WO2012052928A2

WO2012052928A2 - Structure and method for blocking heads of stator windings of electrical machines, in particular of electric generators

Info

Publication number: WO2012052928A2
Application number: PCT/IB2011/054642
Authority: WO
Inventors: Fulvio Zunino; Giorgio Dal Mut; Carlo Benelli; Andreino Olcese; Giada Migliaccio
Original assignee: Ansaldo Energia S.P.A.
Priority date: 2010-10-18
Filing date: 2011-10-18
Publication date: 2012-04-26
Also published as: WO2012052928A3; ITMI20101904A1; IT1402046B1; EP2630720A2

Abstract

A structure (10) for blocking heads of stator windings of electrical machines, in particular of electric generators, comprises at least one tie element (12), in particular made of fibreglass, which is wound around and ties at least one head (7) of the windings and has at least some portions impregnated with a polymeric system; the polymeric system is free from solvents and comprises a bi-component resin, formed by at least one epoxy base resin and by at least one curing/polymerizing agent acting on the base resin, and a chromatic additive sensitive to the density of polymerization of the base resin.

Description

"STRUCTURE AND METHOD FOR BLOCKING HEADS OF STATOR WINDINGS OF ELECTRICAL MACHINES, IN PARTICULAR OF ELECTRIC GENERATORS"

TECHNICAL SECTOR

The present invention relates to a structure for blocking heads of stator windings of electrical machines, in particular of electric generators, and to a method for blocking heads of stator windings of electrical machines, in particular of electric generators.

PRIOR ART

As is known, the heads of the windings of a stator (end windings) of an electric generator (or other electrical machine) are the terminal portions of the stator bars that extend from the stator core.

Said heads must be appropriately supported and blocked, as well as electrically insulated, and various systems are known for providing the mechanical insulating anchorage for the heads.

In particular, it is known to provide ties around the heads, the ties being formed by cords or tapes made of fibreglass englobed in polymeric resins, specifically epoxy resins, polyester resins, or mixtures thereof.

Known tying systems are not altogether satisfactory, above all on account of the polymeric resins resorted to. The resins used are in fact resins (typically epoxy and/or polyester resins) that at room temperature require solvents as additives in order to reduce the viscosity. An excessively high viscosity would render, in fact, complete impregnation of the fibreglass impossible or in any case very difficult. The use of solvents poses, however, problems of safety for the operators and of respect of the environment, in addition to lengthening the polymerization times. In addition, in known methods completion of polymerization of the resins is controlled empirically, by checking that they are no longer sticky or by measuring the time after application. Since, however, the humidity of the air of the environment in which polymerization of the resin takes place can vary a great deal, and since this variation can affect significantly the polymerization rate, complete polymerization is not ensured. The fact of having a correct indication of completion of polymerization is very important, because in the course of the voltage tests, which are always conducted on the entire stator winding at the end of the operations of tying of the heads, the presence of non-polymerized resin can cause surface electrical discharges on the ties themselves and on the heads of the windings, with considerable damage that may even require disassembly and repair of the winding.

OBJECT OF THE INVENTION

An object of the present invention is to provide a structure and a method for blocking heads of stator windings of electrical machines, in particular of electric generators, that will be free from the drawbacks of the known art highlighted herein. In particular, an object of the invention is to provide an alternative structure and method for providing the insulated mechanical anchorage of the heads of the stator windings via ties impregnated with resin in a simple, fast, and effective way .

Specifically, an object of the invention is to provide the ties without resorting to polymeric compositions comprising solvents in such a way as to shorten the polymerization times and reduce safety risks and environmental problems.

A further object of the invention is to make it possible to ascertain in a simple and precise way complete polymerization of the resin in such a way that the electrical tests following upon formation of the ties are always conducted in safety conditions, minimizing the risks of electrical discharges that might cause damage.

In accordance with the above objects, the present invention relates to a structure and a method for blocking stator end windings of electrical machines, in particular of electric generators, as defined in basic terms in the annexed Claim 1 and Claim 9, respectively, as well as, for the preferred additional features, in the dependent claims.

The blocking structure according to the invention is made with a polymeric system (comprising one or more base resins) having the following characteristics:

- it presents low viscosity at room temperature and enables impregnation of the fibreglass tie elements without the use of solvents; avoiding the use of solvents, the polymerization times are shortened and safety risks and environmental problems are reduced;

- it polymerizes at room temperature with a polymerization rate that is adequately slow to enable the impregnation and tying operations;

- it makes it possible to ascertain in a simple and accurate way complete polymerization, by means of a change in colour of the resin itself; the following electrical tests will be always conducted in safety conditions minimizing the risks of electrical discharges that might cause damage.

There then derive the further following advantages as compared to the known art:

- it is not necessary to use solvents to bring the viscosity of the resin to optimal values for impregnation of the fibreglass ties;

- it is not necessary to survey the level of humidity of the air;

- it is not necessary to carry out checks on the stickiness of the impregnated ties;

- the operators do not necessarily have to wear respirators with filters when handling the resins.

BRIEF DESCRIPTION OF THE DRAWINGS

Further characteristics and advantages of the present invention will emerge clearly from the ensuing description of a non-limiting example of embodiment thereof, with reference to the annexed figure, which is a partial schematic view of a terminal region of an electrical machine provided with a structure for blocking the heads of the stator windings made according to the invention.

PREFERRED EMBODIMENT OF THE INVENTION

The annexed figure is a schematic and partial illustration of a terminal region of an electrical machine 1, in particular an electric generator, having a stator 2 and a rotor 3 housed within the stator.

The stator 2 comprises a stator core 4, extending from which are stator bars 5 provided with windings 6 and with respective heads 7 of the windings (end windings) .

The stator core 4 has a circumferential flange 8 connected to a support 9.

The heads 7 of the windings are tied together and/or anchored mechanically to the support 9 via an insulated blocking structure 10, which comprises a plurality of ties 11 formed by tie elements 12, in particular made of fibreglass, impregnated with a polymeric system. The tie elements 12 are, for example, cords, tapes, bands, etc., made of fibreglass, wound around the heads 7 of the windings and/or engaging holes and/or hooks 13 on the support 9.

The polymeric system comprises a bi-component resin, formed by at least one polymeric base resin and at least one curing/polymerizing agent, and at least one chromatic additive sensitive to polymerization; preferably, the polymeric system is basically constituted by the components indicated; in particular, the polymeric system does not include solvents for the base resin nor solvents in general.

Here and in what follows, the term "base resin" indicates a resin or a mixture of resins. According to the invention, the base resin is advantageously a modified epoxy resin free from solvents, which polymerizes in the presence of the curing/polymerizing agent, which is preferably an amine curing agent. For example, the base resin is a glycidyl-epoxy resin and more precisely a glycidyl-ether epoxy resin, for example of the DGEBA (di-glycidyl-ether of bisphenol A) type.

The curing agent is an aliphatic-amine-based agent.

In general, the bi-component resin (i.e., the base resin and the curing agent) is a resin with low viscosity (also at room temperature) and is free from solvents, and changes colour following upon polymerization thanks to the presence of the chromatic additive.

In particular, the polymeric system has a viscosity lower than approximately 400 cP at room temperature. In addition, the bi-component resin polymerizes at room temperature at a controlled and relatively slow rate in such a way as to enable impregnation of the tie elements.

In particular, the polymeric system (formed by the base resin, the curing/polymerizing agent, and the chromatic additive) has a pot-life at room temperature of approximately 6 hours (maximum viscosity 3000 cP) and reaches complete polymerization, once again at room temperature, in approximately 48 hours. The polymeric system and specifically the base resin changes colour as a result of the chromatic additive, which is an additive sensitive to the polymerization density, preferably with a prevalently inorganic base. In particular, the chromatic additive is able to change the colouring of the resin when polymerization of the resin is practically complete.

Examples of formulations of the polymeric system are the following:

- base resin: 100 parts in weight

- curing agent: 5-10 parts in weight

- chromatic additive: 0.03-0.05 parts in weight The structure 10 and precisely the individual ties 11 are made, in the embodiment of the method according to the invention, in the way described in what follows.

A first container is provided containing the base resin and a second container is provided containing the curing/polymerizing agent and the chromatic additive in the due weight proportion.

At the moment of impregnation of the tie elements 12 (for example, cords) made of fibreglass, these are prepared so that they have the necessary length. Alongside the tie elements 12 there are mixed together and stirred, for example in a third container with stirrer, the contents of the first and second containers, to form the complete polymeric system.

Then the tie elements 12 are impregnated with the polymeric system, for example by being dipped in the third container. The impregnated tie elements 12 are then used for tying the heads 7 of the windings appropriately to form the ties 11 and the structure 10 as a whole.

Alternatively, the tie elements 12 not impregnated are first used for tying the heads 7 of the windings, and then the elements 12 installed are impregnated with the polymeric system, for example by injection of the polymeric system with the aid of purposely provided implements (for example, syringes), in a number of points of the ties 11.

The colouring of the resin helps to verify proper impregnation of all the ties 11.

In fact, at the moment of impregnation the resin has a certain colouring. Following upon complete polymerization, the resin and the polymeric system as a whole assume a different colouring, which indicates visually to the operators that polymerization is complete. After the change in colour has been noted, the operators can carry out the customary voltage tests.

Finally, it is understood that further modifications and variations may be made to the blocking structure and method described and illustrated herein, without thereby departing from the scope of the annexed claims.

Claims

1. A structure (10) for blocking heads of stator windings of electrical machines, in particular electric generators, comprising at least one tie element (12), which is wound around and ties at least one head (7) of the windings and has at least some portions impregnated with a polymeric system; the structure being characterized in that the polymeric system comprises a bi-component resin, formed by at least one epoxy base resin and by at least one curing/polymerizing agent acting on the base resin, and is free from solvents.

2. The structure according to Claim 1, wherein the polymeric system comprises a chromatic additive sensitive to the density of polymerization of the base resin.

3. The structure according to Claim 1 or Claim 2, wherein the polymeric system is a system free from solvents and has a viscosity at room temperature lower than approximately 400 cP.

4. The structure according to any one of the preceding claims, wherein the curing agent is an amine curing agent.

5. The structure according to any one of the preceding claims, wherein the tie elements (12) are made of fibreglass.

6. The structure according to any one of the preceding claims, wherein the bi-component resin polymerizes at room temperature at a controlled rate.

7. The structure according to any one of the preceding claims, wherein the polymeric system has a pot-life at room temperature of approximately 6 hours and reaches complete polymerization at room temperature in approximately 48 hours.

8. The structure according to any one of the preceding claims, wherein the base resin is a glycidyl-epoxy resin and more precisely a glycidyl-ether epoxy resin, in particular a DGEBA (di-glycidyl-ether of bisphenol A) resin.

9. A method for blocking heads of stator windings of electrical machines, in particular of electric generators, comprising the steps of: tying at least one head (7) of the windings with a tie element (12); and impregnating, before or after the tying step, at least some portions of the tie element (12) with a polymeric system; the method being characterized in that the polymeric system comprises a bi- component resin, formed by at least one epoxy base resin and by at least one curing/polymerizing agent acting on the base resin, and is free from solvents.

10. The method according to Claim 9, wherein the polymeric system comprises a chromatic additive sensitive to the density of polymerization of the base resin, and the method comprises a step of detecting a variation of colour of the polymeric system.

11. The method according to Claim 9 or Claim 10, wherein the polymeric system is a system free from solvents and has a viscosity at room temperature lower than approximately 400 cP.

12. The method according to any one of Claims 9 to 11, wherein the curing agent is an amine curing agent.

13. The method according to any one of Claims 9 to 12, wherein the tie elements (12) are made of fibreglass.

14. The method according to any one of Claims 9 to 13, wherein the bi-component resin polymerizes at room temperature at a controlled rate.

15. The method according to any one of Claims 9 to 14, wherein the polymeric system has a pot-life at room temperature of approximately 6 hours and reaches complete polymerization at room temperature in approximately 48 hours.

16. The method according to any one of Claims 9 to 15, wherein the base resin is a glycidyl-epoxy resin and more precisely a glycidyl-ether epoxy resin, in particular a DGEBA (di-glycidyl-ether of bisphenol A) resin.