WO2003012955A1

WO2003012955A1 - Stator assembly

Info

Publication number: WO2003012955A1
Application number: PCT/GB2002/003502
Authority: WO
Inventors: Graham Derek Le Flem
Original assignee: Alstom SA
Current assignee: Alstom SA
Priority date: 2001-07-31
Filing date: 2002-07-31
Publication date: 2003-02-13
Anticipated expiration: 2004-01-31
Also published as: GB0118565D0

Abstract

A stator assembly (1) for an electrical rotating machine, such as a high-speed 2-pole motor or generator. The stator assembly comprises a plurality of generally annular laminated core sections (2) arranged along the axis of the machine. Spacer pins (16) are provided between adjacent sections, thereby defining, between each adjacent pair of sections, a radially and circumferentially extending coolant duct (14) enabling coolant to flow between the interior region (25) of the assembly and its exterior surface. A plurality of axially extending channel members (8) are circumferentially spaced apart on the exterior surface to convey pressurised coolant to the ducts (14). Along the length of the assembly (1), alternate first slot openings (22), covered by the channel members (8), and alternate second slot openings (24), extending circumferentially between the channel members, are obturated, but in staggered relationship to each other. This arrangement enables increased economy of manufacture and increased cooling efficiency.

Description

STATOR ASSEMBLY

Field of the Invention

The present invention concerns improvements in or relating to electrical rotating machines, and more particularly to the cooling of components in such machines.

The term 'electrical rotating machine' is intended to cover any form of apparatus having a rotating member which generates, converts, transforms or modifies electric power; amongst other things such machines will comprise motors, generators, synchronous condensers, synchronous converters, rotating amplifiers, phase modifiers and combinations of these in any one machine.

Background of the Invention The ventilation of large 2-pole machines presents the challenge of achieving uniform cooling throughout the length of the machine, and within specification; the longer the axial dimension of the machine, the more difficult this becomes.

It is known, for example in large induction machines, to use so-called "zig-zag" cooling. Briefly, in this form of cooling, ducts for cooling air are formed between confronting surfaces of annular sections of the laminated core of the generally cylindrical stator. Within the ducts, an array of regularly spaced apart baffles or spacers function to space apart the confronting surfaces and guide cooling air between the stator's toothed outer periphery and the stator's inner periphery at the machine's stator-rotor gap. In one arrangement, axially successive ducts take radially inwardly and radially outwardly flowing air alternately. This construction is described in further detail hereinafter with reference to Figs 1 and 2. The cooling is effective and provides uniform cooling along the machine but creates difficulties in complexity of manufacture and is expensive. The trend towards large turbo-type rotor generators and motors presents even further difficulties — such machines are exemplified by generators typically rated from a few MW up to hundreds of MW.

Conventional large turbo-type generator stators use conventional duct spacers (e.g. to define 3 mm wide ducts). Here, the spacers are in the form of strip-like members, such as I-beams, T-sections or rectangular strips (see Fig. 2). Such spacers are affixed mechanically or by welding, e.g. spot welding, to the face of an end lamination of one stator core section and abut against the face of the adjacent end lamination of the next closest section. The spacers extend generally radially and thereby define therebetween generally radially extending passages for the passage of cooling fluid. In reality, the production and attachment of such spacers is a complex and expensive undertaking (for example because of the need to provide spacers of appropriate shape and length for different components). Further, for laminations with other than regular circumferences, a number of such spacers has to be provided which are specifically produced to be the correct fit for the region of lamination to which they are to be affixed.

In another known arrangement, in order to provide even cooling over the length of the stator, separate air chambers are arranged in the frame along the back of the stator (see Fig. 3). These are fed with alternate radially inward flow from outside the stator or radially outward flow from the rotor plus return stator flow. The number of chambers depends upon the length of the stator. Tests on this construction indicate that the rotor tends to self ventilate and is well cooled, but it is more difficult to keep the stator cool. A known 123 MW 60 Hz machine uses 4 chambers in the stator. There remains a need to resolve the problem of how to cool stators, and various different types of ventilation have been considered.

For example, GB-A-2338350 discloses techniques for cooling laminated assemblies of electrical rotating machines in which a component for an electrical rotating machine comprises a plurality of laminations, wherein a passageway for cooling fluid is formed between at least one pair of adjacent laminations, the passageway having therein a plurality of generally cylindrical members extending generally across the passageway, the generally cylindrical members being attached to at least one lamination of each pair of laminations.

However, there is still a need for a design which improves on the normal ventilation associated with turbo-type machines.

Summary of the Invention

The present invention seeks to improve on known types of "zig-zag" cooling through the use of ducts containing the above-mentioned cylindrical members or "pins": the pins in the ducts permit the air to flow circumferentially as well as radially, unlike the strip form of duct spacers which restrict the air to flow mainly radially.

The present invention provides a stator assembly, comprising: a plurality of laminated stator core sections arranged along the axis of the stator assembly, confronting surfaces of axially adjacent core sections being spaced apart by spacer means in the form of a plurality of generally cylindrical members, thereby defining, between each adjacent pair of sections, a radially and circumferentially extending coolant duct for coolant fluid to flow between an interior region of the assembly and an exterior surface region of the assembly, the coolant ducts being connected together by the interior region for flow of coolant between radially inner ends of the ducts, a plurality of axially extending channel members circumferentially spaced apart around said exterior surface region, the channel members being adapted to convey cooling fluid to the coolant ducts, a first plurality of areas of the exterior surface region where the channel members overlie the coolant ducts, the first plurality of areas comprising a first plurality of openings where the coolant ducts intersect the exterior surface, said first plurality of openings being alternately unobturated and obturated in axial succession, and a second plurality of areas of the exterior surface region extending between the channel members, the second plurality of areas comprising a second plurality of openings where the coolant ducts intersect the exterior surface, said second plurality of openings also being alternately unobturated and obturated in axial succession but in a staggered sequence with respect to the openings in the areas overlain by the channel members.

Preferably, for each coolant duct, each obturated first opening is circumferentially adjacent an unobturated second opening and each obturated second opening is circumferentially adjacent an unobturated first opening.

Advantages of such a stator assembly are described hereinbelow, but the use of cylindrical ("pin"-shaped) spacers spanning the gap between adjacent sections allows coolant, typically air, to move tangentially around the stator assembly, as well as radially.

the obturated openings may be obturated by sealing members fixed to the exterior surface of the stator core. However, at least the obturated openings in the first plurality of openings may be obturated by blanking members which form part of the channel members.

Typically, the pins in different coolant ducts are all of substantially equal length, whereby all the passageways have substantially the same dimension parallel to said axis. However, it is possible that the pins are of different length depending on position along the assembly, so as to provide optimal cooling: for example the pins may provide wider passageways towards the centre and narrower towards the ends.

The pins may be attached to one or both of each adjacent pair of sections. Each of the sections preferably comprise teeth at said interior portion, the teeth in one or more of said sections may have holes extending through the teeth parallel to said axis, so as to provide additional paths for cooling air close to the rotor in a direction parallel to the axis. There may be in the region of roughly 100 teeth.

The present invention further provides an electrical rotating machine comprising the above stator assembly and a rotor disposed within the stator assembly, an air gap being defined between the rotor and the stator.

According to preferred embodiments of the invention, the axially extending coolant channels around the exterior surface of the stator core are arranged to bleed off air into alternate ducts along the core instead of using the usual "zigzag" cooling arrangement of bleeding off air into alternate sectors around the periphery of each duct. In the invention, the air must be prevented from exiting the coolant ducts on either side of these coolant supply channels by obturating the slot openings of the coolant ducts in the exterior surface of the stator core where they extend circumferentially between the coolant supply channels. Air then flows into half of the ducts where they are overlain by the supply channels, flows towards the stator bore while at the same time it is free to expand circumferentially within the coolant ducts, passes axially through tooth vents or passes into the stator bore, and flows axially to the adjacent coolant ducts where it is permitted to flow outwards radially and exit the core through the unobturated slot openings which extend between the coolant supply channels. Thus, the complicated prior art "zig-zag" configuration in each coolant duct is eliminated.

An advantage of the invention is that the laminations are much easier to fabricate when compared with those for "zig-zag" winding: pins are easier to align, attach, manipulate, etc. than the vanes required for the "zig-zag" type of cooling. A further advantage is that all sealing is carried out at the back of the stator and therefore can be applied after building the core. It does not require core builders to assemble the sealing as they build the core and can be inspected after core building, and thus, it is easier to fabricate the core when compared to the prior art such as "zig-zag" cooling.

A further advantage of the invention is that the cooling is evenly distributed over the length of the stator. The cooling pattern may be repeated every alternate duct compared to many packets per section for multi-chamber turbo generator cooling methods. This also means that small sections of the stator can be analysed thermally as being more representative of the full stator, thus making thermal analysis much simpler (assuming sufficiently large entry areas are provided at each end of the stator so as not to create an unacceptable entry pressure drop).

An additional advantage is that the number of entry channels is no longer a function of the number of stator slots, contrary to the practice with "zig-zag" cooling arrangements.

The invention is of benefit in the aforementioned turbo-type solid rotor machines, motors and generators and other similar machines.

Further aspects and advantages of the invention will be apparent from the following description and claims.

Brief Description of the Drawings

Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 (PRIOR ART) comprises several views of a known stator assembly employing so-called "zig-zag" cooling; Figure 2 (PRIOR ART) is a partial perspective view of several adjacent sections of the stator assembly of Fig. 1, part of the assembly having been broken away to reveal internal detail;

Figure 3 (PRIOR ART) illustrates a cross-section of another known stator assembly in a large turbo generator;

Figure 4 is a diagrammatic partial perspective representation of several adjacent sections of the stator assembly according to the present invention; .. Figure S diagrammatically illustrates a single section of the stator assembly of Fig. 4;

Figure 6 diagrammatically represents a projection of a view of the outer surface of the stator assembly of Fig. 4 onto a plane; and Figure 7 is a pictorial representation of substantially the same components as shown in Figures 4 to 6.

Detailed Description of the Preferred Embodiments

Referring initially to Fig. 1, several views of a known stator assembly employing so-called "zig-zag" cooling are shown. Figure 1(a) is an axial (drive) end view of the assembly, showing an annular laminated stator core section 102 with stator teeth 104 forming its inner periphery, only some of the teeth being shown for illustrative convenience. The toothed portion defines an inner bore 106 occupied, in use, by the rotor (not shown). Spaced apart around the circumference of the stator are axially extending air supply channel members 108. As also seen in Figure 1(b), which is a cross-sectional view at D-D in Fig. 1(a), the channel members 108 define channels 110 for the supply of pressurised cooling air from an external source (not shown).

Figure 1(c) is a cross-sectional view at A- A in Fig. 1(b) showing a set of radially extending flow-directing members 112 disposed in a regularly spaced apart fashion on the external surface of a lamination of a stator core section

102. This particular stator core section forms the end surface of the assembly and in use, the flow-directing members 112 assist in radially directing cooling air over this end surface.

Figure 1(d) is a cross-sectional view at B-B in Fig. 1(b). The section extends through a cooling duct 114 defined between confronting surfaces of a pair of laminated core sections 102. The confronting surfaces of the pair of core sections are spaced apart by a set of flow-directing spacer members 1 16. Within the duct 1 14, these define between themselves cooling passages having a generally "zig-zag" configuration, in which a radially outer portion of each spacer member 1 16 is skewed anticlockwise from the radial direction by a certain angle, but the outermost portion is then returned to a radial orientation. These anticlockwise skewed spacers are provided, for example, in odd- numbered ducts of the stator assembly.

Figure 1(e) is a cross-sectional view at C-C in Fig. 1(b) showing the arrangement within another cooling duct 114 of a further set of internal spacer members 118. These again define flow passages having a generally "zig-zag" configuration, but in this case a radially outer portion of each spacer member 1 18 is skewed clockwise by a certain angle before being redirected radially. These clockwise skewed spacer members are provided, for example, in even- numbered ducts of the stator assembly. Hence, ducts 114 having clockwise- skewed spacers alternate in axial succession with ducts having anticlockwise- skewed spacers

Figure 1(f) is a part cross-sectional view showing a channel member 108 welded to the outer circumference of the assembly so that channel 1 10 formed thereby can supply cooling air to certain of the cooling air passages 119 defined by spacer members 1 18 within one of the ducts 114.

Figure 2 is a partial perspective view of the three adjacent stator core sections 102 at the left-hand end of the stator assembly of Fig. 1(b), corresponding to Figures 1(c), 1(d) and 1(e). This view better shows the arrangement of flow- directing spacer members 116, 118 in the ducts 114, and the U-shaped channel members 108 defining air supply channels 110 from which cooling air flows into passages 119 within ducts 114 generally in the direction of arrows A, Having reached the radially inner ends of the passages 119, the cooling air enters the air gap between the rotor (not shown) and the stator and then returns to the outside of the machine through passages 121, which are provided in those ducts 114 which, do not connect with the supply channels 110. The air exits the passages 121 generally in the direction of arrows B.

Also shown in Fig. 2 are passages 120 which extend axially through the stator teeth 104 and which convey cooling air parallel to the axis of the machine.

Figure 3 illustrates a cross-section of another known stator assembly in a large turbo generator. Here, circumferentially extending, generally annular chambers 202 are provided around the stator assembly 204, axially spaced apart at suitable intervals. The chambers define channels 206 for the passage of high pressure cool air from an external connected source (not shown) to be forced generally in the direction of arrows E into ducts 208 in the assembly. The cooling air reaches the stator-rotor air gap and can pass in an axial direction, thereby cooling the rotor 209. Thereafter, the hotter, lower pressure air is able to exit the assembly through ducts 210 generally in the direction of arrows F. Heat exchangers 212 are provided to absorb thermal energy from the exiting air.

Figure 4 is a partial perspective view of three adjacent sections 2 of the stator assembly 4 according to the present invention. The construction of the stator assembly is substantially as described above in relation to Figs. 1 and 2, except as set out below.

The assembly 1 is formed from a suitable number of stacked annular laminated stator core sections 2, spaced from each other so as to define ducts 14, or passageways, for the passage of cooling air. Such air is supplied generally in the direction of arrows G from a source (not shown) along channels 10 formed by U-shaped channel members 8. The channel members 8 extend along the outside of the stator core in an axial direction.

Figure 5 illustrates a single section 2 of the stator assembly 1 of Fig. 4. Each of the generally annular sections 2 may be manufactured in accordance with embodiments described in GB-A-2338350. In a normal arrangement the axial sections 2 may be formed from a plurality of laminations, say up to 200 in each section, and between each section are provided the radially extending ducts 14 for cooling fluid e.g. air.

On the surface 6 of at least one section 2 in an adjacent pair of sections are provided (using any of the fixing techniques described in GB-A-2338350) a number of spacer pins 16 in any suitable pattern or configuration, thus providing the necessary spacing between confronting surfaces to define a duct 14 when adjacent sections 2 are in abutment. For illustrative convenience, only a limited number of pins are shown in Figures 4 and 5. While reference is made here to 'pins' 16, it will be understood that these may have the shape of, and be made from the same material as, any of the 'substantially cylindrical members' described in GB-A-2338350.

Each section 2 has its interior toothed region 25 in which the stator teeth 4 may be provided with the above-mentioned axial cooling passages 20, which connect the radially inner ends of adjacent coolant ducts 14 between adjacent core sections 2. Of course, the radially inner ends of the ducts 14 are also connected with each other by the air gap between the rotor and the stator.

Returning to Fig. 4, it will now be explained how the present invention uses the ducts 14 to achieve efficient transfer of cooling air from the channels 10 defined by channel members 8 into the rotor/stator air gap and back to the outside of the machine. It should be noted that in the areas of the external surface of the stator assembly where the channel members 8 overlie the ducts 14, the slot-shaped openings 22, where the ducts 14 intersect the outer surface of the stator core, are alternately unobturated and obturated in axial succession, obturation being achieved in this embodiment by sealing plates 26 which are fixed (e.g., by welding or brazing) to the exterior surface of the stator core sections. Hence, for instance in the example illustrated, (counting from the left) the odd-numbered ducts 14 under channel members 8 are open to receive air from channels 10, flowing in the direction of arrows H, while the even numbered ducts under channel members 8 are sealed. In the areas of the assembly's external surface which lie between the channel members 8, i.e., where channel members 8 do not overlie the ducts 14, the slot openings 24 where the ducts 14 intersect the outer surface of the stator core are similarly alternately unobturated and obturated in axial succession, but in a staggered sequence with respect to the openings 22. Hence, in the example illustrated (again counting from the left), the even-numbered ducts 14 in their span between channel members 8 can eject coolant from the external surface of the assembly in the direction of arrows I, while the odd-numbered ducts are sealed. Thus, along the length of the assembly 1, alternate first slot openings 22 and alternate second slot openings 24 are obturated.

Instead of obturating the slots by applying a sealing plate 26 during production, at least the first slot openings 22 may alternatively be obturated by a blanking piece forming part of - i.e., formed integrally with or affixed to - the channel member 8.

This configuration is illustrated in a different way in Figure 6, which represents a projection of a view of the outer surface of the stator assembly 1 of Fig. 4 onto a plane. It will be seen that, while alternate first openings 22 and alternate second openings 24 are sealed, a sealed first opening is always adjacent an unsealed second opening, and the converse also applies. In other words, first openings 22a, 22c etc., are unsealed, and first openings 22b, 22d, etc. are sealed; and second openings 24a, 24c, etc. are sealed, while second openings 24b, 24d, etc. are unsealed. The result is a form of chess-board pattern or matrix. Returning to Fig. 4, the cooling air sent into the channels 10 defined by channel members 8 passes generally in the direction of arrows H down unsealed first openings 22. Such cool air is unable to escape though circumferentially adjacent but sealed second openings 24 in the same duct 14, but is able to travel radially inwardly and circumferentially within the duct 14, and is forced to travel axially (through and between the teeth 4 near the stator-rotor air gap) down the assembly, where it is able to pass into other ducts 14 and exit the assembly via unsealed second openings 24, generally in the direction of arrows I.

Figure 7 is a more pictorial representation of substantially the same components as shown in Figures 4 to 6, and the same reference numbers indicate the same components. Where the slots 24 extending between the channel members 8 are shown by dashed lines, this indicates that they are obturated by sealing plates fixed flush to the exterior surface. The unobturated slots 22 overlain by the channel members 8 are indicated by dashed lines, but the obturated slots 22 overlain by the channel members 8 are not shown in this figure.

It will be appreciated from Figures 4 to 7 that by configuring the stator assembly 1 in this way the flow of cooling air can efficiently penetrate the inner extremities of the assembly and provide improved extraction of thermal energy from such locations. Furthermore, the invention enables increased economy of manufacture because fewer different types of components are required and the spacers are simpler to manufacture and fit.

Claims

1. A stator assembly, comprising: a plurality of laminated stator core sections arranged along the axis of the stator assembly, confronting surfaces of axially adjacent core sections being spaced apart by spacer means in the form of a plurality of generally cylindrical members, thereby defining, between each adjacent pair of sections, a radially and circumferentially extending coolant duct for coolant fluid to flow between an interior region of the assembly and an exterior surface region of the assembly, the coolant ducts being connected together by the interior region for flow of coolant between radially inner ends of the ducts, a plurality of axially extending channel members circumferentially spaced apart around said exterior surface region, the channel members being adapted to convey cooling fluid to the coolant ducts, a first plurality of areas of the exterior surface region where the channel members overlie the coolant ducts, the first plurality of areas comprising a first plurality of openings where the coolant ducts intersect the exterior surface, said first plurality of openings being alternately unobturated and obturated in axial succession, and a second plurality of areas of the exterior surface region extending between the channel members, the second plurality of areas comprising a second plurality of openings where the coolant ducts intersect the exterior surface, said second plurality of openings also being alternately unobturated and obturated in axial succession but in a staggered sequence with respect to the openings in the areas overlain by the channel members.

2. The stator assembly of claim 1, wherein for each coolant duct, each obturated first opening is circumferentially adjacent an unobturated second opening and each obturated second opening is circumferentially adjacent an unobturated first opening.

3. The stator assembly of claim 1 or claim 2, wherein the obturated openings are obturated by sealing members fixed to the exterior surface of the stator core.

4. The stator assembly of claim 1 or claim 2, wherein at least the obturated openings in the first plurality of openings are obturated by blanking members which form part of the channel members.

5. The stator assembly of any preceding claim, wherein the stator core sections comprise teeth in said interior region, the teeth in at least one of said sections having coolant passages extending through the teeth parallel to said axis.

6. An electrical rotating machine comprising the stator assembly of any preceding claim and a rotor disposed within the stator assembly, an air gap being defined between the rotor and the stator.