A bi-directional isolated DC/DC converter for medium-voltage applications have been discussed for the next-generation electrical grid, such as smart girds. To realize the DC/DC converter for installing on a power distribution system, it should be achieved higher-efficiency and lower-volume. Higher switching frequency enables to reduce the volume of the transformer. However, it is difficult to realize the both higher-efficiency and lower-volume of the DC/DC converter, because it could not operate higher frequency with high power devices such as medium-voltage IGBTs. This paper discusses switching losses and operation limitations for the actual medium-voltage isolated DC/DC converter, in the case of using Si-IGBT. In addition, the experimental system rated at 2.5 kV, 200 kW, and 5kH of the DC/DC converter with a medium-frequency transformer is designed, and the experimental results are shown.