WO2009081430A2

WO2009081430A2 - Stator bar for an electrical machine, and electrical machine comprising said stator bar

Info

Publication number: WO2009081430A2
Application number: PCT/IT2007/000908
Authority: WO
Inventors: Rodolfo Exner; Alessandro Oldrati; Giorgio Vercelli
Original assignee: Ansaldo Energia S.P.A.
Priority date: 2007-12-21
Filing date: 2007-12-21
Publication date: 2009-07-02
Also published as: EP2232677A2; WO2009081430A3; WO2009081430A8

Abstract

A stator bar for an electrical machine (1), having two opposed ends (7), is provided with a main body (10) defined by: a plurality of substantially parallel elongated conductive elements (15) stacked on columns (16) that are set alongside one another, in which each elongated conductive element (15) extends along a path having a plurality of transpositions (20) from one column (16) to the other; and a filling element (18) adapted for filling empty spaces of the main body (10) generated by the transpositions (20); the stator bar (6) is moreover provided with at least one lamina (12) made of conductive material having one end (24) electrically connected to an elongated conductive element (15) of the main body (10).

Description

"STATOR BAR FOR AN ELECTRICAL MACHINE, AND ELECTRICAL MACHINE COMPRISING SAID STATOR BAR"

TECHNICAL FIELD The present invention relates to a stator bar of an electrical machine and to an electrical machine comprising said bar. In particular, the present invention regards a stator bar of an alternator and an alternator .

BACKGROUND ART

A known type of alternator comprises a rotor, extending along a longitudinal axis, and a stator, which is substantially- shaped like a hollow cylinder coaxial to the rotor, which extends around the rotor. The stator basically comprises a cylindrical ferromagnetic core having a plurality of axial slots, two opposed ends, and a plurality of stator bars, each of which is set along a path partly within a respective axial slot and partly defined at the ends, and is coated with a layer of insulating material .

Each stator bar comprises a main body defined by a plurality of elongated conductive elements, generally made of copper and coated with insulating material, which are substantially parallel and stacked on columns set alongside one another. In particular, in order to minimize the losses of power, each elongated conductive element extends along a path having a plurality of transpositions from one column to the other so as to generate a sort of intertwining between the elongated conductive elements of the main body. The geometrical discontinuity generated by the transpositions, however, creates a situation of deformation of the electrical field, which, if not appropriately attenuated, gives rise to phenomena of dissipation of energy. In particular, the transpositions generate in the main body empty spaces full of air, which are responsible for dissipative phenomena, such as partial discharges and the corona effect. To overcome this problem, a conductive or insulating putty is normally used for filling the empty spaces generated by the transpositions. This solution, however, presents some drawbacks .

The putty, in fact, is applied in standard environmental conditions, and consequently it frequently occurs that air bubbles are formed within the main body, or even that said bubbles are englobed in the putty, giving rise to small vacuoles full of air. The air bubbles in the bar and the vacuoles in the putty increase the risk of occurrence of dissipative phenomena, in particular partial discharges, which impair the integrity of the bars (putty and various insulating coatings) , thus jeopardizing the service life of the alternator.

DISCLOSURE OF INVENTION

Consequently, one aim of the present invention is to provide a stator bar that will be free from the drawbacks of the known art referred to above,- in particular, one aim of the invention is to provide a stator bar that will attenuate the dissipative phenomena presented by the stator bars of the known art, and, at the same time, will be easy and economically advantageous to produce.

In accordance with said aims, the present invention relates to a stator bar for an electrical machine comprising two opposed ends, the bar comprising a main body defined by: a plurality of substantially parallel elongated conductive elements stacked on columns set alongside one another, each of which extends along a path having a plurality of transpositions from one column to another; and a filling element adapted for filling empty spaces of the main body generated by the transpositions,- the stator bar is characterized in that it comprises at least one lamina made of conductive material - -

provided with one end electrically connected to a conductive element of the main body.

A further aim of the invention is to provide an electrical machine that will be reliable and efficient.

In accordance with the above aims, the present invention relates to an electrical machine comprising a rotor, extending along a longitudinal axis, and a stator, which has a hollow cylindrical shape coaxial to the rotor and extending around the rotor, the stator comprising a cylindrical core having a plurality of axial slots, two opposed ends, and a plurality of stator bars, each of which is set in a respective slot and is of the type specified in any one of Claims 1 to 16.

BRIEF DESCRIPTION OF THE DRAWINGS

Further characteristics and advantages of the present invention will emerge clearly from the ensuing description of a non-limiting example of embodiment thereof, with reference to the figures of the annexed drawings, wherein:

- Figure 1 is a schematic view in longitudinal cross section of an electrical machine according to the present invention;

- Figure 2 is a cross-sectional view of the stator bar according to the present invention; - Figure 3 is a perspective view, with parts in cross section and parts removed for reasons of clarity, of the stator bar of Figure 1 ; and

- Figure 4 is a longitudinal view, with parts removed for reasons of clarity, of the stator bar of Figure 1.

BEST MODE FOR CARRYING OUT THE INVENTION

With reference to Figure 1, indicated as a whole by 1 is an alternator, which extends along a longitudinal axis A and comprises a rotor 2, which is the mobile coil, and a stator 3, which is the fixed armature of the alternator 1. _ _

The rotor 2 has a substantially cylindrical shape and turns, moved by a turbine (not illustrated) , about its own axis, which coincides with the longitudinal axis A of the alternator 1. The stator 3 substantially has the form of a hollow cylinder coaxial to the rotor 2 , extends around the rotor 2 , and is separated from the rotor 2 by a gap.

The stator 3 comprises a cylindrical ferromagnetic core 4 having a plurality of axial slots 5, a plurality of stator bars 6, each of which is traversed by an induced current, and two opposed ends 7. Each stator bar 6 extends along a first section 8, substantially parallel to the axis A and inside a respective axial slot 5 of the core 4, and along two second sections 9 at the ends 7. In Figure 1, the second sections 9 of the stator bars 6 are indicated collectively with two annular windings set at the ends 7. In Figure 4, instead, the dashed lines indicate the area of separation between the first section 8 of the stator bar 6, inside the respective axial slot 5, and the second sections 9 of the stator bar 6, set at the ends 7.

With reference to Figure 2, each stator bar 6 comprises a main body 10, an insulating coating 11, a lamina 12 made of conductive material, an insulating coating 13, and a conductive coating 14.

The main body 10 substantially has a rectangular cross section and comprises a plurality of substantially parallel elongated conductive elements 15, stacked on two columns 16 set alongside one another, and a filling element 18.

Each elongated conductive element 15 is made of copper and is coated with a layer of insulating material (not illustrated for reasons of simplicity in the attached figures) .

With reference to Figure 3, each elongated conductive element 15 extends along a path having a plurality of rectilinear sections 19 and a plurality of transpositions 20 from one column 16 to the other. In particular, the transpositions 20 are present only along the first section 8 of the stator bar

5 6, inside the core 4. Between the two columns 16, each stator bar 6 comprises a plurality of fixing elements (not illustrated for reasons of simplicity in the attached figures) , which are adapted to guarantee the connection between the columns 16 and between the elongated conductive

LO elements 15. Said fixing elements are preferably made of a material comprising a strip of glass-fibre and epoxy-resin fabric and are appropriately assembled.

The filling element 18 is an insulating putty. The filling L5 element 18 is adapted for filling the empty spaces in the main body 10 principally generated by the transpositions 20.

With reference to Figures 3 and 4, the main body 10 moreover comprises sheets 22 made of insulating material, for example

.0 aramidic paper, which are set between the elongated conductive elements 15 in the areas of the transpositions 20. Said sheets 22 have the function of reinforcing the insulation in the points of intersection of the elongated conductive elements 15, i.e., in the points where one elongated conductive element

25 15 crosses over the other.

With reference to Figures 2-4, the lamina 12 made of conductive material is provided with one end 24 electrically connected to an elongated conductive element 15 of the main 50 body 10 and extends along a substantially rectilinear side of the main body 10.

In particular, the lamina 12 extends parallel to the main body 10 and only along the first section 8 of the stator bar 6, 35 i.e., only in the section in which the transpositions 20 of the elongated conductive elements 15 are present. With particular reference to Figure 4, the end 24 of the lamina 12 is welded to an elongated conductive element 15 substantially at the centre C of one of the transpositions 20

5 of said elongated conductive element 15 set in the proximity of one of the ends 7 of the alternator 1. In the area of welding, said elongated conductive element 15 is without the layer of insulating material (not illustrated in the attached figures), which envelops each elongated conductive element 15.

0

The lamina 12 is made of metal material, preferably copper.

Basically, the lamina 12 provides the so-called internal corona protection of the stator bar 6.

5

With reference to Figures 2-4, the insulating coating 11 substantially coats the main body 10 throughout the section 8 of the stator bar 6 inside the core 4, except for an area 23 (Figure 4) , which extends around the centre C of the

»0 transposition 20 to which the lamina 12 is welded.

With reference to Figure 3, the insulating coating 11 is obtained by means of an insulating tape, wrapped around the main body 10 with an overlap of 50%. Said tape is preferably >5 made of a fabric consisting of glass- fibre and mica paper pre- impregnated with insulating single-component epoxy resin.

Preferably, the lamina 12 is glued to the main body 10, in particular to the insulating coating 11.

50

With reference to Figures 2 and 3, the insulating coating 13 coats the insulating coating 11 and the lamina 12 substantially along the first section 8 of the stator bar 6, whilst it coats the main body 10 along the second sections 9

35 of the stator bar 6. The insulating coating 13 is made of the same material used for the insulating coating 11, i.e., a fabric consisting of glass-fibre and mica paper pre- impregnated with insulating single-component epoxy resin.

The conductive coating 14 substantially coats the insulating coating 13 along the first section 8 of the stator bar 6. In particular, the conductive coating 14 is a tape wound with an overlap of 50% and made of conductive fabric, for example a glass-fibre tape impregnated with a resin containing graphite filler.

Basically, the conductive coating 14 provides the so-called external corona protection of the stator bar 6.

The invention described presents the advantages described in what follows.

The lamina 12 made of conductive material renders the value of the electrical field on the external surface of the stator bar 6 substantially uniform. This enables a sensible reduction in the dissipative phenomena and in the partial discharges that normally jeopardize the duration and the service life of the electrical machine 1. The lamina 12 made of conductive material, in fact, substantially has the same potential as the elongated conductive elements 15 of the main body 10. Thanks to this property, the measurements made on stator bars according to the present invention have presented values of dissipation factor, understood as the amount of active energy that is dispersed, lower than the ones presented by the stator bars of the known art. Basically, the lamina 12 of conductive material attenuates considerably the dissipative effects that derive from the presence of the vacuoles in the insulating putty and of the air bubbles in the main body 10.

Furthermore, the present invention may be applied also to already existing electrical machines that have stator bars already equipped with traditional systems for protection - o —

against dispersion of energy. The application of the lamina 12 made of conductive material is, in fact, possible on the majority of known stator bars and calls for minimal interventions during the maintenance operations necessary for re-insulation of the stator bars.

Finally, it is evident that modifications and variations can be made to the stator bar and to the alternator described herein, without thereby departing from the scope of the annexed claims .

Claims

- -C LA I M S

1. A stator bar for an electrical machine (1) comprising two opposed ends (7) , the bar (6) comprising a main body (10) defined by: a plurality of substantially parallel

5 elongated conductive elements (15) stacked on columns (16) that are set alongside one another, each of said elements (15) extending along a path having a plurality of transpositions (20) from one column (16) to the other; and a filling element (18) adapted for filling empty spaces of the main body (10)Q generated by the transpositions (20) ; the stator bar (6) being characterized in that it comprises at least one lamina (12) made of conductive material provided with one end (24) electrically connected to an elongated conductive element (15) of the main body (10) .

15

2. The bar according to Claim 1, characterized in that the end (24) of the lamina (12) is electrically connected to an elongated conductive element (15) in the area of the transposition (20) of said elongated conductive element (15)

10 set in the proximity of one of the ends (7) of the electrical machine (1) .

3. The bar according to Claim 2, characterized in that the end (24) of the lamina (12) is electrically connected to

>5 the elongated conductive element (15) at the centre (C) of the transposition (20) set in the proximity of one of the ends (7) of the electrical machine (1) .

4. The bar according to any one of the preceding SO claims, characterized in that the lamina (12) extends along the main body (10) substantially parallel to the main body (10) .

5. The bar according to any one of the preceding S5 claims, characterized in that the lamina (12) is set along a side of the main body (10) .

6. The bar according to any one of the preceding claims, characterized in that the lamina (12) is made of copper .

5

7. The bar according to any one of the preceding claims, characterized in that the bar (6) comprises a first section (8), along which the paths of the elongated conductive elements (15) define a plurality of transpositions (20) and

[0 two second sections (9) , along which the paths of the elongated conductive elements (15) are without transpositions (20) , each second section (9) being set at a corresponding end (7) of the electrical machine (1) .

L5 8. The bar according to Claim 7, characterized in that the lamina (12) extends along the main body (10) substantially along the first section (8) of the main body (10) .

9. The bar according to Claim 7 or Claim 8 , ZO characterized in that it comprises a first insulating coating

(11) , which substantially coats the main body (10) along the first section (8) .

10. The bar according to Claim 9, characterized in that 25 the first insulating coating (11) substantially coats the main body (10) along the first section (8) except for an area (23) that extends around the connection between the end (24) and an elongated conductive element (15) of the main body (10) .

50 11. The bar according to Claim 9 or Claim 10, characterized in that the first insulating coating (11) is a tape of glass -fibre and mica-paper fabric pre- impregnated with epoxy resin wrapped around the main body (10) .

55 12. The bar according to any one of Claims 9 to 11, characterized in that the lamina (12) is substantially glued -

to the first insulating coating (11) .

13. The bar according to any one of Claims 9 to 12 , characterized in that it comprises a second insulating coating

5 (13) , which is set around the first insulating coating (11) and the lamina (12) made of conductive material along the first section (8) of the stator bar (6) .

14. The bar according to Claim 13 , characterized in that .0 the second insulating coating (13) is a tape made of glass- fibre and mica-paper fabric pre- impregnated with epoxy resin.

15. The bar according to Claim 13 or Claim 14 , characterized in that it comprises a conductive coating (14) ,

L5 which is set around the second insulating coating (13) along the first section (8) of the stator bar (6) .

16. The bar according to Claim 15, characterized in that the conductive coating (14) is a tape of conductive fabric.

.0

17. An electrical machine comprising a rotor (2), extending along a longitudinal axis (A) , and a stator (3) , which has a hollow cylindrical shape, is coaxial to the rotor

(2) and extends around the rotor, the stator (3) comprising a 25 cylindrical core (4) having a plurality of axial slots (5) , two opposed ends (7) and a plurality of stator bars (6) , each of which is set in a respective slot (5) and is of the type claimed in any one of Claims 1 to 16.