WO2014095322A2

WO2014095322A2 - Stator of an electric machine, comprising a laminated core and construction method

Info

Publication number: WO2014095322A2
Application number: PCT/EP2013/075214
Authority: WO
Inventors: Markus Wolf; Hüdai Demirhan
Original assignee: Voith Patent Gmbh
Priority date: 2012-12-17
Filing date: 2013-12-02
Publication date: 2014-06-26
Also published as: DE102012223318A1; WO2014095322A3

Abstract

The invention relates to a stator for a large electric machine, comprising a stator frame and a laminated core consisting of a plurality of stacked metal sheets The invention is characterised in that the metal sheets are held in position relative to each other with respect to the plane running perpendicularly to the stator axis with the aid of means which are not supported directly in relation to the stator frame and in that the laminated core is held on the stator frame by at least 3 axially parallel struts, in order to absorb tangential forces.

Description

Stator with laminated core of an electrical machine and method of construction

The invention relates to a stator with laminated core for a large electric machine, e.g. a motor generator for a hydroelectric power plant. The laminated core is located in a stator frame and forms together with this the stator of the electric machine.

Stators with laminated cores for large electric machines are known from the general state of the art. In US6448686B1, e.g. executed (column 1 from line 9) that the stator of a generator generally comprises a laminated core and a stator frame. The laminated core is typically cylindrical in shape and comprises a stack of insulated steel sheets. Each plate is a segment of a circular ring and has slots on the inner diameter to accommodate the stator winding and dovetail slots on the outer diameter. The stator frame has a plurality of ledges connected thereto (e.g., by welding), each ledge having a dovetail profile to give the lamination stack the necessary structural support. During stacking of the lamination stack, each individual lamination is manually loaded into the stator frame by hanging the dovetail slots of the louvers into the corresponding dovetail profiles of the lasts of the stator frame.

After the laminated core has been completely stacked, the sheet stack is compressed by means of long clamping bolts and fixed (pressed). These bolts are arranged parallel to the axis of the stator and extend in corresponding openings of the laminated core (see for example EP2237388A1). These bolts are usually electrically isolated to prevent shorting of the superimposed sheets. This prevents that eddy currents can form in the laminated core, which would reduce the efficiency of the electric machine. Within the hollow cylinder formed by the laminated core rotates during operation of the electric machine, the rotor. It is located between the laminated core and the rotor of the so-called air gap. To ensure error-free operation, the air gap must be very homogeneous both in the axial direction and in the circumferential direction. This can only be achieved if the laminated core is stacked very accurately. This affects both the orientation of the laminated core in the axial direction and its roundness. In addition, during operation, mainly tangential forces are transmitted to the stator winding and thus to the laminated core. The known from the prior art dovetail bars make the connection of the laminated core to the stator and must absorb these forces during operation.

In the known prior art, this object is usually achieved in that the dovetail bars are attached to the stator frame with high accuracy and high effort. Some of these also have to be reworked after attachment to the stator frame (see for example DE1958296). The exact alignment of the sheets is accomplished by the attached to the stator dovetail bars alone. The clamping bolts have no function with respect to alignment of the sheets and the absorption of the tangential forces during operation and hold only the sheet stack in the axial direction together.

The known prior art has the following disadvantages. The alignment of the dovetail bars on the stator frame or the subsequent processing of the same is extremely time consuming and costly. If errors are made, it may be that if it later turns out that the dimensional accuracy of the laminated core is not present, the laminated core must be removed in whole or in part, so that the dovetail bars can be corrected. In addition, there are the costs for the time-consuming measuring technology to control the dimensional accuracy.

The inventors now proceed to ensure the dimensional accuracy of the laminated core and the inclusion of the tangential forces during operation a completely different, new and expedient way. The inventors have been guided by the inventive idea to separate said double function of the known from the prior art dovetail bars and implementing each of the two sub-functions building on each other in a new way. It was considered by the inventors, the task of ensuring the dimensional accuracy of the laminated core as a primary task. According to the invention this object is achieved by a stator having the characterizing features of claim 1. The task of receiving the tangential forces is achieved by a stator with the additional characterizing features of the dependent claim 7. Further advantageous embodiments of the stator according to the invention will become apparent from the dependent therefrom dependent claims.

The inventors have recognized that, if the sheets which are usually punched are provided with means which allow an alignment of the stacked sheets to each other in the plane perpendicular to the stator axis with sufficient accuracy, the dimensional accuracy of the entire laminated core by itself results. Neither the sheets nor the positioning means are supported against the stator frame.

The inventors have recognized that in the positioning means according to the invention, an electrical connection between superimposed sheets may result, which may lead to undesirable losses due to eddy currents. It is obvious that in order to avoid this negative effect, the positioning means themselves are made electrically insulating with respect to the sheets. The inventors have recognized, however, that if the positioning means are located on the radially outer edge of the sheets opposite the grooves for receiving the stator winding, the losses are very small and thus negligible. This can be dispensed with a complicated isolation of the positioning means. This is the case when the distance of the positioning means from the radially outer edge of the sheets is not more than 30% of the radial extent of the sheets, preferably not more than 20%. The inventors have further recognized that a sufficiently accurate dimensional accuracy of the laminated core can only be achieved if the number of positioning means per sheet is at least 2. In order not to unnecessarily increase the manufacturing cost, the inventors have recognized that as the optimum in ensuring dimensional stability and minimizing the manufacturing cost, a number of the positioning means per sheet of 2 to 4 results.

The inventors have further recognized that the positioning accuracy in the xy direction (perpendicular to the stator axis) of the sheets to each other by the positioning means according to the invention to ensure the dimensional accuracy of the laminated core requires a tolerance not greater than ± 0.02mm, preferably not greater than ± 0.01 mm is. With these measures, the inventors achieve that the laminated core meets the Maßhaltigkeitsanforderungen. According to the fixation of the laminated core as a whole in the stator frame and the transmission of tangential forces during operation on the stator frame via a number of strips. These strips are inserted into corresponding axially parallel grooves of the laminated core and attached to the stator frame either with suitable claws or welded directly to the stator frame. The solution according to the invention has several advantages over the prior art. On the one hand, clearly fewer strips are sufficient, since the laminated core in the embodiment according to the invention represents a sufficiently rigid body. In the known state of the art, each individual sheet segment must be held by at least one dovetail bar. Since the sheets are stacked in the manner of bricks, even the requirement arises that each sheet must be held by at least two dovetail grooves. The inventors have recognized that in the embodiment according to the invention, the minimum number of strips required is 3, namely for the entire laminated core (not per sheet). With a total of 3 strips in a 120 ° pitch, the laminated core can be fixed in the direction perpendicular to the axis, as a shift of Laminated core in this plane, then no longer possible. However, more than this minimum number of bars may be used as well, depending on the needs of the particular machine design. Since the strips according to the invention no longer serve to ensure the dimensional accuracy of the laminated core, both the strips and the corresponding grooves in the laminated core can be manufactured with much lower tolerance requirements. Another significant advantage of the embodiment according to the invention with a rectangular groove profile lies in the fact that each individual strip does not constitute a fixation of the laminated core in the radial direction. As a result, the laminated core, which heats up during operation, is not hindered by its thermal expansion in the radial direction. Thus, stresses in the laminated core are avoided, which have led to considerable difficulties in the past. For example, it has been observed in some cases in the past that the sheet metal layers had deformed wavy by these thermal effects.

The independent method claim describes the structure according to the invention of a stator with a stator frame and a laminated core. Further advantageous embodiments of the structure according to the invention will become apparent from the dependent therefrom dependent claims.

Further advantageous embodiments of the stator of a large electric machine according to the invention will become apparent from the embodiments, which are described below with reference to the figures.

Showing:

Figure 1 is a sheet in plan view according to the prior art; and FIGS. 2a, 2b, 2c each show a section through a part of a

laminated core according to the invention in different

Embodiments; and 3 shows a sheet according to the invention in plan view; and

Figures 4a, 4b each have a section through the junction between

Laminated core and stator frame of an inventive

Stators in plan view in various embodiments; and

Figure 5 shows a section through a stator according to the invention in

Top view; and

FIG. 6 is a flowchart for a method according to claim 12; and

FIG. 7 is a flowchart for a method according to claim 13; and

8 shows a flow chart for a method according to claim 14

Unless otherwise stated, the z-direction in this application refers to the axial direction of the stator, which coincides with the rotor axis. Perpendicular to this, the x-y plane, in which the sheets extend, spans.

In the illustration of Figure 1, a sheet 10 of a stator in plan view according to the prior art can be seen. It has rectangular recesses 1 1 for inserting the stator winding, openings 12 for performing the clamping bolts and dovetailed recesses 13 for hanging in the corresponding strips which are fixed to the stator frame.

In the illustration of FIGS. 2 a, 2 b and 2 c, a section parallel to the axis of the stator is schematically illustrated by a region of a laminated core according to the invention which contains the means for positioning the metal sheets relative to one another. The sheets are each designated 10. In Figure 2a, the positioning means are realized by pins or projections 20 of the sheets, which engage in corresponding openings 21 of the respective overlying sheets. The pins or projections can have any suitable shape in the sheet metal plane. Of course, the arrangement may as well be inverted in the vertical direction. In the example shown, the uppermost layer of the laminated core is expediently made of sheets which have no pins or projections (not shown in the figure). The pins or projections may be together with the sheet of one piece or be embedded in the sheets or glued or soldered. In the figure, the pins are markedly smaller than the corresponding openings drawn for better visibility. In reality, of course, the best possible fit must be sought in order to achieve the tolerances mentioned in claim 6.

In FIG. 2b, the positioning means are realized by inserts 30 whose extent in the direction of the stator axis (z) is not more than twice the sheet thickness, if the inserts each penetrate exactly two sheets lying one above the other. If the inserts penetrate more than two sheets, then the expansion of the inserts in the z-direction must be adjusted accordingly. The inserts in Figure 2b are located in corresponding recesses of two superimposed sheets. In the sheet plane, the inserts may have any suitable shape. It is conceivable that the deposits fulfill an additional functonality. You can e.g. be hollow and designed as cooling channels for the laminated core.

Figure 2c shows a particularly advantageous embodiment of the positioning means as rods or strips 40, which are located in the corresponding openings of the sheets. The profile of the bars or strips in sheet metal plane can be of any suitable shape. Particularly useful and inexpensive are round rods. The individual bars or strips can penetrate both in one piece the entire height of the laminated core, as itself also extend only over a portion of the height of the laminated core. In the latter case, the bars or strips can then be stacked in sections one above the other, it being expedient that not all joints of the superimposed bars or strips are at the same height or in the same sheet metal position, otherwise the positioning of the sheets relative to each other in this level is no longer guaranteed. In addition, in this embodiment, optionally provided in the upper pressure plates a recess which allows the sticks or strips in the pressed state of the laminated core over the top sheet metal layer beyond.

In addition to the embodiments of the positioning means according to the invention shown in FIGS. 2 a, 2 b and 2 c, of course, other shapes within the scope of claims 1 to 6 are also conceivable. FIG. 3 shows a sheet metal 10 according to the invention with the openings 50 for the bars or strips of the positioning means according to the embodiment of FIG. 2c with round bars. The openings are according to the invention in the region of the sheets with respect to the recesses 1 1 for inserting the stator winding. It can be seen that the distance of the openings 50 from the outer edge of the sheet (compared to the recesses 1 1) is not significantly less than 20% of the radial extent of the sheet. It is particularly advantageous if the openings 50 touch the edge of the sheets so that the openings are part of the outer sheet boundary (i.e., the openings are no longer completely surrounded by the sheet). The recess 51 serves to receive a bar, which causes the connection of the laminated core to the stator frame. This recess does not have to be provided in every sheet. However, it can also be provided several recesses 51 per sheet, depending on the design of the entire electrical machine requires. The openings 12 in turn serve to carry out the clamping bolt.

FIG. 4 a shows a horizontal section through a connection point between a laminated core 60 according to the invention and the stator frame 61 in plan view shown. The strip 62 is located in an axis-parallel groove, which are formed by the recesses 51 in the superimposed sheets. The groove has a rectangular profile (claim 9). On the stator side, the bar 62 is held by a bracket 63 which is fixed to the stator frame 61. A direct attachment of the bar 62 on the stator frame, for example by welding is also possible. It is also conceivable to attach the strips to the frame by means of a mechanism that allows the strips with the help of eg adjusting screws relative to the laminated core align and fix. In the embodiment of FIG. 4 a, it can be seen that the groove in the laminated core and the clamp 63 form a guide of the strip 62. In this guide, the bar can move in the radial direction. This is made possible by the rectangular profile of the groove. The space available for this movement is determined by the gap between the bracket and the bar and between the laminated core and the bar. Advantageously, the gaps will be designed according to the size of the expected thermal expansion of the laminated core during operation. But it can just as well be provided no gaps or only a gap on one side of the bar. Likewise, it is conceivable that the column (s) are filled with an elastic material in order to avoid possible interfering vibrations and associated noises, and nevertheless to provide the required latitude for the thermal expansion.

FIG. 4b shows the same section as FIG. 4a, but the groove in the laminated core has a profile which has the tapering from outside to inside mentioned in claim. The strip 62 then has a corresponding wedge-shaped profile. The advantage of this embodiment is that in this way the laminated core can be fastened very easily (low tolerance requirements) and thereby securely on the stator frame. This embodiment is particularly suitable when thermal deformations during operation are not to be expected. FIG. 5 shows a section in highly schematic representation through a stator according to the invention with the laminated core 60, the stator frame 61, the strips 62 and the clamps 63. It shows the holder of the Sheet metal package 60 in the stator frame 61 with only 3 strips 62. In the embodiment shown, the number of strips 62 and brackets 63 could be increased to 6 very easily, which could then be carried out correspondingly easier, since the forces distributed over more elements. The optimum will certainly depend on the respective machine requirements and the overall design. A major advantage of the solution according to the invention lies in the high flexibility and the associated increase in design flexibility.

FIG. 6 shows a flow diagram for the method of claim 12. V1 designates the manufacture of the sheets. V2 indicates the provision of the stator frame. V3 denotes the stacking of the laminated core. According to the invention, the positioning means are provided before V3. These are essentially openings in the sheets which are applied during punching or cutting of the sheets, and by further means e.g. Bolts, tenons or other inserts that engage in these openings. If these other means are firmly connected to the sheets (such as the pins or projections of Figure 2a), they will be conveniently fabricated together with the sheets. In the other case, these parts can also be manufactured at other times and places. However, they must be available together with the sheets at the time of laminating the laminated core (V3). In V3, the positioning means are used which, according to the invention, are not supported directly on the stator frame, but instead hold metal sheets lying one above the other in position relative to the alignment in the x-y plane. V4 denotes the pressing of the laminated core.

FIG. 7 shows a flow diagram for the method of claim 13. V1, V2 and V4 denote the same processes as in FIG. 6. V3a denotes the stacking and alignment of a sub-stack of sheets and V3b the stacking-up of the remaining sheets to the complete stack of sheets.

FIG. 8 shows a flow diagram for the method of claim 13. V1, V2, V3a and V3b denote the same operations as in Fig. 7. V4a refers to the insertion of strips in radially outwardly located grooves of the laminated core and attaching them to the stator frame. V4b denotes the pressing of the laminated core. The operations V4a and V4b can also be done optionally in reverse order.

Claims

claims

1 . Stator having a stator frame and a laminated core, which contains a plurality of sheets, wherein the sheets are arranged in a plurality of extending in the xy-direction sheet planes and the sheet planes are arranged one above the other in the z-direction, characterized in that positioning means are provided by means of which at least some of stacked sheets of different sheet metal levels are held in the xy direction relative to each other in position and the positioning means are not supported directly on the stator frame.

2. Stator according to claim 1, characterized in that at least one positioning means comprises at least one element which extends in the z direction at least from a first to a second of the sheets to be held in position.

3. Stator according to claim 1 or 2, characterized in that at least one positioning means is provided which comprises at least two of the stacked sheets to be held in position, each stacked at least one opening and a bolt, which each arranged one above the other openings of the stacked sheets be upheld.

4. Stator according to one of claims 1 to 3, characterized in that the distance of the positioning means from the radially outer edge of the sheets is not more than 30% of the radial extent of the sheets, preferably not more than 20%.

5. Stator according to one of claims 1 to 4, characterized in that the number of positioning means per sheet is at least 2, preferably 2 to 4.

6. Stator according to one of claims 1 to 5, characterized in that the positional tolerance of the positioning means in the x-y direction is not greater than ± 0.02mm, preferably not greater than ± 0.01 mm.

7. Stator according to one of claims 1 to 6, characterized in that the laminated core has at least three grooves on the radially outer side, which extend substantially parallel to the axis.

8. Stator according to claim 7, characterized in that the axially parallel grooves have a profile which tapers inwardly from the radially outer edge.

9. Stator according to claim 7 or 8, characterized in that the axially parallel grooves have a rectangular profile.

10. Stator according to claims 7 to 9, characterized in that there are strips in the paraxial grooves, which are fixed to the stator frame.

1 1. Stator according to one of claims 7 to 10, characterized in that the strips are held on the stator frame with brackets.

12. A method for constructing a stator with a stator frame and a laminated core, comprising the steps of: manufacturing the sheets, providing the stator frame, stacking the laminated core, pressing the laminated core, characterized in that before the stacking of the laminated core positioning means are provided with which the Sheet metal can be held in position relative to each other in the xy direction, and that when stacking the laminated core, these positioning means are used free of immediate support on the stator frame.

13. The method according to claim 12, characterized in that in the stator frame, first a partial stack of at least two layers of sheets is stacked, its position perpendicular to the axis relative to Stator frame is aligned with suitable means. Thereafter, the laminated core is completely stacked and pressed.

Method according to one of claims 12 or 13, characterized in that prior to or after the pressing of the laminated core strips in radially outwardly located grooves of the laminated core are inserted and these are fixed before or after pressing on the stator frame.