A VLF Hipot test is a stress test for cables and motors. It is basically an AC hipot test but with a lower frequency. This test is conducted to assess if the sample can handle 2-3 times its rated current. This test is not destructive on good devices. It only damages test devices when there are defective joints, splices or poor insulation.
A very low frequency hipot tester operates by applying a high sine wave ac voltage at a frequency of 0.1 hertz or less. The test voltage is usually two to three times the rated capacity of the test sample. This test is done to stress the test sample and check if it can withstand an additional work load.
The only effective way to test devices with high capacitance is through VLF high potential testing. It uses less power than AC hipot tests because low frequencies have high reactance to capacitance. 50 or 60 hertz has a low reactance to capacitance that’s why more power is needed to get the same results with VLF. Since it uses lower power, flash overs and corona discharges are less common during the test.