Considering an optimum frequency for high potential testing

It has been recognized for many years that a high potential test at the service frequency is a reliable indicator of the suitability of an insulation system for the service period. However, because a high capacitance apparatus requires large charging KVA at the test voltages and service frequency, it is often not convenient nor possible to apply the service frequency high potential test at field installations. The choice is then between applying no voltage at all during field maintenance programs, or to use a substitute for the service frequency on such apparatus as steam turbine generators, hydroelectric machines, large electric motors, or power cables. One substitute often used presently is the d-c high potential test. The testing KVA is minimum in this instance, and primarily for this reason d-c testing techniques have received a great deal of acceptance.