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An Overview of Practices and Trends in Power System Control Centers
AN OVERVIEW OF PRACTICES AND TRENDS IN POWER SYSTEM CONTROL CENTERS T. E. Dy Liacco The Cleveland Electric Illuminating Company and Case Western Reserve University, Cleveland, Ohio, USA
Abstract. This paper reviews the state-of-the-art of the design of control centers for the operation of electric power systems. Modern control centers are distinguished by the integration of new functions designed to enhance system security with the traditional functions of generation control and of supervisory control. The emphasis therefore of the overview presented in this paper is on the practices and trends in control center design which are brought about by considerations of system security. Keywords. Control center; power system control; power system security; power system operation; computer control.
INTRODUCTION The prime objective of the operation of an electric power system is the maintenance of a continuous supply of electric energy to all users served by the system. Once an electric power system is built and placed in operation, then it should stay in continuous operation indefinitely. This is the overall goal of the process and the function of system operation is to meet this goal as best as practicable. "As best as practicable" just about sums up the nature of the decisionmaking requirements which are continuously made of system operation. What is "best" or, equivalently, what is "orr timum", depends on the electrical conditions of the power system, economic factors, environmental restrictions, equipment capabilities, and on many other constraints which have bearing on the operating action or decision. What is "practicable" depends on the tools available to operation, the control capabili ties of the power system, and on the human operators at the operation center and at the power plants and other manned locations. Decision-making problems in system operation are complex and difficult. Adding to the difficulty is the stricture to make decisions within a relatively short time so that action, if needed, may be carried out promptly enough to be of benefit to operation. This obviously requires judicious application of automation in the monitoring and control of the power system.
action to the present-day development of control centers with redundant, real-time computer systems, digital telemetry and control, interactive man-machine interfaces, and advanced monitoring and control programs. With these new control centers it has become practicable to enhance system operation through functions which had not been available pl·eviously. In this paper I will discuss some of the forms and directions in which new computerized functions are being developed in the electric power industry. Special emphasis will be placed on those functions directed to the preservation of system security since it is precisely the incorporation of security-oriented functions which is making the big difference between a modern, advanced control center and the traditional generation or transmission dispatching office. This addition of security considertions has caused substantial increases in the volume of real-time information gathered by control centers plus advances in computer configuration, in the design of man-machine interfaces, and in the sophistication of application software.
COMPUTERIZED SYSTEM OPERATION The computer-based functions which are currently being implemented in power system control centers consist of four major categories: supervisory control, generation control, voltage control, and security functions. Supervisory Control
Automation in power system operation has grown in scope and in variety from purely local automatic control devices which have always been necessary for fast, direct control
Supervisory control has had a long history of application in the power industry. Via
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s upe rvi sory control a control o p erator can remot e l y operate circuit b reakers and moto rize d s witch es, connect and di s connect capacito r b anks or reactors , s tart up or shut down ge neratin g un its, and change transforme r tap s ettings. The u se o f a di g ital compu ter and a CRT ma n-mach ine i n t e rfac e i s a natur a l de vel opment o f s upe rvis o ry co ntro l. What is n ew , however, i s t h e integ rati o n o f supe rvi sory c o ntro l into a powe r sy stem contro l c ente r which p erforms o ther fu n ctions b e In th e p a s t, supe rviso ry contro l had s i de s . been install ed a s a c omp l e t e l y s e p ara te cont r o l system fro m gene rati o n c o n tro l. Th e re i s s till a ten d ency o n t he p art o f some comp anies t o maintain this sep aration for reas ons o f geography , o p erating resp onsibilitie s , or simply the la c k of an integrated p lan.
s ent o v e r t h e interface t o the control center an d factored into the AGC . The AGC algorith m is designed so as to coord inate the generating requirme nts for load re gulation with the req uirements of an optimizing control lay er. The o p timizing algorithm calculate s th e b es t all o cation of gene ration among th e pa rti c i p ating units and e nte r s th e op timum v al ues i n a table which se r v e s as the interface with AGC. Th e re sho uld be two op timizi ng al go rithms f o r g ene ra t ion contro l: one f o r normal ope rating conditi o ns and the o t h er for eme rge ncy o pe ra ti ng c o nditio n s . At t he p r esen t s tate- o fthe art, optimization o f g e neration has be en d eve loped only for normal o pe ration and the criterion is minimum o p erating cost. Thi s al gorithm is commonly known as Economic Dispatch Calculation (EDC).
Generation Control Generation control fulfills the primary function of adjusting the amount of power p lant g e neration to meet th e e ver- c hang ing d e mands of s y stem load. It i s also the function o f g eneration control t o allocate generation in s uch a way that some higher level objective, either determined by economy or by security, is met. Generation control can be viewed as a multi-layer hierarchy of controls. At the direct control layer is the regulatory-type control to meet the continuing variations in load. Direct control is done at two levels: locally , at the power plant b y turbine-generato r controls and centrally, at the system control center b y the so-called Automatic Generation Control (AGe) function. AGC determines the change in total system load and allocates required generation among the generating units which are on-line. The sampling time for AGC i s in the order of a few s econds. The allocations are transmitted over communication channels to the power p lants where the allocation signals are used b y the turbine-generator controllers to adjust the outputs of the generating units. The interfacing between plant controllers and the AGC at the system control center is an important operating feature that, if not p roperly designed, can degrade or even defeat the objective s of generation control. The problem is compounded by the almost complete lack of interaction between system control designers and plant control designers. The use of plant computers for control is still in its infancy. However, the few installations where computers are used for turbine-generator control though not for combustion control, demonstrate more effective and flexible interfacing for generation control. Generating unit characteristics such as response rates, dead bands, dynamic limits, stored energy, can be factored into the local control algorithm. The same information plus others such as status of local control may be
EDC is performed b y the central computer e v e ry f ew minu tes, an inte r v al which is conside rably less fr equent than t h e AGe cy cle. Th e AGC uses the table values calculated by e conomic dispatch as bas e settings around which the generating unit outp uts may be adjusted t o meet the system l o ad changes. Economic d isp atch requires an es timate of total s y stem load. The measureme nt of system load is not a straight-forward matter under the dynamic conditions of the power system. This i s a source of difficulty in the coordination p e rformed by AGC and generally results in unne cessary movements of generating unit outp uts. The interfacing between EDC and AGC is a continuing research problem. Currents efforts are being d irected to the system load estimation problem. The set of constraints applied in economic d ispatch calculation usually consists of a s imple power balance equation and maximum and minimum limits on the real power gene ration of each unit . This is a carry-over from the days of analog control and the early use of small digital computers. With the app lication, however, of larger and more p owerful computers at control centers, it has bec ome feasible t o install a detaile d model of the power s y stem and a full set of real and r e active power e q uations for each node in the network. This model is needed in the control center for other reasons but, once available, it can be used for economic dispatch calculations in lieu of the single power balance e q uation. It is also sometimes necessary to consider constraints related to system security. This problem will be discussed in a later section. Voltage Control The automatic control of system voltage from a control center is not yet a common practice. In the few control centers with this type of control, the determination of voltage settings or, alternatively, the allocation of reactive power, is the result of an
Pra c ti ce s and Tr e nds in Contr o l Ce nters
optimization program where the objective function is either system losses or the sum of absolute voltage deviations from a desired voltage profile, or a weighted combination of both. Linear programming techniques are currently used. Actually voltage control or reactive power dispatch should consider voltage support from a system security viewpoint. Such an approach has not as yet been successfully formulated for on-line control. Security Functions In common usage, the word "security" is understood to be the freedom from danger or risk or, as defined by the Oxford English Dictionary, the "condition of being protected from or not exposed to danger." It is in this common, everyday vein that system security is understood in electric power operation, where operating conditions and the occurrence of disturbances could lead to, or result in, equipment overloads, voltage degradation, frequency decay, system instability, or extensive service interruption. The major distinction between power system control centers of recent years and control centers of the past is the incorporation of functions related to system security. This addition of security considerations has caused substantial increases in the volume of real-time data requirements plus radical changes in computer configuration, design of man-machine interfaces, and in the sophistication of application programs. It should be noted at the outset, however, that in the present state-of-the-art the security functions that are realizable relate only to steady-state conditions. Dynamic security functions are still areas of current research. An understanding of the roles of the various security functions may be obtained by considering the following sequence of operating decisions: 1.
Using real-time system measurements, identify whether the power system is normal or not. If the system is in an emergency, go to step 4. If load has been lost, go to step 5.
2.
If the system is normal, determine whether the system is secure or insecure in the event of a nextcontingency.
3.
If insecure, i.e., there is at least one contingency which can cause an emergency, determine what preventive action should be taken to make the system secure.
4.
Execute proper corrective action to make the system normal.
5.
Restore service to system loads.
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TIle function in step 1 we refer to as "Securi ty Monitoring." The functions in step 2 and 3 make up "Security Analysis." The function in step 4 we call "Emergency Control." The function in step 5 we call "Restorative Control." Emergency Control and Restorative Control at the present state-of-the-art depend almost completely on manual actions by the operator without the benefit of any guidance by the computer. Security Monitoring. - Security Monitoring (SM) is the on-line identification of the actual operating conditions of the power system. SM requires a system-wide instrumentation on a greater scale and variety than that required by a control center without SM. The SM function checks the real-time data basically to determine whether the power system is close to, or in, the emergency state. Part of the SM function is the determination of the actual network topology. This involves a systematic processing of the realtime information about the status, i.e., open or closed position, of circuit breakers and disconnect switches. Although most of the applications of SM make use of the real-time data as acquired from the power system, there is now a trend to process the data first by state estimation procedures. State estimation (SE) produces from the set of system measurements, a "best" estimate of the vector of bus voltage magnitudes and phase angles of the network. The measurement set is understood to contain an adequate degree and spread of redundancy to allow the statistical correlation and correction of the measurements, detect and preferably identify bad data, and yield calculated values for non-telemetered quantities. As presently practiced state estimation is run much less frequently than the scanning rate of the data-acquisition Eubsystem. For functions which require short sampling times raw data is used with, at most, some crude filtering. Although there are just about ten control centers in the world with state estimation in service, the value to operation of this function is becoming more widely acknowledged. Security Analysis. - Security Analysis (SA) consists of two functions. The first function is to determine whether the normal system is secure or insecure. This is commonly known as contingency evaluation since, in practice, the security of a system is determined with reference to a set of nextcontingencies. The second function is to determine what preventive action should be taken when the system is insecure. Presently, only steady-state contingency evaluation is performed. There is still nothing in the way of dynamic security analysis. The earliest method used for contingency evaluation is based on linear sensitivity factors obtained from a completely passive linear network model of the power system.
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These sensitivity factors are commonly known as distribution factors. While present users of distribution factors are apparently satisfied with this method, designers of new control centers are considering the use of methods based on the non-linear model of the power system. Such an approach is now a practical alternative in view of improvements in computational techniques with speeds comparable to the distribution factor method but with better accuracy and facility for easy update. The modern approach to contingency evaluation is based on an On-Line Load Flow (OLF). The network model used by the load flow consists of the detailed internal system and an equivalent of the external system. The topology of the network is updated by the topology determination routine of SM. The bus injections are determined from the statistical information obtained from real-time measurements or, preferably, from the results of a state estimator. The external equivalent consists of an equivalent network with external generation and load. Means for adjusting the equivalent to match real-time conditions are provided. The determination of the preventive action in order to maneuver the system from an insecure to a secure condition is currently done by means of sensitivity factors similar to those used in contingency evaluation. This method finds a feasible solution but not an optimal one. Since normally the power system is being operated at minimum operating cost, system security will have to be obtained at a price. It is therefore necessary, especially in view of high fuel and other operating costs, that an optimization method be used to determine the preventive action. While numerous mathematical programming techniques, linear and non-linear, applied to power systems, have been investigated and written about, no practical on-line technique has as yet been placed in service at a control center. Overview of Security Functions. - Figure I gives an overall picture of how the various security-oriented functions are linked together. Certain support functions are shown in addition to those described in the preceding paragraphs. It will be noted that a simple filtering action to reject glaringly bad data precedes State Estimation. The main output of State Estimation is the vector of complex nodal injections. Using the latest injection vector and previously estimated vectors, the injection vector for some future time, tf, may be forecast. The projected injection vector can be used as inputs for making load flow studies. In addition, the injection statistics may be used for developing pseudo-measurements to be used by State Estimation in case parts of the power system are non-observable. The on-line load flow is shown as being used for security analysis and
also for a real-power optimum power flow which serves the Economic Dispatch Calculation (EDC) •
During an emergency, the Corrective Action (or "emergency control") may be executed manually or automatically depending upon the severity of the emergency. If the emergency is not very critical, such as light overloads, the Corrective Action may be obtained by, in effect, including the overloads as inequality constraints in EDC. (This is not yet practical at this time). This procedure would produce a re-allocation of generation to resolve the emergency. If corrective action by this means is not possible, the operator may direct load transfers to be carried out in the field provided there is time to sustain the overload without incurring equipment damage. More severe emergencies may require immediate load shedding. This can be done manually by supervisory control or automatically by the computer. Time permitting, the amount and location of loads to be dropped may be obtained by some optimization approach which again at this time has not been developed for practical implementation. If a normal system is found by Contingency Evaluation to be insecure the Preventive Action may offer a solution to make the system secure. This would be normally displayed to the system operator. If the cost of the Preventive Action is small, as for instance in a predominantly hydro-generation system, the operator can place the control in effect. Where the cost of the Preventive Action is high and the contingent emergency not too severe, the operator may decide not to take action. Instead he would depend upon the Emergency Control to take care of the problem should it in fact happen. A similar procedure of decision-making would be taken in case no Preventive Action can be found. Here the operator would run a study assuming that the outage has taken place and that there is an emergency. Using the Corrective Action routine in a study mode, the operator can obtain a Contingency Plan. The fact that he has a Contingency Plan which tells him what should be done in case of emergency places the system operator in an alert, ready mode. This, by itself, is a decided advantage over the case where the operator is totally umprepared for an emergency and can not react immediately to correct the situation. There are many aspects of system security which need further research and development. As mentioned previously there are no practical techniques yet available for dynamic security monitoring and analysis. Although there have been reported approaches based on Liaponnov's method and on pattern recognition, these remain on paper and have not been demonstrated in any control center. The problem of dynamic equivalents for on-line use waits in the wings as analysts still struggle with the problem of steady-state equivalents. In the
Pr ac ti ces and Tre n d s i n Contr o l Ce nt e r s
I
MEASUREMENTS
i.
H
NETWORK TOPOLOGY
I
FILTERING
I
150 3
I
I
~
STATE ESTIMATION
I
I
I
•
SECURITY MONITORING
Normal
INJECTION VECTOR, to
..
INJECTION STATISTICS
Emergency
~
1
ON-LINE LOAD FLOW
CORRECTIVE ACTION
L..
/----------
1
ADJUST EXTERNAL EQUIVALENT
INJECTION VECTOR, tf
r
..
I
REAL POWER OPTIMUM POWER FLOW
CONTINGENCY EVALUATION
r-..t---, I
I
EDC
I
L _____
Secure
I
EXIT
Insecure
-.
+
I
I
PREVENTIVE ACTION
Solution
1 I
I ...J
DISPLAY
ASSUME EMERGENCY
I
No Solution
I
CONTINGENCY PLAN
I
DISPLAY
I
Figure 1 - Organization of Security Functions
1
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T. E. Dy Liacco
area of steady-state security analysis there are investigations going on for improvements in contingency evaluation. A definite improvement would be a way of establishing online whether, at any given time, there is a need for contingency evaluation and, if so, which contingencies should be considered. Probabilistic methods are germane to this problem. Emergency control which for a long time has remained virtually untouched by researchers is now being looked at by several investigators. Of interest are the research projects initiated and sponsored by the US Department of Energy. These projects are significant beginnings in attacking the problem of emergency control and may yield some useful results.
COMPUTER HIERARCHIES Organizational Hierarchies System operation depends on local controls at power plants and substations as well as on system-wide monitoring and control at a central location. Inherently, system operation requires a computer hierarchy. In practice, there are various forms of hierarchies depending upon the assignments of operating responsibilities within a company organization or among several organizations. A power system consists of generation, transmission, and distribution subsystems. In general, the distribution subsystem and its operating problems may be viewed separately from the generation and transmission subsystems. Most distribution networks are radial in nature and can be considered as bulk loads at specific nodes of the transmission network. Further, the operating interfaces between the distribution and transmission networks are minimal. It is therefore common practice for electric power companies to have two separate divisions of operating responsibilities or functions. One, for the distribution subsystem, and the other for the combined generation and transmission subsystems, the combination being sometimes referred to as the bulk power system. Throughout the power industry, the development of computer application for operation has been directed primarily to the monitoring and control of the bulk power system. For a single company operation the control of the bulk power system is centralized at the system control center, at least for generation control. Supervisory control may also be located at the same center or decentralized into regional or district centers, each responsible for a portion of the transmission network. A single company may, as in some European and South American countries, own and operate the power system for an entire nation. With the existence of interconnections between two or more companies and where there is a mutually agreed-upon
responsibility for coordinating or even controlling inter-company functions, a higher control level, i.e., a power pool control center, may be established. A hierarchy based on organizational responsibilities may then consist of: a company, or a national, or a pool control at the top level; power plant and substation controls at the bottom level; and several regional or area levels in between. So far the concept of supervisory control has not advanced beyond that of manual remote control for localized operating maneuvers. Designers have not yet fully addressed the implementation of supervisory control for system problems. Thus, control centers today for large systems do not have supervisory control capability but rely on manual orders to lower level regional centers which are equipped with supervisory control. There are interface problems which are not effectively resolved. Should the order from the system control center be carried out directly by the computer at the regional center or should the regional operator receive the order and then initiate it via his computer? Or should the system control center have direct communications to the substation independent of the regional center? What interlocks should be provided? What coordination procedures? The answers vary with operating needs of the system. If there are needs to use supervisory control for security-related or emergency conditions where time is of the essence, supervisory control of critical stations at the system control center level may be preferable to the decentralized approach. When a power system is interconnected with one or more power systems, the result is one large power system. This large power system obeys the same physical laws as any other power system. The flow and distribution of power in an electrical network cannot be controlled on an individual branch basis except through the use of special, costly power equipment. However, if the power system were decomposed into several areas or subsystems, it would be a simple matter to control the aggregate power flows between subsystems without any additional power equipment. The total aggregate flow at the boundaries of a subsystem is obtained by adding up algebraically the flows in the branches connecting the subsystem to the other subsystems. Any discrepancy between the actual aggregate flow and the scheduled aggregate flow can be corrected by adjusting the total generation in the subsystem via AGC. The discrepancy in aggregate boundary flow is usually called the tie-line deviation. In an interconnected system, the tie-line deviation concept makes possible the decentralization of generation control at the company level. In current practice, if a power system is made up of the interconnection
Practices and Trends in Control Centers
of several subsystems belonging to different owners, then it becomes incumbent upon each owner to have tie-line deviation control regardless of how large or how small the subsystem may be, unless the subsystems, by aggreement, belong to a power pool. In pool operation, generation control may either be centralized or decentralized. In a decentralized control of a large power system consisting of several separately-owned subsystems, optimum economic operation may be approximated by periodic economy interchanges between companies. This approach works quite well for normal operating conditions and is generally a more common practice than a centralized economic dispatch for several interronnected companies. During abnormal operating conditions, economic operation may not be the overriding concern. In this case the control objective may no longer be amendable to a decentralized approach. In a power pool where there is an avowed intent to coordinate controls for the mutual benefit of all participants, generation control on a decentralized basis cannot be adapted to execute preventive controls for security improvement or emergency controls to correct steady state emergencies, unless the subsystems are very weakly coupled. The centralized organization especially if supported by a computer hierarchy or network has more flexible interfaces at all levels. It is adaptable to implementation of a system-oriented optimizing layer of generation control in that control strategies may be specified down to the power plant level. When we try to map Security Functions into a computer .hierarchy, we find we have to make design decisions as we had to for supervisory control and generation control. In this instance, however, the problems of proper software interfaces and data transfers in both directions of the hierarchy are much more difficult to resolve. Let us consider a two-level hierarchy such as in a power pool with a pool computer and member company computers or of a large company with a central computer and regional computers. In such a hierarchy should security monitoring be performed at both levels? If so, how should the function be decomposed? Should state estimation be performed at both levels and if so, how should the state estimators be interfaced? What type of data should be transferred from the lower level computers to the top level computer in order to update its network model? Should Security Analysis be performed by each member company as well as by the pool computer? What should the software and data interfaces be? How should the network models and external equivalents be structured for each company and for the pool? There are as yet no clear guidelines developed as to how the best answers to these questions may be arrived at, although investigations into these problem areas are actively going on. One thing is certain.
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The computer hierarchy must be designed so as to accommodate a potentially high volume of data transfers between levels and in both directions. There is a trend towards the application of computer-communication networks. Such networks would provide the means for implementing the software interfaces required for Security Monitoring, Security Analysis, as well as for other system operation functions. It is also evident that the nature of the various algorithms and how they are decomposed have a major bearing on the structure of the hierarchy. Hence in the design process of considering trade-offs, the choice of algorithms and even the development of new ones are important factors.
SUMMARY
In this paper, I have presented a description of functions required for power system operation which are currently implemented by digital computers. Since the distinguishing features of the state-of-the-art in computer control application are the security-related functions, I have elaborated more on those new functions than on the traditional ones of generation and supervisory control which I have assumed are quite well-known. More work remains to be done in the difficult problems of dynamic security analysis, emergency control, and restorative control. It will be many more years before applications in these areas can be reported as being in operation. In my discussions, I have'pointed out that existing computer hierarchies are based on organizational responsibilities rather than on system-theoretic or control-theoretic considerations. An organizational hierarchy has so far been satisfactory for normal operating conditions especially for generation control and supervisory control. In the decentralized approach, the problem of equitable sharing of responsibilities is neatly resolved. However, when security considerations are integrated into the control system design and as we anticipate developments in corrective action to enhance security, we realize that the software and data interfaces with existing hierarchical structures are not easily identifiable. In addition, present structures may not be capable of effectively implementing the desired security functions. The use of digital computer systems for bulk power real-time monitoring and control is definitely on the increase throughout the world. As of this writing, there are about 80 power system control centers in service or under development which have, as a miniautomatic generation control and security monitoring. These control centers are listed in Table 1. This table does not
mum,
T. E. Dy Liacco
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include control centers which are solely for supervisory control and network monitoring. A review of Table I will show to what extent any specific control or security function is being applied or will be applied at control centers. The limitations of this paper do not permit Table I
LIST OF POWER SYSTEM CONTROL CENTERS
In-Service Date June 1969
more details to be presented on these control centers. Table I is a condensed version of a more detailed table which I have compiled containing data on computer memory sizes, number of color CRT's, number of remotes, dynamic wall display, and data on lower level computers in a hierarchy. This detailed table is available on request.
Name of Ccxnpany
Michigan Electric Power Ann Arbor, Michigan
Computer System 1-GEPAC 4020 + l-GEPAC 4060 + 2-GEPAC 4010 + Da ta Links to 2
On-Line Functions· In-Service
Planned
AGC, EDC, SM, SA
Member Companies July 1970
Penn.-Jersey-Maryland (PJM) Interconnection
Norristown, Pennsylvania
Dual IBM 370/158 + 2 IBM System 7 + Da ta Links to 9 Pool MeDi:>er
AGC, EOC,
SM, SA
Locations June 1970
New England Power Exch. West Springfield, Mass.
l-SIGMA 2 + l-SIGMA 2 + Da ta Links to 4 Satellite Computers
AGe, EDC, SM
Dec. 1970
Central Electricity Generating Board
Dual ARGUS 500 + Data Links to 7 Regional Centers
SM, SA, OLF, OSC
Fukuoka, Japan
l-TOSBAC 7000/20 + l-TOSBAC 3000
AGCa, EDC, AVC, SM
Houston Lighting & Power
Duplex SIGMA 5
AGC, EDC, SBC, SVC, SM, SA, OLF, PLSC
l-NORD 1
AGe, EDC, SE, SA, EC, OLF
Dual IBM 370/J55 + Dual Data Links to 8 Member Companies
AGe, EDC, SM, SA
l-HITAC 7250 + 2-HIDIC 100 + l-HIDIC 100 + Data Link to
AGCa, EDC,
london, England Oct. 1971
NOv. 1971
Kyushu Electric Power
Houston, Texas
March 1972
Norwegian Water Resources & Electricity Board
SA, SBC, SE, OLF
Tokke, Norway
June 1972
New York Power Pool Albany, New York
Oct. 1972
TOhoku Electric Power
Sendai, Japan
SH
AVC, SA, OLF
Regional Office with 1-HIDIC 500 + l-HIDIC 100 Oct. 1972
Electric Power Utility Laufenburg Laufenburg, SWi tzerland
l-IBM 1800 + i-IBM S/7
AGCa, SM, SE
Dec. 1972
Cleveland Electric Illuminating Cleveland, Ohio
Dual SIGMA 5 + Data Links to 5-P2000 Plant Computers
AGC, EDC, SBC, SM,
Feb. 1973
OLF, OPF, ASTA, EC
Kansai Electric Power Osaka, Japan
l-HITAC 8300 + 1-flIDIC 500 + l-lIIDIC 100 + Data Link to 2- !Br·! 370/158
March 1973
Commonwealth Edison Chicago, Illinois
Dual SIGMA 5
AGC, EOC,
March 1973
Tokyo Electric Power
ACC a , EOC,
Tokyo, Japan
Dual TOSBAC 7000/20 + Dual TOSBAC 40C
General Public Utilities Reading, Pennsylvania
Dual SIGMA 5 + Data Links to PJM
AGC, EOC,
/lay 1973
SA, SE, SVC, ACR
AGCa, EDC,
SM, SA, OLF
SM, SA, DLF
and 3 Member Companies
SM
SM
SA
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Practices and Trends in Control Centers In-Service Date
July 1973
Name of COI:1pany Interbrabant Schaerbeek, Belgium
Computer System l-Westinghouse P2000 l-Westinghouse P2500 l-Westinghouse P2500 Data Link to CPTE
On-Line Functions* In-Service Planned ~ ~
SBC, SM, SE, SA, OLF, OPF
~
July 1973
Electricit~
de France (EDF) National Control Center Paris, France
1-cn 9080 + 1-cn 9040 + Data Links to Regional Control Centers
AGC a , SM, SA, SE, OLF
Sept. 1973
Southern Services Birmingham, Alabama
Dual IBM 370/158 + 4-AOS 900 + 1 (spare) ~ Video Data Links to 4 Company Dispatch Centers and to 13 Division Control Centers
AGe, EDC, SM
Oct. 1973
American Electric Power Canton, Ohio
I-IBM 1800 + 3-HP2116B + 1 (spare) ~ Data Link to I-IBM 370/165
AGC a ,
Oct. 1973
Philadelphia Electric Philadelphia, Pennsylvania
Trip1e-BURROUGHS 6700 + Data Links to 2 Plant Canputers and to PJM
AGe, EDC, SM, SA
Nov. 1973
Hokuriku Electric Power Toyama, Japan
1-TOSBAC 7000/20 + 1-TOSPAC 3000 + 1-TOSBAC 40
May 1974
Pennsy 1 vania Power & Ligh t Allentown, Pennsylvania
Dual S IGMA 5 + Data Links to pJM and to 6 Division Offices
AGe, EOC, SBC, SM, SA
Sept. 1974
Carolina Power & Light Ra1eigh, North Carolina
Dual S IGMA 5 + 2-GEPAC 3010
AGC, EDC, SBC, SM, SA
Dec. 1974
Bonneville Power Administration Portland, Oregon
Dual PDP-10 + 2-PDP-ll + 1-PDP-ll + Dual GEPAC 4010 + Dual GEPAC 3010 + 1-GEPAC 30CS + Future Dual SEL85
AGe, SM
Dec. 1974
Iowa-Illinois Gas & Electric Davenport, Iowa
Dual SIGMA 5
AGe, EDC, SBC, SVC, SM
Jan. 1975
Sierra Pacific Power Reno, Nevada
Dual SLASH/5
AGC,
April 1975
City of Gainesville Gainesville, Florida
Dual W2500
AGC, EDC, SBC, SVC, SM
June 1975
Public Service Electric and Gas Newark, New Jersey
Dual GEPAC 4010 + 1-GE 4050 + Data Links to PJM
SBC, SVC, SM, SA
Aug. 1975
Wisconsin Electric Power Milwaukee, Wisconsin
Quad CDC SC-1700 + Dual CDC CYBER 72-13 + Data Link to Wisconsin-Michigan Power which has Dual CDC SC-1700 + Video Data Link to 9 Offices
Aug. 1975
Tennessee Valley Authority Chattanooga, Tennessee
AGe, EDC, SM + 3-GEPAC l-SIGMA 3010 + Data Links to 5 Area Dispatch Centers
Oct. 1975
Rheinisch-Westfalisches E1ektrizitatswerk (RWE) Brauweiler, West Gennany
Dual SIEMENS 360
Oct. 1975
Nov. 1975
EOC,
SA, SE, OLF
SE
SA
AGC, EOC,
Ave, SM, SE, EC
NEPEX
Technische Werke der Stadt Stuttgart Stuttgart, West Germany
I-Siemens 306 + Data Link to IBM 370/
SA, OLF
EOC, SM
AGC, £DC,
OLF, OPF
SBC, SM, SA, SE
AGCa, SM, SE, SA,
1-GEPAC 4020 +
AVC, OLF
SA, SE
OLF, OSC
Rhode Island-Eastern Massachusetts-Vermont Westborough, Massachusetts
SVC
AGe, EDC, SM
Da ta Links to
sec,
SM,
SE, SA,
OLF
SA, SE, OLF
T. E. Dy Liacco
1508 In-Service Date
Name of Company
Computer System
On-Line Functions· In-Service ~
Dec. 1975
Middle South Services Pine Bluff, Arkansas
Dual SrGMA 5 + Da ta Links to 3 Member Companies
Dec. 1975
Detroi t Edison Detroit, Michigan
Dual SI C ~ 5 + Cata Link to Michigan Power
S~l
Ontario lIydro Toronto, Canada
Univac MP 11 / 42 + 3-NOVA l:? OO
AGC, EOC , SM, SE
SA, OLF
National Power Administration Warsaw, Po land
Dual COC SC-1774 + CDC 317 0
AGC, EDC, SH
SF, SA, AVC
Dual PDP 11/45 + Da ta Links to
Sr.l, SBC, SVC
Dec. 1975
1976
April 19 76
Societe Pour la Coordination de la Production et ell Trar.sport de L'€'ner g ie Electriquc (CPTE ) National Dispatchin ry
AGC, EDC, SM, OLF, SA
OPF
SE C , SVC,
SA, SE, OLF
Charleroi Regional Dispa tching
Linkebeek, Belgium May 1976
Potorr.ac Electric Power Wa3hington, D.C.
Dual S:GMA 9 + 4-SPC 16/65 + Data Link to PJM + Data Link to IBM 360/65 + Video Data Link to Executive Office
sac, SVC, AVC, SM,
SA, OLF
DTA
June 1976
Eastern Iowa Light & Power Wilton, Iowa
Dual POP 11/35
AGC, EOC, sac, SVC, SM
Dec. 1976
Chubu Electric Power Nagoya, Japan
Tosbac 7000/20 + Tosbac 7000/25 + Dual Tosbac 40-C
AGC, EOC, AVC, SM
Feb. 1977
Swedish State Power Board Stockholm, Sweden
Dual SIGMA 9 + 2-COC System 17
SM
AGC, SA, SE, OLF
April 1977
Board of Public Utilities Kansas City, Kansas
Dual WP 2500
AGC, EOC, SBC, SM
SVC
May 1977
Utah Power & Light Salt Lake City, Utah
Dual SIGMA 5
AGC, EOC, SBC, SVC, SM
SA, SE,
June 1977
Nova Scotia Power Halifax, Nova Scotia
Dual POP 11/35
AGC, SBC SVC, SM
June 1977
Kansas City Power & Light Kansas City, Missouri
Dual COC System 17
AGC, EOC,
Corn Belt Power Co-op
Dual COC System 17
Nov. 1977
sac,
Humboult, Iowa
SM
AGC, EDC, SBC, SM
Early 1978
Louisville Gas & Electric Louisville, Kentucky
Dual HS 4400
AGC, EOC, sac, SVC, SM
Early 1978
Fuerzas Electricas de
Dual GE 4010 + Dual Interdata 70
AGe, EOC, SBC, SVC , SM, OLF
Cata1ufia (FECSA) Barcelona, Spain Early 1978
Southern California Edison Los Angeles, California
Quad COC System 17 + Dual CYBER 73-16 + Data Links to 8 Switching Centers + Video Data Link to Headquarters Office
AGC, NOX, SM, SA, SE, OLF,
Early 1978
Iberduero Bilbao, Spain
Dual Duplex MODCOMP IV + Da ta. Links to 2 Regional Centers
AGC, EOC, SM,
Dual POP 11/40 +
AGC, EOC, sac, SVC, SM
Early 1978
Jacksonville Electric Authority Jacksonville, Florida
Da ta Links to Distribution Center
SE , OLF
Mid 1978
Hidroelectrica Espanola t-tadrid, Spain
Dual 11001001'.1' IV
AGC, EOC, sac, SM
Mid 1978
Public Service of Oklahona Tulsa, Ok lahona
Dua 1 MOOCOMP IV + Data Links to Regional Offices
AGC, EDC, SBC, SM
l1id 1978
lo1.innesota Power & Light Duluth Minnesota
lAlal Xerox 550
AGC, EDC, SBC, SVC,
SM , SA, OLF
1509
Practices and Trends in Control Centers In-Service Date
Name of Company
Computer System
On-Line Functions· In-Service ~
Mid 1978
Ronergo Uationa l Loae Dispatchi ng Bucharest, ROMania
Dual Siemens 330 + ~a ta Links t o 5 Regional Control Ce nters
EDC, SM, SE, SA
I-lid 1978
Gas-Elektrizitats-und l,iasserwerke (CD.') Cologne , h'es t Germany
Dual Sie~ens 33 0 + I-Siemens 330 + Data Links to I Regional Control Cer.ter
EDC, SM, SE, SA, OLF
Mid 1978
Portlanc General Electric Portland, Oregon
Dual MOOCOt1P IV + Video Data Links to 6 Regional Offices
AGe , SBC, SM
Hid 1978
Public Service Conpany of Ne ..... Hanpshire Mancr.cster, ~~cw Hanpshire
Dual S[L 32/55 + Data Links t o ~FPEX
AGe , FDC, SBC, SVC, S!-1, SA , OLF
SE,
Late 1978
Servicios Electricos del Gran Buenos Aires (SEGEh) Buenos Aires, Argentir.a
Late 1978
Virginia Elec tric & Power Richmond, Vi r ginia
Dual Xerox 55 0
AGC, EDC, SM, OLF
Late 1978
Taiwan Power Taipei, Taiwan
Dual Xerox 550
AGC, EDC, SBC, SM, OLF
Late 1978
Northern Indiana Pub lic Service Hammond, Indiana
Dual SEL 32/55
AGC, EDC, SBC, SVC, SM
Late 1978
Hungarian Electric Power Budapest, Hungary
Dual HIDIC-80
AGe, EDC, SM, OLF
Late 1978
Florida Power & Light Miami, Florida
Dual CYBER 173-6 + Quad CDC System 17 + Data Links to 6 Remote Offices
AGC, EDC, SBC, SM, SE, SA
Late 1978
Korea Electric Seoul, Korea
Dual LN CP400
AGe, EDC, SBC, SM
Early 1979
Del~arva Power & Light Wilmington, Delaware
Dual CYBER 172-4 + Quad CDC System 17
AGe, EDC, SBC, SM, SE, SA, OPF
Early 1979
connecticut Valley Electric Exchange System (CONVEX) Berlin, Connecticut
Dual PDPll/70 + Dual PDP11/34 + Data Links to NEPEX + Da ta Link to IBM 370/165
AGC, EDC, SBC, SM, SA, OLF
Early 1979
Electricity Supply Commission of South Africa Johannesburg, South Africa
Dual Xerox 550
AGe, EDC, SBC, SVC, SM, SA, OLF
Early 1979
Florida Power St. Petersburg, Florida
Dual Duplex Xerox 550 + Dual LN CP400 + Data Links to 2 Distribution Dispatching Offices
AGC, EDC,
SM, SA, SE, OLF , OSC
SVC, SM,
SE, SA, OLF
Mid 1979
New England Power Exchange (NEPEX) West Springfield, Mass.
1-IBM 370/148 + l-IBM S/7 + Data Links to 4 Satellite Computers
AGC, EDC, SM, SA, OLF
Mid 1979
State Electric Commission of Victoria Melbourne, Australia
Dual SEL 32/55 + Dual MAC-16 + Data Links to 2 Area COntrol Centers
AGC, EOC, SM
Late 1979
Aqua y Energia Electrica Buenos Aires, Argentina
Dual Siemens 340 + 1-Siemens 340 + Data Links to 6 Regional Control Centers
EDC, SM, SE, SA, OLF, asc
Early 1980
Columbus & Southern Ohio Electric Coluni:ms, Ohio
Quad SLASH/7
AGC, EDC, SBC, SVC, SM, SE, SA, OLF
Early 1980
Imatran Voima Helsinki, Finland
Dual MODCOMP IV + 3-PDP 11/34 + Data Links to 8 District Centers
AGC, EOC, SVC, SM, SE, OLF
T. E. Dy Liacco
1510 In-Service
Date Early 198 0
Mid 1980
Mid 1980
Name of Company Duquesne Light Pittsburgh, Pennsylvania
Israel Electric Israel
Italian Electric Power
State Board (ENEL) National Control Center Rome, Italy
Mid 1980
Early 1981
Cincinnati Gas & Electric Cincinnati , Ohio
Electricite de France (EDF) National Con trol Center
Paris, France
Compu ter System
Dual SEL 32/75 + Data Links to Distribution Control Center
Dual PDP 11/70 + Dual PDP 11/70 + Data Links to 2 Subsidiary Control Centers Dual DEC KL-l0 + Dual PDP 11/70 + Data Links to 8 Area Control
On-Line Functions· In-Service Planned AGe, EOC, NOX, sac, svc, SM, SE, OLF
AGe, EOC, SBC, SVC, SM, SE,
SA, OLF
AGe, EDC, SM,
SE, SA, AVC, EC
Centers
Dual POP 11/70 + Da ta Links to 4 Remote Centers each with PDP 11/34 + Data Links to 2 Companies
AGe, EOC, SM,
Dual MITRA 125 + Third
AGC, SM, SE,
Computer + Dual Solar 16-40 + Data Links to 7 Regional Control
SA
SBC, SM, SBC
Centers
almplemented by analog controller. bDriven by hard wired logic independent of computer. CStroke full graphic. *Legend for on-line functions:
ACR AGe ASTA AVC DTA EC EDC NOX OLF
Automatic Circui t Restoration Automatic Generation Control Automatic System· Trouble Analysis Automatic Vol tage/Var Control Distribution Trouble Analysis Emergency Control Economic Dispatch Control MinimLUn NO x Emission Dispatch On -Line Load Flow
OPF OSC PLSC SA SBC SE SM SVC
Opti mum Power Flow On -Line Short Ci rcuit ~ipe Line Supervising Control Steady-State Security Analysis Supervisory Breaker Control State Estimation Securi ty t-lOni taring Supervisory Voltaqe Control
Abstract. This paper reviews the state-of-the-art of the design of control centers for the operation of electric power systems. Modern control centers are distinguished by the integration of new functions designed to enhance system security with the traditional functions of generation control and of supervisory control. The emphasis therefore of the overview presented in this paper is on the practices and trends in control center design which are brought about by considerations of system security. Keywords. Control center; power system control; power system security; power system operation; computer control.
INTRODUCTION The prime objective of the operation of an electric power system is the maintenance of a continuous supply of electric energy to all users served by the system. Once an electric power system is built and placed in operation, then it should stay in continuous operation indefinitely. This is the overall goal of the process and the function of system operation is to meet this goal as best as practicable. "As best as practicable" just about sums up the nature of the decisionmaking requirements which are continuously made of system operation. What is "best" or, equivalently, what is "orr timum", depends on the electrical conditions of the power system, economic factors, environmental restrictions, equipment capabilities, and on many other constraints which have bearing on the operating action or decision. What is "practicable" depends on the tools available to operation, the control capabili ties of the power system, and on the human operators at the operation center and at the power plants and other manned locations. Decision-making problems in system operation are complex and difficult. Adding to the difficulty is the stricture to make decisions within a relatively short time so that action, if needed, may be carried out promptly enough to be of benefit to operation. This obviously requires judicious application of automation in the monitoring and control of the power system.
action to the present-day development of control centers with redundant, real-time computer systems, digital telemetry and control, interactive man-machine interfaces, and advanced monitoring and control programs. With these new control centers it has become practicable to enhance system operation through functions which had not been available pl·eviously. In this paper I will discuss some of the forms and directions in which new computerized functions are being developed in the electric power industry. Special emphasis will be placed on those functions directed to the preservation of system security since it is precisely the incorporation of security-oriented functions which is making the big difference between a modern, advanced control center and the traditional generation or transmission dispatching office. This addition of security considertions has caused substantial increases in the volume of real-time information gathered by control centers plus advances in computer configuration, in the design of man-machine interfaces, and in the sophistication of application software.
COMPUTERIZED SYSTEM OPERATION The computer-based functions which are currently being implemented in power system control centers consist of four major categories: supervisory control, generation control, voltage control, and security functions. Supervisory Control
Automation in power system operation has grown in scope and in variety from purely local automatic control devices which have always been necessary for fast, direct control
Supervisory control has had a long history of application in the power industry. Via
1499
1500
T. E. Dy Li a cc o
s upe rvi sory control a control o p erator can remot e l y operate circuit b reakers and moto rize d s witch es, connect and di s connect capacito r b anks or reactors , s tart up or shut down ge neratin g un its, and change transforme r tap s ettings. The u se o f a di g ital compu ter and a CRT ma n-mach ine i n t e rfac e i s a natur a l de vel opment o f s upe rvis o ry co ntro l. What is n ew , however, i s t h e integ rati o n o f supe rvi sory c o ntro l into a powe r sy stem contro l c ente r which p erforms o ther fu n ctions b e In th e p a s t, supe rviso ry contro l had s i de s . been install ed a s a c omp l e t e l y s e p ara te cont r o l system fro m gene rati o n c o n tro l. Th e re i s s till a ten d ency o n t he p art o f some comp anies t o maintain this sep aration for reas ons o f geography , o p erating resp onsibilitie s , or simply the la c k of an integrated p lan.
s ent o v e r t h e interface t o the control center an d factored into the AGC . The AGC algorith m is designed so as to coord inate the generating requirme nts for load re gulation with the req uirements of an optimizing control lay er. The o p timizing algorithm calculate s th e b es t all o cation of gene ration among th e pa rti c i p ating units and e nte r s th e op timum v al ues i n a table which se r v e s as the interface with AGC. Th e re sho uld be two op timizi ng al go rithms f o r g ene ra t ion contro l: one f o r normal ope rating conditi o ns and the o t h er for eme rge ncy o pe ra ti ng c o nditio n s . At t he p r esen t s tate- o fthe art, optimization o f g e neration has be en d eve loped only for normal o pe ration and the criterion is minimum o p erating cost. Thi s al gorithm is commonly known as Economic Dispatch Calculation (EDC).
Generation Control Generation control fulfills the primary function of adjusting the amount of power p lant g e neration to meet th e e ver- c hang ing d e mands of s y stem load. It i s also the function o f g eneration control t o allocate generation in s uch a way that some higher level objective, either determined by economy or by security, is met. Generation control can be viewed as a multi-layer hierarchy of controls. At the direct control layer is the regulatory-type control to meet the continuing variations in load. Direct control is done at two levels: locally , at the power plant b y turbine-generato r controls and centrally, at the system control center b y the so-called Automatic Generation Control (AGe) function. AGC determines the change in total system load and allocates required generation among the generating units which are on-line. The sampling time for AGC i s in the order of a few s econds. The allocations are transmitted over communication channels to the power p lants where the allocation signals are used b y the turbine-generator controllers to adjust the outputs of the generating units. The interfacing between plant controllers and the AGC at the system control center is an important operating feature that, if not p roperly designed, can degrade or even defeat the objective s of generation control. The problem is compounded by the almost complete lack of interaction between system control designers and plant control designers. The use of plant computers for control is still in its infancy. However, the few installations where computers are used for turbine-generator control though not for combustion control, demonstrate more effective and flexible interfacing for generation control. Generating unit characteristics such as response rates, dead bands, dynamic limits, stored energy, can be factored into the local control algorithm. The same information plus others such as status of local control may be
EDC is performed b y the central computer e v e ry f ew minu tes, an inte r v al which is conside rably less fr equent than t h e AGe cy cle. Th e AGC uses the table values calculated by e conomic dispatch as bas e settings around which the generating unit outp uts may be adjusted t o meet the system l o ad changes. Economic d isp atch requires an es timate of total s y stem load. The measureme nt of system load is not a straight-forward matter under the dynamic conditions of the power system. This i s a source of difficulty in the coordination p e rformed by AGC and generally results in unne cessary movements of generating unit outp uts. The interfacing between EDC and AGC is a continuing research problem. Currents efforts are being d irected to the system load estimation problem. The set of constraints applied in economic d ispatch calculation usually consists of a s imple power balance equation and maximum and minimum limits on the real power gene ration of each unit . This is a carry-over from the days of analog control and the early use of small digital computers. With the app lication, however, of larger and more p owerful computers at control centers, it has bec ome feasible t o install a detaile d model of the power s y stem and a full set of real and r e active power e q uations for each node in the network. This model is needed in the control center for other reasons but, once available, it can be used for economic dispatch calculations in lieu of the single power balance e q uation. It is also sometimes necessary to consider constraints related to system security. This problem will be discussed in a later section. Voltage Control The automatic control of system voltage from a control center is not yet a common practice. In the few control centers with this type of control, the determination of voltage settings or, alternatively, the allocation of reactive power, is the result of an
Pra c ti ce s and Tr e nds in Contr o l Ce nters
optimization program where the objective function is either system losses or the sum of absolute voltage deviations from a desired voltage profile, or a weighted combination of both. Linear programming techniques are currently used. Actually voltage control or reactive power dispatch should consider voltage support from a system security viewpoint. Such an approach has not as yet been successfully formulated for on-line control. Security Functions In common usage, the word "security" is understood to be the freedom from danger or risk or, as defined by the Oxford English Dictionary, the "condition of being protected from or not exposed to danger." It is in this common, everyday vein that system security is understood in electric power operation, where operating conditions and the occurrence of disturbances could lead to, or result in, equipment overloads, voltage degradation, frequency decay, system instability, or extensive service interruption. The major distinction between power system control centers of recent years and control centers of the past is the incorporation of functions related to system security. This addition of security considerations has caused substantial increases in the volume of real-time data requirements plus radical changes in computer configuration, design of man-machine interfaces, and in the sophistication of application programs. It should be noted at the outset, however, that in the present state-of-the-art the security functions that are realizable relate only to steady-state conditions. Dynamic security functions are still areas of current research. An understanding of the roles of the various security functions may be obtained by considering the following sequence of operating decisions: 1.
Using real-time system measurements, identify whether the power system is normal or not. If the system is in an emergency, go to step 4. If load has been lost, go to step 5.
2.
If the system is normal, determine whether the system is secure or insecure in the event of a nextcontingency.
3.
If insecure, i.e., there is at least one contingency which can cause an emergency, determine what preventive action should be taken to make the system secure.
4.
Execute proper corrective action to make the system normal.
5.
Restore service to system loads.
1501
TIle function in step 1 we refer to as "Securi ty Monitoring." The functions in step 2 and 3 make up "Security Analysis." The function in step 4 we call "Emergency Control." The function in step 5 we call "Restorative Control." Emergency Control and Restorative Control at the present state-of-the-art depend almost completely on manual actions by the operator without the benefit of any guidance by the computer. Security Monitoring. - Security Monitoring (SM) is the on-line identification of the actual operating conditions of the power system. SM requires a system-wide instrumentation on a greater scale and variety than that required by a control center without SM. The SM function checks the real-time data basically to determine whether the power system is close to, or in, the emergency state. Part of the SM function is the determination of the actual network topology. This involves a systematic processing of the realtime information about the status, i.e., open or closed position, of circuit breakers and disconnect switches. Although most of the applications of SM make use of the real-time data as acquired from the power system, there is now a trend to process the data first by state estimation procedures. State estimation (SE) produces from the set of system measurements, a "best" estimate of the vector of bus voltage magnitudes and phase angles of the network. The measurement set is understood to contain an adequate degree and spread of redundancy to allow the statistical correlation and correction of the measurements, detect and preferably identify bad data, and yield calculated values for non-telemetered quantities. As presently practiced state estimation is run much less frequently than the scanning rate of the data-acquisition Eubsystem. For functions which require short sampling times raw data is used with, at most, some crude filtering. Although there are just about ten control centers in the world with state estimation in service, the value to operation of this function is becoming more widely acknowledged. Security Analysis. - Security Analysis (SA) consists of two functions. The first function is to determine whether the normal system is secure or insecure. This is commonly known as contingency evaluation since, in practice, the security of a system is determined with reference to a set of nextcontingencies. The second function is to determine what preventive action should be taken when the system is insecure. Presently, only steady-state contingency evaluation is performed. There is still nothing in the way of dynamic security analysis. The earliest method used for contingency evaluation is based on linear sensitivity factors obtained from a completely passive linear network model of the power system.
1502
T. E. Dy Liacco
These sensitivity factors are commonly known as distribution factors. While present users of distribution factors are apparently satisfied with this method, designers of new control centers are considering the use of methods based on the non-linear model of the power system. Such an approach is now a practical alternative in view of improvements in computational techniques with speeds comparable to the distribution factor method but with better accuracy and facility for easy update. The modern approach to contingency evaluation is based on an On-Line Load Flow (OLF). The network model used by the load flow consists of the detailed internal system and an equivalent of the external system. The topology of the network is updated by the topology determination routine of SM. The bus injections are determined from the statistical information obtained from real-time measurements or, preferably, from the results of a state estimator. The external equivalent consists of an equivalent network with external generation and load. Means for adjusting the equivalent to match real-time conditions are provided. The determination of the preventive action in order to maneuver the system from an insecure to a secure condition is currently done by means of sensitivity factors similar to those used in contingency evaluation. This method finds a feasible solution but not an optimal one. Since normally the power system is being operated at minimum operating cost, system security will have to be obtained at a price. It is therefore necessary, especially in view of high fuel and other operating costs, that an optimization method be used to determine the preventive action. While numerous mathematical programming techniques, linear and non-linear, applied to power systems, have been investigated and written about, no practical on-line technique has as yet been placed in service at a control center. Overview of Security Functions. - Figure I gives an overall picture of how the various security-oriented functions are linked together. Certain support functions are shown in addition to those described in the preceding paragraphs. It will be noted that a simple filtering action to reject glaringly bad data precedes State Estimation. The main output of State Estimation is the vector of complex nodal injections. Using the latest injection vector and previously estimated vectors, the injection vector for some future time, tf, may be forecast. The projected injection vector can be used as inputs for making load flow studies. In addition, the injection statistics may be used for developing pseudo-measurements to be used by State Estimation in case parts of the power system are non-observable. The on-line load flow is shown as being used for security analysis and
also for a real-power optimum power flow which serves the Economic Dispatch Calculation (EDC) •
During an emergency, the Corrective Action (or "emergency control") may be executed manually or automatically depending upon the severity of the emergency. If the emergency is not very critical, such as light overloads, the Corrective Action may be obtained by, in effect, including the overloads as inequality constraints in EDC. (This is not yet practical at this time). This procedure would produce a re-allocation of generation to resolve the emergency. If corrective action by this means is not possible, the operator may direct load transfers to be carried out in the field provided there is time to sustain the overload without incurring equipment damage. More severe emergencies may require immediate load shedding. This can be done manually by supervisory control or automatically by the computer. Time permitting, the amount and location of loads to be dropped may be obtained by some optimization approach which again at this time has not been developed for practical implementation. If a normal system is found by Contingency Evaluation to be insecure the Preventive Action may offer a solution to make the system secure. This would be normally displayed to the system operator. If the cost of the Preventive Action is small, as for instance in a predominantly hydro-generation system, the operator can place the control in effect. Where the cost of the Preventive Action is high and the contingent emergency not too severe, the operator may decide not to take action. Instead he would depend upon the Emergency Control to take care of the problem should it in fact happen. A similar procedure of decision-making would be taken in case no Preventive Action can be found. Here the operator would run a study assuming that the outage has taken place and that there is an emergency. Using the Corrective Action routine in a study mode, the operator can obtain a Contingency Plan. The fact that he has a Contingency Plan which tells him what should be done in case of emergency places the system operator in an alert, ready mode. This, by itself, is a decided advantage over the case where the operator is totally umprepared for an emergency and can not react immediately to correct the situation. There are many aspects of system security which need further research and development. As mentioned previously there are no practical techniques yet available for dynamic security monitoring and analysis. Although there have been reported approaches based on Liaponnov's method and on pattern recognition, these remain on paper and have not been demonstrated in any control center. The problem of dynamic equivalents for on-line use waits in the wings as analysts still struggle with the problem of steady-state equivalents. In the
Pr ac ti ces and Tre n d s i n Contr o l Ce nt e r s
I
MEASUREMENTS
i.
H
NETWORK TOPOLOGY
I
FILTERING
I
150 3
I
I
~
STATE ESTIMATION
I
I
I
•
SECURITY MONITORING
Normal
INJECTION VECTOR, to
..
INJECTION STATISTICS
Emergency
~
1
ON-LINE LOAD FLOW
CORRECTIVE ACTION
L..
/----------
1
ADJUST EXTERNAL EQUIVALENT
INJECTION VECTOR, tf
r
..
I
REAL POWER OPTIMUM POWER FLOW
CONTINGENCY EVALUATION
r-..t---, I
I
EDC
I
L _____
Secure
I
EXIT
Insecure
-.
+
I
I
PREVENTIVE ACTION
Solution
1 I
I ...J
DISPLAY
ASSUME EMERGENCY
I
No Solution
I
CONTINGENCY PLAN
I
DISPLAY
I
Figure 1 - Organization of Security Functions
1
1504
T. E. Dy Liacco
area of steady-state security analysis there are investigations going on for improvements in contingency evaluation. A definite improvement would be a way of establishing online whether, at any given time, there is a need for contingency evaluation and, if so, which contingencies should be considered. Probabilistic methods are germane to this problem. Emergency control which for a long time has remained virtually untouched by researchers is now being looked at by several investigators. Of interest are the research projects initiated and sponsored by the US Department of Energy. These projects are significant beginnings in attacking the problem of emergency control and may yield some useful results.
COMPUTER HIERARCHIES Organizational Hierarchies System operation depends on local controls at power plants and substations as well as on system-wide monitoring and control at a central location. Inherently, system operation requires a computer hierarchy. In practice, there are various forms of hierarchies depending upon the assignments of operating responsibilities within a company organization or among several organizations. A power system consists of generation, transmission, and distribution subsystems. In general, the distribution subsystem and its operating problems may be viewed separately from the generation and transmission subsystems. Most distribution networks are radial in nature and can be considered as bulk loads at specific nodes of the transmission network. Further, the operating interfaces between the distribution and transmission networks are minimal. It is therefore common practice for electric power companies to have two separate divisions of operating responsibilities or functions. One, for the distribution subsystem, and the other for the combined generation and transmission subsystems, the combination being sometimes referred to as the bulk power system. Throughout the power industry, the development of computer application for operation has been directed primarily to the monitoring and control of the bulk power system. For a single company operation the control of the bulk power system is centralized at the system control center, at least for generation control. Supervisory control may also be located at the same center or decentralized into regional or district centers, each responsible for a portion of the transmission network. A single company may, as in some European and South American countries, own and operate the power system for an entire nation. With the existence of interconnections between two or more companies and where there is a mutually agreed-upon
responsibility for coordinating or even controlling inter-company functions, a higher control level, i.e., a power pool control center, may be established. A hierarchy based on organizational responsibilities may then consist of: a company, or a national, or a pool control at the top level; power plant and substation controls at the bottom level; and several regional or area levels in between. So far the concept of supervisory control has not advanced beyond that of manual remote control for localized operating maneuvers. Designers have not yet fully addressed the implementation of supervisory control for system problems. Thus, control centers today for large systems do not have supervisory control capability but rely on manual orders to lower level regional centers which are equipped with supervisory control. There are interface problems which are not effectively resolved. Should the order from the system control center be carried out directly by the computer at the regional center or should the regional operator receive the order and then initiate it via his computer? Or should the system control center have direct communications to the substation independent of the regional center? What interlocks should be provided? What coordination procedures? The answers vary with operating needs of the system. If there are needs to use supervisory control for security-related or emergency conditions where time is of the essence, supervisory control of critical stations at the system control center level may be preferable to the decentralized approach. When a power system is interconnected with one or more power systems, the result is one large power system. This large power system obeys the same physical laws as any other power system. The flow and distribution of power in an electrical network cannot be controlled on an individual branch basis except through the use of special, costly power equipment. However, if the power system were decomposed into several areas or subsystems, it would be a simple matter to control the aggregate power flows between subsystems without any additional power equipment. The total aggregate flow at the boundaries of a subsystem is obtained by adding up algebraically the flows in the branches connecting the subsystem to the other subsystems. Any discrepancy between the actual aggregate flow and the scheduled aggregate flow can be corrected by adjusting the total generation in the subsystem via AGC. The discrepancy in aggregate boundary flow is usually called the tie-line deviation. In an interconnected system, the tie-line deviation concept makes possible the decentralization of generation control at the company level. In current practice, if a power system is made up of the interconnection
Practices and Trends in Control Centers
of several subsystems belonging to different owners, then it becomes incumbent upon each owner to have tie-line deviation control regardless of how large or how small the subsystem may be, unless the subsystems, by aggreement, belong to a power pool. In pool operation, generation control may either be centralized or decentralized. In a decentralized control of a large power system consisting of several separately-owned subsystems, optimum economic operation may be approximated by periodic economy interchanges between companies. This approach works quite well for normal operating conditions and is generally a more common practice than a centralized economic dispatch for several interronnected companies. During abnormal operating conditions, economic operation may not be the overriding concern. In this case the control objective may no longer be amendable to a decentralized approach. In a power pool where there is an avowed intent to coordinate controls for the mutual benefit of all participants, generation control on a decentralized basis cannot be adapted to execute preventive controls for security improvement or emergency controls to correct steady state emergencies, unless the subsystems are very weakly coupled. The centralized organization especially if supported by a computer hierarchy or network has more flexible interfaces at all levels. It is adaptable to implementation of a system-oriented optimizing layer of generation control in that control strategies may be specified down to the power plant level. When we try to map Security Functions into a computer .hierarchy, we find we have to make design decisions as we had to for supervisory control and generation control. In this instance, however, the problems of proper software interfaces and data transfers in both directions of the hierarchy are much more difficult to resolve. Let us consider a two-level hierarchy such as in a power pool with a pool computer and member company computers or of a large company with a central computer and regional computers. In such a hierarchy should security monitoring be performed at both levels? If so, how should the function be decomposed? Should state estimation be performed at both levels and if so, how should the state estimators be interfaced? What type of data should be transferred from the lower level computers to the top level computer in order to update its network model? Should Security Analysis be performed by each member company as well as by the pool computer? What should the software and data interfaces be? How should the network models and external equivalents be structured for each company and for the pool? There are as yet no clear guidelines developed as to how the best answers to these questions may be arrived at, although investigations into these problem areas are actively going on. One thing is certain.
1505
The computer hierarchy must be designed so as to accommodate a potentially high volume of data transfers between levels and in both directions. There is a trend towards the application of computer-communication networks. Such networks would provide the means for implementing the software interfaces required for Security Monitoring, Security Analysis, as well as for other system operation functions. It is also evident that the nature of the various algorithms and how they are decomposed have a major bearing on the structure of the hierarchy. Hence in the design process of considering trade-offs, the choice of algorithms and even the development of new ones are important factors.
SUMMARY
In this paper, I have presented a description of functions required for power system operation which are currently implemented by digital computers. Since the distinguishing features of the state-of-the-art in computer control application are the security-related functions, I have elaborated more on those new functions than on the traditional ones of generation and supervisory control which I have assumed are quite well-known. More work remains to be done in the difficult problems of dynamic security analysis, emergency control, and restorative control. It will be many more years before applications in these areas can be reported as being in operation. In my discussions, I have'pointed out that existing computer hierarchies are based on organizational responsibilities rather than on system-theoretic or control-theoretic considerations. An organizational hierarchy has so far been satisfactory for normal operating conditions especially for generation control and supervisory control. In the decentralized approach, the problem of equitable sharing of responsibilities is neatly resolved. However, when security considerations are integrated into the control system design and as we anticipate developments in corrective action to enhance security, we realize that the software and data interfaces with existing hierarchical structures are not easily identifiable. In addition, present structures may not be capable of effectively implementing the desired security functions. The use of digital computer systems for bulk power real-time monitoring and control is definitely on the increase throughout the world. As of this writing, there are about 80 power system control centers in service or under development which have, as a miniautomatic generation control and security monitoring. These control centers are listed in Table 1. This table does not
mum,
T. E. Dy Liacco
1506
include control centers which are solely for supervisory control and network monitoring. A review of Table I will show to what extent any specific control or security function is being applied or will be applied at control centers. The limitations of this paper do not permit Table I
LIST OF POWER SYSTEM CONTROL CENTERS
In-Service Date June 1969
more details to be presented on these control centers. Table I is a condensed version of a more detailed table which I have compiled containing data on computer memory sizes, number of color CRT's, number of remotes, dynamic wall display, and data on lower level computers in a hierarchy. This detailed table is available on request.
Name of Ccxnpany
Michigan Electric Power Ann Arbor, Michigan
Computer System 1-GEPAC 4020 + l-GEPAC 4060 + 2-GEPAC 4010 + Da ta Links to 2
On-Line Functions· In-Service
Planned
AGC, EDC, SM, SA
Member Companies July 1970
Penn.-Jersey-Maryland (PJM) Interconnection
Norristown, Pennsylvania
Dual IBM 370/158 + 2 IBM System 7 + Da ta Links to 9 Pool MeDi:>er
AGC, EOC,
SM, SA
Locations June 1970
New England Power Exch. West Springfield, Mass.
l-SIGMA 2 + l-SIGMA 2 + Da ta Links to 4 Satellite Computers
AGe, EDC, SM
Dec. 1970
Central Electricity Generating Board
Dual ARGUS 500 + Data Links to 7 Regional Centers
SM, SA, OLF, OSC
Fukuoka, Japan
l-TOSBAC 7000/20 + l-TOSBAC 3000
AGCa, EDC, AVC, SM
Houston Lighting & Power
Duplex SIGMA 5
AGC, EDC, SBC, SVC, SM, SA, OLF, PLSC
l-NORD 1
AGe, EDC, SE, SA, EC, OLF
Dual IBM 370/J55 + Dual Data Links to 8 Member Companies
AGe, EDC, SM, SA
l-HITAC 7250 + 2-HIDIC 100 + l-HIDIC 100 + Data Link to
AGCa, EDC,
london, England Oct. 1971
NOv. 1971
Kyushu Electric Power
Houston, Texas
March 1972
Norwegian Water Resources & Electricity Board
SA, SBC, SE, OLF
Tokke, Norway
June 1972
New York Power Pool Albany, New York
Oct. 1972
TOhoku Electric Power
Sendai, Japan
SH
AVC, SA, OLF
Regional Office with 1-HIDIC 500 + l-HIDIC 100 Oct. 1972
Electric Power Utility Laufenburg Laufenburg, SWi tzerland
l-IBM 1800 + i-IBM S/7
AGCa, SM, SE
Dec. 1972
Cleveland Electric Illuminating Cleveland, Ohio
Dual SIGMA 5 + Data Links to 5-P2000 Plant Computers
AGC, EDC, SBC, SM,
Feb. 1973
OLF, OPF, ASTA, EC
Kansai Electric Power Osaka, Japan
l-HITAC 8300 + 1-flIDIC 500 + l-lIIDIC 100 + Data Link to 2- !Br·! 370/158
March 1973
Commonwealth Edison Chicago, Illinois
Dual SIGMA 5
AGC, EOC,
March 1973
Tokyo Electric Power
ACC a , EOC,
Tokyo, Japan
Dual TOSBAC 7000/20 + Dual TOSBAC 40C
General Public Utilities Reading, Pennsylvania
Dual SIGMA 5 + Data Links to PJM
AGC, EOC,
/lay 1973
SA, SE, SVC, ACR
AGCa, EDC,
SM, SA, OLF
SM, SA, DLF
and 3 Member Companies
SM
SM
SA
1507
Practices and Trends in Control Centers In-Service Date
July 1973
Name of COI:1pany Interbrabant Schaerbeek, Belgium
Computer System l-Westinghouse P2000 l-Westinghouse P2500 l-Westinghouse P2500 Data Link to CPTE
On-Line Functions* In-Service Planned ~ ~
SBC, SM, SE, SA, OLF, OPF
~
July 1973
Electricit~
de France (EDF) National Control Center Paris, France
1-cn 9080 + 1-cn 9040 + Data Links to Regional Control Centers
AGC a , SM, SA, SE, OLF
Sept. 1973
Southern Services Birmingham, Alabama
Dual IBM 370/158 + 4-AOS 900 + 1 (spare) ~ Video Data Links to 4 Company Dispatch Centers and to 13 Division Control Centers
AGe, EDC, SM
Oct. 1973
American Electric Power Canton, Ohio
I-IBM 1800 + 3-HP2116B + 1 (spare) ~ Data Link to I-IBM 370/165
AGC a ,
Oct. 1973
Philadelphia Electric Philadelphia, Pennsylvania
Trip1e-BURROUGHS 6700 + Data Links to 2 Plant Canputers and to PJM
AGe, EDC, SM, SA
Nov. 1973
Hokuriku Electric Power Toyama, Japan
1-TOSBAC 7000/20 + 1-TOSPAC 3000 + 1-TOSBAC 40
May 1974
Pennsy 1 vania Power & Ligh t Allentown, Pennsylvania
Dual S IGMA 5 + Data Links to pJM and to 6 Division Offices
AGe, EOC, SBC, SM, SA
Sept. 1974
Carolina Power & Light Ra1eigh, North Carolina
Dual S IGMA 5 + 2-GEPAC 3010
AGC, EDC, SBC, SM, SA
Dec. 1974
Bonneville Power Administration Portland, Oregon
Dual PDP-10 + 2-PDP-ll + 1-PDP-ll + Dual GEPAC 4010 + Dual GEPAC 3010 + 1-GEPAC 30CS + Future Dual SEL85
AGe, SM
Dec. 1974
Iowa-Illinois Gas & Electric Davenport, Iowa
Dual SIGMA 5
AGe, EDC, SBC, SVC, SM
Jan. 1975
Sierra Pacific Power Reno, Nevada
Dual SLASH/5
AGC,
April 1975
City of Gainesville Gainesville, Florida
Dual W2500
AGC, EDC, SBC, SVC, SM
June 1975
Public Service Electric and Gas Newark, New Jersey
Dual GEPAC 4010 + 1-GE 4050 + Data Links to PJM
SBC, SVC, SM, SA
Aug. 1975
Wisconsin Electric Power Milwaukee, Wisconsin
Quad CDC SC-1700 + Dual CDC CYBER 72-13 + Data Link to Wisconsin-Michigan Power which has Dual CDC SC-1700 + Video Data Link to 9 Offices
Aug. 1975
Tennessee Valley Authority Chattanooga, Tennessee
AGe, EDC, SM + 3-GEPAC l-SIGMA 3010 + Data Links to 5 Area Dispatch Centers
Oct. 1975
Rheinisch-Westfalisches E1ektrizitatswerk (RWE) Brauweiler, West Gennany
Dual SIEMENS 360
Oct. 1975
Nov. 1975
EOC,
SA, SE, OLF
SE
SA
AGC, EOC,
Ave, SM, SE, EC
NEPEX
Technische Werke der Stadt Stuttgart Stuttgart, West Germany
I-Siemens 306 + Data Link to IBM 370/
SA, OLF
EOC, SM
AGC, £DC,
OLF, OPF
SBC, SM, SA, SE
AGCa, SM, SE, SA,
1-GEPAC 4020 +
AVC, OLF
SA, SE
OLF, OSC
Rhode Island-Eastern Massachusetts-Vermont Westborough, Massachusetts
SVC
AGe, EDC, SM
Da ta Links to
sec,
SM,
SE, SA,
OLF
SA, SE, OLF
T. E. Dy Liacco
1508 In-Service Date
Name of Company
Computer System
On-Line Functions· In-Service ~
Dec. 1975
Middle South Services Pine Bluff, Arkansas
Dual SrGMA 5 + Da ta Links to 3 Member Companies
Dec. 1975
Detroi t Edison Detroit, Michigan
Dual SI C ~ 5 + Cata Link to Michigan Power
S~l
Ontario lIydro Toronto, Canada
Univac MP 11 / 42 + 3-NOVA l:? OO
AGC, EOC , SM, SE
SA, OLF
National Power Administration Warsaw, Po land
Dual COC SC-1774 + CDC 317 0
AGC, EDC, SH
SF, SA, AVC
Dual PDP 11/45 + Da ta Links to
Sr.l, SBC, SVC
Dec. 1975
1976
April 19 76
Societe Pour la Coordination de la Production et ell Trar.sport de L'€'ner g ie Electriquc (CPTE ) National Dispatchin ry
AGC, EDC, SM, OLF, SA
OPF
SE C , SVC,
SA, SE, OLF
Charleroi Regional Dispa tching
Linkebeek, Belgium May 1976
Potorr.ac Electric Power Wa3hington, D.C.
Dual S:GMA 9 + 4-SPC 16/65 + Data Link to PJM + Data Link to IBM 360/65 + Video Data Link to Executive Office
sac, SVC, AVC, SM,
SA, OLF
DTA
June 1976
Eastern Iowa Light & Power Wilton, Iowa
Dual POP 11/35
AGC, EOC, sac, SVC, SM
Dec. 1976
Chubu Electric Power Nagoya, Japan
Tosbac 7000/20 + Tosbac 7000/25 + Dual Tosbac 40-C
AGC, EOC, AVC, SM
Feb. 1977
Swedish State Power Board Stockholm, Sweden
Dual SIGMA 9 + 2-COC System 17
SM
AGC, SA, SE, OLF
April 1977
Board of Public Utilities Kansas City, Kansas
Dual WP 2500
AGC, EOC, SBC, SM
SVC
May 1977
Utah Power & Light Salt Lake City, Utah
Dual SIGMA 5
AGC, EOC, SBC, SVC, SM
SA, SE,
June 1977
Nova Scotia Power Halifax, Nova Scotia
Dual POP 11/35
AGC, SBC SVC, SM
June 1977
Kansas City Power & Light Kansas City, Missouri
Dual COC System 17
AGC, EOC,
Corn Belt Power Co-op
Dual COC System 17
Nov. 1977
sac,
Humboult, Iowa
SM
AGC, EDC, SBC, SM
Early 1978
Louisville Gas & Electric Louisville, Kentucky
Dual HS 4400
AGC, EOC, sac, SVC, SM
Early 1978
Fuerzas Electricas de
Dual GE 4010 + Dual Interdata 70
AGe, EOC, SBC, SVC , SM, OLF
Cata1ufia (FECSA) Barcelona, Spain Early 1978
Southern California Edison Los Angeles, California
Quad COC System 17 + Dual CYBER 73-16 + Data Links to 8 Switching Centers + Video Data Link to Headquarters Office
AGC, NOX, SM, SA, SE, OLF,
Early 1978
Iberduero Bilbao, Spain
Dual Duplex MODCOMP IV + Da ta. Links to 2 Regional Centers
AGC, EOC, SM,
Dual POP 11/40 +
AGC, EOC, sac, SVC, SM
Early 1978
Jacksonville Electric Authority Jacksonville, Florida
Da ta Links to Distribution Center
SE , OLF
Mid 1978
Hidroelectrica Espanola t-tadrid, Spain
Dual 11001001'.1' IV
AGC, EOC, sac, SM
Mid 1978
Public Service of Oklahona Tulsa, Ok lahona
Dua 1 MOOCOMP IV + Data Links to Regional Offices
AGC, EDC, SBC, SM
l1id 1978
lo1.innesota Power & Light Duluth Minnesota
lAlal Xerox 550
AGC, EDC, SBC, SVC,
SM , SA, OLF
1509
Practices and Trends in Control Centers In-Service Date
Name of Company
Computer System
On-Line Functions· In-Service ~
Mid 1978
Ronergo Uationa l Loae Dispatchi ng Bucharest, ROMania
Dual Siemens 330 + ~a ta Links t o 5 Regional Control Ce nters
EDC, SM, SE, SA
I-lid 1978
Gas-Elektrizitats-und l,iasserwerke (CD.') Cologne , h'es t Germany
Dual Sie~ens 33 0 + I-Siemens 330 + Data Links to I Regional Control Cer.ter
EDC, SM, SE, SA, OLF
Mid 1978
Portlanc General Electric Portland, Oregon
Dual MOOCOt1P IV + Video Data Links to 6 Regional Offices
AGe , SBC, SM
Hid 1978
Public Service Conpany of Ne ..... Hanpshire Mancr.cster, ~~cw Hanpshire
Dual S[L 32/55 + Data Links t o ~FPEX
AGe , FDC, SBC, SVC, S!-1, SA , OLF
SE,
Late 1978
Servicios Electricos del Gran Buenos Aires (SEGEh) Buenos Aires, Argentir.a
Late 1978
Virginia Elec tric & Power Richmond, Vi r ginia
Dual Xerox 55 0
AGC, EDC, SM, OLF
Late 1978
Taiwan Power Taipei, Taiwan
Dual Xerox 550
AGC, EDC, SBC, SM, OLF
Late 1978
Northern Indiana Pub lic Service Hammond, Indiana
Dual SEL 32/55
AGC, EDC, SBC, SVC, SM
Late 1978
Hungarian Electric Power Budapest, Hungary
Dual HIDIC-80
AGe, EDC, SM, OLF
Late 1978
Florida Power & Light Miami, Florida
Dual CYBER 173-6 + Quad CDC System 17 + Data Links to 6 Remote Offices
AGC, EDC, SBC, SM, SE, SA
Late 1978
Korea Electric Seoul, Korea
Dual LN CP400
AGe, EDC, SBC, SM
Early 1979
Del~arva Power & Light Wilmington, Delaware
Dual CYBER 172-4 + Quad CDC System 17
AGe, EDC, SBC, SM, SE, SA, OPF
Early 1979
connecticut Valley Electric Exchange System (CONVEX) Berlin, Connecticut
Dual PDPll/70 + Dual PDP11/34 + Data Links to NEPEX + Da ta Link to IBM 370/165
AGC, EDC, SBC, SM, SA, OLF
Early 1979
Electricity Supply Commission of South Africa Johannesburg, South Africa
Dual Xerox 550
AGe, EDC, SBC, SVC, SM, SA, OLF
Early 1979
Florida Power St. Petersburg, Florida
Dual Duplex Xerox 550 + Dual LN CP400 + Data Links to 2 Distribution Dispatching Offices
AGC, EDC,
SM, SA, SE, OLF , OSC
SVC, SM,
SE, SA, OLF
Mid 1979
New England Power Exchange (NEPEX) West Springfield, Mass.
1-IBM 370/148 + l-IBM S/7 + Data Links to 4 Satellite Computers
AGC, EDC, SM, SA, OLF
Mid 1979
State Electric Commission of Victoria Melbourne, Australia
Dual SEL 32/55 + Dual MAC-16 + Data Links to 2 Area COntrol Centers
AGC, EOC, SM
Late 1979
Aqua y Energia Electrica Buenos Aires, Argentina
Dual Siemens 340 + 1-Siemens 340 + Data Links to 6 Regional Control Centers
EDC, SM, SE, SA, OLF, asc
Early 1980
Columbus & Southern Ohio Electric Coluni:ms, Ohio
Quad SLASH/7
AGC, EDC, SBC, SVC, SM, SE, SA, OLF
Early 1980
Imatran Voima Helsinki, Finland
Dual MODCOMP IV + 3-PDP 11/34 + Data Links to 8 District Centers
AGC, EOC, SVC, SM, SE, OLF
T. E. Dy Liacco
1510 In-Service
Date Early 198 0
Mid 1980
Mid 1980
Name of Company Duquesne Light Pittsburgh, Pennsylvania
Israel Electric Israel
Italian Electric Power
State Board (ENEL) National Control Center Rome, Italy
Mid 1980
Early 1981
Cincinnati Gas & Electric Cincinnati , Ohio
Electricite de France (EDF) National Con trol Center
Paris, France
Compu ter System
Dual SEL 32/75 + Data Links to Distribution Control Center
Dual PDP 11/70 + Dual PDP 11/70 + Data Links to 2 Subsidiary Control Centers Dual DEC KL-l0 + Dual PDP 11/70 + Data Links to 8 Area Control
On-Line Functions· In-Service Planned AGe, EOC, NOX, sac, svc, SM, SE, OLF
AGe, EOC, SBC, SVC, SM, SE,
SA, OLF
AGe, EDC, SM,
SE, SA, AVC, EC
Centers
Dual POP 11/70 + Da ta Links to 4 Remote Centers each with PDP 11/34 + Data Links to 2 Companies
AGe, EOC, SM,
Dual MITRA 125 + Third
AGC, SM, SE,
Computer + Dual Solar 16-40 + Data Links to 7 Regional Control
SA
SBC, SM, SBC
Centers
almplemented by analog controller. bDriven by hard wired logic independent of computer. CStroke full graphic. *Legend for on-line functions:
ACR AGe ASTA AVC DTA EC EDC NOX OLF
Automatic Circui t Restoration Automatic Generation Control Automatic System· Trouble Analysis Automatic Vol tage/Var Control Distribution Trouble Analysis Emergency Control Economic Dispatch Control MinimLUn NO x Emission Dispatch On -Line Load Flow
OPF OSC PLSC SA SBC SE SM SVC
Opti mum Power Flow On -Line Short Ci rcuit ~ipe Line Supervising Control Steady-State Security Analysis Supervisory Breaker Control State Estimation Securi ty t-lOni taring Supervisory Voltaqe Control