Electrical erosion test and condition assessment of SF 6 CB contact sets

Abstract

Dynamic resistance measurement (DRM) was proved to be an important method for condition assessment of contact sets of SF6 circuit breakers (CBs). The erosion of contact sets due to arc energy is a main factor that influences the electrical lifetime of the extinguishing chamber. In this study, a high-voltage CB synthetic circuit was used to produce fault current for electrical erosion tests on the contact sets. The contact sets were close to the end of their service life after a series of erosion tests. DRMs with DC amperages of 0.5, 1.0, and 1.5 kA were conducted on the two tested breakers in the interval of each erosion test. Five essential diagnostic parameters were extracted from the contact resistance curves as a function of contact travel. The variation of these parameters during the whole erosion tests were investigated to find an effective condition assessment method for contact sets. From the power balance at the contact surface, the material erosion rate due to metal evaporation for each erosion test was calculated and in good agreement to the experimental results. Finally, the contact length and contact resistance were employed as diagnostic parameters for condition assessment of contact sets.