The present invention provides for a static excitation system for a superconducting rotor that comprises multiple brushes (12) in contact with the superconducting rotor winding (6), normally via collector rings and field leads. A power conditioning device (16) is connected to the brushes (12), and an energy storage device (18) is linked to the power conditioning device (16). The power conditioning device provides power from the energy storage device to the superconducting rotor when required, and when power to the superconducting rotor is not required, the power conditioning device takes excess power from the superconducting rotor and stores it in the energy storage device.