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AC testing advantages
1. AC testing is generally much more accepted by safety agencies than DC testing. The main
reason for this is that most items being hipot tested will operate on AC voltages. AC hipot
testing offers the advantage of stressing the insulation alternately in both polarities, which
more closely simulates stresses the product will see in real use.
2. Since AC testing cannot charge a capacitive load the current reading remains consistent
from initial application of the voltage to the end of the test. Therefore, there is no need to
gradually bring up the voltage since there is no stabilization required to monitor the current
reading. This means that unless the product is sensitive to a sudden application of voltage
the operator can immediately apply full voltage and read current without any wait time.
Another advantage of AC testing is that since AC voltage cannot charge a load there is no need
to discharge the item under test after the test.
AC testing disadvantages
One disadvantage of AC testing surfaces when testing capacitive products. Again, since AC
cannot charge the item under test, reactive current is constantly flowing. In many cases, the
reactive component of the current can be much greater than the real component due to actual
leakage. This can make it very difficult to detect products that have excessively high leakage
current.
Another disadvantage of AC testing is that the hipot has to have the capability of supplying
reactive and leakage current continuously. This may require a current output that is actually
much higher than is really required to monitor leakage current and in most cases is usually
much higher than would be needed with DC testing. This can present increased safety risks
as operators are exposed to higher currents.
1.5.1.2 DC Dielectric Withstand Test
DC testing characteristics
During DC hipot testing the item under test is charged. The same test item capacitance that
causes reactive current in AC testing results in initial charging current which exponentially
drops to zero in DC testing.
DC testing advantages
Once the item under test is fully charged, the only current flowing is true leakage current.
This allows a DC hipot tester to clearly display only the true leakage of the product under test.
Another advantage to DC testing is that the charging current only needs to be applied
momentarily. This means that the output power requirements of the DC hipot tester can