A power supply grid system, comprising at least one first transmission line, having a first and second end (201, 202), at least two terminals each having a first port, wherein the first ports are coupled to the first or second ends of the at least one first transmission line, wherein at least one terminal comprises an AC interface adapted to couple the terminal to an AC grid or AC bus bar, a DC interface adapted to couple the terminal to a DC grid or DC bus bar, and at least one switch unit coupled to the at least one first transmission line, wherein the switch unit comprises a control input adapted to receive control commands, wherein the switch unit is adapted to couple based on the control commands received via the control input, the AC interface and the DC interface to the at least one first transmission line such that a combination of DC and AC power is transmitted over the at least one first transmission line, characterised in that the switch unit is also adapted to couple based on the control commands received via the control input the AC interface or the DC interface to the at least one first transmission line such that DC power is transmitted or AC power is transmitted over the at least one first transmission line, wherein the arrangement of at least two terminals and a transmission line is a multi-mode transmission line which is used to transmit electrical energy, wherein the transmission by the multi-mode transmission line is performed in three different operation modes, namely an AC transmission, a DC transmission and a combined AC and DC transmission, wherein the different operation modes are changeable during operation by switching operations. at least one first transmission line, having a first and second end (201, 202), at least two terminals each having a first port, wherein the first ports are coupled to the first or second ends of the at least one first transmission line, wherein at least one terminal comprises an AC interface adapted to couple the terminal to an AC grid or AC bus bar, a DC interface adapted to couple the terminal to a DC grid or DC bus bar, and at least one switch unit coupled to the at least one first transmission line, wherein the switch unit comprises a control input adapted to receive control commands, wherein the switch unit is adapted to couple based on the control commands received via the control input, the AC interface and the DC interface to the at least one first transmission line such that a combination of DC and AC power is transmitted over the at least one first transmission line, characterised in that the switch unit is also adapted to couple based on the control commands received via the control input the AC interface or the DC interface to the at least one first transmission line such that DC power is transmitted or AC power is transmitted over the at least one first transmission line, wherein the arrangement of at least two terminals and a transmission line is a multi-mode transmission line which is used to transmit electrical energy, wherein the transmission by the multi-mode transmission line is performed in three different operation modes, namely an AC transmission, a DC transmission and a combined AC and DC transmission, wherein the different operation modes are changeable during operation by switching operations.