Withstand tests may include a DC withstand or hi-pot (though not to be used on XLPE cables); a line frequency AC hi-pot; a 0.1 Hz AC VLF hi-pot; or a damped AC (DAC), where electrical stresses are created at a frequency ranging from around 50 Hz to several hundred Hertz depending on the test object capacitance.
High voltage testing will also check for local faults. For example, an XLPE cable will tend to turn critical water trees into electrical trees and subsequently cause a failure. Having been subjected to adverse impulses/surges during its service lifetime, testing will be necessary to find and avert imminent in-service failures in the future.
If cable testing highlights a subsequent failure, this indicates that the cable is already in a highly compromised condition. Company staff should be prepared at this stage to make any necessary repairs to the cable at the position indicated by previous tests. After repair, the cable will have a withstand test again until it passes the required voltage of the test.