Medium voltage (MV) switchgear is rated from 1 kV to 38 kV. Many types of switchgear are available in the MV category, such as gas-insulated switchgear (GIS), metal-enclosed switchgear, and metal-clad switchgear. These may be suitable for either indoor or outdoor applications. Generally, in urban areas and industrial applications indoor-type are preferred, while in sparsely populated rural areas outdoor-type may be used. Insulating oil, SF6 gas, or vacuum are used for arc quenching in MV switchgear.
The main purpose of medium voltage switchgear is protection during faulty conditions such as short circuit current interruption. But, they may have other uses too. One of these uses is in electric arc furnaces where the current to be switched may be as much as 8 times the rated current. An electric arc furnace has a rated current of about 2 kA and it is switched on and off around 100 times every day. Commonly, vacuum circuit breakers (VCBs) are used for this application and found to be most suitable and economical as they require very little maintenance.
Another application where MV vacuum circuit breakers are used is in railways traction. Short circuits in the overhead catenary system are frequent and transient in nature. VCBs are best suited for this application due to their small contact gap, short arcing time, and quick breaking.
Types of MV Switchgear