The basic function of an electrical circuit breaker is to offer opening and closing the current carrying contacts. Though, it seems to be very easy. However we must remember, that, one circuit breaker remains at its closed location for maximum period of its life. It is rarely required to function a circuit breaker for opening and closing its contacts. Thus, circuit breaker operation should be very reliable without any delay. For attaining this reliability, the circuit breaker operating instrument becomes more complex than it was first considered.
Opening and closing distance, and stroke between the contacts and speed of moving contacts throughout operation, is the most vital parameters to be considered in designing circuit breaker. Their velocity, traveling distance of moving contacts and contact gap are decided by kinds of arc quenching medium, voltage and current rating of the circuit breaker.
Siemens circuit breaker Opening Operation Prerequisite
Siemens circuit breaker is desired to be at open location as quick as possible. It is because of the restricting contacts erosion and to disrupt the faulty current as speedily as possible. However, total travel distance of the moving contact is not decided only by the requirement of interruption of faulty current, although rather the contacts gap required for withstanding the lightning impulse voltage and normal dielectric stresses appears across the contacts when the CB is at open location.
The requirement for carrying the constant current and for enduring a period of arc in circuit breaker, make it essential to be used for two sets of contacts in parallel. One is the primary contact which is always made up of high conductive materials like copper and the other is arcing contact that is made up of arc resistance materials like molybdenum or tungsten, which has much lower conductivity than the primary contacts. Throughout opening circuit breaker operation, the basic contacts open before the arcing contacts.