Investigating the effects of altitude (air density) on the HVDC breakdown voltage of small rod-plane air gaps

Show simple item record Gora, Tatenda 2016-10-03T08:40:41Z 2016-10-03T08:40:41Z 2016
dc.identifier.citation Gora, Tatenda (2016) Investigating the effects of altitude (air density) on the HVDC breakdown voltage of small rod-plane air gaps, University of Witwatersrand, Johannesburg, <>
dc.description A dissertation submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science in Engineering, 2016
dc.description.abstract The validity of the atmospheric correction method presented in the IEC 60060-1 (2010) standard is analysed and evaluated by means of theoretical and laboratory work. In order to understand the problem, the evolution of the atmospheric correction methods, from as early as 1914, has been presented. A procedure (Calva prediction method) for predicting the direct current (DC) breakdown voltage for an air gap at any altitude was discovered and was also analysed along with the IEC 60060-1 (2010). A critique of some of the atmospheric correction methods commonly used standards was also done. Experiments were carried out at altitudes of 1 740 m (Wits University), 130 m (UKZN HVDC centre) and at less than 2 m above sea level (Scottburgh beach, Clansthal). More tests were conducted using a pressure vessel where high altitude relative air density was simulated. All tests were conducted on rod-plane air gaps using a 15 mm diameter at tip rod. Test results from Scottburgh beach were used as the standard breakdown voltages of the air gaps tested since the environmental conditions were the closest to the conventional standard conditions (stp). The test results obtained were compared with predictions using the Calva method in order to validate the method. The test results were also corrected according to IEC 60060-1 (2010) and compared to the standard breakdown voltages obtained at Scottburgh beach. It was shown that the IEC 60060-1 (2010) is quite suitable for atmospheric correction for data obtained at low altitudes (about 130 m). When applied to high altitude (1 740 m) data, the correction method is accurate and suitable for very small air gaps less than 0.1 m. As the air gap length increased, the corrected results began to deviate from the expected standard voltage. The same trend was shown with the corrected results from the pressure chamber tests. The prediction method by Calva was accurate when compared to the experimental data from the high altitude and low altitude test results. When compared to the data from the pressure chamber, the prediction method had a linear error factor which was di erent for each gap length. It was concluded that the IEC 60060-1 (2010) is not only unsuitable for atmospheric correction for data at relative air densities below 0.8, but also that the correction method is prone to an increase in error as the air gap length increases when the relative air density is higher than 0.8. The Calva prediction method was found to be suitable to use after additional factors are added when applied to high altitude conditions. en_ZA
dc.format.extent Online resource (72 leaves)
dc.language.iso en en_ZA
dc.subject.lcsh Electric power transmission--Direct current
dc.subject.lcsh High voltages--Testing
dc.subject.lcsh Breakdown (Electricity)
dc.title Investigating the effects of altitude (air density) on the HVDC breakdown voltage of small rod-plane air gaps en_ZA
dc.type Thesis en_ZA
dc.description.librarian GR2016 en_ZA

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