Gökhan Cinar

Electromagnetic Dispersion Modeling and Measurements for HVDC Power Cables

This paper provides a general framework for electromagnetic (EM) modeling, sensitivity analysis, computation, and measurements regarding the wave propagation characteristics of high-voltage direct-current (HVDC) power cables. The modeling is motivated by the potential use with transient analysis, partial-discharge measurements, fault localization and monitoring, and is focused on very long (10 km or more) HVDC power cables with transients propagating in the low-frequency regime of about 0-100 kHz. An exact dispersion relation is formulated together with a discussion on practical aspects regarding the computation of the propagation constant. Experimental time-domain measurement data from an 80-km-long HVDC power cable are used to validate the electromagnetic model, and a mismatch calibration procedure is devised to account for the connection between the measurement equipment and the cable. Quantitative sensitivity analysis is devised to study the impact of parameter uncertainty on wave propagation characteristics. The sensitivity analysis can be used to study how material choices affect the propagation characteristics, and to indicate which material parameters need to be identified accurately in order to achieve accurate fault localization. The analysis shows that the sensitivity of the propagation constant due to a change in the conductivity in the three metallic layers (the inner conductor, the intermediate lead shield, and the outer steel armor) is comparable to the sensitivity with respect to the permittivity of the insulating layer. Hence, proper modeling of the EM fields inside the metallic layers is crucial in the low-frequency regime of 0-100 kHz.

A HYBRID METHOD FOR THE SOLUTION OF PLANE WAVE DIFFRACTION BY AN IMPEDANCE LOADED PARALLEL PLATE WAVEGUIDE

The diffraction of E-polarized plane waves by an impedance loaded parallel plate waveguide formed by a two-part impedance plane and a parallel half plane with different face impedances is investigated rigorously by using the Fourier transform technique in conjunction with the Mode Matching Method. This mixed method of formulation gives rise to a scalar Modified WienerHopf equation, the solution of which contains infinitely many constants satisfying an infinite system of linear algebraic equations. A numerical solution of this system is obtained for various values of the surface impedances and waveguide height.

Wave modeling and fault localization for underwater power cables

This paper describes some preliminary results regarding Time-Domain pulse Reflection (TDR) measurements and modeling performed on the Baltic Cable submarine HVDC link between southern Sweden and northern Germany. The measurements were conducted in collaboration between the Linnaeus University, Lund University, Baltic Cable AB and ABB High Voltage Cables AB, and is part of the research project: “Fundamental wave modeling for signal estimation on lossy transmission lines”. Preliminary results on measurements and modeling are included here, as well as a first numerical study regarding the low-frequency dispersion characteristics of power cables. The numerical study shows that the finite conductivity of the cable lead shield has a great impact on the losses at low frequencies (0–1 kHz), and that the low-frequency asymptotics of the propagation constant is consistent with common propagation models based on the skin-effect.

Dispersion Modeling and Analysis for Multilayered Open Coaxial Waveguides

This paper presents a detailed modeling and analysis regarding the dispersion characteristics of multilayered open coaxial waveguides or cables. The electromagnetic model is based on a layer recursive computation of axial-symmetric fields in connection with a magnetic frill generator excitation that can be calibrated to the current measured at the input of the cable. The layer recursive formulation enables a stable and efficient numerical computation of the related dispersion functions, as well as a detailed analysis regarding the analytic and asymptotic properties of the associated determinants. Modal contributions as well as the contribution from the associated branch-cut (nondiscrete radiating modes) are defined and analyzed. Measurements and modeling of pulse propagation on an 82-km-long HVDC power cable are presented as a concrete example. In this example, it is concluded that the contribution from the dominating axial-symmetric transverse magnetic mode is sufficient, and that the contribution from the branch-cut is negligible for all practical purposes, and in particular if the exterior domain is lossy. The main contribution of this paper is to provide the necessary modeling and analysis tools for a quantitative study of these phenomena.

Simulation of electromagnetic pulses in waveguides at large distances

This paper presents accurate analytical expressions in the time domain for discrete electromagnetic waveguide modes for large distances together with a discussion of the errors. The main application is source localization for high voltage direct current submarine power cables. The research behind this paper is part of the project “Fundamental wave modelling for signal estimation on lossy transmission lines” funded by the Swedish Research Council and ABB High Voltage Cables AB in Sweden.

TEM Wave Scattering by a Step Discontinuity on the Outer Wall of a Coaxial Waveguide

In this paper, the propagation of TEM waves along a coaxial waveguide with a step discontinuity on its outer wall is investigated rigorously by applying the direct Fourier transform and reducing the problem into the solution of a modified Wiener-Hopf equation. The solution for the field terms are determined in terms of an infinite number of unknown coefficients, which satisfy an infinite set of linear algebraic equations. These equations are solved numerically and the effect of area ratio is presented graphically at the end of the analysis. The same problem is also analyzed by applying the mode-matching technique and the results of the two approaches are compared. It is observed numerically that the Wiener-Hopf technique provides a better convergence than the mode-matching technique.

Diffraction of a normally incident plane wave by three parallel half-planes with different face impedances

The diffraction problem of plane waves by a set of three parallel half-planes one of which is placed in the opposite direction and having characterized with different surface impedances on upper and lower faces is solved by mode-matching method where available and Fourier transform technique elsewhere. The solution includes two independent Wiener-Hopf equations each involving infinite number of expansion coefficients which satisfy an infinite system of linear algebraic equations. After the determination of these coefficients numerically, some graphical results are presented showing the influence of the surface impedances and the distances between the half-planes on the diffracted and transmitted waves.

Plane Wave Diffraction by Tandem Impedance Slits

The diffraction of E-polarized plane waves by a tandem impedance slit waveguide is investigated rigorously by using the Fourier transform technique in conjunction with the Mode Matching method. This mixed method of formulation gives rise to a scalar Wiener-Hopf equation of the second kind, the solution of which contains infinitely many constants satisfying an infinite system of linear algebraic equations. A numerical solution of this system is obtained for various values of the surface impedances, slit width and the distance between the slits, through which the effect of these parameters on the diffraction phenomenon are studied.

Scattering of a TEM wave by a large circumferential gap on a coaxial waveguide

In the present work, the scattering of a TEM wave by a gap on the outer wall of a coaxial waveguide is analyzed rigorously. The formulation of the related boundary-value problem in terms of Fourier integrals leads to a modified Wiener–Hopf equation which is first reduced into a pair of Fredholm integral equations of the second kind and the diffraction coefficients related to the reflected, transmitted, and radiated fields are determined explicitly for large gap width compared to the wavelength. At the end of the analysis, numerical results illustrating the effects of the cross-sectional area of the coaxial cylindrical waveguide and the gap width on the fields are presented.

Wiener-Hopf Analysis of Plane Wave Diffraction by an Impedance Strip Attached on a Perfectly Conducting Half-Plane

Abstract In this article, diffraction of a plane wave by an impedance strip on a perfectly conducting half-plane, which represents a metallic half-plane with a material coating near its edge, is investigated rigorously. In order to obtain an analytical solution to such a problem, where the lateral boundary conditions are different in the three-part mixed boundary-value problem, the Fourier transform and spectral iteration technique is applied. The diffracted field is analyzed numerically with respect to the surface impedance of the strip and the strip width. The results are illustrated graphically.