This paper proposes a technique to approximate a multi-layer earth structure by a homogeneous conductivity soil in ground return impedance calculations. An equivalent realvalued conductivity parameter is obtained, which can be used with reasonable accuracy in a simpler expression or in commonly available EMTP software, such as the Line Constants routine of the Alternative Transients Program (ATP). Several actual soil models are evaluated at frequencies ranging from from 1 Hz to 2 MHz. Results show that the proposed method is accurate for modeling most power system problems, from steady-state conditions to transients commonly verified in electrical systems. The proposed expression is easy to use and introduces a considerable performance gain in terms of floating-point operations, compared to the analytical formulation of the general multi-layer soil structure.

The electromagnetic interference (EMI) of overhead transmission lines (OHLs) to aboveground pipelines sharing the same right-of-ways has been a research topic for many years. Most studies focus on investigations of the induced currents and voltages at the mains frequency (50/60 Hz). However, significant voltage levels can also be induced, when the pipeline is subject to high-frequency excitation. The representation of earth conduction effects is very important to estimate accurately the level of the EMI. This article presents a detailed high-frequency analysis of OHL/pipeline configurations taking into consideration the frequency-dependent (FD) soil properties. Wise's earth formulation is adopted for the calculation of the earth return impedances and shunt admittances. Propagation characteristics, frequency-domain, and transient responses are calculated by using both the FD soil models and constant soil properties, as well as the classical transmission line approach of Carson. Frequency-domain responses calculated with Wise's formulation are compared against those obtained using the MoM-SO method of EMTP software.

This article describes the problem of electromagnetic interferences between power lines and metallic structures, caused by inductive and conductive coupling mechanisms, and the main risks to which personnel and facilities are exposed. An EMTP-based implementation is proposed to predict induced voltage levels on a target circuit, due to interferences caused by overhead power lines under steady-state nominal load, as well as fault conditions, using generalized formulas to represent the N -layered soil. Results are tested by means of a case study of a real shared right-of-way project and comparisons with results obtained using industry-standard software. Results show that the proposed method is accurate, with errors smaller than 8%. Stress voltage values in the interfered pipeline are the order of 50 kV, exposing the structure coating to risk of breakdown, which may lead to corrosion and pipeline failure. A mitigation is designed and proven to reduce voltage values to safe levels, in compliance with the nominal limits from the manufacturer.

Electromagnetic interference (EMI) between overhead lines (OHL) and nearby pipelines may cause high-induced voltages. Their computation is important for the safe and reliable operation of the pipeline and necessitates the accurate evaluation of earth conduction effects on the impedance and admittance parameters of all conductors. In this article, a detailed formulation of the impedance and admittance parameters of OHL/pipeline configurations is presented and new expressions for the calculation of the mutual impedance and admittance between the overhead conductors and the buried pipeline are introduced. The mutual parameters for an OHL/pipeline configuration are evaluated by the new formulas and compared with those derived from existing ones, the method of moments and the finite element method. The propagation characteristics are also calculated justifying the use of the mutual admittance, that is typically disregarded in power systems EMI calculations. Transient simulation results with the developed formulas are performed to evaluate the importance of the proposed approach on EMI studies.