Effect of altitude on impulse and 60-cycle strength of electrical apparatus

ALTITUDE is accompanied by a lowering of the air density, and, accordingly, it affects the performance of electrical apparatuses which depend on the air for operation. Thermal performance is affected because of the reduced heat dissipated by convection. Similarly the dielectric strength suffers a decrease with lower air density. The windage losses of machines and damping of instruments are less, but, in either case, the amount is not of consequence. At very high altitudes commutation may present a major problem and storage batteries become affected adversely. The interrupting capacity of some circuit-interrupting devices is also affected, the amount depending on various conditions. These are well-known instances where altitude is a factor in the operation of electrical apparatus.