Patent EA-001487-B1 (EA)
Title: Synchronous compensator plant
Inventor: LEIJON MATS
IPC: H01F27/00
Filed: 1997-05-27
Abstract: 1. A synchronous compensator plant comprising at least one rotating electric machine having at least one winding, characterized in that the winding in at least one of the electric machines comprises an insulation system including at least two semiconducting layers, each layer constituting essentially an equipotential surface and also including solid insulation disposed therebetween. 2. A plant as claimed in claim 1, characterized in that at least one of the layers has substantially the same coefficient of thermal expansion as the solid insulation. 3. A plant as claimed in either of claims 1 or 2, characterized in that the insulation is built up of a cable (6) intended for high voltage and comprising one or more current-carrying conductors (31) surrounded by at least one semiconducting layer (32, 34) with intermediate insulating layer (33) of solid insulation. 4. A plant as claimed in claim 3, characterized in that the innermost semiconducting layer (32) is at substantially the same potential as the conductor(s) (31). 5. A plant as claimed in either of claims 3 or 4, characterized in that the one of the outer semiconducting layers (34) is arranged to form essentially an equipotential surface surrounding the conductor(s) (31). 6. A plant as claimed in claim 5, characterized in that said outer semiconducting layer (34) is connected to a selected potential. 7. A plant as claimed in claim 6, characterized in that the selected potential is earth potential. 8. A plant as claimed in any of claims 3-7, characterized in that at least two of said layers have substantially the same coefficient of thermal expansion. 9. A plant as claimed in any of claims 3-5, characterized in that the current carrying conducting comprises a plurality of strands, only a few of the strands being uninsulated from each other. 10. A plant as claimed in any of claims 1-9, characterized in that the winding consists of a cable comprising one or more current-carrying conductors (2), each conductor consisting of a number of strands, an inner semiconducting layer (3) being arranged around each conductor, an insulating layer (4) of solid insulation being arranged around each inner semiconducting layer (3) and an outer semiconducting layer (5) being arranged around each insulating layer (4). 11. A plant as claimed in claim 10, characterized in that the cable also comprises a metal screen and a sheath. 12. A plant as claimed in any of the preceding claims, characterized in that the magnetic circuit is arranged in a rotating electric machine, the stator (3) of which is cooled at earth potential. 13. A plant as claimed in any of the preceding claims, characterized in that the magnetic circuit of the electric machine comprises a stator winding placed in a slot (5), said slot (5) being designed as a number of cylindrical openings (7) running axially and radially outside each other, having substantially circular cross section and separated by narrow waist parts (8) between the cylindrical openings. 14. A plant as claimed in claim 13, characterized in that the phases of the stator winding are Y-connected. 15. A plant as claimed in claim 14, characterized in that the Y-point of the stator winding is insulated from earth potential or connected to earth potential via a high-ohmic impedance and protected from over-voltages by means of surge arresters. 16. A plant as claimed in claim 14, characterized in that the Y-point of the stator winding is earthed via a suppression filter of third harmonic type, which suppression filter is designed to greatly reduce or eliminate third harmonic currents in the electric machine at the same time as being dimensioned to limit voltages and currents in the event of faults in the plant. 17. A plant as claimed in claim 16, characterized in that the suppression filter is protected from over-voltages by means of surge arresters, the latter being connected in parallel with the suppression filter. 18. A plant as claimed in claims 3 and 14, characterized in that the cable (6) constituting the stator winding has a gradually decreasing insulation seen from the high-voltage side towards the Y-point. 19. A plant as claimed in claim 18, characterized in that the gradual decrease in the insulation thickness is stepwise or continuous. 20. A plant as claimed in claims 13 and 18, characterized in that the circular cross section (7) of the substantially cylindrical slots (5) for the stator winding has decreasing radius seen from the yoke portion towards the rotor. 21. A plant as claimed in any of claims 12-20, characterized in that the machine can be started from a local power supply. 22. A plant as claimed in claim 21, characterized in that the machine has two or more poles.