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.