GB2304236A

GB2304236A - Impregnated end windings in an electrical machine

Info

Publication number: GB2304236A
Application number: GB9616529A
Authority: GB
Inventors: Hans-Joachim Lutz; Stephan Usbeck
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1995-08-10
Filing date: 1996-08-06
Publication date: 1997-03-12
Anticipated expiration: 2016-08-06
Also published as: GB2304236B; ITMI961677A1; IT1283670B1; ES2116232B1; ES2116232A1; FR2738414A1; FR2738414B1; JPH09103038A; ITMI961677A0; DE19529392A1; GB9616529D0

Description

ELECTRICAL MACHINE 2304236 The present invention relates to an electrical

machine, especially polyphase alternating current generator.

Known electrical machines constructed as polyphase alternating current generators comprise a stator and a rotor, which can be a claw pole rotor. The stator comprises a stator lamination body which encompasses the rotor and in which the windings are arranged in, for example, a meander shape. The windings are laid into grooves in the body and have winding heads extending axially beyond the circumference of the stator lamination stack. In order to avoid chafing of the lacquered wires of the windings by shocks and vibrations during use, it is known to impregnate the windings by, for example, immersing these completely in an impregnating resin. A compact winding body results after the setting of the resin. Instead of dip impregnation with an impregnating bath, it is possible to wrap the windings. It has proved that machines with impregnated or wrapped windings have a greater noise output during operation than machines in which the windings are unimpregnated or unwrapped, thus are laid freely into the stator lamination body.

the disadvantage exists circuit, particularly at According to the In case of freely placed windings, however, of possible chafing and thus of a shortthe crossing points of the wires. present invention there is provided an electrical machine, in particular a polyphase alternating current generator, with a stator which comprises a stator lamination body and is associated with several windings, wherein the windings are laid into grooves of the body and winding heads, which project axially 2 - beyond the body, with crossing winding portions are formed around the circumference of the stator, characterised in that the winding heads of the windings are impregnated in such a manner that an impregnation- free region remains between the stator lamination stack and the impregnation.

A machine embodying the invention may have the advantage that the windings are protected against chafing and that it has a relatively low noise development. Due to the winding heads of the windings being impregnated in such a manner that an impregnation-free region remains between the stator lamination body and the impregnation, it is possible on the one hand to protect critical regions in the winding heads against chafing and on the other hand to decouple the winding heads from the body by the impregnation-free region in such a manner that an oscillatory transient of the entire stator due to resonance vibrations and the noise development connected therewith are reduced. Consequently, an electrical machine provided with such an impregnation has a favourable damping behaviour relative to oscillations occurring during the operation. A groove impregnation of the winding strands can also be dispensed with.

In addition to the impregnation of the winding heads, the winding strands extending in the grooves of the body can be bound by preimpregnated paper as groove insulation, which in the case of sufficient heating of the machine can liberate an impregnating resin. Consequently, heat transfer from the winding wires to the body can be improved, wherein the outer winding wires, which are cemented together by the groove insulation, can conduct the heat away to an increased degree by way of the paper to the body. The removal of the heat from the body can be effected in known manner by, for example, a fan arrangement. By this additional measure, it is ensured that a machine operating in a thermally critical range can be provided with the winding head partial impregnation without having to forego a sufficiently high heat transfer between the winding strands and the body. The damping or the oscillatory behaviour of the machine can also be ensured to a large extent by the impregnation-free region between the body and the winding heads.

An embodiment of the invention will now be more particularly 10 described with reference to the accompanying drawings, in which:

Fig. 1 Fig. 3 is a schematic view of a claw pole polyphase alternating current generator embodying the invention; Fig. 2 is a diagram showing oscillation curves of different polyphase alternating current generators; and is a diagram showing noise level curves of different polyphase alternating current generators.

Referring now to the drawings there is shown in polyphase alternating current generator 10; substantially parts relevant to the invention are shown and a detailed i is dispensed with for reasons of clarity. The generator 10 Fig. 1 a only those llustration comprises, shown in dashed lines, a claw pole rotor 14 mounted on a rotor shaft 14 to be secure against rotation relative thereto. The rotor 14 comprises claw poles 18 extending from a first pole wheel 16 and claw poles 22 extending from a second pole wheel 20. The claw poles 18 and 25 22 are finger-shaped and arranged in alternation around the circumference of the rotor 14. The generator 10 further comprises a stator 24, which is formed by a stator lamination stack or body 26 connected with a housing (not shown). The body 26 encompasses the claw pole rotor 14 co-axially with the shaft 12 and carries windings 28, which are arranged in grooves (not shown) in the body. The windings 28 extend in meander shape around the circumference of the body 26 so as to form winding heads 30, which project axially beyond the body. Since the generator 10 has in total three windings separated from each other, the heads 30 of the individual windings 28 cross each other several times around the circumference of the body.

To clarify this, two windings 28 with their winding heads 30 are illustrated in Fig. 1.

The winding heads 30 have an impregnated region 22 as illustrated in hatched lines in Fig. 1. The impregnated region 32 is such that an impregnation-free region 34 remains between the body 26 and the region 32. Thus, the winding portions in the grooves of the body 26 and in the region 34 have no impregnation; the impregnation is restricted exclusively to the heads 30. The impregnation-free region 34 has a length 1. The impregnated region 32 of the winding heads 30 is produced by, for example, dipping the body 26, ready-assembled with the windings 28, into a bath of an impregnating resin. In that case, dipping of the winding heads 30 is carried out to an immersion depth t which is so chosen that the impregnation-free region 34 having the length I remains. The length 1 is at least one millimetre. After setting of the impregnating resin, the winding heads 30 of the windings are rigidly connected together so that the individual wires of the windings 28 cannot move relative to each other in use of the generator 10 as intended. It is thereby prevented that chafing, in particular of mutually crossing wires of the windings 28, occurs. The winding heads 30 are decoupled in terms of oscillation from the body by way of the impregnationfree region 34. Consequently, transmission of oscillations, in particular resonant oscillations which could lead to noise development, is prevented. According to the thickness of the winding, an adequate decoupling of the oscillations is achieved with a length 1 of 0.1 to 2 millimetres.

The oscillation and noise behaviour is clarified by reference to the comparative illustration of three characteristic curves shown in Figs. 2 and 3. The solid line curve a denotes a polyphase alternating current generator 10 with a completely impregnated winding, i.e. the winding heads 30 as well as the winding strands extending in the grooves of the stator lamination body are impregnated completely with resin. The windings 28 and the body then form a rigid structure. The dashed line curve b was recorded for a polyphase alternating current generator 10, the windings 28 of which were not impregnated completely. The dotted line curve c is for a polyphase alternating current generator embodying the invention, i.e. one in which merely the winding heads 30 are impregnated, as illustrated in Fig. 1, and with the impregnation-free intermediate region 34.

With respect to oscillation measurements - which are illustrated in Fig. 2 - with the aid of a so-called drivingpoint measurement, for which the transfer function is entered as modulus (A/F) in decibels as a function of frequency, it is clear from comparison of the characteristic curves that a stator oscillation induced by shock is damped best in the case of a polyphase alternating current generator with the winding heads 30 impregnated according to the invention. It results from this, as clarified by Fig. 3 in which the noise level GP of the generator is entered in decibels as a function of rotational speed, that the noise behaviour of the generator with winding heads impregnated according to the invention is the most favourable. Wi th rising rotational speed of the generator, the noise level difference between the completely impregnated stator and the not completely impregnated stator becomes increasingly apparent.

- 7

Claims

1. An electrical machine comprising a stator which comprises a laminated body and a plurality of windings extending in grooves of the body and forming winding heads with crossing portions, the winding heads being disposed around the circumference of the body and projecting outwardly thereof and being impregnated in such a manner that an impregnation-free region is present between the body and an impregnated region outwardly of the impregnation-free region.

2. A machine as claimed in claim 1, wherein the impregnation-free region has a length radially of the body determined by depth of entry of the winding heads into an impregnation bath.

3. A machine as cl aimed in claim 2, wherein the length is substantially 0.1 to 2.0 millimetres.

4. A machine as claimed in claim 3, wherein the length is least 1.0 millimetres.

5. A machine as claimed in any one of the preceding claims, wherein the strand portions of the windings extending in the grooves are enclosed in pre-impregnated paper.

6. A machine as claimed in claim 5, wherein an impregnation of the strand portions is settable, when the body reaches a predetermined temperature, by way of the thermal sensitivity of the paper.

7. A machine as claimed in any one of the preceding claims, wherein the impregnated region of the winding heads is separated by the impregnationfree region from any impregnation of the winding strand portions in the grooves.

8. An electrical machine substantially as hereinbefore described with reference to Fig. 1 of the accompanying drawings.