Conference Agenda

Lightning strikes to conductors of overhead lines may cause high transient induced voltages at neighboring pipelines. Thus, the computation of these voltages is important for the safe and reliable pipeline operation. This work investigates the effects of line parameters and soil modelling on the transient voltages induced at an aboveground pipeline due to lightning strikes to a phase conductor of a nearby overhead transmission line. Three different earth formulations are evaluated: the Carson, Wise, and the method of moments with surface operator combined with the extended transmission line approaches. Computations are performed using both frequency- and time-domain models, as well as constant and frequency-dependent soil electrical properties. CIGRE lightning current waveforms are employed in simulations derived on the basis of the statistical distributions of their parameters for negative first return-strokes. Transient induced voltage waveforms differ among the evaluated lightning currents, with higher peak values for shorter and steeper current wavefronts. Conservative results are obtained for the constant soil properties and Carson’s earth formulations, which neglect, respectively, the dispersion of soil electrical properties and displacement current.

This paper investigates the numerical performance of the Wedepohl series and of the Gauss-Kronrod quadrature to calculate ground- and sea-return impedances of power cables. Many computational routines to calculate ground-return impedances of cables used in EMTP-type programs have been proposed without technical justification of their application range. In this paper, we explore the convergence and accuracy of the Wedepohl series based on the number of terms in the series and as a ratio test. As a result, an accurate and stable numerical algorithm to compute ground- and sea-return impedances is proposed. The proposed method is capable of accounting for very low resistivity values and large depths.

This paper presents a three-parameter transmission line high impedance fault (HIF) model for the Alternative Transients Program (ATP)/ATPDraw. Real-world HIFs caused by vegetation contact on lines belonging to a Brazilian utility are firstly investigated to identify representative features of the fault resistance behavior during the disturbance period. Then, a data regression method is applied to obtain a time-domain function which emulates the fault resistance. Finally, an ATP/ATPDraw transmission line HIF model is developed and described in detail. For the sake of simplicity, only three parameters are proposed to be used in the model, namely: Initial resistance, final resistance and resistance decaying time constant. To prove the proposed model is representative, real HIF records are compared against ATP/ATPDraw simulated ones. The obtained results show the proposed model satisfactorily emulates the effects of real HIFs.

This paper proposes a tower-foot grounding system model compatible with EMT programs which might be useful for the simulation of lightning transients in overhead lines. The proposed model is based on the solution of the telegrapher’s equations and the application of the classical Marti’s
transmission line model. The model is implemented in the Alternative Transients Program (ATP) and validated considering a benchmark electromagnetic model. Its accuracy is evaluated and shown both in terms of the simulated ground potential rise (GPR) and line overvoltages developed through the insulator strings due to lightning currents. Finally, the model accuracy is also demonstrated in terms of the line backflashover outage rate.

This paper presents a new modeling approach based on idempotent decomposition of the nodal admittance matrix for representation of cables and overhead lines (OHL). By subjecting the idempotent matrices rather than the nodal admittance matrix to rational fitting, the poor observability of the smallest eigenvalues in the lower frequency range is overcome. Unlike the well-known method of characteristics (MoC), this alternative representation yields a so general fully-coupled admittance matrix suitable to tackle scenarios encompassing short and long lengths. Besides retaining the frequency dependence of parameters, the proposed phase-domain model showed to be accurate and suitable to circumvent the requirement of small time-steps.

This paper proposes small-argument approximations for two closed-form equations that were recently derived for the calculation of the ground-return impedance and admittance of underground cables. The proposed expressions are shown to be accurate up to 1 MHz for a typical cable configuration and frequency-dependent ground parameters. Their accuracy is also demonstrated in the calculation of transients on underground cables taking as reference results obtained with more general formulations.