Developing Automated Gas Recovery System for SF_6/N_2 Insulation Gas Mixtures

摘要

We have already three gas insulated power lines in service applying SF_6/N_2 gas mixtures, the two in Europe and the rest in South Asia. To cope with the global warming issue on gas insulated power apparatus, we have been investigating the recovery of SF_6 from those apparatus. This paper describes an automated gas recovery method that secures SF_6 gas concentration in the recovered gas at a high and desired level. The gas mixtures investigated contain 5-20 vol. % of SF_6 in N_2. We adopt a membrane method to separate the two gas species, in which two membrane separators are connected in cascade. There are several factors that affect the concentration of SF_6 in the recovered gas. As the concentration greatly depends on recovery gas flow speed, we control the speed by using a piezo-valve. For driving the piezo-valve, we use a voltage regulator together with an infrared gas concentration online monitor. This link allows PID control of the SF_6 gas recovery system. Successful operation results of this automated system, as well as the basic recovering characteristics of the cascaded system, are demonstrated after a brief review on gas recovery methods.