Study on the Developing Regularity of Partial Discharge at the Interface Defects of Cable Accessories under Thermal Cycling

Abstract

Partial discharge (PD) is one of the main causes of the interface insulation deterioration of cable accessories. Studies have shown that temperature has an important influence on the PD development, but the effect of temperature on the PD initiation is still not fully understood. This paper investigated the developing regularity of PD at the interface defects of the cable accessories under thermal cycling. An electro-thermal co-aging platform with a cable accessory having semiconductive-layer protrusion defect was firstly designed and introduced in the paper. The experiment loop in the platform was thermally cycled in air by using a current transformer to induce a current in the cable conductor. Cycle duration was 9.5 h with 8h/ON and 1.5h/OFF. Afterwards, PD numbers, PD amplitude and PRPD (Phase Resolved Partial Discharge) spectrum were collected and analyzed comparatively. Obtained results show that temperature change caused by current on-off control will result in temporary PD excitation. PD numbers and amplitude increase rapidly as the temperature rises or falls quickly. When temperature stabilizes, however, the increment slows down. Phenomenon above can be interpreted to the interface pressure change caused by thermal expansion and contraction of the interface insulation, namely “Breathing Effect”. The research revealed that PD signals in the interface defect are more easier to be detected when cable accessories are operating under high temperature gradient, which may provide practical references for PD field test of cable accessories.