Effect of Altitude on Electric Breakdown and Flashover of Aircraft Insulation

This paper reports a rather extensive investigation made to determine the requirements for insulation clearances for aircraft electric apparatus rated up to 600 volts and intended for use at altitudes up to 65,000 feet. All the tests were conducted on the ground under simulated high-altitude conditions. Tests were made with a variety of materials, including the actual rocker ring of a high-production 28.5-volt d-c generator. A table of recommended striking distances and creepage distances to meet these conditions is given. These recommendations are compared with certain existing standards. It is shown that the clearances and spacings required for high-altitude operation cannot be checked by a sea-level dielectric test without injuring the solid insulation, unless the tests are made in a partial vacuum.