GB2126804A

GB2126804A - Insulating parts of electric machines

Info

Publication number: GB2126804A
Application number: GB08323549A
Authority: GB
Inventors: Malcolm Otty
Original assignee: Individual
Current assignee: Individual
Priority date: 1982-09-03
Filing date: 1983-09-02
Publication date: 1984-03-28
Also published as: GB8323549D0

Abstract

Joints (31) in and terminal parts of coils and conductors of rotating and other electric machines are insulated by applying a tube (11) of compressible material capable of absorbing resin and surrounded by a heat shrink sleeve (12) which is then heat shrunk to compress the tube. <IMAGE>

Description

SPECIFICATION Insulating parts of electric machines This invention relates to insulating joints in and terminal parts of coils and conductors in rotating and other electric machines.

Conventionally, insulation is applied to such coils and conductors by wrapping a resinimpregnated or impregnatable material helically around the same and curing the resin with which the material is impregnated to form a rigid insulation. Although mica paper has been principally used in recent years, it was proposed in UK Patent Application No. 30939/78 to use instead a stitch bonded fabric of high temperature fibres such as Nomex (RTM) which, on account of its greater flexibility, enabled sharp bends in coils to be wrapped without the insulation gaping leaving weak spots in the insulation.

Although this fabric is a substantial improvement over conventional wrapping materials, its use in the conventional manner limits the advantages to be derived from the textile properties of the material.

It is now found that a compressible material such as a textile material can be used in novel ways to improve the efficiency with which coils and conductors can be insulated and to provide improved insulation therefor.

The invention comprises a method for insulating joints in an terminal parts of coils and conductors in electric machines comprising applying a tube of a compressible material capable of absorbing resin and surrounded by a heat shrink sleeve and heat shrinking the sleeve to compress the tube.

If the tube comprises high termperature fibre such as Nomex (RTM) it can be used in the highest class of insulation.

The tube may be knitted of filament or staple yarn, or may be fabricated from stitch bonded fabric by cut-and-sew methods.

The compressed tube desirably forms a matrix affording a path for resin so that resin in a flowable state can be applied to an end of the tube whereby thoroughly to impregnate the tube.

However, a "resin-rich" technique can be used in which the tube of compressible material is preloaded with a resin which can be heat activated so as to be rendered flowable when the tube is compressed whereby thoroughly to impregnate the tube.

Heat shrink tube is, of course, well known and commercially available in a range of diameters. Its use as an electrical insulator is also known. In connection with the present invention, of course, its electrical insulating properties are of little or no importance, since it is used essentially to compress an impregnated or impregnatable primary insulating material.

An insulator according to the invention can be a tube open at both ends or can be closed at one end so as to form a cap - the latter is especially useful for capping inter-coil connections.

Embodiments of insulators and methods for insulating joints in and terminal parts of coils and conductors in rotating electric machines according to the invention will now be described with reference to the accompanying drawings, in which Figure 1 is a perspective view of one embodiment of insulator, Figure 2 is a perspective view of another embodiment of insulator, Figure 3A is a section through an insulator being applied to a brazed joint between conductors, before shrinking, Figure 3B is a section through the arrangement shown in Figure 3A after shrinking, Figure 4 is a view of an interturn connection with an applied insulator, and Figure 5 is a view of an end of a diamond coil showing another application for an insulator like that of Figure 1.

The insulator shown in Figure 1 comprises a tube 11 open at both ends of a compressible material such as a circular knitted fabric tube of filament or staple yarn of a high temperature fibre such for example, as Nomex (RTM). The tube 11 is enclosed in a sleeve 12 of heat shrink material.

Figure 2 shows an insulator in the form of a cap, closed at one end and comprising a tube 11 of compressible material, for example, stitch bonded fabric made by stitching a batt of high temperature fibres with stitching threads of high temperature filament, as more particularly described in Patent Application No. 30939/78.

The closed end 11 a of the tube 11 is closed by stitching with the same high temperature thread.

The heat shrink sleeve 12 is also closed at the end 1 a of the tube 1 1, by welding.

Flgure 3A shows a brazed joint 31 between conductors 32, 33. Before the joint is made, an insulator 34 like the one shown in Figure 1 is passed over one of the conductors as shown in broken line. After the joint 31 has been made, the insulator is moved over the joint 31.

Once in position, the sleeve 12 is heat shrunk as by blowing hot air at a suitable temperature so as to compress the material of the tube 11 as shown in Figure 3B. In this condition, the fibrous, textile nature of the material still allows resin in a flowable condition to pass as by capillary action throughout the material within the shrunk sleeve.

The resin can be introduced by immersing the joint in liquid resin so that it enters at the ends and it is merely necessary to ensure that the heat shrink sleeve does not seal to the conductors at the ends, though this is usually taken care of by the tendency of the sleeve to shrink slightly away from the ends of the tube.

Alternatively, a heat-activatable resin can be incorporated in the material of the tube 11 so as to be rendered flowable by heat when the tube 11 is compressed by heat shrinking the sleeve 12.

Figure 4 shows how a cap-like insulator like the one shown in Figure 2 fits over the end of a crimped or brazed interturn connection 41. The insulator extends to cover the normally wrapped insulation 42 of the ends 43, 44 of the coils being connected. After heat shrinking, the entire stator or at least the end thereof can be dipped in resin.

Figure 5 shows how an insulator like the one shown in Figure 1 can be used to improve the insulation of the end of a diamond coil 51.

Ordinarily, the normal wrapped insulation, either resin-rich, or impregnated after winding, extends to near the end of terminal 52. However, this insulation is liable to be damaged when the terminals are adjusted during winding stator.

According to the invention, the wrapped insulation is cut back over the region that is likely to be flexed during winding - back nearly as far as the point 53 where the last coil tie is situated. An insulator like that shown in Figure 1 is then slipped over the bared end so as to overlap the remaining wrapped insulation. Before, or preferably after winding, the heat shrink sleeve is shrunk to compress the material of the inner tube.

The end of the coil can be dipped as before. This operation can, or course, be combined with making the interturn connections as described above in connection with Figure 4.

In addition to rotating electric machines such as motors and alternators or generators, the insulation techniques herein described can of course be used with equal effectiveness in static equipment such as transformers and electromagnets, and also linear motors.

Claims

1. A method for insulating joints in and terminal parts of coils and conductors in rotating and other electric machines comprising applying a tube of a compresible material capable of absorbing resin and surrounded by a heat shrink sleeve and heat shrinking the sleeve to compress the tube.

2. A method according to claim 1, in which the tube comprises high temperature fibres.

3. A method according to claim 1, in which the tube is knitted.

4. A method according to claim 1, in which the compressed tube forms a matrix affording a path for resin so that resin in a flowable state can be applied to an end of the tube whereby thoroughly to impregnate the tube.

5. A method according to claim 1, in which the tube of compressible material contains a resin which can be heat-activated so as to be rendered flowable when the tube is compressed whereby thoroughly to impregnate the tube.

6. A method for insulating joints in and terminal parts of coils and conductors in rotating and other electric machines substantially as hereinbefore described with reference to the accompanying drawings.

7. An insulator for joints in an terminal parts of coils and conductors comprising a tube of a compressible material capable of absorbing resin surrounded by a heat shrink sleeve.

8. An insulator according to claim 7, in which the tube comprises high temperature fibre.

9. An insulator according to claim 7, in which the tube is knitted.

10. An insulator according to claim 7, in which the tube is free from resin, but is adapted to form a matrix, when compressed, affording a path for resin so that resin in a flowable state can be applied to an end of the tube whereby thoroughly to impregnate the tube.

1 1. An insulator according to claim 7, in which the tube of compressible material contains a resin which can be heat-activated so as to be rendered flowable when the tube is compressed whereby thoroughly to impregnate the tube.

12. An insulator for joints and terminals of rotating and other electric machines substantially as hereinbefore described with reference to the accompanying drawings.

13. An electric machine comprising joints and terminal parts of coils and conductors insulated by a method according to any one of claims 1 to 6 or by an insulator according to any one of claims 7 to 11.