Space charge formation in silicone rubber

Dependence of space charge distribution on voltage m application time is observed by pulsed electro-acoustic method in silicone rubber sample. Aluminum and copper are used as lower and upper electrodes, and a dc electric stress of 5-70 kV/mm is applied. Test results show that the primary space charges in samples are heteropolar under low and high electric stress, but the space charges inside silicone rubber adjacent copper electrode may change to homopolar charges under medium electric stress, originated from injected and migrated charges. The heteropolar charges inside silicone rubber adjacent aluminum electrode distribute in a wider scope under low stresses. The polarity of space charges in middle of sample depends on the polarity of aluminum electrode under high stress. An unstable phenomenon of space charges appears under electric stress of 70 kV/mm. It can be assumed as an indication of dielectric breakdown. The formation of charges is analyzed.