Effectiveness of different design solutions to control internal faults in MV switchgear

The incidence of an internal fault in MV switchgear is very rare and it is even more rare for an internal fault to result in injury to personnel. The most probable causes of an internal fault are well known and manufacturers take great care in the choice of materials and design and development of equipment to minimise the incidence of such faults. However, when such an incident does occur, it can have very serious consequences on operating personnel, substation equipment and possibly the general public. International and National specifications exist that define performance criteria the MV equipment can achieve to mitigate these effects. This paper describes some of the solutions that have been successfully employed, mainly in the UK, but also in Europe to control and limit the effects of internal faults.