Measurement Of Space Charges In Polyethylene Using The Electro-acoustic Pulse Method

A modified electro-acoustic pulse method was used for measuring the space charge distribution and studying the processes of injection, accumulation and release of charges in polyethylene (PE) in a dc electrical field of 70.7 MV/m. A new charge decay phenomenon was observed. It showed that the decay time of volume charges in a sample to which the voltage had been applied for a long period was much shorter than that in another one to which the voltage had been applied for a short time under a same dc stress. For example, the charge decay time in PE was about one day (24 hours) when the application time of electrical field (70.7 x 10 MV/m) was 28.5 hours, and was more than one week (168 hours) when less than 6 hours. Finally, an accumulative model of space charges was proposed and the effect of space charges on pre-breakdown process of solid dielectrics was discussed.