"BINDING ELEMENT FOR AN ELECTRIC MACHINE, MANUFACTURING METHOD OF SAID BINDING ELEMENT AND ELECTRIC MACHINE COMPRISING SAID BINDING ELEMENT"

TECHNICAL FIELD

The present invention concerns a binding element for the anchorage of a stator bar of an electric machine, a manufacturing method of said binding element and an electric machine comprising said binding element.

In particular, the present invention concerns a binding element for the anchorage of a stator bar of an alternator at the heads of the alternator.

BACKGROUND ART

A known type of alternator comprises a rotor, extending along a longitudinal axis, and a stator, which has a substantially hollow cylindrical shape coaxial with the rotor and which extends around the rotor. Basically, the stator comprises a cylindrical core equipped with a plurality of axial slots, two opposite heads and a plurality of stator bars, each of which is placed along a path defined in part inside a respective axial slot and in part at the heads.

During operation of the alternator, the stator bars are subjected to continuous stresses, both from the electrical viewpoint and from the mechanical viewpoint. In particular, these stresses are concentrated at the heads of the alternator and are particularly high during the phases of starting the alternator or in the case of a short circuit. This results in vibration and/or movements of the stator bars arising, which, in the end, cause damage to the stator bars themselves. To better support this type of stresses, as a rule, the stator bars are bound together at the heads of the stator and anchored to a support structure of the stator via a plurality

of binding elements . Each binding element comprises a plurality of glass filaments wound to form a strand and a polymeric composition impregnating the plurality of filaments . However, binding elements of this type have some drawbacks.

During operation of the alternator, particularly during starting and in the case of a short circuit, the mechanical and electrical stresses often cause cracks in the polymeric composition of the binding elements, which causes a weakening of the anchorage and sometimes even the breaking of the binding element .

DISCLOSURE OF INVENTION

One object of the present invention is to provide a binding element that will be free from the drawbacks of known art pointed out here,- in particular, one object of the invention is to provide a stable binding element resistant to the electrical and mechanical stresses that occur during operation of the alternator. In accordance with these objectives, the present invention concerns a binding element for the anchorage of a stator bar of an electric machine comprising a plurality of glass filaments wound to form at least one strand and a polymeric composition impregnating the plurality of filaments, the binding element being characterized in that the composition is a nanocomposite.

A further object of the invention is that of providing a simple and effective manufacturing method of a binding element. In accordance with these objects, the present invention concerns a manufacturing method of a binding element for the anchorage of a stator bar of an electric machine comprising the phase of impregnating a plurality of glass filaments wound to form a strand with a polymeric composition; the method being characterized in that the composition is a nanocomposite.

Finally, another object of the present invention is that of providing a reliable electric machine. In accordance with these objects, the present invention concerns an electric machine comprising a rotor, extending along a longitudinal axis, and a stator, which has a hollow cylindrical shape coaxial with the rotor and extends around the rotor,- the stator comprising two opposite heads, a plurality of stator bars and at least one binding element for the anchorage of at least one stator bar as claimed in any of claims 1 to 9.

BRIEF DESCRIPTION OF THE DRAWINGS

Further characteristics and advantages of the present invention shall appear clear from the description that follows of non- limitative examples of embodiment, with reference to the figures in the enclosed drawings, where:

- Figure 1 is a schematic view, with parts in section and parts removed for clarity, of an electric machine according to the present invention;

- Figure 2 is a top view of a detail of the electric machine in Figure 1;

- Figure 3 is an enlarged-scale perspective view of the detail of the electric machine in Figure 2;

- Figure 4 is an enlarged-scale perspective view of the detail of the electric machine in Figure 2 ; and - Figure 5 is a sectional view of the binding element according to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

In Figure 1, reference numeral 1 indicates an electric machine for the production of energy. In particular, an alternator is shown in its entirety, it extends along a longitudinal axis A and comprises a rotor 2, which is the mobile inductor, and a stator 3, which is the fixed armature of the alternator 1.

The rotor 2 has a substantially cylindrical shape and, driven by a turbine (not shown), rotates around its own axis, which

is coincident with the longitudinal axis A of the alternator 1. The stator 3 has a substantially hollow cylindrical shape, coaxial with- the rotor 2, it extends around the rotor 2 and is separated from the rotor 2 by an air gap.

The stator 3 comprises a cylindrical core 4 equipped with a plurality of axial slots 5, a plurality of stator bars 6, each of which is traversed by an induced current, and two opposite heads 7. Each stator bar 6 extends along _t a first section 8, substantially parallel to axis A and inside a respective axial slot 5 of the core 4, and along two second sections 9 in at the heads 7. The second sections 9 of the stator bars 6 are collectively indicated in Figure 1 with two annular windings arranged at the heads 7.

With reference to Figure 2, each second section 9 of each stator bar 6 comprises two curved portions 11, (see also Figure 3) two parallel portions 12 with respect to axis A of the electric machine 1 (see also Figure 4) and an oblique portion 13 with respect to axis A of the electric machine 1. In particular, each second section 9 comprises, in sequence, a parallel portion 12, a curved portion 11, an oblique portion 13 , a curved portion 11 and a parallel portion 12.

The parallel portions 12 are associated with a support structure 15 integral with the stator 3. In particular, the support structure 15 comprises a plurality of spacers 17 placed between one stator bar 6 and another. Preferably, the spacers 17 are made of an electrically insulating material, such as vetronite for example .

With reference to Figure 3, each spacer 17 maintains a preset distance between one stator bar 6 and the adjacent stator bar 6 and is provided with a through hole 18, which extends parallel to the axis A (Figure 2) of the alternator 1.

With reference to Figures 3 and 4 , the alternator 1 comprises a plurality of binding elements 20 for the anchorage of the stator bars 6 in correspondence to the heads 7 of the stator 3.

With reference to Figure 5, each binding element 20 comprises a plurality of glass filaments 21 wound to form a strand 22 and a polymeric composition 23 impregnating the plurality of filaments 21.

Each filament 21 has a diameter with a size substantially between 0.03 mm and 0.06 mm and has a length substantially between 1 and 1.5 m.

In the non-limitative example in Figure 5, there are seven filaments 21 and they are wound, preferably in a spiral, to form a strand 22 having a diameter substantially between 0.9 and 0.20 mm.

The strand 22 has a plurality of empty spaces 24 of relatively small dimensions between one filament 21 and another. These empty spaces 24 are filled with the impregnation composition 23 to avoid the onset and propagation of partial discharges in the binding element 20. The composition 23 also covers the outer surface of the strand 22 so as to form a thin layer 25, with thickness in the order of a millimetre, for example, around 1.50 mm.

The impregnation of the strand 22 with the composition 23 takes place by dipping the strand 22 in the composition 23 and successively passing the strand 22 through a nozzle in order to eliminate the composition 23 in excess.

The composition 23 is a nanocomposite. By the term nanocomposite,- a material with at least two components, in which one of the component materials has particles of

nanometric size, is intended. In detail, the composition 23 comprises a resin, preferably a polyester, added with a particle material having particles of nanometric size, preferably an inorganic clay with particles of nanometric size, commonly known as nanoclay.

The resin used is two-component and thermosetting. By the term two-component, it is intended that the resin is obtained by the polymerization of liquid resin thanks to the addition of a crosslinking agent.

The nanoclay is mixed with the liquid resin before the crosslinking agent is added.

Preferably, a special nanoclay deriving from a highly purified natural montmorillonite is used. This type of nanoclay has a lamellar structure.

Before being added to the liquid resin, the nanoclay is preferably treated with quaternary amines to give rise to chemical groups bonding with the polymeric chains and uniformly dispersed between the nanoclay lamellas. In this way, the mixture of the liquid resin and nanoclay generates a nanocomposite in which the nanoclay is substantially dispersed in liquid resin in a uniform manner. In particular, the liquid resin modified with nanoclay can assume two different types of morphology: an exfoliative morphology and an intercalary morphology.

The intercalary morphology is characterized by a regular insertion of the polymer between the layers of clay, while the exfoliative morphology is characterized in that it comprises a layer of nanoclay of approximately one nanometre randomly dispersed in the polymer.

The amount of nanoclay that is mixed with the liquid resin is

substantially between 1% and 5% by weight with respect to the liquid resin.

The composition 23 is consequently obtained by mixing the nanoclay with the liquid resin and then the crosslinking agent. .Once these components are mixed, the strand 22 is impregnated as previously described.

Figure 3 shows a first application of the binding element 20. In particular, the binding elements 20a and 20b used for the anchorage of the stator bars 6 to the spacers 17 of the support structure 15 are shown.

In detail, Figure 3 shows two binding elements 2Oa ₇ each of which follows several times a winding path defined by an axial section 30 inside a first hole 18a of a first spacer 17a, an axial section 31 inside a second hole 18b of a second spacer

17b and two transversal sections 32 with respect to axis A

(Figure 2) , which join the two axial sections 30 and 31 and extend along the inner side of the head 7 of the stator 3 in contact with the stator bars 6. In particular, with reference to the non-limitative example in Figure 3, two spacers 17c and

17d and three stator bars 6 are placed between the first spacer 17a and the second spacer 17b.

A first variant, not shown, provides for the placing of a stator bar 6 between the first spacer 17a and the second spacer 17b.

A second variant, not shown, provides for the placing of at least two stator bars 6 and at least a third spacer 17c between the first spacer 17a and the second spacer 17b.

Figure 3 also shows two binding elements 20b, each of which runs several times along a winding path defined by an axial section 34 inside a third hole 18c of the third spacer 17c, in

between spacer 17a and spacer 17b, and an axial section 35 that extends on the inner side of the head 7 of the stator 3 in contact with a respective binding element 20a.

In Figure 3, the binding elements 20a and 20b run only once along the respective winding paths for reasons of clarity. It is understood that each binding element 20a or 20b can run any number of times along the winding path.

Essentially, binding elements 20a contribute to the anchorage of the stator bars 6 between spacer 17a and spacer 17b, while binding elements 20b contribute to the anchorage of the binding elements 20a through blockage around spacer 17c.

Figure 4 shows a second application of the binding element 20. In particular, Figure 4 shows a binding element 20c for the anchorage of a stator bar 6a to an adjacent stator bar 6b along the respective curved portions 11. The binding element 20c runs several times around the stator bar βa and several times around both of the stator bars 6a and 6b. In Figure 4, only three windings of the binding element 20a around the stator bar 6a and around the stator bars 6a and 6b are shown for simplicity and clarity, it being possible of course to have any number of windings .

A variant, not shown, of this application contemplates using more than one binding element 20c for anchoring the two adjacent stator bars 6a and 6b.

The present invention has the following advantages.

The binding element 20 according to the present invention has greater mechanical resistance to breakage and therefore the onset of cracks in the composition 23 of the binding element 20 decreases significantly with evident advantages from the viewpoint of reliability. The greater mechanical resistance to

breakage is mainly due to an increase in the elastic properties of the composition 23 of the binding element 20.

Furthermore, the binding element 20 according to the present invention exhibits increased dielectric strength in the composition 23 thanks to the nanoclay additive. In fact, the nanocharges present in the composition 23 cause a barrier effect against phenomena of onset and propagation of partial discharges .

Finally, precisely thanks to the increased mechanical resistance to breakage and the increased dielectric strength, the binding element 20 according to the present invention is characterized by smaller dimensions with respect to traditionally-used binding elements as the quantity of composition 23 utilized can be reduced to a minimum. This results in a reduction in dimensions of the electric machine 1 due to the presence of the binding elements 20, with evident advantages for the ventilation of the stator bars 6.

.Finally, it is clear that modifications and variants can be made to the binding element, the manufacturing method of the binding element and the electric machine describer herein, without leaving the scope of the enclosed claims.