Behavior of XLPE medium voltage cable under switching impulse

An investigation was held to characterize the behavior of high voltage XLPE insulated cable models under unidirectional switching impulses in dry and wet environment. The models refer to 18/30 kV cables , have a nominal electric field on the conductor of 4 kV/mm. Different stress tests were performed to reproduce in laboratory possible service conditions. Three types of environment were considered: (1) dry conditions at room temperature, (2) wet conditions in water-filled tank at room temperature, (3) wet conditions in water filled tank at 90°C water temperature. For each environment condition, cable models were submitted to 50 impulses of amplitude 4 p.u. in respect to the nominal AC voltage. This stress corresponds to a maximum electric field of 16 kV/mm on the conductor. For each environment the tests were repeated on 10 cable samples. Switching impulse dielectric strength (SIDS) was chosen as reference parameter for the analysis of the insulation degradation after each stress test. Results show good performances of XLPE insulation under switching impulse in dry and wet conditions.