A hipot test may use either ac or dc and is well known
for its use as a proof test of the completed machine winding,
where the winding must withstand the voltage
(2UN + 1) kVac (it is higher for a dc test) without failure.
But the objective of using the hipot test for qualification is
to determine the characteristic voltage of failure for the
insulation system. This requires the application of destructive
ramped or stepped voltage to sample coils, and the
voltage at failure is then recorded. Several samples must be
tested to ensure a good statistical distribution. Techniques
for HV withstand tests are covered in [12].