A converter is described. The converter includes at least one medium voltage stage including an inverter circuit, at least one medium frequency transformer, a first winding of the transformer being electrically connected to the medium voltage stage, at least one DC output stage, the DC output stage being electrically connected to a second winding of the medium frequency transformer, and a plurality of containers having a volume. Each container is configured for holding an insulating fluid inside the volume. Each container has provided within the container one of the at least one medium frequency transformer to be electrically insulated by the fluid. The container includes at least one connector for fluidly connecting the volume with a fluid circuit. A first container of the plurality of containers is fluidly connected to a second container of the plurality of containers via the connector, the at least one connector comprising a valve for opening and/or closing the connector, wherein the valve is configured for fluidly separating the first container from the second container when the connector is closed by the valve.