Electricity: conductors and insulators – With fluids or vacuum – With cooling or fluid feeding – circulating or distributing
Reexamination Certificate
2001-01-12
2003-04-22
Paladini, Albert W. (Department: 2827)
Electricity: conductors and insulators
With fluids or vacuum
With cooling or fluid feeding, circulating or distributing
C174S125100, C029S599000, C505S230000, C505S231000
Reexamination Certificate
active
06552260
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a superconducting cable. More particularly, the present invention relates to a superconducting cable which comprises a core material, a multilayer superconducting conductor, and a magnetic shielding layer, and in which AC (alternating current) losses are reduced by means of analysis of current distribution within the superconducting cable.
The present invention also relates to a method of analyzing the current distribution within a superconducting cable. More particularly, the present invention relates to a method of analyzing the current distribution within a superconducting cable which comprises a core material, a multilayer superconducting conductor, and a magnetic shielding layer to calculate accurately AC losses of the superconducting cable.
2. Description of the Related Art
There has already been known a superconducting conductor which is formed into a multilayer construction by means of helically winding a tape-shaped superconducting wire around a core material at a constant pitch. Such a superconducting conductor suffers from a problem called “unbalanced current distribution.” Specifically, the further inward a superconducting layer, the smaller a current density. In contrast, the further outward a superconducting layer, the greater a current density. AC losses are thought to increase with an increase in unbalanced current distribution. Hence, a decrease in AC losses has been sought.
The invention described in Japanese Patent Examined Publication No. Sho. 29-6685 has been known as a basic technique pertaining to a reduction in the unbalanced current distribution of a multilayer conductor and a decrease in AC losses of the same. The invention relates to a technique of adjusting impedance of each layer by means of controlling a pitch at which the wires are helically wound in each layer. Further, Published Japanese National Stage of International Application No. Hei. 11-506261 describes the construction of a superconducting cable having a magnetic shielding layer which is formed by winding a superconducting wire.
In connection with a superconducting conductor, there has not yet been established a specific procedure for controlling a winding pitch because of the following reasons. A current-voltage characteristic of a superconducting conductor is nonlinear, and the effective resistance of the superconducting conductor is changed by an electric current flowing through the superconducting conductor. Without consideration of these factors, the current distribution and AC losses of the superconducting conductor cannot be predicted. Further, a specific method of taking into consideration the effective resistance has not yet been established.
Moreover, there has not yet been established a method of analyzing the current distribution and AC losses of a superconducting conductor in consideration of a core material and a superconducting magnetic shielding layer. The reason for this is that an equivalent circuit into which a high-temperature superconducting conductor is to be modeled has not yet been established.
An AC-loss characteristic of a superconducting conductor including a core material and a magnetic shielding layer has not been made definite experimentally. A theoretical model considering the resistance and impedance of the core material has not yet been reported. One of the reasons for this is that numerical computation considering the resistance and impedance of the core material becomes very complex.
SUMMARY OF THE INVENTION
It is therefore a first object of the invention to provide a superconducting cable; particularly, a superconducting cable which comprises a core material and a multilayer superconducting conductor, and in which AC losses are reduced by means of accurate analysis of current distribution within the superconducting cable.
Further, it is a second object of the invention to provide a method of analyzing accurately current distribution within the superconducting cable; particularly, a superconducting cable which comprises a core material and a multilayer superconducting conductor to calculate AC losses of the superconducting cable.
The present invention is based on the finding that an AC loss arising in a cable has a minimum value not when electric currents in the respective layers are made uniform, but when electric currents flowing through wires of a conductor layer are made uniform. Hence, the first object of the present invention is achieved by means of optimizing a pitch at which a superconducting wire of a conductor layer is to be wound and a pitch at which a superconducting wire of a magnetic shielding layer is to be wound.
More specially, the cable according to the first aspect of the present invention is a superconducting cable which comprises a core material; conductor layers formed by means of helically winding superconducting wires around the core material; electrically insulating layers; and magnetic shielding layers formed by means of helically winding superconducting wires around the electrically insulating layer.
Through processes (1)-(4) provided below, electric currents flowing through the conductor layers and the magnetic shielding layers are analyzed, and a pitch of the conductor layers and a pitch of the magnetic shielding layers are set on the basis of the result of analysis of electric currents flowing through the conductor layers and the magnetic shielding layers.
(1) A process of modeling the core material, the conductor layers, and the magnetic shielding layers (for the occasion that has arisen) as a circuit including at least induced reactance.
(2) A process of inputting parameters including specifications of the core material, including the size and specific resistance thereof; specifications of the superconducting wire, including a critical current (hereinafter abbreviated “Ic”) and size thereof; specifications of the conductor layers, including the direction and pitch at which the superconducting wires are to be helically wound, the thicknesses and outer diameters of the conductor layers, and the number of conductor layers; and frequencies and electric currents to be supplied.
(3) A process of computing the inductance and effective resistance of the circuit through use of the inputted parameters.
(4) A process of preparing a circuit formula on the basis of the model and computing the current distribution within each of the layers.
Preferably, the pitch of the superconducting wires including the magnetic shielding layer (that is; the pitch of the conductor layer and the pitch of the magnetic shielding layer) is set such that the absolute value of the analyzed current falls within a range of ±30% with reference to value I
all
c
obtained by means of dividing the current I
all
, which is provided to the conductor layer with a predetermined value, by the number of wires “n
c
” used for constituting the conductor layer. More preferably, the absolute value of the analyzed current falls within a range of ±20% with reference to value I
all
c
, and more preferably within a range of ±5% with reference to value I
all
c
. In a case where respective layers are formed from substantially the same number of wires; for example, a case where the conductor is formed from a smaller number of layers, an AC loss can have minimum value by means of making electric currents flowing through the respective layers uniform. Even when the layers differ from each other in critical current (Ic) because of a magnetic field or the influence of deflection associated with helical winding of a wire, the analysis by way of the four processes (1) through (4) can be performed by means of defining the critical current (Ic) of the wires for each layer.
The second object of the present invention is achieved by means of modeling a core material and a conductor layer into a suitable equivalent circuit and further modeling a magnetic shielding layer for the occasion that has arisen
More specially, the method according to the second aspect of the present i
Fujikami Jun
Honjo Shoichi
Kato Takeshi
Masuda Takato
Matsuo Kimiyoshi
Paladini Albert W.
Sumitomo Electric Industries Ltd.
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