What is the testing of sf6 cb? And what tybe of mecanism? And why we don't use vacum cb in high voltage?

SF6 Circuit breakers can be tested for timing, resistance, and insulation not unlike any breaker. The SF6 gas can be tested for purity, moisture and decomposition products.

Vacuum, or near vacuum is used in High Voltage breakers, most often by having the current breaking contacts in a vacuum, often called a vacuum bottle because the early ones looked like bottles with operating arms sticking out each end.

Sometimes the vacuum bottle is inside a vessel filled with SF6 gas. This makes for a breaker with a very small footprint and since an arc is not passed through the SF6 it will not have decomposition products.