Stabilized mineral oil capacitors

The stabilization of chlorinated capacitor impregnants by chemical additives has been practiced by a number of capacitor manufacturers for several years. Anthraquinone has been the most widely used stabilizer, and has been added to chlorinated diphenyl and chlorinated naphthalene to the extent of 0.5 to 1.0% by weight. The purpose of stabilization is to increase the d.c. life and to avoid undesirable changes in insulation resistance and power factor of capacitors in d.c. service. The benefit is illustrated by the 10- to 300- fold increase in life observed in accelerated life tests. The improvement noted in a particular case depends upon the nature and concentration of stabilizer and the conditions of test.