Developing test methods for interfacial ageing in composite insulators

High voltage insulation systems consist of a combination of different insulating materials, exposed to multiple stresses during operation. Outdoor composite insulators used in transmission lines are typically made of two solid polymeric materials bonded together to form the insulator. Work reported here contributes to the evaluation of degradation within internal interfaces by developing tests to investigate interfacial tracking, with a view to replicating the tracking phenomena seen within composite insulators in service. The present paper highlights high voltage tests on dielectric interfaces with needle electrodes generating local high fields to initiate tracking. FEA has been used to design an experiment with controlled electric field magnitudes over a 1 m sample. Moreover, information from monitoring partial discharges and surface temperature is used to understand the inception and propagation of tracking activity within the structure.