High voltage machines operating at high altitude — Dielectric considerations

Rotating electrical machines must be designed for the environment in which they operate. High voltage generators and larger motors are normally designed to run under standard environmental air pressure and humidity. Machines running in special conditions such as close to the sea, in underground caverns, under water or in high humidity require special designs. The specific conditions have to be considered from the beginning as they can influence the size, the sealing, the covering and several other components of the machine. The main influence of operating machines at higher altitudes is the reduced air density. This air density influences the cooling efficiency and the dielectric strength of the air. These two effects have a direct influence on the design of electric machines. The influence of air density on the dielectric strength of air gaps is investigated and described in this paper.