLC module. This can be done by use of a data card or Ethernet.
Since it’s a lab, and we want to create a network the Ethernet cable is used.
Figure 3-6: PLC Module Connection to Computer
b) PLC Module
The PLC module is the heart of the whole system since it helps in implementing the
control program in order to achieve desired results. Although there are many PLCs on the
market, the Siemens LOGO! 0BA7 was the PLC module of choice due to the following
reasons:
i. It’s the only readily available PLC module in Uganda
ii. It’s cheap
iii. Programming in LOGO! Soft Comfort is very easy, with practice
iv. It’s very efficient and robust
v. It has sufficient documentation
The Siemens LOGO! was designed as a micro automation module for industry for
switching and controlling and handles 24 digital and 8 analog inputs. The logo control

48
system is perfectly suited for small-scale automation projects and simplifies design by
replacing many time switches, counters and protective relays.
In this application, it controls through analog and digital inputs and outputs the varying
load-constant speed operation of an induction motor. Also, the PLC continuously
monitors the inputs and activates the outputs according to the control program. This PLC
system is of modular type composed of specific hardware building blocks (modules),
which plug directly into a proprietary bus: a central processor unit (CPU), a power supply
unit, input-output modules I/O, and a program terminal. Such a modular approach has the
advantage that the initial configuration can be expanded for other future applications such
as multi-machine systems or computer linking.
Figure 3-7: Siemens 0BA7 PLC Module
PLC Module Installation
The PLC module is mounted on a rail and screwed in place. It’s then connected to
(12/24V | 0.8/2.0A) D.C power supply as shown below (note safety fuse)

49
Figure 3-8: PLC Module Power Connection
c) Temperature Sensor
Temperature Sensor Element (PT100) was specified for use and provides an analogue
output depending on the measured temperature.
Figure 3-9: RT100 Temperature Sensor
For a PT100 sensor, a 1 °C temperature change will cause a 0.384 ohm change in
resistance, so even a small error in measurement of the resistance (for example, the
resistance of the wires leading to the sensor) can cause a large error in the measurement
of the temperature. For precision work, sensors have four wires- two to carry the sense
current, and two to measure the voltage across the sensor element. It is also possible to
obtain three-wire sensors, although these operate on the (not necessarily valid)
assumption that the resistance of each of the three wires is the same. A two wire element
was however the one specified in this design for purposes of simplicity in connection.

50
The temperature probe is connected with signal wires and the sensor element is inserted
into the motor and fitted on the stator windings to measure their temperature when the
motor is running. Because of the low signal levels, it is important to keep any cables
away from electric cables, motors, switchgear and other devices that may emit electrical
noise. Using screened cable, with the screen grounded at one end, may help to reduce
interference. When using long cables, it is necessary to check that the measuring
equipment is capable of handling the resistance of the cables. Most equipment can cope
with up to 100 ohms per core which is also the recommended maximum for the
installations in the lab.
Temperature Measurement
During the thermal measurements, some regions are particularly interested. They are the
embedded stator bar outer surface, embedded stator-bar inner surface, embedded stator
core outer surface, which are respectively represented as (i), (ii) and (ii). Since the stator
winding temperature is of more interest, the sensor is located on the stator as shown
below.
Figure 3-10: Stator Core and Wire

51
Table 3: Temperature Sensor Characteristics
Signal Status 0
Input current
< 5V d.c
< 1.0 mA
Signal Status 1
Input current
> 8V d.c
> 1.5 mA
It’s connected to the analog inputs on an expansion module as shown below
Figure 3-11: RT100 Temperature Sensor Connection to PLC
An expansion module with a grounded potential power supply is used. The sensor is
connected as shown above and since it’s a two wire connection, terminal M1+ and IC1
are short circuited
Motor Contactor Connection to PLC
The motor’s speed drive/contactor/relay inputs are connected at the PLC outputs as
shown (max 16A). The PLC can also allow multiple loads to be connected.

52
Figure 3-12: PLC Connection to Contactor
d) Human Machine Interface/ Remote User
The PLC can support remote user inputs from a computer or HMI using Ethernet
connection. The Network input can be from the LOGO! PLC that supports an Ethernet
connection to a remote PC running the LOGO!Soft Comfort programming software,
Human Machine Interface or other LOGO PLC modules.
Figure 3-13: PLC Ethernet Connection
One LOGO! 0BA7 can support up to 8 communication connections with other Siemens
devices via Ethernet. You can select the following communication parameters:
Motor contactor Other load

53
a) Other LOGO! 0BA7 controllers
b) PC running LOGO!Soft Comfort V7.0 programming software
c) HMI with Ethernet access
d) SIMATIC S7 controllers with Ethernet access
Addressing the Devices
You need to ensure that all network settings have been made correctly for successful
communication to take place. Read out the IP address of LOGO!. Change to the menu
and select the item Network; IP address. Here you set the required address.
Then configure the network connection of your PC. Select the respective connection in
the network connections (Start; Settings; Network connections). Open the properties,
PC with LOGO!Soft
HMI
PLC module
PLC module (main)
SIMATIC S7 controller
Figure 3-14: PLC Networking

54
select the Internet Protocol TCP/IP and open the properties. Assign an additional IP
address and a subnet mask that match the set LOGO! addresses.
Figure 3-15: Addressing PLC Devices
Once the devices have been networked, the lab can be ran, LOGOsoft allows you to
directly program the PLC module or to download the PLC program onto the module.
Hence it’s easy to modify program parameters instantly as need requires. Different
functionalities can be examined by the lecturer and students generate programs that can
generate the desired outcomes.
PLC Precautions to be taken
1. Do not connect an external power supply in parallel to the output load of a DC
output. This is because a reverse current can develop at the output if a barrier
device hasn’t been installed, such as a diode.
2. Switch off power before you remove or insert an expansion module.
3. Always keep separate the AC wiring, Low Voltage signal wiring and High
Voltage DC circuits with high frequency switching cycles respectively.
Induction Motor Specifications
The suitable electric motor for the lab should be a 3-phase y connected induction motor
with properties close to these

55
Table 4: Induction motor specifications
Voltage 340-415
Frequency 50Hz
Power 4.0 kW
Current 9.1 A
Speed 1410 rpm
Power factor 0.80
3.5 PowerLab Features
The power systems lab consists of studies on radial and meshed power systems
respectively. Therefore, two programs were designed to cater for both radial and
meshed/ring power systems. This is because radial power systems have a high X/R ratio
so they don’t converge for numerical methods. The Matlab script was been implemented
using Gauss Siedel because Matlab script does not support sparse matrices. The diagram
below summarizes the overall structure of all the programs.
Figure 3-16: Summary of Power Lab Program Structure
LABVIEW
Parameterize the Power
MATLAB
Numerical computation with
graphical and numerical
output
Inputs for Matlab script

56
The actual program code is done in Matlab. LabVIEW creates an environment for the
Matlab script to run. It creates an interface in which the user can change the parameters
of the Power System under study.

57
4 Chapter Four: PRESENTATION AND DISCUSSION OF
RESULTS
4.1 TransientStability Studies
Transient Analysis is performed to study system behavior as it moves from one state to
the other. In this lab, transient stability study is used to simulate faults and sudden load or
generation impacts. The results identify system weaknesses, if any, and recommend
critical time to isolate the local machine to avoid damage. Transient stability study is also
required when synchronous machines are installed. Load Flow analysis effectively
maintains power voltage and power levels thus prevents overloading, brownouts, and
under/over voltage conditions at nodes in the power system.
In simple terms therefore, the main goal of transient stability simulation of the power
system is to analyze the stability of a power system in a time window of a few seconds to
several tens of seconds under different fault conditions. Stability in this aspect is the
ability of the system to quickly return to a stable operating condition after a disturbance
such as for example a tree falling over an overhead line resulting in the automatic
disconnection of that line by its protection systems.
Figure 4-1: Radial Power System

58
Consider the radial power system above on which transient stability is to be carried out.
The parameters can be changed to simulate a fault occurring at Bus 1, Bus 2 or Bus 3. As
an example, suppose we want to simulate a fault at bus one with a critical clearing time of
160ms. The results are as follows:
Figure 4-2: Transient Stability Front Panel
4.2 Load Flow Studies
The load flow studies aim at showing the direction of power/current in case of a fault or
in the generator power. For the lab, two power systems, radial and mesh respectively
were considered and simulation panels made. The load low studies are carried out on
each of the power system; in which the user can simulate desired load conditions.

59
Radial Power System
Generator Transformer 1 line 1 Transformer 2 line 2 Transformer 3
20MVA 50MVA R= 50MVA R= 40MVA
11kV 11/132kV X= 132/33kV X= 33/0.415kV
Industrial load Domestic load
0-50MVA 0-20MVA
p.f= 0.4-0.85 p.f=0.6-0.95
Voltages at the buses are calculated in different load conditions using KCL and the
required input power at the generators. The simulation panel where simulations can be
done is shown below.
Figure 4-3: Radial Power System

60
Figure 4-4: Radial Load Flow Front Panel
Ring/Mesh Power System
Figure 4-5: Mesh Power System

61
A simulation panel was developed in a similar manner as for the redial system. This is
shown below:
Figure 4-6: Ring Power System Load Flow Panel
Program Description
The program has a LabVIEW interface which enables the user to change the inputs into a
Matlab script for different fault conditions. It was implemented using a step by step
numerical solution to the swing equation;
Stability of the power system is determined from the plot of angle (delta) against time.
The program can allow the user to input:
1. Critical clearing time of circuit breakers (tc)
2. The location of the fault
3. The mechanical/electrical power at the time of fault and the fault reactance
(Pm)

62
The power systems programs are implemented using LabVIEW 2010 students’ edition
and MATLAB 2012a. Matlab code is designed to run in a matlab script in LabVIEW
while the LabVIEW is used to generate a user interface with which the user can alter the
power system parameter.
Why use both LabVIEW and MATLAB
LabVIEW is a kind of graphical programming language which can be used to establish
Virtual instruments for oneself conveniently. Despite there being some information
processing functions in LabVIEW, it doesn’t fully cater for the need of various numerical
computation and analysis.
However, MATLAB is good for numerical analysis and processing. Therefore, it is
necessary to integrate LabVIEW with MATLAB. Inside LabVIEW there are library
functions which are convenient to connect some software standards such as TCP/IP, SQL
database, DDE, and Active X. Though those modes can be used to call MATLAB
programs in LabVIEW, the process is relatively overelaborated. However, the MATLAB
Script node linking LabVIEW with MATLAB can also be realized using Active X mode;
i.e. LabVIEW as Active X automatic controller, MATLAB as Active X automatic Server.
Using the MATLAB Script node, a user can load *.m programs into block diagram or
edit *.m files in a block diagram. In this report we adopt the node mode to call MATLAB
programs in LabVIEW. Another advantage is the possibility of LabVIEW to thread.
How the end user can access the labs
All the programs can be published on the tech intranet and run remotely by students in
browser as shown below.

63
Figure 4-7: Lab Running in Internet Explorer
Hence the lab supports remote usage and each client can access the same lab and carry
out the simulations. However, LabVIEW run time engine (34MB) would have to be
installed on each of the machines on the intranet.

64
5 Chapter Five: CONCLUSIONS AND
RECOMMENDATIONS
5.1 Summary
This research has presented the design of computer based power and machines labs. The
lab can be used to simulate load flow and transient studies by using LabVIEW and
Matlab for both meshed and radial power systems. The design for a PLC based motor
temperature control system is also presented and is based on Siemens LOGO PLCs as
well as LOGOSoft! Comfort software for programming the PLC system.
5.2 ResearchContribution
The project has the potential to greatly improve how practical concepts in power systems
and machines can be taught to university students. Throughout the development of the
labs, a lot of theoretical information was generated for example in PLCs and load flow
and transient stability in power systems. The documentation will introduce to students
basic PLC programming which is essential in today’s automated industry. The research
also acts as a platform for which further developments in computer based labs can be
carried out either to improve on the system or to provide similar learning tools for other
course units
5.3 Conclusions
From the above discussions, it is clear that whereas physical power and machines labs
have been a somewhat effective means of doing power systems and machines studies,
computer based power and machines labs could go the extra mile in aiding the existing
physical labs. This is evident in their numerous advantages that have been explicitly
highlighted throughout the report. The labs can be accessible on a LAN, and the power
systems parameters can be changed to suit the tutor’s interests both for load flow and
transient stability as well as with the PLC system

65
5.4 Recommendations
We would also like the university to give a higher priority to projects which directly
affect the university students when it comes to funding. This project in particular could
be fully implemented or applied later on as a learning tool in the students’ curriculum.
The main obstacle was that it didn’t get funding, yet the equipment is quite expensive and
this limited our ability to clearly demonstrate the full functionality of the Computer based
power and machines lab.
5.5 Challenges
We faced a number of challenges in this project and some of the major ones included:
1) LabVIEW Math Script and Formula script limitations
i. Mat lab script cannot create executable programs and hence users
cannot create their own programs independently.
ii. Formula node doesn’t work with matrices, and complex numbers.
2) The lab can only run in internet explorer. LabVIEW RunTime Environment
works only for internet explorer and not with other browsers
3) LabVIEW Matlab script doesn’t support sparse matrices so Gauss Siedel
numerical method was used in the stead of Newton Raphson.
4) We failed to work with Umeme due to too much beaucracy
5) Expensive industrial equipment as the budget of US 2300$ was made.
6) All PLC software which was free required hardware to be in place.
7) Lack of hardware, equipment is expensive to buy or hire
8) Unlicensed software tools which had limited capabilities
9) There’s no online java support for Siemens LOGO, hence program has to be
directly installed on computers.

66
REFERENCES
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Linear Regression Approach. Kuwait: ublic Authority for Applied Education and
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[3] B.Venkataraman, B. P. (n.d.). Fundamentals of a Motor Thermal Model and its
Applications in Motor Protection.
[4] By Hossein Seifi, M. S. (2011). Electric Power System Planning: Issues,
Algorithms and Solutions. London: Springer.
[5] Cory, B. W. (4th Edition). Electric Power Systems. . John Wiley and Sons. .
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[9] El-Hawary, M. E. (Copy right 2008). Introduction to Electrical Power Systems.
John Wiley and Sons Inc.
[10] et.al, A. A.-D. ( 2004.). Load flow solution using Hybrid Particle Swarm
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[11] Gheorghe CARTINA, G. G.-C. (2007). POWER SYSTEM ANALYSIS
USING MATLAB TOOLBOXES. 6th International Conference on
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[12] GOLKAR, M. A. (2007). A Novel Method for Load Flow Analysis of
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[13] Grainger, J. J. (Copy right 1994). Power System Analysis. McGraw-Hill
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[14] Hans-PetterHalvorsen. ( 2011). LabVIEWMathScript Tutorial. . Telemark
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[15] Hollingsworth, M. (n.d.). Introduction to Modern Data Acquisition with
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[16] Instrument, N. (2012, April 4th). Retrieved from Developing Algorithms
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[31] Pei, F. Y. (2004). Joint Programming using LABVIEW and MATLAB.
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natural Resources Canada.

69
APPENDIX
Appendix I: Gauss flow chart
START
Form Y-bus
Assume bus
voltages V(0)
i=1,2,…,n i≠ slack
bus
Let m=0
Let maximum voltage change
ΔVmax
(m)
= 0 i=1
Let
ΔVi
(m)
- ΔVmax
(m)
= ε
Is ε>0 ?
Vi
(m)
=Vi
(m+1)
i=i+1
Calculate bus
voltages and
angles
ΔVi
(m)
=|ΔVi
(m)
|)
Is i slack bus?
Is
Is (1-n) ≤ 0?
m=m+1

70
Appendix II: Matlab script for transient Stability
t=0 ; % initiating time
tf=0 ;
tfinal=4 ; % time end
tstep=0.001; % incremental time change
n=(tfinal-t)/tstep;
f=50; % frequency
H=2.52;M=H/(180*f) ; % contant of inertia
i=1;
E=1.2;V=1; % internal generator emf and terminal emf
x1=0.112;x2=0.223;x3=0.30; % reactances between different buses
x4=x1+x2+x3;
Pmaxbf=E*V/(x4); % maximum power before fault
delta=asin(Pm/Pmaxbf); % angle in radians
ddelta=0; % initiating angle to zero radians
time(1)=0;
ang(1)=delta;
time(1)=0 ;
switch m % m is the bus on which the fault occurs
case 1
x=x1;
Pmaxdf=V*E/x;
case 2
x=x1+x2;
Pmaxdf=V*E/x;
case 3
x=x1+x2+x3;
Pmaxdf=V*E/x;
end
Pmaxaf=2.00 ; % power after the fault

71
while t<tfinal, % iterations in relation to time
if (t==tf),
Paminus=Pm-Pmaxbf*sin(delta) ;
Paplus=Pm-Pmaxdf*sin(delta) ;
Paav=(Paminus+Paplus)/2 ;
Pa=Paav ;
end
if (t==tc),
Paminus=Pm-Pmaxdf*sin(delta) ;
Paplus=Pm-Pmaxaf*sin(delta) ;
Paav=(Paminus+Paplus)/2;
Pa=Paav;
end
if(t>tf && t<tc),
Pa=Pm-Pmaxdf*sin(delta) ;
end
if(t>tc),
Pa=Pm-Pmaxaf*sin(delta) ;
end
ddelta=ddelta+(tstep*tstep*Pa/M) ;
delta=(delta*180/pi+ddelta)*pi/180;
deltadeg=delta*180/pi ;
t=t+tstep ;
time(i)=t;
ang(i)=deltadeg ;
i=i+1 ;
end

72
Appendix III: Matlab Script for radial power system
%This program calculates the Voltages and phase angles at two busbars in
apower system.
%These are the base voltages of the three regions of the power system.
Vb1=11e3,Vb2=133e3,Vb3=33e3,Vb4=0.415e3;
%Calculation of base Currents
Ib1=Sb/(sqrt(3)*Vb1);
%Calcalation of base impedances
Zb1=Vb1*Vb1/Sb;
Zb2=Vb2*Vb2/Sb;
Zb3=Vb3*Vb3/Sb;
Zb4=Vb4*Vb4 /Sb;
%This initialises the industrial load voltage to 32400V and the domestic
Voltage to 400V
Vd=400;
Vi=32400;
%Per unit impedendace for the respective power systems component
zt1=0.01*i ; Zt2=0.01*i; Zt3=0.1*i; Z1=0.02+ 0.04*i;Z2=0.1+0.2*i; Zg =
0.1*i;
%Bus 1 is the Slack bus with 1V p.u
V1=1;
%Zt is the per unit impendance after the generator but before the industrial
load
Zt=zt1+Z1+Zt2+Zg;
%Zm is the per unit impedance after the industrial load but before the
domestic load
Zm=Z2+Zt3;

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