Expert systems for power system control in Western ... - IEEE Xplore

Expert Systems for Power System Control in Western Europe Dagmar Niebur This paper presents a survey of research and development activities of West European utilities, manufacturers and research institutions in the domain of expert system applicat i o n s f o r power s y s t e m control. T h e development of 12 expert system applications in different project states from prototype to practical use in an electric utility is studied. Emphasis is laid on practical issues like choice of application areas, power system size, labor efforts and choice of hardware and software.

Power System Monitoring and Control In his fundamental paper in 1967, Dy Liacsystem operation [ 11. He distinguishes 3 operating states called preventive (or normal), emergency and restorative states. Different control objectives are assigned to each state. Safe and economic operation are of major concem during the preventive state. Tasks like voltagevar control and economic dispatch fall in this category. In the emergency state the main objective is the prevention of a complete system collapse without disconnecting too many customers. Corrective switching, generator and load shedding are possible countermeasures taken in an emergency state. The main issue during the restorative state is the quick and safe retum into the normal state by connecting those customer loads disconnected during the emergency state and by adjusting the power generation. These restorative actions include, for example, switching operations in substations. The main objective of power system monitoring is data acquisition and evaluation either for power system analysis, planning or CO defined a control concept for power

control. State estimation, fault diagnosis and alarm processing fall into this category. Since the type of control actions to be taken depend on the results of these tasks, this paper will concentrate on projects for monitoring as well as for control of power systems. Monitoring and control functions in a utility environment are only partly automated. Automation functions solve tasks described by mathematical models which normally simplify real-world conditions or apply only to a limited set of these. The operator’s aid is always needed if the mathematical model is no longer valid for the given situation. For example, state estimation can, in principle, be solved on a computer by using the least square algorithm. But it notoriously suffers from unknown network topology. Solving voltage-var control problems with linear programming might result in infeasible solutions because, for instance, transformer tap changes can only be carried out in discrete steps. Slow computing time or divergence of the algorithm may be another handicap where the model has to be adjusted with the operator’s help. Finally, lack of methodology combined with the problem of incomplete or false data leaves tasks like alarm handling, line fault diagnosis or system restoration entirely to the operator. Although part of power system control, system restoration is planned offline. A limited number of possible blackout scenarios is simulated off-line and restoration checklists are prepared according to their results. Expert systems have been proposed to s o l v e these t a s k s to o v e r c o m e these obstacles and to take into account the operator’s knowledge. For general information see [2].

Presented at the Fifth IEEE International Symposium on Intelligent Control, Philadelphia, PA, September 5-7, 1990. The author is currently at the Jet Propulsion Luboratoq, California Institute of Technology, Pasadena, CA 91109, on leave from the Swiss Federal Institute of Technology, Luusanne, CH-1015 Luusanne, Switzerland. This work was partly supported by the US.Department of Energy through an agreement with the National Aeronautics and Space Administration.

A tutorial introduction to expert systems applications in power systems can be found in Dillon and Laughton [3]. A bibliographical survey covering 1983-1988 is presented in the paper of Zhang, Hope and Malik [4]. A detailed overview of the state of the art of expert system applications to power systems

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0272-1708/91/0600-0034$01.o00199 IIEEE

Surveys on Expert Systems for Power Systems

for the period from 1983-1989 is given by Liu and Dillon [SI. This paper studies some activities of West European universities and industrial environments with emphasis on the latter. Research in an industrial environment is primarily application-driven. The choices of research activities of these industrial research and development centers reflect the need of expert systems in specific domains. Although implementation and field tests of expert systems in power system control centers have been reported world-wide, (see for example [6] or [7],) this case study is restricted to Westem Europe due to the huge amount of available information. The following publications describe R&D activities at the Norwegian Institute of Technology and the Norwegian Research Institute for Electric Supply [8], the Swedish State Power Board [9], the Danish Utility Elkraft [ 101, the French State Power Board EDF [ 111 or [12], and the Italian State Power Board ENEL [ 131. R&D activities in West Germany are covered in [ 141.

CIGRE Activities In 1986, the lntemational Conference on Large High Voltage Electric Systems, CIGRE founded Task Force TF 38.2.7 on Expert Systems for Power System Analysis and Techniques. TF 38.2.7 became Working Group 38.6 in 1989. As a result of a survey issued by TF 38.2.7, three new task forces were founded. They are collecting information on expert systems for voltage-var control, alarm processing and monitoring, and they will investigate the state of the art of practical applications. At the 1990 CIGRE conference in Paris a panel of experts discussed issues raised in the special report on Practical Applications of Expert Systems in Control, Operation and Protection of Power Systems [ 151. In 1987, TF 38.2.7 distributed a questionnaire to workers in 15 countries worldwide covering information about 68 expert system projects. In this report, monitoring and control of power systems were identified as the main application areas. (Other areas were system analysis, planning, education and training simulators.) In fact more than half of all

/€E€ Control Systems

projects implement or improve functions like fault diagnosis, alarm handling, state estimation, voltage-var control, switching operations and system restoration. A summary of the survey has been published in [ 161.

Case Studies of Project Developments The first application in power systems, an expert system for restoration, was published in 1983 [17]. Main seed efforts can be observed since 1987. How mature is the technology and how are industrial environments like manufacturers and utilities involved in the development? These issues will be discussed by studying the subsequent development of selected projects mentioned as ideas or prototypes in the CIGRE survey or by other sources. Neither the CIGRE survey nor this selection of case studies can cover the area completely. But this study of project efforts, choice of hardware and software and choice of application areas can help to avoid bottlenecks in future developments. In order to get information on the present states of these projects, 13 research institutions, manufacturers and utilities were asked to fill out the questionnaire shown in the appendix. In the following section the answers to the questionnaire and the comments by the developers are briefly cited and summarized. The questionnaire was filled out by 10 institutions with 12 project descriptions. Projects whose titles are marked by * were mentioned as ideas or prototypes in the CIGRE survey. The corresponding tables show the various project state phases in the first column and the duration in months of these phases in the second column. The level of effort in person months is shown in the third and fourth column if provided by the answers to the questionnaire.

sages. In December 1984, after2 years discussion with human experts, a prototype was built in SL3, an ALGOL68 related language developed by AEG for process control. The prototype used “if-then-else” rules. Field testing of the prototype resulted in an improvement of the human-machine interface, an introduction of an interface to a simulator and a compression of the if-then-else rules into decision patterns. From July 1987 on, the prototype has been operating in the realtime environment. Because the system has been implemented on the SCADA computer, coupling with the data-base, im-

I

June 1991

I

Table I State

Duration (months)

Ideaeasibility Study Prototype Total

12 24 36

plementation of the human-machine interface, coupling to data acquisition and system buffer and message recording took 50% of the development. The manufacturer was not involved. The effort took 9 person months. Because of other priorities of the utility further development has been postponed. The expert system treats alarm messages from 58 substations of a 380/220 kV network. The current data base recorded about 1800 messages of protection devices, 550 breaker tripping messages and 150 other real-time related messages for pattern comparison. For technical details see [18]. Remarks: The prototype is an applicationdriven development urged by the needs of the utility and can be regarded as a pioneering work in this area. Note that in 1982 the expert system methodology for power systems applications was far from being a mature techno1ogy .

Automatic Fault Diagnosis and Evaluation E Hein; Energieversorgung Schwaben, Germany Scope: Selection and sorting of disturbance related messages, construction of reaction pattems of involved feeders, construction of reaction pattems of the network, identification of the nature of the event with pattem recognition techniques, identification of the location of the event, documentation and recording of the event including date, time, duration, location, disturbance type, involved lines, number of involved feeders and number of alarm messages sorted by time or origin. The project started in August 1982 after a disturbance producing a huge number of mes-

system does not move towards voltage collapse as the demand changes, and that it will cope under credible contingency conditions. (See Table I). The system was developed in collaboration between Imperial College and the former CEGB, now National Grid Company (NGC). The prototype runs on a general purpose workstation in the Poplog environment. Parts of it are implemented in Pop 1 1, Prolog, Pascal and Fortran. Coupling with the real-time system will probably take 30% of the whole effort. There is no collaboration with the manufacturer of the real-time system. The ap-

Utility

X X

X

plication currently treats a 39-bus, 60-line system but is intended to treat a 400-bus, 700-line network. For technical details see [ 191 or [20]. Remarks: T h e d e v e l o p e r s h a v e implemented an algorithmic method for the determination of vulnerable nodes in reactive areas in a logic programming language.

EM: An Expert System f o r Power System Operation; J. Keronen, Technical Research Center of Finland Scope: A knowledge based system to support switching plan generation and checking in power transmission system control center.(See Table 11). The system runs on a dedicated workstation, a Symbolics 3645 Lisp-computer and is implemented in the KEE environment in Lisp. The load flow software is written in Fortran. The project has been split up into 2 subprojects. The main project conceming switching planning will be installed at the Helsinki Energy Board where the prototype is currently being tested. Another part dealing with event analysis has been installed as a demonstration system at Imatran Voima, the Finnish national power board. The full scale prototype works with the complete model of Helsinki Energy Board’s 110 kV meshed interconnected trans-

Reactive Reserve Management in the Operational Planning of Power Systems B. Cory, Imperial College, U.K. Scope: A methodology is proposed to determine the output or setting of existing voltage-var control devices so that the allocation of the reactive reserve guarantees that the

I

Research Institution

Table I1 State Ideaeasibility Study Full Scale Prototype (Full system) Total

Duration (months)


Utility

12

4

2

24 36

24 28

6 8

35

mission network consisting of 18 substations and 4000 components. Coupling with the realtime system takes an estimated effort of 2040% of the whole development. The project has been interrupted due to labor problems for field tests. So far, the effort was about 4 person-years. The work has been mainly financed by the Finnish Ministry of Trade and Industry, supported by the Helsinki Energy Board and Imatran Voima. For technical details see [21].

Decision Support System for Security Assessment; W H o f f ” n , University of Dortmund, Germany

meta-rules and heuristics have been added for the control of the inference process. The fastest version runs as fast on a PC as a FORTRAN version developed for comparison. Other applications of the same concept were developed during the last years. Two knowledge based systems for handling even faulty alarms and for working out preventive actions in order to maintain the secure network state were especially promising.

NEDEX :Network Event Diagnosis Expert System; U. b e w e n , Siemens Erlangen, Germany

Scope: An application-independent concept of knowledge representation has been defined. Generic and non-generic rules allow the application of algorithms as well as direct coupling with external databases. A first knowledge base implemented for the task of contingency selection proved the new concept to be valid and powerful. The expert system reduces the computational effort by roughly 70% compared to a full outage computation. Afield test at a German utility gives encouraging results. (See Table In.)

Scope: Fault location of a short circuit event in the high voltage grid taking into consideration fault clearance by back-up devices. (See Table IV.) NEDEX is a joint project of a manufacturer, Siemens Erlangen, and a utility, VEW Dortmund. Currently the full system is under development. The system runs on a general purpose workstation and is implemented in Nexpert Object and C. Coupling with the realtime system will probably take 15% of the

Table III

State IdeaFeasibility Study Prototype Full system Field test Total

Duration (months)

6

Manufacturer

X X X X

12 36

9

X

63

The inference engine running on a PC, Tektronix workstation or a VAX is implemented in PROLOG. Results and network data can be displayed via a graphic interface. An explanation facility gives the reasons for certain results. Coupling with the real-time system is scheduled to take 20% of the development For technical details see [22]. The first 3 phases of the work have been entirely f u n d e d by t h e university of Dortmund, a public university. The system is current!y in field test in a utility operating a 110/220 kV network consisting of about 120 busses. The network has 30 substations, 100 transformers and 100 other components like shunts, cable, overhead lines. On a Compaq AT, 20 MHz clock, the response time for the establishment of contingency lists i s about 90 s. Remarks: According to the developer 3 different PROLOG versions have been implemented. In order to accelerate execution speed

36


whole effort. The collaborating utility, VEW, manages a network on the 380/220/110 kV level and it consists of about 200 substations, 300 bus bars, 800 feeders, 300 lines, 70 transformers and 50 injection points. All alarm-bursts of VEW have been analyzed successfully. Response time is about 30 s. Remarks: The prototype has been developed in Prolog, see [23], while according to the answer to the questionnaire the full system is currently implemented in Nexpert Object.

OSP: Optimization and Enpert Systems for Reactive Management and Voltage Monitoring and Control; L.Barruncho, Instituto Superior Tecnico (IST), Technical University of Lisbon, Portugal Scope: Creation of a new embedded energy management system (EMS) application which is reactive management and voltage monitoring and control. The objective of the expert system, one of the several functions of the application, is tertiary voltage control. (See Table V.) The system was developed in collaboration between IST and Electricidade de Portugal, the national power board as one of the future functional expansions for EDP’s newly installed EMS [24]. It has been developed in OPS83 and Fortran on a VAXstation 11. AFT was used for console emulation. In the utility’s control center

thesystemisimplementedontheSCADA,aVax 8600. Coupling with the real-time system takes 3040% of the development.The manufacturer provides the development environment but is not directly involved. A formal demonstration was held in September 1990 during field tests. The work is based on a prototype for voltage-var control developed by Liu and Tomsovic [25]. The expert system is currently providing a decision aid for operators.One of the long-term goals is a closed loop control for a subset of control actions. The system treats the whole Portuguese network, whose size is up to 300-400buses in the dynamic topology (including the neighboring Spanish equivalent). The investigators point out that the architecture of the new application will support bigger systems without great loss of performance. For technical details see [26]. For global quality assurance a Petri-Net based method for the validation and consistency of the rule base has been developed, see [27].

ISSDA: An Intelligent Substation Switching Research lnsitutionecision Aid; D. Niebul; Swiss Federal Institute of Techoy,L.uusanne,Switzerland Scope: Substation monitoring includes alarm handling and establishment of switching

Table IV State IdeaReasibility Study Prototype Full system(estimated) Total

Duration (months) 12

50 >25

Utility X X X

-I

Manufacture

X X X

>87

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I

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Table V State

Duration (months)

IdedFeasibility Study Prototype Full system Field test Total

12 6 12 6 36


r I

12 6 18

SEPP Event Monitoring in EHV Substations; P. Fauquembergue, EDF: France Scope: Fault analysis focusing on the behavior of the protection system in order to detect malfunctions. It is used a posteriori for careful analysis and understanding of the events.(See Table VII.) The prototype has been developed at EDFDER in collaboration with the National Center of Scientific Research (CNRS). It is implemented in Alouette on a Sun workstation [29]. The full system runs on a Vax station 3500 and is implemented in the Knowledge Craft environment which includes Lisp, OPS5 and

~

Table VI

fi State

Duration (months)

For the next phase, the scope of the project has been enlarged to system restoration of a distribution network at the request of SEL, the power board of the city of Lausanne which will partly fund the followon project. The current restoration model treats part of the radial operated network at 50 kV consisting of 16 substations and 24 lines. Its implementation in Nexpert Object on an Apollo workstation is under way. The estimated effort for the follow-on phase will be 7 person years during 3.5 years. The work will be carried out in collaboration between EPFL, SEL and ICE. a consultant. ICE will integrate the system into SEL‘s realtime environment. The following two projects have been developed by the Research & Development Division of Electricite de France (EDF-DER), the French national grid. In this case study, EDF-DER has been classified bhas a research institution.


1

10

12 12 24

Ideaeasibility Study Prototype Total

June 1991

Utility

12 6 12 6 36

operations in order to reconfigure a substation after an emergency state. A methodology for alarm handling has been established. A rulebased system for the simulation of switching operations and proposition of switching strategies to the operator has been developed as a demonstrator of new programming techniques.(See Table VI.) The system runs on a Apollo DN 3000 and is implemented in extended CPROLOG with graphic software written in C. Coupling with the real-time system was not intended for the prototype. For technical details see [28]. The seed effort has entirely been funded by EPFL, the Swiss Federal Institute of Technology of Lausanne.

AMPERE: A Knowledge-Based System for Network Reconfiguration A.Hertz, EDF: France

11 21

CRL. A PC serves as an interface with the SCADA. The communication software is written in Pascal. Coupling with the real-time system took 20 person months which corresponds to 30% of the whole development effort. The system currently has a communications link to the Terrier EHV substation which operates on the 400 and 225 kV level. The substation has a control center monitoring 4 satellitesubstations.For technicaldetails see [30].

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Scope: S e a r c h f o r E H V n e t w o r k reconfiguration in case of overloaded transmissionlines. Ampereis designed as asecurity analysis tool for real-time decision support for dispatchers (See Table VIII.) The prototype has been developed at EDFDER in collaboration with the manufacturer Companie Generale d’Electricite (CGE). It runs on a Sun 3 and is implemented in Spoke, an object oriented language developed by (CGE). Numerical algorithms are implemented in FORTRAN. Coupling with the realt i m e s y s t e m w i l l t a k e 3 0 % of t h e development. For technical details see [3 11. At present, the whole French 400 kV network and part of the 225 kV network with 300 to 400 lines are modeled. The system is now under test at the Services des Mouvements d’Energie, EDF’s department responsible for dispatching activities. Due to other priorities of the utility, dispatchers are constrained to test AMPERE only during certain periods of the day. Ampere is not yet installed in a control room. Main funding comes from the government. EDF also has an increasing number of research contracts with universities or the National Scientific Research Centers. The following two projects have been carried out by Labein, an R&D institute sponsored by the Basque Government and by Iberduero, the Basque utility supplying approximately a quarter of Spain’s area. Iberduero operates a transmission network from 132 kV up to 380 kV consisting of 120 substations. Its load is 4000 MW. LAIDA; J.Corera, Iberduero S. A, Spain Scope: Diagnosis of faults and overloads taking place in the network, using the alarms of breakers and protective relay operation and also the status of breakers and switches to establish the topology. In addition an explana-

Table VI1 State Ideaeasibility Study Prototype Full system, Field test Dubugged system (including Validation Total

Duration (months)


14

18

27-30 12) 44

-50 68

37

I

I

Table VI11 Research Institution

Utility

11 1 12

1I

IdeaFeasibility Study Prototype Field test (up to now) Total

Manufacturer

::I I1

Application Fields

Table IX State

Duration (months)

Ideseasibility Study Prototype Full system Field test Debugged system Total

4 7 18

ARCHON; J.Corera, lherduero S. A, Spain Scope: Archon is a project sponsored by the European Community as a part of the European Strategic Programme for Research and Development i n Information Technology (ESPRIT). Archon deals with cooperation between expert systems. There are several applications within that project and two large demonstrators, one of them being Iberduero's Restoration System, that will evaluate the states of the network after a big disturbance and elaborate the sequence of actions to restore the service. The system is composed of five agents. Part of the system has been implemented - evaluation of the black-out area, identification of malfunctioning equipment - and the schedulers of actions for restoration are being designed at present. (See Table X.) The system will run on 3 Sun SPARCstation 1 and is implemented in Lisp, CLOS and C. Iberduero estimates that this system will be one of the largest of its kind.

38


Utility

11 '

3 10 30 2 2 47

5 6 40

tion of the operations of the elements involved in t h e d i s t u r b a n c e i s automatically reported.(See Table IX.) The system runs on a Sun SPARCstation 1 and is implemented in the ART environment in Lisp and C. Graphics run under SUNVIEW and GKS. Coupling with the real-time system took 5 % of the development For technical details see [32]. The work was concluded in 1989. The system works now on-line in the control center. Remark: LAIDA is the only system in practical use covered by this case study!

monitoring and control and three years after the described projects were mentioned as ideas, the first expert systems arenow implemented in several utility control centers in WesternEurope. Although this paperdoesnot pretend to coverall the workaccomplished in this area, general tendenciescan beobserved.

4 7 8 3

Alarm handling and system restoration which have been mentioned in [33] as issues of major concern for operators in control centers are successfully treated with expert system technology. In fact. five out of the twelve projects solve alarm handling, e v e n t monitoring and event analysis tasks.

D l

Collaboration

25

Knowledge-Based Instruction Handling for Process Control; H.L. Pedersen, Elkrafi Power Co., Ltd., Denmark Scope:: In the central control room of the utility, numerous written instructions inform the personnel how to handle specific situations. An knowledge-based system has been developed in order to prevent the violation of these instructions. The system provides flexibility by allowing the easy addition or removal of instructions independent of other parts of the system.(See Table XI.) The system runs on a dedicated workstation, Microexplorer. It was implemented in Lisp and OdinlTor, a tool developed for ESPRIT project No 96. The project was stopped after field tests because of problems with the expert system shell and the hardware. However, one of the conclusions drawn from this experience was that the concept of expert system application for instruction handling was valid since the expert system itself worked as intended.

Summary Seven years after the first publication in the area of expert systems for power system

All these project developments involve utilities from the start of the project on. The two restoration projects under development also involve utilities. Planning tasks like network reconfiguration tasks and establishment of switching operation lists can now be used for power system control. In the d e s c r i b e d c a s e s o n l y three manufacturers are directly involved in the system development and one in the field test. All projects except two involve research institutions which provide methodology as well as manpower. Good planning of the collaboration between research institution and utility has been shown to be essential for the successful accomplishment of the project, (see also bottlenecks). Choice of Software Nearly all developers still experiment with the programming language. Languages like Prolog or Alouette have shown to be well suited for prototyping. But for the full system development four out of six systems are or will be implemented in a more user-friendly environment a s provided by tools like Knowledge Craft or Nexpert Object. However, it is still an open question whether dis-

Table X State Ideaeasibility Study Full system (up to now) Full system (estimated) Total

Duration (months) 9 21 30


Utility

6 20 30 36

26 42 32

6

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Table XI State IdeaEeasibility Study Prototype Full system Field test Total

Research Institution 3

3

patchers in the control center share the opinion on the user-friendliness of these environments with the developers or whether the complexity of these environments tends to overburden the operator. On the other hand, zero-order logic shells, which usually run on a PC, are not applied in the described projects. Hybrid environments which provide the possibility of integrating existing algorithmic software and knowledge based software are of major concem for power system applications. Ten out of the twelve projects use several programming languages.

Choice of Hardware General purpose workstations are the general choice for this new application. Only two systems are implemented on the SCADA and two use specialized Lisp-based workstations. Advantages of workstations are clearly a versatile and user-friendly programming environment, providing virtually every programming language. They now outperform older main frame computers and their costs have dropped to the level of costs of personal computers. Local area networking permit easy upgrading of computing power and decentralization.

Effort The average effort for the development of an expert system until field test takes about five person years. Approximately 30% of this effort is used for the integration of the expert system in the real-time environment. Interestingly this amount was about 5% for LAIDA, the only operational expert system. In view of the complexity of energy management systems in general and the fact that the majority of the systems has to be integrated without the involvement of the manufacturer, this number seems small. The effort for development and implementation of “classical” software like contingency analysis or state estimation lie in the order of 10 person years. It was further pointed out by Hertz of EdF in the comments to the questionnaire that in the case of power plant control the

June I99 J

Utility

Manufacturer

15

2

1 2 18

15 10 3 30

Other

6

and H. L. Pedersen for their valuable collaboration on the questionnaire. Special thanks go to A. Germond, Swiss Federal Institute of Technology, Lausanne and H. Kirkham, Jet Propulsion Laboratory for helpful information and discussions.

References 6

knowledge acquisition phase including discussion with the technical experts only takes a few months. This is different for power systems asopposedtopowerplants.

Bottlenecks Projects are submitted to the field test either as a full scale prototype (three systems) or in the full system state (five systems). But three out of eight systems mention delays due to labor problems in the testing utilities whose priority is clearly not the test of new software but the economic operation of the network. The question whether these delays are due to reluctant acceptance of the new technology, overestimation of the need of this new technology or simply insufficient manpower, has to be investigated. The issue of maintenance like updating and consistency checks of the rule-base has only been addressed by one application. As soon as the projects move from field test to daily application, maintenance of expert systems will become a major concern.

Conclusion Expert systems for power system control have left the idea state and are becoming a more market oriented application. After having been promoted as being capable of solving any problem and after being blamed for promising too much, expert systems are finally being tested in a real-world environment, the power system control center. Looking at the large number of expert system concepts published in the area and considering the average effort of 5 person years per project until field test, a large increase of the number of expert systems operating in control centers can be expected in future.

Acknowledgment The author is grateful to L.Barmncho, J. Corera, B. Cory, P. Fauquembergue, A. Hertz, E Hein, W. Hoffmann, J. Keronen, U. Lowen

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[2] D.A. Waterman, A Guide to Expert Systems. Reading, MA: Addison-Wesley, 1986. [3] T.S. Dillon and M.A. Laughton, Eds., Expert System Applications in Power Systems. Englewood Cliffs, NJ: Prentice-Hall, 1990. [4]Z.Z. Zhang, G.S. Hope, and O.P. Malik, “Expert systems in electrical power systems - A bibliographical survey,” IEEE Trans. Power Systems, vol. T-PWRS-4, pp. 1355-1361, Oct. 1989. 151 C.C. Liu and T. Dillon, “State-of-the-art of expert system applications to power systems,” Int. J. Electric Power Energy Syst., to be published, 1991.

[6] S. Moriguchi, H. Sakaguchi, M. Kunugi, K. Shimada, and K. Suzuki, “An expert system for power system fault analysis and restoration,” in Proc. CIGRE Study Comm. 39 Meet., Tokyo, Japan, Oct. 6-3 1, 1987,pap. AI 87 02, p. 23- 1 ff. [7] EPRl EL-6680, CRAFT: On-Line Expert System for Customer Restoration Fault Testing, Final Rep., 1989. [8] A.T. Holen, “Expert systems applied to power systems. Why and how? Scope of research and development activities at NTWEFI,” in Proc. Symp. Expert System Application to PowerSyst., StockholmHelsinki, Aug. 1988,pp. 1.12-1.16. [9] F. Bergquist and G. Fabricius, “Experiences from a methodological approach to expert system design”, in Proc. Second Symp. Expert Syst. Application to Power Syst., July 1989,Seattle, WA, p. 140 ff. [lo] K. Dyre, K., O.J. Olesen, and W. Bergstrem, “New concepts in power applications,”in Proc. IFAC Symp. Power Systems, Modelling and Control Appl.,

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1121Y. Harmand, A. Hertz E. Mondon, and 0.Paillet, “Applications of A.1. techniques in the field of power system monitoring and control- current stage of development at EDF,”to be published. [ 131 P. Mirandola and M. Gallanti, “Research projects and current applications of KBS’sin ENEL - Part 1: A generaloverview- PartI1:Ashort presentationof three prototypes,” in Proc. UNIPEDWCORECH-IERE WorkshopExpert Syst., Milan, Italy, Jan. 1987. [ 141“Expertensysteme,”Elektmtechn. ZeitschnflBd. 111, Heft 5, Mar. 1990. [ 151A.J. Germond, D. Niebur, P. Van Son, “Practical

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applications of expert systems in control, operation and protection of power systems,” Spec. Rep., Pmc. CIGRE, Pans, France, Aug. 1990. [ 161CIGRE TF 38.02.07 (convener Y. Tamura), “An

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Navarro-Perez, “Integrating logic programming and algorithmic software for reactive reserve management,” in Pmc. Second Symp. Expert Syst. Appl. Power Syst., Seattle, WA, p. 4458 ff., July 1989. [20] R. Rios-Zalapa, “Reactive reserve management in the operational planning of power systems,” Ph. D. Thesis, Imperial College, London, Mar. 1990. [21]J. Keronen, “Knowledge-basedevent analysisin electric power networks,” in Proc. Second Symp. Expert Syst. Application to PowerSy.%,Seattle,WA,July 1989,p. 232 ff. [22]E. Handschin and W. Hoffman&“Experiencewith the development of a knowledge based system for security assessment,” in Proc. IASTED-PowerHigh Tech,Valencia, Spain,July 1989. [23]I? Dietze, U. Lowen,andP. Stelzner,“Untersuchungen von Netzstorungen mit einem Expertensystem,” Elektrotechn. Zeitschnp Bd. 1 11, Heft 5, pp. 226231, Mar. 1990.

[24]B. Barazash, A. Vidigal,L. Barmncho,and J. Gin, “Implementation and field experience of edp energy management system,’’IEEE Compuer Applicationsin Power; vol. 3, pp. 9-13, Jan. 1990. [25]C.C. Liu and K. Tomsovic, “An expelt system assisting decision making of reactive power/voltage control,” IEEE Trans. Power Syst., vol. T-PWRS-I, pp. 195-201,Aug. 1986.

[26] L. Barmncho, J.P. Sucena Paiva, and C.C. Liu, C.C., “VoltagdVAR control optimization and knowledge oriented approach An applicationfor the present run-time environments,“ in Pmc. Second Symp. Expert Syst. Application to Power Syst., Seattle, WA, July 1989,pp. 444 ff. [U] K. Tomsovicand L. Barmncho, “Petri net representationas an evaluationmethodfor a voltagecontrol

expert system,” in Pmc. Second Symp. Expert Syst. Application to Power Syst., Seattle, WA, p. 409 ff., July 1989. [28] D. Niebur, M. Stalder, A. J. Germond, “ISSDA, an intelligent substation switching decision aid,” in T.S. Dillon and M.A. Laughton, Eds. Expert System Applications to Power Systems. Englewood Cliffs, NJ: Prentice-Hall, 1990. [29]P. Brezillon,P. Fauquembergue,and A. Hertz, A., “Synthesisof events in an EHV substation:An expert system approach,” in Proc. IFAC Symp. Power Syst., Modelling and Control Applications, Bmsds, Belgium, Sept. 1988,pp. 16.6.1-16.6.5 [30]P. Fauquembergueandl,. Perrot,“Anexpertsystem forthe fault analysisof electric powersystems,”in Proc. Second Sytnp. Expert Syst. Applicution to Power Syst.,

Seattle,WA, July 1989,p. 264 ff.

[31]0.PailletandL.Dubost,“AMPERE,Aknowledgebased system for network reconfiguration,” in Proc.

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Stockholm-Helsinki,Aug. 1988,p. 8-32ff. [32]I.Laresgoiti,J.Perez,J.Amantegui,andJ.Echavarri, “LAIDA. Development of an expert system for disturbanceanalysis in an electricalnetwork,” in P m . Symp. Expert Syst. Application to Power Syst., Stockholm-Helsinki,Aug. 1988,p. 4-32 ff. [33] W.R. Prince, E.K. Nielson, and H.D. McNair, “A survey of c m n t operational problem,’’ IEEE Trans. PowerSyst., vol. T-PWRS4, pp. 1492-1498,Oct. 1989.

Dagmar Niebur obtained the M.Sc. degree in mathematics from the University of Dortmund, Germany, in 1984, and the M.Eng. in Computer Science and a Postgraduate Certificate in Artificial Intelligence from the Swiss Federal Institute of Technology of Lausanne (EPFL) in 1987.Since 1987 she has been a Research Engineer at the Electric Power SystemsLaboratory at EPFL. Since 1990she has been with the Jet Propulsion Laboratory, California Institute of Technology, Pasadena,CA,on leave fromEPFL. Her research interest is in artificial intelligence applied to electric power systems.She has published severalpapers in this area. She is a member of the CIGRE Task Force on “Expert Systems for Alarm Handling and Monitoring” and she has served as Technical Secretary of the ClGRE Working Group 38-06 “Expert Systems for Power Systems”. She is a senior member of the IEEE.

Doctoral Dissertations Purdue University The information about doctoral dissertations should be typed double-spaced using the following format and sent to:

Prof. Bruce H. Krogh Dept. of Electrical and Computer Eng. Camegie-Mellon University Pittsburgh, PA 15213. Beijing University of Aeronautics and Astronautics

Ronald A. Perez, “Integrated Propulsion-Airframe Dynamics & Control.” Date: August 1990. Supervisor: Prof. Osita D. I. Nwokah. Current Address: Mechanical Engineering

Department, University of Wisconsin-Milwaukee, PO Box 784, Milwaukee, WI 53201. Massachusetts Institute of Technology

YongHua Li, “On the Control of Real Time Discrete Event Systems.”

David L. Trumper, “Magnetic Suspension Techniques for Precision Motion Control.”

Date: September 1990. Supervisor: WeiBing Gao. Current Address: The Seventh Research

D a t e : September 1990. Supervisor: Prof. James K. Roberge. Current Address: Dept. of Electrical En-

Division, Beijing University of Aero. & Astro., Beijing 100083, China.

gineering, University of North Carolina at Charlotte, Charlotte, NC 28223.

40

University of British Columbia, Canada Ye Fu, “Robust Adaptive Control”. Date: January 1990. Supervisor: Guy A. Dumont. Current Address: Pulp and Paper Center,

2385 East Mall, University of British Columbia, Vancouver, BC, Canada, V6T 1W5. University of Colorado at Colorado Springs Daniel J. Stech, “A New Approach for

the Solution of Optimal Control Problems on Parallel Machines.” Date: November 1990. Supervisor: Pieter A. Frick. Current Address: Frank J. Seiler Research

Laboratory, FJSRL/NH, U.S. Air Force Academy, CO 80840. (continued on next page)

/E€Control Systems