Testing of cables was traditionally conducted with DC voltages in the past, which was also known as DC hipoting. Once polymeric cables (XLPE, EPR, etc.) were introduced into the electric grid and readily being tested with DC, a considerable rise in premature failures occurred. These failures were being attributed to trapped space charge within the defects of the insulation due to enhanced charge migration in one direction (DC electric field). Once testing was completed and AC power frequency was reapplied in service, a significant field enhancement could occur at these defects leading to a fast-growing electrical tree and subsequent failure. An illustration of the space charge effect after DC testing a XLPE cable is shown below.

Space charges created in voids of polymeric cables during DC testing.