GB2343060A

GB2343060A - Casing for an electrical machine

Info

Publication number: GB2343060A
Application number: GB9924900A
Authority: GB
Inventors: Philip Gordon Stonall
Original assignee: ELECTRODRIVES Ltd
Current assignee: ELECTRODRIVES Ltd
Priority date: 1998-10-21
Filing date: 1999-10-21
Publication date: 2000-04-26
Anticipated expiration: 2019-10-21
Also published as: GB2343060B; GB9924900D0; GB9822915D0; WO2000024111A1; AU6479599A

Abstract

A casing for an electrical machine having a rotor and a stator (3) which surrounds the rotor comprises a pipe (1) of thermally conductive material for carrying coolant and arranged in contact with the outer surface (2) of the casing. The pipe may comprise a plurality of straight lengths (5) arranged parallel with the rotational axis of a motor and curved end sections (6) to interconnect the straight sections in series with one another.

Description

2343060 CASING This invention relates to a casing for a rotatable

electrical machine such as an electric ac or dc motor or a generator.

In general an electrical machine comprises an inner rotor and an outer stator and it is known to provide a casing in the form of a cooling jacket around the stator. For example US Patent 5707667 discloses a jacket comprising two concentric cylinders with coolant flowing in the space between and European Patent Application 793328 discloses a jacket comprising two concentric cylinders, the outer one being corrugated to define a double helical channel carrying coolant.

When an electrical machine having a cooling jacket is used in a situation where the stator is in an evacuated space, electric discharges often occur between the metal parts carrying currents, and a metallic e g steel, cylinder is usually provided in the gap between the rotor and the stator to prevent these unwanted discharges. However, the presence of such a cooling jacket and/or the cylinder, reduces the electrical efficiency of the machine.

It Is an object of the present Invention to provide a casing which substantially overcomes or reduces the aforementioned disadvantages.

In accordance with the invention a casing for an electrical machine having an inner rotor and an outer stator comprises a pipe of thermally conductive material for carrying coolant maintained in contact with the outer surface of the stator.

Preferably the pipe comprises a plurality of straight lengths located against the outer surface of the stator, for example, in the case of an ac motor along the outer surface of the motor stator, each length extending axially. The lengths are joined by curved sections so that the coolant flows in one direction along one length and in the opposite direction along the next adjacent length.

Preferably means such as spring means is provided to urge the pipe against the outer surface of the stator. For example the casing may include an outer housing and a plurality of spring clips, positioned internally of the housing. provided to urge the pipe against the outer surface of the machine.

The pipe and the spring means may be embedded in a settable material 2 such as an epoxy resin.

One embodiment of the invention, a casing for an ac induction motor, will now be described by way of example only with reference to the accompanying drawings of which.

Figure 1 shows a transverse cross-section through the casing according to the invention secured to the stator of an ac induction motor-, Figure 2 shows a longitudinal cross-section on line A-A of Figure 1 - Figure 3 shows an end view of the pipe and outer surface of the stator-, and Figure 4 shows a developed plan view of the pipe before being secured in position in contact with the outer surface of the stator.

As shown in Figure 1 a casing according to the invention comprises a pipe 1 of stainless steel configured as shown in Figure 3, located against the cylindrical outer surface 2 of the stator 3 of an ac induction motor and within a housing 4, also of stainless steel.

As shown especially in Figure 4 the pipe 1 is shaped to comprise twelve straight lengths 5 joined together by curved e g semi-circular, sections 6 whereby fluid flowing through the pipe travels first in one direction along one length and then in the opposite direction along the next adjacent length The two ends 7 and 8 of the pipe are supported respectively in two apertures in an end ring 9. The two apertures lead into an array of passages 10 formed in a mounting face 11 which is secured to the end ring 9 by circumferentially spaced apart bolts 12. The mounting face I I Is also provided with an aperture 13 to receive a hermetically sealed plug through which cables 15 connecting to the stator windings 14 pass.

Secured to the end ring 9 on the other side to the mounting face 11 is the stainless steel housing 4. This is generally cylindrical and of sufficient length to cover the stator 3 and the ends of the stator windings 14 (see Figure 2). The housing 4 is corrugated and formed with six axially extending channels 16 each having a base 17 which lies directly against the outer surface 2 of the statorThe six regions 18 between the channels 16 are each circumferentially wider than a channel 16. Each region 18 encloses two lengths 5 of the pipe 1 - With 3 the exception of the region 18 containing the two lengths which are connected to the end ring, each region contains a spring clip comprising a rectangular piece of suitable material such as spring steel or plastic sheet bent to have a shallow V cross-section of two halves with a large included obtuse angle. The apex 20 of each clip presses against the interior of the respective region 18 and the two halves press the two lengths 5 within the respective region against the outer surface 2 of the stator 3.

In its natural state i e before being assembled into the housing 4, the obtuse angle of each clip 19 is less than that shown in Figure 1. The action of positioning the clips as shown causes the obtuse angle of each to increase. There is no need for a clip in the region containing the two lengths which are connected to the end ring 9 since the positions of the apertures receiving the ends 7 and 8 ensure close contact of these lengths with the outer surface 2 of the stator 3.

The curvature of each section 6 of the pipe 1 is such that the natural circumferential length (when curved) of the assembly shown in Figure 4 Is slightly less than the circumference of the outer surface 2 of the stator. The straight lengths 5 of the pipe are thus pressed closely against the outer surface 2 so as to make good thermal contact in the position as shown in Figure 3.

As shown in Figure 2 a hollow generally cylindrical space having an internal diameter equal to the internal diameter of the stator 3, an external diameter equal to that of the interior of the housing 4 (including the regions containing the pipe lengths 5 and clips 19) and extending from the mounting face 11 to the end of the housing further from the end ring 9, is filled with a suitable settable material such as an epoxy resin and cured, thereby encapsulating the stator, stator windings, pipe and clips. If necessary the interior surface of the cured epoxy resin may be machined so as to ensure that it has the correct internal diameter.

The casing in accordance with the invention and as shown in the drawings provides good cooling characteristics for the stator when a coolant such as water is pumped through the pipe 7 through the apertures in the mounting face 11. Further because the whole of the stator, associated windings 4 and coolant pipe is encapsulated, the motor can be used -in a vacuum e g associated with and/or driving a vacuum pump, without any unwanted electric discharge or reduction in efficiency occurring.

Claims

CLAIMS-

1. A casing for an electrical machine having an inner rotor and an outer stator comprising a pipe of thermally conductive material for carrying coolant maintained in contact with the outer surface of the stator.

2. A casing according to Claim 1 wherein the pipe comprises a plurality of straight lengths located against the outer surface of the stator.

3. A casing according to Claim 1 or Claim 2, wherein the machine comprises an electric motor and the lengths extend along the outer surface of the motor stator, each length extending parallel with the rotational axis of the motor.

4. A casing according to either of Claims 2 or 3, wherein axially extending lengths of the pipes are joined by curved end sections so that the coolant flows in one direction along one length and in the opposite direction along the next adjacent length.

5. A casing according to any one of the preceding Claims wherein an outer housing is provided to surround axially extending lengths of the pipe whereby the pipe lies sandwiched between the outer housing and an outer surface of the stator.

6. A casing according to Claim 5, wherein the outer housing comprises a plurality of axially extending corrugations to define a plurality of recess regions at least some of which contain an axially extending length of the pipe.

7. A casing according to Claim 6, wherein each recess region contains an axially extending length of pipe.

8. A casing according to Claim 6 or Claim 7, wherein each or at least one said recess region contains two lengths of pipe.

9. A casing according to any one of the preceding Claims wherein bias means is provided to urge the pipe against the outer surface of the stator.

10. A casing according to Claim 9, wherein the bias means comprises spring means.

11 A casing according to Claim 10 when dependent on any one of claims 5 to 8, wherein the housing supports a plurality of spring clips arranged to urge the pipe against the outer surface of the stator.

6

12. A casing according to Claim 11, wherein at least some of the recess regions contain one of said spring clips to urge the two lengths of pipe against the outer surface of the stator.

13. A casing according to any one of the preceding Claims wherein the pipe is embedded in a settable material.

14. A casing according to any one of the of Claims 10 to 12, wherein the pipe and the spring means are embedded in a settable material.

A casing according to Claim 13 or Claim 14, wherein the settable material is an expoxy resin..

16. A casing for a rotatable electrical machine substantially as described herein with reference to the accompanying drawings.

17. An electric motor comprising a rotor, a stator which surrounds the rotor and a casing according to any one of the preceding claims arranged with the pipe thereof in thermal contact with the outer surface of the stator.

18. An electric motor according to Claim 17, wherein the location means is provided for location of and fluid interconnection with two ends of the pipe.

19. An electric motor according to Claim 18, wherein the motor comprises an end ring provided with two apertures respectively to act as location means to support said two ends of the pipe.

20. An electric motor according to Claim 19, wherein said apertures communicate with passages in a mounting face member secured to said end ring.

21. An electric motor according to Claim 20, wherein said mounting face member is provided with a sealing plug which is in sealed contact with cables connecting to motor windings.

22. An electric motor according to any one of Claims 18-21, wherein the spacing of the ends of pipe when in an unstressed condition is less than the major circumferential distance between the said location means whereby the pipe is inherently urged to bear against the outer surface of the stator when it has been subjected to applied forces to cause it to lie around the outer surface of the motor with the ends of the pipe in fluid communication with said location means- 7

23. An electric Motor substantially as described herein with reference to the accompanying drawings.

C v o o cc,