Tank pressure variation in sealed transformers

IN A modern power transformer only the insulation, oil, and fibrous materials, show appreciable deterioration under normal operating conditions. Consequently, it is only natural that much effort has been applied to the problem of preventing or retarding this deterioration. Many schemes for this purpose have been devised; open air breather, dehydrating breather, conservators, gas-oil seals, sealed tanks, inert gas atmospheres, and thermosiphon clay filters are examples. These devices have one or two objectives: to prevent the entrance or to minimize the effects of moisture, or to exclude oxygen and minimize the effects of oxidation. The simplest and one of the most effective methods is to seal the transformer tank.