WO1999035728A1

WO1999035728A1 - A stator for an electric alternating current machine

Info

Publication number: WO1999035728A1
Application number: PCT/SE1999/000006
Authority: WO
Inventors: Per-Olof Berg; Maija Parviainen; Peter Stering; Anders WALLENÅS; Henry Siberg; Torbjörn Wass; Anders Björklund
Original assignee: Asea Brown Boveri AB; ABB AB
Current assignee: ABB AB
Priority date: 1998-01-07
Filing date: 1999-01-07
Publication date: 1999-07-15
Anticipated expiration: 2000-07-07
Also published as: SE9800019D0; SE9800019L; AU2195199A; SE520850C2

Abstract

A stator for an electric alternating current machine comprises a stator body (1) adapted to receive a rotor and at least two windings (6, 8, 10) of coils of wires with conductors each surrounded by an insulating sheath running to and fro substantially in the axial direction of the stator body and returning through loops (3) axially outside the stator body. The insulating sheath of the wires comprises an inner layer electrically insulating and surrounding the conductor and an outer protective layer of a material with a high resistance to mechanical influence and quick temperature changes, and loops belonging to different windings bear against each other or are mutually separated by only air and are allowed to come to bear against each other at at least one location.

Description

A STATOR FOR AN ELECTRIC ALTERNATING CUR- RENT MACHINE

FIELD OF THE INVENTION AND PRIOR ART

The present invention relates to a stator, which comprises a stator body adapted to receive a rotor and at least two windings of coils of wires with conductors surrounded by an insulating sheath of their own and running to and fro substantially in the axial direction of the stator body and returning through loops axially outside the stator body, in which loops belonging to dif- ferent windings are located close together at at least one location.

The invention relates to such a stator in machines intended to operate as motors and/or generators and is not restricted to the number of phases, but it comprises also the one-phase case, since in the case of a one-phase alternating current motor this has two windings in the form of a start winding and a power winding. The invention is also applicable to any number of poles of said alternating current machine and is neither restricted with respect to operation voltage, powers and frequencies of said alternating current.

The stator may also be associated with speed control through different types of motor operation, but the problem upon which the invention is based is particularly accentuated for alternating current motors in frequency converter operation, and the inven- tion and said problem will for that sake hereinafter be described for a stator of the type defined in the introduction adapted for exactly this application so as to illuminate the invention and said problem but accordingly not in any way be limitative.

So called inserts are arranged between coil loops belonging to different windings in such stators already known not only at said location but so as to at all physically separate such loops from each other, said inserts being called phase inserts in the case of a plurality of phases and when the loops accordingly belong to different phase windings, these inserts being of an insulating material, usually sheaths of polyester fibres or aramid fibres, polyester film or laminate combinations of these materials. These inserts are arranged so as to prevent flash overs between the conductors of loops belonging to different windings as a consequence of the potential differences existing between them. Such inserts have been considered to be necessary also if the insulating sheath surrounding the respective conductor as such is dimensioned for withstanding potential differences occurring without any risk of flash over or local partial discharges, so called glow discharges, which could destroy the insulation and lead to a failure of the motor. It is namely so that the wire coils are, when handled for applying them in the stator, normally through so called picking winding, not at least as a consequence of the requirement of the highest possible filling degree and shortest possible coil ends resulting in combination in a packing being as dense as possible, exerted to mechanical stresses which may result in the formation of cracks and scratches deteriorating the voltage withstanding capability of the insulating sheath at certain locations. Furthermore, the windings are especially in frequency converter operation sometimes subjected to temperature changes being comparatively fast, which have a tendency to locally lower the breakdown field of the respective wire remarkably through cracks formed by contractions and ex- pansions of the insulating sheath. Said inserts have so far been applied by hand, which has required a considerable amount of time and resources. This application by hand has normally also made it necessary to apply one winding at the time in the alternating current machine in question and then apply a layer of inserts thereon by hand before the stator body may be returned to an automatized process so as to apply the next winding. This means that considerable disturbances in the automatized process and an additional time consumption result from the application of said inserts. It has been tried to reduce this inconvenience by applying all the windings on the stator body at once and then try to press down said inserts between the different coil loops to be separated from each other, but this is troublesome and for some types of machines not possible.

SUMMARY OF THE INVENTION

The object of the present invention is to provide the stator with such a construction that said problems mentioned above may be reduced to a large extent.

This object is according to the invention obtained by providing a stator of the type defined in the introduction with a combination of on one hand that the insulating sheath of the wires comprises an electrically insulating inner layer surrounding the conductor and an outer protective layer of a material having a high resistance to mechanical influences and rapid temperature changes and on the other that the loops belonging to different windings at said one location are bearing against each other or mutually separated by only air and are allowed to come to bear against each other.

Thus, the present invention is based upon the understanding that it is possible to at least at one said location manage without said inserts between loops belonging to different windings when using wires with an insulating sheath formed by an inner layer electrically insulating and surrounding the conductor and an outer protective layer of a material with a high resistance to mechanical influence and quick temperature changes. It has been found that when the wires of the winding coils are made in that way flash overs between different loops belonging to different windings may be efficiently avoided also when said inserts are absent. Experiments have even shown that for a given thickness of the insulating sheath of the wires a stator of the type according to the invention without any inserts may resist higher loads or stresses with respect to temperature changes than a conventional stator with conductors with an insulating sheath of a conventional material and inserts. This is explained by the fact that the wires may take the comparatively rough handling when the winding coils are applied in the stator body better than conven- tional wires and also quick temperature changes thanks to the existence of said outer protective layer.

Thus, the working movement to apply an insert between said windings at at least said one location may thereby be avoided and labour time and resources may thereby be saved. The saving will be the highest when, which is the case in a preferred embodiment of the invention, the loops belonging to different windings are located close to each other at several locations and bear against each other or are mutually separated by only air at all these locations, since in such a case the working moment to apply said inserts may be totally omitted and it will be possible to apply all the windings in one single working step or in an immediate succession in an automatized process without any intermediate removal of the stator body from this process.

It is pointed out that the definition "or mutually separated by only air" is meant for emphasizing that there is no extra insulating member between loops belonging to different windings at the locations in question, but it is of course completely possible that they are separated by a hardened impregnation agent, such as an impregnating resin, by which the whole winding coils are impregnated for stabilisation thereof.

According to another preferred embodiment of the invention the outer protective layer is of a material protecting the inner insulating layer against glowing. By giving the outer protective layer also this feature the insulating sheath of the wires will withstand higher voltages, so that it is neither during extreme conditions any disadvantage that there are no inserts between the different windings where these are located close to each other.

According to another preferred embodiment of the invention the outer layer is formed by an organic polymer provided with a powdered filler, and the filler constitutes at least 10% of the vol- ume of the outer layer and is formed by Cr₂0₃ , Fe₂0₃ or a mixture of Cr₂0₃ and Fe₂0₃. A wire with an outer layer of this type is already known through the Swedish patent 8701214-2 of the applicant, and it has been found that a wire having exactly such an outer layer of the insulating sheath as described in that patent combines the properties of high resistance to mechanical influences and quick temperature changes and protection against partial discharges in a favourable way, which makes an arrangement of said inserts between loops belonging to different windings superfluous without any negative consequences at all.

According to another preferred embodiment of the invention the organic polymer is a conventional wire insulating paint. Examples of such paints are given in said Swedish patent, and it has been found to be advantageous for the properties of the wire in- sulating desired as well as the application thereof that the organic polymer is present in this form.

According to another preferred embodiment of the invention the outer layer is thinner than the inner layer, which is advanta- geous for maintaining the dielectric losses in the insulation at a low level. According to another preferred embodiment of the invention the windings are formed by a so called PREST-wire. This wire, which is developed by the applicant and is the subject of the Swedish patent mentioned above, has turned out to result in windings, the wires of which resist mechanical stresses, quick temperature changes and high voltages without any arrangement of said inserts in a better way than stators already known having windings formed by a traditional wire and with said in- serts.

According to another preferred embodiment of the invention the stator is made for a three-phase machine and has one winding for each phase, and the different windings are located close to- gether and bear against each other or are mutually separated by only air through loops at different locations axially outside the stator body. In the case of such a three-phase machine two working moments are saved, since in a stator of such a machine already known inserts have to be applied after the application of a first phase winding in the stator body and then after a subsequent application of a second phase winding in the stator body, which means a considerably longer time with respect to the invention, since the stator body has to be removed from the machine, robot or the like, which carries out the application of the winding coils in the stator body, twice.

According to another preferred embodiment of the invention the stator windings are adapted to be connected to a device for frequency converter operation of an alternating current motor of which the stator form a part. It is exactly in such a frequency converter operation of alternating current motors in which it has so far been important to have said inserts as a consequence of thermal variations to which the winding coils are exerted in such an operation, a.o. as a consequence of harmonic currents gen- erated and giving rise to additional current heat losses com- pared to the case of running the motor directly connected to the network voltage.

Further advantages as well as advantageous features of the in- vention will appear from the following description and the other dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

A stator according to the prior art is firstly briefly described hereinafter and a stator according to a preferred embodiment of the invention is then described while referring to the appended drawings. In the drawings:

Figs 1 and 2 are simplified perspective views illustrating a stator already known during different stages of the production thereof,

Fig 3 is a view corresponding to Fig 2 of a stator according to a preferred embodiment of the invention, but which has all the windings applied in the stator body,

Fig 4 is a very simplified partially sectioned view of the stator in Fig 3 as seen in the radial direction,

Fig 5 is a view of the stator according to Fig 3 in axial direction simplified as in Fig 4,

Fig 6 is a simplified sectioned view through a part of a wire used for the windings of the stator according to Fig 3, and

Fig 7 is a graph illustrating temperature variations of the windings in stators during a procedure of comparing tests of stators according to the prior art and according to the invention. BRIEF DESCRIPTION OF A STATOR ACCORDING TO THE PRIOR ART

It is schematically illustrated in Figs 1 and 2 how a stator for an electric three-phase alternating current motor for sine feeding or with a frequency converter feeding is manufactured. The stator has a stator body 1 of iron adapted to receive a rotor not shown in the interior 2 thereof. The motor has four poles and it is illustrated in Fig 1 how a first phase winding 6 of coils of wires with conductors 4 surrounded by an insulating sheath of their own runs to and fro substantially in the axial direction of the stator body by being received in axial slots 5 in the stator body. The coils return through loops 3 arranged axially outside the stator body 1 . The coils are drawn into said slots by hand or by a ma- chine, in which the wires are subjected to mechanical influence and if the wires are constructed conventionally they may be damaged, for example through local formations of cracks and scratching away of the insulation. It is namely important to get as many wires as possible into each slot 5, which means con- siderable stresses thereon when they are inserted into the slots. When a phase winding is brought into place so called phase inserts 7 of insulating material, for example blades of polyester fibres, are glued to the inner side thereof and around, as illustrated in Fig 1 . This is made by hand and takes a not negligible period of time to do. Furthermore, the stator body has usually to be removed from the working station, in which the stator windings are applied. Then when such phase inserts have been applied circumferential coils belonging to another phase winding 8 are introduced into slots 5 intended therefore in the same way as for the first phase windings. Loops belonging to different windings will then have a phase insert therebetween, which is particularly important when they run close to each other, as in their points of intersection in the region where coil loops 3 are formed out of a part of the respective coil running axially and are transformed in such a one, respectively. When this has been done phase inserts are then in the way described above applied on the inner side of the loops belonging to the other phase winding 8 before the third phase winding is applied in the same way.

It is illustrated in Fig 4 how coils belonging to different windings run in the axial direction of the stator body at substantially the same distance to the axis of the stator, so that they leave the stator body at points located substantially along a joint circumference around the axis of the stator. Loops belonging to differ- ent windings overlap each other with respect to the extension in the circumferential direction of the stator, so that coil loops belonging to different windings have to extend at different distances from the axis of the stator, as illustrated in Fig 2, in which the loops 6 of the first phase winding are bent radially outwardly with respect to the loops belonging to the second phase winding 8. As appears from Figs 1 and 2 three subsequent slots as seen in the circumferential direction will be intended for the first phase winding, the three subsequent ones for the second phase winding, and finally the three following ones for the third phase winding, whereupon this is repeated four times.

This arrangement of the phase windings, which as such is conventional, also appears from Fig 5, and these phase windings are applied through so called picking winding. The third phase winding is then provided with the reference numeral 10.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

A stator according to a preferred embodiment of the invention is illustrated in Fig 3, and the same reference numerals have been used in this Figure for elements with correspondence in the stator illustrated in Figs 1 and 2. The stator according to the in- vention differs from the one according to the prior art by the fact that no phase inserts are arranged between the different phase windings, but these are allowed to come to bear against each other, where this is necessary. The process for applying the stator windings will as understandable be considerably simplified with respect to the prior art.

This is enabled by the construction of the insulating sheath surrounding the conductor of the wires used in the windings of the stator according to the present invention, and how this insulating sheath is constructed is schematically shown in Fig 6, which is a longitudinal cut through a part of such a wire. The wire in question is a so called PREST-wire, as this is described in the Swedish patent 8701214-2 of the applicant, which means that the electric conductor 1 1 of the wire is surrounded by an insulating sheath 12, which is formed by an inner layer 13 of insulat- ing material, such as for example a prefabricated polymer film, for example of polyester, polyesterimide, polyamideimide, polyimide, polypropylene or the like. An outer protective layer 14 of a material with a high resistance to mechanical influence and quick temperature changes and also with a high glowing resis- tance is arranged outside the inner layer 13. The outer layer is formed by an organic polymer, such as a conventional wire insulating paint, such as polyesterimide, polyamideimide, polyu- rethane, epoxy resin or the like, which is provided with a powdered filler to at least 10% by volume, namely between 10 and 40% by volume, of the outer layer, in which the filler is formed by Cr₂0₃ , Fe₂0₃ or a mixture of Cr₂0₃ and Fe₂0₃ . The outer layer is then preferably thinner than the inner layer, so that di- electrical losses in the insulation are kept at a low level. The existence of the outer layer 14 makes the insulation of the wires very persistent to the mechanical treatment they are subjected to during the application of the coils in the stator body and later temperature changes in operation of the motor, so that the insulating sheath of the wires well manage to withstand the potential differences which may occur between the loops of adjacent phase windings, where these are located close together, without any risk for electrical breakdowns, which would destroy the insulating sheath.

Comparing experiments have been carried out so as to check the resistance of the windings of the stator according to the invention designed according to Fig 3 with respect to a stator designed as indicated in Fig 2 for extreme conditions. Five different motors manufactured in an automatized production work shop were cycled between 60°C and 180°C during three minutes with a maximum temperature gradient of 60°C/minute, such as illustrated in Fig 7. The rated voltage for these motors was 380 V. The results appear from the table below.

It appears from these experiments that motors provided with PREST-wires and without phase inserts completely surprisingly could take more cycles than standard motors with phase inserts.

A motor of the type according to the invention is driven in fre- quency converter operation through the utilization of pulse width modulation (PWM) for generating alternating currents with a desired frequency, in which this frequency may typically be between 50 and 200 Hz, while the pulse width modulation frequency is typically in the region 1 -3 kHz. Alternating voltages above 300 V and also above 500 V are well conceivable without the requirement of any phase inserts when using a wire of the type suggested by the invention. The invention is of course not in any way restricted to the preferred embodiment described above, but many possibilities to modifications thereof will be apparent to a man with skill in the art, without departing from the basic idea of the invention.

The number of phases as well as of poles of the alternating current machine may as mentioned above for example be another. The windings could also be arranged in another way with respect to the stator body.

The pole number may for example be 2. 4, 6, 8, 10 or the machine could have numerous poles. Furthermore, the windings may be combined with different pole numbers for two speed motors, for example with 2/4, 2/8, 4/6, 4/8 and 6/8 poles.

Claims

1. A stator for an electric alternating current machine, which comprises a stator body (1 ) adapted to receive a rotor and at least two windings (6, 8, 10) of coils of wires with conductors (1 1 ) surrounded by an insulating sheath (12) of their own and running to and fro substantially in the axial direction of the stator body and returning through loops (3) axially outside the stator body, in which loops belonging to different windings are lo- cated close together at at least one location, characterized by the combination of on one hand that the insulating sheath of the wires comprises an electrically insulating inner layer (13) surrounding the conductor and an outer protective layer (14) of a material having a high resistance to mechanical influences and rapid temperature changes and on the other that the loops belonging to different windings at said one location are bearing against each other or mutually separated by only air and are allowed to come to bear against each other.

2. A stator according to claim 1 , characterized in that the outer protective layer (14) is of a material protecting the inner insulating layer (13) against glowing.

3. A stator according to claim 1 or 2, characterized in that the outer layer (14) is formed by an organic polymer provided with a powdered filler, and that the filler constitutes at least 10% of the volume of the outer layer and is formed by Cr₂0₃ , Fe₂0₃ or a mixture of Cr₂0₃ and Fe₂0₃.

4. A stator according to claim 3, characterized in that the organic polymer is a conventional wire insulating paint.

5. A stator according to any of claims 1 -4, characterized in that outer layer (14) is thinner than the inner layer (13).

6. A stator according to claim 4 or 5, characterized in that the windings (6, 8, 10) are formed by so called PREST-wire.

7. A stator according to any of claims 1-6, characterized in that loops (3) belonging to different windings (6, 8, 10) are located close together in several locations and bear against each other or are mutually separated only by air at all these locations.

8. A stator according to any of claims 1 -7, characterized in that it is made for a three-phase machine and has one winding (6, 8, 10) for each phase, and that the different windings are located close together and bear against each other or are mutually separated by only air through loops (3) at different locations axially outside the stator body.

9. A stator according to claim 8, characterized in that coils belonging to different phase windings (6, 8, 10) run in the axial direction of the stator body at substantially the same distance from the axis of the stator, so that they leave the stator body (1 ) at a point located substantially along a joint circumference around the axis of the stator, that loops belonging to different windings overlap each other with respect to the extension in the circumferential direction of the stator, so that coil loops belonging to different windings have to extend at different distances from the axis of the stator, and that said locations comprise, as seen in the radial direction, points of intersection of loops (3) belonging to different phase windings (6, 8, 10) in the region (9) where the coil loops are born out of one part of the respective coil running axially and transformed into such.

10. A stator according to claim 9, characterized in that said locations, at which the loops belonging to different phase windings bear against each other or are mutually separated by only air, also are there along a mid part of the respective loop (3) running substantially in the circumferential direction of the stator.

11. A stator according to any of claims 1-10, characterized in that it is designed as a part of an electric alternating current motor.

12. A stator according to claim 1 1 , characterized in that the windings thereof are designed to be connected to a device for frequency converting operation of the motor.

13. A stator according to claim 1 1 or 12, characterized in that it is designed for a motor with four poles.

14. A stator according to claim 1 1 , characterized in that it is designed for a one-phase motor and has two different windings, namely a start winding and a power winding.