A static electrical device assembly comprising: a static electrical device comprising a housing and a winding system having at least one winding, the winding system being located inside a coolant space of the housing, the coolant space containing coolant which is in heat conductive connection with the winding system; a heat exchanger system comprising a first heat exchanger adapted for cooling of the coolant by transferring heat into ambient air, and a second heat exchanger adapted for recovering heat from the coolant, both the first heat exchanger and the second heat exchanger being in fluid connection with the coolant space; a flow passage for ambient air connection, the flow passage being adapted to provide a route for air flow between outdoor air and the first heat exchanger; a sensor system comprising at least one temperature sensor adapted to provide information relating to temperature of the static electrical device; and a control system (CTRL) adapted to control the heat exchanger system based on information provided by the sensor system, wherein the heat exchanger system comprises a heat recovering pump adapted to transfer coolant between the coolant space and the second heat exchanger, and the control system (CTRL) is adapted to control the heat recovering pump, characterized in that the heat exchanger system further comprises a shutter arrangement adapted to adjust a surface area of the flow passage in order to regulate an air flow between outdoor air and the first heat exchanger, the control system (CTRL) is adapted to control the shutter arrangement between an open state and an enclosed state, in the enclosed state cooling power of the first heat exchanger is at least 50 % lower than in the open state, and wherein the static electrical device assembly comprises a heat pump, which is adapted to use the second heat exchanger as a source of heat and the control system has a heat recovery operating state in which the control system is adapted to maximise operating efficiency of the heat pump. a static electrical device comprising a housing and a winding system having at least one winding, the winding system being located inside a coolant space of the housing, the coolant space containing coolant which is in heat conductive connection with the winding system; a heat exchanger system comprising a first heat exchanger adapted for cooling of the coolant by transferring heat into ambient air, and a second heat exchanger adapted for recovering heat from the coolant, both the first heat exchanger and the second heat exchanger being in fluid connection with the coolant space; a flow passage for ambient air connection, the flow passage being adapted to provide a route for air flow between outdoor air and the first heat exchanger; a sensor system comprising at least one temperature sensor adapted to provide information relating to temperature of the static electrical device; and a control system (CTRL) adapted to control the heat exchanger system based on information provided by the sensor system, wherein the heat exchanger system comprises a heat recovering pump adapted to transfer coolant between the coolant space and the second heat exchanger, and the control system (CTRL) is adapted to control the heat recovering pump, characterized in that the heat exchanger system further comprises a shutter arrangement adapted to adjust a surface area of the flow passage in order to regulate an air flow between outdoor air and the first heat exchanger, the control system (CTRL) is adapted to control the shutter arrangement between an open state and an enclosed state, in the enclosed state cooling power of the first heat exchanger is at least 50 % lower than in the open state, and wherein the static electrical device assembly comprises a heat pump, which is adapted to use the second heat exchanger as a source of heat and the control system has a heat recovery operating state in which the control system is adapted to maximise operating efficiency of the heat pump.