Smartcoil - Design, assembly and test of a 10 MVA superconducting air coil fault current limiter

Within a German government funded project the partners Siemens AG and KIT have developed an iron-free inductive current limiter. The project aimed at a device for the medium voltage range, i.e. U = 10 kV with a nominal power of 10 MVA. One phase of this limiter was designed, manufactured and successfully tested. The limiter is based on a stack of closed superconducting ReBCO rings inserted into a conventional reactor coil. Under normal operation conditions, the rings shield the inner part of this coil. With the occurrence of a short circuit the superconducting rings quench and the impedance of the reactor coil becomes effective. The paper reports the principles of the design and the development of the superconducting ReBCO rings. It describes in detail the test of such rings, in particular the contactless determination of contact resistances and critical currents. Of particular importance was the development of a cryostat which minimizes the distance between the primary reactor coil and the superconducting insert. Finally, the device was tested in the Siemens test field in Berlin under the most relevant operation conditions. The limiting behavior complied with the predicted properties.