Application of Hourly Meteorological Records to Atmospheric Correction Factors in Insulation Coordination under Switching Impulse Voltage

It is well known that air density and humidity have significant effects on the flashover strength of insulators and air gaps. IEEE Standard 4-1995 and IEC Standard 60060-1 both call for the application of correction factors to ac, switching-surge, and lightning-surge flashover levels in laboratory testing. However, atmospheric conditions vary over a wide range at different times and locations, which makes it difficult to determine the insulation level of transmission lines based on a few measurements of local atmospheric conditions. Based on the 20-year meteorological records of the Atmospheric Environment Service of Canada, the variation of the air pressure, temperature, and humidity in Alberta was investigated. The atmospheric correction factors for HV flashover voltage of air gaps under switching impulse voltage (SI) were then calculated for each hour. The correction factor was found to be a function of the elevation. This calculation method is helpful for insulation coordination of transmission lines.