Nuclear Power Engineering

Questionable System GroundingPractices at Nuclear Power Plants

Baxter, F.D.

Author Affiliation: ConsultantAbstract: A number of questionable system grounding practices

have been identified at nuclear power plants. These practices could re-sult in unforeseen degradation of the ac Class 1E Power System. (Class1E is the safety classification of the electrical systems and equipmentutilized to mitigate accidents at nuclear power plants). This paper pro-vides an overview of System Grounding with emphasis on the chal-lenges faced with ungrounded and high resistance grounded systems. Itexplains how design deficiencies are to be treated with respect to thesingle failure criterion, then gives a few examples of questionable sys-tem grounding practices that have been observed at nuclear powerplants in the U.S., categorizing these as potential design deficiencies.

Key Words: Grounding, nuclear power generation, safety.Preprint Order Number: PE-039EC (12-2001)Discussion Deadline: May 2002

Power System Analysis,Computing, and Economics

Forecasting Next-Day ElectricityPrices by Time Series Models

Nogales, F.J.; Contreras, J.; Conejo, AJ.; Espinola, R.

Author Afflliation: E.T.S. De Ingenieros Industriales, SpainAbstract: In the framework of competitive electricity markets,

power producers and consumers need accurate price forecasting tools.Price forecasts embody crucial information for producers and consum-ers when planning bidding strategies in order to maximize their benefitsand utilities, respectively. This paper provides two highly accurate yetefficient price forecasting tools based on time series analysis: dynamicregression and transfer function models. These techniques are ex-plained and checked against each other. Results and discussions fromreal world case studies based on the electricity markets of mainlandSpain and Califomia are presented.

Keywords: Electricity markets, market clearing price, forecasting,time series analysis.

Preprint Order Number: PE-212PRS (12-2001)Discussion Deadline: May 2002

Development of a Hybrid Modelfor Electrical Power Spot Prices

Davison, M.; Anderson, C.L., Marcus, B.; Andersen, K.

Author Affiliation: The University of Westem Ontario, CanadaAbstract: In recent years a great deal of interest has been paid to the

market-based pricing of electrical power. Electrical power contracts of-ten contain embedded options, the valuations of which require a sto-chastic model for electricity prices. Successful stochastic models existfor modeling price variations in traditional commodities. Electricity iscritically different from these commodities as it is difficult to store and,on short time scales, its price is highly inelastic. This has important im-plications for stochastic spot price models of electricity. Several sto-chastic models of electricity spot prices already exist. In these randommodels price retums play a dominant role.

In this paper we lead a guided tour through existing electricity pricedata to motivate a new stochastic electricity price model that is differentin that it directly models price. We apply the new model to the problem ofpricing options on electrical power and discuss these preliminary results.

Keywords: Electricity pricing, energy pricing, forward prices, op-tion pricing, power pricing, spot price model.

Preprint Order Number: PE-332PRS (12-2001)Discussion Deadline: May 2002

Improvements on the Duality-Based MethodUsed in Solving Optimal Power Flow Problems

Lin, C-H.; Lin, S-Y; Lin, S-S.

Author Affiliation: KaoYuan Institute of Technology, Kaoshiung,Taiwan; National Chiao Tung University, Hsinchu, Taiwan

Abstract: To improve the previously developed dual-type (DT)method used in solving optimal power flow (OPF) problems with alarge number of thermal-limit constraints, we propose two new tech-niques in this paper. The first one is a graph-method-based decomposi-tion technique, which can decompose the large-dimension projectionproblem caused by the large number of thermal-limit constraints intoseveral independent medium-dimension projection subproblems at theexpense of a slight increment of the dual problem's dimension. The sec-ond technique is an active-set strategy-based DT method, which cansolve the medium-dimension projection subproblems efficiently. Wehave used the DT method embedded with these two new techniques insolving numerous OPFs with a large number of thermal-limit con-straints. The test results show that the proposed techniques are very ef-ficient and effectively improve the DT method for handling a largenumber of thermal-limit constraints.

Keywords: Optimal power flow, thermal-limit constraints, nonlin-ear programming, graph method, decomposition.

Preprint Order Number: PE-082PRS (12-2001)Discussion Deadline: May 2002

A Market Approach to Long-TermSecurity of SupplyVazquez, C.; Rivier, M.; Perez-Arriaga, Ij.

Author Affiliation: Universidad Pontificia Comillas, Madrid,Spain

Abstract: The problem of ensuring that there is enough generationcapacity to meet future demand has been an issue in market designsince the beginning of the deregulation process. Although ideally themarket itself should be enough to provide adequate investment incen-tives, there are several factors that prevent this result from beingachieved, and some actual markets have already experienced problemsrelated with a lack of generation capacity. A regulatory framework toaddress this question is presented. The procedure is based on an orga-nized market where reliability contracts (based on financial call op-tions) are auctioned, so both their price and their allocation among thedifferent plants are determined through competitive mechanisms. Thisresults in a stabilization of the income of the generators and provides aclear incentive for new generation investment, with a minimum of regu-latory intervention. Additionally, the method represents a mar-ket-compatible mechanism to hedge demand from the occurrence ofhigh market prices.

Keywords: Capacity markets, capacity payments, long-term guar-antee of supply, generation adequacy, wholesale market design, elec-tricity markets.

Preprint Order Number: PE-180PRS (12-2001)Discussion Deadline: May 2002

Power System Topological ObservabilityAnalysis Including Switching Branches

Costa, A.S.; Lourenco, E.M.; Clements, K.A.

Author Affiliation: Universidade Federal de Santa Catarina,Florianopolis, Brazil; Worcester Polytecnic Institute, Worcester, MA

Abstract: The conventional topological observability analysis basedon the network representation at the bus-branch level is generalized to in-clude the explicit modeling of circuit breakers and switches. This gener-

IEEE Power Engineering Review, March 200258

alization is motivated by the present trend towards a more detailedrepresentation (at the substation level) of the power network in state esti-mation studies. After developing the topological representation ofswitching branches according to their current status, it is shown that ex-isting algorithms for observability and criticality analysis can be adaptedto solve the extended problem. Results of the proposed approach for gen-eralized observability and criticality analysis are validated by checkingtheir consistency with numerical state estimation results.

Keywords: Power system observability analysis, power systemstate estimation, graph theoretic methods.

Preprint Order Number: PE-810PRS (12-2001)Discussion Deadline: May 2002

Power System Communications

Analytic Model of the Measure ErrorsCaused by Communications Delay

Luque, J.; Escudero, J.I.; Perez, F.

Author Affiliation: Universidad de Sevilla, SpainAbstract: The protocols and communication systems used in the

control of the electric networks create delays due to various factorssuch as limitation of the transmission speed, retransfer among nodes,processing time, etc. These delays introduce some errors in the mea-surements used in the control center, which depend on the magnitude ofthe delay and the evolution of the measurements. In this paper an ana-lytic model of the relationship between measurement error and delay ispresented. The validity of the model is compared with experimentaldata from an electric network.

Preprint Order Number: PE-079PRD (12-2001)Discussion Deadline: May 2002

Power System Dynamic Performance

Modeling of UPFC Operation UnderUnbalanced Conditions With Dynamic Phasors

Stefanov, PC.; Stankovic, A.M.

Author Affiliation: University of Belgrade, Yugoslavia; Northeast-em University, Boston, MA

Abstract: The paper describes an analytical large-signal mode orunbalanced operation of the unified power flow controller (UPFC).This nonlinear, time-invariant model is expressed in terms of dynamicsymmetric components, and it is validated on a benchmark power sys-tem example taken from the literature. The model is evaluated via simu-lations in unbalanced operation and during unbalanced (one phase toground) faults. In both cases it achieves a very good accuracy in addi-tion to a reduction in simulation time when compared with detailedtime-domain models.

Keywords: Dynamic phasors, FACTS, UPFC, unbalanced condi-tions, dynamical models.

Preprint Order Number: PE-354PRS (12-2001)Discussion Deadline: May 2002

PMU Configuration for SystemDynamic Performance Measurementin Large Multiarea Power Systems

Kamwa, I.; Grondin, R.

Author Affiliation: Hydro-Quebec/IREQ, CanadaAbstract: Effective assessment of the dynamic performance of the

power system requires wide-area information from properly distributedphasor measurement units (PMUs). However, to maximize the infor-

mation content of the captured signals, the sensors need to be locatedappropriately, with due account given to the structural properties under-lying the given system. In this paper, two numerical algorithms are pro-posed to achieve this goal. They aim to maximize the overall sensorresponse while minimizing the correlation among sensor outputs so asto minimize the redundant information provided by multiple sensors.The sensor responses of interest are the bus voltage magnitude and theangle and frequency coherency indices, which are estimated by meansof a statistical sampling of power system response signals from a tran-sient-stability program. Through the "successive addition" scheme,one of these algorithms easily incorporates mandatory locations suchas tie-line busses and large generator step-up transformers. The pro-posed approaches are first illustrated on the Hydro-Queibec transmis-sion grid and then on a 9-area/67-bus/23-machine test networkdesigned with well-defined geographical boundaries and prespecifiedweak interties between electrically coherent areas.

Keywords: Digital fault recorders, optimal sensor location, PMU,state estimation, wide-area control, wide-area monitoring.

Preprint Order Number: PE-094PRS (12-2001)Discussion Deadline: May 2002

Control Loops Selection for DampingInter-Area Oscillation's of Electrical Networks

Heniche, A.; Kamwa, I.Author Affiliation: Laval University, Canada; Hydro-Quebec,

CanadaAbstract: This paper reports on results of a study whose objective is

to demonstrate that a systematic yet straightforward method based onwell-known system theoretical analysis tools can be applied to selectthe control loops that improve the inter-area dynamic stability whileminimizing the interactions among local and global controllers. Twocomplementary measures are involved in the measurement and controlsignals selection : the geometric measures, which allow the choice ofsignal pairs maximizing the controllability and observability ofinter-area modes, and the singular-value based total interaction mea-sure, which focuses on minimizing the interactions between the local orglobal loops at the inter-area natural frequency. As a practical illustra-tion of the proposed measurements and controllers pairing scheme, thelinearized model of a nine-area, twenty-three-generator power systeminvolving nine inter-area modes is used. The results obtained show thatcommunication links between areas may deem necessary on the onehand to improve the inter-area modes observability/controllability andon the other hand to reduce the interaction between the control loops atthe inter-area natural frequencies. The usefulness of such an analysis inminimizing the number of communication links without degrading theoverall control system performance is highlighted.

Keywords: Inter-area oscillations, global control, electrical net-works, power system stabilizers, controllability, observability, interac-tion, singular values.

Preprint Order Number: PE-651PRS (12-2001)Discussion Deadline: May 2002

Power System Instrumentationand Measurement

Harmonic Study of the Le Blanc Transformerfor the Taiwan Railway Electrification System

Huang, S.R.; Chen, B.N.

Author Affiliation: Feng Chia University, Taichung, TaiwanAbstract: The harmonic current of the Le Blanc transformer of the

Taiwan railway system is measured to determine how it reduces thepower supply capacity to the trolley (nonlinear load). Improvements tothe harmonic current in point-of-common-coupling (PCC) after addingthe double-tuned filter to the load side are also described.

IEEE Power Engineering Review, March 2002 59