Aging evaluation of insulation materials for environmentally-friendly compact gas-insulated equipment

摘要

This paper evaluates the aging of insulation materials such as insulators and dielectric coatings on high-voltage (HV) electrode for compact gas-insulated equipment that reduces the environmental impacts. This environmentally-friendly gas-insulated equipment features compact apparatus using minimum SF6 by utilizing the insulation techniques such as advanced dielectric coatings and functionally graded material (FGM). In this compact equipment, micro-size defects inside solid insulator would become more harmful than conventional equipment. It is also essential to evaluate the aging performance of the dielectric coatings. In addition, the equipment life extension is a great concern by applying new materials like FGM. Considering the above, the following three topics are discussed. Firstly, the influence of micro-size defects inside on solid insulator aging is investigated. Three kinds of micro-defects and their critical sizes, which cause small partial discharge (PD, defined as 1 pC) compared to PD levels specified in IEC (5 pC) and the Japanese standard (JEC, 10 pC), are studied. It is found that a crack is the most harmful micro-defect to be detected. Secondly, V-N and V-t characteristics of advanced thick and thin dielectric coatings on HV electrodes, which has 1.5 times higher dielectric performance than bare electrode, are investigated. The V-N characteristic of the thick dielectric coating shows that the degradation by repetitive discharges is not so severe. The insulation design of the coating for repetitive discharges for disconnecting switch and earthing switch can be carried out by using the V-N characteristic. The V-t characteristic of the thin dielectric coating suggests that the long-term degradation constant is comparable to that of casting epoxy. Lastly, extension of equipment lifetime by applying FGM to insulators is investigated. The lifetime is evaluated from the V-t characteristic of the fabricated FGM samples. The insulator lifetime made of FGM is expected to be around 2 - 8 times longer than that of a conventional insulator. It is concluded that the above aging evaluation method of solid insulation materials and the advanced dielectric coating is one of the essential techniques to realize compact gas-insulated equipment with low environmental impacts. Henceforth, the techniques can be the basis of the design of environmentally-friendly gas-insulated equipment to maintain its reliability and to extend its life.