A novel system for the prolongation of the lifetime of power transformers by reduced oxidation and aging

One of the key components of electrical power distribution networks are power transformers. The insulation of these devices usually consists of mineral oil and cellulose based solid material. Although long time experience has shown, that this kind of insulation is very reliable, it is also well known, that it is exposed to aging. Two major factors, accelerating the aging, are water and oxygen. The rate of water adsorption and the presence of oxygen mainly depend on the construction of the transformer. In Europe, most of the power transformers are of free breathing type. Aging tests have shown, that the rate of aging of insulating materials in contact with oxygen is higher, thus the aging of free breathing transformers is higher, too. To achieve a reduced rate of aging the contact of the insulating materials with the environment has to be stopped, thus the insulating materials have to be separated from the atmosphere. The conversion of a free breathing transformer into a sealed one to accomplish this obligation is expensive and usually affords a transport of the transformer to an adequate workshop to install a membrane in the conservator. For an aged transformer with an already severely degraded insulation such a renovation is not always efficient, especially if the costs of the treatment are compared to the prolongation of the lifetime resulting thereof. A novel idea for the lifetime prolongation of free breathing power transformers, that can be installed with minor expenditure on site, is presented in this contribution. The insulation is covered with a nonpolluting layer of a gas heavier than air, thus creating a "flexible blanket" which hampers the uptake of water and excludes oxygen from the insulation. Experiments on the aging behavior and on the electrical and dielectrical properties of the insulating materials under the covering gas are presented and the results of these tests are discussed under the aspects of a least affected transformer operation.