Study of Space Charge in SC Shield / XLPE Interface and Mid-Voltage Cable Perfomance

Abstract

Three experimental mid-voltage cables C2, C3 and C4 with cross-linked polyethylene (XLPE) isolation, rated respectively as Medium, High and Low in perforation tests over 150KV, are studied. All these cables have been systematically measured by Electroacoustic Pulse (PEA) and Thermally Stimulated with Depolarization Currents (TSDC), using 120 KV of polarization voltage in samples as received, annealed at 90 kV and 120°Cup to 672 hours. Measured internal charge of cable C4 at least doubles that of cables C2 and C3. The interfacial phenomenon has been studied by Infrared spectroscopy measurements Attenuated total reflectance (ATR) that show chemical components that migrate, spread, and transport from the external semiconductor layer to the cross-linked polyethene isolation during the thermic treatment of the cable. The PEA measurements using 120 kV/mm electric field showed the formation and propagation of space charge packet from SC to isolation. These results are coherent with TSDC measurements that also show differences in the areas under the curve of current as a function of temperature for each cable type C2, C3and C4. This is a result of the amount of charge accumulated. To sum up, combination of PEA, TSDC and ATR measurements is a useful tool in understanding charge relaxation processes and XLPE cable performance.