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Why is VLF Hipot Testing Preferred over DC?

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VLF hipot test is a special version of an alternating current high potential test but at very low frequencies. Typically, this frequency is around 0.1 Hertz versus the more typical 50 or 60 Hertz found with other hipot testing methods. 

A direct current test is one that is used to measure how effective the insulation of a wire is relative to another wire. Most often the insulation tested is between windings on a transformer or coil. Also, it can be between two cables. The high voltage is placed across two wires that are essentially an open circuit. However, there will be some leakage current at these high voltages. It is sometimes the leakage current that is specified as a maximum, but commonly a meter will be calibrated to display the resistance. This resistance is called insulation resistance and is a good measure of isolation between two wires. 

An AC test under the same conditions as a DC hipot test will produce a potential break down that can occur due to the amount of capacitive charge that builds up between the windings or cables. This build up can produce an arcing effect resulting in a breakdown between the wires. This type of HV diagnostics is important if there is the possibility of an AC voltage build up during a short circuit. If so, this is the preferred test. 

The electrical test equipment needed will be dependent upon the test done, and our friendly, supportive staff can help you determine the best models for your project needs. Give us a call at 866-352-5550 or submit your request for rental quote online to learn more.