D-C overpotential testing on high-voltage generators

OVERPOTENTIAL TESTS are applied to electric apparatus to demonstrate the ability of the insulation to withstand a specified voltage for a certain period of time. Industry standards accept overpotential tests as the only reliable tests for the dielectric level of machine insulations. Practically all recognized standard overpotential tests on electric machinery are made with alternating current. During the past several years, investigation of d-c overpotential testing indicated basic advantages over a-c testing and that direct current could be used as a satisfactory overpotential test on large high-voltage machines.