Keywords: Harmonics, HVdc, converter impedance.Preprint Order Number: PE-288PRS (03-2002)Discussion Deadline: August 2002

Network-Constrained Multiperiod Auctionfor a Pool-Based Electricity Market

Motto, A. L.; Galiana, F.D.; Conejo, AJ.; Arroyo, J.M.

Author Affiliation: McGill University; University of Castilla-LaMancha.

Abstract: This paper presents a multiperiod electricity auctionmarket tool that explicitly takes into account transmission congestionand losses as well as intertemporal operating constraints, such asstart-up costs, ramp rates, and minimum up and down times that may beincluded in any generating unit's composite bid. This approach, whichrequires only existing mixed-integer linear solvers, provides the marketoperator with a valuable tool for scheduling participants in a competi-tive market where transparency, fairness, and confidentiality of partici-pants' data are of paramount concem. Under this framework, onlynetwork data is of public domain; producers are not required to revealcorporate data, and they have more flexibility in specifying the struc-ture of their composite bid. This paper demonstrates and illustratesthrough numerical studies using test systems that an efficient and faircompetitive electricity market can be implemented taking into accountnetwork constraints and losses.

Keywords: Pool-based electricity market, social welfare maximi-zation, nodal pricing, congestion management, mixed-integer linearprogramming.

Preprint Order Number: PE-640PRS (03-2002)Discussion Deadline: August 2002

An Individual Welfare MaximationAlgorithm for Electricity Markets

Abstract: An algorithm that allows a market participant to maxi-mize its individual welfare in electricity spot markets is presented. Theuse of the algorithm in determining market equilibrium points, calledNash equilibria, is demonstrated. The start of the algorithm is a spotmarket model that uses the optimal power flow (OPF), with a full repre-sentation of the transmission system and inclusion of consumer bid-ding. The algorithm utilizes price and dispatch sensitivities availablefrom the Hessian matrix and gradient of the OPF to help determine anoptimal change in an individual's bid. The algorithm is shown to besuccessful in determining local welfare maxima, and the prospects forscaling the algorithm up to realistically sized systems are very good.Nash equilibria are investigated assuming all participants attempt tomaximize their individual welfare. This is done by iteratively solvingthe individual welfare maximization algorithm until all individuals stopmodifying their bids.

Keywords: Power systems, economics, welfare maximization,OPF, markets, Nash equilibrium.

Preprint Order Number: PE-122PRS (03-2002)Discussion Deadline: August 2002

Identifilcation of Circuit BreakerStatuses in WLS State Estimator

Korres, G.N.; Katsikas, PJ.

Author Affiliation: National Technical University of Athens.Abstract: This paper presents a method for probabilistic modeling

and identification of breaker statuses in power system state estimation.The conventional WLS state estimator is extended by incorporating theactive and reactive power flows on circuit breakers and their statuses asstate variables. Additional pseudo measurements for each circuitbreaker are also introduced. The status of each circuit breaker is ob-tained through SCADA or entered by operators. Depending on the re-dundancy and quality of real-time measurements, the method canestimate the correct breaker statuses. A scheme for observability analy-

sis and bad data processing for analog and topological measurements isalso utilized. The method is illustrated with a 12-node system.

Keywords: Network topology, circuit breaker, breaker status,bus/branch model, observability, bad data processing.

Preprint Order Number: PE-491PRS (03-2002)Discussion Deadline: August 2002

On Walrasian Equilibrium forPool-Based Electricity Markets

Motto, A.L.; Galiana, F.D.; Conejo, Aj.; Huneault, M.

Author Affiliation: McGill University; University of Castilla-LaMancha; Hydro-Quebec Research Institute (IREQ).

Abstract: We present a single time period decentralized electricitymarket clearing model that includes reactive power and demand re-sponsiveness in addition to the more common framework of genera-tion-side competition for the real power commodity. The approachallows self-interested agents, namely producers and consumers, inde-pendently to maximize their individual surpluses subject to prices. Thisis consistent with the notion of a competitive market as defined in equi-librium theory. An auctioneer computes equilibrium prices that achievepower balance at every network node, as required by Kirchhoff's laws.The overall scheme is justified by duality theory, for which there is arich theoretical support, and convergence is achieved using a Newtonprice-updating algorithm.

Keywords: Auction, market coordination, market equilibrium,mathematical programming, optimization methods, power generationdispatch, power generation economics, power generation scheduling,power system economics.

Preprint Order Number: PE-284PRS (03-2002)Discussion Deadline: August 2002

Power System Communications

A Zonal Load Estimation Method forUnbalanced, Radial Distribution Networks

Wan, J.; Nan Miu, K.

Author Affiliation: Drexel University.Abstract: This paper investigates the problem of load estimation in

unbalanced radial power distribution networks. The problem is formu-lated as a weighted-estimation problem with equality and inequalityconstraints. Properties of the measurement Jacobian are exploited todevelop a solution algorithm that decomposes the network into severalsmaller zones. Detailed tests on a 20-bus unbalanced radial distributionnetwork are presented with promising results.

Keywords: Load estimation, distribution system.Preprinting Order Number: PE-362PRD (03-2002)Discussion Deadline: August 2002

Attenuation Characteristics of High-RateHome-Networking PLC SignalsKim, C.J.; Chouikha, M.F.

Author Affiliation: Howard University.Abstract: This paper reports on an experimental investigation of

the influence of the HF signal attenuation on the load in residences andoffices. A laboratory test and actual measurements were performed in aresidence and an office. The experiments show that the attenuationcharacteristics are more dependent on the number of loads than the typeof loads connected. Also, the concentration of loads was found to deter-mine where the maximum attenuation of the HF signals would occur.The types and the size of the loads, however, did not affect the attenua-tion characteristics of the HF signals. Therefore, for a successful highrate PLC home networking, the analysis on the placement of the loads

IEEE Power Engineering Review, June 200258

may have to be considered for better understanding of signal attenua-tion for PLC modems and other PLC-to-media adapters.

Keywords: Power line carrier, PLC modem, home networking, sig-nal attenuation.

Preprint Order Number: PE-262PRD (03-2002)Discussion Deadline: August 2002

Power System Dynamic Performance

Dynamic Security Border Identification UsingEnhanced Particle Swarm Optimization

Kassabalidis, I.N.; El-Sharkawi, M.A.; Moulin, L.S.; Alves daSilva, A.P

Author Affiliation: University of Washington, Federal Engi-neering School at Itajuba.

Abstract: The ongoing deregulation of the energy market increasesthe need to operate modem power systems close to the security border.This requires enhanced methods for vulnerability border tracking. Thehigh-dimensional nature of power systems' operating space makes thisdifficult. However, new multiagent search techniques, such as particleswarm optimization, have shown great promise in handlinghigh-dimensional nonlinear problems. This paper investigates the useof a new variation of particle swarm optimization to identify points onthe security border of the power system, thereby identifying a vulnera-bility margin metric for the operating point.

Keywords: Particle swarm optimization, border tracking, securityassessment, vulnerability assessment, system dynamics.

Preprint Order Number: PE-293PRS (03-2002)Discussion Deadline: August 2002

Coordinated System ProtectionScheme Against Voltage Collapse UsingHeuristic Search and Predictive Control

Larrson, M.; Karlsoon, D.

Author Affiliation: Lund University; ABB Automation ProductsAB.

Abstract: A coordinated system protection scheme (SPS) againstvoltage collapse based on model predictive control and tree search ispresented. It optimally coordinates dissimilar and discrete controls,such as generator, tap changer, and load shedding controls, in presenceof soft and hard constraints on controls as well as voltages and currentsin the network. The response with the coordinated SPS is compared toan SPS based on local measurements using simulation of the Nordic 32test system. In terms of the amount of load shedding required to restorevoltage stability, the simulations indicate that load shedding based onlocal criteria is near optimal in the system studied. However, when gen-erator controls are considered also as emergency controls, the coordi-nated scheme reduces the amount of required load shedding by 35%compared to the local scheme.

Keywords: Power system dynamic stability, voltage control, pre-dictive control, search methods, trees, heuristic search, Nordic test sys-tem, wide-area protection.

Preprint Order Number: PE-816PRS (03-2002)Discussion Deadline: August 2002

An Approach to the Initializationof Dynamic Induction Motor Models

Ruiz-Vega, D.; Asiain, T.; Olguin, D.

Author Affiliaiton: University of Liege; Escuela Superior deIngenieria Mecainica y Electrica of the Instituto Politecnico Nacional.

Abstract: This paper proposes a steady-state method as a solutionto the problem of initializing the dynamic models of induction motors

in transient stability studies. The results of the proposed method arecompared to those obtained by two conventional initialization methodsthat are used in current production-grade simulation programs, in a testpower system that includes an industrial subsystem with a significantamount of induction motor loads. It is also shown that using a correctinitialization method for these dynamic devices is important, becausethe choice of the method can modify the results of the dynamictime-domain simulation and, therefore, the assessment of power sys-tem stability.

Keywords: Induction motor models, power flow methods, transientstability simulation, numerical initialization.

Preprint Order Number: PE-060PRS (03-2002)Discussion Deadline: August 2002

Stochastic Evaluation of Turbine-Generator ShaftTorsional Torques in an HVAC/DC Power System

Omar Faried, S.; Aboreshaid, S.

Author Affiliation: University of Saskatchewan; General Organi-zation for Technical Educational and Vocational Training.

Abstract: This paper presents a Monte Carlo based approach toevaluate the maximum torsional torques induced in turbine-generatorshafts during faults on a HVac/dc power system. In this context, investi-gations have been conducted on a large turbine-generator model takinginto consideration the uncertainty of various factors associated with thepractical operation of a power system. The results of these investiga-tions are presented in the form of probability distributions of the maxi-mum torsional torques induced in the turbine-generator shaft sections.A risk index that reflects the likelihood that the torque induced in a tur-bine-generator shaft exceeds its design value is also presented. More-over, the paper presents a method for calculating the expected lifeexpenditure ratio and the expected lifetime of turbine-generator shafts.

Keywords: Turbine-generator shaft torsional torques, stochastictechniques, HVdc transmission, synchronous machines.

Preprint Order Number: PE-566PRS (03-2002)Discussion Deadline: August 2002

Power System Instrumentationand Measurement

Extended Analysis of Ground ImpedanceMeasurement Using the Fall-of-Potential MethodMa, J.; Dawalibi, F.P

Author Affiliation: Safe Engineering Services and TechnologiesLtd.

Abstract: An extended analysis of ground impedance measurementusing the fall-of-potential method is presented. An interesting curverepresenting the exact locations of the potential probe when the poten-tial and current probes are in different directions is obtained for the firsttime. Curves representing measurement error are also presented for thecase when the potential probe is placed in locations where the correctground impedance cannot be measured. A similar analysis for groundimpedance measurements in multilayer soils is also discussed. Thestudy presented in this paper has extended the theory of the conven-tional fall-of-potential method and the results obtained can serve as apractical guide for ground impedance measurements made using thismethod.

Keywords: Ground impedance measurement, ground resistancemeasurement. grounding, fall-of-potential.

Preprint Order Number: PE-574PRD (03-2002)Discussion Deadline: August 2002

IEEE Power Engineering Review, June 2002 59