peak current and about 25% or more of the return stroke charge trans-ferred in the first millisecond passed to the neutral conductor througheach of the two closest arresters on either side of the strike point. Thebulk of the peak current then flowed from the neutral conductor toground through the groundings of the two closest arresters. The chargetransferred in the first millisecond from the neutral to the eight systemgroundings, six at arrester stations and one at each of the two line-endpoles, appears to be distributed inversely to the low-frequency, low-cur-rent grounding resistances. From our measurements of return strokecurrent division and in view of the available data on the currents of firststrokes in natural lightning, we estimate that over half of natural firststrokes would result in an arrester failure in our test distribution line,which is representative of some distribution lines in service, withinabout 450 ,us of the initiation of the first return stroke current flow, inthe absence of fiashovers and other altemative current paths that mightbe provided by transformers or underground cable connections to allowthe stroke current to bypass the arrester. Additional first stroke currentflow beyond about 450 gs and currents associated with subsequentstrokes and potentially other processes should further increase the like-lihood of arrester failure.
Keywords: Lightning, MOV arresters, grounding electrodes,power distribution lines.
Preprint Order Number: PE-139PRD (06-2002)Discussion Deadline: November 2002
Switchgear
New Fault Diagnosis of Circuit Breakers
Lee, Dennis S.; Lithgow, Brian; Morrison, R.E.
Author Affiliation: Monash University.Abstract: Wavelet packets and neural networks have been used to
analyze the vibration data of circuit breakers for the detection of incipi-ent circuit breaker faults. Wavelet packets are used to convert measuredvibration data from healthy and defective circuit breakers into waveletfeatures. Selected features highlighting the differences between healthyand faulty condition are processed by a back-propagation neural net-work for classification. Testing has been done for three 66 kV circuitbreakers with simulated faults. Detection accuracy is shown to be farbetter than other classical techniques such as the windowed Fouriertransform, stand alone artificial neural networks or expert system. Theaccuracy of detection for some faults can be as high as 100%.
Keywords: Wavelet transforms, neural networks, vibrations, tran-sient analysis, monitoring, circuit breakers.
Preprint Order Number: PE-052PRD (06-2002)Discussion Deadline: November 2002
Transformers
Design of a High Power BrushlessLinear Variable Transformer
Rezaei-Zare, A.; Faiz, J.; Mohseni, H.
Author Affiliation: University of Tehran.Abstract: High power variable transformers are required for use in
advanced high voltage - high power laboratories. However, their designis always confronted with various difficulties caused by different physi-cal and electromagnetic design constraints. This paper presents a newdesign for a high power brushless linear variable transformer. The pro-posed design has desirable features such as low short circuit impedancewhich may be useful for different tests particularly high current tests,over a wide range of power requirement. An analytical design proce-dure is followed, after which a finite element analysis is used to confirmthe analytical design results.
Keywords: Linear variable transformer, transformer, short circuitimpedance, finite element analysis.
Preprint Order Number: PE-253PRD (06-2002)Discussion Deadline: November 2002
Reducing Losses in Distribution Transformers
Olivares, Juan Carlos; Liu, Y; Canedo, J.; Escarela-Perez, R.;Driesen, J.; Moreno, P
Author Affiliation: Virginia Polytechnic Institute and State Uni-versity; CINVESTAV; Katholieke Universiteit Leuven; UniversidadAutonoma Metropolitana-Azcapotzalco.
Abstract: This paper examines three methods of reducing distribu-tion transformer losses. The first method analyzes the effects of usingaluminum electromagnetic shields in a distribution transformer. Thegoal of placing electromagnetic shields in the distribution-transformertank walls is to reduce the stray losses. A 500 kVA shell-type trans-former was used in the experiments. The overall results presented indi-cate that stray losses can be considerably reduced whenelectromagnetic shielding is applied in the transformer tank. In the ex-periment, the tank walls were lined with aluminum foil. The possibilityof reducing the dielectric losses was shown through experiments in thesecond method. The third method analyzes the behavior ofwound-cores losses in distribution transformers as a function of jointconfiguration design parameters. The joint configuration used in thispaper is called step-lap joint.
Keywords: Dielectric losses, loss measurements, shielding, trans-former, transformer cores.
Preprint Order Number: PE-394PRD (06-2002)Discussion Deadline: November 2002
Proposed Standards for Frequency ConversionFactors of Transformer Performance Parameters
Girgis, Ramsis S.; Beaster, B.; teNyenhuis, Ed G.
Author Affiliation: ABB Power T&D Company Inc.; ABB PowerTransformers.
Abstract: This paper presents the development of appropriate fre-quency conversion factors for performance parameters of transformers.These factors are needed in order to allow manufacturers to convertmeasured values from 60 to 50 Hz and vice versa. Conversion factorsare necessary when equipment at a manufacturer's test facility allowsdirect measurement at one frequency and not the other. These factorsare developed for no load loss, exciting current, load loss, and noiselevel using both analytical and actual tested data. Measured data, pro-vided by several manufacturers, was used to confirm the theoretical re-sults. This paper will be used as a basis for proposing standardfrequency conversion factors in the IEEE/ANSI and IEC test standardsfor power and distribution transformers. Such a standard will make itpossible for manufacturers to use the same frequency conversion fac-tors and hence have a more uniform accuracy of the reported test data atboth 50 and 60Hz.
Keywords: Curved conductor, heavy current, surface temperature,current conducting ability.
Preprint Order Number: PE-106PRD (06-2002)Discussion Deadline: November 2002
A Wide-Band Lumped Circuit Model ofEddy Current Losses in a Coil with a CoaxialInsulation System and a Stranded ConductorHolmberg, Par; Leijon, Mats; Wass, Torbjorn
Author Affiliation: Uppsala University; ABB Corporate Research.Abstract: This paper presents a wide-band lumped circuit model of
eddy current losses in a coaxially insulated coil. The wide frequencyrange of the model is achieved by means of dual and extended Cauercircuits, equivalent circuits used for eddy current modeling. The com-plete lumped circuit reproduces the expected response well. However,
IEEE Power Engineering Review, September 2002 61
because of resonances in the coil, the model cannot be experimentallyverified for higher frequencies than 5 kHz. The parameters of thelumped circuit are mainly acquired from field calculations and aggre-gate the eddy current losses In the stranded conductor of each tum. Theaggregate considers the contact resistance between the strands. Theeddy current model can be used as a part of a complete model of the coilintended for e.g. lightning impulse simulations, as the winding isdiscretised into short pieces. The results of the paper are of special in-terest for coaxially insulated electric machines, such as the commer-cially available Powerformer and Dryformer.
Keywords: Eddy currents, skin effect, stranded conductors, coils,windings, cables, electromagnetic transient analysis, circuit transientanalysis, circuit modeling.
Preprint Order Number: PE-140PRD (06-2002)Discussion Deadline: November 2002
Transmission and Distribution
Deterioration Diagnosis for SiliconeRubber Housing of Polymer Insulatorsby Infrared Ray SpectrometryKoshino, Yukihiro; Umeda, Itsuki;Arakawa, Katsumi; Burnham, Jeff
Author Affiliation: NGK Insulators, Ltd.; NGK-Locke, Inc.Abstract: This paper describes pretreatment surface cleaning and
analytical methods for evaluating deterioration of silicone rubber hous-ing for out door high voltage insulators. Various solvents and washingmethods were studied for effectiveness in removing different contami-nation types deposited on the surfaces of the silicone housing prior toanalytical investigation. An effective method and combination of sol-vents were found. The analytical methods of SEM, EDX, XPS, FT-IR,and FT-IR-ATR were evaluated for effectiveness in measuring surfacedeterioration on aged insulators. The presence of aluminum nitride,which was generated by corona discharge and moisture, could easily beanalyzed with FT-IR-ATR. Silicone insulator test specimens used in thetests were naturally aged in service and artificially aged by corona dis-charges and UV. Indexes of deterioration, derived from selected analyt-ical techniques found suitable, were created which were correlated withexposure duration. The purpose of the test program was to determinethe feasibility of predicting intrinsic longevity of polymer insulators bystudying and quantifying deterioration modes and processes.
Keywords: Polymer insulator, silicone housing, deterioration diag-nosis, corona deterioration index, infrared ray spectrometry.
Preprint Order Number: PE-550PRD (06-2002)Discussion Deadline: November 2002
The Potential Use of Voltage-SourcedConverter-Based Back-to-Back Tiein Load Restorations
Noroozian, M.; Edris, Abdel-Aty; Kidd, David E.; Keri, Albert J.E.
Author Affiliation: ABB Utilities AB; Electric Power Research In-stitute; American Electric Power.
Abstract: This paper presents a control algorithm for a volt-age-sourced converter-based back-to-back (VSC-BTB) tie that enablesa "transient free" load transfer between the tie sides. The studies wereperformed for the recently commissioned Eagle-Pass VSC-BTB inter-connecting the Electric Reliability Council of Texas (ERCOT) trans-mission network in the United States to the Comisi6n Federal DeElectricidad (CFE) transmission network in Mexico. The objective ofthe algorithm is realization of the transfer of load from one side of theVSC-BTB to the other side of the tie without interruption of the powersupply to the Eagle-Pass load. The developed algorithm has been vali-dated through simulation studies, describing the load transfer process.
Keywords: Frequency matching, angle synchronization,back-to-back (BTB), load transfer, load restoration, phase-locked loop(PLL), switching sequence, voltage-sourced converter (VSC).
Preprint Order Number: PE-064PRD (06-2002)Discussion Deadline: November 2002
Real-Time Digital Processing of GPSMeasurements for Transmission Engineering
Mensah-Bonsu, C.; Heydt, Gerald T.
Author Affiliation: Arizona State University.Abstract: The global positioning system (GPS) is a state-of-the-art
timing and positioning system based on 24 or more satellites launchedand maintained by the United States government. Power engineeringapplications based on the GPS include phasor measurement, position-ing applications such as surveying and mapping, and potentially in de-riving real-time data on transmission lines that will allow them to beloaded to a dynamic (thermal or security) limit. Inherent errors in GPStechnologies are discussed, and the differential GPS method is de-scribed for accuracy enhancement. Further digital processing needs arenecessary for meeting the accuracy requirements of certain specific ap-plications. The focus of this paper is on the digital signal processing(DSP) of differential GPS (DGPS) measurements. The paper describesa methodology for further improving DGPS altitude measurements forthe purpose of accurate determination of high voltage overhead con-ductor sag. The Haar wavelet transforms (HWT) and least squares pa-rameter estimation (LSPE) techniques are considered.
Keywords: GPS, overhead conductor sag, wavelet analysis, leastsquares parameter estinsation, dynamic thermal line rating, transmis-sion engineering.
Preprint Order Number: PE-671PRD (06-2002)Discussion Deadline: November 2002
High Temperature Sag Modelfor Overhead Conductors
Chen, Shelley L.; Black, William Z.; Fancher, Mike
Author Affiliation: Cordis Corporation; Georgia Institute of Tech-nology; Alcan Cable.
Abstract: As electric utilities strive to operate their transmissionlines at higher temperatures, several constraints exist that make thisgoal difficult to achieve. Load may not flow over a desired path, eventhough the transmission line may have sufficient thermal capacity.Even if system components that allow power to flow over selected cir-cuits are available and in place, there is still an absolute thermal limitplaced on an aluminum conductor to prevent annealing of the conduc-tor and excessive sag. This paper describes the combination of areal-time ampacity and a sag/tension program resulting in both a designand operational tool that can be used to predict the instantaneous tem-perature and sag of a wide variety of conductor designs. The resultingprogram is specifically designed to predict conductor temperature andsag for temperatures as high as 2,500 'C. The accuracy of the programis evaluated by comparing the predicted sag with the sag measured ontwo ACSR conductors mounted on a full-scale outdoor test facility. Theaccuracy of the predicted sag decreases as the average conductor tem-perature increases. For temperatures less than 1,500 'C, nearly 70% ofthe time the sag program predicted sags within about 5% of measuredvalues. However, when the conductor temperature was greater than1,500 'C, the predicted sags were within 5% of the measured valuesonly about 65% of the time.
Keywords: Ampacity, sag/tension, high temperature operation,high temperature sag.
Preprint Order Number: PE-731PRD (06-2002)Discussion Deadline: November 2002
IEEE Power Engineering Review, September 200262
