Rotor of an electrical machine

Abstract

Rotor (10) of an electrical machine, in particular a hydrogenerator, comprising: a rotor yoke (12) with axial winding slots (13) distributed around the outer circumference; Winding bars (14, 15) of a rotor winding which are inserted into the winding slots (13) and whose winding ends (16, 17) emerging axially from the rotor yoke (12) form a winding head (11); a retaining device (19,...,28) which is designed to retain the winding head (11) against centrifugal forces acting on the winding head (11), wherein the retaining device (19,...,28) comprises a plurality of radial bolts (24), each of which has heads (25) firmly connected to a shaft (31), wherein the retaining device (19,...,28) has a retaining strip (23) which runs in the axial direction on the winding head (11), and the plurality of radial bolts (24) are arranged one behind the other in the axial direction and are designed to press the retaining strip (23) from the outside against the winding head (11); at least one hammer-shaped recess (19) designed to receive at least one counter-bar (20) provided with threaded holes for screwing in the plurality of radial bolts (24) for fastening the bolts (24) to the outer circumference of an axial extension (21) of the rotor yoke (12) located within the winding head (11), wherein the axial extension (21) is arranged in the winding head (11) and wherein the radial bolts (24) belonging to a respective retaining bar (23) are screwed into a common counter-bar (20); and Means (28, 32, 33) for securing the plurality of radial bolts (24) against rotation, wherein the radial bolts (24) each have a recess (32) with a rectangular contact surface (33) at the inner end and the radial bolts (24) are secured against rotation by securing strips (28) which are axially inserted into the hammer-shaped recesses (19) and rest against the contact surfaces (33).

Description

TECHNICAL FIELDThe present invention relates to the field of electric machines. It relates to a rotor of an electric machine, in particular of a hydraulic generator.PRIOR ARTDue to the changed market economic conditions on the open electricity markets and the improved technologies in the field of power electronics, the issue of variable-speed drives for energy production has gained importance. For this purpose, double-fed asynchronous machines are preferably used, in particular at powers above 60 MVA.The stator of this type of machine does not differ from the salient pole synchronous machines customary for this application. Machines of this type are characterized in that they are equipped with a three-phase winding both on the stator and on the rotor. Usually, the end windings of the rotor winding are arranged on a cylindrical surface (see e.g. DE 195 13 457 A1).Due to the centrifugal force, the winding bars during operation tend to move radially outwards away from the center. The difficulty with the above mentioned embodiment of the end windings is to sufficiently protect the rods of the winding from deformation by mechanical forces. In general, three solutions are available for this purpose:• In smaller machines, the entire end winding is wound with several layers of steel wire. This is not useful for larger diameters for production reasons.• In machines with diameters greater than 2 metres, the end windings are fastened either by radial bolts or threaded rods with a holder on the axial extension of the rotor yoke, as described in the above-mentioned publication, or• The entire winding head is surrounded by a shrunk-on steel cylinder, as is known in the case of solid-pole synchronous machines.DE 195 13 457 A1 focuses primarily on the description of the overall construction with the associated winding head support system. The bolts used here serve for the radial support of the rotor end windings and are anchored in the axially raised rotor yoke (see FIGS. 4 and 5 of the publication with the bolts 37). The bolts are threaded rods which are screwed on the one hand into the rotor yoke by being screwed into threaded rulers (36) accommodated in a supporting ring arrangement and on the other hand absorb the centrifugal forces arising on the air gap side by means of rectangular individual elements and nuts. The disadvantage of the system described lies in the large number of individual parts and the associated risk of destroying the machine in the event of loss of a bolt or a nut.DE 701 612 A discloses a winding head of a rotor winding of an electric machine with ring segments fastened to the outer side of the winding head against the action of the centrifugal forces, which ring segments are fastened to a winding carrier ring lying below the winding head by means of radial screw bolts and nuts.DE 10 2005 051 349 A1 discloses a rotation prevention device for a screw connection with a screw head braced against a contact of a body and with a securing plate supported in a form-fitting manner against the body and against a shoulder surface of the screw head.GB 1910 / 14 680 A discloses a rotor assembly having windings having winding ends projecting beyond the pole pieces secured to an armature shaft by a plurality of radial bolts each having heads fixedly connected to a shaft. In one embodiment, the bolt heads are rounded.The development described below is more closely related to the bolts used and in particular their secure fixing.SUMMARY OF THE INVENTIONIt is the object of the invention to further develop the rotor mentioned at the beginning in such a way that the disadvantages of the known solution are avoided and in particular a secure fixing of the radial bolts results.The object is achieved by the totality of the features of claim 1 and claim 7.It is essential for the invention that the radial bolts have heads firmly connected to the shank. On the one hand, this drastically reduces the number of components used. On the other hand, the danger is eliminated that external nuts or washers can become detached and damage or completely destroy the machine.According to one embodiment of the invention, the heads of the radial bolts are connected to the shank in a materially bonded manner, preferably forged or welded. This facilitates the use of specially shaped heads in particular.In order to reduce the air resistance of the rotating rotor, it is advantageous if the heads of the radial bolts have an aerodynamically favorable shape, wherein in particular the heads of the radial bolts are rounded on the upper side and have two straight flanks on opposite sides for tightening the bolts.According to one aspect of the invention, a plurality of radial bolts arranged one behind the other in the axial direction are configured in order to press a common retaining strip running in the axial direction from the outside against the winding head. This achieves a uniform pressure distribution of the tightened bolts on the winding head without the number of inserted elements having to be increased substantially by separate washers. In order to keep the air resistance low in this case as well, the retaining strips have rounded longitudinal edges to improve aerodynamics.According to a further aspect of the invention, hammer-shaped recesses are provided for fastening the bolts to the outer periphery of an axial extension of the rotor yoke located within the winding head, into which recesses counterbars provided with threaded bores are inserted in the axial direction for screwing in the radial bolts, wherein in particular the radial bolts belonging to a respective retaining bar are screwed into a common counterbar. This not only simplifies the assembly, but also keeps the number of components small.Furthermore, means are provided for securing the radial bolts against rotation, wherein in particular the radial bolts each have a recess with a rectangular contact surface at the inner end, and the radial bolts are secured against rotation by securing strips which are axially inserted into the recesses and bear against the contact surfaces.BRIEF EXPLANATION OF THE FIGURESThe invention will be explained in more detail below with reference to exemplary embodiments in conjunction with the drawing. They show FIG. 1 shows the winding head, viewed from the outside in the radial direction, with a retaining device according to a preferred exemplary embodiment of the invention; FIG. 2 shows an enlarged detail from FIG. 1 with the aerodynamically shaped heads of the radial bolts; FIG. 3 is a top view of the winding head from FIG. 1 ; FIG. 4 shows an enlarged detail from FIG. 3 with the fastening and securing elements for the radial bolts; and FIG. 5 shows two different views of a radial bolt as is used in the retaining device of FIG. 1 in two FIGS. 5(a) and 5(b).WAYS OF CARRYING OUT THE INVENTIONThe proposed solution is based on the idea of reducing the number of individual parts of the winding head retaining device and at the same time of securing all parts mechanically against detachment by vibrations. This achieves a substantial increase in the safety of the system.FIG. 1 shows a section of a rotor 10 of a large hydraulic generator / motor, viewed from the outside in the radial direction, with a winding head 11 which is equipped with a retaining device according to a preferred exemplary embodiment of the invention. The basic structure of the rotor 10 can be found in the publication cited at the beginning. The rotor 10 has a cylindrical rotor yoke 12 with axial winding slots 13 distributed on the outer circumference. Winding bars 14, 15 of the rotor winding are inserted into the winding slots 13 (in each case one above the other in pairs). The winding ends 16, 17 which emerge axially from the rotor yoke 12 are cranked and are electrically connected to one another at the ends by means of round lugs 18 according to a predetermined winding or phase pattern. The winding ends 16, 17 are part of the winding head 11.Within the winding head 11 extends in the axial direction a (cylindrical) axial extension 21 of the rotor yoke 12, which is closed at the end by a pressing plate 29, on which a plurality of axial clamping bolts 30 are supported, which hold the laminated core of the rotor yoke 12 together in the axial direction. On the outer periphery of the extension 21, a plurality of wheel rims 34 are arranged one behind the other in the axial direction, in which hammer-shaped recesses 19 are provided distributed uniformly over the periphery, which serve for the fastening of the inventive retaining device for the winding head 11. The retainer includes a plurality of radial bolts 24.As can be seen from FIGS. 2 and 5, radial bolts 24 are used, which have heads 25 firmly connected to the shank 31. The heads 25 are preferably firmly connected to the bolts 24 by a material bond, for example by forging or welding. Thus, in particular, bolts 24 with forged-on or firmly welded heads 25 are used. The heads 25 have two opposite straight flanks 26, 27 which serve to tighten the bolts 24 with a fork wrench or the like. Furthermore, instead of rectangular washers, axially extending retaining strips 23 are used, which distribute the retaining forces of the bolts 24 uniformly over the winding or the winding head 11.The screw heads 25 and the retaining strips 23 are further distinguished by their aerodynamic shape (round heads 25 and rounded edges of the retaining strips 23), which leads to a reduction in the friction losses during operation.The radial bolts 24 extend in the radial direction through the winding head 11 and are accommodated in the hammer-shaped recesses 19 in the axially widened rotor yoke ( 21). The bolts 24 are retained by means of a counter-strip 20 offset with threaded bores. Corresponding to the retaining strip 23 on the front side, the counter strip 20 runs over the length of the rotor yoke extension. Each bolt 24 can thus be screwed in individually and brought to the necessary tension. Between the winding head 11 and the extension 21 of the rotor yoke 12 there are additionally arranged axial spacer bodies 22, through which the bolts 24 extend.As can be seen from FIG. 5, the otherwise round bolts 24 have at the free end a recess 32 with a rectangular contact surface 33. This has the following reason: the bolts 24 are tightened to the necessary tension by means of suitable tools, so that in the end position the straight flanks 26, 27 of the screw heads 25 are perpendicular to the longitudinal axis of the machine; as is shown in FIGS. 1 and 2. In this position, the rectangular bearing surface 33 of the ends of the bolts 24 runs parallel to the flanks of the hammer-shaped recesses 19. As soon as all the bolts 24 of a row (retaining strip 23) are now attached, a securing strip 28 (FIG. 4 ) can be introduced into the remaining recess. The securing strip 28 is dimensioned such that the bolts 24 can no longer be rotated. This principle allows in a simple manner the securing of all the parts of the retaining device to prevent accidental loosening of the screwed parts. Furthermore, it is also possible to secure the bolts 24 on both sides with an inserted strip in the same manner if the ends of the bolts are correspondingly provided with two parallel contact surfaces. Finally, a further possibility for securing would be to provide the bolts 24 with slots at the rear, through which a metal wire can be inserted for securing purposes.LIST OF REFERENCE CHARACTERS10 Rotor 11 winding head 12 rotor yoke 13 winding groove 14, 15 winding rod 16, 17 winding end (cranked) 18 round eyelet 19 cutout 20 counter-strip 21 extension (rotor yoke) 22 spacer body 23 retaining strip 24 bolt 25 head (bolt) 26, 27 flank 28 securing strip 29 pressing plate 30 clamping bolt 31 shank 32 recess 33 contact surface 34 wheel rim

Claims

Rotor (10) of an electric machine, in particular of a hydraulic generator, which has: a rotor yoke (12) with axial winding slots (13) arranged distributed on the outer circumference; winding bars (14, 15) of a rotor winding, which are inserted into the winding slots (13) and whose winding ends (16, 17), which emerge axially from the rotor yoke (12), form a winding head (11); a retaining device (19,..., 28) which is configured to retain the winding head (11) against centrifugal forces acting on the winding head (11), wherein the retaining device (19,..., 28) comprises a plurality of radial bolts (24) which each have heads (25) which are fixedly connected to a shank (31), wherein the retaining device (19,..., 28) has a retaining strip (23) which runs in the axial direction on the winding head (11), and the plurality of radial bolts (24) are arranged in series one behind the other in the axial direction and are configured to press the retaining strip (23) against the winding head (11) from the outside; at least one hammer-shaped recess (19) configured to receive at least one counter-strip (20) provided with threaded holes for screwing in the plurality of radial bolts (24) for fastening the bolts (24) on the outer periphery of an axial extension (21) of the rotor yoke (12) located inside the winding head (11), wherein the axial extension (21) is arranged in the winding head (11) and wherein the radial bolts (24) belonging to a respective retaining strip (23) are screwed into a common counter-strip (20); and means (28, 32, 33) for securing the plurality of radial bolts (24) against rotation, wherein the radial bolts (24) each have a recess (32) with a rectangular contact surface (33) at the inner end and the radial bolts (24) are secured against rotation by securing strips (28) which are axially inserted into the hammer-shaped recesses (19) and contact the contact surfaces (33).Rotor according to Claim 1, characterized in that the heads (25) of the radial bolts (24) are connected to the shank (31) in a materially integral manner.Rotor according to Claim 2, characterized in that the heads (25) of the radial bolts (24) are welded to the shank (31).Rotor according to Claim 1 or 2 or 3, characterized in that the heads (25) of the radial bolts (24) have an aerodynamically favourable shape.Rotor according to Claim 4, characterized in that the heads (25) of the radial bolts (24) are rounded on the upper side and have two straight flanks (26, 27) on opposite sides for tightening the bolts (24).Rotor according to claim 1, characterised in that the retaining strips (23) have rounded longitudinal edges for improving aerodynamics.Rotor (10) of an electric machine, in particular of a hydraulic generator, which has: a rotor yoke (12) with axial winding slots (13) arranged distributed on the outer circumference; winding bars (14, 15) of a rotor winding, which are inserted into the winding slots (13) and whose winding ends (16, 17), which emerge axially from the rotor yoke (12), form a winding head (11); a retaining device (19,..., 28) which is configured to retain the winding head (11) against centrifugal forces acting on the winding head (11), wherein the retaining device (19,..., 28) comprises a plurality of radial bolts (24) which each have heads (25) which are fixedly connected to a shank (31), wherein the retaining device (19,..., 28) has a securing strip (28) which is configured to secure the plurality of bolts (24) against rotation, wherein the radial bolts (24) each have a recess (32) having a rectangular contact surface (33) at the inner end, wherein the securing strip (28) is axially inserted into a hammer-shaped recess (19) formed on the outer periphery of the rotor yoke (12) and is arranged in contact against the rectangular contact surfaces (33).

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