I want to find out the method which is used in industrial insulation resistance testers (Megger) to accelerate the depolarization of transformer insulation. Depolarization current of 3 phase transformer takes more than 1000 sec to go lower than 100nA but industrial testers allow you to do the tests with lower than 1min delay between tests (at least we do three tests: LV to ground, HV to ground and HV to LV). They just reduce the voltage to zero and discharge the geometrical capacitance. So that means you can do the whole of the tests less than 10 min but as above mentioned if they do not use any acceleration mechanism, they can not measure the correct value in the second and third tests.

Do you have any idea?