PD- type- dependent spectral bandwidth in solid polymer dielectrics

Nyamupangedengu, Cuthbert
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This thesis is on the study of partial discharge (PD) frequency spectral response to: (a) variations in supply voltage frequency and (b) time of ageing under continuous PD activity. The work extends knowledge on how to interpret frequency domain PD measurements. In addition to fundamental knowledge, the thesis also conceives two novel PD diagnosis tools that are based on spectral analysis. The work contributes to the ongoing efforts by Cigré WG D1.33 on producing an International Electrotechnical Commission (IEC62478) standard in response to the growing interest in unconventional PD diagnosis methods. Unconventional PD diagnosis methods include spectral analysis techniques where information is extracted from selected portions of the PD spectra. Literature shows that there is inadequate knowledge on characterisation of PD mechanisms through spectral analysis, and this can compromise the efficacy of frequency domain PD diagnosis techniques. It is imperative that interpretation of PD spectral measurements be informed by adequate knowledge on the factors that influence PD spectral content. The PD defects studied in this work are those commonly found in solid polymeric insulation such as shielded power cables. The experimental investigations established that firstly, PD spectral content of each defect type responds distinctly to variations in the sinusoidal supply voltage frequency in the range 20 to 400 Hz. Secondly, under long term ageing conditions, PD frequency spectral features of each defect type evolve uniquely. The findings are interpreted in terms of space charge dynamics theory of PD mechanisms. It is concluded that spectral analysis based PD diagnosis should take into account PD spectral dependency on the supply voltage frequency as well as ageing induced evolution. To my family and friends “Nature obeys its laws faithfully. It is up to the observer to make correct interpretations”. Jan P. Reynders AND “All truth in any sphere is the gift of God and comes to men through the Spirit of God” William Barclay, 1967