Comparative Laboratory Evaluation of Premolded Joints for Medium Voltage Cables

This paper provides information on laboratory performance of 15 and 35 kV premolded joints from three manufacturers. Data on partial discharge, ac and hot impulse voltage breakdown tests, and dissection of breakdowns are presented for joints that were tested immediately after their assembly and after one year aging immersed in room temperature water (15-30degC), under operating voltage. The test program was repeated twice using joints acquired with a two-year interval. The two batches showed similar performance indicating that all three manufacturers provide consistent quality joints. AC breakdown strength of the joints practically did not change with aging. In contrast, their impulse breakdown strength decreased noticeably. Joints having partial discharge levels up to 5000 pC were included in the study. No obvious correlation was found between the presence of partial discharge and the joints ultimate dielectric strength.