Analysis and characterization of water tree condition in XLPE cables from dielectric spectroscopy measurement in frequency domain

Degradation phenomenon due to water treeing has been identified as one of the main causes of cable failures in Cross-Linked Polyethylene (XLPE) cables. This research work presents on the development for the analysis of water tree conditions in the XLPE cable. The water tree condition is divided into three stages which are beginning, intermediate and critical. The method used to measure and obtain the data to determine the condition of the cable is called high voltage dielectric spectroscopy. It involves the measurement of capacitance and dielectric loss as a function of frequency at high voltages. The voltage levels used initially are all below the service voltage level and at the low frequency range. Based on the dielectric response measurement signals obtained, observation and numerical analysis were conducted to study the response of the cable and determine their water tree stages. Initially, the observation and analysis of the results are carried out by referring to the theory of the dielectric response. Then the research concentrates on analyzing the data from the dielectric spectroscopy measurement to perform the numerical analysis to obtain the characteristics of each water tree stages. Four different parameters were extracted from the Dielectric Spectroscopy response in the frequency domain and these parameters were found to be able to categorize the three different stages of water tree condition in the XLPE cables.

I. Introduction

Cross linked polyethylene (XLPE) insulation cables have been widely used in Malaysia for both distribution and transmission power system applications. XLPE insulated cable is used because it ensures cost efficiency in operation besides lower environmental and maintenance requirements compared to older systems [1]. The degradation phenomenon called water treeing was encountered to affect medium voltage power XLPE cables in late 1960s.