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A computer hierarchy structure for electric power utility
Computers ind. Engng Vol. 21, Nos 1-4, pp. 507-511, 1991 Printed in Great Britain. All rights reserved
0360-8352/91 $3.00+0.00 Copyright © 1991 Pergamon Press plc
& Computer H i e r a r c h y S t r u c t u r e
for Blectrio
Power U t i l i t y
Kamren K. Kamzanl Control Processing Unlimited, Inc. Louisville, Kentucky 40207
&li K. Kamrani University o f Louisville Louisville, Kentucky 4 0 2 9 2
Dr. J u l i u s P. Wong University of Louisville Louisville~ K e n t u c k y 40292
Dr. Hamid R. P a z s e e i University of Louisville Louisville, K e n t u c k y 40292
second method, information of the controlled system is directly feed to the computer by proper interfacing devices. The data analysis, and calculation of deciding factors is done by computer. It will recommend the proper action for the proper controlling device to the human operator and the controlling of devices (e.g. relays in switching centers) is performed by the operator. Computers in third method will receive data directly from the process, and it will both recommend actions required to operator, and send some controlling commands to the controlling devices . The operator in this method will adjust the devices affected by the action taken by the computer. The final method is the fully automated control. In this method, computer will receive all the required data from the process, and after performing necessary analysis, it will automatically generate the proper controlling command to the process. The operator is responsible for monitoring the process and updating the required controlling algorithms. Figure 1 illustrates a layout of automatic control of power systems. Electric power system structure is reviewed in the second section of this article. The third section will discuss the computer process control (CPC) with proper interfacing functions, distributive process control (DPC), and hierarchial computer control (HCC) with description of each level in the hierarchy. Finally, the computer controlled structure of power system is proposed in the hierarchial format. The supporting business functions in power utility is also discussed.
Abstract This paper presents a layout for a hierarchial computer system structure for electric power utility. The pyramidal control structure or hierarchial computer system is divided into four levels. These levels include: i) Corporate computer, 2) Factory computers, 3) Center computers, and 4) Cell/Remote computers. The paper also discusses the domain and the components of the proposed structure.
Introduction The consistency, flexibility and real time control of computer assisted devices have lead electric utility companies to further consider the use of computers to monitor, control, and maintain the power system facilities and office functions. Since 1970, engineers have sought ways to use computer to better control the functions of electric power utility companies and more recently the use of microcomputers to control substations. An electric power system consists of the power generating plants, power transmission lines, distribution lines, the respective transformers substations and, load centers. The prime objective of computer controlled power system is the status and performance monitoring of the system and its operation at optimum level with regard to quality and quantity of the generated power, cost, and the benefits of various services available to customers[l]. The process of computerizing does not indicate the total elimination of human from the operation process. There are four methods of control using computers. First method is when computer recommends the path of actions based on the information given to the computer, gathered and developed by operators. Final decision and the adjustment to the process is done by operators. In
An overview of Electric Power System 8tructure An electrical power system be defined as a system interconnected subsystems which 507
can of
508
Proceedings of the 13th Annual Conference on Computers and Industrial Engineering
convert non-electrical energy into electrical form, transport it over a great distance and transform it into a specific form for the user. Power systems must be reliable, safe, efficient, economical, and nonhazardous to environment. The main parts of a power system include: l)Generation: Generators represent the source of electrical energy and they are the power conversion devices which convert the non-electrical energy into electrical form. Power generated by generators are ranged form 100KW to 1300MW with voltages ranging form 480V to 30kV. Power for electric power system may be generated by several major methods. One method is the generation with thermal power stations which utilize the energy of fuel. Another method is the hydro power stations, which utilize water power. There are also methods which utilize both thermal power and water power. Other methods are also available. 2)Transmission: Power is moved from generation sites to the areas of use, using transmission lines. The voltages on these lines can be as large as 765KV. Device that links the generator to transmission lines is called transformer, since it transforms the lower generation voltages to the higher transmission voltages. As the voltage increases, the current is simultaneously decrease. There are two basic transmission designs: underground, and overhead. The overhead design is more common. These types of lines can cover distances up to hundreds of kilometers. Factors such as weather, particularly lighting must be considered during the design. 3)Distribution: Transmission lines deliver their power to substations, where voltage is stepped down. Individual circuits extend to the customers from the substations. These circuits are primary distribution points. There are two basic design for primary distribution points. Radial design which allows the flow of power in only one direction, from substations to customers, and loop design where customers receive power from more than one direction. At secondary distribution points, voltage is stepped down to proper utilization level. An example of secondary distribution point is the pole transformer. 4)Utilization: The power generated may be used by 3 different types of consumer: i) lighting and domestic needs, ii) industrial motors, and iii) energizing various furnaces, kilns, and plants[2,3]. Process Control Computer
The term computer process control (CPC) is defined as the use of digital computers to monitor and control industrial processes. Objectives of automating and computerizing the process are generalized into several area. The computer system maximizes the availability and reliability. It minimizes operating and maintenance requirements. It optimized capacity and quality. There are also some intangible benefits associated with computer system, which are its flexibility for future expansion and the valuable operational information provided to the user for decision making[4,5]. Figure 2 illustrates the general data structure for CPC implementation. Analog-to-digital and digitalto-analog devices are used for proper interfacing of the process to the computer. Analog-to-digital convertor (ADC) devices will convert the incoming analog data from the device and convert these information to digital forms which is recognized by the digital computer and digital-toanalog convertor (DAC) devices are used to translate and transmit the required action from computer to process. Three methods of CPC are often used. The logic for preplanned method is designed to consider all possible situations. In second method proper controlling variables are calculated and applied to the process directly by the computer. Direct digital control method require ADC, DAC and proper sensors. In the third and final method, computer is used to maintain the optimum level of performance. Figure 3 illustrates the hierarchy of these three methods. Distributive process control (DPC) is a form of instrumentation that is used to control the process of large systems[6]. Two major work areas considered in a DPC system are the central control station and remotely located controlled stations where the information is transmitted between these two locations continuously. The central control station is equipped with devices to monitor process conditions and to manipulate the control functions for the process. The information transmitted from the processing area are displayed on a cathode ray tube and the required changed are made by the keyboard. The hardware at central control area consists of computer, video display, system keyboard, and peripheral devices such as disks and printers. The controlling module for process area of DPC measures the analog signals of controlled variable with required feedback information (discrete inputs) and it will generate the proper output signal to interfacing devices that can change
Kamrani et al.: Electric Power Utility
the condition of the process. The required hardware at remote area includes power supply, input/output handling devices, and proper devices for computation means. The communication paths include cables connecting each remote location to the central controller or a data highway connecting all the remote stations to each other and the central controller. Data highways allow the DPC to live up to its name, allowing the distribution of control function and information through out the entire plant. The length of data highway may vary up to 5 miles depending on the traffic capability and required transmission speed. Fiber optics cables are the most recent innovation for data transmission. These cables can carry more information and they are much l i g h t e r than coaxial cables. Due to their design features, fiber optics will eliminate problems such as electromagnetic and frequency interferences. They are also safe in flammable environment. Computer control system reliability depends both on reliable hardware and reliable software. This has resulted in centralizing the development of computer software for process control. The task is to break down the software into independent pieces. This top-down process task must continue until the piece is small enough to be implemented. After implementation, pieces are tested, put together, and tested again. This process continues until all pieces are put together. The steps for design and implementation of reliable software for process control can be summarized as: architectural design interface design, detail design and coding, integration and system test planning.
Hierarchial
509
tasks of each level in hierarchial structure may be grouped into three levels: Monitor and Control Levels: Control of each operating unit which uses material and energy. These operating units are controlled by the supervisory functions from upper levels, to perform at maximum efficiency. The control within the level reacts to alarms and emergencies within the area of its control. The functional tasks of first level is fixed and it will not require human interaction, but functions within the rest of the levels will require human interaction. Supervisory and Area Control Leve]: This level performs supervisory task to optimize the operation, coordinate system and determining the local production level. The supervisory task assures the limit on the material and energy used. It also responds to alarms and any other emergencies of the units under its control by shutting down or other actions. These tasks are performed at level 3. Production schedulinq, ODerationa] Manaaements, and Intracompany Communications Level: The overall firm production control and system optimization systems is done in this level. This level decides the production rate based on optimum combination of demanded time, energy, material, and cost based on management, decision and customer needs. The reliability assurance and availability of systems are the functions of all levels. These tasks are based on fault detection redundancy and other built in methods which are included within the levels during the design and implementation. Figure 4 illustrate the hierarchial computer control.
Computer C o n t r o l
Computer networking to the process has been greatly simplified due to the development of distributed digital control system. Based on this, a hierarchial control structure can be developed in which upper level computers depends on lower level devices for process monitoring and data collection, and lower level systems depends on the higher level systems for sophisticated controlling functions for plant optimization. Using this structure, computers in different levels can combine the production, scheduling and management functions with process control functions. In large systems, each level is controlled by separate computers, but the control of two or more levels in small systems can be performed by one large computer. The
Computer H i e r a r c h y S t r u c t u r e E l e c t r i c Power U t i l i t y
for
The proposed hierarchy structure is illustrated in Figure 5. The center computers for transmission and power plant linked to a factory computer since the conditions affecting transmission will also affect the function in power plant. The factory computer performs the task to coordinate the processes for power plants and transmission. Data processing, daily, weekly, and monthly reports for plants are developed in this computer system. The computer system also monitor and perform the business related functions at plant level. The factory computer is capable of handling large data processing for complex transmission and power generation
510
Proceedings of the 13th Annual Conference on Computers and Industrial Engineering
process activities. Information concerning distribution is processed in center and cell/remote computers. Managerial tasks and information are directly transmitted to corporate computer. The corporate computer collects data from factory computer and summarizes the plant operations and performance for the entire firm. Other functions performed by corporate computer are : customer information, customer billing , trouble call management,transfer load management,feeder line section, load survey, report generation, strategic p l a n n i n g , resource management, electronic mail service, and finance. Figure 6 illustrate the corporate computer and its office network. Cell/remote microcomputers are responsible for controlling the process. They are also capable of transmitting all or a portion of data to upper levels. The processes include : Generation: Thermal/hydro, cooling towers, feed water, evaporator, heat exchange, turbine, generator speed, voltage, frequency, miscellaneous temperature/flow/pressure controls. Transmission: Pre/post fault recording, operator-event recording, event time tagging, feeder load monitoring, feeder harmonic/noise recording, remote transfer of fault recording, protective relay monitoring, high voltage switch gear monitoring, voltage on the bus, current draw, power flow, and weather information. Distribution: Pre/post fault recording, operator-event recording, event time tagging, feeder load monitoring, feeder harmonic/noise recording, remote transfer of fault recording, protective relay monitoring, voltage, current draw, real power flow, reactive power flow power factor, weather information, medium voltage switch gear status, and monitoring and control. Center minicomputers perform supervisory control and optimization of the controlled activities of microcomputers. These computers are also capable of transmitting data to factory computer for more information. Functions in this level include : Generation : Plant wide data acquisition, display, monitoring, annunciation, perform data logging, perform long term data archival, automatic testing, automatic turbine start-up, program down load capability, and generation power optimization. Transmission: Alarm management, automatic generation control (AGC) , state estimation, contingencies, buy/sell negotiation, unit
commitment, load flow, load forecasting, capacity calculation, power flow optimization, program down load capability, switch gear control, and protective relay remote setting. Distribution: Monitoring activities: distribution load management, alarm management, time data gathering, power system event logging, geographical mapping, time/event logging, and program down load capability. Calculation activities: state estimation and optimization, security analysis, power flow, power quality monitoring, and feeder analysis. All computes within the hierarchy should be able to communicate with each other. Local area networks (LANs) are used for transmitting the information within these levels. A LAN usually contains four major components, transmission path, interface between the path and protocol logic, protocol logic control components, and the work station. Conclusion
Power utility operation can be improved by automating the processes such as security and telecommunication, computer aided designs, plant instrumentation and control systems and computer aided maintenance. The productivity, analysis and transmission of information by power utility management and supervisory personnel can also be improved with office automation services. Some of the critical activity and tasks for design and implementation of this computerized system include: i. Development of design strategy: Who needs plant information? What types of information do they need? How is the information delivered? What are the operator-machine interface requirements? What power utility processes require optimization? 2. Establishing system architecture: Identify the process and method for optimization, identify plant requirements, determine the best architecture for application, development plant-wide control strategy and relational data base. 3. System design and specification: Generation of control strategy, distribution and transmission control strategy, typical control circuits, control panel configuration standards, standardized equipment and selection of reliable and knowledgeable vendors. 4. Communication: Local area network protocol and topologies, data exchange specification, data base compatibilities. 5. Start-up support: System
Kamrani
e!
a/.: Electric Power Utility
511
acceptance test procedure, vendor field support, coordinating test schedule with production, involve the user, staff training support.
Oommm, Co~tr~
Stet~
~
References
1. V. A. Venikov, "Cybernetics in Electric Power Systems," 1978, Mar Publishers, Moscow. 2. C. A. Gross, "Power System Analysis," second edition, John Wily & Sons, 1986. 3. G. L. Kusic, "Computer-Aided Power Systems Analysis," Prentice-Hall, 1986. 4. "Using Cost-Benefit Analysis to Select Digital Control System", Instrument Society of America, 1978. 5. B. G. Liptak~ and K. Venczel, "Process Control, Instrument Engineers' Handbook", Chilton Book Company, 1989. 6. K. Kamrani, A. Kamrani, and H. Parsaei,"Distributive Computer Control Design for Electric Utility," Proceeding of the Fifth International Power System Conference, November 1990, Tehran, Iran.
u,,=on.~l,m
$yet|m AoJuot Co,mna.a*
l°] ~;~t ~OIt@l oo..:~
l.x~.
1 Figture 3. CPC Hierarchy |
- kurd.
•
,
Nmlnnsl r|tl~q
~'~1
°
mmanlll,etlan
I
t
.......
I
Yi~e 4. Hierarchial Control Functions
Computer
~
P,l^,
I
um~i~,
7i~e S. Computer Hierarchy Structure for Electric Power Utility
F i g u r e i. Layout of Automatic control of Power Systems Co, D = e m Comeu**,
O~era~
Data Diwtril~utad Rel~t~at D a t a B~ee r"
~ £ g u r o 2 . General Data Structure for CPC Implementation
F I ~ E O 6. Corporate Computer and its Office Network
0360-8352/91 $3.00+0.00 Copyright © 1991 Pergamon Press plc
& Computer H i e r a r c h y S t r u c t u r e
for Blectrio
Power U t i l i t y
Kamren K. Kamzanl Control Processing Unlimited, Inc. Louisville, Kentucky 40207
&li K. Kamrani University o f Louisville Louisville, Kentucky 4 0 2 9 2
Dr. J u l i u s P. Wong University of Louisville Louisville~ K e n t u c k y 40292
Dr. Hamid R. P a z s e e i University of Louisville Louisville, K e n t u c k y 40292
second method, information of the controlled system is directly feed to the computer by proper interfacing devices. The data analysis, and calculation of deciding factors is done by computer. It will recommend the proper action for the proper controlling device to the human operator and the controlling of devices (e.g. relays in switching centers) is performed by the operator. Computers in third method will receive data directly from the process, and it will both recommend actions required to operator, and send some controlling commands to the controlling devices . The operator in this method will adjust the devices affected by the action taken by the computer. The final method is the fully automated control. In this method, computer will receive all the required data from the process, and after performing necessary analysis, it will automatically generate the proper controlling command to the process. The operator is responsible for monitoring the process and updating the required controlling algorithms. Figure 1 illustrates a layout of automatic control of power systems. Electric power system structure is reviewed in the second section of this article. The third section will discuss the computer process control (CPC) with proper interfacing functions, distributive process control (DPC), and hierarchial computer control (HCC) with description of each level in the hierarchy. Finally, the computer controlled structure of power system is proposed in the hierarchial format. The supporting business functions in power utility is also discussed.
Abstract This paper presents a layout for a hierarchial computer system structure for electric power utility. The pyramidal control structure or hierarchial computer system is divided into four levels. These levels include: i) Corporate computer, 2) Factory computers, 3) Center computers, and 4) Cell/Remote computers. The paper also discusses the domain and the components of the proposed structure.
Introduction The consistency, flexibility and real time control of computer assisted devices have lead electric utility companies to further consider the use of computers to monitor, control, and maintain the power system facilities and office functions. Since 1970, engineers have sought ways to use computer to better control the functions of electric power utility companies and more recently the use of microcomputers to control substations. An electric power system consists of the power generating plants, power transmission lines, distribution lines, the respective transformers substations and, load centers. The prime objective of computer controlled power system is the status and performance monitoring of the system and its operation at optimum level with regard to quality and quantity of the generated power, cost, and the benefits of various services available to customers[l]. The process of computerizing does not indicate the total elimination of human from the operation process. There are four methods of control using computers. First method is when computer recommends the path of actions based on the information given to the computer, gathered and developed by operators. Final decision and the adjustment to the process is done by operators. In
An overview of Electric Power System 8tructure An electrical power system be defined as a system interconnected subsystems which 507
can of
508
Proceedings of the 13th Annual Conference on Computers and Industrial Engineering
convert non-electrical energy into electrical form, transport it over a great distance and transform it into a specific form for the user. Power systems must be reliable, safe, efficient, economical, and nonhazardous to environment. The main parts of a power system include: l)Generation: Generators represent the source of electrical energy and they are the power conversion devices which convert the non-electrical energy into electrical form. Power generated by generators are ranged form 100KW to 1300MW with voltages ranging form 480V to 30kV. Power for electric power system may be generated by several major methods. One method is the generation with thermal power stations which utilize the energy of fuel. Another method is the hydro power stations, which utilize water power. There are also methods which utilize both thermal power and water power. Other methods are also available. 2)Transmission: Power is moved from generation sites to the areas of use, using transmission lines. The voltages on these lines can be as large as 765KV. Device that links the generator to transmission lines is called transformer, since it transforms the lower generation voltages to the higher transmission voltages. As the voltage increases, the current is simultaneously decrease. There are two basic transmission designs: underground, and overhead. The overhead design is more common. These types of lines can cover distances up to hundreds of kilometers. Factors such as weather, particularly lighting must be considered during the design. 3)Distribution: Transmission lines deliver their power to substations, where voltage is stepped down. Individual circuits extend to the customers from the substations. These circuits are primary distribution points. There are two basic design for primary distribution points. Radial design which allows the flow of power in only one direction, from substations to customers, and loop design where customers receive power from more than one direction. At secondary distribution points, voltage is stepped down to proper utilization level. An example of secondary distribution point is the pole transformer. 4)Utilization: The power generated may be used by 3 different types of consumer: i) lighting and domestic needs, ii) industrial motors, and iii) energizing various furnaces, kilns, and plants[2,3]. Process Control Computer
The term computer process control (CPC) is defined as the use of digital computers to monitor and control industrial processes. Objectives of automating and computerizing the process are generalized into several area. The computer system maximizes the availability and reliability. It minimizes operating and maintenance requirements. It optimized capacity and quality. There are also some intangible benefits associated with computer system, which are its flexibility for future expansion and the valuable operational information provided to the user for decision making[4,5]. Figure 2 illustrates the general data structure for CPC implementation. Analog-to-digital and digitalto-analog devices are used for proper interfacing of the process to the computer. Analog-to-digital convertor (ADC) devices will convert the incoming analog data from the device and convert these information to digital forms which is recognized by the digital computer and digital-toanalog convertor (DAC) devices are used to translate and transmit the required action from computer to process. Three methods of CPC are often used. The logic for preplanned method is designed to consider all possible situations. In second method proper controlling variables are calculated and applied to the process directly by the computer. Direct digital control method require ADC, DAC and proper sensors. In the third and final method, computer is used to maintain the optimum level of performance. Figure 3 illustrates the hierarchy of these three methods. Distributive process control (DPC) is a form of instrumentation that is used to control the process of large systems[6]. Two major work areas considered in a DPC system are the central control station and remotely located controlled stations where the information is transmitted between these two locations continuously. The central control station is equipped with devices to monitor process conditions and to manipulate the control functions for the process. The information transmitted from the processing area are displayed on a cathode ray tube and the required changed are made by the keyboard. The hardware at central control area consists of computer, video display, system keyboard, and peripheral devices such as disks and printers. The controlling module for process area of DPC measures the analog signals of controlled variable with required feedback information (discrete inputs) and it will generate the proper output signal to interfacing devices that can change
Kamrani et al.: Electric Power Utility
the condition of the process. The required hardware at remote area includes power supply, input/output handling devices, and proper devices for computation means. The communication paths include cables connecting each remote location to the central controller or a data highway connecting all the remote stations to each other and the central controller. Data highways allow the DPC to live up to its name, allowing the distribution of control function and information through out the entire plant. The length of data highway may vary up to 5 miles depending on the traffic capability and required transmission speed. Fiber optics cables are the most recent innovation for data transmission. These cables can carry more information and they are much l i g h t e r than coaxial cables. Due to their design features, fiber optics will eliminate problems such as electromagnetic and frequency interferences. They are also safe in flammable environment. Computer control system reliability depends both on reliable hardware and reliable software. This has resulted in centralizing the development of computer software for process control. The task is to break down the software into independent pieces. This top-down process task must continue until the piece is small enough to be implemented. After implementation, pieces are tested, put together, and tested again. This process continues until all pieces are put together. The steps for design and implementation of reliable software for process control can be summarized as: architectural design interface design, detail design and coding, integration and system test planning.
Hierarchial
509
tasks of each level in hierarchial structure may be grouped into three levels: Monitor and Control Levels: Control of each operating unit which uses material and energy. These operating units are controlled by the supervisory functions from upper levels, to perform at maximum efficiency. The control within the level reacts to alarms and emergencies within the area of its control. The functional tasks of first level is fixed and it will not require human interaction, but functions within the rest of the levels will require human interaction. Supervisory and Area Control Leve]: This level performs supervisory task to optimize the operation, coordinate system and determining the local production level. The supervisory task assures the limit on the material and energy used. It also responds to alarms and any other emergencies of the units under its control by shutting down or other actions. These tasks are performed at level 3. Production schedulinq, ODerationa] Manaaements, and Intracompany Communications Level: The overall firm production control and system optimization systems is done in this level. This level decides the production rate based on optimum combination of demanded time, energy, material, and cost based on management, decision and customer needs. The reliability assurance and availability of systems are the functions of all levels. These tasks are based on fault detection redundancy and other built in methods which are included within the levels during the design and implementation. Figure 4 illustrate the hierarchial computer control.
Computer C o n t r o l
Computer networking to the process has been greatly simplified due to the development of distributed digital control system. Based on this, a hierarchial control structure can be developed in which upper level computers depends on lower level devices for process monitoring and data collection, and lower level systems depends on the higher level systems for sophisticated controlling functions for plant optimization. Using this structure, computers in different levels can combine the production, scheduling and management functions with process control functions. In large systems, each level is controlled by separate computers, but the control of two or more levels in small systems can be performed by one large computer. The
Computer H i e r a r c h y S t r u c t u r e E l e c t r i c Power U t i l i t y
for
The proposed hierarchy structure is illustrated in Figure 5. The center computers for transmission and power plant linked to a factory computer since the conditions affecting transmission will also affect the function in power plant. The factory computer performs the task to coordinate the processes for power plants and transmission. Data processing, daily, weekly, and monthly reports for plants are developed in this computer system. The computer system also monitor and perform the business related functions at plant level. The factory computer is capable of handling large data processing for complex transmission and power generation
510
Proceedings of the 13th Annual Conference on Computers and Industrial Engineering
process activities. Information concerning distribution is processed in center and cell/remote computers. Managerial tasks and information are directly transmitted to corporate computer. The corporate computer collects data from factory computer and summarizes the plant operations and performance for the entire firm. Other functions performed by corporate computer are : customer information, customer billing , trouble call management,transfer load management,feeder line section, load survey, report generation, strategic p l a n n i n g , resource management, electronic mail service, and finance. Figure 6 illustrate the corporate computer and its office network. Cell/remote microcomputers are responsible for controlling the process. They are also capable of transmitting all or a portion of data to upper levels. The processes include : Generation: Thermal/hydro, cooling towers, feed water, evaporator, heat exchange, turbine, generator speed, voltage, frequency, miscellaneous temperature/flow/pressure controls. Transmission: Pre/post fault recording, operator-event recording, event time tagging, feeder load monitoring, feeder harmonic/noise recording, remote transfer of fault recording, protective relay monitoring, high voltage switch gear monitoring, voltage on the bus, current draw, power flow, and weather information. Distribution: Pre/post fault recording, operator-event recording, event time tagging, feeder load monitoring, feeder harmonic/noise recording, remote transfer of fault recording, protective relay monitoring, voltage, current draw, real power flow, reactive power flow power factor, weather information, medium voltage switch gear status, and monitoring and control. Center minicomputers perform supervisory control and optimization of the controlled activities of microcomputers. These computers are also capable of transmitting data to factory computer for more information. Functions in this level include : Generation : Plant wide data acquisition, display, monitoring, annunciation, perform data logging, perform long term data archival, automatic testing, automatic turbine start-up, program down load capability, and generation power optimization. Transmission: Alarm management, automatic generation control (AGC) , state estimation, contingencies, buy/sell negotiation, unit
commitment, load flow, load forecasting, capacity calculation, power flow optimization, program down load capability, switch gear control, and protective relay remote setting. Distribution: Monitoring activities: distribution load management, alarm management, time data gathering, power system event logging, geographical mapping, time/event logging, and program down load capability. Calculation activities: state estimation and optimization, security analysis, power flow, power quality monitoring, and feeder analysis. All computes within the hierarchy should be able to communicate with each other. Local area networks (LANs) are used for transmitting the information within these levels. A LAN usually contains four major components, transmission path, interface between the path and protocol logic, protocol logic control components, and the work station. Conclusion
Power utility operation can be improved by automating the processes such as security and telecommunication, computer aided designs, plant instrumentation and control systems and computer aided maintenance. The productivity, analysis and transmission of information by power utility management and supervisory personnel can also be improved with office automation services. Some of the critical activity and tasks for design and implementation of this computerized system include: i. Development of design strategy: Who needs plant information? What types of information do they need? How is the information delivered? What are the operator-machine interface requirements? What power utility processes require optimization? 2. Establishing system architecture: Identify the process and method for optimization, identify plant requirements, determine the best architecture for application, development plant-wide control strategy and relational data base. 3. System design and specification: Generation of control strategy, distribution and transmission control strategy, typical control circuits, control panel configuration standards, standardized equipment and selection of reliable and knowledgeable vendors. 4. Communication: Local area network protocol and topologies, data exchange specification, data base compatibilities. 5. Start-up support: System
Kamrani
e!
a/.: Electric Power Utility
511
acceptance test procedure, vendor field support, coordinating test schedule with production, involve the user, staff training support.
Oommm, Co~tr~
Stet~
~
References
1. V. A. Venikov, "Cybernetics in Electric Power Systems," 1978, Mar Publishers, Moscow. 2. C. A. Gross, "Power System Analysis," second edition, John Wily & Sons, 1986. 3. G. L. Kusic, "Computer-Aided Power Systems Analysis," Prentice-Hall, 1986. 4. "Using Cost-Benefit Analysis to Select Digital Control System", Instrument Society of America, 1978. 5. B. G. Liptak~ and K. Venczel, "Process Control, Instrument Engineers' Handbook", Chilton Book Company, 1989. 6. K. Kamrani, A. Kamrani, and H. Parsaei,"Distributive Computer Control Design for Electric Utility," Proceeding of the Fifth International Power System Conference, November 1990, Tehran, Iran.
u,,=on.~l,m
$yet|m AoJuot Co,mna.a*
l°] ~;~t ~OIt@l oo..:~
l.x~.
1 Figture 3. CPC Hierarchy |
- kurd.
•
,
Nmlnnsl r|tl~q
~'~1
°
mmanlll,etlan
I
t
.......
I
Yi~e 4. Hierarchial Control Functions
Computer
~
P,l^,
I
um~i~,
7i~e S. Computer Hierarchy Structure for Electric Power Utility
F i g u r e i. Layout of Automatic control of Power Systems Co, D = e m Comeu**,
O~era~
Data Diwtril~utad Rel~t~at D a t a B~ee r"
~ £ g u r o 2 . General Data Structure for CPC Implementation
F I ~ E O 6. Corporate Computer and its Office Network