Keywords: Auto transformer, voltage ratio, internal phase angle,active power flow, reactive power flow, tap changer.

Preprint Order Number: PE-467PRD (11-2001)Discussion Deadline: April 2002

Modeling Transformers withInternal Incipient Faults

Wang, H.; Butler, K.L.

Author Affiliation: Texas A&M University, College Station, TXAbstract: Incipient fault detection in transformers can provide

early warning of electrical failure and could prevent catastrophiclosses. To develop the transformer incipient fault detection technique, atransformer model is required, to simulate internal incipient faults. Thispaper presents a methodology to model internal incipient windingfaults in distribution transformers. These models were implemented bycombining deteriorating insulation models with an internal short-cir-cuit fault model. The internal short-circuit fault model was developedusing finite element analysis. The deteriorating insulation model, in-cluding an aging model and an arcing model connected in parallel, wasdeveloped based on the physical behavior of aging insulation and thearcing phenomena occurring when the insulation was severely dam-aged. The characteristics of the incipient faults from the simulationwere compared with those from some potential experimental incipientfault cases. The comparison showed that the experimentally obtainedcharacteristics of terminal behaviors of the faulted transformer weresimilar to the simulation results from the incipient fault models.

Keywords: Distribution transformer, internal incipient windingfault, modeling, finite element analysis, arcing, aging.

Preprint Order Number: PE-267PRD (11-2001)Discussion Deadline: April 2002

Recognition of Impulse Fault Patternsin Transformers Using Kohonen'sSelf-Organizing Feature Map

De, A.; Chatterjee, N.

Author Affiliation: Jadavpur University, Calcutta, IndiaAbstract: Determination of the exact nature and location of faults

during impulse testing of transformers is of practical importance to themanufacturer as well as designers. The presently available diagnostictechniques more or less depend on expert knowledge of the test person-nel, and in many cases are not beyond ambiguity and controversy. Thispaper presents an artificial neural network (ANN) approach for detec-tion and diagnosis of fault nature and fault location in oil-filled powertransformers during impulse testing. This new approach relies on highdiscrimination power and excellent generalization ability of ANNs inthe complex pattern classification problem, and overcomes the limita-tions of conventional expert or knowledge-based systems in this field.In the present work, the self-organizing feature map (SOFM) algo-rithm with Kohonen's learning has been successfully applied to theproblem with good diagnostic accuracy.

Keywords: Artificial neural network, fault diagnosis, impulsetesting, transformer, self-organizing feature map.

Preprint Order Number: PE-166PRD (11-2001)Discussion Deadline: April 2002

Transmission and Distribution

FPGA Realization of Wavelet Transform forDetection of Electric Power System Disturbances

Huang, Sj.; Yang, TM.; Huang, J.T.

Author Affiliation: National Cheng Kung University, Taiwan

Abstract: Realization of wavelet transform on field- programmablegate array (FPGA) devices for the detection of power system distur-bances is proposed in this paper. This approach provides an integral sig-nal-processing paradigm, where its embedded wavelet basis serves as awindow function to monitor the signal variations very efficiently. By us-ing this technique, the time information and frequency information canbe unified as a visualization scheme, facilitating the supervision of elec-tric power signals. To improve its computation performance, the pro-posed method starts with the software simulation of wavelet transform inorder to formulate the mathematical model. This is followed by the cir-cuit synthesis and timing analysis for the validation of the designated cir-cuit. Then, the designated portfolio can be programmed into the FPGAchip through the download cable. The completed prototype will be testedthrough software-generated signals and utility-sampled signals, in whichtest scenarios covering several kinds of electric power quality distur-bances are examined thoroughly. From the test results, they support thepracticality and advantages of the proposed method for the applications.

Keywords: Wavelet transform, FPGA, disturbances.Preprint Order Number: PE-1 16PRD (11-2001)Discussion Deadline: April 2002

Expert System for Classification andAnalysis of Power System Events

Styvaktakis, E.; Bolen, M.HJ.; Gu, I.Y.H.

Author Affiliation: Chalmers University of Technology, Gbteborg,Sweden

Abstract: This paper presents an expert system that is able to clas-sify different types of power system events to the underlying causes(i.e., events) and offer useful information in terms ofpower quality. Theexpert system uses the voltage waveforms and distinguishes the differ-ent types of voltage dips (fault-induced, transformer saturation, induc-tion motor starting), as well as interruptions (nonfault, fault induced). Amethod for event-based classification is used, where a segmentation al-gorithm is first applied to divide waveforms into several possibleevents. The expert system is tested using real measurements and the re-sults show that the system enables fast and accurate analysis of datafrom power quality monitors.

Keywords: Power quality, voltage dips (sags), expert systems,Kalman filtering, power system monitoring.

Preprint Order Number: PE-364PRD (11-2001)Discussion Deadline: April 2002

The Effect of Longitudinally Varying SoilConductivity on the Ground-Mode Low-FrequencyPropagation Parameters of Overhead Power Lines

Faria, J.A.B.

Author Affiliation: Institute Superior Tecnico, Lisboa, PortugalAbstract: An analysis is developed for the evaluation, at power fre-

quencies, of the propagation parameters of an overhead line sectionsuspended above a nonhomogeneous soil whose conductivity ran-domly varies along the line length. The line section is broken down intoa number of homogeneous uniform elemental cells, the length and con-ductivity of each cell, as well as the total number of cells, being ran-domly generated. The main result of this research is that conductivityrandom fluctuations give rise to negligible variations of the wave prop-agation parameters being analyzed. This leads to the conclusion that thestandard practice of assigning the soil, in each line section, a uniformconductivity equal to its average value, can be safely employed with nosignificant errors incurred. In addition, a perturbation theory approachis developed, allowing not only an interpretation of the computation re-sults obtained, but providing also a clear understanding of the roleplayed by the different variables pertaining to the problem.

Keywords: Power transmission lines, propagation,nonhomogeneous ground, random media, perturbation methods.

Preprint Order Number: PE-286PRD (11-2001)Discussion Deadline: April 2002

IEEE Power Engineering Review, February 200264