WO1997007585A2

WO1997007585A2 - Stator for an electric machine and impregnating and insulating process for the stator of an electric machine

Info

Publication number: WO1997007585A2
Application number: PCT/DE1996/001489
Authority: WO
Inventors: Rainer Müller; Michael Schulten
Original assignee: Siemens Aktiengesellschaft
Priority date: 1995-08-21
Filing date: 1996-08-08
Publication date: 1997-02-27
Also published as: WO1997007585A3

Abstract

A stator (1) for an electric machine (15), in particular a turbo-generator, has an insulating layer (13) made of a powder coating (5). Also disclosed is a process for impregnating and insulating the stator (1) of an electric machine (15) by totally impregnating the stator (1) with an impregnating resin (4), then coating it with a powder coating (5) at a temperature from 20 °C to 70 °C. The thus obtained insulating layer (13) achieves with a single coating application a resistance to heat and tracking currents higher than that achieved by wet coating. The powder coating (5) preferably contains an epoxy resin based on bisphenol-A. Since the powder coating (5) contains no solvents and is used up to 99 %, the insulating layer (13) is produced in a particularly environmentally friendly manner.

Description

description

Stator for an electrical machine and method for impregnating and isolating the stator of an electrical machine

The invention relates to a stator, which has an insulation layer, for an electrical machine, in particular for a turbogenerator. Furthermore, the invention relates to a method for impregnating and isolating the stator of an electrical machine, in particular a large machine with an electrical power consumption or output of more than 20 MVA, preferably more than 50 MVA.

The stator of a large electrical machine usually has a ferromagnetic and electrically conductive carrier body and electrical conductors which are wound around the carrier body as winding elements. The conductors have at least one electrically highly conductive metal wire or metal rod, in particular a large number of such metal rods, and are surrounded by an insulating sleeve which is enveloped by an electrically semiconductive protective layer. The insulating sleeve of a winding element usually consists of a mica-containing material to be impregnated or impregnated with a filler. The filler is a synthetic resin, preferably a thermosetting epoxy resin system, for example a thermosetting mixture of an epoxy resin and an acid anhydrite. Winding elements can be winding bars with rod-shaped base bodies, in particular approximately straight base bodies with bent ends, and also form coils with base bodies made of wound wires. Winding bars are usually used in dynamo-electric machines of very high performance, for example in turbogenerators. Form coils are preferred for use in low-power dynamo-electric machines. To produce a component with winding elements for a large dynamoelectric machine, the so-called all-soaking process is used, among other things. Here, the winding elements receive their filler impregnation only after installation in the corresponding carrier body. With the whole impregnation method, precise shaping of the winding elements by pressing or the like is largely superfluous. The grooves containing the winding elements are essentially completely filled with the filler in the carrier body, so that the winding elements are largely immovably fixed in the grooves of the carrier body without further blocking measures. The whole impregnation process gives the component consisting of carrier body and winding elements a unified surface.

Further explanations for the use of the whole impregnation process in the production of components for a large dynamoelectric machine can be found in WO 91/01059 AI and EP 0 379 012 A2. These documents describe the production of arrangements from ferromagnetic and electrically conductive carrier bodies and winding bars, which are subjected to the all-soak process in the manner described above. Furthermore, DE 36 36 008 AI and US Pat. No. 3,990,029 provide information on the complete impregnation process in the production of components for dynamoelectric machines, although these documents relate to arrangements with winding bars, the insulating sleeves of which are already impregnated when installed in the carrier body are.

GB-PS 910,297 describes a method for producing a protective coating for electrical wires made of resin, in which these wires are connected to a solid unit by means of the resin. Applications here are the wire windings for the rotor and stator of an electrical machine; An epoxy powder resin is used for the coating, the electric wire winding itself being used as resistance heating when applied. Alternatively the powder resin is cured by heating in a curing oven, the powder resin accumulating in a temperature range between 120 ° and 230 ° and curing in a temperature range between 150 ° and 175 °. The coating of the wire windings with powder resin is preferred to a soaking in liquid resin, since this soaking is disadvantageous for various reasons.

DE 35 28 492 A1 describes a method for applying a protective layer to electrical components which have wire windings. In particular, such components are anchors and stators of electrical machines of low electrical power. The protective layer here consists of an epoxy resin that is applied as a coating powder. The

Protective layer made of the coating powder can be applied to a liquid resin impregnation and serve as mechanical protection against abrasion and as protection against moisture and thus against corrosion. The powder coating has a thickness between 80 μm and 300 μm. The electrical components to be coated are preheated to a temperature of between 100.degree. C. and 300.degree. C., the wire windings being operated as resistance heating. The powder coating is carried out by spraying using nozzles, the grain size of the powder being at least 60% below 125 μm. A powder coating based on bisphenol-A epoxy resin can be used as the coating powder.

The object of the invention is to provide a stator for a large dynamo-electric machine with an environmentally compatible, in particular εolation layer that can be produced without a solvent. Another object of the invention is to provide a method for isolating and impregnating a stator of a large electrical machine.

According to the invention, the object directed to a stator is achieved by an insulation layer which consists of a hoarded powder paint. The stator has a hollow cylindrical carrier body which extends along a longitudinal axis and which has grooves on the inner ring facing the longitudinal axis. These grooves are each directed along the longitudinal axis and each take up at least one, preferably two, electrical conductors. The carrier body can consist of circular ring segments stacked on top of one another, for example made of dynamo sheets. The carrier body or the circular ring segments are in particular ferromagnetic and electrically conductive. The electrical conductors are rod-shaped or ribbon-shaped as winding elements, the conductors partially protruding from the carrier body in the so-called winding head. This winding head is also preferably coated with an insulation layer made of a powder coating.

An insulation layer made of a hardened powder lacquer distinguishes itself from an insulation layer made of a conventional wet lacquer, which contains about 50% solvent when applied before drying and is applied as a room temperature-curing two-component lacquer in a two-coat process, especially in that

The powder coating contains no solvents,

• there is almost no loss of powder coating, • the powder coating not adhering to the stator can be collected and recycled,

A high heat class is achieved, for example heat class F or H, i.e. a heat resistance of 155 ° C or 180 ° C, • a higher tracking resistance is achieved,

• a second painting process is not necessary.

A second complete impregnation is also possible through an insulation layer with a powder coating, for example in the course of a repair, since the insulation layer made of powder coating is resistant to the impregnating resin used in the complete impregnation process. With a wet paint, however, there is a risk that εich dissolves in the impregnating resin. The insulation layer brings about a homogenization of the surface, protection against corrosion, an increase in the tracking resistance and an improvement in the resistance to glow.

The insulation layer preferably has mica, as a result of which the insulation capacity can be increased and specifically adjusted. The mica can, for example, be mixed with the powder coating in powder form. The mica can optionally also be split mica, i.e. in fine-leaf form, during the coating process.

The insulation layer preferably has an epoxy resin, in particular based on bisphenol-A. A powder coating with such an epoxy resin has the advantage that it can be fully cured at a low baking temperature of approx. 140 ° C. As hardeners, this is the case, as in the article "Epoxy resin powder coatings with low stoving temperature" by H.F. Lauterbach in the specialist brochure on surface technology, edition 1983, "Daε electrostatic powder coating in development and application", publisher F. Ebert, Technik + Kommunikationεverlagε GmbH, Berlin, described, phenolic ("NT") hardener into consideration. According to the article, such powder coatings can achieve very good mechanical and chemical properties, which can be changed in a targeted manner by increasing the crosslinking density on both the resin and the hardener side.

The stator is preferably completely coated with the insulation layer on the inner circumference of the carrier body, in the winding head region of the conductors protruding from the carrier body and / or on the outer circumference, so that a closed surface to achieve high corrosion protection, high creep resistance and high glow resistance is reached. This is particularly advantageous in the winding head area. Through a complete covering with the insulation layer soiling can be easily removed, for example by lubricating oil.

The insulation layer is preferably applied to an impregnation layer which contains an impregnating resin. This is particularly advantageous in the case of a stator of a turbogenerator which has been impregnated with an impregnating resin, for example an epoxy resin, as part of the complete impregnation process. Through the impregnating resin, the grooves are completely filled, so that a largely smooth surface is formed on the inner circumference of the carrier body from the impregnation layer. The electrical conductors or pairs of electrical conductors are wrapped with a band containing mica, which is impregnated with the impregnating resin. The conductors protrude out of the carrier body in a winding head region and are spaced apart there at least in regions, so that they are each individually surrounded by the insulation layer.

The insulation layer preferably has a layer thickness of 40 μm to 200 μm. This achieves effective protection against corrosion and high creep resistance. In this way, a largely homogeneous surface is achieved on the component.

The object directed to a method for impregnating and isolating a component of an electrical machine is achieved according to the invention in that the stator is impregnated with a hollow-cylindrical support body which extends along a longitudinal axis in a complete impregnation with an impregnating resin and then at a temperature of 20 ° C to 70 ° C is coated with a powder coating. The carrier body has grooves on the inner circumference facing the longitudinal axis, which are recessed radially outward and directed along the longitudinal axis, each groove receiving at least one electrical conductor. The complete impregnation can be carried out in the so-called vacuum pressure impregnation process (VPI). Here, the stator is placed in an impregnation system introduced into a closed container, into which container the impregnating resin is introduced. The impregnating resin is pressed into depressions of the stator under a pressure of about 4 bar. After the impregnating resin has hardened, the stator is cooled. The stator is preferably kept at a temperature of 50 ° C. during coating with the powder coating. For this purpose, cooling to 50 ° C. can take place immediately after the impregnation process has been carried out, or the stator can be cooled to a lower temperature and heated to 50 ° C. at a later point in time. At a temperature of 50 ° C, better adhesion of the powder coating is achieved compared to room temperature. A powder coating is preferably used which cures at a temperature from 120 ° C. to 200 ° C., in particular 140 ° C. For this purpose, after coating with the powder coating, the stator is heated to a corresponding temperature, for example up to 140 ° C., and is kept at this temperature for the duration required for curing the powder coating, for example 10 minutes to 20 minutes ¬ th.

Suitable for applying the powder coating to the component of the electrical machine are the electrostatic powder spray (EPS), the electrostatic fluidized-bed method and an electrostatic fluidized-bed coating, as described, for example, in the book "Manufacturing Processes in Device Technology". Grünwald, 2nd edition, Carl Hanser Verlag Munich, 1985, Section 9.5.2.4, or in the book "Introduction to Manufacturing Technology" by H.-J. Warnecke, Teubner Verlag Stuttgart, 1990, Chapter 6, Section 6.2, are described. In electrostatic powder spraying (EPS process), the powder is applied using so-called corona spraying pistols or tribo-pistols. In both cases, excess powder coating not adhering to the component can be recovered and thus reused. Epoxy resin powders with curing times of 15 minutes to 5 minutes at temperatures of 140 ° C. or 210 ° C. are particularly suitable as powder coatings. With these epoxy resin powders are very good good mechanical and chemical layer properties achieved. Other powder coatings include polyurethane powder coatings, polyester powder coatings and acrylic resin powder coatings. Compared to common paints, such as wet paints, these powder paints have the advantage that the hardening mechanism has to be created by polyaddition and is therefore environmentally friendly. A very high utilization of up to 99% is possible. After hardening and cooling, a single-layer coating is present with a uniform insulation layer thickness in the range between 40 μm and 200 μm as well as a high hardness and resistance of the insulation layer. With the powder sintering process (fluidized bed sintering), greater layer thicknesses of approximately 200 μm to 1000 μm with specific properties, such as high resistance to corrosion and chemicals, can be achieved. Powder coatings can also be stored safely, and due to the high level of utilization, there is only little disposal effort.

The powder coating preferably has a powder grain size of 30 μm to 100 μm. The powder grain size is predominantly smaller than 70 μm, for example approximately 66% of the powder grains have a powder grain size of more than 32 μm, approximately 15% of more than 63 μm and approximately 2% of more than 90 μm.

The method for impregnating a stator of a large electrical machine and the insulation layer are explained in more detail with the aid of the exemplary embodiments shown in the drawing. Show it:

1 shows a longitudinal section of a turbogenerator, partly in a side view, and FIG. 2 shows a cross section through the stator of a turbogenerator.

1 shows in a longitudinal section an air-cooled turbo generator 15 for an electrical power of 20 MVA to 300 MVA. The turbogenerator 15 has a stator housing 12 in which A generator rotor 9 is mounted on and between two bearings 10. The generator rotor 9 is directed along a longitudinal axis 7 and is rotationally symmetrical with respect to this. The rotor 9 is also enclosed by a stator 1 directed along the main axis 7. The stator 1 has a hollow cylindrical support body 17 which has a plurality of circular ring segments 2 arranged one behind the other in the direction of the longitudinal axis 7 and made of ferromagnetic and electrically conductive dynamo sheets. The carrier body 17 has grooves 6 running on its inner circumference 8 along the longitudinal axis 7

(see FIG 2). A conductor bar 3 is guided in each of the grooves 6 (see FIG. 2). The conductor bars 3 are formed on the ends of the carrier body 17 facing the bearings 10 to form respective winding heads 16. An exciter 11 is connected to a bearing 10 on the rotor 9. The stator 1 has a longitudinal extension in the direction of the longitudinal axis 7 which is significantly larger than its diameter. Accordingly, the conductors 3 are also oriented essentially in the longitudinal direction.

2 shows in a cross section not to scale the stator 1 of the turbogenerator 15. The cross section of the stator 1 is a circular ring 2 which is, for example, a dynamo sheet made of ferromagnetic and electrically conductive material. Grooves 6 are arranged on the inner circumference 8 of the stator 1 and are directed along the longitudinal axis 7 (see FIG. 1). The grooves 6 are cut radially away from the longitudinal axis 7 into the metal sheets. A conductor rod 3 is arranged in each groove 6, which consists, for example, of two copper rod packs which are separate from one another. By means of a complete impregnation of the stator 1, impregnating resin 4 is introduced or applied in the grooves 6 and on the inner ring 8. The spaces in the grooves 6 between the conductor rod 3 and the stator 1 are thus completely filled with impregnating resin 4. A closed smooth surface in the form of an impregnation layer 14 made of impregnating resin is formed on the inner circumference 8. An insulation layer 13 is made of this by a coating a hardened powder coating 5, in particular an epoxy resin based on bisphenol-A, is applied. This insulating layer 13, which surrounds the entire stator 1, including the winding head 16 and the outer circumference, achieves a smooth surface, a high level of protection against corrosion, a high tracking resistance and a high glow resistance of the turbo generator 15. In addition, the insulation layer 13 from the powder coating 5 has a heat resistance of 155 ° C. to 180 ° C., which corresponds to a heat class F or H. By using the powder coating 5, these properties are already achieved with a single coating process; a second painting process is not necessary.

The invention is characterized by the application of an insulation layer made of a hardenable powder coating on a stator of a turbogenerator. With a single painting process, the stator receives an insulation layer which, compared to insulation layers made of a two-component wet coating, guarantees a significantly improved tracking resistance and a higher heat resistance. In addition, the

Production of the insulation layer from powder coating is very environmentally friendly, since no solvents are used and the powder coating can be used to almost 99%. The insulation layer is particularly suitable for a stator with a carrier body and winding elements, which are impregnated together in a complete impregnation process.

Claims

claims

1. Stator (1) of an electrical machine with a hollow-cylindrical carrier body (17) extending along a longitudinal axis (7), which has grooves (6) on its inner circumference (8) facing the longitudinal axis (7) each extend along the longitudinal axis (7) and each of which at least contains a rod-shaped or ribbon-shaped electrical conductor (3), an insulation layer (13) being pre-read from a hardened powder coating (5) on the inner circumference (8) hen is.

2. Stator (1) according to claim 1, in which the insulation layer (13) has a proportion of mica.

3. Stator (1) according to one of the preceding claims, wherein at least the carrier body (7) is completely covered with the insulation layer (13).

4. Stator (1) according to one of the preceding claims with an impregnation layer (14) made of an impregnating resin (4), on which the insulation layer (13) is applied.

5. Stator (1) according to one of the preceding claims, in which each electrical conductor (3) is essentially individually coated with the insulating layer (13) in a winding head region (16).

6. Stator (1) according to one of the preceding claims, in which the insulation layer (13) has a layer thickness of 40 μm to 200 μm.

7. stator (1) according to any one of the preceding claims, wherein the powder coating (5) an epoxy resin, in particular based on bisphenol-A, aufweiεt.

8. A method for impregnating and isolating a stator (1) of an electrical machine with a hollow cylindrical carrier body (17) which extends along a longitudinal axis (7) and which has grooves (6) on the inner circumference (8) facing the longitudinal axis (7) ), each of which at least contains a rod-shaped or ribbon-shaped electrical conductor (3), the stator (1) being impregnated in a complete impregnation with an impregnating resin and then at a temperature of 20 ° C to 70 ° C with a powder coating ( 5) is coated.

9. The method according to claim 8, in which the powder coating (5) is cured at a temperature of 120 ° C to 200 ° C, in particular 140 ° C.

10. The method according to claim 8 or 9, in which the powder coating (5) by means of electrostatic powder spraying (EPS) or by the electrostatic whirl bath method is applied.

11. The method according to any one of claims 8 to 10, in which a powder coating with a powder grain size of 30 μm to 100 μm, in particular predominantly less than 70 μm, is used.

12. The method according to one of claims 8 to 11, in which a powder coating (5) with an epoxy resin based on Biεphenol-A is used.