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Breakdown mechanisms and their implication on new test methods for power distribution medium voltage cables systems


Research objectives and content
i 1) Further evaluate the effectiveness of the negative half cycle test in detecting defects in a variety of cables. This would include both defects artificially introduced into lengths of cables and the application of the test to sections of used cables containing known defects introduced in service.I The type of defects which are identified by this method would be found. These would be compared and contrasted with the types of defects found by conventional 50Hz testing. 2) Identify the mechanisms which lead to failures preferentially occuring in the negative half cycle. This would include a review of breakdown mechanisms, and modelling of the behaviour of the insulation material in this regime. 3) Determine to what degree, if any, the negative half cycle test results m retained space charge in the insulation material. and to what extent this influences the subsequent breakdown strength of the cable. Techniques will be developed to measure the space charge introduced in a defect, to support the techniques availalbe for determining space charge generally.4) Investigate the influence of frequency on the breakdown characteristics and introduction of space charge effects in order to determine the optimum frequency of the half negative wave for detecting defects. Initial limited factorial experiments will be carried out. These will provide a macroscopic description of the behaviour which will be refined by modelling. The outputs from the model will then be confirmed experimentally. Training content (objective. benefit and expected impact)
The training content of this work is considerable. It is expected that extensive technology transfer will take, place during the research which has many novel aspects and is expected to form the basis of a PhD thesis at UMIST. The problem area is European wide in its relevance and the problem is of considerable industrial interest.I The applicant will be trained in an Industrial Laboratory with access to the many additional opportunities I provided for the UMIST PTP students.
Links with industry / industrial relevance (22)
The project is of direct. irnmediate and relevant importance to electricity suppliers cable manufacturers etc. across Europe.

Funding Scheme

RGI - Research grants (individual fellowships)


United Kingdom