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 / 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. / GR2016
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:wits/oai:wiredspace.wits.ac.za:10539/21106 |
| Date | January 2016 |
| Creators | Gora, Tatenda |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | Online resource (72 leaves), application/pdf |
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