Joint and jointing method in a permanent magnet synchronous machine
The invention relates to a joint between a copper short-circuiting ring ( 1 ) and a copper bar ( 2 ) of the damper winding in a permanent magnet synchronous machine, wherein the end of the bar is jointed to a hole ( 9 ) disposed in the short-circuiting ring by welding them together at the mating surfaces. Further, the invention relates to a corresponding method. According to the invention the short-circuiting ring ( 1 ) includes a blocking structure for limiting the heat flux from being conducted further into the short-circuiting ring from the weld between the short-circuiting ring and the bar.
1. A method for welding together a copper short-circuiting ring and a copper bar of a damper winding in a permanent magnet synchronous machine, wherein an end of the bar is jointed to a hole disposed in the copper short-circuiting ring by welding the copper bar and the copper short-circuiting ring together at mating surfaces, wherein at least one of the copper bar and the copper short-circuiting ring to be welded is shaped in a vicinity of the mating surfaces to be welded so that free conduction of heat outside the weld in the copper bar or the copper short-circuiting ring to be welded is limited, and wherein a magnetic circuit of the permanent magnet synchronous machine is short-circuited before welding for an area to be welded to minimize leakage of flux preventing the welding.
2. The method according to claim 1 , wherein the free conduction of heat to the bar is limited by providing the end of the bar with a central recess.
3. The method according to claim 1 , wherein the free conduction of heat to the short-circuiting ring is limited by machining a groove around the hole disposed in the short-circuiting ring, to a distance from the hole.
4. The method according to claim 1 , wherein the short-circuit is made by an iron mass extending from under the short-circuiting ring of a rotor, from around the bars and from contact thereto, along the outer casing of the rotor in the vicinity of the mating surfaces to be welded.
5. The method according the claim 4 , wherein the iron mass is used to cool the permanent magnet poles of the rotor at the bars to be welded.
6. The method according to claim 5 , wherein the iron mass is cooled by a cooling circulation surrounding the iron mass and/or passing through the iron mass.