Methods based on both time (t)-domain and frequency (f)-domain have been used for electromagnetic transient (EMT) analysis using both circuit‑theory and field‑theory approaches. Methods based on circuit theory are fast and convenient but may become inapplicable to many engineering problems due to simplifications such as the transverse electromagnetic assumptions. Moreover, t‑domain‑based techniques rely on approximate methods to account for frequency dependence, which is an essential characteristic of electric conductors, equipment and soil environment. In this paper, f-domain solutions obtained from the method of moments (MoM) discretization of the electric field integral equation (EFIE) are converted to t‑domain using the numerical Laplace transform (NLT) by means of post‑processing. This circumvents the need to formulate the EFIE and MoM based on the complex frequency which would be required for their application to conventional NLT. Hence, existing MoM implementations can be used to perform a full-wave 3‑D EMT analysis for a wide range of power system applications. Examples include energizations of 3‑D power system networks with fast and non‑vanishing excitations such as step functions, as well as modeling non‑linear elements using the piecewise linear approximation. Results from experimental measurements, finite‑difference t‑domain method, and EMT‑type software confirm the validity of the proposed method for power system transients in the range of microseconds down to nanoseconds.

Published in: IEEE Transactions on Power Delivery

Accurate solutions of electromagnetic scattering problems involving objects made of materials with large permittivity contrasts are considered. Problems are formulated with different commonly used combined surface integral equations (SIEs). All studied formulations are discretised through the method of moments with rooftop basis functions over flat quadrilaterals represented as bilinear surfaces, with razor‑blade functions being used for the testing procedure. The accuracy of the results is first investigated in detail for several frequencies and permittivity values using different numerical measures. It is shown that numerical instabilities may appear at frequencies corresponding to the physical resonances of the object, in particular in the near field and for large material parameter contrasts. The example of a dielectric resonator (DR) with cubic geometry is considered for the purpose of analysis, especially since to achieve smaller DR type antennas, it is necessary to use higher contrast materials. The accuracy of the combined surface integral equations to determine the natural resonant modes of the DR is investigated. It is found that the resonance modes can be accurately determined by exploring the radar cross section (RCS) of the DR in free space only if a proper combination of the electric and magnetic fields equations is applied.

Published in: IET Microwaves, Antennas & Propagation

IEEE Standard 80-2013 provides the substation grounding system designer with simple formulae and tabulated data for the estimation of the maximum fault current that can flow through various types and sizes of conductor, for a given duration, before failure due to fusing occurs. Copper conductors are given exhaustive and reasonably accurate treatment. Other types of conductors, however, are given short thrift. Copper-clad steel (CCS) conductors, whose steel cores provide an effective heat sink, appear not to have been studied at all. As a result, the standard provides only an unrealistic simplified methodology based on fixed physical constants to be used for the calculation of CCS current-carrying limits. Computer modeling and lab testing have demonstrated that the highly non-linear heat absorption characteristics of the CCS core, when properly considered, yield considerably different fault current-carrying capacity than IEEE Standard 80-2013 would lead design engineers to expect. A theoretical framework for the calculation of these values is presented. Computed values are compared with those obtained by an independent accredited high voltage test laboratory.

Published in: 2022 IEEE IAS Petroleum and Chemical Industry Technical Conference (PCIC)

This paper introduces a novel approach to analyze corrosion effects and to model electrochemical problems with non‑linear boundary conditions. The computation of the electrical current distribution along protected structures is based on an automated algorithm involving the polarization curves and an integrated iterative process. The method is first used to solve a well‑known benchmark test problem and the results are compared to those obtained using the benchmark analytical expression. Then, an example of a realistic cathodic protection system aimed at mitigating stray currents from a HVDC electrode on a pipeline is described and discussed. It is shown that the proposed iterative approach accurately computes the electrochemical potential process. This approach constitutes the core effort in the development of an accurate non‑linear polarization solver.

AMPP Annual Conference Expo 2023, Denver, Colorado, March 19-23, 2023

This paper examines electromagnetic field effects inside a substation when lightning hits a transmission tower located just outside a substation. An integral formulation of Maxwell’s equations is used to model the whole structure including power line, towers, grounding network, control cables, shielding system and lightning channel. Computations are carried out using the Method of Moments (MoM) for surface‑wire integral equation in a stratified medium. This article focuses exclusively on conductor and cable ground potential rise as well as soil potentials since they exhibit the most representative electromagnetic field (EMF) effects of a lightning event in such environments. The study has shown that it is possible to examine accurately and realistically the performance of 3D complicated network system in a substation, including transmission lines, during transient and lightning conditions. This exact computation analysis can help develop more appropriate standards and mitigation measures to prevent most severe, lightning strikes in a well‑designed substation, resulting in significant economical savings in outages avoidance and equipment damages.

Ground 2023 & 10^th LPE, Belo Horizonte, Brazil, May, 2023