Non-linear conductivity in electrical insulation

Previous work by the authors has involved producing a non-linear conductivity characteristic in a thermoset polymer (polyester) by the introduction of particulate ZnO. This work has now been extended to cover a thermoplastic material (LDPE). Filler/resin ratios have been varied to obtain a critical level at which the conductivity of the resulting polymer is significantly increased at high electric fields in comparison to its conductivity at low electric fields. The close similarity in the non-linear behaviour of the thermoplastic polymer and the thermoset polymer suggests that ZnO filled LDPE will permit enhanced conductivity at high electric fields which has applications in the area of surge absorption whereby short term overvoltages, caused by phenomena such as lightning and switching, can be partially dissipated in the insulation ahead of specific surge arrester equipment. This application is particularly relevant to the power cable industry.