Suggestion:
AC HiPot test performs AC dielectric withstand test
DC HiPot test performs DC dielectric-withstand test
Essentially, they are used for insulation tests required for insulation evaluations
AC has the advantage of being fast; you can perform a production line test in 2 seconds or less. It has the disadvantage of requiring relative high current, so if you want your test to discriminate on the basis of current, discrimination will be difficult.
Some people believe that AC tends to damage insulations, particularly the Y capacitors.
DC has the advantage of requiring very low current. It is easy to set a very low trip current for DC, and to use DC for current discrimination. However, it tends to be slow because of the need to charge the capacitances at a low rate (slow ramp-up).
DC is often specified when it is desired to cancel out the fault currents resulting from the capacity coupling that occurs between the current carrying wires and ground. As direct current does not pass through the capacitor, the leakage reading is far lower. This allows the products true internal leakage to be measured without being masked by the capacitor leakage. This is a simple and low cost test method that is suitable in many cases. This is particularly important when testing for very low levels of fault current such as the 10 to 100 microamperes specified in some medical applications. It is also used when testing products containing RFI filters because of their high line to ground capacity. The use of a DC test voltage does present some problem. The most important of these is the safety problem, particularly when testing RFI protected products. When a DC test potential is applied to the product, the capacitors to ground retain the charge voltage after the connection is broken. A person contacting the product, even hours afterwards, is subjected to a substantial risk of shock. To prevent this, a direct short circuit must be placed across the output following the test. From a quality assurance stand point the DC test has the disadvantage that it does not create the stress reversals present in an AC test. To offset this, a longer test duration or higher test voltage is normally specified. A capacity compensation circuit avoids this problem and should be considered in some applications.
Although equipment under test is not specified, a common application of overpotential testing is for shielded MV cables. §4 of ANSI/IEEE Std 400-2001 Guide for Field Testing and Evaluation of the Insulation of Shielded Power Cable Systems gives some comparisons of the two, along with VLF methods.
USUALLY, not always:
The DC hipot breakdown voltage is much higher than the
AC peak hipot breakdown.
In testing coaxial cables have had the DC withstand (not breakdown) voltage more than 4 times the peak AC breakdown voltage.
If equipment is used at DC, usually a DC test is prefered, if the equipment is used at AC, then an AC test is prefered.
For pulse applications?
Comment on the previous posting: Essentially, the DC test for DC and AC test for AC sound plausible; however, other aspects come into picture, e.g. cable length, testing equipment set-ups, test experiences from the past, procedural requirements, etc.
