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In this work, a new model for the simulation of fast transients on nonuniform multiconductor transmission lines is presented. The proposed model is based on the method of characteristics of partial differential equations theory and includes a variation of the electrical parameters with the distance and frequency. In addition, Norton circuits for the transmission line ends, which allow the inclusion of the model into general-purpose programs, are presented. Results obtained with the proposed model are compared with those obtained with the Electromagnetic Transients Program and the Numerical Laplace Transform method. Index Terms--Fast transients, frequency-dependent parameters, method of characteristics, nonuniform multiconductor transmission lines.

This paper describes a computer model for calculating the surge propagation in the winding of electrical machines. The model considers the winding as a combination of a multiconductor transmission line and a network of lumped parameters. The frequency dependence of the winding electrical parameters is calculated and incorporated into the analysis by means of Foster and Cauer circuits. The multiconductor transmission line provides the surge propagation characteristics for the winding model and its parameters are calculated from machine design characteristics. Finally, this hybrid model is validated by a comparison of calculated and measured results inside a high-voltage machine winding. Index Terms--Surge distribution, switching transients, winding electrical parameters.

In this paper, a computer model that describes the dynamic arc behavior in the high- and low-current regions before current zero is proposed. The model divides the current and voltage waveform in two regions. A differential equation for both regions which unifies current and voltage time derivatives is obtained by means of a generalized function method. The computer waveforms reproduced with the model show good agreement with measured results published in [1] in the low and high current regions, but further comparison with other test measurements are required to know if the model has any feature of predictability. Index Terms--Arc model, Cassie and Mayr type differential equations, circuit breaker, electric arc modeling.

This paper presents a new approach to model a transmission tower for lightning performance studies. It consists of representing each part of the tower by equivalent vertical and/or horizontal transmission lines as required. While horizontal line parameters are obtained from standard line formulas, specific expressions are derived for the parameters of vertical lines. Moreover, mutual coupling between any two parallel vertical transmission lines is taken into account. Transient waveforms obtained using the proposed method are compared with experimental data obtained using a reduced-scale model and field experiments. The agreement between simulated results and experimental measurements is satisfactory. Index Terms--Vertical transmission lines, nonuniform transmission lines, transmission tower modeling, transient analysis, mutual impedance, reduced-scale model (RSM).

This paper describes a computer model for surge distribution studies in the winding of electrical machines. The computer model takes the coil as the basis for the analysis and uses multiconductor transmission line theory to obtain the transference matrix for the winding. Several practical formulations based on machine design characteristics are used for calculating electrical parameters. Flux penetration into the iron core and mutual coupling between coils in different_phase windings are incorporated into the analysis. The model was validated by a comparison of predicted and calculated results in a high voltage motor. Keywords: computer simulation, switching transients, surge distribution, electrical machines, electrical parameters.

This paper addresses the problem of transient overvoltages in electrical motors during sequential pole closure in industrial installations. A computer model that includes the circuit breaker, high-voltage cable and electrical motor is proposed. Multiconductor transmission line theory and modal analysis are applied to the components and the piecewise Fourier transform is used to simulate sequential pole closure. The mechanism of sequential pole closure is analyzed including parallel capacitors and series inductors. Critical times for switching transients are calculated. Finally, the effect of several system and machine parameters on transient overvoltages is investigated. Keywords--Overvoltages, simulation, switching transients, electrical machines, sensitivity analysis, dielectric stresses.

This paper presents a comparative study of neural network (NN) efficiency for the detection of incipient faults in power transformers. The NN was trained according to five diagnosis criteria commonly used for dissolved gas analysis (DGA) in transformer insulating oil. These criteria are Doernenburg, modified Rogers, Rogers, IEC and CSUS. Once trained, the neural network was tested by using a new set of DGA results. Finally, NN diagnosis results were compared with those obtained by inspection and an annalist. The study shows that NN rate of successful diagnosis is dependant on the criterion under consideration, with values in the range of 87-100%. Index Terms--Fault diagnosis, neural networks, power transformer testing.