Toroidal inductively coupled superconducting fault current limiter with interleaved windings

The characteristics and performance of small prototype inductively-coupled fault current limiter (FCL) are described. The FCL in question has an unusual toroidal geometry in which primary and secondary coils are interleaved to minimise leakage fields and leakage inductance and maximise the effective utilisation of superconducting material. The paper investigates the effect of winding configurations and geometry on the electromagnetic properties of the FCL. The construction of the prototype uses superconducting secondary coils made from double-sided YBCO thick film layers on ring shaped zirconia substrates. The primary windings were made of planar coils of copper wire. An interleaved winding structure produces a leakage inductance that is less than one-tenth of that obtained with an equivalent 'E' core transformer. Computed and measured leakage impedance are shown to be in good agreement. Transient and current limiting measurements demonstrate that the proposed FCL displays typical characteristics. The advantages of interleaved winding configurations are demonstrated directly by varying the degree of interleaving of the windings on the prototype FCL.