Development of techniques for growing electrical trees in 66 kV cable cores

Dynamic cables used for connection of offshore floating renewable energy sources are subjected to strain from tidal motions and there is little knowledge on the effects of strain on electrical tree growth. Laboratory electrical trees are often grown in small-scale opaque samples for visual imaging of degradation. Here, combined electromechanical test techniques have been developed to examine electrical tree characteristics in full-scale cable core experiments to examine the scalability of laboratory work. Testing methodology has been developed for testing on 66 kV power cable samples energized to grow electrical trees from a needle electrode. Partial discharge (PD) data was recorded, and optical microscopy used for imaging of tree growth post-testing. PD behavior was consistent with studies conducted in laboratory scale needle-plane tests, but the final tree geometries were shorter in length and width than expected in many cases. Follow-up investigations to review the electrode geometry are presented. It has been shown that only by careful control of conditions can samples be fabricated which will allow combined electrical and mechanical testing in future.