Ruslan Papazyan

Extraction of high frequency power cable characteristics from S-parameter measurements

A technique is developed for extraction of the wave propagation properties of power cables from S-parameter measurements. The method extracts the complex propagation constant and the characteristic impedance, as well as the LCRG telegraphers equation parameters. The extraction process is developed after clarifying the effect of the connection between the measurement port and the power cable. It is concluded that treating the connection solely as a characteristic impedance change could lead to considerable errors in the parameter extraction. Furthermore, the method corrects for electrical lengths, which are not accounted for by the standard network analyzer calibration. The extraction is demonstrated for a medium voltage cross linked polyethylene (XLPE) cable over the frequency range 300 kHz to 300 MHz. The results are compared to a time domain short pulse propagation method for cable characterization. Both measurement methods are evaluated against a cable model.

Calibration for time domain propagation constant measurements on power cables

A method has been developed for characterising the wave propagation properties of medium voltage (MV) power cables. The technique is based on time and frequency domain analysis of short pulse propagation. Particular attention is paid to the measurement calibration, as samples with arbitrary characteristic impedances cause significant multiple reflections in the test set-up.

Wave propagation on power cables with special regard to metallic screen design

The high frequency properties of coaxial power cables are modeled using time- and frequency-domain numerical simulations. This is required due to the complex helical structure of the outer metallic screen. The finite element (FEM) and finite difference time domain methods (FDTD) have been employed to study the effect of screen spiralization. It is established that this screen design causes a dependence of the cable high frequency characteristics on the surrounding medium. Analytical model based on modal analysis of wave propagation in coaxial cables confirms the numerical observations.

Comparing Wave Propagation Characteristics of MV XLPE Cable and Covered-Conductor Overhead Line using Time Domain Reflectometry Technique

In this paper, the wave propagation characteristics of single-phase medium voltage (MV) cross-linked polyethylene (XLPE) cable are determined using time domain reflectometry (TDR) measurement technique. TDR delivers the complex propagation constant (attenuation and phase constants) of lossy cable transmission line as a function of frequency. The frequency-dependent propagation velocity is also determined from the TDR measurements through the parameters extraction procedure. The TDR measurement results for MV XLPE cable and covered-conductor (CC) overhead line are compared and it is proved that CC line has lower attenuation and higher propagation velocity than power cable. The measurement results can be used to localize the discontinuities in XLPE power cables and for PD detection to monitor falling trees on the MV CC overhead lines.

Diagnosis of moisture in oil/paper distribution Cables - Part II: Water penetration in cable insulation - experiment and modeling

For Pt.I see ibid., vol.19, no.1, p.9-14, January 2004. Dynamics of water penetration in mass impregnated cable insulation has been studied. For experimental purposes, artificial damage has been inflicted to a 40-cm-long cable sample and water ingress has been continuously monitored by frequency response measurements. A similar experiment has been conducted on 2.8-m-long cable sample, where both frequency response and time-domain reflectometry (TDR) measurements have been performed. After termination of both experiments, actual moisture content has been measured radially and axially. Based on dielectric measurements, a model of water ingress has been developed and diffusion coefficients have been estimated for mass impregnated cable paper.

Localization of Insulation Degradation in Medium Voltage Distribution Cables

The paper presents a methodology for successful localization of degraded insulation in medium voltage cables. Extensive work has been performed on development of cable models and characterization of new and degraded cable material to support the diagnostic technique. A non-destructive technique has been developed using differential time domain reflectometry (TDR) measurements. The main application has been localization of water treed sections of XLPE cables where the voltage dependence of the permittivity of water treed insulation has been used as diagnostic criteria.

High frequency characterisation of water-treed XLPE cables

Time Domain Reflectometry (TDR) has been used for localisation of transmission line discontinuities in various applications. One of the challenges when applying TDR is to obtain knowledge of the high frequency characteristics of both the degraded and the undegraded sections of the cable. The wave propagation characteristics of water-treed XLPE cables are investigated in this study. The parameters are extracted from the cable S-parameters measured with a Network Analyzer (NA) in the frequency range from 300 kHz to 300 MHz. The cable samples are characterised at different temperatures and with different water content of the water trees. The effect of the application of nominal voltage for extended period on the cable wave propagation characteristics is also shown. High voltage dielectric spectroscopy is used as a reference method for estimation of the level of water tree deterioration.

Modeling the Wave Propagation Properties of Power Cables using Numerical Simulations

The high frequency properties of coaxial power cables are modeled using time- and frequency-domain numerical simulations. This is required due to the complex helical structure of the outer metallic screen. It is established that this screen design causes a dependence of the cable characteristics on the surrounding medium