ABSTRACT
In normal operating conditions, a circuit breaker is in the closed position and some current flows through the closed contacts. The circuit breaker opens its contacts when a tripping signal is received. This chapter presents the different circuit breaker models proposed and applied to date in opening and closing operations, as well as the procedures that can be used for estimating the parameters to be specified in these models. It summarizes the physical phenomena involved in circuit interruption and the main breaking technologies used in modern circuit breakers. In a real circuit breaker, an electric arc is formed after contacts start separating; it changes from a conducting to a non-conducting state in a very short period of time. Some SF6 circuit breaker designs use rotating arc techniques, one of which utilizes an electromagnetic coil. Circuit breakers built in the beginning of the twentieth century were mainly oil circuit breakers.
