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Machine Interface for Commonwealth Edison Company’s System Security
NEI,! CONTROL SYSTEH IHTH AN ADVANCED
~\AN/~1ACHINE
INTERFACE FOR
COHNONHEALTH EDISON COHPANY'S SYSTEH SECURITY
T. C. Cihlar Superintendent System Pmver Supply Commonwealth Edison Company Chicago, Illinois United States of America
ABSTRACT Rapid changes are planned and occurring in the method of controlling and monitoring the generation and transmission systems of electric utilities. New control centers containing process digital computers and digital data acquisition systems and control equipment are being constructed. New and improved methods of man -machine interface are being employed . Computers receive data from the electric generation and transmission system and accomp lish control action and operate interface devices to act as a tool for the system dispatcher. These new tools improve the security and economic operation of bu lk power systems. This paper describes the new control system for Commonwealth Edison Company. COHHom,EALTH EDISON COHPANY Before describing the Commonwealth Edison Company System Power Supply Office and operating practices it wou ld be appropriate to describe Commonwealth Edison Company itself so that decisions made in equipment app lication can be better understood. Commonwealth Edison Company serves 2.7 mi lli on customers, principa lly in the northern third of Illin ois . Our service area is about 13,000 square miles with a population of 8 mi lli on . We opera t e generating capacity totaling about 17,000 HH in 15 generating stations and 3 substation peaking unit l ocations. Summer peak l oad in 1974 was approximate l y 13,500 HW. l,e have 23 high vo lt age lines interconnecting with 8 contiguous e l ectric utilities. (Figure 1) Commomvealth Edison Company operates 10,982 HH of fossil fueled units plus 5,480 ~, of nuclear fueled units. In addition to this we share in the Consumers Power-Detroit Edison Ludington pumped storage hydro plant in the amount of 624 ~[W . 1,704 HI-' of the 10, 982~, of fossil units consist of fast start peaking units. Unit sizes range up to 850 ~~ fo r fossi l and 1, 040 ~J for nuclear. Commonwea lt h Edison Company Pm"er Supp l y operations are structured in two levels. The System Power
Supp l y Office is responsible for the integrity and continuity of operation of the interconnected high vo ltage transmission network and the generation supp l ying the network. This office is assisted in the operation of the transmission system by 7 Division Power Supply Offices l ocated in each of the 7 Commonwealth Edison Company Divisions. Each of the Division Power Supp l y Offices is responsible for directing the operation of the transmission, subtransmission, and some e l ements of the distribution systems in the Division a r ea . The Division operation of the transmission system is coordinated with the System Power Supp l y Office. SYSTEH POWER SUPPLY OFFICE A new System Power Supp l y Office bui lding, having a ll new equipment, was put into service in Harch of 1973. Septembe r of 1973 marked the successful completion of avai l abi lity tests of full on -line oper ation of the new equ ipment which provides one of the most advanced computerized dispatch systems operating in the Un it ed States . This was the result of a project begun 3~ years ear li er with Leeds and North rup Company (L&N), supp lier of both equipment and computer programs. The building is a one story reinforced concrete structure with 18" thick walls pr oviding fa ll-out protection. It is approximately 15,000 square feet in area. The layout is shown in Figure 2. Hultip l e sources of e l ectric service to the bui l ding is provided. Norma l feed is from two separate 12KV feed ers through two identical 75KVA solid state inverter systems. The inverters convert A-C to O-C and back to A-C to provide isolation from system disturbances. Each inverter provides power for approximate l y one ha lf of the system, but each is capable of providing power fo r the enti r e bui lding and equipment . A static switch a llows the dispatch equipment to be powered from either in ver ter system without interrupti on during switching . In the event of loss of a ll A-C service from the Commonwealth Edison Company system, a l ead ca lci um battery is capable of maintaining inverter power for one - half hour. This is amp l e time to start an 800 kilowat~ emergency diesel. This diesel is fueled from an underground storage tank which has a 14 day oi l supp l y.
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COMMONWEALTH EDISON COMPANY ELECTRIC SYSTEM
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a EQUIPMENT
LAYOUT
HARDl-.JARE As with any computer control system, there are four basic functions that must be performed. Facilities must be available to gather data, process the information, display the results, and control the process. These functions are provided in our system by the hardware configuration shown in Figure 3. Telemetering The gathering of data is accomplished by L&N Conitel supervisory equipment, receiving data from 70 remote stations located throughout the Commonwealth Edison Company system. The data then pass to the dual LN5500 control computer system for processing, storage, display, and control functions. Converted data are displayed upon the color cathode ray tubes (CRT), printers, mapboard and recorders in the dispatch office. Control sicinals are transmitted to the generating units through the conitel system. Computers The dual LN5500 computer system is used to provide a secure operating environment for the dispatchers. This is accomplished b y maintaining the computers in a master-reserve state. A data link and failover logic allow the reserve computer to assume control in the event of a failure of the master. The data link passes system status information to the reserve computer. Failover logic allows the reserve computer to switch all devices needed for control. These circuits, along with peripheral switching, provide a large degree of flexibility and security in the event of a malfunction of either the software or hardware. The two computers are Xerox Data Systems Sigma 5's. Each has 48,000 words of core memory which is expandable to 64,000 words. InclJded is hardware for floating point arithmetic operation and power failsafe operation. Floating point provides ease and accuracy in the numerous calculations. Power failsafe operation provides for a safe shutdown and automatic restart in the event of a power interruption. Each system has two rapid access data storage (RAD) units. The RAD is a rotating disc type of memory used for bulk data storage. Each RAD is capable of storing six megabytes (1.5 million words) of information. Because of their size, all system programs are stored on RAD, and transferred into core memory when needed.
printer, a special CRT monitor, and keyboard printers are used by programmers for program development and data entry. Consoles The input/output devices used by the dispatcher are mounted in consoles. Data on system status or generation control action is requested through the consoles. There are three consoles in the dispatch office - two for dispatch operations and one for operations planning and studies. The two operating consoles are identical in design and capabilities. The planning console is similar, but restricted in operating capability. There are two data request keyboards on each console, each providing a matrix array of 352 possible selections through 32 pushbuttons. With these, any of the system displays and studies may be displayed on one of the color CRT monitors at each console. There are three CRT's on the operating consoles, one on the planning console. The dispatchers enter data through the CRT with the use of a keyboard which is similar to a typewriter keyboard. The consoles contain the necessary controls for system operation. Two special chart recorders at each operating console are provided for trending of any telemetered or calculated data. In addition to the consoles, chart recorders and a mapboard and printers display the results of the many program calculations to the dispatcher. Mapboard The 10 foot by 40 foot Siemens Corp. dynamic mapboard contains over 56,000 removable tiles, each individually set in a lar'ge steel matrix. The board is controlled through solid-state switching, showing the status of all major transmission lines through the use of lights. This enables the dispatchers to view the overall status of the transmission system at a glance and to detect a change of status almost instantly. Printers The A.B. Dick Company Video jet printers are unique de v ices. They print at a rate of 250 charact e rs per second by squirting a fine stream of ink droplets on paper. The characters are formed by applying an electrostatic charge to each drop and deflecting the stream to produce a dot matrix array. These printers are advantageous for application in an operating environment because of their speed and quietness. Data ACquisition and Control
To increase flexibility and security the Computer system employs peripheral switching. This feature provides the ability to switch any of the peripherals, such as the rapid access data storage units (RADS), card readers, magnetic tapes, line printer or card punch, between the two computers. I/O Devices Various input/output devices are required for man and machine to communicate with each other. The card readers, card punch, magnetic tapes, line
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The dispatch office link to the outside world is the Conitel data acquisition and control s y stem. (Figure 4) This system has one master station communicating with 70 remotes over eight communications circuits. The master station has dual multiplexors and eight normal line buffers. As a security measure, a ninth line buffer is provided as a spare to handle one or more communications circuits in the event of hardware failures of other buffers. The Conitel master addresses each remote in turn, using octal coded addresses. The remote
DIRECT 110
DIRECT 110 XDS SIGMA 5
( TELETYPE ) PERIPHERALS SWITCHES
RAPID ACC ESS STORAG E DEvICE ( 6 MEGABYTE)
FIG . 3 SIMPLIFIED BLOCK DIAGRAM OF DIGITAL DISPATCH SYSTEM
FAILOVER
RELAYS
LINE
PHONE LINE
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FIG . 4 CONIT E L DATA GATHER ING SYS TEM
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responds with data associated for that address. The remot e stations are located at all generating stations, major transmission substations, and the int e rconn ec ti ng tie lin es to eight neighboring utiliti es . Te lemet e r ed data include transmission line, transforme r, and gene ratin g unit megawatts and megava rs, and bus kilovolts. Circuit b reakers are monito red for status and change of status. Accumulat o rs store and telemeter pulses from watthour meters on ge neratin g units, auxiliary power and tie lines each hour.
on predicted weather conditions. This peak load is then entered into the computer Load Forecasting Program. This program calculates and stores a forecast of hourly loads for a seven day period based on pre-set load patterns for that season of the year. The output of this pro g ram is displayed, on demand, on a CRT and is automatically stored for use by other programs. Scheduled Interchange Program There is a program to handle all Scheduled Interchanges with eight utility neighbors of Commonwealth Edison Company. The scheduled interchange is entered b: keyboard into the computer using the CRT display format provided for each neighbor. Information specifying the type of interchange, start time and date, stop time and date, megawatts to be received or delivered, ramp rate, and ramp time is entered by the dispatcher. The computer will store interchan ge schedules up to one year in the future. Pricing information may also be entered throu gh the CRT. This information is processed and stored by the computer for use in automatic generation control, interchange energy accounting, data lo gg ing and various study programs.
Fi gu re 5 details the various scan times for obtaini ng t e le metered data. Wea ther conditions are telemetered from six weather stations l oca ted throu g hout the Commonwealth Edison Company system. Information o n dry-bulb and dew point temp e ratur e , li ght intensity, and wind speed and direction are sensed and telemetered to the dispatch off ice. These data are used for analysis of load patterns. In addition to data gatherillg, the Conitel system is r es ponsible for the system control functions. After gathering the required data, computer prog rams calculate the control action required of each gene ratin g unit for load-frequency control and economic dispatch. The Conitel master receives the request from the computer and transmits it to the prop e r r emote station. The addressed remote receives the control code and initiates the required action by the generating unit.
Unit Commitment
At the generating station, the Conitel remote outputs pulses to the economic generation console (EGC) unit controller for each generating unit. The unit controller is the interface be tween the Conitel System and the governor motor or the electrohydraulic control of the unit. The controller provides security by inhi bi ting output control pulses if a malfunction is detected. Digital setters on the EGC for each ge nerating unit provide for high and low limits which restrain unit loadin g to desired limits. These limits, along with economic control limits, are telemetered through the Conitel System for use in system control pro g rams. In addition to the dual digital system an analog back-up control is provided. This equipment provides a second level of ba ck-up for gene ration control of all generating units in the infrequent event of outages to both digital systems. The analo g control is the "broadcast" type and does not provide economic dispatch. The analog system telemeters the 345KV and 765KV tie line loadin gs . The l38KV tie line loadings and the scheduled net interchange va lues must be entered through manual setters.
Af ter load forecasting and scheduled interchan ge information are available to the computer the unit commitment program can be run. The output of this is a list of the most economical schedule of ge nerators needed to satisfy the hourly load and reserve requirement plus the net interchan ge schedule for a 24 hour period. Security Monitoring Many pro g rams are used to accomplish the constant system monitoring essential to system security. The dispatcher has several means of monitoring the system. There is an array of recording charts displaying such things as total system generation, net system load, scheduled and actual net interchan ge, system frequency, transmission tie lin e loadin gs , area control error, and total output from each generating station. The computer is continuously scanning a va ri e t y of information to be displayed at the push of a button on one of the CRT's. For instance, the dispatcher can display Generation Review for each station. This display indicates for each gene ratin g unit such information as actual and desired gene ration, control status, control limits, and fuel type. Another display is the System Summary showing the amount of system reserve ge neration, area control error, frequency, load, net interchan ge, and t ot al ge neration.
SOFTHARE Extensive software is used in conjunction with the hardware just described. Some of the more important pro g rams and their use by the dispatcher will be discussed. Load Forecasting Program The dispatcher estimates the daily peak load based
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The System Generation Review displays actual loadin g s on all gene rators indiv idually and station totals for the entire Commonwealth Edison Company system. Units on manual control display their loadin g in white while units on automatic dispatch display their loadin g in red.
Automatic Generation Control Automatic gene rati on control is the principal realtime control function of the computer control system. It combines l oad -frequ ency control and economic dispa t ch functions . Th e purpose is to economically r egu late the power output of Commonwealth Edison Company gene rat ors in r es ponse to changes in customer demands, system frequency, interchange schedules, and tie line power flow. Frequency and interchange sch edu l es mus t be kept within pre-determined limit s while maintaining adequate generation reserves. The computer utilizes a periodic real-time program to determine gene r ating res e r ves . If desired r ese r ves are not available, the dispatcher is notified through a larms . Control action is t aken in respons e to the actual and anticipated area contro l error such that the units on automatic regulation wi ll be economically loaded. Th e amount and frequency of control action is increased in accordance with the probability that additional action is required. Any known system changes, such as an interchange schedule or a unit being ramp-loaded, may be fed forward i n anticipation of a control error. The control system has an emergency assist feature which automatically by -passes economic considerations when t he area control e rr or exceeds a predetermined limit and sends control pulses to all units. Accounting and Logg ing Extensive accounting and logg ing capabilities exist in the Commonwealth Edison Company dispatching c omputers. The system is programmed to print hourly operating data pertaining to load, generation, and int e rconnect ion operations in both hourly and daily summaries. The computer accounts gene rator and tie line megawatt hours, unit on-off times, interchange schedule start-stop times and megawat thours for interc ompany transacti ons, and other significant accounting and ope rating information. The hourly and daily operating data are stored in the computer for a 24 hour period. After midnight the previous day's data are transferred from RAD memory to mag netic tape. The tape is then sent to a Company business c ompute r l ocation for processing and use by other interested Commonwea lt h Edison Company departments. Al arms The computer is also used as an extensive alarming device . The system has been programmed to display alarm messages on a CRT and on the alarm printer. These alarms indicate power system ope rating problems, such as ove rl oads and vo ltages out of limits and the status of the computer, peripheral equipment, and data acquisition and control system. All dispatcher - entered data and control inf ormation are checked by the computer for correctness of format and procedure. Any inconsistencies or mal functions of equipment will trigger an appropriate alarm message .
facilities at generating stations and substations and the major transmission lines. Lines out of service are shown li gh t ed . Overloaded lines and transformers and bus vo ltages out of limits caus e pulsing illumination. A change of status is shown by f lashing lights for lin es , circuit breakers, and transformers. At a glance, the dispatcher sees the condition of the bulk transmission network . The map board , along with printed alarm messages, directs the dispatcher to CRT displays of one -line diagrams for the stations and substations. Realtime information is displayed on the one -line diagrams, such as r ea l and reactive power flows on all lines, gene ratin g unit output, circuit breake r status and bus vo ltages . In addition to being able to monitor system status, the dispatcher has two types of programs that alert him to potential problems. The first monitors for overloads and the second tests for the effects of contingencies before they occur . Overload Monitor The overload monitor program enab les him to find heavily-loaded elements before trouble develops. It calculates MVA from telemetered megawatt and megavar va lues and compares this va lue to limit data for each line or transformer. If out of limits, the program alarms the quantity by displaying it in red on CRT displays, printing an alarm l og message and initiating the map board display. Contingency Evaluation Program The contingency evaluation program aut omatica lly performs contingency tests for loss of principal transmission e l ements , loss of gene rating units, or othe r major disturbances in the sy stem. Each hour on a periodic basis, or when initiated by the dispatcher from the console, or by s ystem changes, a mathematical model of the system is calculated for load flow analysis. The power system model is tested in an on-line mode against 20 pre-set contingencies, previously selected with the help of the engineering staff. Each hour the computer program automatically runs through these and, if the system passes the tests, the dispatcher is informed that the contingency eva luation tests were comple~ ed satisfactorily. If any test fails, the elements that have fai led and the contingency that caused the failure are alarmed on a CRT display and printed record. This then gives the dispatcher a chance t o correct situations which mi ght cause a problem. For example, he might rearrange transmission, restore a line to service that was out for maintenance, or change the generation or interchange schedule. Before actually taking what he be lie ve s to be the ri ght corrective action, he can manually change the system model and initiate another test to see if his action would correct the potential problem.
Transmission System Status The computer driven mapboard is the primary display of transmiss i on system status. The board is a dynamic display of the status of transmission
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The practice in selecting the 20 severe contingencies is to have the engineering staff select 10 of the contingencies and the dispatchers to select 10 contingencies. The staff people select the 5
most severe credible contingencies to which the system could be subjected. They also select 5 contingencies which appear to be most severe for the system as it exists at the time. The dispatcher then selects the remaining 10 contingencies. Load Flow Study Program In addition to the 20 severe contingencies that are run hourly by the contingency evaluation program, the computer system is used to simulate any system condition through a load flow study program. This program allows the dispatcher or staff engineer to take the current system data base, or a base case data base, and move it to a study work file. With a group of study CRT one-line diagrams and tabular CRT data displays representing the total system, the dispatcher can change any quantity or quantities in the data base to values and/or states representing a contingency condition. He can then run a load flow study to evaluate the effects of the assumed contingency on the total system. Using this very flexible tool, the dispatcher can plan his system for the next hour, day, week, or even next year. While studies, such as the load flow study, can be run from either of the dispatching consoles, the third console (the planning console) is usually used to avoid .interfering with the operating responsibilities of the dispatchers. This console is similar to the other two, except that it does not have full control capabilities and has one four color CRT with access to all system displays. A logging printer is provided for hard copy output of study data. In addition to the load flow study there are other programs for study of system operation which are normdlly conducted at the planning console. These include energy pricing, generating unit maintenance scheduling, and load forecasting. Data obtained from these are made available to the dispatchers.
pushbuttons themselves are actually small rear projection displays which project eleven different English-language legends on each pushbutton screen. To select a given CRT display, the dispatcher pushes a group-selector pushbutton which has a legend indicating a group of CRT displays. The multiplexed pushbutton panel then projects the name of every CRT display in this group. He next pushes the button which projects the name of the CRT display he desires. He then pushes a "data request" pushbutton signaling the computer, which immediately interrogates the pushbutton panel and presents the desired CRT display to the dispatcher. This three step operation is accomplished in less than five seconds. In designing the man-machine interface and analyzing the data available from the computer and the data required by the dispatcher, it became apparent that new man-machine interface techniques were required to avoid overwhelming the dispatchers with non-pertinent data. Management by exception information display techniques were developed which avoided this problem. The bulk power mapboard is an example of this technique. A computer program analyzes the system circuit breakers to determine the status of the system transmission. This program then indicates the status of the transmission lines (not the circuit breakers) on the bulk power mapboard. The dispatcher no longer has to analyze the status of circuit breakers to determine the status of his transmission system. Various summary CRT displays were developed to present the dispatcher with summaries of various system operating conditions. Critical alarm highlighting techniques were developed to call the dispatchers attention to critical alarms. When an abnormal situation occurs, the dispatcher is made aware of the problem, and he then selects other CRT displays to get a more detailed picture of the problem. At the consoles the dispatchers have typewriterlike keyboards for data input to the computer via the CRT displays. Such inputs are operating data and simple words or abbreviations. For example, if the dispatcher wants to initiate an interchange schedule he types in the desired ~v quantity with the start and stop times on the CRT display for the neighboring utility he is exchanging power with. This quantity is then entered directly into the computer data base through "verify" and "enter" pushbutton operations.
MAN/MACHINE INTERFACE Because of its extreme importance to the successful operation of a dispatch office the man-machine interface was carefully designed in consultation with the dispatch office personnel to assure that it would meet their needs for efficient, effective and convenient operation. Of prime importance during design was the requirement to have a man-machine interface that would be simple, fast, and straightforward. This was made clear to the prime contractor, L&N, before the project began and \vas held forward as the goal throughout the project. A simple, easy-to-use, English language-oriented interface was developed. This means that when a dispatcher wants to communicate with the computer, or the computer with him, there is no special coding or key book needed to find displays or different study programs. The man-machine interface guides the dispatcher through the correct procedures by asking simple questions via the CRT displays.
For any equipment failure the system is programmed to output a simple English message that the particular piece of equipment has failed. For communications errors from remote locations, the computer outputs the location and type of communication error that occurred. In various kinds of studies or control functions the computer must have certain instructions from the dispatcher before it can complete the computations. Again, this involves typing either short English words or numbers. Another simplification in the man-machine interface is the ability to accomplish most functions by selecting only one CRT display. From this one
The dispatcher uses a unique multiplexed pushbutton panel to control the CRT displays. The
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of our computer systems analysts and three of our Operational Ana l ysis people spent from 6 months to 2 yea rs in formal training at L&N and the various schooling and courses avai lable. After the formal training our Computer Systems Analysts took an active part (under the supervision of L&N) in the program development.
display the dispatcher can obtain the information he wants or he can input the required information to the computers. From a programming point of view there were easier and more efficient ways that could have been used, but the emphasis was always on the dispatcher's needs and his convenience in system operation.
Throughout the project Computer Systems Ana l ysts, engineers from Station Electrical Engineering, System Planning and Operational Analy sis Departments and Power Supp l y Department dispatchers and staff were actively involved with many visits to the L&N factory. A special effort was made to invo l ve the dispatchers in decisions concerning operating functions and man - machine interface.
PROJECT PLANNING AND IMPLEMENTATION The steps and timing leading to the successful completion of a project of this type are of interest to others planning similar projects. In 1967 a joint study of bulk power system operating requirements was undertaken with General Electric Company. Engineering and Operating personnel from Commonwealth Edison Company were assigned to the study group to work with specialists from General Electric. This study, completed in 1969, analyzed all aspects of system security including monitoring of system operation and display of significant information for the dispatcher, contingency evaluation to determine the effects of loss of transmission or gene ration facilities before they might occur, development of corrective strategy to prepare for possible trouble or improve an already difficult situation, and to control system operation to more nearly optimize production costs with the constraints of security of operation. The study clearly established the requirement for large digital computers, a comprehensive data acquisition system, new generation control techniques, and carefully designed control and information display facilities.
As equipment was delivered from the computer manufacturer and other suppliers, and L&N completed their equipment manufacturing the system was assembled on the L&N factory test floor for testing. Four of the remote stations and a generating unit control console were retained there to provide simulated real-time data and control. The computer programs were tested and integrated into the system in this environment . Dispatchers and Power Supply Engineers participated in factory pre-shipment tests. Equipment was shipped to Commonwealth Edison Company at the end of October, 197 2 and installation and initial checkout of equipment were completed by about mid-December. Concentrated training of Power Supply Department people then began and proceeded simultaneously with computer program tests and preparations for going into service. On March 29, 1973 the new system was put into full service and this signalled the start of a successful 180 day performance test.
In the spring of 1969, a Project Task Force was appointed which represented all interested areas of Commonwealth Edison Company - Engineering, Planning, Power Supply, Operational Analysis, Computer Systems; Generating Stations and Statistical Research. The task force wrote the project specification which defined the scope and areas of responsibility and provided a genera l description of the project to bidders. Equipment and computer program functional requirements were specified, including both application programs and the control, or executive, program. Finally the gene ral requirements for supporting the project, testing the system and shipment were specified.
A key to the successful equipment and system acceptance and take-over by Commonwealth Edison Company personnel was the close cooperation between L&N and Commonwealth Edison during the equipment installation and start-up, and the test period. All disciplines (hardware, software, and engineering) worked side-by-side with their counterparts to ensure, first, a successful installation and second, a smooth take-over by Commonwealth Edison Company.
At the same" time the task force investigated systems suppliers and developed a list of qualified builders. Copies of the specification we re submitted to qualified bidders and proposals were received by December of 1969. Afte r analysis of proposals a letter of intent was signed with Leeds and Northrup Company in March of 1970 and specific design work began immediately.
OPERATING EXPERIENCE We have found that our new control system has given us more exact control of our generating units. This causes less severe swings on boi lers and auxiliary equipment, and allows us to have more units on automatic control than we have had in the past. In addition to moneta r y savings, our control effort (matching load and generation) has improved and we have become a better interconnected neighbor .
L&N had the responsibility for both hardware and
software in the system. Design and manufacturing work was done at their plant in Nort h Wa les, Pennsylvania. In July of 1970, Commonwealth Edison Company assigned a project engineer and he and his family took up residence in North Wa les and stayed through the factory test phase which ended in mid 1972.
We are able to study planned transmission line outages in advance and eva luate these outages with confidence. This has resulted in a lar ge reduction in the schedu lin g of work at times of premium la bor rates. The a lmost instantaneous indications of generation
At various times during this two year period five
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and transmission system unplanned occurrences, plus the critical information about the remaining system, allows the Dispatcher to react quickly and then observe the results of his actions. We have been able to restore line loadings and bus voltages to normal levels much quicker with our new equipment. finally, the increase in automation of the Dispatcher's work allows him more time to study his existing system and to anticipate what his system will be in the near future. He has more complete control and can react to unplanned outages quicker and with more confidence. CONCLUSION This project has produced one of the most advanced systems for control and security analysis in the industry. One measure of success is the enthusiastic acceptance and use by the dispatchers. They are the most vocal proponents of their computer system and perhaps this is the best test. The computer system is under-going continual change. Four computer system analysts and three operational analysis people are assigned to the System Power Supply Office and are working full time to add improvements to existing computer tasks and assigning new tasks to the computer. The vast majority of these changes are initiated by dispatcher ideas and requests. After the predictable period of software debugging and replacement of marginal components in some of the hardware, our experience is that the performance of our programs and equipment is excellent much better than we had hoped for. All those associated with the new System Power Supply Office feel that the goal of enhancement of security and economics in the operation of the Commonwealth Edison Company bulk power system has been achieved.
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~\AN/~1ACHINE
INTERFACE FOR
COHNONHEALTH EDISON COHPANY'S SYSTEH SECURITY
T. C. Cihlar Superintendent System Pmver Supply Commonwealth Edison Company Chicago, Illinois United States of America
ABSTRACT Rapid changes are planned and occurring in the method of controlling and monitoring the generation and transmission systems of electric utilities. New control centers containing process digital computers and digital data acquisition systems and control equipment are being constructed. New and improved methods of man -machine interface are being employed . Computers receive data from the electric generation and transmission system and accomp lish control action and operate interface devices to act as a tool for the system dispatcher. These new tools improve the security and economic operation of bu lk power systems. This paper describes the new control system for Commonwealth Edison Company. COHHom,EALTH EDISON COHPANY Before describing the Commonwealth Edison Company System Power Supply Office and operating practices it wou ld be appropriate to describe Commonwealth Edison Company itself so that decisions made in equipment app lication can be better understood. Commonwealth Edison Company serves 2.7 mi lli on customers, principa lly in the northern third of Illin ois . Our service area is about 13,000 square miles with a population of 8 mi lli on . We opera t e generating capacity totaling about 17,000 HH in 15 generating stations and 3 substation peaking unit l ocations. Summer peak l oad in 1974 was approximate l y 13,500 HW. l,e have 23 high vo lt age lines interconnecting with 8 contiguous e l ectric utilities. (Figure 1) Commomvealth Edison Company operates 10,982 HH of fossil fueled units plus 5,480 ~, of nuclear fueled units. In addition to this we share in the Consumers Power-Detroit Edison Ludington pumped storage hydro plant in the amount of 624 ~[W . 1,704 HI-' of the 10, 982~, of fossil units consist of fast start peaking units. Unit sizes range up to 850 ~~ fo r fossi l and 1, 040 ~J for nuclear. Commonwea lt h Edison Company Pm"er Supp l y operations are structured in two levels. The System Power
Supp l y Office is responsible for the integrity and continuity of operation of the interconnected high vo ltage transmission network and the generation supp l ying the network. This office is assisted in the operation of the transmission system by 7 Division Power Supply Offices l ocated in each of the 7 Commonwealth Edison Company Divisions. Each of the Division Power Supp l y Offices is responsible for directing the operation of the transmission, subtransmission, and some e l ements of the distribution systems in the Division a r ea . The Division operation of the transmission system is coordinated with the System Power Supp l y Office. SYSTEH POWER SUPPLY OFFICE A new System Power Supp l y Office bui lding, having a ll new equipment, was put into service in Harch of 1973. Septembe r of 1973 marked the successful completion of avai l abi lity tests of full on -line oper ation of the new equ ipment which provides one of the most advanced computerized dispatch systems operating in the Un it ed States . This was the result of a project begun 3~ years ear li er with Leeds and North rup Company (L&N), supp lier of both equipment and computer programs. The building is a one story reinforced concrete structure with 18" thick walls pr oviding fa ll-out protection. It is approximately 15,000 square feet in area. The layout is shown in Figure 2. Hultip l e sources of e l ectric service to the bui l ding is provided. Norma l feed is from two separate 12KV feed ers through two identical 75KVA solid state inverter systems. The inverters convert A-C to O-C and back to A-C to provide isolation from system disturbances. Each inverter provides power for approximate l y one ha lf of the system, but each is capable of providing power fo r the enti r e bui lding and equipment . A static switch a llows the dispatch equipment to be powered from either in ver ter system without interrupti on during switching . In the event of loss of a ll A-C service from the Commonwealth Edison Company system, a l ead ca lci um battery is capable of maintaining inverter power for one - half hour. This is amp l e time to start an 800 kilowat~ emergency diesel. This diesel is fueled from an underground storage tank which has a 14 day oi l supp l y.
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HARDl-.JARE As with any computer control system, there are four basic functions that must be performed. Facilities must be available to gather data, process the information, display the results, and control the process. These functions are provided in our system by the hardware configuration shown in Figure 3. Telemetering The gathering of data is accomplished by L&N Conitel supervisory equipment, receiving data from 70 remote stations located throughout the Commonwealth Edison Company system. The data then pass to the dual LN5500 control computer system for processing, storage, display, and control functions. Converted data are displayed upon the color cathode ray tubes (CRT), printers, mapboard and recorders in the dispatch office. Control sicinals are transmitted to the generating units through the conitel system. Computers The dual LN5500 computer system is used to provide a secure operating environment for the dispatchers. This is accomplished b y maintaining the computers in a master-reserve state. A data link and failover logic allow the reserve computer to assume control in the event of a failure of the master. The data link passes system status information to the reserve computer. Failover logic allows the reserve computer to switch all devices needed for control. These circuits, along with peripheral switching, provide a large degree of flexibility and security in the event of a malfunction of either the software or hardware. The two computers are Xerox Data Systems Sigma 5's. Each has 48,000 words of core memory which is expandable to 64,000 words. InclJded is hardware for floating point arithmetic operation and power failsafe operation. Floating point provides ease and accuracy in the numerous calculations. Power failsafe operation provides for a safe shutdown and automatic restart in the event of a power interruption. Each system has two rapid access data storage (RAD) units. The RAD is a rotating disc type of memory used for bulk data storage. Each RAD is capable of storing six megabytes (1.5 million words) of information. Because of their size, all system programs are stored on RAD, and transferred into core memory when needed.
printer, a special CRT monitor, and keyboard printers are used by programmers for program development and data entry. Consoles The input/output devices used by the dispatcher are mounted in consoles. Data on system status or generation control action is requested through the consoles. There are three consoles in the dispatch office - two for dispatch operations and one for operations planning and studies. The two operating consoles are identical in design and capabilities. The planning console is similar, but restricted in operating capability. There are two data request keyboards on each console, each providing a matrix array of 352 possible selections through 32 pushbuttons. With these, any of the system displays and studies may be displayed on one of the color CRT monitors at each console. There are three CRT's on the operating consoles, one on the planning console. The dispatchers enter data through the CRT with the use of a keyboard which is similar to a typewriter keyboard. The consoles contain the necessary controls for system operation. Two special chart recorders at each operating console are provided for trending of any telemetered or calculated data. In addition to the consoles, chart recorders and a mapboard and printers display the results of the many program calculations to the dispatcher. Mapboard The 10 foot by 40 foot Siemens Corp. dynamic mapboard contains over 56,000 removable tiles, each individually set in a lar'ge steel matrix. The board is controlled through solid-state switching, showing the status of all major transmission lines through the use of lights. This enables the dispatchers to view the overall status of the transmission system at a glance and to detect a change of status almost instantly. Printers The A.B. Dick Company Video jet printers are unique de v ices. They print at a rate of 250 charact e rs per second by squirting a fine stream of ink droplets on paper. The characters are formed by applying an electrostatic charge to each drop and deflecting the stream to produce a dot matrix array. These printers are advantageous for application in an operating environment because of their speed and quietness. Data ACquisition and Control
To increase flexibility and security the Computer system employs peripheral switching. This feature provides the ability to switch any of the peripherals, such as the rapid access data storage units (RADS), card readers, magnetic tapes, line printer or card punch, between the two computers. I/O Devices Various input/output devices are required for man and machine to communicate with each other. The card readers, card punch, magnetic tapes, line
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The dispatch office link to the outside world is the Conitel data acquisition and control s y stem. (Figure 4) This system has one master station communicating with 70 remotes over eight communications circuits. The master station has dual multiplexors and eight normal line buffers. As a security measure, a ninth line buffer is provided as a spare to handle one or more communications circuits in the event of hardware failures of other buffers. The Conitel master addresses each remote in turn, using octal coded addresses. The remote
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responds with data associated for that address. The remot e stations are located at all generating stations, major transmission substations, and the int e rconn ec ti ng tie lin es to eight neighboring utiliti es . Te lemet e r ed data include transmission line, transforme r, and gene ratin g unit megawatts and megava rs, and bus kilovolts. Circuit b reakers are monito red for status and change of status. Accumulat o rs store and telemeter pulses from watthour meters on ge neratin g units, auxiliary power and tie lines each hour.
on predicted weather conditions. This peak load is then entered into the computer Load Forecasting Program. This program calculates and stores a forecast of hourly loads for a seven day period based on pre-set load patterns for that season of the year. The output of this pro g ram is displayed, on demand, on a CRT and is automatically stored for use by other programs. Scheduled Interchange Program There is a program to handle all Scheduled Interchanges with eight utility neighbors of Commonwealth Edison Company. The scheduled interchange is entered b: keyboard into the computer using the CRT display format provided for each neighbor. Information specifying the type of interchange, start time and date, stop time and date, megawatts to be received or delivered, ramp rate, and ramp time is entered by the dispatcher. The computer will store interchan ge schedules up to one year in the future. Pricing information may also be entered throu gh the CRT. This information is processed and stored by the computer for use in automatic generation control, interchange energy accounting, data lo gg ing and various study programs.
Fi gu re 5 details the various scan times for obtaini ng t e le metered data. Wea ther conditions are telemetered from six weather stations l oca ted throu g hout the Commonwealth Edison Company system. Information o n dry-bulb and dew point temp e ratur e , li ght intensity, and wind speed and direction are sensed and telemetered to the dispatch off ice. These data are used for analysis of load patterns. In addition to data gatherillg, the Conitel system is r es ponsible for the system control functions. After gathering the required data, computer prog rams calculate the control action required of each gene ratin g unit for load-frequency control and economic dispatch. The Conitel master receives the request from the computer and transmits it to the prop e r r emote station. The addressed remote receives the control code and initiates the required action by the generating unit.
Unit Commitment
At the generating station, the Conitel remote outputs pulses to the economic generation console (EGC) unit controller for each generating unit. The unit controller is the interface be tween the Conitel System and the governor motor or the electrohydraulic control of the unit. The controller provides security by inhi bi ting output control pulses if a malfunction is detected. Digital setters on the EGC for each ge nerating unit provide for high and low limits which restrain unit loadin g to desired limits. These limits, along with economic control limits, are telemetered through the Conitel System for use in system control pro g rams. In addition to the dual digital system an analog back-up control is provided. This equipment provides a second level of ba ck-up for gene ration control of all generating units in the infrequent event of outages to both digital systems. The analo g control is the "broadcast" type and does not provide economic dispatch. The analog system telemeters the 345KV and 765KV tie line loadin gs . The l38KV tie line loadings and the scheduled net interchange va lues must be entered through manual setters.
Af ter load forecasting and scheduled interchan ge information are available to the computer the unit commitment program can be run. The output of this is a list of the most economical schedule of ge nerators needed to satisfy the hourly load and reserve requirement plus the net interchan ge schedule for a 24 hour period. Security Monitoring Many pro g rams are used to accomplish the constant system monitoring essential to system security. The dispatcher has several means of monitoring the system. There is an array of recording charts displaying such things as total system generation, net system load, scheduled and actual net interchan ge, system frequency, transmission tie lin e loadin gs , area control error, and total output from each generating station. The computer is continuously scanning a va ri e t y of information to be displayed at the push of a button on one of the CRT's. For instance, the dispatcher can display Generation Review for each station. This display indicates for each gene ratin g unit such information as actual and desired gene ration, control status, control limits, and fuel type. Another display is the System Summary showing the amount of system reserve ge neration, area control error, frequency, load, net interchan ge, and t ot al ge neration.
SOFTHARE Extensive software is used in conjunction with the hardware just described. Some of the more important pro g rams and their use by the dispatcher will be discussed. Load Forecasting Program The dispatcher estimates the daily peak load based
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The System Generation Review displays actual loadin g s on all gene rators indiv idually and station totals for the entire Commonwealth Edison Company system. Units on manual control display their loadin g in white while units on automatic dispatch display their loadin g in red.
Automatic Generation Control Automatic gene rati on control is the principal realtime control function of the computer control system. It combines l oad -frequ ency control and economic dispa t ch functions . Th e purpose is to economically r egu late the power output of Commonwealth Edison Company gene rat ors in r es ponse to changes in customer demands, system frequency, interchange schedules, and tie line power flow. Frequency and interchange sch edu l es mus t be kept within pre-determined limit s while maintaining adequate generation reserves. The computer utilizes a periodic real-time program to determine gene r ating res e r ves . If desired r ese r ves are not available, the dispatcher is notified through a larms . Control action is t aken in respons e to the actual and anticipated area contro l error such that the units on automatic regulation wi ll be economically loaded. Th e amount and frequency of control action is increased in accordance with the probability that additional action is required. Any known system changes, such as an interchange schedule or a unit being ramp-loaded, may be fed forward i n anticipation of a control error. The control system has an emergency assist feature which automatically by -passes economic considerations when t he area control e rr or exceeds a predetermined limit and sends control pulses to all units. Accounting and Logg ing Extensive accounting and logg ing capabilities exist in the Commonwealth Edison Company dispatching c omputers. The system is programmed to print hourly operating data pertaining to load, generation, and int e rconnect ion operations in both hourly and daily summaries. The computer accounts gene rator and tie line megawatt hours, unit on-off times, interchange schedule start-stop times and megawat thours for interc ompany transacti ons, and other significant accounting and ope rating information. The hourly and daily operating data are stored in the computer for a 24 hour period. After midnight the previous day's data are transferred from RAD memory to mag netic tape. The tape is then sent to a Company business c ompute r l ocation for processing and use by other interested Commonwea lt h Edison Company departments. Al arms The computer is also used as an extensive alarming device . The system has been programmed to display alarm messages on a CRT and on the alarm printer. These alarms indicate power system ope rating problems, such as ove rl oads and vo ltages out of limits and the status of the computer, peripheral equipment, and data acquisition and control system. All dispatcher - entered data and control inf ormation are checked by the computer for correctness of format and procedure. Any inconsistencies or mal functions of equipment will trigger an appropriate alarm message .
facilities at generating stations and substations and the major transmission lines. Lines out of service are shown li gh t ed . Overloaded lines and transformers and bus vo ltages out of limits caus e pulsing illumination. A change of status is shown by f lashing lights for lin es , circuit breakers, and transformers. At a glance, the dispatcher sees the condition of the bulk transmission network . The map board , along with printed alarm messages, directs the dispatcher to CRT displays of one -line diagrams for the stations and substations. Realtime information is displayed on the one -line diagrams, such as r ea l and reactive power flows on all lines, gene ratin g unit output, circuit breake r status and bus vo ltages . In addition to being able to monitor system status, the dispatcher has two types of programs that alert him to potential problems. The first monitors for overloads and the second tests for the effects of contingencies before they occur . Overload Monitor The overload monitor program enab les him to find heavily-loaded elements before trouble develops. It calculates MVA from telemetered megawatt and megavar va lues and compares this va lue to limit data for each line or transformer. If out of limits, the program alarms the quantity by displaying it in red on CRT displays, printing an alarm l og message and initiating the map board display. Contingency Evaluation Program The contingency evaluation program aut omatica lly performs contingency tests for loss of principal transmission e l ements , loss of gene rating units, or othe r major disturbances in the sy stem. Each hour on a periodic basis, or when initiated by the dispatcher from the console, or by s ystem changes, a mathematical model of the system is calculated for load flow analysis. The power system model is tested in an on-line mode against 20 pre-set contingencies, previously selected with the help of the engineering staff. Each hour the computer program automatically runs through these and, if the system passes the tests, the dispatcher is informed that the contingency eva luation tests were comple~ ed satisfactorily. If any test fails, the elements that have fai led and the contingency that caused the failure are alarmed on a CRT display and printed record. This then gives the dispatcher a chance t o correct situations which mi ght cause a problem. For example, he might rearrange transmission, restore a line to service that was out for maintenance, or change the generation or interchange schedule. Before actually taking what he be lie ve s to be the ri ght corrective action, he can manually change the system model and initiate another test to see if his action would correct the potential problem.
Transmission System Status The computer driven mapboard is the primary display of transmiss i on system status. The board is a dynamic display of the status of transmission
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The practice in selecting the 20 severe contingencies is to have the engineering staff select 10 of the contingencies and the dispatchers to select 10 contingencies. The staff people select the 5
most severe credible contingencies to which the system could be subjected. They also select 5 contingencies which appear to be most severe for the system as it exists at the time. The dispatcher then selects the remaining 10 contingencies. Load Flow Study Program In addition to the 20 severe contingencies that are run hourly by the contingency evaluation program, the computer system is used to simulate any system condition through a load flow study program. This program allows the dispatcher or staff engineer to take the current system data base, or a base case data base, and move it to a study work file. With a group of study CRT one-line diagrams and tabular CRT data displays representing the total system, the dispatcher can change any quantity or quantities in the data base to values and/or states representing a contingency condition. He can then run a load flow study to evaluate the effects of the assumed contingency on the total system. Using this very flexible tool, the dispatcher can plan his system for the next hour, day, week, or even next year. While studies, such as the load flow study, can be run from either of the dispatching consoles, the third console (the planning console) is usually used to avoid .interfering with the operating responsibilities of the dispatchers. This console is similar to the other two, except that it does not have full control capabilities and has one four color CRT with access to all system displays. A logging printer is provided for hard copy output of study data. In addition to the load flow study there are other programs for study of system operation which are normdlly conducted at the planning console. These include energy pricing, generating unit maintenance scheduling, and load forecasting. Data obtained from these are made available to the dispatchers.
pushbuttons themselves are actually small rear projection displays which project eleven different English-language legends on each pushbutton screen. To select a given CRT display, the dispatcher pushes a group-selector pushbutton which has a legend indicating a group of CRT displays. The multiplexed pushbutton panel then projects the name of every CRT display in this group. He next pushes the button which projects the name of the CRT display he desires. He then pushes a "data request" pushbutton signaling the computer, which immediately interrogates the pushbutton panel and presents the desired CRT display to the dispatcher. This three step operation is accomplished in less than five seconds. In designing the man-machine interface and analyzing the data available from the computer and the data required by the dispatcher, it became apparent that new man-machine interface techniques were required to avoid overwhelming the dispatchers with non-pertinent data. Management by exception information display techniques were developed which avoided this problem. The bulk power mapboard is an example of this technique. A computer program analyzes the system circuit breakers to determine the status of the system transmission. This program then indicates the status of the transmission lines (not the circuit breakers) on the bulk power mapboard. The dispatcher no longer has to analyze the status of circuit breakers to determine the status of his transmission system. Various summary CRT displays were developed to present the dispatcher with summaries of various system operating conditions. Critical alarm highlighting techniques were developed to call the dispatchers attention to critical alarms. When an abnormal situation occurs, the dispatcher is made aware of the problem, and he then selects other CRT displays to get a more detailed picture of the problem. At the consoles the dispatchers have typewriterlike keyboards for data input to the computer via the CRT displays. Such inputs are operating data and simple words or abbreviations. For example, if the dispatcher wants to initiate an interchange schedule he types in the desired ~v quantity with the start and stop times on the CRT display for the neighboring utility he is exchanging power with. This quantity is then entered directly into the computer data base through "verify" and "enter" pushbutton operations.
MAN/MACHINE INTERFACE Because of its extreme importance to the successful operation of a dispatch office the man-machine interface was carefully designed in consultation with the dispatch office personnel to assure that it would meet their needs for efficient, effective and convenient operation. Of prime importance during design was the requirement to have a man-machine interface that would be simple, fast, and straightforward. This was made clear to the prime contractor, L&N, before the project began and \vas held forward as the goal throughout the project. A simple, easy-to-use, English language-oriented interface was developed. This means that when a dispatcher wants to communicate with the computer, or the computer with him, there is no special coding or key book needed to find displays or different study programs. The man-machine interface guides the dispatcher through the correct procedures by asking simple questions via the CRT displays.
For any equipment failure the system is programmed to output a simple English message that the particular piece of equipment has failed. For communications errors from remote locations, the computer outputs the location and type of communication error that occurred. In various kinds of studies or control functions the computer must have certain instructions from the dispatcher before it can complete the computations. Again, this involves typing either short English words or numbers. Another simplification in the man-machine interface is the ability to accomplish most functions by selecting only one CRT display. From this one
The dispatcher uses a unique multiplexed pushbutton panel to control the CRT displays. The
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of our computer systems analysts and three of our Operational Ana l ysis people spent from 6 months to 2 yea rs in formal training at L&N and the various schooling and courses avai lable. After the formal training our Computer Systems Analysts took an active part (under the supervision of L&N) in the program development.
display the dispatcher can obtain the information he wants or he can input the required information to the computers. From a programming point of view there were easier and more efficient ways that could have been used, but the emphasis was always on the dispatcher's needs and his convenience in system operation.
Throughout the project Computer Systems Ana l ysts, engineers from Station Electrical Engineering, System Planning and Operational Analy sis Departments and Power Supp l y Department dispatchers and staff were actively involved with many visits to the L&N factory. A special effort was made to invo l ve the dispatchers in decisions concerning operating functions and man - machine interface.
PROJECT PLANNING AND IMPLEMENTATION The steps and timing leading to the successful completion of a project of this type are of interest to others planning similar projects. In 1967 a joint study of bulk power system operating requirements was undertaken with General Electric Company. Engineering and Operating personnel from Commonwealth Edison Company were assigned to the study group to work with specialists from General Electric. This study, completed in 1969, analyzed all aspects of system security including monitoring of system operation and display of significant information for the dispatcher, contingency evaluation to determine the effects of loss of transmission or gene ration facilities before they might occur, development of corrective strategy to prepare for possible trouble or improve an already difficult situation, and to control system operation to more nearly optimize production costs with the constraints of security of operation. The study clearly established the requirement for large digital computers, a comprehensive data acquisition system, new generation control techniques, and carefully designed control and information display facilities.
As equipment was delivered from the computer manufacturer and other suppliers, and L&N completed their equipment manufacturing the system was assembled on the L&N factory test floor for testing. Four of the remote stations and a generating unit control console were retained there to provide simulated real-time data and control. The computer programs were tested and integrated into the system in this environment . Dispatchers and Power Supply Engineers participated in factory pre-shipment tests. Equipment was shipped to Commonwealth Edison Company at the end of October, 197 2 and installation and initial checkout of equipment were completed by about mid-December. Concentrated training of Power Supply Department people then began and proceeded simultaneously with computer program tests and preparations for going into service. On March 29, 1973 the new system was put into full service and this signalled the start of a successful 180 day performance test.
In the spring of 1969, a Project Task Force was appointed which represented all interested areas of Commonwealth Edison Company - Engineering, Planning, Power Supply, Operational Analysis, Computer Systems; Generating Stations and Statistical Research. The task force wrote the project specification which defined the scope and areas of responsibility and provided a genera l description of the project to bidders. Equipment and computer program functional requirements were specified, including both application programs and the control, or executive, program. Finally the gene ral requirements for supporting the project, testing the system and shipment were specified.
A key to the successful equipment and system acceptance and take-over by Commonwealth Edison Company personnel was the close cooperation between L&N and Commonwealth Edison during the equipment installation and start-up, and the test period. All disciplines (hardware, software, and engineering) worked side-by-side with their counterparts to ensure, first, a successful installation and second, a smooth take-over by Commonwealth Edison Company.
At the same" time the task force investigated systems suppliers and developed a list of qualified builders. Copies of the specification we re submitted to qualified bidders and proposals were received by December of 1969. Afte r analysis of proposals a letter of intent was signed with Leeds and Northrup Company in March of 1970 and specific design work began immediately.
OPERATING EXPERIENCE We have found that our new control system has given us more exact control of our generating units. This causes less severe swings on boi lers and auxiliary equipment, and allows us to have more units on automatic control than we have had in the past. In addition to moneta r y savings, our control effort (matching load and generation) has improved and we have become a better interconnected neighbor .
L&N had the responsibility for both hardware and
software in the system. Design and manufacturing work was done at their plant in Nort h Wa les, Pennsylvania. In July of 1970, Commonwealth Edison Company assigned a project engineer and he and his family took up residence in North Wa les and stayed through the factory test phase which ended in mid 1972.
We are able to study planned transmission line outages in advance and eva luate these outages with confidence. This has resulted in a lar ge reduction in the schedu lin g of work at times of premium la bor rates. The a lmost instantaneous indications of generation
At various times during this two year period five
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and transmission system unplanned occurrences, plus the critical information about the remaining system, allows the Dispatcher to react quickly and then observe the results of his actions. We have been able to restore line loadings and bus voltages to normal levels much quicker with our new equipment. finally, the increase in automation of the Dispatcher's work allows him more time to study his existing system and to anticipate what his system will be in the near future. He has more complete control and can react to unplanned outages quicker and with more confidence. CONCLUSION This project has produced one of the most advanced systems for control and security analysis in the industry. One measure of success is the enthusiastic acceptance and use by the dispatchers. They are the most vocal proponents of their computer system and perhaps this is the best test. The computer system is under-going continual change. Four computer system analysts and three operational analysis people are assigned to the System Power Supply Office and are working full time to add improvements to existing computer tasks and assigning new tasks to the computer. The vast majority of these changes are initiated by dispatcher ideas and requests. After the predictable period of software debugging and replacement of marginal components in some of the hardware, our experience is that the performance of our programs and equipment is excellent much better than we had hoped for. All those associated with the new System Power Supply Office feel that the goal of enhancement of security and economics in the operation of the Commonwealth Edison Company bulk power system has been achieved.
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