AC testing gives a charging current that is extremely large compared to other types of testing. AC frequently is used for high-potential testing; voltage is increased to some specified point to see if the insulation can stand that particular voltage. It is a GO/NO-GO type of test and can cause deterioration of the insulation, in contrast to a DC test which is basically non-destructive.
If an AC test voltage has been used and you want to use DC tests as an alternative, you will need to increase the maximum DC test voltage somewhat to obtain equivalent results.
In some cases, AC testing may be more suitable for proof testing of equipment. You run the voltage up to the selected value and the equipment either passes or doesn’t pass the test. With the DC test, you get a more qualitative picture; you can meter the leakage current as you increase the voltage and obtain specific values of insulation resistance.
As the size of your equipment increases, there are also marked economic advantages in DC over AC testing. As the test voltage increases, both the cost and weight of AC equipment go up much faster than with comparable DC test equipment. This is because the AC test set must supply the charging current which becomes and remains very high in the larger machines.
The High Voltage VLF-65E 65 kV VLF Tester is the latest addition to the new generation of VLF AC Hipots from HVI that use a dry-type, air cooled, solid state design with microprocessor control.
The HV Diagnostics HVA60 VLF /DC high voltage test instrument; is the instrument of choice when a single instrument is required that can test the full range of Medium Voltage cables available- that is 35kV rated cables and below.