UBC Theses and Dissertations
The electrical breakdown characteristics of oil/paper insulation under fast front impulse voltages Wang, Mengguang
Gas Insulated Substation (GIS) and Gas Insulated Transmission Line (GITL) have found broad application in power system over the last twenty years. Disconnect switch operations in this equipment causes transient voltages with rise times as fast as 5 to 20 nanoseconds and magnitudes as high as 2.5 pu. There is very little information on the effect of these transients on oil/paper insulated equipment connected to the GIS and GITL. There have been reports of transformer and bushing failures which may have been caused by these transients. In the investigation reported in this thesis, the electrical breakdown properties of oil/paper insulation under fast front impulse were studied. A test system was built to generate a high voltage fast front (rise time less than 10 ns) and to apply this voltage to oil/paper samples. The breakdown characteristics of oil/paper insulation was investigated using different types of paper, types of oil and number of layers of paper. Insulation breakdown voltage vs breakdown time (V-t) data was obtained with the fast front step waveform and V₅₀ breakdown data was obtained with the fast front waveform and lightning and switching impulse waveforms. The V-t data was analyzed using the histogram, Weibull distribution and equal area criterion methods. A 2% probability V-t curve was generated and fits the data well. The V₅₀ test results showed that the fast front impulse waveform has the lowest breakdown voltage and the switching impulse has the highest breakdown value.