Development of a vacuum switch carrying a continuous current of 36 kA DC

This paper describes the development of a vacuum switch carrying a continuous current of 36 kA DC. This switch consists of three vacuum interrupters connected in parallel. Generally, it is required to reduce the resistive loss and to increase the heat removal capability for increasing the current carrying capability of VCB. Then, maximizing the cross section of the conductor, and shortening the current path are principally important. However, a coil structure which produces an axial magnetic field to extinguish the arc stably, makes it difficult due to the geometric complexity. Then, the authors adopted unique design of the coil structure to solve this difficulty. The newly developed vacuum interrupter is possible to carry a current of 8 kA without any cooling, which is twice that of the largest VCB available at present in the world. Moreover, introducing the forced-air cooling enhanced the performance up to 12 kA by improving the cooling efficiency. They are verified through a heat running test.