Electricity: conductors and insulators – Conduits – cables or conductors – Superconductors
Patent
1998-03-05
1999-12-21
Sough, Hyung-Sub
Electricity: conductors and insulators
Conduits, cables or conductors
Superconductors
1741281, 505231, 505239, 505887, H01B 1208
Patent
active
060051949
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to an a.c. cable with at least one cable core having two concentric conductor arrangements of stranded single conductors as a.c. forward and return conductors.
BACKGROUND INFORMATION
German Patent No. 38 11 051 C describes an A.C. cable having concentric conductor arrangements, with one of the arrangements being formed of a plurality of conductor layers formed by individual conductors laid helix-like at predefined wire angles around a carrier body.
The development of a.c. cables with electric conductors containing superconducting metal oxide compounds as conducting materials is of particular interest today. Such superconducting metal oxide compounds with high critical temperatures T.sub.c of preferably over 77 K, which can be cooled with liquid nitrogen at normal pressure, are generally known. These compounds are therefore also referred to as high-T.sub.c or high-temperature superconducting materials (abbreviated as HTSC materials). Suitable metal oxide compounds include in particular cuprates, for example, Y--Ba--Cu--O or (Bi,Pb)--Sr--Ca--Cu--O system-based cuprates.
Conductors allowing superconducting cable cores of a.c. cables to be built can be constructed from these HTSC materials for electric power transmission with low losses and small cross sections. Economic advantages are thus achieved in comparison with conventional normally conducting cables, since the a.c. field losses, including the energy consumed in a refrigeration system used to dissipate said losses, are lower than the losses in a comparable normally conducting cable.
Estimates and loss measurements on cable models lead to the expectation that this object cannot be easily achieved if cable cores with a plurality of layers of strip-shaped HTSC elementary conductors, for example, are required for the current-carrying capacity in question. It is considered that this is due to the movement, accompanied by losses, of the magnetic self-field flux into and out of the superconductor and induced eddy currents in metallic conductor components.
According to a known, empirically supported loss theory, the magnetic field on the conductor surface should be selected to be as small as possible. This theory, however, applied to an a.c. cable, means that the diameter of the cable cores should be sufficiently large so that the current can be carried with a single layer of single superconductors. This, however, causes problems regarding transportation, and storage, capacitance, coolant.
No measures are currently known to eliminate these problems.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an A.C. cable with at least one cable core having two concentric conductor arrangements of stranded single conductors as A.C. forward and return conductors, with at least one of the conductor arrangements formed as a plurality of conductor layers formed by individual conductors laid helix-like at predefined wire angles around a carrier body with the cable of the present invention, most of the aforementioned problems, in particular when using superconducting materials, do not occur. An a.c. cable according to the present invention should also be applicable to normally conducting cables.
The present invention is based on the fact that, in a cable core, with a single layer of conductors stranded with a wire angle .alpha., current I follows spiral paths and has, in addition to an axial component I.sub.z= I cos .alpha. along the cable core axis (z direction), an azimuthal component I.sub..phi. =I sin .alpha. in the peripheral direction. Therefore, a single layer with specific current density J generates two magnetic field components: field is purely azimuthal: the field is homogeneous and is directed along the cable axis z: cable axis (in the z direction), surface (=the current in a strip-shaped single conductor per unit of strip width).
In such a single-layer cable core, the alternating field losses are caused by the field component of the outside surface individual conductor layers must
REFERENCES:
patent: 3730966 (1973-05-01), Aupoix et al.
patent: 4673775 (1987-06-01), Nigol et al.
M. Garber, IEEE, 4 pages (from 505/886), 1979 no month.
J. F. Bussiere, "The Development of Low-Loss Nb3Sn for AC Power Transmission", IEEE Transactions on Magnetics, vol. MAG-13, No. 1, pp. 131-137, Jan. 1977.
Siemens Aktiengesellschaft
Sough Hyung-Sub
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