Lightning Impulse Ageing of Hv Cable Insulation

Lightning impulses can lead to accelerated ageing of extruded cables. Electrical behaviour of a dielectric material when experiencing a lightning impulse is different to that for DC or power frequency applied voltages. Pre-designed shaped HDPE material samples have been manufactured using a mould tool. The samples then have been electrically aged using an impulse generator. A real-time software based monitoring tool has been designed to control the impulse wave-shape and process the measurement data. Sets of identical lightning impulses were applied to samples and this was then followed by ramped AC breakdown tests. The obtained results were analyzed using Weibull distribution to identify any differences in lifetime between aged and unaged samples. Measurements of dielectric loss and space charge were also undertaken to identify the impulse ageing mechanism.