Space charge behavior in polyethylene under AC electric fields

Polyethylene has been widely used as the insulation of high voltage power cables due to its excellent dielectric properties and electrical performance. The existence of space charge in polymeric insulators is a significant issue with respect to life expectation. It can alter the local electric field and initiate possible partial discharge or eventual breakdown. This appears relatively more severe under dc applied fields than in the ac case. Research results have been extensively reported about space charge in polymers under dc electric stress. In contrast, space charge behavior under ac stress has not been fully examined or understood. However, the improvements in material processing and manufacturing have led to these materials being used under high ac electric fields. The effect of space charge under ac conditions can be an issue affecting the electrical performance of the material and needs to be carefully examined. At Southampton, a fast pulsed electro-acoustic (PEA) system equipped with 2 kHz HV pulse generator has been developed in order to acquire the fast dynamics of space charge in polyethylene under ac voltages. Space charge in low density polyethylene under ac voltages of 0.1 Hz to 50 Hz has been measured and detailed results are discussed in the paper.