Estimated number of successful switchings of a 6kV pole gas switch

The frequent (20000 times) switching ability of a puffer-type SF6 gas switch as a switch to move usual opening points is verified by the presumption based on the data of a less number (up to 5000) of load switching tests. The variation of measured arc times is approximated by a saturating function of switching number and the cumulative arc time up to the No 20000 switching is estimated. CF4 gas is generated as one of cracked gases of SF6 in the presence of the material of a tested nozzle and increases cumulatively with increasing switching number without being absorbed in an absorbent. A linear relation is experimentally found between the cumulative arc time and the amount of CF4 proportional to the consumed mass of the nozzle. The consumed mass and corresponding enlarged diameter of the nozzle at the No 20000 switcing are estimated. Several model worn nozzles of different enlarged diameters including the estimated one were prepared and the switching with any of the model nozzles was quite successful. The arc time measured with the model worn nozzle of the estimated diameter (No 20000) agrees roughly with the corresponding estimated arc time and both arc times are not longer than the arc time to initiate the failure of switching. It is concluded that the switch under test will maintain sufficient switching ability still at the No 20000 switching as well.