VLF hipot testing is the most preferred method of testing medium voltage cables and other electrical devices. Unlike other tests which may have an effect on your devices, this test doesn’t degrade electrical devices because it uses lower power compared with other hipot testing methods.
Testing cable insulators is very important to ensure its continuous operation. Hipot testing is a stress test done to verify if the insulator can withstand its rated current. However, other hipot tests can degrade good insulators and shorten their operating life. DC hipot testing can damage a good dielectric due to the very high voltage used. This test is prone to treeing and flash overs.
VLF hipot testing is done by injecting a low frequency sine wave into the conductor for a few minutes to verify if it will be able to withstand the current. Due to the very low frequency used, VLF hipot testing uses less power compared to other tests. It takes advantage of the cable’s capability of being a capacitor and its reactance to low frequency AC voltage. Because of the low power needed, the test equipment is less bulky and more portable.