Insulation resistance and dielectric-absorption characteristics of large A-C stator windings

THERE HAS BEEN considerable discussion and differences of opinion relative to the significance of insulation-resistance measurements. Numerous investigations have been made and investigators have placed varying degrees of importance on their findings.^1,2,3,4 Nevertheless, insulation-resistance measurements are used widely as a nondestructive insulation test to aid in judging the suitability of machine windings for proof test or for service. Therefore, data on average values and normal spread of the insulation resistance of new insulation are of general interest. It is the belief of the authors that in order to interpret properly insulation-resistance data, a sufficiently large number of machines must be examined to permit statistical analysis.^5,6 Furthermore, insulation studied must be segregated according to detailed construction since broad insulation classifications such as AIEE class A or class B do not specify necessarily the order of insulation resistivity. Also, the effect of other important factors such as temperature and physical-design characteristics must be considered.