Investigation of Defect Insulation Systems with Deferent Artificial Cavities Consisting of High Voltage Power Cable

The insulation lifetime of power cables is determined by several factors. One of the most important of these is the occurrence of partial discharge (PD) at the dielectric. The ability to detect and locate a PD source is limited by attenuation of the high frequency PD pulses as they propagate through the cable to the sensor. Therefore, it is necessary to understand the high frequency response of such cables. The aim of this thesis is to develop an accurate frequency-dependent cable model for detecting and locating degraded insulation regions on power cables, caused by partial discharge activities. Numerical methods can calculate field distribution in the vicinity of nonstandard shape cavities, which generate PDs, and are difficult to calculate by analytical methods. The simulated results show the important influence of the shape of cavity on the electric stress within it. Cavity stress enhancement increases as the permittivity of the dielectric increases. The increase is greater for cavities with large diameter to thickness ratios. A cavity with its axis parallel to the applied field direction has a higher stress enhancement. In addition, the stress distribution in the cavities is smaller for spherical cavities than for cylindrical types.an investigation into the possibility of detecting different PD patterns and signals when conducting PD tests using different sensor bandwidths is also presented in this thesis. The occurrence of discharge activity was created by an artificial defect manufactured in the single core cable insulation. The artificial defect generated an internal discharge and was used to investigate the PD signal propagation on cross-linked polyethylene (XLPE) cable. Capacitance coupled external sensors have been applied for the PD detection measurements and the results show that these external sensors have a number of advantages compared to high frequency current transformer (HF-CT) sensors for the detection of PD pulses.