Electricity: magnetically operated switches – magnets – and electr – Magnets and electromagnets – Superconductive type
Reexamination Certificate
2000-03-06
2002-10-29
Donovan, Lincoln (Department: 2832)
Electricity: magnetically operated switches, magnets, and electr
Magnets and electromagnets
Superconductive type
C324S318000
Reexamination Certificate
active
06472966
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a superconductive high-current switch.
BACKGROUND OF THE INVENTION
Switches usable for switching high power, are, as a rule, of a complicated construction as specific measures need to be taken to counteract the formation of electric arcs and to eliminate arcs formed, respectively. A useful quantity for assessing a power switch is the switching capacity related to a unit of volume (current * voltage/component volume). With the conventional switches, this value is relatively small, due to construction expenditures.
What is disadvantageous in the conventional high-current switches is, furthermore, the relatively long switching time that usually is indicated for a complete switching cycle consisting of activation and deactivation of an electric circuit.
For solving the problems indicated hereinbefore, the applicant has already suggested a superconductive high-current switch (WO89/05044) in which plate-shaped insulating carriers having a high-temperature superconductive material vapor-deposited therein are arranged in a housing in stacked manner.
High-temperature superconductors are in particular such conductors having a transition temperature of more than approx. 80° K. Typical high-temperature superconductive materials are ABa
3
CuO
7
(wherein A=Y, La, Nd, Sm, Eu, Gd, Ho, Xr, Lu) as well as Y
1.2
Ba
0.8
CuO
4
.
The switch function of a superconductive high-current switch consists in the transition between the superconducting and normally conducting state, and vice versa. In the superconducting state, the switch is closed, i.e. current flows without electric resistance through the switch unit. By suitable cooling of the switch, the latter is brought to the superconducting state. For opening the switch, there are various mechanisms possible, for example heating of the superconductive material by electrical heating, by laser beam etc. Further possibilities are the application of external magnetic fields and the introduction of an additional current phase. As regards to further details, reference is made to the above indicated WO publication.
In the normally conducting state of the superconductive material, a considerable electrical resistance is present between the input terminal and the output terminal of the switch. Due to the construction of the known superconductive high-current switch, the dielectric strength is relatively low. In addition, to the material data of the superconductor in the normally conducting and superconducting states, the dielectric strength of the assembly determines the attainable switching capacity. Consequently, the low dielectric strength of course means a relatively low upper limit for the switching capacity.
SUMMARY OF THE INVENTION
It is the object of the invention to provide a superconductive high-current switch which distinguishes itself by a relatively high dielectric strength along with a high switching capacity per component unit of volume. In particular, a switch is to be provided for high powers, having switching capacities of preferably more than 1 MVA, in particular more than 1 GVA. particular, a switch is to be provided for high powers, having switching capacities of preferably more than 1 MVA, in particular more than 1 GVA.
With a superconductive high-current switch, this object is met according to the invention by the following features:
a) there is provided at least one layer having a winding of a superconductive, in particular high-temperature superconductive, current conductor section so as to form a high-current switch unit;
b) within each winding layer, the line routing is such that the current to be switched flows in opposite directions in radially adjacent current conductor sections; and
c) there is provided a switching control means capable of effecting in the current conductor section a change between the conditions “superconducting” and “not superconducting”.
In the superconductive high-current switch according to the invention, the switching control means actively brings the current conductor sections—at least in part—from the state present at the particular moment (superconducting
ormally conducting) to the other state (normally conducting/superconducting) in order to thus “open” and “close” the switch, respectively. The current conductor section in the winding layer—electrically constitutes a continuous current conductor between an input terminal and an output terminal of the switch. As will still be elucidated in more detail further below, a specific embodiment of the invention is provided with a single, continuous current conductor, e.g. in the form of a pre-insulated wire. In a preferred embodiment, several layers with one winding means each are lined up adjacent each other in the direction of the winding axis. What is essential in this respect is that the voltage present between switch input and output is distributed to several layers in axial direction of the assembly. Due to this, the voltage to be switched is distributed to several layers so that very high dielectric strength is obtained. In the superconducting state, there are considerable currents flowing. By means of the switch according to the invention, it is thus possible to obtain high switching capacities. All embodiments of the invention distinguish themselves by a relatively simple, but definitely very compact construction, so that the electric switching capacity related to the unit of volume of the switch is considerable, which makes the switch according to the invention superior as compared to conventional switches.
An additional specific feature of a power switch is the switching speed. According to the invention, the current direction within each layer in the individual current conductor sections extends such that the current flow direction is opposite in adjacent current conductors. Due to the fact that each winding means of a conductor naturally has a certain inductance, the switching operation in a switch is impaired by the energy stored in the inductance. Due to the opposite current flow direction according to the invention, a low-inductance construction is obtained, so that the switching speed is thus high.
In a specific embodiment of the invention, the individual lined-up layers of the high-current switch according to the invention have the same or at least a similar structure, in particular with current conductor sections adjacent in axial direction having virtually the same radial. distance from the winding axis. In such axially adjacent current conductors of adjacent layers, the current flow directions in a less expedient embodiment may be in the same direction, but preferably the current flow directions. are also opposite in the axially adjacent current conductor sections as well. When the current flow directions are opposite not only in radially adjacent but also in axially adjacent current conductor sections, the particularly, advantageous properties of the high-current switch according to the invention, as elucidated hereinbefore specifically for one winding layer each, are still enhanced. This holds in particular for the inner mechanical forces between the current-conducting parts, which remain very low despite the compact construction and thus permit the conduction of higher currents.
The effects and advantages of the invention elucidated in the following concern various embodiments relating to the design of the current conductor sections, the layer structure, the entire structure of the switch with its specific electrical and mechanical features and the construction and operation of the switch in consideration of the superconductivity of the current conductor material.
In order to effectively exploit the high dielectric strength, the high switching capacity and the high switching speed, there should be provided a minimum number of layers, which possibly should be an even number of layers for reasons of symmetry. Preferred are at least four layers.
Superconductors are available in the market in various embodiments, e.g. as pre-insulated wire. In a preferred embodiment of the invention
Ehrhart Peter
Muller Anton
Scholderle Hermann
Sturm Evi
Weck Werner
Donovan Lincoln
Kunitz Norman N.
Magnet-Motor Gesellschaft fur magnetmotorische Technik mbH
Venable
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