Experimental Evidence of Hot Electrons in Insulating Polymers

Insulating polymers used in Electrical Engineering age under the combined effects of electrical, thermal, mechanical and environmental stresses. Of particular relevance is the electric stress that can initiate material degradation reactions through energetic processes such as partial discharges and hot electrons. Although the degradation can take specific form depending on the time scale and the specific situation (micro-void formation or enlargement, decohesion between fillers and matrix in the case of multiple-internal interfaces, formation of conducting paths by percolation of aged domains, electrical treeing), excited states generated by hot electrons and other sources could be a common feature in the early stage of electrical ageing. We present recent experimental results advocating hot electrons processes at applied field away from the breakdown field.