Maria Cristina Tavares

A new procedure to derive transmission-line parameters: applications and restrictions

The objective of this paper is to show an alternative methodology to calculate transmission-line parameters per unit length. With this methodology, the transmission-line parameters can be obtained starting from impedances measured in one terminal of the line. First, the article shows the classical methodology to calculate frequency-dependent transmission-line parameters by using Carsons and Pollaczecks equations for representing the ground effect and Bessels functions to represent the skin effect. After that, a new procedure is shown to calculate frequency-dependent transmission-line parameters directly from currents and voltages of an existing line. Then, this procedure is applied in a two-phase and a three-phase transmission line whose parameters have been previously calculated by using the classical methodology. Finally, the results obtained by using the new procedure and by using the classical methodology are compared. The article shows simulations results for a typical frequency spectrum of switching transients (10 Hz to 10 kHz).

Quasi-modes multiphase transmission line model

Abstract This article presents a new model to represent transmission lines including the frequency dependence of longitudinal parameters. The model uses the natural modes, for ideally transposed lines, and ‘quasi-modes’ for non-transposed lines, and is applied to lines that have a vertical symmetry plane. The line is represented through π -circuits, with one π -circuit for each mode. The transformation matrix is modeled using ideal transformers. The model is described for three-phase lines, dc lines, double three-phase lines and six phase lines. A 440 kV three-phase transmission line illustrates it and is compared with a frequency dependent EMTP line model, the Semlyen one.

Behavior of overhead transmission line parameters on the presence of ground wires

Initially this paper shows the ground wire reduction process for generic multiphase transmission lines and after, the ground wire reduction process for a specific 440-kV three-phase overhead transmission line. Following this, the influence of the ground wire reduction process considering two situations is shown: first, considering frequency independence and second, when these parameters are considered as frequency dependent. This paper presents analytical results for generic multiphase transmission lines. For a specific 440-kV three-phase overhead transmission line, analytical and graphic results are shown considering real data for every frequency between 10 Hz and 1 MHz.

Half-Wave Length Line Energization Case Test - Proposition of a Real Test

In Brazil big blocks of energy will be transported through distances between 2500 and 3000 km to the strong network nodes. Among the AC transmission systems alternatives being analyzed the half-wave length transmission seems to be the natural solution as the lengths involved are around a half-wave length of a 60 Hz frequency system, as the Brazilian one. As there is no half-wave transmission system in operation in the world, there is a major sense of caution in order to be the first to construct and use this new AC-link. In order to give some support a field test with a set of existing similar 500 kV lines that could be connected in series was proposed to simulate the AC-link behavior under some controlled switching. The proposed AC-link test was simulated in PSCAD/EMTDC.

Transmission system parameters optimization-sensitivity analysis of secondary arc current and recovery voltage

Summary form only given. This paper shows the importance of optimizing the transmission system parameters from its conception, considering altogether the relevant options and possibilities, in order to have the better cost-performance result. The presented results were obtained in the study of a real transmission system expansion, based on an 865 km long line. The single-phase auto-reclosing (SPAR) procedure was one of the aspects carefully studied, in order to assure adequate transmission reliability. The secondary arc current was mitigated through the traditional solution of using the neutral reactor on the existing shunt reactor banks, which permitted the reduction of the secondary arc current to acceptable values, assuring natural arc extinction and successful SPAR. The way of obtaining the optimized value for the neutral reactor and its implications on the system performance are important aspects, which are discussed in this paper.

Implementation and Performance Evaluation of a Reclosing Method for Shunt Reactor-Compensated Transmission Lines

This paper proposes a new control method to reduce overvoltages due to three-phase reclosing for shunt compensated transmission lines (TL). The method detects the first minimum voltage region of the beating across the circuit breakers after protection dead time and works independently of voltage zero crossing, reducing significantly the reclosure time. The controller was tested on a Real Time Digital Simulator (RTDS) and its performance was compared to the traditional preinsertion resistor approach and another existing control method.

New mode domain multiphase transmission line model-Clarke transformation evaluation

This paper presents a new model to represent three-phase transmission lines in transient studies, including the frequency dependence of longitudinal parameters. The frequency dependence is represented with synthetic circuits, with a cascade of /spl pi/-circuits for each mode. The transformation matrix used for the entire frequency range is the Clarke one. The exact eigenvectors of the nontransposed line are analyzed in the frequency domain for some earth resistivity and compared to Clarke components.

Voltage harmonic content of long artificially generated electrical arc in out-door experiment at 500 kV towers

This study involves the application of Short Time Discrete Fourier Transform in order to obtain the harmonic content of voltage between the terminals of 647 artificially generated long electrical arcs. Non-confined tests were conducted on three 500 kV towers specially built inside a laboratory facility, in order to represent as close as possible actual transmission line conditions. The 1-s duration arcs were artificially generated along the 4 m insulator string of a 500 kV tower by imposing a sustained 60 Hz current. The arc voltage harmonic content can be used to identify the moment at which the arc is stabilized in the air and only after this instant measured data can be used to derive mathematical arc model. A statistical analysis of the results, considering only the period for which the arc is stabilized, enabled the establishment of the harmonic signature of the electric arcs for a large arc current amplitude range. From the results it can be stated that an accurate arc model should properly reproduce the presented harmonic content for any arc current level.

Visual evaluation of the length of artificially generated electrical discharges by 3D-snakes

The secondary arc extinction is the main concern in single-phase auto reclosure (SPAR) switching studies, since it dictates whether the reclosure will be successful or not. In this context, a function that describes the arc length variation over time (l(t)) is an important information not only for dynamic response but also for the analysis of transient arc processes. Given that purely electrotechnical approach only gives a profile of the curve l(t), the application of techniques based on image analysis has been considered for obtaining such function. In this paper, a new approach based on 3D-reconstruction and the tracking of an electrical arc is proposed for performing a computer-based evaluation of variations in its length. It was applied a three-dimensional active contour named 3D-snake that is geometrically represented by a B-spline, which evolves in 3D space. This new model is much less dependent on the determination of homologous points than the ad hoc approaches found in the literature for recovering 3D geometry of electrical discharges based on image analysis. In addition, the proposal presented is capable of tracking the evolution of the electrical discharge taking into account the time dependence between consecutive pairs of frames in two videos providing the required function l(t).

Quasi-modes three-phase transmission line model — comparison with existing frequency dependent models☆

Abstract This paper presents a new model to represent multiphase transmission lines in transient studies, including the frequency dependence of longitudinal parameters. The frequency dependence is represented with synthetic circuits, with a cascade of π-circuit for each mode. A real transformation matrix is used for the entire frequency range and it is modeled through ideal transformers in a transient program like ATP, as described. An application of the methodology is presented for an actual 440 kV single three-phase transmission line where some transients results simulated in ATP are presented. The model is compared to two ATP line models, JMarti and Semlyen.