As the power system generation requirements for aerospace airplanes and spacecraft systems increase, higher voltage levels may be desired to reduce power system losses and weight. The principal objection to using high-voltage power and electronic systems and components is the probability of corona and/or partial discharges. This is especially true for vehicles operating in the altitude-pressure zone between 50,000 feet and 120,000 feet.
Densely-packaged power systems and electronic modules utilize very small spacings between parts and printed circuit board traces. There exists a multitude of spacing-air density conditions where the corona or partial discharge Paschen law minimum voltage pressure-spacing characteristic is satisfied to produce corona, partial discharges or gas breakdown initiation. For air, the critical pressure-spacing product density to satisfy the Paschen minimum of 327 volts dc, or 200 volts ac, is 0.7 torr -cm. Immediately it can be seen that these voltages exceed the nominal aerospace recommended voltages of 270 volts dc, or 200 volts ac. But the Paschen minimum may be exceeded during power system abnormalities of over-voltages, transients, and induced voltages from outside sources. Thus, the corona, partial discharge and voltage breakdown are concerns.
This paper will be based on the breakdown characteristic of air rather than a multitude of other gases and/or gas mixtures. However, it must be remembered that many other gases and gas mixtures either have much lower or higher corona initiation or breakdown voltage characteristics than air at the Paschen law minimum. The objection to corona, partial discharges and voltage breakdown is that the pulses and wide bandwidth frequencies emanating from the presence of the discharges may generate noise that may be radiated or conducted into sensitive circuits and may create circuit operation malfunctions, the deterioration of electrical insulation by chemical reactions caused by the ionized air and its dissociated gases, and the probability of ignition of low-flammability gases caused by minute arcs. All these problems have high priority with respect to mission success.