We find there are often plenty of questions from readers about the differences between VLF, AC and DC hipot testing methods. And of course, plenty of arguments surround whether DC testing should be performed or completely replaced by VLF testing.
It is clear from past experience that DC testing has garnered criticism by those who feel it is ineffective at detecting flaws in the quality of electrical insulation and could possibly have detrimental effects as well. With that in mind, we thought it good to address questions about VLF high potential testing to provide clarity to the issue.
What exactly is VLF?
VLF Hipot stands for Very Low Frequency, High Potential testing. This frequency is usually at 0.1 hertz or lower. VLF testing is AC high potential testing with a much lower output frequency. VLF can be used for field testing of cables and rotating machinery that wasn’t previously practical using AC tests at power system frequency, due to size and power requirements of the equipment.
Where is VLF used?
When testing highly capacitive loads, VLF has a much lower power requirement than equipment that operates at power system frequency. For the most part, much of this testing is performed on solid dielectric cabling and rotating machinery. While many utilities do not use VLF cable testing, this method does allow users to inspect installation quality for damage due to a variety of influences over time, including high voltage (thumping) and poor workmanship. It is especially good for new installations or repairs of cable prior to re-energizing.
With multiple locations to better serve your needs, Protec offers a large range of VLF Hipots with rental options that work for you.
Related electrical test equipment available for rent from Protec:
Editor’s Note: This post was originally published on June, 2014 and has been updated freshness, accuracy and comprehensiveness.