Experimental study of a transformer with superconducting elements for fault current limitation and energy redistribution

Numerous proposed and developed superconducting fault current limiters and self-limiting transformers limit successfully fault currents but do not provide uninterrupted supplying of consumers. A design investigated in the work combines the functions of a conventional transformer with the functions of fast energy redistribution and fault protection. The device constitutes a transformer containing an additional high-temperature superconducting (HTS) coil short-circuited by a thin film HTS switching element. Fault current limitation and redistribution of the power flow to a standby line are achieved as a result of a fast transition of the superconducting switching element from the superconducting into the normal state. Transient and steady-state characteristics were experimentally investigated. A mathematical model of the device operation was proposed, and the calculated results were found to be in good agreement with the experimental data. The application field and basic requirements to such devices were discussed and it was shown that the proposed device meets these requirements.Comment: 15 pages incl. 4 figures. Submitted to "Cryogenics

Thermal state of superconducting films on wide substrates

The stationary thermal state and propagation of a normal zone in a long superconducting film on a wide substrate are analyzed analytically. Expressions describing voltage-current characteristics and temperature-current dependence of the film are derived for the flux creep, flux flow and normal regions. It is shown how the flux creep influences the conditions of the thermal stability. In particular, it is found that the bistability of the thermal state can appear in this regime. Under the boiling crisis, the temperature-current dependence for a film differs markedly from that for a wire and is characterized by a smooth temperature increase with the current. A "mixed" regime is analyzed where the flux flow and normal states exist simultaneously with the boundary between them parallel to the film axis. Expressions for the propagation velocity of a normal zone along a narrow film are obtained which show that this velocity in films is sufficiently higher than in wires.Comment: 17 pages, 10 figures, submitted to "Cryogenics