Measurement of swarm parameters of c-C4F8/CO2 and its insulation characteristics analysis |
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Authors: | Liu-chun Zhang Deng-ming Xiao Dong Zhang Bian-tao Wu |
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Institution: | (1) Department of Electrical Engineering, Shanghai Jiaotong University, Shanghai, 200240, China |
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Abstract: | In c-C4F8 and c-C4F8/CO2 mixtures, the swarm parameters including ionization coefficient, attachment coefficient and effective ionization coefficient
were obtained at the ratio of the electric field strength to the gas density between 150–550 Td by the steady-state Townsend
(SST) method. Static breakdown voltages at each ratio were also measured at the SST condition. The limiting field strengths
were obtained by two methods: computing the density-normalized effective ionization coefficient as a function of the overall
density-reduced electric field strength; and measuring static breakdown voltages as a function of the product of gas density
and electrode separation. Good agreement was obtained by these two methods, which ensures the correctness of the former method.
The limiting field strengths of c-C4F8 and c-C4F8/CO2 mixtures were compared with those of pure SF6, SF6/CO2 mixtures and pure c-C4F8. It is found that buffer gas CO2 does not reduce the limiting field strengths of c-C4F8 greatly, the limiting field strengths of c-C4F8/CO2 mixtures are higher than those of SF6/CO2 mixtures or even pure SF6, and so c-C4F8/CO2 mixtures are suggested to be possible substitutes for SF6.
Foundation item: the National Natural Science Foundation of China (No. 50777041) |
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Keywords: | c-C4F8/CO2 SF6 steady state Townsend (SST) swarm parameters dielectric strength |
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