Absorption studies on high-voltage machines

IN CONJUNCTION with basic studies of a-c and d-c test methods to evaluate the conditions of machine insulations, a number of dielectric absorption tests were made on new high-voltage stator windings using d-c test voltages ranging from 5,000 to 40,000 volts. A total of 78 machines rating from 15,000 to 135,000 kva were tested. Because the application of high-potential d-c test voltages is necessarily limited to machines whose insulation is capable of withstanding such voltages without damaging effects, the voltage class of all of the machines tested was in the range of 11.0 to 14.4 kv. The insulation was essentially the same for the entire group of machines consisting of multiple layers of continuously applied mica tape.