Detection and Control of Ion Flow and Space Charge in Equipment for DCUHV Transmission Line and Compartment Gas Insulated Transmission Line

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In this work, ion flow field with respect to ion flow electroinjection phenomena under DCUHV lines and breakdown phenomena along the spacer surface in gas insulated system are investigated to find the similarity law in ion flow field and to find optimum electrode and spacer shapes under particle-contaminated condition in the gas insulated system.The results can be summarized as follows.1) The similarity law in ion flow field is clarified and formulated to find a control method of ion flow field and apply information on ion flow field obtained in an experimental setup to another setup with a different size.2) Particle-initiated breakdown characteristics of conical spacers are measured and fundamental parameters determining the breakdown voltage of a dielectric spacer contaminated by metallic particles is found.3) Breakdown mechanism along the spacer surface contaminated by a metallic particle is confirmed. That is, with shorter particles the discharge threshold field strength is higher than the field for the discharge propagation and the breakdown voltage is determined by the discharge threshold conditions, and with larger particles the relationship reverses.4) Three methods for the improvement of insulation performance of particle contaminated spacer are proposed.:metal insert method, recessed electrode method and shield ring method. It is confirmed by the experiment that the proposed metal insert method is the best one and rises the breakdown voltage as high as about 50% in air and about 30% in SF_6 gas.