A research organised by EPRI (electric power research institute) on medium voltage XLPE cables found that DC high potential at 80% of the factory value
a. Subsequently reduces the life of the cable and
b. It did not identify significantly weakened cable.
Based on above research recommended maintenance proof test voltage = 60% of the factory test voltage.
Maintenance and repair:
Before attempting for any corrective maintenance on power cables like replacement of lugs or jointing of cables following should be taken care
a. IR value should be good and it should be comparable to the previous values.
b. The quality of joints should be such that it **** not add any resistance to the circuit. Before jointing is commenced it is advisable that IR of both sections of cable to be jointed be checked.
c. Before jointing a paper insulating cable (for PVC cables this step is not required), the paper insulation should be tested for the presence of moisture by immersion in hot compound for paraffin wax at a temperature between 120°C and 140°C. the presence of moisture indicated by the formation of bubbles when a piece of the paper is immersed in hot compound. Use only single strip of the paper.
d. In case dia of *** to be used for crimping is slightly more than dia of cables, then use some loose strand before doing crimping of lug. While crimping it should be ensured that homogeneity of cramped conductor strands is achieved otherwise it will add resistance and create over heating.
