A Newton-Raphson Method Based onEigenvalue Sensitivities To ImproveHarmonic Voltage Performance

Varricchio, S.L.; Martins, N.; Lima, L.T.G.

Author Affiliation: CEPEL; Universidade Federal Fluminense.Abstract: This paper describes a Newton-Raphson method that ac-

curately shifts a set of electrical network poles and transfer function ze-ros to more suitable locations in the complex plane to improve theharmonic voltage performance of a system. The descriptor system ap-proach is used for the computer modeling of electrical networks of anytopology and their subsequent modal analysis. The pole and/or zeroshifts are carried out by appropriate changes in the system elements(e.g., capacitor and/or reactor banks). Eigenvalue sensitivity coeffi-cients are used to help determine those element changes that are themost cost-effective and also to compute the Jacobian elements for theNewton method. These changes may be carried out without impactingthe system operating point. Results are presented for a realistic systemmodel in order to show the potential applications of the method.

Keywords: Eigenvalue sensitivities, harmonics, Newton-Raphson,pole shifts, transfer function zeros.

Preprint Order Number: PE-021PRD (09-2002)Discussion Deadline: February 2003

Modeling Nonuniform Transmission Lines for TimeDomain Simulation of Electromagnetic Transients

Ramirez, A.1; Semlyen, A.; Iravani, R.

Author Affiliation: University of Toronto.Abstract: Transmission lines with nonparallel conductors or signif-

icant sags and vertical structures such as towers can be viewed andmodeled as nonuniform lines (NUL). The parameters of NULs are dis-tance dependent. This paper presents a mathematical model for timedomain simulation of electromagnetic transients in multiphase NULstaking into account the frequency dependence of the parameters. Themodel is based on the traveling wave phenomenon and accommodatesany NUL geometry. The model can be interfaced with time domain pro-grams, such as EMTP. The proposed methodology is validated by com-paring results with those obtained from a frequency domain modelusing the numerical Laplace transform (LT), the method of characteris-tics (MC), and also with test results reported by other investigators.

Keywords: Electromagnetic transients, nonuniform line, frequencydependence.

Preprint Order Number: PE-309PRD (09-2002)Discussion Deadline: February 2003

A Novel Placement Strategy for FACTS Controllers

Sharma, N.K.; Ghosh, A.; Varma, R.K.

Author Affiliation: Indian Institute of Technology.Abstract: A new method called the extended voltage phasors ap-

proach (EVPA) is proposed for placement of FACTS controllers inpower systems. While the voltage phasors approach (VPA) identifiesonly the critical paths from voltage stability viewpoint, the proposedmethod additionally locates the critical buses/line segments. The re-sults of EVPA are compared with the well-established line flow index(LFI) method for 9-bus, 39-bus, and 68-bus systems. The EVPA pro-vides accurate indication for the placement of FACTS controllers

Keywords: FACTS, placement, and voltage stability.Preprint Order Number: PE-318PRD (09-2002)Discussion Deadline: February 2003

Network Reconfiguration of DistributionSystems Using Improved Mixed-IntegerHybrid Differential Evolution

Su, C.T.; Lee, C.S

Author Affiliation: National Chung Cheng University.

Abstract: This study proposes an effective method of network re-configuration to reduce power loss and enhance the voltage profile bythe improved mixed-integer hybrid differential evolution (MIHDE)method for distribution systems. This research aims to recognize bene-ficial load transfers so that the objective function composed of powerlosses is minimized and the prescribed voltage limits are satisfied. Theproposed method determines the proper system topology that reducesthe power loss according to a load pattem. Mathematically, the problemof this research is a mixed-integer combinatorial optimization problemwell suited to the application of MIHDE.

Keywords: Network reconfiguration, power loss reduction, switch-ing operation, mixed-integer hybrid differential evolution.

Preprint Order Number: PE-447PRD (09-2002)Discussion Deadline: February 2003

Estimation of Wooden Cross-Arm Integrity UsingArtifi'cial Neural Networks and Laser Vibrometry

Stack, J.; Harley, R.G; Springer, P; Mahaffey, J.A.

Author Affiliation: Georgia Institute of Technology; NEETRAC;Air2 LLC.

Abstract: A significant problem faced by utility operators is thedegradation and failure of wooden cross-arms on transmission line sup-port structures. A nondestructive, noncontact, reliable method is pro-posed that can evaluate the structural integrity of these cross-armsquickly and cost-effectively. This method utilizes a helicopter-based la-ser vibrometer to measure vibrations induced in a cross-arm by the heli-copter's rotors and engine. An artificial neural network (ANN) thenuses these vibration spectra to estimate cross-arm breaking strength.The first type of ANN employed is the feed-forward artificial neuralnetwork (FFANN). After proper training, the FFANN can reliably dis-cern healthy cross-arms from those that are in need of replacementbased on vibration spectra. Next, a self-organizing map is applied tothis same problem, and its advantages are discussed. Finally, anFFANN-based data compression scheme is presented for use as a pre-processor for the vibration spectra.

Keywords: Data compression, neural networks, laser measure-ments, nondestructive testing, self-organizing feature maps, transmis-sion lines.

Preprint Order Number: PE-878PRD (09-2002)Discussion Deadline: February 2003

Distribution of the Traction Return Currentin AC and DC Electric Railway Systems

Mariscotti, A.

Author Affiliation: Universit'a di Genova.Abstract: The problem of the determination of the real distribution

of the return current in electric railway traction systems is considered.One or more conductors (depending on the specific supply system) arepurposely set up to carry the traction return current flowing from therolling stock axles back to the supply (i.e., substation); yet, part of thereturn current flows through signalling conductors (disturbing current)and through the earth, depending on the value of the electric parametersof the system, on the circuit arrangement and on the relative position ofthe supply, the rolling stock and signaling devices. The amplitude (as apercentage of the total return current) of the disturbing current may behigh enough to cause interference to signaling. This work investigatesthe behavior of the return current in ac and dc electric railway systems,on the basis of a reference system for the variation of the most impor-tant electrical parameters. The definition of the transfer function be-tween the return current and the signalling circuit variables is animportant element for the compatibility analysis between train detec-tion systems, rolling stock and infrastructure, to promote the cross-ac-ceptance of rolling stock in Europe and abroad.

Keywords: Guideway transportation power systems, power systemharmonics, power distribution interference.

Preprint Order Number: PE-082PRD (09-2002)Discussion Deadline: February 2003

IEEE Power Engineering Review, December 200266