Medium voltage hybrid transfer switch

This paper describes a hybrid transfer switch (HTS) made up of the solid-state switches and the high-speed mechanical switches in parallel. In the proposed HTS, the solid-state switches can be turned off and turned on at any given instant so that the transfer time can be minimized under all kinds of power line disturbances. Also the solid-state switches are bypassed during steady-state operation by the mechanical switch, and only conducted during a transfer or other such operation. This eliminates the need for any type of cooling equipment for the solid-state switches. Three different control concepts for the solid-state switches are given and compared through the computer simulations. Experimental equipment was designed and built with a solid-state AC switch, composed of 20 IGBTs in series and 5 IGBTs in parallel, rated to 11 kV_RMS/125 A. Experimental results are given for the series connected solid-state switches. Finally conclusions are given.