The University of Dodoma University of Dodoma Institutional Repository http://repository.udom.ac.tz
Information and Communication Technology Master Dissertations
2012 Automation of electric power supply systems: TANESCO case study
Joseph, Richard
The University of Dodoma
Joseph, R. (2012). Automation of electric power supply systems: TANESCO case study. Dodoma: The University of Dodoma http://hdl.handle.net/20.500.12661/1467 Downloaded from UDOM Institutional Repository at The University of Dodoma, an open access institutional repository. Automation of Electric Power Supply Systems:
TANESCO Case Study
By
Richard Joseph
A Dissertation Submitted in Partial Fulfillment for the Award of Degree of Master of
Science in Telecommunications Engineering
University of Dodoma
September, 2012
CERTIFICATION
The undersigned certify that he has read and hereby recommend for acceptance by the
University of Dodoma dissertation entitled AUTOMATION OF ELECTRIC
POWER SUPPLY SYSTEMS: TANESCO Case Study in fulfillment of the requirements for the degree of Master of Science in Telecommunications Engineering of the University of Dodoma.
……………………………………………………
Prof. N.H. Mvungi
(SUPERVISOR)
Date ………………………………
i
DECLARATION AND COPYRIGHT
I RICHARD JOSEPH, declare that this dissertation is my own original work and that it has not been presented and will not be presented to any other University for a similar or any other degree award.
Signature……………………………………………….
No part of this dissertation may be reproduced, stored in any retrieval system, or transmitted in any form or by any means without prior written permission of the author or the University of Dodoma.
ii
DEDICATION
This work is dedicated to my beloved parents, Mr. /Mrs. Joseph Innocent Mushi for their support since I was young up to this stage.
God bless them.
iii
ACKNOWLEDGEMENT
I would like first of all to thank the Almighty God whom I have a strong belief that He paved the right way for me to start this dissertation.
My sincere thanks go to the My Research Supervisor Prof. N. H. Mvungi who guided me to accomplish this study. His untiring patience and hard work enabled me to cruise through difficulties during this study.
Special thanks go to my Employer ST. Augustine University of Tanzania (SAUT) and also Vice Chancellor of SAUT Rev. Dr. C. Kitima for giving me permission and scholarship for pursing this Masters degree of Telecommunications Engineering.
Further thanks go to Mr. Suleman Nyarukunyo, Dr. Anatory, Dr. Mvuma and
TANESCO staffs for their contribution and advising me during this study.
Lastly, I would like to thank my parents Joseph and Yasinta for guiding me throughout my life.
Special thank to all.
The Almighty God blesses you for your contributions, Amen.
iv
ABSTRACT
An electric power system includes a generating subsystem, a transmission subsystem and a distribution subsystem. An electrical power network is larger and more complex so that, automation of power system is required to monitor and control an electrical power network. Automation of power system mean use of computer to collect data along power network, transferring data to a distribution control centre, displaying the data and carrying out analysis for control decision and improvement in system operation. Currently, TANESCO has feedback concerning the real-time (automatic system) operation at the level of the generation subsystem to high voltage level, but has no feedback concerning the real-time status of their networks at medium and low voltage level. Therefore, the use of automation system in TANESCO entire network will facilitate reduction of number of activities along electrical power network, number of staffs, operational costs and provide better service to consumers.
This study was aimed to determine the concepts of automation of management of power systems from generation points to end users in which researcher included the challenges involved in automation of power systems. Also, researcher described communication systems identified for automation of power systems and monitoring systems of automation of power systems.
Challenges involved in automation of power system were established in this study.
Also, four communication systems (PLCs, Optical Fibers, Satellite Communications and Wireless Communications) for automation of power systems were identified but,
v two communication systems (PLCs and Optical fiber) were selected as most effective communication systems for automation of power systems. Monitoring tools such as
ETAP software and PSS/E software were identified; PSS/E tool was selected because of its availability. With the aim of determining the concepts of automation of management of power systems, researcher conducted simulation using PSS/E tool and the parameters were used during simulation are power flow and short circuit condition.
This study employed case study design; Studying different documents and Interview guide are the methods were used to collect data related to communication systems, monitoring tools and challenge involved in automation of power systems.
It is recommended for utility company to use automation of power systems. The use of power system automation reduces numbers of activities, staffs and failure can be observed timely to effect action timely and this means that, makes quick fault detection, isolation, service restoration and therefore better services to consumers.
vi
TABLE OF CONTENTS
DECLARATION AND COPYRIGHT ...... ii DEDICATION ...... iii ACKNOWLEDGEMENT ...... iv ABSTRACT ...... v TABLE OF CONTENTS ...... vii LIST OF TABLES ...... x LIST OF FIGURES ...... xi LIST OF ABBREVIATIONS ...... xii CHAPTER ONE ...... 1 INTRODUCTION AND BACKGROUND ...... 1 1.0 Introduction ...... 1 1.1 Background Information ...... 1 1.2 Statement of the Problem ...... 4 1.3 Objectives of study ...... 6 1.3.1 Main objective ...... 6 1.3.2 Specific objectives ...... 6 1.4 Research Questions ...... 6 1.5 Significance of study ...... 6 1.6 Dissertation Organization ...... 7 CHAPTER TWO ...... 8 LITERATURE REVIEW ...... 8 2.0 Introduction ...... 8 2.1 Definition of key terms...... 8 2.2 Power Distribution Automation Concept ...... 11 2.2.1 Distribution Management System ...... 12 2.2.2 Distribution Automation System ...... 12 2.3 Supervisory Control and Data Acquisition Systems (SCADAs)...... 13 2.3.1 SCADA Functionality ...... 13 2.3.2 Applications of SCADA ...... 15
vii
2.3.4 SCADA Installed in Tanzania ...... 16 2.4 Benefits of the Power System Automation ...... 19 2.5 Empirical Literature ...... 21 2.6 Power Delivery Network ...... 29 CHAPTER THREE ...... 33 Research Methodology ...... 33 3.1 Introduction ...... 33 3.2 Research Design ...... 33 3.3 Data Types and Sources ...... 34 3.4 Data Collection Techniques ...... 34 3.4.1 Interview...... 34 3.4.2 Studying Documents ...... 35 3.5 Identification of Communication systems ...... 35 3.6 Identification of monitoring tools ...... 35 3.7. Reliability and Validity of data ...... 36 CHAPTER FOUR ...... 37 FINDINGS AND DISCUSSIONS ...... 37 4.0 Introduction ...... 37 4.1 The Challenges for Automation of Power Systems ...... 37 4.2 Monitoring of Power System ...... 41 4.2.1 Computer ...... 41 4.2.2 Monitoring tools ...... 42 4.2.2.1 Energy Technology Assistance Program (ETAP) ...... 42 4.2.2.2 Power System Simulator for Engineering (PSS/E) ...... 43 4.2.3 Simulation Parameters ...... 43 4.3 Communications ...... 48 4.3.2 Power Line Communication (PLC) ...... 50 4.3.2.1 Narrowband (NB) PLC ...... 51 4.3.2.2 Broadband PLC ...... 52 4.3.2.3 Advantages of Power Line Communication ...... 53 4.3.2.4 Challenges for Power Line Communication ...... 54 4.3.3 Optical Fiber ...... 55
viii
4.3.3.1 Advantages of Optical fiber ...... 57 4.3.3.2 Challenges for Optical Fiber ...... 58 4.3.4 Satellite Communications...... 59 4.3.4.1 Advantages of Satellite Communications ...... 63 4.3.4.2 Challenges for Satellite Communications ...... 64 4.3.5 Wireless Communications ...... 65 4.3.5.1 Advantage of Wireless Communication ...... 67 4.3.5.2 Challenges for Wireless Communication ...... 68 4.3.6 Suggested Communication Techniques ...... 69 CHAPTER FIVE ...... 72 CONCEPTS OF AUTOMATION OF POWER SYSTEMS ...... 72 CHAPTER SIX ...... 77 CONCLUSIONS, RECOMMENDATIONS AND FUTURE RESEARCHES ...... 77 5.1 Conclusions ...... 77 5.2 Recommendations ...... 78 5.3 Future researches ...... 79 REFERENCES ...... 80 ON LINE REFERENCES ...... 84 APPENDIX I ...... 85 Interview Guide for Challenges Facing in Automation of Power Systems ...... 85
ix
LIST OF TABLES
Table 2.1: Summary of communication system development activities for electric utility companies...... 25
Table 4.1: Typical links frequency bands...... 60
x
LIST OF FIGURES
Figure 2.1: Distribution concepts as an umbrella term (Green & Wilson, 2007)...... 11
Figure 2.2: Primary power network substation ...... 31 Figure 2.3: Secondary power networks ...... 32 Figure 4.1: Electrical line diagram ...... 45
Figure 4.2: Electrical line diagram with increasing the capacity of loads ...... 46
Figure 4.3: Three phase short circuit fault analysis line diagram ...... 47
Figure 4.4: An elementary communication link ...... 49 Figure 5.1: The concepts of automation of power system ...... 74
xi
LIST OF ABBREVIATIONS
A.C - Alternating Current
AMR - Automatic Meter Reading
AMM - Automatic Meter Management
AGLAS- Airfield Ground Lighting Automation System
ADSL - Asymmetric Digital Subscriber Line
BPSK - Binary phase shift keying
CENELEC- European Committee for Electro-technical Standardization
CPU - Central Processing Unit
CCITT- Committee Consultative International Telegraph and Telephone
CD - Compact Disc
CMMS- Computerized maintenance management systems
DER - Distributed Energy Resources
DCSK - Differential code shift keying
DSL - Digital Subscriber Line
DVD - Digital Versatile Video
DAS - Distribution Automation System
DDE - Dynamic Data Exchange
EMI - Electro Magnetic Interference
FFH - Fast Frequency Hopping
FM - Frequency Modulation
FSK - Frequency Shift Keying
GEO - Geostationary Earth Orbit
xii
GCC - Grid Control Centre
GPS - Global Positioning System
IT - Information Technology
IP - Internet Protocol
IEEE - Institute of Electrical and Electronic Engineers
I&C - Instrumentation and Control
Kbps - Kilobits per second kV - kilo-Volt
LEO - Low Earth Orbit
MEO - Medium Earth Orbit
Mbps - Megabits per second
MCM - Multi-Carrier Modulation
NB - Narrow Band
OFDM - Orthogonal Frequency Division Multiplexing
PSK - Phase Shift Keying
PLC - Power Line Communication
QAM - Quadrature Amplitude Modulation
QPSK - Quadrature Phase Shift Keying
RAM - Random Access Memory
ROM - Read Only Memory
RTUs - Remote Terminal Units
SFSK - Spread frequency shift Keying
SCADAs- Supervisory Control and Data Acquisition system
xiii
VSAT - Very Small Aperture Terminal
VFT - Voice Frequency Telegraphy
V - Volt
TANESCO- Tanzania Electric Supply Company
TTCL - Tanzania Telecommunication Company Limited
xiv
CHAPTER ONE
INTRODUCTION AND BACKGROUND
1.0 Introduction
This chapter discusses the background information, statement of the problem, objectives of the study, research questions, Significance of the study and dissertation organization.
1.1 Background Information
Power systems automation is the act of controlling the power system automatically using appropriate instrumentation and control devices. Power system automation includes monitoring and control of processes associated with generation and delivery systems of power to customers. Electric power utilities worldwide are increasingly adopting the computer aided monitoring, control and management of electric power distribution systems to reduce cost of operations, maintenance and services and to provide better services to electricity consumers. Reliable on-line information acquisition, remote control and efficient power system management are increasingly becoming a requirement by electric power utility companies. As power networks become larger and more complex, power sources increase, control and power devices spread over larger geographical areas that are sometimes hostile. Considering the extensive size of the power supply network for a national grid system, centralized information on health of the network and devices, remote control and servicing of network, customers and power sources can be achieved by utilizing information technology taking advantages of
1 available high-speed computer and communication technologies. The system of monitoring and control of electric power distribution networks is also called
„„Distribution Automation System (DAS)” (Gupta and Varma, 2005).
The Institute of Electrical and Electronic Engineers (IEEE) has defined DAS as a system that enables an electric utility to remotely monitor, coordinate and operate distribution components in real-time mode from remote locations (Bassett et al, 1988). The distribution automation system is based on an integrated technology, which involves collecting data and analyzing information to make control decisions, implementing the appropriate control decision in the field and also verifying that the desired result is achieved ( Bunch, 1984).
The power utility company in Tanzania, Tanzania Electric Supply Company
(TANESCO) is already implemented power system automation in electric power stations and high voltage transmission sides but not in the medium and low voltages transmission sides of the network. As a result, various distribution activities such as monitoring (of distribution transformers, read metering, rotten wooden poles for replacement, transmission conductors and the like), coordination (of voltages by maintaining and adjusting voltages) and operation (of recording metering, construction and planning of new service lines, line maintenance by upgrading or re-conductoring, attend customer complaints and the like) of medium and low voltage sides in Tanzania are done manually. This means TANESCO has not installed sensors, processing and signal transmission systems to facilitate easy access to certain information necessary to adequately monitor, coordinate and control its systems. At the moment, to obtain
2 information on the status of the TANESCO electric supply network and systems staff, either conduct surveys on distribution areas or receive notification from customers in the affected areas. Not only is this exercise expensive but creates misunderstanding between TANESCO and its consumers, especially in the event of blackout, low voltage, voltage fluctuation and the like when these anomalies remain un-attended for long periods of time. The DAS can also monitor the quality of the supplied power. One reason why it is necessary to monitor the quality of power is due to economic considerations. This is because poor quality power will affect the performance of equipment such as transformers, circuit breakers and the like, all of which depend on constant and stable power supply. The lack of quality power can result into mis- operation and damage to equipment thus resulting into disruption of operations and other anomalies.
TANESCO has installed in its network a system that monitors network performance in electric power stations and high voltages transmission sides. The monitoring system referred to as Supervisory Control and Data Acquisition system (SCADA) is currently installed in Dar-es-Salaam at its control centre. This SCADA monitors performance of electric power stations, high voltages transmissions and grid substations. But technical faults related to power failures such as disconnections, fallen poles and the like are transmitted for visual observation at either the Dar es Salaam SCADA system control centre or at the respective regional substation control centre.
It is therefore necessary for TANESCO to use power system automation in its entire network include low and medium voltages networks to reduce operation costs as
3 everything will be done automatically remotely, timely and will provide better services to consumers.
1.2 Statement of the Problem
Electric power in Tanzanian power system at the moment is transmitted using 220kV,
132kV and 66kV transmission lines and then stepped down to medium voltages of 11kV or 33kV in substations. The voltage is further stepped down to a low voltage 380V supplying customers for 3-phase and 230V for single phase for residential, commercial or industrial use. TANESCO operates distribution networks in most of the urban and in some of the rural areas. Monitoring and control functions of major equipment for high power transmission lines such as line isolation, breakdown of transmission lines, occurred of faults etc are performed by SCADA and control boards located at substations. These control boards receive notification automatically where upon receipt; they are analyzed by an operator who gives status to determine the fault before deciding on the necessary actions to take. This process of fault analysis takes a considerable amount of time, depending on the complexity of the system. However, the automatic fault notification process applies to high voltages only. There is no notification from affected areas in the case of faults occurring on the medium and low voltages transmission lines other than physical inspection by TANESCO staff through survey.
Furthermore, the system does not provide information on illegal temper or usage of the utility.
In addition, network have extended to rural areas with rough terrain making frequent surveys even less likely, particularly during the rainy season when incidents are more
4 frequent and many roads are not readily passable making survey difficult. Therefore, the emergency repair team of TANESCO response will rely on customer reporting failures and feasibility to access network facilities at respective sites.
Therefore, the use of automation to monitor, control and manage power system shall facilitate a reduction in activities and the need for staffs to make long journey to survey the power network and its systems saving staffs time and transport costs. Furthermore, failure can be observed timely to facilitate timely corrective action. This problem is in the entire distribution (medium and low voltages) network which is extensive.
Therefore, this is a problem since it is the largest network and affects directly customers connected to the network.
It is time for TANESCO to use appropriate communications technique on power distribution systems to perform actions like reading the electricity meter, monitoring the power consumers, finding faults along the systems, detecting illegal electricity usages etc. Also, TANESCO can use their power line to provide communications to facilitate their internal and external communications.
Hence, automation allows utilities to implement flexible control of distribution systems, which can be used to enhance efficiency, reliability and quality of electrical service while optimizing operational costs. Flexible control also results in more effective utilization and life-extension of the existing distribution system infrastructure (Gupta and Varma, 2005).
5
1.3 Objectives of study
1.3.1 Main objective
The main objective of this study is to determine the concepts of automation of management of power systems from generation points to end users.
1.3.2 Specific objectives
Specific objectives of this study are;
To establish challenges facing automation of power systems.
To identify monitoring systems for automation of power systems.
To identify appropriate communications technique for automation of
power systems.
1.4 Research Questions
Research questions of this study are;
What are challenges existing in automation of power systems?
Which monitoring tools can best support automation of power systems?
Which communication system(s) can be most effective in automation of
power systems?
1.5 Significance of study
The significance of this study is;
This study will enable power utilities companies to know and be aware of
effective automation scheme for power systems components which can
facilitate reduction of maintenance and operational costs of its network
6
and simplify the monitoring and controlling of power systems making
them more efficient and effective.
The result will help utilities companies to understand the challenges to be
overcome to implement automation of power systems for the entire
network.
1.6 Dissertation Organization
This dissertation is organized as follows; chapter two describes the literature review on power systems automations, chapter three describes how the study is designed and it was conducted, chapter four presents findings and discussion and chapter five gives conclusions and recommendations for future research.
7
CHAPTER TWO
LITERATURE REVIEW
2.0 Introduction
This chapter is divided into six main parts; part one provides definition of the power system automations and other keys terms, part two describes concept of power system automations, part three gives details of SCADA, part four describes benefits of power system automation, part five provides empirical literatures and last part describes power delivery network in Tanzania.
2.1 Definition of key terms
There are many definitions regarding to automation, power system automations and distribution automation system. In this research work, researcher tried to took some of them.
The term automation means the use of computing (intelligent) devices that may be linked together over a communications network and running special purpose software to execute a sequence of actions automatically to fulfill a specific objective.
According to Higgins et al (2008), the term automation of power system refers to computer-based remote control of power system equipment which simplifies such processes as restoring power to customers blacked out caused by a fault. For example, control of sectionalizing switches can be done by remote manual control using SCADA.
8
In national networks SCADA is a feature that had been incorporated in all zone substations for at least three decades. In TANESCO network SCADA is extended to all regional and district sub-stations connected to the national grid network. The improvements in technology, SCADA has made it cost effective for consideration for extension to distribution system equipment as well.
Also, the IEEE has defined Distribution Automation System as a system that enables an electric utility to remotely monitor, coordinate and operate distribution components, in a real-time mode from remote locations (Bassett et al 1988).
In Public interest energy research draft project report (2008), it was reported that, many definitions of distribution automation have been promulgated with no single definition being better necessarily than the other. However, a very broad definition used is:
“Distribution Automation includes any automation which is used in the planning, engineering, construction, operation, and maintenance of the distribution power system, including interactions with the transmission system, interconnected distributed energy resources, and automated interfaces with end-users.” This definition therefore includes any automation used for distribution and Distributed Energy Resources (DER) equipment in substations, along feeders, in distribution networks, and up to the end-user including the meter. Distribution automation thus includes all equipment, communications, as well as the data and software applications needed to utilize, operate, and manage the automation.
9
Power system automation is an act of controlling the power through automated processes within computers and intelligent Instrumentation and Control (I&C) devices.
It consists of three major processes, namely, data acquisition, power system supervision and power system control all working in a coordinated automatic fashion. Data acquisition refers to collecting data in the form of measured analog current or voltages values or the open or closed status of contact points. Power system supervision is carried out by operators and maintenance engineers through this acquired data either at a remote site represented by computer displays and graphical wall displays or locally, at the device site, in the form of front-panel displays and laptop computers. Control refers to sending command messages to a device to operate I&C (a collect of devices that monitor, control and protect the system is referred as I&C system) and power system devices (Mc Donald, 2006; Kreiss, 2003; Ackerman 2002).
Remote Terminal Units; this connects to physical equipment such as sensors and changes the electrical signals from the equipment to digital data and then sends digital data to the supervisory system.
Programmable Logic Controllers; this device is used for automating, monitoring and control of industrial facilities. It is used as separately or in combination with a SCADA or other system. Programmable Logic Controllers connect directly to both field data interface devices and incorporate programmed intelligence devices in the form of logical procedures that will be executed in the event of certain field conditions occur.
10
Local automation; the switch operation by protection or local logic based decision- making operation.
Centralized automation; this is an automatic switch operation using remote control from central decision making for fault isolation, network reconfiguration, and service restoration.
2.2 Power Distribution Automation Concept
The concept of power distribution automation originates from the generic word of automation to the whole distribution system and operation and covers the whole range of functions from protection to monitoring and control using related information technologies. This concept merges simultaneously with the ability to combine local automation, remote control of switching devices, and central decision making into an interconnected, flexible, and cost effective operating architecture for power distribution systems. This is shown in Figure 2.1.
Figure 2.1: Distribution concepts as an umbrella term (Green & Wilson, 2007).
11
The concept of the distribution automation has two terms that are used in the utility companies. These are distribution management system and distribution automation system.
2.2.1 Distribution Management System
According to Green and Wilson (2007), the distribution management system has a control room focus, which provides an operator a view of the network. It coordinates all the downstream real-time functions within the distribution network with the non-real- time (manually operated devices) information needed to properly control and manage the network on a regular basis. The key to a distribution management system is the organization of the distribution network model database, access to all supporting information technology infrastructure, and applications necessary to populate the model and support the other daily operating tasks. A common human machine interface and process optimized command structure is vital in providing operators with a facility that allows intuitive and efficient performance of their tasks.
2.2.2 Distribution Automation System
Green and Wilson (2007) revealed that the Distribution Automation System fits below the distribution management system and includes all the remote-controlled devices at the substation and feeder levels (e.g., circuit breakers, reclosers, auto-sectionalizers), the local automation distributed at these devices, and the communications infrastructure. It is a subsystem of the distribution management system covering all real-time aspects of the downstream network control process.
12
2.3 Supervisory Control and Data Acquisition Systems (SCADAs)
SCADA is an acronym for Supervisory Control and Data Acquisition systems that is used to monitor and control operation of technical equipment in industries such as telecommunications, water and waste control, energy, oil and gas refining equipment and transportation. These systems include the transfer of data between a SCADA host computers, Remote Terminal Units and/or Programmable Logic Controllers, and operator terminals (NCS, 2004).
The SCADA system collects information such as occurrence of leakage on a pipe line, relays the information back to a central site and sends a signal to alert the local power station that a leakage has occurred. Further, SCADA also analyses and determines whether the leakage is critical or not and displays the information. These systems can be relatively simple such as limiting their use to monitor electric network power of a small office building, or very complex as a system for monitoring activities in a nuclear power plant. SCADA can also be used to monitor the operation of a water system.
2.3.1 SCADA Functionality
a) Alarms/ Event Monitoring
In the event of faults, the SCADA system must be able to detect, display, record, identify the type of fault and notify service providers to take corrective action.
Likewise, the SCADA system also records alarms and fault events to enable engineers and programmers to review and determine the causes.
13
b) Data Acquisition System
SCADA is a centralized system that is able to receive data from remote points. It has an option of transmitting or receiving data in either analog or digital form (IEC, 2004).
c) Operator Interface
A SCADA system collects all information about a process and then displays it to the operator to know what is going on with the process.
d) Data Bases and Data Logging
Most applications require recipes, data logging and other means of reading and writing information. SCADA systems can log large amounts of data to disk for later review which is helpful for solving problems as well as providing information to improve the process.
e) Maintenance Management Interface
Data collected through the computer system can be used as input to more sophisticated
Computerized Maintenance Management Systems (CMMS). CMMS that are condition- based or predictive-based maintenance need current information on the condition of equipment in the plant; information that may have already been collected in the plant‟s computerized automation system. The automation system can act both as a data collection point for data needed for control and protection functions, and for data needed to trigger maintenance activities, using out-of-limits conditions (IEC, 2004).
14
f) Logging/Archiving
Logging is the medium term storage of data on the disk, where as archiving is the long term storage of data on disk or any other permanent storage medium. Logging of data can be performed at a set frequency, or only initiated if the value changes or when a specific predefined event occurs. The logged data is time stamped and can be filtered when viewed by the user (Prasanna and Gayatri, 2009).
g) Report Generation
Raw data collected by the computer system is necessary for the generation of reports that are used for operations and maintenance decisions. Computer database management and document preparation capabilities are becoming powerful tools for increasing plant efficiency. The multi-tasking capabilities of the computer provide report generation capability while accomplishing real-time control and monitoring of plant functions.
Computer-based documentation capabilities include the following; sequence of events recording, automated operator‟s log, historical data recording, trend reporting (IEC,
2004).
2.3.2 Applications of SCADA
According to Prasanna and Gayatri (2009), the common applications for SCADA systems include water and waste treatment, control and monitoring petroleum and hydro carbon processing, power generation, remote telecommunications and plant machinery maintenance. Unlike in plant process control systems, SCADA systems typically include a remote telecommunication link. Real-time measurements and controls at remote
15 stations are transferred to a Central Processing Unit through the communication link.
Large systems can monitor and control 10-2000 remote sites, with each site containing as many as 2000 input and output points.
2.3.3 Advantages and Disadvantages of SCADA Technology
Advantages of SCADA system include wide area connectivity and pervasive; routable, parallel polling, redundancy and hot standby large addressing ranges, integration of
Information Technology (IT) to automation and monitoring networks, standardization; reduce down time, limit the frequency of accidents, improve record keeping; increase throughput (Prasanna and Gayatri, 2009).
Disadvantages of SCADA Technology include Internet Protocol performance over head; web enabled SCADA host users to remotely monitor, control remote sites via a web browser introduces security concerns (Prasanna and Gayatri, 2009). The second disadvantage is communication between different computers; it needs configuration if it is to interwork with other stations. Further, data processing and databases have to be duplicated across all computers in the system thus resulting in low efficiencies. The last disadvantage is lack of systematic approach to acquire data from plant devices, if two operators need the same data the Remote Terminal Unit must be interrogate twice.
2.3.4 SCADA Installed in Tanzania
As there is a growing demand for power in Tanzania, new power networks are being developed and expanding in size to meet growing consumer requirements. This means
16 power networks are becoming more complex and difficult to manage, monitor and control. Power consumers are getting concerned on unpredictable power disruptions and the consequences on the economy, all of which depend on availability of constant and uninterrupted electric power supply for production, transmission and distribution. On the other hand TANESCO finds it difficult to cope with consumer demands for continuous power which implies that power interruption must be restored as soon as possible whenever they occur. Therefore, supervisory control of electric power generation, transmission and distribution operations is needed in order to have comprehensive overview of substations and power stations for enabling the operating staff to take timely appropriate measures to meet the above conditions.
Therefore, in order to improve reliability in operation of the interconnected network in
Tanzania, TANESCO installed the SCADA in 1989. It was in January 1991 when
SCADA was connected to the Ubungo 220/132/33 kV substation for monitoring and control of the interconnected grid power network on the National Grid Control Centre
(GCC).
Due to lack of connectivity with the power stations a system (MicroSCADAs) was installed in the year 2000 at the GCC to monitor and control the operations of power stations and one grid substation.
Currently, the communication media being used to transfer data collected by the remote control units from substations is Power Line Communications (PLC) and Optical Fiber cable. Nearly half of the installed RTUs communicate with the National Grid Control
17
Centre System through Power line communication and the other half communicate through optical fiber using the PLC as back-up.
Also, the TANESCO telecommunications system provides voice communication services needed to control the operation of its interconnected electricity generation, transmission and distribution system. The SCADA system transmits data over voice grade circuits using several voice frequency telegraphy (VFT) channels using frequency modulation (FM) in accordance with CCITT recommendations R.35 (50 Baud), R.37
(100 Baud) and R.38A (200 Baud). Separate VFT channels are also provided for telephony and telex systems. The TANESCO telephone system currently has 15 automatic exchanges with a maximum capacity of 288 connections out of which 75 connections are used as trunk lines. TANESCO telephone system has more sophisticated traffic handling facilities than those available on the Tanzania Telecommunication
Company Limited (TTCL) network. TANESCO telephone system, for example, offers a conference facility, multi-address signaling and prioritized customer categories. The telex system operated by TANESCO links 10 substations and offers full duplex communication between the substations (Luhanga, 1994).
Furthermore, the problem of this SCADA system installed in Tanzania is that it does not provide efficient services because it monitors performance of electric power generations, high voltage transmission only but the medium voltage transmission and a distribution system (low voltages) which constitutes extensive networks are excluded. Also, technical faults related to power failures such as disconnections, fallen poles and the like
18 in the transmission network are still transmitted to Dar es Salaam SCADA system control centre or at the respective regional substation control centre.
2.4 Benefits of the Power System Automation
There are many benefits of the power system automation presented by many researchers.
These include;
In Public interest energy research draft project report 2008, it was reported that the benefits of Distribution Automation functions are divided into three categories: customer benefits, utility benefits, and societal benefits. Often the same function is provided in all three categories, but in different ways and to different degree. Each of the three categories (customer, utility, and societal) address 5 different types of benefits;
a) Direct financial benefits
The benefits include lower costs, avoids costs, stability of costs were reported in the area of distribution automation.
b) Power reliability and power quality benefits
The benefits include reducing number and length of outages, reducing number of momentary outages, “cleaner” power and reliable management of distributed generation in concert with load management and/or micro-grids.
19
c) Safety and security benefits
The benefits include increasing visibility into unsafe or insecure situations, increasing physical plant security, increasing cyber security, privacy protection, and energy independence.
d) Energy efficiency benefits
The benefits include reducing energy usage, reducing demand during peak times, reducing energy losses, and the potential to use “efficiency” as equivalent to
“generation” in power system operations.
e) Energy environmental and conservation benefits
The benefits include reducing greenhouse gases and other pollutants, reducing generation from inefficient energy sources, and increasing the use of renewable sources of energy during off-peak.
According to Gupta et al (2003), the benefits of the distribution automation are reduced technical loss, support for commercial loss reduction, improved cash flow, low service restoration time, reduction in equipment damage, availability of system information, better operational planning, remote load control and shedding, and improved power quality and reliability.
According to Brown et al (1991), Indian utility companies‟ distribution system, the technical and commercial losses are around 45%. It is visualized that the technical part of the losses can be brought down to the minimum value with the implementation of
20
Distribution Automation system. Currently reported transformer failure rate was around
15-20 % in Indian distribution systems which were mainly attributed to non-availability of transformer health parameters and its loading conditions. This can be brought down to around 1% with the help of Distribution Automation system. Therefore, cost/benefit analysis of Distribution Automation system can justify easily the capital investment for distribution automation system.
With respect to the benefits explained above, the automation of power system has not yet been give due attention by the utility companies and manufacturing companies in the developing countries especially in Tanzania. However, the Utility companies have realized the need for Distribution Automation system, which can be retrofitted in the existing distribution network to get better system operation through remote monitoring, control, metering and coordination.
2.5 Empirical Literature
An electric power system consists of three principal divisions: generation, transmission, and distribution systems. The generation plants produce electricity using fossil fuels, nuclear fuels, natural gas, water falls, oil, etc. Transmission lines transfer electricity to substations near customers. Distribution systems directly supply electricity to customers.
In power systems, one of the most exciting and potentially profitable recent developments is the increasing use of automation techniques in monitoring, control, and assessment. Generation plants and transmission lines have been controlled automatically for a long time by means of Power System Stabilizers, Automatic Voltage Regulators,
Load Frequency Control, Automatic Generation Control, and Flexible A.C Transmission
21
System devices. However, Distribution Automation Systems (DAS) have recently been developed and are still being expanded gradually (Choi et al, 2008).
The slow takeoff of distribution automation is hardly surprising. Most utilities have long wished for real-time monitoring and remote control of system elements such as substations, intelligent devices, power lines, capacitor banks, feeder switches, fault analyzers and other physical facilities. Distribution Automation Systems are a key to providing two-way communication with these elements, as well as to identifying and isolating faults, restoring service, etc, all being accomplished automatically (Newton and
Evans, 2009).
According to Boknam et al (2007), Distribution Automation Systems provide remote supervision and control of switches, such as pole mounted switches and pad-mounted switchgears on medium voltage distribution networks. It can be remotely controlled either automatically or manually, so that it can provide automatic isolation of faulty sections, which enables quick and accurate recovery of a stable power supply, and also minimizes of service outage areas and units of distribution sections.
Distribution automation is one of the means to reduce the duration of supply interruptions due to unexpected outages. The average duration per interruption to customers on unexpected outages can be improved by using remote control facilities and real-time power information for the distribution network.
22
Kyirul (2005) wrote that, the main purpose of distribution automation is to increase the efficiency of power supply at the distribution side in response to a fault or an outage. In conventional systems, when fault occurs, action such as opening and closing of breakers, reclosers and sectionalizing switches at substations are done manually the substation‟s operator or trained personnel. So, when the system goes down, the operator needs to localize the fault location and analyze the system to determine the fault and then decide on the necessary action to be taken. This process will normally require considerable amount of time, depending on the complexity of the system. However, with distribution automation system in place, the role is taken over by a computer-based system. The computerized controller can monitor the system and decide on the proper actions instantly and immediately. Therefore, the amount of time needed to act on the fault is significantly reduced. Although in terms of efficiency, the advantages far outweighs the disadvantages, other factors such as implementation cost must be considered because the capital cost for DAS installation is quite high. This is the reason for it not being a common feature in many power supply networks. So, in determine the viability of the implementation, all the factors must be taken into consideration.
Thiyagarajan and Palanivel (2010) claimed that, maintenance of a transformer is one of the biggest problems in the Electricity Board. During strange events for some reasons the transformer is burned out due to the over load and short circuit in their winding.
Also, the oil temperature is increased due to the increase in the level of current flowing through their internal windings. This results in an unexpected raise in voltage, current or temperature in the distribution transformer. Therefore, it was proposed to automate the
23 distribution transformer from the Electricity Board substation to reduce the problems of maintenance of a transformer in the Electricity Board.
Nevertheless there is still a serious problem of getting a single communication technology which can be used in the distribution automation system. Many communication technologies have various limitations such as distortation, capactiy to operate in long distance and costs.
Kim (2009) revealed that, there are many studies focusing on automation of power systems. However, there is no unique communication solution or model that can be applied to distribution automation in electric utility companies. Each utility company has its own unique system whose characteristics determine the requirements for the communication system.
Lippincott (2011) reported that, at the distribution automation layer, many critical functions and actions are automated. These include monitoring of critical feeders, fault detection, isolation and restoration to reduce outage duration and impact. These systems also support shifting loads between sources to help avoid or alleviate overload conditions, controlling capacitor banks and more. Many smart grid utility operators are finding the need for more secure, reliable, efficient forms of communication to deploy distribution automation effectively. No single technology satisfies all requirements and priorities of system managers, especially communication requirements as complex as smart grid‟s. Think of the communications link as an enabler or catalyst of grid
24 continuity. It resembles the highway system: It doesn‟t do anything itself, but connects everything together.
Many researchers and several international organizations are currently developing the required communication channels and the international communication standard for electric system automation.
Goodman (2004) presented the summary of these communication system development activities are as show in table 2.1 below.
Table 2.1: Summary of communication system development activities for electric utility companies.
25
Furthermore, selection of the communications technique for implementations of the remote control/reporting facilities is the most difficult task in automating a distribution network. To date trial tests appear to indicate that the choice of communication medium is vital thus, requiring further research in this area.
A different number of information systems have been introduced to automate offices and industries as a result; selection of “right” choices of information technology solutions is rather a complex multi-criteria decision-making problem (Ward and Peppard, 2004;
Belton and Stewart 2002; Clemen and Reilly 2001).
A considerable research has been performed on the technical side of utility information technology system development; but, less attention has been paid to provide the utility company decision-makers with systematic methods for proper selection of their information technology facilities, which meet performance and cost requirements of the utility information technology system (Marihart, 2000).
Despite the considerable amount of ongoing research, there still remains significantly challenging tasks for the research community to address both benefits and shortcomings of each communication technology. Since each communication technology has its own specific and detailed technical requirements. However, some of the technologies for meeting those requirements have universal themes that present the key challenges to implementing automation of power systems.
26
Marihart (2000) also presented various methods and media of power systems
Information technology (IT) infrastructures. However, it was a qualitative description of the methods that was interesting enough, but no quantitative figure was given there. A design report of distribution automation sub-systems and components has been the subject of a great deal of papers presented in power systems literature (Marihart, 2000).
All of them focused on the technical facet of electrical and information engineering issues; though some of them develop mathematical models, concentrating on the electrical or information technology dilemma, rather than its systems approach.
With respect to the use of information technology in utility companies, many factors have been cited such as improved operational costs, customer expectations in terms of power quality etc, all of which lead to changes in performance of utility companies.
Kim (2009) revealed that, in the past years, most automation in electric utilities has been in the substation and at the enterprise level. This is due primarily to the potentially high cost of implementing distribution automation (DA), the lack of economic justification for such expenditures, and the unique and difficult technical challenges of implementing
DA on a widespread basis. However, this situation is changing drastically. There are a number of factors that drive the change within electric companies to apply state-of-the- art IT. These factors are; increased customer expectations in terms of power quality and reliability, the growing number of regulatory incentives in increasing the performance and affordability of DA communication choices, and an increased variety and capability of automation devices and software. An efficient, reliable, and secure communication infrastructure is vital for successful DA implementation.
27
In Network Protection & Automation Guide (2002), it is reported that cost is the main driving factor in the application of an automation scheme to a distribution network.
Costs may arise in many different ways such as revenue loss during outages, costs of handling customer complaints, costs of maintenance/control staff, and cost of compensation to consumers for outages. Furthermore, there are inevitable costs to be incurred to introduce an automation scheme: cost of implementation (capital cost), cost of operation, cost of maintenance. It is necessary that the total saving in costs must exceed the total implementation costs, if the scheme is to be viable. According to Belgur
(2009) Distribution Automation applications are classified into three functional groups based on their function and the target area they impact within a utility company. These are namely, automated switching and system restoration, power quality enhancement, load control and demand response (demand side management). It is noted that the values and the benefits that can be derived out of these implementations differs from one utility company to the other. Although, the financial advantages to the utility company may not be easily recognized, it is recommended to automate our future power distribution networks.
The results of research work by number of researchers cited in this chapter, it can be observed that, automation of power system has existed for many years and many researches focusing on issues of automation of power systems are still being conducted.
As automation of power systems has been going on for many years it is evident that the extent to which automation has been applied was guided by a combination of availability of appropriate technology and cost. For many years, available technology of the day limited the application of automation to those parts of the distribution system where loss
28 of power supply has had impact on consumers. The technology was not available to handle large amount of geographically dispersed networks. When technology improved to address limitations, the implementation costs was prohibited (not cost effective solution).
2.6 Power Delivery Network
The power delivery system network in Tanzania is a large infrastructure covering most parts of inhabited area. The power sources such as Kidatu, Mtera, Kihansi, Hale,
Nyumba ya Mungu, Pangani, Ubungo Generation and Tegeta Generation plants and other generation plants in Tanzania, all are interconnected and each generate at a given voltage that is stepped up to 220 kV and transported on high voltage (220 kV) grid and then stepped down to medium voltage 11 kV or 33 kV in main substations. The 11 kV and 33 kV provides the primary distribution network. The voltage is further stepped down to a low voltage grid of 380V to form a secondary distribution network. This network is composed of a large number of smaller capacity substations to feed a large number of customers. Hence, the secondary distribution network is much bigger and more complex. Figure 2.2 shows the whole network includes the primary power network substation from generation points to main regional substations and figure 2.3 shows the secondary power network substation feeding the distributions network.
In figure 2.3, the customers are grouped in a low voltage grid from a secondary substation (distribution transformer), where each household/consumer is connected to the 380V power line for three phase and 230V for single phase. There are several low
29 voltages power line connected to each substation. Each low voltage power lines consist of four wires, that is, three phase lines and a neutral.
Both figure 2.2 and 2.3 shows block diagram of TANESCO power network which is big and very complex to manage and control since it is not computerized especially the low and medium voltages networks. This makes monitoring activities along power network very involving, difficult and costly. Based on the studies presented in this literature review computerization of the power systems from generation points (power sources) to end users, will simplify monitoring activities along power network making them more efficient reducing TANESCO‟s operational costs while enhancing reliability and quality of services delivered to consumers.
30
Figure 2.2: Primary power network substation
31
Figure 2.3: Secondary power networks
32
CHAPTER THREE
Research Methodology
3.1 Introduction
This chapter describes how the study was designed and how it was conducted. Also, it shows structure and strategy of study that was used to obtain answers to research questions and research objectives.
To make sure that these procedures were adequate in order to realize the set objectives and hence to obtain accurate answers to the research questions, there was a need to careful select the type of research design (Kothari, 2004).
3.2 Research Design
Research design is the arrangement of conditions for collecting and analyzing data in a manner that aims at combining tools relevance with the research purpose Kothari (2004).
It shows the systematic arrangement and strategies that guide the researcher to achieve the set research objectives.
The research work is a case study type. A case study is the most appropriate in this work since it entails a detailed and intensive analysis of a single case. Wimmer &Dominick
(2000) variously define research design as a conceptual structure within which research is conducted. According, a research design is a blue print of how the study intends to answer research questions. The purpose of using this was to determine the concept of
33 automation of management of power systems from generation points to end users for communication as an integral part. Hence, the researcher looked at different communication systems perceived to be suitable for automation of power systems, for monitoring and control systems for automation purposes. The challenges involved were also looked at.
3.3 Data Types and Sources
In this particular study, both primary and secondary data were used. Primary data were collected from the field in TANESCO. Secondary data were collected from various relevant research papers, publication, un-publication materials, journal papers and E- sources.
3.4 Data Collection Techniques
There are several ways of collecting the appropriate data which differ considerably in context of costs, time and other resources at the disposal of the researcher. The researcher collected data through interviews and from different documents.
3.4.1 Interview
Interview assist in counterchecking and ascertaining the information collected through questionnaires Winner & Dominick (2000). Interviews allowed the researcher to supplement explanations and offered an opportunity to probe deeper into issues. In this study, the interview technique was used to collect data from TANESCO staffs.
34
3.4.2 Studying Documents
By using internet search, books, publications, academic journal and other documents were visited which assisted the researcher some conclusion.
3.5 Identification of Communication systems
Four communication technologies that were considered feasible for power system automation were identified in this study and these are Power Line Communication
(PLC), Optical Fiber, Satellite Communication and Wireless Communication. Out of four identified communication technologies, two of them (PLC and Optical Fiber) were selected as most effective communication technologies for automation of power systems. The criteria used to select PLCs and Optical fiber communication technologies are; capacity, coverage, security, reliability, accuracy, and availability.
3.6 Identification of monitoring tools
Two monitoring tools were identified in this study and these are Energy Technology assistance Program (ETAP) software, Power System Simulator for Engineering (PSS/E) software. PSS/E tool was selected and the criterion used to select this tool is availability although there could be appropriate, affordability, flexibility, user friendly, easy to use and feature rich. In order to determine the concepts of automation of management of power systems, researcher conducted simulation study using PSS/E and the parameters were used to simulate the system in figure 4.1 are power flow and short circuit conditions.
35
3.7. Reliability and Validity of data
Any data would be worthless if it is not reliable or valid. Effort was made to ensure that data for this study were as reliable as possible by designing the research instruments as per recommended principles and proper selection of people to be interviewed and other sources. A careful analysis of relevant literature was made to examine instruments that have been used in similar studies (Wimmer & Dominick, 2000) and (Comry & Lee
1992).
36
CHAPTER FOUR
FINDINGS AND DISCUSSIONS
4.0 Introduction
In this chapter, the researcher presents the facts, which were discovered during the study on AUTOMATION OF ELECTRIC POWER SUPPLY SYSTEMS: TANESCO
Case Study. The researcher discusses the finding from the empirical data by considering the research questions.
Question one: what are challenges existing in automation of power systems
Researcher addressed this question as detailed in the section that follows;
4.1 The Challenges for Automation of Power Systems
Key TANESCO staffs in the control centre at Ubungo were interviewed and different documents were studied which included un-publications, books, publications and academic journal.
TANESCO staffs considered communication technique as the main challenge for automation of power systems. Currently TANESCO has system called SCADA which monitors performance of the power network from TANESCO generation plants to high transmission voltage. The system is using two communication techniques, PLC and
Optical fiber. To get reliable communication, Optical fiber has been deployed along the high tension power lines used as main communication media because of it several
37 advantages such as high bandwidth, capacity and security while PLC has been used to provide back-up system because of limitation in Bandwidth and capacity. Therefore, optical fiber is much better medium for back hall compared with PLC. Also distance for optical fiber is much higher.
Up to date there is no single communication technology that has been used for automation of power systems and this is because each of communication technology has its advantages and challenges. For reliable, effective and accurate communications many utility companies such as TANESCO have been using a combination of several technologies to monitor and control the performance of its electrical power network.
Other challenges in automation of power systems identified in this work are as follows;
a) Global warning and Greenhouse gas emissions
Most of our energy is from fossil fuels which cause the problem of global warming due to the emission of greenhouse gases and therefore resulting to changes of weather conditions. Electric power systems are generally designed to operate during periods of stable weather and loading patterns. These design assumptions may be strained by extreme weather due to climate change. The weather includes destructive events such as heavy rains, falling down of power poles, high winds as well as extremes weather of heat and cold, which affect both individual equipment failure and system operations
(Kezunovic et al, 2008). Therefore, these impacts of weather in power system bring a raft of operational problems which cannot be solved with existing technology.
38
b) Lifetime Expectations
Currently primary apparatus lifetime is between 40 to 60 years. But electronics apparatus is 15 years. Automation of power systems uses electronic apparatus; so that replacement is needed after a very short time compare to primary apparatus and therefore, can disturb performance of power network and can increase operational costs to utility company. This can be challenge if and only if preventive maintenance is not used.
c) Adoption of main stream technology
The continuing advancement of computing technology has brought down the cost of implementing communications interfaces to the point where data concentrators and gateways are becoming common replacements for large Remote Terminal Units (RTUs).
The declining costs is the driving factor in the development of the industrial automation software market which led to an extensive growth in the number of different industrial automation software products that supports Dynamic Data Exchange (DDE). It has grown in availability of industrial automation communications drivers with DDE compatibility (Mackiewicz, 2003). However, the process of communication interface process has not changed for decades hence requiring new processor every 6 months and new operating system every 2 years. Therefore, it can affect performance of automation of power systems.
d) Reliability
Automation of power systems requires high reliability devices to make electronic equipment maintenance free. Hence, electronic equipment that fails to operate should be
39 replaced with new one. Safe and reliable operation is a must even in case of failure in electronic equipment. This requires manufacturers to manufacture devices with standby capability to take over the network function in case of a device failure.
e) Initial Cost and People Expectations
In most utility companies especially in developing countries, initial cost of establishing automation system is high hence a number of utility companies have failed to automate their electrical power networks.
Some people expect that most of the utility companies will come forward for large scale distribution automation. However, such companies found it difficult to justify distribution automation based on hard cost benefit figures. Furthermore, Business instability due to deregulation and restructuring of the power industry slowed down wide scale implementation of distribution automation (Gupta and Varma, 2005).
f) Security and System Integration
In DAS, the distribution system manages by for a large amount of data compared to that of transmission system. This makes system integration for DAS challenging because of the need to keep track of data names, formats, engineering units, time stamps, and other consistency aspects of data management would be a large undertaking. However, it has to be done to ensure reliability and sustainability.
Question two; which monitoring tools can best support automation of power systems?
The researcher addressed this question as detailed in the section that follows;
40
4.2 Monitoring of Power System
4.2.1 Computer
A computer is an essential device in DAS which is composed of hardware and software parts. Hardware; the physical equipments required to create, use, manipulate and store electronic data (Roper &Millar, 1999). These physical hardware equipments are computer processing unit, memory, storage device, input device, output devices.
Software is the computerized instructions that operate a computer, manipulate the data and execute particular functions and tasks (Roper &Millar, 1999). The software is held either on computers hard disk, Compact Disc (CD)-Read Only Memory (ROM), Digital
Versatile Video (DVD) or on a diskette and is loaded from the disk into the computer
Random Access Memory (RAM) as and when required. The software components include word processing applications, Spreadsheets, Database, Payroll, Presentation tools, Desktop publishing, Multimedia applications.
Monitoring software is a database management application equipped with statistical analysis and plotting tools and wrapped in a user friendly interface. It offers the ability to process and analyze many types of data by integrating all of the information from numerous monitoring instruments into one relational database. Therefore, the data monitored at the system are not only important for day to day operations but also for system planning and future works of utility companies.
41
Power system monitoring software offers real time power monitoring through an intelligent graphical user interface. Power system monitoring software functions include checking the condition of the network, estimating missing system states, detecting network abnormalities, and providing alarms based on operating conditions and status changes. Therefore, the above functions of power system monitoring software are usual viewed in a computer using monitoring software.
Monitoring of power system offers information about power flow, demand, and the quality of power. Power system monitoring is an essential in identifying current and potential power quality issues and addressing them before they cause interruptions or disturbances.
4.2.2 Monitoring tools
There are a number of power monitoring tools in the market, however available one for this study are ETAP software, and PSS/E software. The selection of PSS/E software by researcher is based on availability however it provided a sound testing vehicle for management of automation. The parameters use to simulate and provide the results are load flows and short circuit conditions.
4.2.2.1 Energy Technology Assistance Program (ETAP)
ETAP provides complete integrated electrical engineering software solutions including arc flash, load flow, short circuit, transient stability, relay coordination, optimal power flow and more. ETAP offers real time application of intelligent power monitoring,
42 energy management, system optimization, advanced automation and real time prediction. ETAP is used for designing, simulation, operation, control, optimization and automation of generation, transmission, distribution and industrial power systems.
Furthermore, ETAP provides smart grid application of enabling electrical utilities to plan, coordinate and safely operate their grid system.
4.2.2.2 Power System Simulator for Engineering (PSS/E)
Power System Simulator for Engineering (PSS/E) is a software used for simulating, analyzing and optimizing power system performance and providing probabilistic and dynamic model features. It provides transmission planning and operations engineer a broad range of methodologies for use in the design and operation of a reliable network.
The PSS/E tool has technically advanced features, and is a widely used commercial application. It is recognized as the most featured, time-tested and best performing commercial electrical transmission regulator available. Hence, Information Technology
(IT) offer the user with the advanced and proven for wide ranging services to automate different aspects of power systems from design, to generation, transmission, distribution and its management.
4.2.3 Simulation Parameters
There are many power systems parameters but for the purpose of this work the researcher has limited for simulation purposes. Using PSS/E software, two parameters
43 load flow and short circuit conditions were selected because load flow and short circuit conditions are parameters which are significant in faulty conditions.
During PSS/E simulation for load flow and short circuit conditions, researcher has assumed an electrical line diagram in figure 4.1. The generator in figure 4.1 has been assumed to have a base voltage of 33 kV and generates active power and reactive powers of 8.9 MW and 1.8 MVAR. The maximum active and reactive powers generated by the generator in a diagram are 10 MW and 2 MVAR and minimum active and reactive power are 0 MW and -2 MVAR.
a) Power Flow
Power Flow is an important tool involving numerical analysis applied to power system.
It analyzes the power systems in normal steady-state operation. Furthermore, it focuses on various forms of Alternating Current (AC) power such as voltages, voltage angles, real power and reactive power.
In figure 4.1, the black lines indicate bus bar with voltage 0.4 kV, the blue lines indicate bus bar with voltage 11 kV, the red lines indicate bus bar with voltage 33 kV and the end arrow lines indicate that lines are connected to users/load. The numbers with decimal points that are shown along the line diagram are the active and reactive power of the lines.
44
Figure 4.1: Electrical line diagram
The researcher conducted simulation using figure 4.1 and the results showed that the active and reactive power generated were 8.9 MW and 1.8 MVAR, the maximum active and reactive power were 10 MW and 2 MVAR with the minimum active and reactive power of 0 MW and -2 MVAR. These results indicate that, the system has no problem.
The loads connected in bus bars number 9,10,11 and 12 in figure 4.1 were assumed to have capacity of (0.4, 0.3), (0.7, 0.5), (0.5, 0.4), (0.6, 0.5) where the first number inside a bracket is the active power measured in MW and second number is the reactive power measured in MVAR. Also, the simulation was conducted using figure 4.2 where the load capacity in figure 4.1 were increased to (1.1, 0.8), (1.1, 0.8), (1.3, 1.0), (1.2, 0.9). The
45 results showed that both the lines and transformers color connected between bus bars number 5, 6, 7, 8 and number 9, 10, 11 and 12 changes from black color observed for simulation of data in figure 4.1 to dark color indicating that bus bars number 9, 10, 11, and 12 are overload. Also, the color of the line from generator to bus bar number 2 changes from red for loads in figure 4.1 to dark because the active and reactive power
12.3 MW and 5.5 MVAR between generator and bus bar number 2 exceeded the maximum active and reactive power of the system 10 MW and 2 MVAR.
Figure 4.2: Electrical line diagram with increasing the capacity of loads
b) Short Circuit Condition
Short Circuit is an electrical circuit that allows a current to flow along an unintended path, where no or a very low electrical impedance is encountered. In circuit analysis, the
46 term short circuit is used by analogy to designate a zero impedance connection between two nodes. This makes the two nodes to be at the same voltages. The simulation of three phase short circuit fault analysis conducted using configuration and load conditions in figure 4.1 and the output is shown in figure 4.3.
Figure 4.3: Three phase short circuit fault analysis line diagram
During simulation researcher selected bus bar number 7 to introduce three phase short circuit fault condition for analysis resulting in large amount of current to bus bar number
7 compare to the others.
With respect to the simulation conducted and output where shown for configuration and condition given in figures 4.1, 4.2, 4.3, the aim was to show what the utility operator at the control centre will view from an automatic management system for power networks
47 indicating its using monitoring software. This was necessary since it could not be done on an actual network. It also serves facility for operators of a real time system.
Therefore, whenever problem concerning power network occurs the utility operator will automatically get indication and send report to required department for control decision.
Question Three; Which communication system(s) can be most effective in automation of power systems?
The researcher addressed this question as detailed in the section that follows;
4.3 Communications
Communications can be generally defined as transfer of information from one point to another or from source to destination or from transmitter to receiver. The interchange of data between any two devices across a communication channel involves using some type of electrical signal which carries this data.
Usually, the communication channels could be a power line communication, satellite, optical fiber link or wireless. Each type of these communication channels medium have unique transmission characteristic which should match with signal properties for efficient signal handling otherwise a different technology has to be deployed/ developed to adapt usage of channels.
48
Figure 4.4: An elementary communication link
In fig 4.4, the signal from the source is transmitted through a respective channel and the receiver receives and removes the destabilized and distorted signal from the channel, amplify it and restore it as close as possible to its original form. The format of signal is an important factor in efficiently and reliably sending signal across a network. The signals emitted by information sources can be in analog or digital formats or both.
Communications allows utility companies to attain objectives such as intelligent monitoring, security, load balancing and the like by providing the necessary link between network information sources and the control centre. By using two-way communications system, data can be collected from sensors and meters located throughout the grid and transmitted to the grid operator‟s control room providing operator the ability to manage the grid from the control room.
49
Therefore, developments in various signals processing communication channels have facilitated monitoring in real time the conditions and performance of electric power systems elements. Each communication channel has its own advantages and disadvantages that must be evaluated to determine the best appropriate communication technique for electric power system automation.
4.3.2 Power Line Communication (PLC)
Power Line Communication or Power line carrier is a system that carries information over electric power lines designed for optimal delivery of electric power. Broadband over Power Lines (BPL) refer to the use of power line for transmission of information at data rates of between 500 kbps and 3 Mbps, which is almost the same as that for DSL and cable modem transmission rates (Gilbert, 2006).
Electrical power is transmitted over high voltage transmission lines, distributed over medium and low voltages, and used inside buildings at low voltage. Hence, to effectively use of Power Line for communications for the entire electrical power network needs the system to be applied at network segments transmission to secondary distribution. However, to make use of PLC to provide communications for remote measurement and control function, standardization for all levels of power supply network is essential and is going.
Electric power supply network is designed for power transmission and not for telecommunication purposes. Therefore, there are challenges for utility companies to use
50
PLC technology to send and receive information on power grid using the existing infrastructure. However, the main advantage for utility companies to use Power Line
Communication is in the reduction of operational costs since they own the network and they shall be in control of their communication infrastructure. They can also rent extra capacity to other users and generate revenue.
Power line communication can be classified into Narrowband and Broadband PLCs.
4.3.2.1 Narrowband (NB) PLC
NB PLC is classification of power line communications that transmit signal below 500 kHz. Specifically; Europe‟s CENELEC has authorized frequencies up to 148.5 kHz for broadly deployable PLC system. In this frequencies range, high voltage transmission lines have been used to carry data to distances ranging from hundreds of meters to a few kilometers (Mike, 2011).
NB PLC is being used for various applications to offer a two way communications capability to deliver data to variety utility company applications. Therefore, it facilitates utility companies to detect, classify and detect remotely possible equipments failures.
There are two types of NB PLC; Low data rate NB PLC and High data rate NB PLC.
Low data rate PLC; Offers frequency range from 9 kHz to 150 kHz and data rate is less than 10kbps and using modulation techniques like FSK, BPSK, FFH, SFSK and
51
DCSK. Also, NB PLC has no or low Forward Error Correction and it can be applied in
Automatic Meter Reading (AMR), Power Line Area Network (Arivus, 2009).
High data rate PLC; offers frequency range from 150 kHz to 500 kHz. High data rate
NB PLC data rate varies from 50kbps to 1Mbps, and it uses Orthogonal Frequency
Division Multiplexing (OFDM) and Multi-Carrier Modulation (MCM). It has strong forward error correction for high reliability designed and finally it can be applied in
Energy Management, Smart Grids and Metering and Automatic Meter Reading (AMR)/
Automatic Meter Management (AMM) (Arivus, 2009).
4.3.2.2 Broadband PLC
Broadband PLC systems provide data rates of more than 2 Mbps whereas the narrowband networks can carry only a small number of voice channels and have data with very low bit rates. Broadband PLC networks offer capability for realization of more sophisticated telecommunication services; multiple voice connections, high-speed data transmission, transfer of video signals, and narrowband services as well. Therefore, PLC broadband systems can be conceived as an alternative telecommunications technology
(Hrasnica et al, 2004).
Currently broadband PLC provides data rates beyond 2 Mbps in the outdoor arena which includes medium-voltage and low–voltage supply networks and up to 12 Mbps in the in- home area. Some manufacturers have already developed product prototypes providing much higher data rates of about 40Mbps (Hrasnica et al, 2004).
52
Medium voltage is used for providing point to point connections covering distances up to several hundred meters while low voltage is used for providing the “last mile” of the telecommunication access networks for areas with electrical installations.
4.3.2.3 Advantages of Power Line Communication
a) Wide Coverage Area
Power Line Communication offer wide coverage, this is because the power line network is installed nearly in all urban areas in Tanzania and in some rural areas. This is very important particularly to access substations in rural areas where there is usually no reliable communication infrastructure.
b) Low Cost
Since power lines are transmitting electrical power, there is no need to build new basic communication infrastructure because PLC utilizes the existing power lines to carry the communication signals to facilitate communications over power lines. Therefore, Power
Line Communication can be cost effective and can offer substations a cheaper way for remote monitoring of power usage and outages.
c) High bandwidth
PLC technology has currently a maximum bit-rate of up to 45 Mbps. The downstream speed is up to 27 Mbps and the upstream speed is up to 18 Mbps. PLC has the higher
53 access speeds, compared to ADSL having at 512 Kbps and internet cable at 1.5 Mbps
(Lee, 2002).
d) Easy installation
Power line communication can be implemented conveniently in all places provided with grid power supply. Therefore, it lends itself ready for use for communication purposes when the challenges involved are overcome.
4.3.2.4 Challenges for Power Line Communication
a) High noise source
The power lines present a very noisy environment for data communications due to a number of noise sources such as, radio signal, power supplies, electrical motors interferences and the like (Pavlidou et al 2003), as results of high bit error rates during communication which affect the performance of PLC.
b) Capacity
New PLC enabling technological advances has recently enabled production of a prototype power line communication modem which achieves a maximum data rate of 45
Mbps. However, the average data rate per end user will be lower than the maximum data rate depending on coincident utilization, i.e., the number of users on the network at the same time and the applications being used. Thus, technical problems should be addressed with various field tests before the PLC technology is widely deployed
(Gungor et al, 2006).
54
c) Signal attenuation and distortion
The attenuation and distortion of signals are huge in power lines because of physical topology of the power network and load impedance fluctuation over the power lines.
Furthermore, there is signal attenuation at specific frequency bands due to wave reflection at the terminal points. Therefore, the communication over power lines is not very common because of high signal attenuation and distortion experienced by signal
(Gungor et al, 2006).
d) Security
Power line cables are not twisted and without shielding hence power lines radiates amount of Electro Magnetic Interference (EMI) and this EMI can be received by radio receivers. Therefore, to prevent the interception of vital data by an unauthorized person, a proper encryption technique has been used.
4.3.3 Optical Fiber
Optical fiber is a glass or plastic fiber that carries light along its length. Optical fibers are widely used in fiber optic communications, which facilitates transmission over longer distances and at higher bandwidths (data rates) than other forms of communications.
Optical fibers are used instead of metal wires because signals travel along them with lower loss, and they are also immune to electromagnetic interference.
55
Light is kept in the core of the optical fiber by total internal reflection. This causes the fiber to act as a waveguide. Optical fibers which support many propagation paths or transverse modes are called multi-mode optical fibers, while those which can only support a single mode called single-mode optical fibers.
Although optical fibers can be made out of transparent plastic, glass, or a combination of the two, the optical fibers used in long-distance telecommunications applications are always made of glass, because of their lower optical attenuation characteristics. Both multi-mode and single-mode optical fibers are used in communications where multi- mode optical fiber used for short distances and single-mode optical fiber used for long distance links.
Because of the tighter tolerances required to couple light into and between single-mode optical fibers, single-mode transmitters, receivers, amplifiers and other components are generally more expensive than multi-mode optical fiber components.
The optical fiber cable transmission channel is made up of varying numbers of either single- or multi-mode optical fibers, with a strength member in the center of the cable and additional outer layers to provide support and protection against physical damage to the cable during installation and to protect against effects of the elements over the long periods of time. The optical fiber cable is connected to the terminal equipment that allows slow speed data streams to be combined and then transmitted over the optical cable as a high-speed data stream. The optical fiber cables are linked in intersecting rings to offer self-healing capabilities to protect against equipment damage/ failure.
56
4.3.3.1 Advantages of Optical fiber
a) Long distance signal transmission
Optical fiber has low loss of signal less than 0.3 db/km therefore; there is possibility for fewer repeaters for transmission over a long distance. The low attenuation and superior signal integrity available in optical fiber systems enable longer interval of signal transmission than for metallic based systems. It is not atypical for optical systems to go over 100 kilometers without active or passive signal processing.
b) Large bandwidth, light weight and small diameter
Data transmission rate up to 1.6 Tbps is available carrying large amount of data in field deployed systems and up to 10Tbps in laboratory systems. The small diameter and light weight of optical fiber cable allow easy and practical installations saving valuable conduit space.
c) Immunity to electrical interference
Optical fiber has no metallic components and can be installed in areas with high electromagnetic interference such as utility lines, power carrying lines and railroad tracks.
d) Increased signal security
The dielectric nature of optical fiber makes it impossible to remotely detect the signal being transmitted within the cable. This makes accessibility of the optical fiber signal require physical intervention of the cable which is easily detectable by security
57 surveillance. This makes optical fiber attractive to governmental bodies, banks, utility companies and other entities demanding high level of security.
e) Designed for future application needs
Today optics fiber is inexpensive shall continue to be cheaper, as electronics prices fall and optical pricing remains low. In many cases, fiber solutions are less costly than copper. Therefore, optical fiber will continue to play a vital role in telecommunication systems requiring large bandwidth.
f) Enhanced Safety
Optical fiber provides a high degree of operational safety because it does not have the problem of ground loops, sparks and potentially high voltages inherent in copper lines.
High electrical resistance in optical fiber cable makes optical fiber so safe to use near high-voltage equipment or between areas with different earth potentials.
4.3.3.2 Challenges for Optical Fiber
a) Cost
In Tanzania optical fibers has been deployed in the communication network backbones and has been used within TANESCO power network from generation plants to high voltage level for communication purposes, but it is costly to extend network over a large geographical area. This involves the cost of deploying optical fiber over TANESCO‟s medium and low voltage networks with numerous terminations to suit remote control and monitoring of electrical equipments and network. Hence, optical fiber network may
58 not be the best option for providing last mile connectivity for the utility companies for automation of its entire power system network.
4.3.4 Satellite Communications
Satellite is a microwave repeater in the space and there are more than 750 satellites in the space; most of them are used for communications. The satellites have been used for wide area network communications, weather forecasting, television broadcasting, amateur radio communications, internet access and the global positioning system etc.
A communication satellite is a specialized wireless receiver or transmitter-receiving radio waves from one location and transmitting them to another also known as a bent pipe-that is launched by a rocket and placed in orbit above the earth. The task of satellite in the communications network is to serve as a repeater. This mean satellite receives a signal from one station and rebroadcasts signal to another station. A typical satellite has
32 transponders. Reception and retransmission are completed by a transponder. A single transponder on a Geostationary Earth Orbit (GEO) satellite is able to handle about 5,000 data channels.
Each Transponder works on a specific radio frequency wavelength, or “band.” Satellite communications work on three primary bands: C, Ku and Ka. C was the first band used with longer wavelength, needing a larger antenna. Ku is the band used by most current
Very Small Aperture Terminal (VSAT) systems. Ka is a new band allocation that is not yet in wide use. Of the three, it has the smallest wavelength and can use the smallest antenna.
59
Satellite up links and down links can operate in different frequency bands; the up-link is a highly directional, point to point link and the down-link can have a footprint providing coverage for a substantial area spot beam. Table 4.1 shows typical links frequency bands and their issues.
Table 4.1: Typical links frequency bands. BAND UP-LINK (GHz) DOWN-LINK ISSUES (GHz) C 4 6 Interference with ground links Ku 11 14 Attenuation due to rain Ka 20 30 High Equipment cost
Therefore, the combination of individual transponder volumes and the number of transponders in orbit means today's communication satellites are an ideal for transmitting and receiving almost any kind of content, from simple data to the most complex and bandwidth-intensive video, audio and data content.
There are three types for satellite orbits; Low Earth Orbit (LEO), Medium Earth Orbit
(MEO), Geostationary Earth Orbit (GEO).
60
a) Geostationary Earth Orbit
A satellite in a geostationary orbit appears to be in a fixed position to an earth-based observer. At the Geostationary orbit the satellite covers 42.2% of the earth‟s surface.
Theoretically, three geostationary satellites provide 100% earth coverage.
The GEO satellites are at an altitude of 35,768 km and complete exactly one rotation in a day. Since the period is exactly one day, GEO satellite appeared to be stationary from a fixed point on the earth. These satellites have large footprints that can cover up to 34% of the earth‟s surface. Due to high altitude of the satellite the delays can be large. Also, the high altitude of the orbit has a main disadvantage of link budget. Global coverage of small mobile phones and data transmission can see delays in the range of 275 ms. Since footprints are large, frequency reuse is not generally possible.
Majority of current satellite communication systems use GEO orbits. The geostationary orbit is useful for communications applications because ground based antennas, which must be directed toward the satellite, can operate effectively without the need for expensive equipment to track the satellite‟s motion. Particularly for applications that need a large number of ground antennas (such as direct TV distribution), the savings in ground equipment can more than justify the extra cost and onboard complexity of lifting a satellite into the relatively high geostationary orbit.
61
b) Medium Earth Orbit
MEO is defined simply as the area between LEO and GEO. The primary satellite systems in this region are the Global Positioning System (GPS) satellite constellations.
MEO satellites are at about 6,000 to 20,000 km above the earth‟s surface. MEO orbits can either be circular or elliptical. Circular orbit MEO‟s are called the Intermediate circular orbit (ICO).
To provide global coverage through MEO satellites a constellation of about 10-12 satellites located on 2 to 3 MEO orbits are required. Satellite period is about 6 hours.
MEO based systems are Starlynx (Hughes), WEST MEO (Matra Marconi).
c) Low Earth Orbit
LEO satellites are located about 500 to 1,500km above the earth‟s surface. To provide global coverage through LEO satellites require large number of satellites located on many different LEO orbits (a typical system may cover only a specific area rather than globe). Since these are located close to the earth, the satellite travel at high speed relative to a terrestrial observer hence large Doppler shifts can be observed at the receiver.
Satellite period is about 90-120 minutes.
The advantage of LEO is to provide shorter delays for faster communications. However, for reliable communications they need a constellation of satellites so that communications can be maintained as one satellite moves out of range and another move
62 within range of the ground station. Therefore, LEO satellites are not too expensive to construct, they have less powerful, and have shorter life span.
Satellite communication can provide innovative solutions for remote control and monitoring of substations. It provides a wide geographic coverage area, and is a good option communication infrastructure for power system automation to provide access to any remote substations. In power system automation, VSAT satellite services are offered for remote substation monitoring applications and in recent developments in power system automation, satellite communication used for remote control, monitoring of substations and for Global Positioning System (GPS) based time synchronization, offer microsecond in time synchronization application.
Furthermore, satellites can provide a backup communication system for the existing substations communication network, enabling routing of vital data in case of congestion or link failures in communication (Ekici et al, 2002).
4.3.4.1 Advantages of Satellite Communications
a) Geographic coverage
Satellite communications have single characteristics over conventional long distance transmissions. This type of communication is capable of spanning over long distance irrespective of the physical condition. Thus, satellite provides a cost–effective solution for coverage of large geographical area in a short period particularly where there is no communication infrastructure in place which is typical for remote substations.
63
b) Higher Bandwidth
Satellite communication provides high bandwidth capacity. Therefore, satellite is used for the broadcasting of video streaming. Higher bandwidth can be used for the transmission of vital data and messages within substations.
c) Rapid Installation
Users in satellite communications do not need cabling to get high speed services. A remote substation can link a satellite communication network by only acquiring the necessary technical equipments.
4.3.4.2 Challenges for Satellite Communications
a) Long delay
With respect to the transmission characteristics for satellite communication, round–trip delay is higher than that of terrestrial network. Substation messages are vital and may not tolerate delays typical for GEO substations. To make sure that effective, efficient and reliable transmission of these substation messages from one substation to other substation, with acceptable round trip delay lower satellite orbits have to be used.
b) Channel characteristics
Performance of satellite channels differ depending on their influence by weather or the fading conditions. These conditions degrade the efficiency of the entire satellite communication system.
64
4.3.5 Wireless Communications
Wireless communication is a growing segment of the telecommunications industry, with the potential to offer high speed, high quality information interchange between portable devices located anywhere.
There are several wireless technologies. These are Mobile radio, Microwave system,
Conventional radio, Bluetooth and the like.
According to Network Protection & Automation Guide 2002, mobile radio is type of wireless communication which is currently a good-looking option for telecommunication companies. Many telecommunication companies provide packet- switched data methods to business customers. Packet-switched data methods are right choice to both urban and rural areas. But there is main problem in urban areas because of shielding effects of antennas by buildings or parked vehicles. This problem is experienced by communications methods radio connectivity. Also, in rural areas, investment is required to cover a given area, and this takes time to complete, which depends on the telecommunications service provider involved. Since mobile telecommunications service providers are eager to expand their service coverage and sites for the needed pole is handily be located along the right-of-way of the distribution system lines. However, it is not cost effective for a large part of the rural areas.
Wireless communication technologies have potential advantages in order to remotely control and monitor electric power systems, for example savings in cabling costs because there is no need to re-cable network.
65
Utility companies that need wireless communication options have two choices;
a) Utilizing an existing communication infrastructure of a public network, e.g.,
public cellular networks,
This allows a cost-effective solution as a result of the savings initial capital
investment needed for the communication infrastructure.
b) Installing a private wireless network.
This allows utility companies to have control over their communication
network. But, private wireless networks require a significant installation
investment as well as the maintenance cost.
Wireless communication technology has already been used in electric power system automation especially in developed countries. Currently, Short Message Service functionality of the cellular network has been used to monitors electric power systems.
In Tanzania, TANESCO is using this technology to communicate with its main meters in substations even in some urban sites.
The cellular network control channel is also utilized in some alarm-based electric power systems monitoring cases. But this communication technology is fitted to the applications that use small amount of information and therefore provide Quality of
Service for computerized electric power system monitoring applications.
66
Furthermore, wireless applications include multimedia internet enabled cell phones, smart homes and appliances, automated highway systems, video teleconferencing and distance learning and autonomous sensor network.
4.3.5.1 Advantage of Wireless Communication
a) Mobility
Allow user to access data while they are on the move because wireless communication is deployed in all places where is available.
b) Flexibility
No need to re-cable or reconfigure network while someone change office and no unnecessary downtime is associated with such a move. It is also someone can add in a communication device to the system or remove one from the system without any disruption to the rest of the system.
c) Cost
Initial cost of operation and maintaining wireless communication at the site is minimum this is due to wireless technology allows users to access information while they are on the move, resulting in cost of cabling is ignored.
67
d) Speedy installation
A Wireless network is configured speedily and it is also be easier and cheaper to install in area where there is already infrastructure. Therefore, initiation of communication is within the coverage area, as resulting of deploying short communication infrastructure.
e) Efficiency
Since wireless communication has wide bandwidth it can improve and increase efficiency communication.
4.3.5.2 Challenges for Wireless Communication
a) Interference problem
Interference is the degradation of a wireless communication signal caused by electromagnetic radiation from another source. The electrical interference is caused by computers and digital equipment, heavy electrical equipment, lighting systems and faulty electrical devices. Therefore, the effect of interference is to slow down a wireless transmission or totally impeding it depends on the strength of the signal. Further, wireless communication can be lost due to congestion when too many wireless users interfere each other.
b) Security
Security in wireless communication is an aspect of computer security. All organizations with any number of entities are vulnerable to security breaches caused by rogue access point. Verification communication entities are performed to make sure that all registered
68 equipments may communicate using the network as results registered equipments may receive the information. Form of encryption is needed for communication to avoid interception of information transmitted over the network by devices not taking part in the communication.
c) Capacity
A limited bandwidth capacity and high bit error are things to pay attention during design of any wireless communication system because they will affect quality of service in wireless communication. Also, the application data rate per user is lower than the total bandwidth capacity, for example maximum data rate of IEEE 802.11b is 11 Mbps while the average data rate is approximately 6 Mbps.
d) Limited coverage
Private wireless networks offer a limited coverage for example the coverage of IEEE
802.11b is 100 m approximately, so wireless is difficult to reach in some places where no signal is available. Furthermore, a wireless communication service is also problem to remote substation where areas are less densely populated.
4.3.6 Suggested Communication Techniques
A communication infrastructure is one of the aspects which play a greater role in automation of power systems. However, there are many problems that require to be overcome to realize automation of power systems to the level of distribution networking.
This includes identification of appropriate communication technique. Hence, to identify
69 suitable communication systems for automation of management of power systems, researcher has explored four communication techniques namely Satellite
Communication, Optical Fiber, Wireless Communication and Power Line
Communication. Communication technique is an essential player in connecting control center of utility company, generation plants, high voltage level, medium voltage level, main substations, and equipments along transmission line, low voltage level and consumers. The criteria used for analyzing while exploring the available communication technique for automation of power systems are capacity, coverage, security, reliability, accuracy and availability. After exploring communication techniques, researcher is coming with the following suggestion;
Since PLC is using existing infrastructure in electrical power utility for communication, hence, it is a cost effective solution and it offers a wide coverage. However, it impaired by signal distortion, noise and capacity limitation challenges.
Satellite communication is considered as one of the most obvious available communication technology for remote monitoring because of its large coverage and possibility of rapid installation. However, it suffers with the problem with delay and operational cost.
The Optical fiber communication method has many advantages such as high capacity, immunity characteristics for EMI, increase signal security etc. But, cost of installing new optic fiber communication infrastructure is expensive however; this constraint is overcome by the advantages offered.
70
Wireless communication appears to be an attractive option considering its coverage in the country and the strong competition for business and it has already been used for power system automation in the automation of read metering. It is cost effective solution. However, it suffers with the vital issues of operational costs, capacity, security, and coverage.
Therefore, after presenting the above communication media, researcher suggests PLC and Optical Fiber as the most effective communication media in automation of power systems from generation point to end users. Optical fiber can be used as back haul network because it posses several advantages such as high bandwidth, increase signal security etc while PLC can provide the last mile connectivity since TANESCO own the power network to be used for PLC. Also, Wireless network can be used when PLC systems are not in place.
71
CHAPTER FIVE
CONCEPTS OF AUTOMATION OF POWER SYSTEMS
Basically, Power System Automation allows for automatic, computerized control of utility power network facilities with little or no human intervention. Power System
Automation offers utility companies ability to automatically monitor, coordinate and remotely operate devices such as re-closers and sectionalizing switches. Automation system allows power generation, transmission systems and distribution system to be monitored and controlled from a remote location, even if they were far away from the systems location.
In figure 5.1, at the power generations, automation includes the ability to check generated reactive power, active power, power factors, root mean square value of voltage and current, frequency variation etc. At the Transmission line, automation includes the ability to check fault location, circuit breaker, bus-bar isolation, line isolation, falling of power poles etc. At the transformers, automation includes the ability to check oil level, over-current, voltage control, transformer trip etc. At the substations and feeders, automation includes supervisory control of circuit breakers, load tap changers, regulators, re-closers, sectionalizers, switches and substation capacitor banks etc. Remote data acquisition is required in order to achieve effective use of the supervisory control function. At the end users location, automation includes the ability to remotely: read meters, connect/disconnect services and control consumer loads etc.
72
Data is collected along the power network, transferring data to a regional control centre and then to central control centre, displaying the data and carrying out analysis for control decision and improvement in system operation. In automation to the level of distribution network due to the increase in network activities, the primary monitoring and control centre need to be at district level as shown in figure 5.1.
In figure 5.1, the electrical parameters (e.g. root mean square values of voltage and current, frequency, active power etc.) and other various quantities (e.g. switch status, winding temperature, oil level, over-current, overload, meter readings etc.) are recorded in the field at the power stations, transformers, substations, feeders and consumer location using a data acquisition device called Remote Terminal Unit (RTU). These quantities are transmitted to a regional computer control and then to central computer control through a communication media. In this study, the researcher suggests PLCs and
Optical Fibers as the most effective communication media in automation of power systems from generation point to end users. Optical fiber can be used as back haul network because it posses several advantages such as high bandwidth, increase signal security etc while PLC can provide the last mile connectivity since TANESCO own the power network to be used for PLC. Also, Wireless network can be used when PLC systems are not in place.
.Data is acquired by means of appropriate transducer for the applicable quantity like current transformers, voltage transformers to collect required information status. The acquired data is processed packaged and transmitted to respective control and monitoring centre, where it is displayed using a Graphic User Interface. In the event of a
73 system quantity crossing a pre-defined threshold, an alarm is generated at the locality and/or at the control centre. The necessary action will then be determined by the computer and the command will then be sent to the RTU to be executed.
Power Flow Monitoring & Control Remote monitoring Signals & Control stations
Reactive power generated, Power station Active power generated, 10.5kV Frequency generated, Root mean square value of current and voltage etc
Communication media (PLC & Optical Fiber) Transformer 10.5 / 220kV
Line isolation, Bus-bar isolation, circuit breaker, fault location, earth surface, etc Transmission system District Control Regional Centre substations Transformer trip, Over-current, feeders feeders Fuel level, voltage control, Transformer turn ratio, magnetizing 220/ 33kV inductance, capacitance, impedance etc Regional Control Centre
Central Control Transformer centre 33/11kV
Distribution system
Transformer 11/ 0.4kV
Meter Readings, End connection/disconnection Users / services, overload, Illegal load use of electricity
Figure 5.1: The concepts of automation of power system
74
The importance and significance of collecting data along power network and storing data in data storage facility systematically (Monitoring system) was emphasized in this work. It is through monitoring system that utility company can capture data, process and disseminate information in a systematic way for the intended purposes. This forms the heart of automation to achieve optimal power system performance and effective energy management and to reduce operational costs and provides better service to consumers.
The useful functions of the network monitoring system is to provide alarm to operator and register when something is wrong, slow or failing systems and notifies the utility operator such occurrences. Typical facts that network monitoring should provide alert to a utility operator includes system overload, over-current, transformer trip, transformer oil level, lost network connections, power outages etc. Hence, Significance of network monitoring in network management is pegged on three goals in network management: perform monitoring, fault monitoring and account monitoring. It will assist in finding network trends and locate network problems quickly.
Therefore, due to advancement in the communication technology, ensures that information and status of network elements and control signals can be transported, processed, displayed/ acted on reliable for remote operation manually or automatic.
Therefore, automation is no longer for operation of power stations only but can be extended to cover transmission system, substation and distribution system reliably.
Automation ensures self-healing power system that responds rapidly to real-time events with appropriate action. Furthermore, automation of power system facilitates the power
75 system to operate in best optimal way, based on accurate information provided in a timely manner to decision making application and devices.
76
CHAPTER SIX
CONCLUSIONS, RECOMMENDATIONS AND FUTURE RESEARCHES
5.1 Conclusions
The study was aimed to determine the concepts of automation of management of power systems from generation points to end users. The study established the challenges involved in automation of power systems. Also, four communication technologies
(PLCs, Optical fiber, Satellite and Wireless communications) were identified in this study; two of them PLCs and Optical fiber were selected as best appropriating communication technologies for automation of power systems from generation points to end users. The criteria used to select PLCs and Optical fibers are capacity, coverage, reliability, accuracy and availability. Two monitoring tools ETAP and PSS/E software were identified in this study. PSS/E tool was selected as supporting monitoring tools in automation of power systems and the criterion used to select this tool is availability although there could be appropriate, affordability, flexibility, user friendly, easy to use and feature rich.
The study established challenges involved in automation of power system. Those challenges established are important to take care before establishing any automatic power systems.
Also, the study discovered that, monitoring systems/tools are important in automation of power systems, because system operator at a control centre in utility company can view
77 online information about power quality, demand and flow by using appropriate monitoring system. He/she can perform real- time monitoring of network services and devices effectively and efficiently.
Lastly, the study found that, there is no single communication media to use in automation of power system. Utility companies have been used combination of more than one technology to get reliable, effectively and accurate communication and provide better services to consumers. This is because the available communication systems such as PLC, Optical fiber, Satellite and Wireless communications, all have got advantages and challenges and depend on each other to get reliable communication. It is being recommended to use optical fiber as back haul network and PLCs to provide the last mile connectivity since power utility companies own the power network to be used for
PLCs. Also, wireless network could be used when PLC systems are not in place.
5.2 Recommendations
Researcher recommended to utility companies such as TANESCO to use automation of power system in its whole network i.e. from generation to distribution network to reduce number of activities as everything will be done automatically and will provide better services to consumers. As power network is large and more complex thus, the use of automation facilitates reduction of operational cost and the need for staffs to make long journey to survey the power network.
78
It also noted that the use of automation provides better real time monitoring and remote control of system elements such as substations, intelligent devices, power lines, capacitor banks, feeder switches, fault analyzers and other physical facilities.
It is further recommended to use automation of power system to offer remote supervision and control of switches, such as pole mounted switches and pad-mounted switchgears on medium voltage distribution networks. It can also offer automatic isolation of faulty sections, which allows quick and accurate recovery of a stable power supply, and reduces the out of service areas by unit of distribution sections.
5.3 Future researches
Below are the future research areas of this study;
a) Investigate how PLC system can be used for services application such as Smart
grid (Automatic Meter Reading, Network grid management, home automation
and improving power quality monitoring).
b) The future of ICT for power system: challenges and security.
c) Computer Aided Monitoring and Control of Distribution Transformers.
d) Substation and Feeder Level Automation; Indigenous Auto Reclosures and
Sectionalizers, Intelligent Electronic Devices (IEDs).
79
REFERENCES
Ackerman.W .J , (2002), “The Impact of IEDs on the Design of Systems Used for
Operation and Control of Power Systems”, Power System Management and Control
Conference, 17-19 April 2002.
Ahmed, M. M. , Soo ,W.L. , Hanafiah, M. A. M. and Ghani, M. R. A.
“Development of customized distribution automation system for secure fault isolation in low voltage distribution”, University Technical Malaysia Melaka (UTeM) ,Malaysia.
Azadeh A., Tarverdian S. (2007), “Integration of genetic algorithm, computer simulation and design of experiments for forecasting electrical energy consumption”,
Energy Policy, Vol. 35, pp. 5229- 41, 2007.
Arivus, (2009), “OFDM-Based high Speed Narrowband PLC”, Approved for Smart
Metering and Smart Grids, 2009.
Bassett. D, Clinard. K, Grainger. J, Purucker. S and Ward. D (1988), “Tutorial course: Distribution Automation‟‟, IEEE Tutorial publication 88EH0280-8-PWR, 1988.
Belton V. and Stewart T. J. (2002), “Multiple criteria decision analysis”, An integrated approach. Kluwer Academic Pub., Norwell, MA2002.
Brown .D.L, Skeen. J. W, Daryani. P, Rahimi. F.A, (1991), “Prospects for
Distribution Automation at Pacific Gas & Electric Company”, IEEE Transactions on
Power Delivery, vol. 6, No. 4, October 1991.
Bunch. J.B, (1984), “Guidelines for Evaluating Distribution Automation”, EPRI Report
EL-3728, 1984.
Carvalho P. M. S. and Ferreira L. A. F. M. (2005), “Distribution quality of service and reliability optimal design”, IEEE Trans. on PS, Vol. 20, No. 4, pp. 2086-92, 2005.
80
Comry, A.L, & Lee, H.B (1992), “A first course in factor analysis”. 2nd ED Hillsdale,
N.J, Lawrence Erlbaum, 1992.
Clemen R. T. and Reilly T. (2001), “Making Hard Decisions”, Duxbury Thomson
Learning, CA, US, 2001.
Chowdhury A. A. and Custer D. E. (2005) , “A value based probabilistic approach to designing urban distribution systems”, Electrical Power and Energy Systems, Vol. 27, pp. 647–655, 2005.
David Kreiss, Kreiss Johnson Technologies (2003), “Non-operational data: The untapped value of substation automation” Utility Automation &Engineering T&D,
September, 2003.
Dobson. I, Dong. Y and Kezunovic .M,, „Impact of Extreme Weather on Power System
Blackouts an Forced Outage”, USA.
Evans. N and Newton. C. (2009), “T & D automation building blocks (are) the embryonic and emergent stages of what is today termed the Smart Intelligent Grid.”
Motorola, Inc. 1301 E. Algonquin Road, Schaumburg, Illinois 60196 U.S.A, 2009.
Fereidunian.A, Lesani .H, Lucas .C, Lehtonen .M and Nordman .M.M (2006), “A
Systems Approach to Information Technology (IT) Infrastructure Design for Utility
Management Automation Systems”, Iranian Journal of Electrical & Electronic
Engineering, Vol. 2, Nos. 3 & 4, July, 2006.
Goodman. F (2004), “Technical and system requirements for advanced distribution automation”, Electric Power Research Institute Technical Report 1010915, June, 2004.
Gilbert, H (2006), “Understanding Broadband over Power line”, Auerbach Publishers,
Now York.
81
Gupta R.P and Varma. R.K (2005) , “Power Distribution Automation: Present
Status‟‟, 2005.
Gupta R.P, Sachchidanand,and Srivastava. S.C, (2003), "Automated Verses
Conventional Distribution System", Proceedings of the Third International Conference on Power and Energy Systems EuroPES-2003, Spain, September, 2003.
Gungor. V.C, Lambert. F.C (2006), “Computer Networks” United States, 2006.
Honary. B, Pavlidou. N, Vinck. A.J.H,and Yazdani. J, (2003) “Power line communications: state of the art and future trends”, IEEE Communications Magazine,
April, 2003.
Hrasnica .H , Haidine .A, Lehnert. R , (2004) “Broadband Powerline Communications
Network Design”, John Wiley & Sons , England, 2004.
Higgins N, Vyatkin V, Nair C and Schwarz K ,(2008), “Distributed Power System
Automation with IEC 61850, IEC 61499 and Intelligent Control” 2008.
International Electrotechnical Commission (IEC, 2004-04), “Hydroelectric power plant automation”, Guide for computer- based control, first Edition Geneva,
Switzerland.
James Northcote-Green and Robert Wilson (2007), “Control and Automation of
Electric Power Distribution System”.
Jang.H.S, Qureshi.M, Raza. A, Kumar.D,Kim. S.S, Song.U.S, Park.M.W,
Yang,.H.S, Park.B.S ,(2008), “A Survey of Communication Network Paradigms for
Substation Automation” , IEEE, 2008.
John Mc Donald (2006), “LADWP Taps Non Operational Data with Power System
Data Mart Project”, P & E Magazine, March/April 2006.
82
John J.Metzner, Kwang Y.Lee and Myongsoo Kim, (2008), “Design and implementation of last-mile optical network for distribution automation”, IEEE
Transactions on power delivery paper no.TPWRD-00599-2008, June 2008.
Kyirul A .B B ( 2005), Remote Terminal Unit for distribution automation system,
Malaysia, 2005.
Lakshmi Prasanna. M and Gayati. A, “SCADA Technology” Sri Sai institute of technology and science.
Lee.O.G, (2002), “Focus: Power grid access,” Network Magazine, 2002.
Marihart D. J. (2000), “Communication Technology Guidelines for EMS/SCADA
Systems”, IEEE Trans. On PWRD, Vol. 16, No. 2, pp. 181-188, April 2000.
Melovic D. and Strbac G.(2003), “Statistical Model for Design of Distribution
Network”, Proc. Of PowerTech, Bologna, Italy, June, 2003.
National Communication System(NCS),(2004), Technical Information Bulletin 04-1,
Supervisory Control and Data Acquisition (SCADA) Systems, Communication technologies, Inc. Virginia 20151, 2004.
Network Protection &Automation Guide, (2002), “Distribution System Automation,
2002.
Palak Parikh, “ES 586b Course Project Report: Distribution System Automation”.
Pavlidou. N, Vinck. A.J.H, Yazdani. J, Honary. B, (2003) “Power line communications: state of the art and future trends”, IEEE Communications Magazine, April, 2003.
Peppard. J and Ward. J, (2004), “Strategic planning for information systems”, John Wiley and Sons Ltd, Chichester, England, 2004.
83
Public interest energy research (Pier) draft project report (2008), “Benefits and challenges of distribution automation (DA)”, Use case scenarios and assessments of DA functions, USA, 2008.
Ralph Mackiewicz (2003), “The Impact of Standardized Models, Programming
Interfaces, and Protocol on Substations” SISCO Inc, USA, 2003.
Roper,M and Millar, L, 1999, “A study programme; Understanding Compute”
“Managing public sector records; ”, International Records Management Trust, United kingdom, 1999.
Simon H. A. (1957), “Models of man: social and rational” , John Wiley and Sons, Inc.,
New York. 1957.
Thiyagarajan & Palanivel (2010), “An efficient monitoring of substations using microcontroller based monitoring system, July, 2010.
Wimmer, R.D, & Dominick, J.R 2000, Mass media research; an introduction, 6th ED,
NY, Wadsworth Publishing, 2000.
ON LINE REFERENCES www.gcflearnfree.org/computerbasics/1 retrieved on 22th April, 2012 www.wikipedia.org/wiki/intranet retrieved on 10th April, 2012 www.compnetworking.about.com retrieved on 18th April, 2012
84
APPENDIX I
Interview Guide for Challenges Facing in Automation of Power Systems
Dear Madam/ Sir
I am a Master of Science in Telecommunications Engineering student at University of
Dodoma. In fulfillment of the dissertation requirements, I am conducting a study entitled
“Automation of Electric Power Supply Systems: TANESCO Case Study”. The specific objective of this study is to establish challenges facing automation of power system.
Your cooperation in answering the following question is highly appreciated.
Thank you.
General Question
1. With respect to your SCADA system, what are the challenges existing in
automation of power system.
………………………………………………………………………………
85