| In order to realize the ambitious goal of global energy interconnection and optimize the energy structure as well as support the long-distance ultra-high voltage power transmission project in these days of our country, a large amount of gas insulated equipment are applied widely as the key part of power system. Gas insulated equipment develop quickly and used widely in high and ultra-high voltage field owing to its high stability, less maintenance work, smaller floor space, and flexible configuration.Nowadays, SF6 is adopted as the main insulation medium of gas insulated equipment, which is considered a kind of dangerous greenhouse gas to environment. Global climate warming caused by greenhouse effect brings disastrous consequences to our living conditions. Electric devices account much for the emission of SF6, which makes it urgent to find a kind of environment-friendly substitute insulating gas. Besides, the decomposed products of SF6 under discharge may be corrosive to internal material and poisonous to power workers.In the early period of global research and development of environment-friendly insulated devices, mastering the formula and key technique of substitute gas is vital to electrical development of our country. According to the above circumstance, systematic investigation of the insulating characteristics of CF3I/CO2 mixed gases under power-frequency voltage was carried out firstly, which could provide useful information for the best mixed ratio of CF3I/CO2 and the design of internal structure in matching devices. Then insulating characteristic of CF3I/CO2 and CF3 I were tested under a kind of normal insulating defect of free metal particles defect, and the influence of metal particles on the thermodynamic characteristics and transmission properties of CF3 I discharge plasma were calculated theoretically. The overall performance of CF3I/CO2 under typical defects were tested for the choice of internal metal materials of electrical devices. Finally, the influence of moisture, the main hazardous material on gas insulated equipment, on the insulating performance of CF3 I were conducted experimentally and theoretically, which proved the harmful effect of moisture on the new insulating medium and provided theoretical foundation for the standard constitution of moisture content. The main work and results are shown as follows.(1) Aiming at the several disadvantages of testing equipment of gas insulating characteristics, double tank structure of insulation property test equipment was designed in order to enhance the safety and accuracy of experiment. The electric field or the defect type can be changed through different tailor-made electrodes to realize the multi-functionalization of the experimental platform.(2) Incipient discharge voltage of positive half cycle was proposed as one of the standards to evaluate gas insulation characteristic under power frequency alternating voltage. Incipient discharge voltages of different mixed ratios, voltages, and distances in both positive and negative half cycles under power frequency partial discharge were measured aiming at needle to board electrode, which could prove that CF3I/CO2 performed as good as or even better than SF6/CO2 in the aspects of partial discharge characteristic and sensitivity to the uniformity of electric field. CF3I/CO2 with the mixed ratio of 30% at the atmosphere pressure of 0.3MPa performs best in the partial discharge characteristics and meets the requirement of condensing temperature.(3) By simulating the possible different electric fields inside the devices, the influence of electric field utilization coefficient on the power frequency breakdown performance of CF3I/CO2 and CF3 I were tested systematically. In different electric field, CF3I/CO2 performed as good as or even better than SF6/CO2 in the aspect of breakdown characteristics with good stability as well. The breakdown performances of CF3I/CO2 with the mixed ratio of 30% at the atmosphere pressure of 0.3MPa was better than that of SF6 at the pressure of 0.15 MPa.(4) Synergistic effect of CF3I/CO2 and SF6/CO2 mixed gases under different uniformity of electric field were compared and analyzed: Synergistic effect of CF3I/CO2 under extremely non-uniform electric field was better than that of SF6/CO2. With the increase of gas pressure, the synergistic effects of SF6/CO2 and CF3I/CO2 improved gradually and tend to be saturated. Furthermore, the adjunction of CO2 improved the sensitivity of CF3 I and SF6 to electric field with a more obvious effect to CF3 I.(5) Power frequency breakdown performance of CF3I/CO2 under free metal particle defect was investigated. The breakdown voltages of CF3I/CO2 under different conditions were coincided with that of SF6/CO2, with breakdown performance of CF3I/CO2 of 30%mixed ratio at the pressure of 0.3MPa equal to that of SF6 at the pressure of 0.2~0.25 MPa.(6) The influences of the amount of metal particles and the species of metal elements on the insulation performances of CF3 I were studied by experimental and thermodynamics calculation. The results show that, the metal particles of Cu, Al and Fe will lead to the decrease of breakdown voltage of CF3 I. The larger the amount of particles is, the lower the breakdown voltage is. Compared with Fe, the particles of Cu and Al cause more serious damage to insulation property of CF3 I. Thermodynamics calculation show that, the ionization in the plasma of CF3 I and metal particles mainly occur at the temperature of 10 k K. With the increase of the amount of metal, specific heat of plasma containing Cu and Fe decreases and the conductivity of three CF3I-metal plasma improve. The calculation show that, Cu and Al can bring more obvious enhancement to the conductivity of CF3 I, which makes it easier for discharge to develop.(7) For the first time, the experiment of capacity test of partial discharge of CF3 I with moisture of different contents proved that, H2 O can be harmful to the insulating performances of CF3 I. Theoretical research was carried out to investigate the discharge process and products species of CF3 I with and without moisture. The decomposed mechanism and main products were obtained, which provides the evidence that the adjunction of H2 O does harm to the self-recovery process and promotes the decomposed process, thus leading to the decrease of insulating property. |
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