Moisture equilibrium between gas space and fibrous materials in enclosed electric equipment

THE USE of an inert gas in enclosed electric equipment has increased considerably in recent years. In transformers an inert gas is used in the space provided above the transformer fluid to allow for its volumetric expansion with temperature rise. There the function of the gas is to provide an inert medium by which the pressure at the surface of the transformer fluid is kept slightly above atmospheric. Thus the fluid is not exposed to the moisture and oxygen of the air, as it is with the so-called “open-breather” or “oil-conservator” types unless the latter communicate with the outside atmosphere through chemical agents. In gas pressure cables, however, the inert gas is used at pressures up to approximately 15 atmospheres in order that the cables may operate successfully at electric stresses that are higher than otherwise would be possible.^1–3