A discussion of D-C high-potential test voltage for aircraft electrical insulation

D-c high-potential test voltage that will detect aircraft equipment insulation flaws in a manner equivalent to the 60-cycle rms high-potential test voltage now specified is investigated. The purpose of equipment high-potential tests is stated to be the detection of insulation faults which are shown to be of two categories: 1. holes, cracks, discontinuities, and all faults which result in small-hole air gaps in insulation; and 2. marginally thin insulation, and insulation where the effective thickness has been reduced by the inclusion of foreign matter. A d-c/a-c rms test-voltage ratio of 1.41 is established for the detection of small-hole defects in insulation. Because insulation materials of the type used in aircraft equipment are not available in sufficiently thin thicknesses for breakdown tests at the currently used 1,500-volt 60-cycle rms high-potential test voltage, conclusive data could not be obtained regarding the d-c/a-c high-potential test-voltage ratio necessary to detect marginally thin insulation. A d-c/a-c high-potential test-voltage ratio of 1.6 is tentatively suggested for detecting marginally thin insulation pending further investigation.