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 ultimate 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 a cavity of non-standard shape which generates PDs, and is difficult to calculate by analytical methods. The simulated results show the important influence of the shape of cavity on the electric stress within it. The 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 cavity is smaller for spherical cavities than for cylindrical types. The research results show that the semi-conducting layers response voltage increases as frequency increases. This indicates that the semi-conducting layers can have high sensitivity for detection of partial discharge signals and this may be a useful feature to incorporate in the design of cables and in the application of cable models. By using ATPDraw, FEM and EMTP-RV techniques, three different types of cable models are developed. The simulated results give a good agreement with the measured results on the single and three phase power cable. The developed cable model can use for reconstruction of PD source signal by using the receiving signal captured at the cable ends. It is important to use the true pulse shape because it is characteristic of the PD type and location. 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 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. In addition, development of a method to detect cross-coupling of PD signals between phases of a three core cable and location of the PD source on the three phase cable. In order to visualize recorded data gained by PD measurement of three phase cable under test, the 3PARD diagram was used. Each data pulse is assigned to a single dot in the (scatter plot) diagram. The measured results show that the 3PARD diagram allowed the user to identify the fault between phases with PD location. The model used for reconstruction which includes the effect of semicon material in the losses provides accurate reproduction of the propagation characteristics of high frequency PD pulses and the thesis work had used such a model to reconstruct PD waveforms of site PDs from the measured signal for the first time. The use of the original waveform is important for PD identification and location in the practical situation.
| Identifer | oai:union.ndltd.org:ADTP/275817 |
| Date | January 2009 |
| Creators | O, Hio Nam Johnson , Electrical Engineering & Telecommunications, Faculty of Engineering, UNSW |
| Publisher | Awarded by:University of New South Wales. Electrical Engineering & Telecommunications |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | Copyright O Hio Nam Johnson ., http://unsworks.unsw.edu.au/copyright |
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