SPARK CONDITIONING PROCEDURES FOR VACUUM INTERRUPTERS IN-CIRCUIT BREAKERS

The breakdown voltage between the open contacts of vacuum circuit brea kers (VCB) immediately after manufacturing is low and subject to high scatter. Whiskers, covered with adsorbed gas layers influence the brea kdown process, especially if they are present on the contacts. To atta in a sufficiently high breakdown voltage, these unknown and undefined surface conditions must be improved. The procedure used to increase th e breakdown voltage is called 'conditioning'. Though several technical papers report various conditioning procedures, a comparison of the ef fectiveness of these different procedures is still missing. The reason for this is due to the use of different contact materials, contact co nfigurations, gap distances as well as different treatment of the circ uit breaker components before assembly. This paper aims to fill this g ap and to report on the comparison of several usual conditioning proce dures applied to a large number of 12 kV circuit breakers of a standar d design. A large number of conditioning experiments have been made an d statistically evaluated. Additional studies have been performed in a vacuum test chamber in which the contacts could be interchanged easil y. The aim of the investigation was to find out the most important par ameters of conditioning and to explain the underlying physical process es. The studies show that the conditioning procedure can be optimized based on the findings described in this paper.