Evaluation of varnishes for hermetic use

The history of the hermetic motor industry is one of conservatism. Due to the high reliability required of the hermetic system and the tremendous replacement costs of an inadequate system, manufacturers tend to stick with an established system rather than initiate change. When a change is finally initiated, it is only after thorough study and testing have shown that said change will not be detrimental to the hermetic system. General Electric Hermetic Motor Product Department, although a leader in initiating improvements in the hermetic motor industry, is no exception to this rule and the tests we use to evaluate a varnish for hermetic use are described in this paper. The paper will not attempt an industry wide survey of varnish evaluation techniques, but will deal only with those tests used by the General Electric Hermetic Motor Products Department.