Dispersion modeling and analysis for multilayered open coaxial waveguides

TL;DR

This paper develops a detailed electromagnetic model for multilayered open coaxial waveguides, enabling analysis of dispersion characteristics crucial for long power cable monitoring and fault detection.

Contribution

It introduces a recursive computational method for dispersion analysis, including modal and branch-cut contributions, applicable to very long power cables.

Findings

Branch-cut contributions can dominate at certain frequencies for long cables.

The model accurately predicts pulse propagation on an 82 km HVDC cable.

Modal analysis helps understand wave propagation phenomena in multilayered cables.

Abstract

This paper presents a detailed modeling and analysis regarding the dispersion characteristics of multilayered open coaxial waveguides. The study is motivated by the need of improved modeling and an increased physical understanding about the wave propagation phenomena on very long power cables which has a potential industrial application with fault localization and monitoring. 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 (non-discrete 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 second TM mode as well as from the branch-cut is negligible for all practical purposes. However, it is also shown that for extremely long power cables the contribution from the branch-cut can in fact dominate over the quasi-TEM mode for some frequency intervals. The main contribution of this paper is to provide the necessary analysis tools for a quantitative study of these phenomena.