Cable Testing Using a Tan Delta Bridge and VLF Hipot

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A Tan Delta bridge is used for testing the insulation of new and repaired cables. It is usually used in conjunction with a VLF hipot to detect hidden problems. This is done before applying power back to ensure it is safe to operate.


A cable acts like a capacitor and will only allow capacitive currents to flow and shifts it to 90 degrees. However, if contaminants like moisture or dirt are present, it will allow resistive currents to flow and its phase will be lesser than 90 degrees. This is how hidden defects are detected using Tan Delta testing. This method works by energizing a cable with a VLF high potential tester. Then the loss angle is measured and checked if it is within its operating limits. An 
AC hipot cannot be used for this purpose because of the cable’s reactance at 60 Hertz. Using a low frequency test voltage on very long cable installations need less power compared to 60 Hertz.

If you need a reliable Tan Delta Bridge or VLF high potential tester, consider renting through Protec. We have a wide selection of high voltage equipment for cable testing and other electrical applications. Contact us and learn more about our rental options.