Converter and method of operating a converter

A method of operating a converter, the method comprising:

• providing the converter, the converter including:
• at least one medium voltage stage including an inverter circuit;
• at least one medium frequency transformer, a first winding of the medium frequency 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;
• wherein each container is configured to hold an electrically insulating fluid inside the volume;
• wherein each container has provided within the container one of the at least one medium frequency transformer to be electrically insulated by the fluid;
• wherein the container includes at least one connector for fluidly connecting the volume with a fluid circuit;
• and
• wherein 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 including a valve configured to open and/or close the connector, wherein the valve is further configured to fluidly separate the first container from the second container when the connector is closed by the valve,
• the method further comprising:
• while the fluid circuit is unobstructed by the valve, converting a medium voltage AC power into a low voltage DC power while circulating the fluid in the fluid circuit to cool the medium frequency transformer.