ABSTRACT
This chapter shows that many very detailed physical processes have to be taken into account, if the simulation is required to be very close to reality. It describes the design principle of vacuum interrupters and of low- and medium-voltage vacuum switching devices. The chapter deals with the influence of contact material on the performance of vacuum arcs in the vicinity of current zero. Low-voltage air contactors and air circuit-breakers are two categories of switching devices that have to switch regular loads. The contactor is used specifically to switch motor loads, the circuit-breaker additionally has to switch short-circuit currents. In contrast to circuit-breakers, the currents in contactors are not extremely high, so the drawbacks of the double-break, namely higher contact resistance and higher total contact force, are acceptable. Circuit-breakers provided with fast-acting trip- and contact-opening mechanisms, where the arc voltage is rapidly increased on short-circuit to limit the actual current to values well below the prospective currents.
