GB2392013A

GB2392013A - Method of joining stator segments and of mounting stator to a suspension structure

Info

Publication number: GB2392013A
Application number: GB0306049A
Authority: GB
Inventors: Leit Jonson; Jonas Holmgreen
Original assignee: Alstom SA
Current assignee: Alstom SA
Priority date: 2002-03-26
Filing date: 2003-03-18
Publication date: 2004-02-18
Also published as: SE0200928D0; GB0306049D0

Abstract

A generator stator core 100 comprises layered sheet segments 400, where each sheet segment in one layer overlaps two sheet segments in an adjacent layer. The sheet segments are securely fixed in radial and tangential directions by dovetail connections 402 comprising wedge-shaped slots 504 running axially at the outer periphery of the stator core. Rails 502 are fitted into slots 504 and are clamped radially outwards against the wedging action of the slots 504 by springs 506. A tool (fig.5c), used in the installing of the springs 506, acts on spring straining elements 510a,b to bring the springs 506 to their strained position (fig.5b).

Description

AN ARRANGEMENT AND METHOD FOR JOINING TOGETHER SHEET

SEGMENTS OF A STATOR CORE.

TECHNICAL FIELD

s The present invention relates generally to suspension of an electric generator. In particular, the invention relates to an arrangement and method for joining together sheet segments in a stator core of the electric generator, and for joining the stator core to a suspension 10 structure.

BACKGROUND OF THE INVENTION AND PRIOR ART

In electric generators, energy is converted between a mechanical state and an electrical state by means of a 1s generated magnetic field and windings in a rotating rotor

and a stationary stator, in a well-known manner. The stator normally comprises a tube-shaped stator core which interacts with the generated magnetic field, as the rotor rotates

therein. The stator core is therefore subjected to radial 20 forces from the magnetic field during operation, resulting;

in an oscillating elastic deformation to the core. These oscillations give rise to vibrations which are transferred to the suspension structure of the stator.

Typically, a stator core is built up from metal 25 sheets formed as sheet segments, which are arranged side by side around the rotor, and being axially packed in plural layers. This is a practical way of building a stator core of considerable size and weight, in particular for large generators such as power plant generators, which is well 3() known in the art. Each sheet segment in one layer overlaps two sheet segments in an adjacent layer, and the whole sheet package is axially clamped together as a rigid structure by

means of axially extending clamping bolts or the like. The sheet layers must then be positioned and aligned with high accuracy, which in previous solutions can be obtained by using relatively complex supporting and guiding arrangements 5 in the frame. The core is then assembled directly in the frame, and after the sheet segments have been positioned and oriented correctly, the bolts are tightened.

Since the stator core is subjected to considerable static and dynamic forces, it is important that the sheet 10 segments are clamped together axially, and that the core is securely fixed radially and tangentially to a stator frame, ensuring that no relative displacement of segments in adjacent layers occurs during operation.

It is however a problem that a stator core, built Is up from plural sheet layers being clamped together axially by bolts or the like, may not be held together properly.

Thus, there is a risk that sheet segments may be mutually displaced during operation of the generator, resulting in; wear and a degradation of the electric performance.

2() Moreover, it is a problem to securely suspend the stator; core on a foundation or the like in a way that avoids mutual displacement of sheet segments. The clamping force exerted by axial bolts or the like must then be sufficiently great to provide necessary friction forces between the sheet 2s segments in adjacent layers, ensuring that no such displacement occurs. It is also desirable to facilitate the assembly of a stator core.

Furthermore, previous solutions require relatively complex and expensive separate supporting elements, e.g., 30 arranged around the outer periphery of the stator core, which must be designed to withstand the vibrations and static loads involved during operation. During assembly, the

core must be built up when being supported by a suspension frame of the generator, which is a difficult procedure.

SUMMARY OF THE INVENTION

5 the object of the present invention is to reduce or eliminate the problems outlined above. This object and others are obtained by providing a secure and reliable arrangement for holding the sheet package of a stator core tightly together, and for enabling an easy assembly 10 procedure. The inventive arrangement is relatively simple in a construction, and is also used for suspending the core on a foundation or the like.

The invention thus provides an arrangement and = method for joining together sheet segments in a stator core; -

15 of an electric generator, wherein the stator core is built up from metal sheets formed as sheet segments being arranged -

in plural adjacent layers, such that each sheet segment in one layer overlaps two sheet segments in an adjacent layer.

The sheet segments are jointed and held together in mutually 20 fixed positions by a number of dovetail connections. Some axially clamping device, such as bolts, is of course still necessary in order to hold the sheet package together axially. Each dovetail connection comprises a wedge-shaped 2s elongated rail being fitted into a correspondingly wedge shaped elongated slot, running axially at the outer periphery of the stator core. The dovetail connection further comprises means for clamping the rail in a radial -

directlon outwards against the wedging action of the 30 dovetail profile of the slot.

In a method of assembling a stator core, the sheet segments are positioned such that wedge-shaped recesses in

the sheet segments are aligned to form wedge-shaped elongated slots, having a dovetail profile and extending axially at the outer periphery of the sheet package.

Elongated rails are fitted into the slots to form a 5 plurality of dovetail connections for joining and fixing the sheet segments in radial and tangential directions. The rails are then clamped radially outwards against the wedging action of the dovetail profile of the slots.

The present invention provides a relatively simple 10 and reliable solution for ensuring that the sheet plates are not mutually displaced in radial and tangential directions without relying on sufficient friction forces created by axially clamping forces. The invention also enables easy assembly of the core without requiring suspension and 5 support in a frame.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described in more, detail and with reference to the accompanying drawings, in 20 which:;' - Fig. la is a schematic end view of a sheet package of a previously known stator core.

- Fig. lb is a schematic perspective view of the sheet package of Fig. la.

25 - Fig. 2 is a detailed view of a stator core.

- Fig. 3 is a detailed view of a dovetail connection according to one embodiment.

- Fig. 4 is a schematic end view of a suspended stator core. 30 - Fig's 5a-c illustrate a dovetail connection according to another embodiment.

( Fig's 6a-c illustrate a dovetail connection according to yet another embodiment.

DESCRIPTION OF PREFERRED EMBODIMENTS

5 Fig's la and lb illustrate a previously known -

stator core of an electric generator. The stator core 100 is built up from metal sheets formed as sheet segments 102, which are placed side by side around the rotary centre, leaving a central hole 104 in which a rotor, not shown, can lo rotate. The sheet segments 102 are arranged in plural adjacent layers 106, as illustrated in Fig. lb, forming an axially extending tube-like sheet package constituting the stator core 100. -

The sheet segments 102 in one layer are located in 15 a circumferentially overlapping fashion in relation to the sheet segments in the next and previous layers, such that each sheet segment in one layer overlaps two sheet segments i in an adjacent layer, as indicated by dashed lines in Fig la. 20 The whole sheet package is held together axially by means of plural axially extending tightened bolts 108, of which only one is shown in the figures. The clamping force exerted by the bolts 108 must then be sufficiently great to provide necessary friction forces between the sheet segments 2s in adjacent layers, ensuring that no mutual displacement occurs between the sheet segments during operation.

Furthermore, supporting elements, not shown, are typically -

arranged around the outer periphery of the stator core in -

order to hold the sheet package together during operation 31) and to guide the sheets during assembly.

he present invention presents a relatively simple solution for ensuring that the sheet plates are not mutually _n _

displaced in radial and tangential directions, without -

relying on sufficient friction forces between the sheets in addition to a supporting structure.

Fig. 2 illustrates a detailed part of a stator i core comprising a plate package as described above, where a -

sheet segment 200 in an upper layer partly overlaps two sheet segments 202a, 202b in an underlying layer, as indicated with dashed lines. Axially extending clamping bolts 203 are used to hold the entire plate package together 10 axially However, the present solution does not rely on sufficient friction forces created by the tightened bolts.

The three sheet segments 200, 202a,b are instead securely fixed in radial and tangential directions by means -

of dovetail connections 204, which will be described in more; 5 detai1 below. The dovetail connections 204 can also be utilized for suspending the stator core to a foundation, not shown. A selected number of dovetail connections 204 can i thus be fixed to a suspension structure. Two adjacent dovetail connections 204 may for example be fixed to a 20 flange or lug device 206, e.g., by means of welding. The lug device 206 is used for supporting a yoke 208 which is suspended on a foundation, not shown. The suspension arrangement may be advantageously designed in accordance with applicant's co-pending patent application "An apparatus 2s and method for suspending a stator core of an electric generator", no. Fig. 3 illustrates an exemplary dovetail -

connection 300 in more detail, as seen in an axial direction. The dovetail connection 300 comprises a elongated lo rail 302 having a wedge- shaped cross-section. the rail 302 is fitted into a correspondingly wedge- shaped elongated slot 304, running axially at the outer periphery of the stator

core. The dovetail connection 300 further comprises means for clamping the rail 302 in a radial direction outwards against the wedging action of the dovetail profile of the slot 304. In the example of Fig. 3, the rail clamping means 5 is a pressurised flat tube 306 pressing the rail radially outwards. According to a clamping technique previously known per se, a flat copper tube may be filled with an epoxy resin under pressure to expand the tube, which then presses the 10 rail 302 radially outwards. The epoxy resin is then solidified to provide a maintained force against the rail 302. However, other methods for pressing the rail 302 radially outwards may also be used, which will be exemplified below. The present invention is thus not limited 5 to any particular method of clamping the rail 302.

Fig. 4 is a view of a stator core lOO, where each sheet layer includes a number of sheet segments 400 overlapping sheet segments in adjacent layers, as in Fig's la, lb. Each sheet segment 400 comprises two wedgeshaped 20 recesses which are axially aligned in the sheet package to form elongated slots into which rails are fixed, as described above. In this way, the sheet segments are tightly fixed in radial and tangential directions.

Thus, in each sheet segment 400, a dovetail 25 connection 402a on one side connects to overlapped sheet segments on that side in adjacent layers above and below, and a dovetail connection 402b on the opposite side connects to overlapped sheet segments on that side in the adjacent layers. In this way, the dovetail connections 402 link 30 segments to segments in a chained fashion, such that the whole sheet package is tightly held together in a play-free manner.

As illustrated in Fig. 4, the entire sheet package of the stator core 100 may be suspended to a foundation, not shown, by fixing connections between a suspension structure and a selected number of the rails in the dovetail 5 connections 402. In this example, four dovetail connections 402 in adjacent rails are fixed to a lug member 206, of which there are four, making a total of sixteen dovetail connections 402 being used for suspension. The remaining eight dovetail connections 402 are unused for suspension but 1() contribute to transfer dynamic and static forces to the fixing connections. Any number of the dovetail connections may of course be used for suspension of the stator core 100 to a foundation, within the scope of the invention.

By this inventive arrangement, forces and loads on IS the stator core will be evenly distributed and taken by the wedges of the dovetail connections. In this way, static loads, vibrations and shock pulses, are satisfactorily withstanded, which may occur during operation of the.

electric machine.; 20 During assembly of the core, the recesses of each -

sheet segment may be aligned by using elongated guiding bars or the like, not shown, for guiding the sheets into a correct orientation. Such guiding bars may thus be placed resting axially in the slots formed by previously added 25 layers. As a new layer of sheets is added, the recesses are -

radially and tangentially guided by the bars for positioning the sheets correctly. Any number of guiding bars may be used in this way, distributed around the periphery of the core.

the guiding bars may preferably have circular cross 30 S actions. -

As mentioned above in connection with Fig. 3, the rail 302 may be clamped against the wedging action of the

( dovetail profile of the slot 304 by different means. Two alternative and inventive embodiments will now be described with reference to Fig's 5a-c and 6a-c, respectively.

Fig's 5a and 5b show two different stages in a 5 process for assembling a dovetail connection 500, as seen in an axial direction. A rail 502 is fitted into a correspondingly wedge-shaped elongated slot 504, as in the! example of Fig. 3. Fig. 5c shows the dovetail connection 500 in a radial view, or in the view AA of Fig. 5b, during the assembly process.

A rail clamping device comprises a spring sheet! 506 which is slightly curved or bent in a circumferential: direction when being unstrained, having its convex side facing the bottom surface of the rail 502, as shown in Fig. -

5 5a. The rail clamping device further comprises two spring straining elements SlOa, 510b in the form of elongated strips or bars, being positioned at the concave side of the -

curved spring sheet 506. ' The dovetail connection 500 can be assembled in 20 the following way. Firstly, the sheet segments in all layers are positioned with its two wedge-shaped recesses aligned to form axially extending elongated slots, such as the slot 504. Then, the rail 502 is inserted axially from one end of: the slot 504, into an unstrained radial position in the 25 slot Next, the spring sheet 506 is inserted into the slot -

504 under the rail 502. The two spring straining elements 510a, 510b are also inserted into unstrained middle positions under the rail 502, as shown in Fig. 5a.

Next, with reference to Fig. 5c, a relatively 30 narrow spring straining tool 512, positioned between the two spring straining elements SlOa, 510b and, is moved in the axial direction, as indicated by an arrow in Fig. 5c. The

( tool 512 comprises an enlarged or thicker sliding tail portion 514 which forces the two spring straining elements 510a, 510b apart sideways into spring straining positions, i.e., from the middle area of the spring sheet 506, as shown s in Fig. 5a, to its edge areas, as shown in Fig. 5b. In these spring straining positions, the elements 510a, 510b rest on -

the slot bottom and press the edges of the spring sheet 506 towards the bottom surface of the rail 502, wherein the -

curved spring sheet is straightened and exerts a maintained 10 radial force on the rail, as indicated with a middle arrow -

in Fig. 5b. 'the rail is thus clamped against the wedging action of the dovetail profile of the slot 504, thereby providing a tight dovetail connection fixing the sheet segments. 5 The rail 502 may comprise a bottom recess 508 for receiving the spring sheet 506. Further, the bottom of the slot 504 may comprise two opposite small locking shoulders 516 over which the two spring straining elements 510a, Slob slide during assembly, preventing that they slide back 20 towards the unstrained middle position shown in Fig. Sa -

during operation.

Fig's 6a-c illustrate a modification of the dovetail connection shown in Fig's 5a-c, and the same -

reference numbers are used for corresponding details. As in -

25 Fig's Sa-c, a rail clamping device comprises a spring sheet -

600 being slightly curved or bent in a circumferential direction when unstrained, and having its convex side facing the bottom surface of the rail 502. The rail clamping device is modified such that the spring sheet 600 is provided with 3() a protruding rim 602 extending radially inwards along one side and resting at the bottom of the slot 504. The rail clamping device further comprises a single spring straining

element 604 in the form of an elongated strip or bar. The spring straining element 604 is forced into a spring straining position acting at the edge of the spring sheet 600 opposite to the rim 602, as shown in Fig. 6a.

5 An elongated spring straining tool 606 may be used for forcing the spring straining element 604 away from the -

rim 602 into the spring straining position, comprising at least two mutually displaced rolls or wheels 608. Fig's 6b -

and 6c illustrate an embodiment with three such rolls 608.

10 'I'he spring straining tool is inserted between the spring -

straining element 604 and the rim 602, and is used for assembling the dovetail connection 500 in a similar manner as described in connection with Fig's 5a-c.

The spring straining tool 512 or 606 comprises -

5 generally an enlarged tail portion, such as the thicker sliding tail portion 514 or the at least two mutually -

displaced rolls or wheels 608, as described above, for -

assembling any of the two described dovetail connections of Fig's 5a-c, 6a-c.

20 The spring straining element 604 may further be -

slightly wedge-shaped, as shown in Fig. 6a, to facilitate its sliding movement sideways during assembly. 'I'he bottom of ' ' the slot 504 may further be provided with a shoulder 610 for -

retaining the rim 602 of the spring sheet 600 as the 25 opposite edge is pressed against the bottom surface of the -

rail 502.

By using the invention, the sheet package of a stator core is held tightly together as a rigid structure, which can be suspended on a foundation or the like in a 30 simple and secure manner. Mutual displacement is also prevented between sheet segments. Moreover, the sheet

package can be assembled without requiring suspension and guiding by means of supporting elements in a frame.

While the invention has been described with reference to specific exemplary embodiments, the description

5 is only intended to illustrate the inventive concept and should not be taken as limiting the scope of the invention.

Various alternatives, modifications and equivalents may be used without departing from the spirit of the invention, which is defined by the appended claims.

. . .. ...DTD:

Claims

1. An arrangement for joining together sheet segments in a stator core (lOO) of an electric generator, wherein the s stator core its built up from metal sheets formed as sheet segments being arranged in plural adjacent layers of a sheet package, such that each sheet segment (200) in one layer overlaps two sheet segments (202a,b) in an adjacent layer, characterized by a plurality of dovetail 0 connections (204, 300, 402, 500) for joining and fixing the sheet segments in radial and tangential directions, wherein each dovetail connection comprises: - a wedge-shaped elongated rail (302, 502) being fitted into a correspondingly wedgeshaped elongated slot (304, 15 504) having a dovetail profile and running axially at the outer periphery of the stator core, and - means for clamping the rail radially outwards against the wedging action of the dovetail profile of the slot.

20

2. An arrangement according to claim l, characterized in that the rail clamping means comprises a pressurized flat tube (306) pressing the rail (302) radially outwards.

3. An arrangement according to claim l, characterized in 25 that the rail clamping means comprises a spring sheet (S06, 600) being slightly curved or bent in a circumferential direction when unstrained, having its convex side facing the bottom surface of the rail (502), and pressing the rail radially outwards when strained.

3()

4. An arrangement according to claim 3, characterized in that the rail clamping means further comprises two spring

straining elements (510a,b) in the form of elongated -

strips or bars, acting on the concave side of the curved spring sheet at opposite edges thereof.

5 5. An arrangement according to claim 4, characterized in -

that the bottom of the slot (504) is provided with two opposite small locking shoulders (516), preventing that the two spring straining elements (510a,b) slide back towards unstrained middle positions during operation.

6. An arrangement according to claim 3, characterized in that the spring sheet (600) is provided with a protruding rim (602) extending radially inwards along one side and resting at the bottom of the slot (504), and that the 15 rail clamping means further comprises a single spring straining element (604) in the form of an elongated strip -

or bar, acting on the concave side of the curved spring; sheet (600) at the edge thereof opposite to the rim (602).

20 '

7. An arrangement according to claim 6, characterized in: that the bottom of the slot (504) is provided with a shoulder (610) for retaining the rim (602) of the spring sheet (600) as the opposite edge is pressed against the 25 bottom surface of the rail (502). 3

8. An arrangement according to any of claims 1 - 7, characterized in that each sheet segment (200, 202a,b, 400) comprises two wedge-shaped recesses which are 30 axially aligned in the sheet package to form elongated dovetail slots into which the rails are fixed, forming -

the dovetail connections (204, 402).

9. An arrangement according to any of claims 1 - 8, characterized in that a selected number of the dovetail connections (209, 402) are used for suspension of the 5 stator core to a foundation.

10. An arrangement according to claim 9, characterized in that the rails of the selected dovetail connections are connected to a suspension structure (206, 208).

11. A method of assembling a stator core (100) of an electric generator, wherein the stator core is built up from metal sheets formed as sheet segments being arranged in plural adjacent layers of a sheet package, such that 15 each sheet segment (200) in one layer overlaps two sheet segments (202a,b) in an adjacent layer, characterized by the following steps:: positioning the sheet segments such that wedge-shaped recesses in the sheet segments are aligned to form wedge 20 shaped elongated slots (304, 504), having a dovetail profile and extending axially at the outer periphery of-

the sheet package,;;; - fitting elongated rails (302, 502) into the slots to form a plurality of dovetail connections (204, 300, 402, 2s 500) for joining and fixing the sheet segments in radial and tangential directions, and - clamping the rails radially outwards against the wedging action of the dovetail profile of the slots (304, 504).

12. A method according to claim 11, characterized in that the rails are clamped radially outwards by the following substeps: - inserting a spring sheet (506) into each slot (504), 5 the spring sheet being slightly curved or bent in a circumferential direction when unstrained and having its convex side facing the bottom surface of the rail (502), - inserting two spring straining elements (510a,b) in the form of elongated strips or bars into unstrained lo positions under the spring sheet (506), - inserting a spring straining tool (512, 606) between the two spring straining elements, and - forcing the two spring straining elements apart sideways into spring straining positions by moving the IS spring straining tool in the axial direction, thereby pressing the rail (502) radially outwards.

13. A method according to claim 12, characterized in that the two spring straining elements are forced apart 20 sideways into their spring straining positions by an enlarged tail portion (514, 608) of the spring straining tool (512, 606.;;

14. A method according to claim 11, characterized in that 25 the rails are clamped radially outwards by the following substeps: - inserting a spring sheet (600) into each slot (504), being slightly curved or bent in a circumferential direction when unstrained, having its convex side facing so the bottom surface of the rail, and being provided with a protruding rim (602) extending radially inwards along one side and resting at the bottom of the slot,

- inserting a single spring straining element (604) in the form of elongated strip or bar into an unstrained position under the spring sheet (600), - inserting a spring straining tool (512, 606) between S the spring straining element (604) and the rim (602), and - forcing the single spring straining element (604): sideways away from the rim (602) into a spring straining position by moving the spring straining tool in the axial direction, thereby pressing the rail (502) radially 10 outwards.

15. A method according to any of claims ll - 14, characterized in that a spring straining tool (512, 606) is used comprising a thicker sliding tail portion (514) 15 or at least two mutually displaced rolls or wheels (608).