Cuthbert Nyamupangedengu - Academia.edu (original) (raw)

Papers by Cuthbert Nyamupangedengu

This paper presents an investigation into characteristics of double cavity partial discharges. Hi... more This paper presents an investigation into characteristics of double cavity partial discharges. High Density Polyethylene (HDPE) is used as the insulation in the test specimen. Firstly, an electric field simulation using FEMM was used to observe the influence of the gap distance between the two cavities. This was to observe the electric field magnitude in the cavities for the same applied voltage across the parallel plate electrodes. It was observed that the electric field within the cavities is inversely proportional to the gap size between the cavities. For identically sized 1 mm diameter cavities, the electric field magnitudes within cavities influenced each other for gap length less than 3.5 mm. Beyond 3.5 mm, the crossinterference of the electric fields in the two cavities became negligible. Based on the simulation results, a gap length of 1 mm was used in the physical experiments. The test samples were prepared by placing a defected HDPE disc between two healthy discs. The resu...

Partial discharge (PD) tests on power cables are now conducted at Very Low Frequencies (VLFs) as... more Partial discharge (PD) tests on power cables are now conducted at Very Low Frequencies (VLFs) as it is technically and economically convenient, yet power cables operate and fail at power frequency. A comparative study is conducted in accordance with IEC 60270. Surface PD parameters in air at VLF (0.02 Hz and 0.1 Hz) and at power frequency (50 Hz) sinusoidal test voltages are presented. PD measurements were performed in a fairly constant temperature and humidity environment. Six polyethylene disk samples were prepared with a diameter of 132 mm and 4.25 mm thickness for each test frequency. The sample thickness was chosen to correspond to the insulation thickness of 6.35/11 kV XLPE insulated power cables. PD inception voltage and PD magnitude increased with frequency whilst PD extinction voltage showed no peculiar trend. Repetition rate increased with frequency and statistical operators such as kurtosis and skew of mean pulse height and pulse count of PD phase resolved patterns (PDPRPs) decreased with frequency. The findings are explained using the known theory of surface PD mechanism. Knowledge obtained from this work is used to qualitatively model the behaviour of surface PD parameters with frequency. Possible practical implications of the findings are also outlined.
Keywords: Surface PDs, very low frequency, power frequency, repetition rate, phase resolved patterns, kurtosis, skew

IEEE Transactions on Dielectrics and Electrical Insulation, 2012

Partial discharge (PD) spectral response to variations in the supply voltage frequency was experi... more Partial discharge (PD) spectral response to variations in the supply voltage frequency was experimentally investigated through laboratory-based tests. The PD spectral content of each defect type responded uniquely to variations in the sinusoidal supply voltage frequency in the range 20 to 400 Hz. The findings are interpreted using the theory of space charge dynamics in PD mechanisms. Prospective diagnostic applications

IEEE Transactions on Dielectrics and Electrical Insulation, 2000

A study on the influence of supply voltage magnitude and frequency on partial discharge (PD) puls... more A study on the influence of supply voltage magnitude and frequency on partial discharge (PD) pulse shapes is presented in this paper. Ultrawide band (UWB) time resolved PD pulse measurements were carried out on artificial PD defects using test voltage frequency range of 10-400 Hz and voltage range of 2-11 kV. The manner in which the PD pulse shape responded

2012 Annual Report Conference on Electrical Insulation and Dielectric Phenomena, 2012

This paper presents results of a comparative study of the behavior of electrical tree partial dis... more This paper presents results of a comparative study of the behavior of electrical tree partial discharges (PD) in clean epoxy and a MgO/epoxy resin nanocomposite. It was found that the PD phase-resolved patterns (PDPRP) of tree discharges in both clean epoxy and nanocomposite epoxy exhibited two distinct categories of small and big discharge pulses. In nanocomposite epoxy however, the average PD magnitude was orders of magnitude smaller and the repetition rate much lower than in clean epoxy. The difference is attributed to nanoparticles that block tree channels thereby effectively reducing the rate of electrical tree induced degradation of the nanocomposite.

This paper presents an investigation into characteristics of double cavity partial discharges. Hi... more This paper presents an investigation into characteristics of double cavity partial discharges. High Density Polyethylene (HDPE) is used as the insulation in the test specimen. Firstly, an electric field simulation using FEMM was used to observe the influence of the gap distance between the two cavities. This was to observe the electric field magnitude in the cavities for the same applied voltage across the parallel plate electrodes. It was observed that the electric field within the cavities is inversely proportional to the gap size between the cavities. For identically sized 1 mm diameter cavities, the electric field magnitudes within cavities influenced each other for gap length less than 3.5 mm. Beyond 3.5 mm, the crossinterference of the electric fields in the two cavities became negligible. Based on the simulation results, a gap length of 1 mm was used in the physical experiments. The test samples were prepared by placing a defected HDPE disc between two healthy discs. The resu...

Partial discharge (PD) tests on power cables are now conducted at Very Low Frequencies (VLFs) as... more Partial discharge (PD) tests on power cables are now conducted at Very Low Frequencies (VLFs) as it is technically and economically convenient, yet power cables operate and fail at power frequency. A comparative study is conducted in accordance with IEC 60270. Surface PD parameters in air at VLF (0.02 Hz and 0.1 Hz) and at power frequency (50 Hz) sinusoidal test voltages are presented. PD measurements were performed in a fairly constant temperature and humidity environment. Six polyethylene disk samples were prepared with a diameter of 132 mm and 4.25 mm thickness for each test frequency. The sample thickness was chosen to correspond to the insulation thickness of 6.35/11 kV XLPE insulated power cables. PD inception voltage and PD magnitude increased with frequency whilst PD extinction voltage showed no peculiar trend. Repetition rate increased with frequency and statistical operators such as kurtosis and skew of mean pulse height and pulse count of PD phase resolved patterns (PDPRPs) decreased with frequency. The findings are explained using the known theory of surface PD mechanism. Knowledge obtained from this work is used to qualitatively model the behaviour of surface PD parameters with frequency. Possible practical implications of the findings are also outlined.
Keywords: Surface PDs, very low frequency, power frequency, repetition rate, phase resolved patterns, kurtosis, skew

IEEE Transactions on Dielectrics and Electrical Insulation, 2012

Partial discharge (PD) spectral response to variations in the supply voltage frequency was experi... more Partial discharge (PD) spectral response to variations in the supply voltage frequency was experimentally investigated through laboratory-based tests. The PD spectral content of each defect type responded uniquely to variations in the sinusoidal supply voltage frequency in the range 20 to 400 Hz. The findings are interpreted using the theory of space charge dynamics in PD mechanisms. Prospective diagnostic applications

IEEE Transactions on Dielectrics and Electrical Insulation, 2000

A study on the influence of supply voltage magnitude and frequency on partial discharge (PD) puls... more A study on the influence of supply voltage magnitude and frequency on partial discharge (PD) pulse shapes is presented in this paper. Ultrawide band (UWB) time resolved PD pulse measurements were carried out on artificial PD defects using test voltage frequency range of 10-400 Hz and voltage range of 2-11 kV. The manner in which the PD pulse shape responded

2012 Annual Report Conference on Electrical Insulation and Dielectric Phenomena, 2012

This paper presents results of a comparative study of the behavior of electrical tree partial dis... more This paper presents results of a comparative study of the behavior of electrical tree partial discharges (PD) in clean epoxy and a MgO/epoxy resin nanocomposite. It was found that the PD phase-resolved patterns (PDPRP) of tree discharges in both clean epoxy and nanocomposite epoxy exhibited two distinct categories of small and big discharge pulses. In nanocomposite epoxy however, the average PD magnitude was orders of magnitude smaller and the repetition rate much lower than in clean epoxy. The difference is attributed to nanoparticles that block tree channels thereby effectively reducing the rate of electrical tree induced degradation of the nanocomposite.