Modeling of Water Trees based on Investigation of Water Tree Degradation of 6.6 kV XLPE Cable Subjected to Accelerated Water-treeing Test and Calculation of DC Leakage Current and AC Superposition Current and Estimation of AC Breakdown Voltage by Transient Electric Field Analysis

Abstract

The authors were able to generate a penetrated water tree in an extruded three layer (E-E type) 6.6 kV XLPE cable subjected to an accelerated water-treeing test, and measured DC leakage and AC superposition currents of the cable. In this study, the penetrated water tree was modeled and DC leakage and AC superposition currents were calculated by using transient electric field analysis, and the calculated currents and measured ones were compared. In addition, the conductivity of water trees was selected so that the calculated AC superposition current was equivalent to the average value of the measured values, and DC leakage and AC superposition currents were calculated for a non-bridged water tree obtained after the accelerated water-treeing test. Furthermore, the shapes of water trees were assumed as spheroidal ones, and the DC leakage current, AC superposition current and AC breakdown voltage were analyzed when the length and width of the water tree changed.