Month: November 2014

Siemens Circuit Breaker: Its Operation And Functionality

siemens circuit breaker

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.

Medium Voltage Switchgear: Short Circuit Current Interruption


From 3KV to 36KV switchgear system; it is classified like MV switchgear or medium voltage switchgear. These switchgears are of a lot of kinds. They may perhaps be of metal enclosed outdoor type, metal enclosed indoor type, outdoor type with no metal enclosure, and so on. The interruption medium of this switchgear might be oil, vacuum and SF6. The main necessity and requirement of MV power network is to disrupt the current in faulty condition irrespective of what kind of CB is utilized in the MV switchgear system. It may perhaps be competent of functioning in other conditions as well. Medium Voltage Switchgear should be highly capable of:

1) Usual ON/OFF switching operation.
2) Short circuit current disruption.
3) Switching of capacitive and inductive currents.
4) Several special applications.

All the above stated function should be carried with high degree of security and consistency.

Short Circuit Current Disruption

The main attention of circuit breaker design is that every circuit breaker must be competent of interrupting short circuit current with high degree of protection and consistency. The number of faulty tripping occurred in total life span of circuit breaker generally depends upon the location of the system, quality of environment condition and system. If the tripping number is high, the excellent option is vacuum circuit breaker since it might not need any maintenance till 100 faulty trippings with short circuit current till 25KA. While other circuit needs maintenance after 15 to 20 faulty trippings with same short circuit CB current.

The reunited substations in rural areas are usually of outdoor type, and the majority of them are unattended sort. Therefore for this kind of applications maintenance free outdoor form, medium voltage switchgear is most appropriate. Porcelain clad vacuum circuit breaker meets this requirement against the usual indoor kiosks.