In the early 1990’s reports started to surface indicating that DC Hipot testing could be the blame for latent damage experienced by extruded medium voltage cable insulation (XLPE and EPR). After receiving these reports the Electrical Power Research Institute (EPRI) funded two studies relating to XLPE and ethylene propylene rubber (EPR) cables. These studies (EPRI reports TR-101245 and EL-6902) yielded the following conclusions regarding XLPE cable:
– DC Hipot testing of field-aged cable reduces its life.
– DC Hipot testing of field-aged cable generally increases electrical tree growth.
– DC Hipot testing before energizing new medium voltage cable doesn’t cause any reduction in cable life.
Current versions of most industry standards no longer include DC Hipot testing of extruded cables (XLPE and EPR) as a maintenance test. Of those that still do, all have reduced the recommended test duration times. As an alternative to DC Hipot testing Very Low Frequency or VLF Hipot has gained considerable popularity in the industry as an acceptable test for acceptance and maintenance testing of medium and high voltage cables. Keep in mind that with withstand testing, insulation defects are caused to break down or fault at the time of testing. Faults are repaired, and the insulation is retested until it passes the withstand test. The withstand test is considered a destructive test.
Protec Equipment Resources has a range of advanced high voltage test equipment from High Voltage Incorporated and HV Diagnostics to choose from and industry experts to discuss your cable testing needs or concerns.