VLF hipot —very low frequency hipot — is an AC high potential instrument used for testing the dielectric strength of insulating materials at 0.1 Hz or lower. Instead of having to perform DC testing because high potential test equipment that operates at power system frequency are large, heavy and therefore not very portable, VLF high potential testing makes testing cables and electrical apparatus in the field more practical and economical.
Where DC testing can leave harmful space charges in microscopic voids of solid insulation, testing with a VLF hipot exposes cable defects without harming good insulation. When you perform cable or generator testing with a VLF hipot at 0.1 Hz, it requires 600 times less power than at 60 Hz and 500 times less power than at 50 Hz. The added benefit of this type of test equipment translates into portability benefits for field testing applications. The VLF hipot test is a go/no go stress test where the load either holds the test voltage or breaks down. What could be simpler for exposing defects in cables and generators?
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Editor’s Note: This post was originally published October, 2010 and has been updated freshness, accuracy and comprehensiveness.