Mohamed Bekhaled

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.

Preliminary tests on a superconducting power transformer

Test results for a 50-Hz single-phase power superconducting transformer are presented and discussed. The near-ambient-temperature iron core, of conventional shape, is situated in a fiber-glass reinforced-composite inner vessel which is vacuum insulated from the He bath. The iron core is cooled by an inner channel. Inter-leaved low-voltage and high-voltage windings are wound around the inner vessel by halved formers and cooled by natural convection in a 4.21 K He bath. The tests demonstrated construction feasibility (showing considerable weight reduction compared with nonsuperconducting designs); increased efficiency for power levels of about 1 MVA; and fault current strongly limited by the high value of conductor matrix resistivity. >

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.