An apparatus includes a converter having an AC side and a DC side, a switch adapted to be connected to a transmission line on a first side and connected to a load on a second side connected to the AC side, an energy storage device, connected to the DC side. In a first operating mode, the switch is closed, such that an energy storage current flows to/from the energy storage device to charge/discharge the energy storage device, respectively. In a second operating mode, the switch is open, preventing current from flowing from the transmission line to the converter, and the energy storage device supplies a direct current which is converted to an alternating current by the converter. In the first operating mode, the apparatus is configured such that power transfer on the transmission line corresponds to a surge impedance loading of the transmission line, by affecting the energy storage current.