Van Doan Pham

Experiments with a high voltage (40 kV) superconducting fault current limiter

Abstract Fault current limiters are devices that restrict fault currents without appreciable delay, so that they can protect electrical grids and devices more efficiently than classical circuit-breakers. Extremely low response times (a few microseconds) are provided by low- T c superconducting conductors, which combine a high critical current density and a high normal-state resistivity, with a vanishing heat capacity. Due to the risks of dielectric breakdown and overheating, the rated voltages have been limited to a few kV up to now. A significant step forward was recently attained with the successful tests of a 40 kV rms prototype; the device accepts rated currents of 315 A rms , and protects the line from any current over 1100 A peak (less than one tenth of the ordinary fault current). Its design and test results are presented here, with a tentative extrapolation to higher-rated currents and voltages.

Hybrid superconducting AC fault current limiter principle and previous studies

It is pointed out that one of the most promising uses of the low AC loss ultrafine wires in electrical devices is the fault AC current limiter. The superconducting AC current limiters may be separated into two kinds: resistive and inductive ones. For the resistive limiter, the superconducting winding triggers and assumes the limitation. For the inductive one, the superconducting winding plays only the role of trigger while the fault current is limited by another winding, superconducting or normal. In this case, a limited heating of the superconducting coil and then a very short recovery time may be anticipated. It will enable one to quickly restore the service. On the other hand, the current in the trigger coil may be chosen lower than the rated current so that the choice of the superconducting wire may be easier. The use of a judicious magnetic circuit improves the performance of the inductive current limiter as it decreases the voltage drop in rated operation and the heating of the superconducting coil during fault. >

Progress on superconducting current limitation project for the French electrical grid

Electricite de France, GEC ALSTHOM and Alcatel Alsthom Recherche, initiated in project for the definition, experimental validation and economic evaluation of superconducting fault current limiters adapted to the French grid system. As a first step, a device of 63 kV-1.25 kA is investigated, which has the function to limit the 25 kA fault current at 5300 A/sub peak/. A very compact and low-inductance design has been selected, based on resistive limitation. Considerations concerning the general design, conductor protection, high voltage insulation, cryogenic system and interaction with the grid, are developed in this paper. >

25 kV Superconducting Fault Current Limiter

Our technological progress in die field of superconductivity over the last ten years made possible the manufacture of industrial lengths of conductors, consisting of NbTi ultra-fine filaments, embedded in a Cu-30 wt % Ni matrix; 50 Hz losses are greatly reduced, and the electrical resistance beyond the critical current is very large. Such conductors offer numerous new perspectives, through which the design of electrotechnical machines could be reconsidered. This paper describes the main features of a 50 Hz single-phase fault current limiter, constructed in our laboratories, which present some electrical and cryogenic properties: S-N transition limiting the fault current to a value a few percent above the threshold current within a few µs, high voltage insulation capabilities, moderate cryogenic losses during steady state and in transient conditions.