Device for DC transmission comprising - a superconducting transmission line having at least one superconducting conductor element, and - a cooling device for cooling a radially inner region of the transmission line with the aid of a fluid coolant to a temperature below a critical temperature of the superconducting conductor element, - wherein the superconducting transmission line has a vacuum-insulated sleeve for thermally isolating the inner region of the transmission line from a warmer outer surrounding area, - wherein the cooling device comprises at least one feed device for feeding coolant at an end region of the transmission line into the radially inner region of the transmission line, - wherein the transmission line, given an axial longitudinal extent of at least 20 km, is free of axially internally arranged feed devices for feeding coolant, - wherein the transmission line has an electrically conductive line shield which surrounds the superconducting conductor element in an annular manner and - an annular dielectric insulation layer between the superconducting conductor element and the line shield and - at least one coolant channel (25a, 25b), which surrounds the superconducting conductor element in an annular manner, for transporting fluid coolant along a longitudinal direction of the transmission line, - characterized in that the dielectric insulation layer is formed substantially by the annular coolant channel which is filled with coolant, and - there are radially continuous axial segments and/or azimuthal segments of the transmission line, in which segments the dielectric insulation layer is formed entirely by fluid coolant. - a superconducting transmission line having at least one superconducting conductor element, and - a cooling device for cooling a radially inner region of the transmission line with the aid of a fluid coolant to a temperature below a critical temperature of the superconducting conductor element, - wherein the superconducting transmission line has a vacuum-insulated sleeve for thermally isolating the inner region of the transmission line from a warmer outer surrounding area, - wherein the cooling device comprises at least one feed device for feeding coolant at an end region of the transmission line into the radially inner region of the transmission line, - wherein the transmission line, given an axial longitudinal extent of at least 20 km, is free of axially internally arranged feed devices for feeding coolant, - wherein the transmission line has an electrically conductive line shield which surrounds the superconducting conductor element in an annular manner and - an annular dielectric insulation layer between the superconducting conductor element and the line shield and - at least one coolant channel (25a, 25b), which surrounds the superconducting conductor element in an annular manner, for transporting fluid coolant along a longitudinal direction of the transmission line, - characterized in that the dielectric insulation layer is formed substantially by the annular coolant channel which is filled with coolant, and - there are radially continuous axial segments and/or azimuthal segments of the transmission line, in which segments the dielectric insulation layer is formed entirely by fluid coolant.