High-temperature effects on flashover in air

Paschen´s law has been confirmed experimentally for millimetric gaps at temperatures up to 1100° C, and the flashover voltages obtained were independent of electrode material. The effect of electrode hot spots at temperatures up to 1200° C was investigated in different electric fields, the bulk of the test gap being at room temperature. Under uniform-field conditions, hot spots caused a substantial lowering of flashover voltage, but their effect decreased with increase in the divergence of the field. A hot spot in the region of least electric stress had no significant effect when the ratio of maximum to minimum stress exceeded a value of the order of, but greater than, the ratio of hot spot to ambient temperature. Evidence is advanced in support of the view that the operation of Trigatron gaps can be explained in terms of hot-spot formation.