Dimitrios A. Tsiamitros

Earth return path impedances of underground cables for the two-layer earth case

The influence of earth stratification on underground power cable impedances is investigated in this paper. A rigorous solution of the electromagnetic field for the case of underground conductors and a two-layer earth is presented. Analytic expressions for the self and mutual impedances of the cable are derived. The involved semi-infinite integrals are calculated by a novel, numerically stable, and efficient integration scheme. Typical single-core cable arrangements are examined for a combination of layer depths and earth resistivities, based on actual measurements. The accuracy of the results over a wide frequency range is justified by a proper finite-element method formulation. The differences in cable impedances due to earth stratification are presented. Finally, a simple switching transient simulation is examined to evaluate the influence of the earth stratification on transient voltages and currents.

A systematic approach to the evaluation of the influence of multilayered Earth on overhead power transmission lines

The influence of earth stratification on overhead power transmission line impedances is investigated in this paper. A systematic comparison of existing approaches is done, while results are also obtained using a finite-element method formulation. A novel numerical integration technique is proposed for the calculation of the infinite integrals involved. Typical single- and double-circuit line configurations are examined for a combination of layer depths and earth resistivities over a wide frequency range. The influence of the layer depth is also investigated. Results show significant differences from those, corresponding to the case of homogeneous earth. Using the multilayered earth return impedances in transient simulations, the transient responses show that differences occur mainly in cases of asymmetrical faults, justifying the need for a detailed earth model implementation.

Earth Return Impedances of Conductor Arrangements in Multilayer Soils—Part II: Numerical Results

The influence of earth stratification on the conductor impedances is investigated in this paper. The generalized expressions for the self and mutual impedance of conductors in the multilayer earth case, which have been derived in a companion paper, are implemented on typical overhead power transmission lines and underground single-core power cable arrangements for discrete and exponential variations of earth resistivity. The accuracy of the results over a wide frequency range is justified by a proper finite-element method formulation. The differences in the impedances due to earth stratification are presented. The influence of the earth stratification on the actual transient responses of the conductor arrangements is also investigated.

Impedances and Admittances of Underground Cables for the Homogeneous Earth Case

A general formulation for the calculation of the influence of the earth return path on the impedances and the admittances of underground multiconductor power cable arrangements is presented in this paper. The expressions for the self and mutual earth correction terms are derived by a rigorous solution of the electromagnetic-field equations. The involved semiinfinite integrals are calculated by using a suitable numerical integration technique. The propagation characteristics of a single insulated conductor and of a typical three-phase single-core cable arrangement are investigated and are compared to the corresponding ones obtained by other approaches. Finally, the cable parameters calculated by the proposed method are used in a simulation of a fast transient in a three-phase single-core cable.

Earth Return Impedances of Conductor Arrangements in Multilayer Soils—Part I: Theoretical Model

The influence of earth stratification on the conductor impedances is investigated in this paper. A general solution of the electromagnetic-field equations for the case of overhead and underground transmission-line conductors of arbitrary topology and multilayer earth is presented. Generalized expressions for the self and mutual impedances of the conductors are derived. All existing approaches result from the generalized equations, when the corresponding approximations are applied. A suitable integration scheme is also proposed for the calculation of the complex integrals involved in the expressions.

A PLC based energy consumption management system. Power line performance analysis: Field tests and simulation results

In powerline communications the signal transmission characteristics of the power line carrier are very significant. This paper presents part of the research work done on the development of an integrated Energy Consumption Management System based on powerline communications. Field test results, concerning signal transmission characteristics on power lines in pilot installations are reported. The well known EMTP is used for the simulation of the transmission path. Simulation results, obtained for the no-load and for the full load cases and after the implementation of carrier wave traps, are compared to the actual measurements from field tests, showing satisfactory agreement. The influence of line length and of line terminations is also investigated for both underground cables and overhead distribution lines.

Homogenous Earth Approximation of Two-Layer Earth Structures: An Equivalent Resistivity Approach

The homogenous earth representation of two-layer earth structures for earth return impedance calculations is investigated in this paper. This representation is based on equivalent resistivity, which takes properly into account the electromagnetic and the geometrical properties of the two earth layers. The equivalent resistivity can be used in the relatively simpler formulas for the earth return calculations for the case of homogenous earth. The new expression is implemented for six actual cases of two-layer earth structures involving combinations of overhead and underground conductors. Results show that the equivalent resistivity approach can lead to significant simplifications in most cases of switching transient simulations in the presence of two-layer earth structures

Earth return path impedances of underground cables for the multi-layer case: a finite element approach

The lossy earth return path influences significantly the electrical parameters of underground power cables, especially in cases where transient simulation models are of interest. The use of approximations for the calculation of earth correction terms proves to be inaccurate at high frequencies or low earth resistivities. The infinite integral terms representing the earth influence are high oscillatory in cases of underground cables and therefore difficult to integrate numerically. The scope of this paper is to present and compare results, obtained by a novel numerically stable and efficient integration scheme to those obtained by a finite element method formulation for several single core cable configurations and for homogeneous and multi-layered earth. Significant differences between impedances are recorded, especially for high frequencies and low earth resistivities.

Equivalent resistivity approximation of two-layer earth structures for earth return impedance calculations

The equivalence conditions between homogeneous and two-layer earth structures are investigated in this paper. The analysis is based on the comparison between the two-layer and the homogeneous earth return impedance relations. The aim is the derivation of a new simple formula to connect the homogeneous earth equivalent resistivity with the two-layer earth electromagnetic and geometric properties. Thus, the relatively simple expressions for the impedance calculation of the homogeneous earth case can be used for two-layer earth models. The new formula is implemented for six actual cases of two-layer earth models. The two-layer earth impedances are calculated for various configurations, including overhead transmission lines, underground cable systems and a combination of overhead line and underground conductor. The calculated impedances are compared to the corresponding for the homogeneous earth, using the equivalent resistivity given by the new formula.