Electric transformer having superconductive coils

Details Electric transformer having superconductive coils Electric transformer having superconductive coils

1999-09-17

2001-09-18

Mai, Anh (Department: 2832)

Inductor devices

Separable

C361S219000

Reexamination Certificate

active

06292080

ABSTRACT:

The invention relates to an electric transformer having superconductive coils at the primary coil and/or secondary coil.
BACKGROUND OF THE INVENTION
In the conventional manner, metal-matrix superconductive conductors are used to make electric transformers presenting high power per unit mass and high efficiency. Metal-matrix superconductive conductors make it possible to obtain current densities that are much higher and losses that are much lower than can be obtained with solid superconductors or with non-superconductive conductors.
Nevertheless, the low electrical resistance of the metal matrix (e.g., made of silver or silver alloy) does not make it possible to limit short-circuit currents effectively, so it is necessary to define the transformer and the other electrical equipment present on the line in such a manner as to enable them to withstand high short-circuit currents, or else to add in series apparatus that is dedicated to limiting current. In the conventional manner, such apparatus can be made using solid superconductors that present high electrical resistance when the currents exceed their normal capacities.
OBJECTS AND SUMMARY OF THE INVENTION
The object of the invention is to combine the transformer and current limiter functions in a single device and to do so under good conditions, in particular concerning overall size.
The idea on which the invention is based is to use a quantity of solid superconductor that is just sufficient to limit the current and to make it contribute to creating ampere-turns, taking care to locate it in regions of the transformer where the magnetic field is weakest, with this particular disposition making it possible to achieve a considerable reduction in the losses from the solid superconductor.
More particularly, the invention provides an electric transformer comprising a primary coil and a secondary coil each constituted by at least a first coil formed by winding one or more metal-matrix superconductive conductors, wherein the first coil of the primary coil or of the secondary coil is connected in series with at least one second coil formed by a solid superconductive tube machined to form a solenoid, said second coil being disposed coaxially with said first coil and having a current-limiting function.
With the transformer design of the invention, the volume of the machined superconductive tubes is kept down to the minimum necessary for limiting short-circuit currents effectively, while metal-matrix superconductive conductors are used for the remainder of the coils.
In a first advantage of the invention, the machined superconductive tube(s) can be located in the primary coil for a voltage-raising transformer or in the secondary coil for a voltage-lowering transformer. They thus operate at high current and at low voltage, i.e., large sectional area and small number of turns, which is more appropriate to this type of coil, and also reduces dielectric problems while limiting current.
In a particular embodiment of the transformer of the invention, the machined superconductive tube(s) is/are located in regions of the transformer where the magnetic field is weakest, which has the useful consequence of considerably reducing loses therein, and of increasing the current density they can carry.
Preferably, each superconductive tube is in mechanical and electrical contact with a tube made of a highly resistive metal alloy, the assembly being machined into the form of a solenoid; in addition to providing mechanical reinforcement, the metal alloy tube favors the propagation of the transition and reduces the heating of the superconductive tube while current limitation is taking place.


REFERENCES:
patent: 5379020 (1995-01-01), Meier et al.
patent: 5912607 (1999-06-01), Kalsi et al.
patent: 4418050A1 (1995-01-01), None
patent: 0 081 854 A (1980-11-01), None
patent: 0 154 779 A1 (1985-09-01), None
patent: 2 321 137 A (1998-07-01), None
F. Van Overbeeke et al “Design and Operation of a Protection System for Transformers with Superconducting Windings”, CRYOGENICS, vol. 25, No. 12, Dec. 1985, pp. 687-694, XP002104440.

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