Europäisches Patentamt *EP001455433A1* (19) European Patent Office Office européen des brevets (11) EP 1 455 433 A1 (12) EUROPEAN PATENT APPLICATION (43) Date of publication: (51) Int Cl.7: H02K 3/24 08.09.2004 Bulletin 2004/37 (21) Application number: 04100762.6 (22) Date of filing: 26.02.2004 (84) Designated Contracting States: (71) Applicant: Alstom Technology Ltd AT BE BG CH CY CZ DE DK EE ES FI FR GB GR 5400 Baden (CH) HU IE IT LI LU MC NL PT RO SE SI SK TR Designated Extension States: (72) Inventor: Mayor, Kevin AL LT LV MK 5408, Ennetbaden (CH) (30) Priority: 07.03.2003 GB 3053006 (54) Multi-path Cooling of a Turbo-Generator Rotor (57) A turbo-generator having a rotor (1) with direct lel twin ducts for multi path cooling, the inlets (4) and fluid cooling, the rotor (1) comprising rotor conductors outlets (5) of the flow paths in adjacent axial ducts (A, (2) arranged around a central rotor body. Each rotor con- B) being offset from each other. According to the present ductor (2) having axial cooling ducts (A,B), and a sub invention, a turbo-generator having a rotor (1) with an slot (3) is arranged below the main winding slot, is improved cooling scheme of the rotor windings to mini- wherein axial cooling ducts (A,B) are provided as paral- mize the hotspot temperature within the rotor windings is provided. EP 1 455 433 A1 Printed by Jouve, 75001 PARIS (FR) 1 EP 1 455 433 A1 2 Description [0007] The German laid open patent DE 1 120 575 describes a similar cooling scheme with each conductor Technical Field having two axial ducts for the flow of the coolant. Each axial duct is fed in a way similar to that described for DE [0001] The present invention relates to the field of dy- 5 1 036 370. The arrangement of the radial gas inlets and namo electric machines. It relates to a turbo-generator outlets to each axial duct is axially offset such that a having a rotor and a stator concentrically surrounding cross flow arrangement in adjacent ducts is achieved. the rotor and separated from the rotor by an air gap, and This cross flow scheme serves to reduce the tempera- also having a cooling arrangement with cooling fluid ture hotspots within the conductor closer to that of the flowing through corresponding cooling passages in the 10 average conductor temperature for that section of the rotor. winding. [0008] All of the known cooling schemes described Related Prior Art above have draw backs and insufficiencies. With pure radial or axial cooling schemes the hotspot temperature [0002] To ensure trouble-free operation and to utilize 15 is dependent on the length of the axial section of the the full output potential of a turbo generator, large gen- winding. It is not reduced by cross flow cooling within erators must be cooled in order to dissipate the heat loss adjacent ducts. However, the cross flow schemes rely which occurs in the windings and cores of the rotor and on gas flow from the sub slot reversing its flow direction stator. A fluid such as air or even hydrogen is generally to travel in the cross flow sense in some of the cooling used for the cooling and is fed through corresponding 20 paths. This reversal of the flow direction is known to re- bores or slits in the rotor and stator and then cooled sult in low flow conditions within the lower sections of down again in a cooler. the coil stack. The effect of this condition can be reduced [0003] ln the rotor, the cooling medium flows axially by a higher flow in the adjacent duct and (depending on from the ends into corresponding bores of the rotor con- the winding insulation arrangement) by radial conduc- ductor toward the inside, issues radially into the air gap 25 tion of heat within the coil and to the coolant in the sub- between stator and rotor after absorbing the rotor heat slot. loss, and can then flow either axially in the air gap out- ward, or radially through cooling channels in the stator Summary of the Invention core. [0004] The laid open German patent application DE 30 [0009] Accordingly, the technical problem to be 40 11 450 A1 describes a simple radial cooling scheme solved by the present invention is to provide a turbo- for a rotor winding of a turbo generator. According to this generator having a rotor with an improved cooling disclosure, the cooling gas enters the rotor winding via scheme of the rotor windings to minimize the hotspot a sub slot which is machined below the main winding temperature within the rotor winding conductors. Fur- slot. The gas then passes radially outwards through 35 ther, the manufacturing costs should be kept low and ventilation holes in the winding conductors to the air gap the reliability high. of the machine. According to this scheme, the radial [0010] This problem is solved by a turbo-generator holes are inclined in order to achieve a better flow con- having the features of claim 1. Preferred embodiments dition within the cooling channels and improve the cool- of the present invention are described in the dependent ing compared to pure radial flow machines. 40 claims. [0005] Other cooling schemes describe the use of one [0011] According to the present invention the cooling or more inner channels within the conductor. A cooling gas passes through twin axial ducts in the rotor conduc- medium passes through these channels axially for a cer- tors and is fed to these axial ducts from a sub slot situ- tain distance before exiting the conductor. The inlets and ated beneath the main winding slot. The flow in these outlets to and from these axial sections are generally 45 conductors is fed in such a way that the coolant flow formed by radial cooling ducts similar to pure radial cool- direction within the sub slot is maintained within the in- ing schemes. dividual conductors. The inlets from the sub slot and ex- [0006] The German laid open patent DE 1 036 370 hausts to the machine air gap are arranged such that describes a cooling scheme wherein each conductor multiple, parallel flow paths exist through the slot portion has a single axial duct. The cooling medium passes 50 of the rotor winding. The number of parallel flow paths through these single axial ducts. In this case the cooling is greater than or equal to three. medium, generally gaseous air or hydrogen, is fed to the [0012] Each flow path comprises one or more inlets conductor stack in the slot portion from a sub slot ma- from the sub slot which feeds one or more conductors chined below the main winding slot. The gas then pass- within the coil stack; an axial path length within one of es axially along the conductors in both the forward and 55 the axial ducts within the stack of conductors; and an reverse direction based on the flow direction in the sub exhaust vent to the machine air gap. slot. After a certain distance the gaseous medium ex- [0013] The inlets and outlets of the flow paths in the hausts radially into the air gap. adjacent axial ducts within one conductor are offset from 2 3 EP 1 455 433 A1 4 each other by a length which is a part of the length of Description of the Preferred Embodiments the axial portion of the flow path within the conductors, preferably half the length. This offset of the inlets and [0020] Referring now to the drawings, wherein like ref- outlets serves to minimize the hotspot temperature with- erence numerals designate identical or corresponding in the rotor winding conductors. 5 parts throughout the several views, a first preferred ex- [0014] The arrangement of maintaining the flow direc- emplary embodiment of the invention is reproduced in tion from the sub slot ensures a more even flow distri- FIG. 1 in a schematic longitudinal section of one half of bution of the fluid flow within the conductors than the a rotor 1. cooling schemes known in the prior art in which the flow [0021] The upper portion is representing the rotor direction is reversed. 10 winding 2 made of E-section or tubular copper as con- [0015] Thus, the present invention achieves a good ductor and the lower elongated channel is representing flow distribution within the conductor stack by keeping the sub slot 3 for feeding coolant C to the winding 2. The a forward flow direction in the conductors compared to sub slot 3 is arranged between the rotor shaft (not the sub slot. Further, the present invention limits the con- shown) and the winding 2. In the drawing of figure 1, the ductor hotspot temperature by offsetting the inlets and 15 left edge represents the rotor body end 7. outlets in adjacent ducts. [0022] In figure 1 the axial cooling ducts A are repre- [0016] A preferred embodiment of the present inven- sented by dashed lines and the axial cooling ducts B are tion provides a cross flow arrangement at the center of represented by solid lines. The axial cooling ducts A and the rotor winding where the winding sections fed from B are provided as twin ducts for unidirectional multi path each end of the rotor meet. This cooling arrangement 20 cooling. has the advantage that the feeding of fluent from the sub [0023] The axial ducts A and B are respectively con- slot is more evenly distributed.