Space charge distribution measurement in XLPE cable for detection of the water tree location

The correlation between charge distribution in aged XLPE cable and water tree location have been studied. The space charge radial distribution and different angular location in the insulating wall of a service aged XLPE cable, induced by application of a dc stress, was measured using the pulsed electro-acoustic (PEA) method. Furthermore, a cross-section of sliced insulating wall was observed by optical microscopy to compare with the radial space charge distribution. The cable under investigation was electrically aged in service at 6.6 kV for 25 years in wet conditions. From the results of both observation of the space charge distribution and location of water tree, the water tree was found at the angular location in which the space charge was observed. On the other hand, the water tree was not found at the angular location in which the space charge was never observed. Judging from the results, the space charge measurement of the PEA method seems to be useful for the diagnosis of the water tree in aged cable.