Impulse breakdown of insulators and air gaps of similar electrode configurations: effects of temperature

Comparative measurements are reported on the breakdown, under lightning and switching impulses, of a concentric electrode arrangement in which the inter-electrode space is spanned either by an insulator surface or by air. Temperature in the system has been varied in the range 10<T<100°C. The variation of positive and negative 50% flashover voltage, and the times to breakdown at 100% flashover, are presented for each temperature level tested. Flashover voltages, analysed as a function of relative air density δ, show a variation of the form δ^m, where 0.8<m<1.0 for positive polarity and m>1.0 for negative polarity at the highly stressed electrode. Variations are the same, in the presence or absence of the insulator surface, but absolute positive flashover voltages are lower across the surface, than in air, while negative flashover voltages are higher. Times to breakdown decrease with increasing temperature