A method for resin injection in a generator stator

Abstract

A method to inject resin to secure a bar into a slot of a generator and an apparatus to perform the injection are provided. According to the method, a tube between is inserted between the bar and the slot. The steps of injecting a resin, with a viscosity, between the bar and the slot via the tube, and retracting the tube by a predetermined distance are repeated until the tube has been retracted out of the generator or until the tube has been retracted by a predefined amount.

Description

A METHOD FOR RESIN INJECTION IN A GENERATOR STATORBACKGROUND

[0001] Generators, and in particular three-phase synchronous generators are often used on power generation activities to generate grid-suitable electricity using a prime mover such as a gas turbine, steam turbine, wind turbine, hydro turbine, and the like. The generators generally include a stator that remains stationary during operation and a rotor that rotates with respect to the stator. The rotor often includes two or more poles that when rotated interact with the stator to generate the desired current at the desired frequency and voltage.BRIEF SUMMARY

[0002] Stator bars can become loose over time especially in generators that are operated with frequent load changes or are exposed to transient events. When the bars become loose, a gap may be formed between the bars and the slot in the core which may affect the mechanical and / or electrical properties of the generator; thereby, reducing the life of the generator.

[0003] Vacuum Pressure Impregnation (VPI) is a known process that uses a vacuum and pressure to seal materials with resin. Single Vacuum Pressure Impregnation (SVPI) have relatively easy bar replacement and various ways to add insulation or tight wedges to secure the bars in the slot. Global Vacuum Pressure Impregnation (GVPI) have the bars glued to the slot during impregnation. Currently a rewind, which is expensive and time consuming, would be needed to secure the bars.

[0004] To avoid a complete rewind of a GVPI stator winding for loose windings, a method to secure the bar in the slot is provided.

[0005] According to an embodiment, a first tube is inserted into an insertion location between the bar and the slot, a first resin is injected and the first tube is retracted by a predetermined distance, where the injecting of the first resin and the retracting of the first tube are repeated until the first tube has been retracted out of the generator or retracted by a predefined amount. The first resin has a first viscosity and is injected between the bar and the slot via the first tube. The embodiment may further include a second tube that is inserted into an insertion location between the bar and the slot, a second resin is injected and the second tube is retracted by a predetermined distance, where the injecting of the second resin and the retracting of the second tube are repeated until the second tube has been retracted out of the generator or retracted by apredefined amount. The second resin has a second viscosity and is injected between the bar and the slot via the second tube. While one would reasonably understand that the steps of injecting and retracting would stop one the tube is fully retracted from the generator, it may be desirable to stop prior to the retraction, for example avoid resin from overflowing the gap. Furthermore, it is possible that the second tube is the same as the first tube and that the insertion is a reinsertion of the first tube into the insertion location.

[0006] The tube may be inserted at any location between the slot wall and the bar that is large enough to accommodate the tube. It would be understood that a gap between the corner of the slot wall and the bar generally has more space than a gap between the slot wall and the bar. As such, the insertion location would typically be the corner.

[0007] One skilled in the art would understand that different resins can have different viscosities and that a lower viscosity resin, also referred to as less viscous or thinner resin, has the ability to spread more easily than a higher viscosity resin, also referred to as more viscous or thicker resin. It may be desirable for the resin to be thinner, having wicking properties, in order to spread and fill small areas, to wick from the corner to in between the bar and a wall, or in between the bar and a block. In contrast, a thicker viscosity may resist spreading and fill in the larger gaps.

[0008] A gap size to be filled with resin or the orientation of the bar may be used to determine the resin viscosity for the resin to be injected, whether a single resin is injected, or in the case of multiple resin injections, the order of the resins. For example, a less viscous resin may be injected followed by a more viscous resin or vice versa where a more viscous resin may be injected followed by a less viscous resin.

[0009] The less viscous resin may be less than 1200 centipoise (cP) but greater than OcP. The more viscous resin may be in the range of 2000 to 10000 cP.

[0010] The selection of the viscosity may be based on the orientation of the bar in the stator. It would be appreciated that the bars in the stator in situ have different orientations. The tube is inserted at least 100 mm into a gap. The tube may be inserted at greater distances such as 0.5 meter or 1 meter into the slot. The insertion amount may be based on the size of the gap. The tube is inserted longitudinally, along the stator axis, into the gap. It would be understood that the stator axis is the longitudinal direction of the stator and that the stator axis is parallel to the rotor axis.

[0011] The first resin and the second resin may be different formulations. The first resin or the second resin may be an epoxy based resin.

[0012] The predetermined distance may be based on the viscosity of the resin being inserted to get the desired coverage of the resin or may be a distance to a location of a radial cooling channel to avoid applying resin into a radial cooling aperture. In a particular embodiment, the radial cooling apertures are separated by a distance, which is stator dependent, and may be in the range of 10 mm to 150 mm. The viscosity of the resin may be used to adjust the rate in which the tube is retracted, wherein the tube is retracted faster when injecting the less viscous resin then when injecting the more viscous resin. The less viscous resin may be injected at a rate between 5 and 20 seconds per 100 mm. The more viscous resin may be injected at a rate between 10 and 30 seconds per 100 mm.

[0013] An aramid fiber filler may be inserted into gap prior to an injection or an insertion of the tube. The aramid fiber filler may be coated with resin prior to the insertion of the aramid fiber. The aramid fiber filler may be useful for larger gap sizes. For example, a gap size larger than 0.25 mm.

[0014] The addition of the resin or aramid fiber filler re-establishes the bond between the bar and the slot to stabilize the bar. The method allows for the bar to be reattached to the slot without the removal of the stator or the rotor.

[0015] Prior to the insertion of the tube, the gap between the bar and the slot may be cleaned to remove contaminants. For example, by blowing air and applying alcohol. Additionally, after the injection of the resin, a further cleaning may occur to remove resin from a radial cooling aperture. The further cleaning may include using a brush and alcohol to remove unwanted resin.

[0016] The properties, features and advantages of the invention described above, as well as the manner in which they are achieved, will be explained in more detail in connection with the figures in the following description of the example and variations thereof. The example and the corresponding variations serve to explain the invention and do not limit the invention to the combinations of features indicated therein, even with respect to functional features. Moreover, any of the features disclosed in the example below may be considered in isolation and suitably combined with the features of any of the above embodiments and their further aspects.BRIEF DESCRIPTION OF THE DRAWINGS

[0017] To easily identify the discussion of any particular element or act, the most significant digit or digits in a reference number refer to the figure number in which that element is first introduced.

[0018] FIG. 1 is a cross-sectional view of a generator taken along the generator centerline, rotational, or longitudinal axis.

[0019] FIG. 2 is a perspective view of a rotor suitable for use in the generator of FIG. 1.

[0020] FIG. 3 is a perspective view of a portion of a stator suitable for use in the generator of FIG. 1.

[0021] FIG. 4 illustrates a schematic view of a cross section portion of a stator slot.

[0022] FIG. 5 illustrates a schematic view of a cross section portion of a stator slot.

[0023] FIG. 6 illustrates a schematic view of a cross section portion of a stator slot to show gaps and insertion locations.

[0024] FIG. 7 illustrates a method 700 in accordance with an embodiment.

[0025] FIG. 8 illustrates further actions for the method 700 of FIG. 7.DETAILED DESCRIPTION

[0026] Before any embodiments are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in this description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting.

[0027] Various technologies that pertain to systems and methods will now be described with reference to the drawings, where like reference numerals represent like elements throughout. The drawings discussed below, and the various embodiments used to describe the principles of the present disclosure in this patent document are by way of illustration only and should not be construed in any way to limit the scope of the disclosure. Those skilled in the art will understand that the principles of the present disclosure may be implemented in any suitably arranged apparatus. It is to be understood that functionality that is described as being carried out by certain system elements may be performed by multiple elements. Similarly, for instance, an element may be configured to perform functionality that is described as being carried out bymultiple elements. The numerous innovative teachings of the present application will be described with reference to exemplary non-limiting embodiments.

[0028] Also, it should be understood that the words or phrases used herein should be construed broadly, unless expressly limited in some examples. For example, the terms “including,” “having,” and “comprising,” as well as derivatives thereof, mean inclusion without limitation. The singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. Further, the term “and / or” as used herein refers to and encompasses any and all possible combinations of one or more of the associated listed items. The term “or” is inclusive, meaning and / or, unless the context clearly indicates otherwise. The phrases “associated with” and “associated therewith,” as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like. Furthermore, while multiple embodiments or constructions may be described herein, any features, methods, steps, components, etc. described with regard to one embodiment are equally applicable to other embodiments absent a specific statement to the contrary.

[0029] Also, although the terms "first", "second", "third" and so forth may be used herein to refer to various elements, information, functions, or acts, these elements, information, functions, or acts should not be limited by these terms. Rather these numeral adjectives are used to distinguish different elements, information, functions or acts from each other. For example, a first element, information, function, or act could be termed a second element, information, function, or act, and, similarly, a second element, information, function, or act could be termed a first element, information, function, or act, without departing from the scope of the present disclosure.

[0030] In addition, the term "adjacent to" may mean that an element is relatively near to but not in contact with a further element or that the element is in contact with the further portion, unless the context clearly indicates otherwise. Further, the phrase “based on” is intended to mean “based, at least in part, on” unless explicitly stated otherwise. Terms “about” or “substantially” or like terms are intended to cover variations in a value that are within normal industry manufacturing tolerances for that dimension. If no industry standard is available, a variation of twenty percent would fall within the meaning of these terms unless otherwise stated.

[0031] As illustrated in FIG. 1, a generator 100 includes a stator 300 and a rotor 200 supported for rotation within the stator 300. The stator 300 includes a stator housing 102 that surrounds and substantially encloses a stator core 104. Typically, the stator core 104 is made- up of a number of laminations 106 stacked in a longitudinal direction (along a rotational axis). Each lamination 106 includes cut outs or is otherwise shaped to define the desired features of the rotor core, including a bore 108 that is sized to receive the rotor 200.

[0032] In some constructions, a stator cooling system 110 is provided to cool the stator 300 and improve the efficiency and power density of the stator 300. In some constructions, a cooling gas is employed as a stator coolant. However, larger stators 300 may include liquid cooling such as water cooling.

[0033] The rotor 200 includes a rotor shaft 112, a rotor shaft extension 114, and two retaining rings 116 coupled to the rotor shaft extension 1 14. The illustrated rotor shaft extension 1 14 is supported for rotation by a bearing 118 positioned at each end of the rotor 200. A turbine coupling 120 is positioned at one end of the rotor 200 to facilitate connection of the rotor 200 to a turbine (e.g., combustion turbine, steam turbine, hydro turbine, wind turbine, etc.) or to another prime mover. The opposite end of the rotor 200 may include an exciter coupling 122 that allows for connection to an exciter or other rotating equipment.

[0034] The generator 100 illustrated in FIG. 1 is a synchronous generator 100. However, asynchronous generators or motors could include the features described herein.

[0035] FIG. 2 illustrates the rotor 200 of FIG. 1 in greater detail. The rotor shaft 112 includes a series of rotor slots 202 that extend longitudinally along the rotor shaft 112. Rotor windings 204 are positioned within the rotor slots 202 to define one or more pairs of poles. In the illustrated construction two poles are formed by the rotor windings 204. However, other constructions could include four poles, eight poles or more poles if desired. The rotor 200, sometimes referred to as a field, may also include a commutator 206 that provides a connection to an exciter that provides electrical current at a desired voltage to the stator windings to generate a magnetic field.

[0036] The rotor 200 may also include a rotor cooling system 208 that operates to cool the rotor 200. In some constructions, the rotor 200 is air-cooled with other constructions employing another fluid such as hydrogen.

[0037] Turning to FIG. 3, the stator core 104 is illustrated in greater detail. The stator core 104, in most constructions, is formed from a series of laminations 106 that are stacked in thelongitudinal direction. Each of the laminations 106 includes a number of teeth 302 that are evenly spaced circumferentially around the stator core 104 to define a series of slots that extend the length of the stator core 104. Bars 304 are positioned within the slots and are electrically connected to one another to define a series of windings 306. In the illustrated generator 100, the windings 306 are arranged to define three phases. Generally, the three phases are electrically arranged to define a delta-circuit or a Y-circuit as may be desired. Of course, other constructions could include a single phase if desired.

[0038] As part of the stator cooling system 110, each of the bars 304 may include one or more coolant passages 308 that allow for the flow of coolant along the length of the bar 304.

[0039] In operation, an exciter or other system provides current at a desired voltage to the rotor 200. The current flows through the rotor windings 204 to establish two magnetic poles in a two-pole generator and more poles in higher pole generators. The turbine, or other prime mover is coupled to the rotor 200 and operates to rotate the rotor 200 at a desired speed. For a synchronous generator with a two-pole rotor 200, the rotor is rotated at 3600 RPM to generate 60 Hz electricity. For electricity at 50 Hz, the rotor 200 is rotated at 3000 RPM.

[0040] The rotating magnetic field of the rotor 200 interacts with the windings 306 of the generator to induce an alternating three phase current at a frequency that is proportional to the speed of the rotor 200. Each of the rotor 200 and the stator 300 are cooled to increase the current density of the rotor 200 and the stator 300 while also maintaining a desired efficiency and maintenance interval.

[0041] FIG. 4 illustrates a schematic of a cross section of a portion of a stator slot 400 for a GVPI type stator. The stator slot portion 400 includes slot walls 406 that form a channel that houses a bar 304. The stator slot portion 400 further includes a block 402, which is a wedge or a spacer. A spacer is provided between adjacent bars 304 whereas a wedge is arranged on the most radially outward bar 304. A filler 404, e g., resin, is arranged between each slot wall 406 and the bar 304 and between the bar 304 and the block 402. It would be understood that the resin 404 covers more or all the space between the bar 304 and the slot wall 406 or block 402 and that the illustration is merely for clarity to show where the filler 404 is formed and not the length or amount of resin.

[0042] If the filler 404 has deteriorated or otherwise does not exist between the bar 304 and the slot walls 406 or the block 402, the bar 304 may become loose in the slot. FIG. 5 illustratesa schematic of a cross section of a stator slot portion 500 in an exaggerated situation where no filler 404 exists between the bar 304 and the slot walls slot wall 406 or the block 402.

[0043] FIG. 6 illustrates a schematic of a cross section of the stator slot portion 500 with insertion location 602 for a tube. Gaps occur where there is no filler and may be present in the corner where the bars are rounded, corner gap 606, or be present between the slot wall sides and the bar, wall gap 604. The illustrated insertion locations 602 are located in the corner gaps 606. The corner gap 606 is approximately 3 mm, between the bar 304 and the corner of adjoining slot walls 406 or the bar 304 and the block 402. This is a larger clearance than the wall gap 604. It would be understood that an insertion location may occur at any gap large enough to accommodate the tube.

[0044] FIG. 7 includes a method to inject resin to secure a bar into a slot of a generator. In block 702, method 700 inserts a first tube into a gap between the bar and the slot. In block 704, method 700 injects a first resin, with a first viscosity, between the bar and the slot via the first tube. In block 706, method 700 retracts the first tube by a predetermined distance. In block 708, method 700 wherein the injecting of the first resin and retracting of the first tube are repeated until the first tube has been retracted out of generator or until the tube has been retracted by a predefined amount.

[0045] The method 700 of FIG. 7 may further include the actions 800 of FIG. 8. In block 802 the actions 800 inserts a second tube injecting a first resin, with a first viscosity, between the bar and the slot via the tube. In block 804, actions 800 injects a second resin, with a second viscosity, between the bar and the slot via the second tube. In A 806, actions 800 retracts the second tube by a predetermined distance. In block 808, actions 800 wherein the injecting of the second resin and retracting of the second tube are repeated until the tube has been retracted out of generator or until the second tube has been retracted by a predefined amount.

[0046] The injection of the resin re-establishes the bond between the bar and the slot to stabilize the bar. The first resin fills in at least a portion the wall gap. The second resin fills in at least a portion of the insertion gap and may further fill in a portion of the wall gap. An aramid fiber filler may be inserted to one of the gaps prior to the injection of the resin.

[0047] It is particularly challenging to insert a tube in the small insertion gap between and to direct the tube along the slot. That is there is a certain flexibility needed to insert the tube but a certain rigidity to snake the tube down the slot. The end of the tube is designed to allow it to be inserted while also directing the resin with minimal flow losses where it is intended to go. Thedesign of the tube maintains rigidity, allowing the position to be controlled and the flow of resin to be precisely metered by removing the tube at a pre-defined rate while injecting the resin.

[0048] The method allows for the bar to be reattached to the slot while the stator is in place, in-situ.

[0049] Although an exemplary embodiment of the present disclosure has been described in detail, those skilled in the art will understand that various changes, substitutions, variations, and improvements disclosed herein may be made without departing from the spirit and scope of the disclosure in its broadest form.

[0050] None of the description in the present application should be read as implying that any particular element, step, act, or function is an essential element, which must be included in the claim scope: the scope of patented subject matter is defined only by the allowed claims. Moreover, none of these claims are intended to invoke a means plus function claim construction unless the exact words "means for" are followed by a participle.

Claims

CLAIMSWhat is claimed is:

1. A method to inject resin to secure a bar into a slot of a generator, comprising: inserting a first tube into a gap between the bar and the slot; injecting a first resin, with a first viscosity, between the bar and the slot via the first tube, and retracting the first tube by a predetermined distance wherein the injecting of the first resin and retracting of the first tube are repeated until the tube has been retracted out of generator or until the tube has been retracted by a predefined amount.

2. The method of claim 1, comprising inserting a second tube injecting a first resin, with a first viscosity, between the bar and the slot via the tube, and injecting a second resin, with a second viscosity, between the bar and the slot via the second tube, and retracting the second tube by a predetermined distance, wherein the injecting of the second resin and retracting of the second tube are repeated until the tube has been retracted out of generator or until the tube has been retracted by a predefined amount.

3. The method of claim 1, wherein the injecting of the first resin is performed during the retracting of the first tube.

4. The method of claim 2 or 3, wherein the injecting of the second resin is performed during the retracting of the second tube.

5. The method of any one of claims 2 to 4, wherein the first viscosity is less viscous than the second viscosity, and wherein the second viscosity is more viscous that the first viscosity.

6. The method of any one of claims 2 to 4,wherein the second viscosity is less viscous than the first viscosity, and wherein the first viscosity is more viscous that the second viscosity.

7. The method of claim 5 or 6, wherein the less viscous resin is in the range of less than 1200 cP and more than OcP.

8. The method of claim 5 or 6, wherein the more viscous resin is in the range of 2000 to 10000 cP.

9. The method of any one of claims 1 to 8, comprising selecting the first viscosity based the position of the bar in the stator core.

10. The method of any one of claims 2 to 9, selecting the second viscosity based the position of the bar in the stator core.

11. The method of any one of claims 1 to 10, comprising selecting a rate of retracting the first tube based on the viscosity of the first resin.

12. The method of any one of claims 2 to 11, comprising selecting a rate of retracting the second tube based on the viscosity of the second resin.

13. The method of any one of claims 5 to 12, wherein the rate of retraction is faster when injecting the less viscous resin than the rate of retraction of injecting the more viscous resin.

14. The method of any one of claims 5 to 13, wherein the less viscous resin is injected at a rate between 5 and 20s.

15. The method of any one of claims 6 to 14, wherein the viscous more resin is injected at a rate between 10 and 30s.

16. The method of any one of claims 1 to 15, comprising selecting the predetermined distance based on the first viscosity.

17. The method of any one of claims 2 to 16, comprising selecting the predetermined distance based on the second viscosity.

18. The method of any one of claims 1 to 17,wherein predetermined distance relates to a location of a radial cooling aperture in order to avoid inserting the first or second resin into the radial cooling aperture.

19. The method of any one of claims 1 to 18 comprising inserting an aramid fiber filler a wall gap or an insertion gap.

20. The method of any one of claims 1 to 19, wherein the first tube is inserted at least 100 mm.

21. The method of any one of claims 2 to 20, wherein the second tube is inserted at least 100 mm.

22. The method of any one of claims 1 to 21, wherein the first tube is inserted longitudinally relative to the stator axis.

23. The method of any one of claims 2-16 or 18-22, wherein the second tube is inserted longitudinally relative to the stator axis.

24. The method of any one of claims 1 to 23, wherein the first viscosity is less than 1200 cP.

25. The method of any one of claims 2 to 24, wherein the second viscosity is in the range of 2000 to 10000 cP.

26. The method of claim 22,27. The method of any one of claims 1 to 25, wherein the bar and the slot are part of a generator core having been manufactured via GVPI.

28. The method of any one of claims 1 to 25, wherein the bar and the slot are part of a generator core having been manufactured viaSVPI.

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