EIS aging estimation and threshold values

The aging of electrical insulation material is one of the main topics for designers of electrical appliances. Much effort has been devoted to prepare statistical or physical methods of life time estimation in real operation of electric machinery. One of the problems in the estimation of insulation operational life is the existence of threshold values at which the change of aging mechanisms occurs. The following is a rule for aging tests: aging must be performed so that the aging mechanism is the same as that in real operation. However, properly distinguishing different aging mechanisms is a real challenge. It can be expected that electrical insulating systems of high voltage machinery are operating under threshold value in case of electrical aging. We can determine the aging mechanism in a variety of ways, e.g., from aging data of large rotary machines and transformers, where the insulation systems were traditionally designed to encounter electrical stress under three kilovolts per millimeter. From more than fifty years of aging data, we can find examples of electrically unaged insulation. Of course, other aging mechanisms occur during this time (thermal, PDs, mechanical, etc.). Aging tests become disproportionately long, as we attempt to approach a level of operating stress. A method to estimate a threshold value for specific aging parameters is presented in this paper on example of thermal aging.