Patent EA-000993-B1 (EA)
Title: Electomagnetic device
Inventor: LEIJON MATS
IPC: H01F27/28
Filed: 1997-05-27
Abstract: 1. Electromagnetic device comprising a magnetic field generating electric circuit including at least one electric conductor having an insulation system characterized in that the insulation system comprises an electric insulation (4) formed by a solid insulation material and exteriorly of the insulation an outer layer (5) which has an electrical conductivity which is higher than that of the insulation to make t he outer layer capable by connection to earth or otherwise a relatively low potential of operating to equalise potential and substantially enclose the electrical field arising as a consequence of said electric conductor (2) inwardly of the outer layer (5) that the insulation system comprises interiorly of the insulation (4) an inner layer (3) that said at least one electric conductor (2) is located interiorly of the inner layer (3) and that the inner layer has an electrical conductivity which is lower than the conductivity of the electric conductor but sufficient for the inner layer to operate for equalisation of potential and accordingly for equalisation with respect to the electrical field exteriorly of the inner layer (3). 2. Electromagnetic device comprising at least one electric conductor (2) having an insulation system characterized in that the insulation system comprises at least two potential layers (3, 5) and between those layers an electric insulation (4) consisting of a solid insulation material, and that the potential layers and the solid insulation present substantially similar thermal properties. 3. A device according to claim 1 or 2 characterized in that said at least one conductor (2) forms at least one induction turn. 4. A device according to any preceding claim, characterized in that the inner and/or outer layer (3, 5) comprises a semiconducting material. 5. A device according to any preceding claim characterized in that the inner layer (3) and/or the outer layer (5) has a resistivity in the range 10<-6> Ωxcm-100 kΩxcm, suitably 10<-3>-1000 Ωxcm, preferably 1-500Ωxcm. 6. A device according to any preceding claim, characterized in that the inner layer (3) and/or the outer layer (5) has a resistance which per length meter of the layer is in the range 50 μΩ-5 MΩ. 7. A device according to any preceding claim, characterized in that the solid insulation (4) and the inner layer (3) and/or the outer layer (5) are formed by polymeric materials. 8. A device according to any preceding claim, characterized in that the inner layer (3) and/or the outer layer (5) and the solid insulation (4) are rigidly connected to each other over substantially the entire interface. 9. A device according to any preceding claim, characterized in that the inner layer (3) and/or the outer layer (3) and the solid insulation (4) are formed by materials presenting substantially equal thermal coefficient of expansion. 10. A device according to any preceding claim, characterized in that the solid insulation (4) has been obtained by extrusion. 11. A device according to claim 10, characterized in that the inner layer (3) and/or the outer layer (5) has been provided by extrusion simultaneously with extrusion of the solid insulation (4). 12. A device according to any preceding claim, characterized in that the conduct or (2) and its insulation system constitutes a winding formed by means of a flexible cable (1). 13. A device according to claim 12, characterized in that the area of said at least one electrical conductor of the cable is in the range 2-3 000 mm<2> whereas the external diameter of the cable is between 20 and 250 mm. 14. A device according to any preceding claim, characterized in that the inner layer (3) and/or the outer layer (5) comprises a polymeric material containing an electrically conducting constituent. 15. A device according to any preceding claim, characterized in that the inner layer (3) is in electric contact with the at least one electric conductor (2). 16. A device according to claim 15, characterized in that said at least one electric conductor (2) comprises a number of strands and that at least one strand of the electric conductor (2) is at least in part uninsulated and arranged in electric contact with the internal layer (3). 17. A device according to any preceding claim, characterized in that there are, interiorly of the inner layer (3b), several electrical conductors (2b) insulated from each other. 18. A device according to claim 17, characterized in that an inner layer (3a) according to any preceding claim is arranged about each of said plurality of electrical conductors. 19. A device according to claim 17, characterized in that there are, inwardly of the inner layer (3b), further layers (30) about each of said plurality of conductors (2b), said further layers (30) having properties corresponding to those of the inner layer. 20. A device according to any preceding claim, characterized in that the conduct or (2) and its insulation system is designed for high voltage, suitably in excess of 10 kV, in particular in excess of 36 kV and preferably more than 72,5 kV. 21. A device according to any preceding claim, characterized in that the outer layer (5) is divided into a number of parts, which are separately connected to ground or otherwise a low potential. 22. A device according to any preceding claim, characterized in that it is constituted of a rotating electric machine. 23. A machine according to claim 22, characterized in that the magnetic field generating electrical circuit thereof is arranged in the stator and/or rotor of the machine. 24. A machine according to any of claims 22-23, characterized in that the magnetic field generating circuit comprises one or more magnetic cores (8) having slots (10) for the winding (1). 25. A machine according to claim 22-24, characterized in that, with connection o f the outer layer (5) to ground potential, the electrical field of the machine out side the outer layer will be near zero both in the slots (10) and in the coil-end-region. 26. A machine according to any of claims 22-25, characterized in that the slots (10) are formed as a number of cylindrical openings (12) separated by a narrower waist portion (13) between the cylindrical openings. 27. A machine according to claim 26, characterized in that the cross section of the openings of the slots (10) decreases, counted from a back portion (8) of the magnetic core. 28. A machine according to claim 27, characterized in that the cross section of the slots (10) decreases continuously or discontinuously. 29. A machine according to any of claims 22-28, characterized in that it is constituted of a generator, motor or synchronous compensator. 30. A machine according to claim 29, characterized in that the generator is a hydro generator or turbo generator. 31. A machine according to any of claims 22-30 characterized in that it is directly connected to a power network for high voltage suitably 36 kV and more without intermediate transformer. 32. A device according to any of claims 1-21, characterized in that it is constituted by a power transformer/reactor. 33. device according to claim 32 characterized in that it comprises a magnetic core. 34. A device according to claim 32 or 33 characterized in that it is air-wound thus being formed without a magnetic core. 35. A device according to any of claims 32-34 comprising at least two galvanically separated windings, characterized in that the windings (25-27) are concentrically wound. 36. A high voltage electric power plant comprising one or more electromagnetic devices according to any of claims 1-35. 37. An electric power network comprising one or more electromagnetic devices according to any of claims 1-35. 38. A method for electric field control in an electromagnetic device comprising a magnetic field generating circuit having at least one winding (1) with at least one electric conductor (2) and an electric insulation (4) present externally thereof characterized in that the insulation (4) is formed by a solid insulation material and that an outer layer (5) is provided externally of the insulation said outer layer (5) being connected to ground or otherwise a relatively low potential and having an electrical conductivity being higher than the conductivity of the insulation (4) but lower than the conductivity of the electrical conductor (2) so as to function for equalization of potential and cause the electrical field to be substantially enclosed in the winding internally of the outer layer (5) and that an inner layer (3) is provided inwardly of the solid insulation (4) said at least one electric conductor (2) being provided inwardly of the inner layer (3) said inner layer (3) having an electrical conductivity which is lower than that of the electric conductor but sufficient f or making the inner layer to function equalizing with respect to the electric field exteriorly of the inner layer (3). 39. A method in production of a magnetic circuit for a rotating electric machine, where the magnetic circuit's arranged in the stator and/or rotor of the rotating electric machine and comprises a magnetic core (8) having slots (10) for a winding, said slots being formed with openings (12), a flexible high voltage cable (1) is used as a winding and that this high voltage cable is threaded into the openings (12). 40. A cable for forming a magnetic field generating winding in an electromagnetic device comprising at least one electric conductor (2) with an insulation system including at least two potential layers and between these layers an insulation made of a solid electric insulation material, where the potential layers and the solid insulation exhibit substantially similar thermal properties.