GB2033670A - Supporting stator end windings of electric machine - Google Patents

Abstract

An arrangement for supporting stator end windings of an electric machine comprises a rigid inner ring 8 and an outer ring 12, both rings being made of electrically insulating material. The inner ring 8 is mounted coaxially with the inner bore of the stator core 1 and supports the end portions of a stator bar winding, and the outer ring 12 externally embraces these end portions. Both rings are mounted and secured together along the head portions 5 of end windings, the inner ring 8 being attached to Z-shaped members 15 arranged adjacent to the end portions and preventing the inner ring from axial displacements relative to the end portions. This is achieved due to the fact that the projection 18 of each Z-shaped member, facing the end surface of the core 1, is positioned between winding bars at their outlet from core slots 2, and is rigidly connected with a bracket 20 movably associated with a clamping plate 6 of the core 1 and attached to the outer ring 12. Thus, the arrangement for supporting the end windings and the end windings themselves makes up a rigid integral unit resistive to the action of vibrations arising during operation of the electric machine and axially displacable under thermal expansion of the winding bars. <IMAGE>

Description

SPECIFICATION Arrangement for supporting stator end windings of electric machine The present invention relates to electric machines, and more particularly to arrangements for supporting stator end windings of an electric machine.

The present invention can most advantageously be used in powerful and superpowerful turbogenerators wherein stator electric windings experience considerable electrodynamic loads and thermal effects during machine operation.

According to the present invention, there is proposed an arrangement for supporting stator end windings of an electric machine, comprising an inner ring and an outer ring secured to each other and made of electroinsulating material, the inner ring being mounted coaxially with the bore of a stator core and supporting stator and windings, and the outer ring externally embracing the end windings and being movably connected with the stator core, wherein, according to the invention, the inner ring is secured to the outer ring substantially along a portion of the end windings heads and attached to Zshaped members adjoining to end windings and preventing the inner ring from axial displacements relative to the end windings by means of projections, the projection of each Z-shaped member, facing an end surface of the core, being positioned between winding bars at the outlet of said bars from core slots and rigidly connected with one of the brackets movably connected with a core clamping plate and secured to the outer ring.

The advantage of the proposed arrangement for supporting stator end windings of an electric machine resides in that the inner and outer supporting rings are mounted essentially along the portion of the end windings heads, i.e. in the zone of maximum level of end winding vibrations, thus considerably decreasing the level of end winding vibrations which appear under the influence of electrodynamic loads during operation of an electric machine.

Moreover, in the construction of the proposed arrangement slot and end portions of stator winding bars are movably secured relative to the stator core and not connected with the stator frame, thus providing the possibility of displacement of end windings during their thermal extension and considerably decreasing the probability of their exposure to stator frame vibrations.

It is advisable that the inner ring be attached to the outer ring by means of pins and gaskets made from moulding and hardening material, disposed between these rings and stator end windings.

Itis also advisablethatthe projection of the Z-shaped member, facing the stator core end, should be secured to the bracket by pins, the bracket being attached to the outer ring.

Such a connection of said elements of the arrangement provides ease of assembling and ensures a reliable operation of the proposed arrangement for supporting end windings.

Moreover the pins should be made of nonmagnetic material.

The pins can be made of nonmagnetic steel with an electrically insulating coating.

The pins can be made also of fiberglass material.

The use of these materials prevents from the induction of eddy currents in the pins and their sub sequent heating due to these currents.

Furtheron the arrangement for supporting stator end windings of an electric machine is explained by a detailed description of its embodiment with refer ence to the accompanying drawing, which illustrates a longitudinal sectional view of a part of the stator of an electric machine with an arrangement for support ing stator end windings, according to the invention.

Referring now to the drawing it will be seen that in a stator core of an electric machine, specifically, in the core I of a powerful turbogenerator, made up of magnetoconductive stacks, there are slots, such as the slot 2 wherein the stator winding is laid, said winding having end portions of an upper3 and a lower 4 (according to the drawing) winding bars the connection of which forms a head 5. On both end surfaces of the I there are elements mounted to pro vide clamping of the magnetoconductive stacks in an axial direction and comprising at the end shown in the drawing a clamping plate 6 and a coupling pin 7.

The arrangement for supporting stator end wind ing, according to the invention, comprises an inner ring 8 having a large cross-sectional area, made of electrically insulating material, and having a suffi ciently high value of stiffness dictated by considera tions given hereinbelow. The inner ring 8 is mounted coaxially with the bore of the core I and at a distance from the end surface of the latter, that distance being determined by the length of the end windings, and has a cylindrical inner surface 9 which diameter is substantially equal to that of the bore of the core I, and an outer surface comprising a conical portion 10 and a cylindrical portion 11.The end winding are supported by the inner ring 8 in such a way that an inclined part of the end portion of the upper bar 3 is adjacent to the conical part 10, and the head 5 is adjacent to the cylindrical part II of the outer surface of that ring.

Externally to the stator end windings and embrac ing them there is mounted an outer ring 12 having a small cross-section area as compared to the cross sectional area of the inner ring 8. The outer ring 12 adjoins with its inner surface the head 5, pressing the end portions against the inner ring 8. The outer ring 12 and the inner ring 8 are attached together by means of coupling pins 13.Therewith, to attain tight connection of the rings 8 and 12 with the end wind ings, between the end portion and the head 5 of the upper bar 3 and the outer surface 10, 11 of the inner ring 8, facing said end portion, and between the head 5 of the end portion of the lower bar 4 and an innersurafce of the outer ring 12, facing said end portion, there is disposed a gasket 14 made from moulding and hardening material possessing adhe sive properties. Said material provides reliable seal ing of assembling clearance between end portions and the inner ring 8 and the outer ring 12, completely filling inherent non-uniformity of that clearance, and increases the rigidity of attachment of these rings to the end windings.

The inner ring 8 is secured to axially positioned Z-shaped members which prevent that ring from axial displacements relative to the end portions, of which members is shown in the drawing of Z-shaped member 15. A projection 16 of the Z-shaped member 15 is secured to the inner ring 8 by means of a pin 17, and the projection 18 of that member is positioned between upper bars 3 of the stator winding at their outlet from the slot 2 of the core I. The projection 18 of the member 15 has a configuration corresponding to the configuration of the portions of the upper bars 3, to which it is adjacent.

The outer ring 12 by means of a stud 19 is secured to bracket 20 made of electrically insulating material and movably connected with a chute-shaped yoke 21 accommodating that bracket and made of nonmagnetic steel, said yoke being attached to the clamping plate 6 thus providing the possibility of axial displacement of end windings along with the inner 8 and outer 12 rings relative to the stator cores.

The Z-shaped member 15 is rigidly connected with the bracket 20 due to the fact that the projection 18 of that member is secured by means of a pin 22 to an end 23 of the bracket 20, located underneath that projection.

The end portions of the upper and lower bars 3,4 of the stator winding are laid onto bandage rings 24 supported by the bracket 20 and joined together by means of cord bindings 25. Between the bandage rings 24 are positioned separating spacers 26 which, in turn, are secured to the bracket 20 by means of cords 27 disposed in the openings formed in that bracket. The chute-shaped yoke 21 is rigidly fixed to the clamping plate 6 by means of pins 28. Each of the pins 13, 17, 22 and 28 is provided with nuts 29,30,31 and 32, respectively.

The operation of the proposed arrangement for supporting stator end windings of an electric machine is as follows.

During operation of a turbogenerator, the stator end windings are exposed, as mentioned hereinabove, to variable electrodynamic loads tending to cause end winding vibrations primarily in radial and tangential directions. However, in the proposed arrangement for supporting end windings the level of vibrations is considerably decreased due to the sufficent rigidity of the construction, primarily determined by a rigid connection of the elements included into the arrangement. Therewith is formed a closed chain of rigidly secured element, comprising: inner ring 8 - Z-shaped member 15 with the projection 18 - coupling pin 22- electroinsulating brac-- ket bracket 20 - outer ring 12 - coupling pins 13 with the gaskets 14 made from moulding and hardening material, laid over the head 5 of end windings - inner ring 8.That chain provides the integrity of the end windings and their supporting elements, which exhibit resistance to forces acting upon them, as a single unit.

An appreciable contribution to the rigidity of the entire construction of the proposed arrangement is the rigidity of the inner ring 8 the operation of which is based on the following. The arrangement of end windings with the simplest supporting elements (bandage rings, cord bindings etc), being joined as a single unit has its inherent specified rigidity C, reduced mass M, and a natural vibration frequency expressed by

Under the influence of variable electrodynamic forces the magnitude of vibration A of such system will be determined by the amount of the disturbing force R, the value of rigidity C, the degree of tuning out from the forcing oscillation frequency w, and a damping factor , integrated into the following expression

As it was found, the natural rigidity C of the stator end windings cannot be increased over a certain value defined by the geometric dimensions of end windings and physical properties of the materials used for their support. Along with that, the magnitude of the frequency of end winding natural vibrations in many cases approximates the frequency of forcing vibrations (100 or 120 Hz). In that case the magnitude of the vibration A increases along with the increase of the disturbing force F. To ensure a considerable decrease of the magnitude of the vibration A, the inner ring 8 should have natural rigidity C1 largerthan the rigidity C of the end windings without that ring.Therewith the decrease of the magnitude of the vibration A is due to the increase of the total rigidity, determined by C and C1 as well as due to the change in the value of the natural oscillation frequency of the entire system caused by the change of its total rigidity.

The increase of rigidity of the inner ring 8 in the arrangement for supporting end windings, according to the invention, is achieved due to the choice of the material used in the manufacture of the inner ring 8 with rather high modulus of elasticity, and due to the choice of cross-sectional area of that ring commensurable with the cross sectional area of the end windings. The last mentioned measure is obtained, in turn, by means of a suitable choice of a minimum inner diameter of the inner ring 8, possible forthe given type aturbogenerator, and by the choice of the optimum thickness of that ring owing to its mounting preferably at the portion of the heads 5 of end windings.

More precisely, the geometrical dimensions of the inner ring 8 of the proposed arrangement of end windings used in the stator of a two pole turbogenerator, are chosen proceeding from the following considerations. To obtain the required rigidity properly correlated to the total rigidity of the entire supporting system that ring should have its main frequency of natural bending oscillations exceeding the frequency of the action of the disturbing force in no less than 25 percent.As, for example, in a tur bogenerator with an operating frequency of 50 Hz and, respectively, with a forcing vibration frequency of 100 Hz, the frequency f, of natural vibrations of the inner ring 8 is determined by the relationship

where h - ring thickness Rm - average radius of the ring K 4 7 104 cm/sec - coefficient that primarily depends upon the shape and material of the ring, and is chosen to meet the condition that the modulus of elasticity is E=2.8 105 kg/cm2.

Thus, the mounting of the inner ring 8, having an enlarged cross section area and, consequently, an increased mass, along the heads 5 of the end windings, changes also the natural vibration frequency of the entire arrangement for supporting end windings, which causes consequent decrease of the magnitude of the vibration A. That provides the possibility of suitable variation of the natural oscillation frequency of the end winding supporting system, and, consequently, of the system vibration level, by means of changing the location of the inner ring 8 on end windings or by predetermining the value of the cross section area.

During variation of the length of the slot winding portion due to its temperature changes, end windings combined with the inner ring 8 and the outer ring 12 will be freely displacing in an axial direction relative to the stator core 1 due to the fact that the bracket 20, secured to the outer ring 12 and rigidly connected with the inner ring 8 by means of the Z-shaped member 15, has the possibility of displacement in the chute-shaped yoke 21 attached to the clamping plate 6 of the core 1, said yoke being stationary in that case. Similarly, during the thermal explansion of the stator core 1, the movement of the clamping plate 6 will not influence the position of end windings, since the chute-shaped yoke 21 is freely displacing relative to the bracket 20 which is stationary in that case.

In the proposed arrangement for supporting the stator end windings the inner ring 8, the outer ring 12, the Z-shaped members 15, and the brackets 20 are made of electrically insulating material, such as fiberglass material based on epoxy resins, and the coupling pins 13,22 are made of nonmagnetic material, such as nonmagnetic steel with an electrically insulating coating or fiberglass material mentioned above.

The proposed arrangement for supporting stator end windings of an electric machine provides: - possibility of choice of the required rigidity of the inner ring, and also - possibility of altering a natural vibration frequency relative to a forcing vibration frequency, and thus finally - essential increase of end winding support reliability due to a considerable decrease of the level of maximum vibrations appearing during operation of an electric machine, by means of mounting a rigid inner ring into the zone of the end winding heads.

The elements comprising the arrangement are easy in fabrication and its construction is convenient in assembling and in the maintenance of an electric machine.

Claims (7)

1. An arrangement for supporting stator end windings of an electric machine including a stator core having slots arranged around the periphery thereof, an inner bore, clamping plates on end surface, and a bar winding laid into the slots and having end portions with heads, which arrangement comprises an inner ring made of electrically insulating material, mounted coaxially with the inner bore of the core, and supporting the end portions; an outer ring made of electrically insulating material and externally embracing the end portions; the inner ring being secured to the outer ring substantially along the heads of the end portions; a plurality of Z-shaped members secured to the inner ring and adjoining the end portions; the projection of each ofthe Z-shaped members, facing the end surface of the core, being positioned between winding bars at their outlet from the core slots, and preventing the inner ring from axial displacements relative to end portions; a plurality of brackets, each bracket being movably connected with the clamping plates and having one end attached to the outer ring and the other end attached to the projection of one of the Z-shaped members.

2. An arrangementforsupporting statorend windings of an electric machine as claimed in Claim 1, wherein the inner ring is secured to the outer ring by means of pins and gaskets made from moulding and hardening material, disposed between said rings and the stator end windings.

3. An arrangementforsupporting statorend windings of an electric machine as claimed in any of the Claims 1 or 2, wherein the projection of the Z-shaped member, facing the end surface of the stator core, is secured to the bracket by means of pins, said bracket being attached to the outer ring.

4. An arrangementforsupporting statorend windings of an electric machine as claimed in any of the Claims 2 or 3, wherein the pins are made of nonmagnetic material.

5. An arrangement for supporting stator end windings of an electric machine as claimed in Claim 4, wherein the pins are made of nonmagnetic steel and have a insulating coating.

6. An arrangementforsupporting statorend windings of an electric machine as claimed in Claim 4, wherein the pins are made of fiberglass material.

7. An arrangementforsupporting statorend windings of an electric machine, as described hereinabove with reference to the accompanying drawing.