Apparatus ratings at high elevations

摘要

The Ambient Air Within And Surround-ing any electrical equipment serves two independent purposes: insulation, and cooling. Dielectric breakdown strength of air-its insulating integrity-depends upon its density. For atmospheric air, density is a function of pressure, which is greatest at the earth's surface and decreases with elevation (Figure 1). Whatever the density, the presence of dust and moisture in the air can seriously reduce its insulation capability, just as solid insulation suffers from surface contamination.