WO1997013312A1

WO1997013312A1 - An energy storage and conversion apparatus

Info

Publication number: WO1997013312A1
Application number: PCT/GB1996/002409
Authority: WO
Inventors: David Tod Fullwood; Andrew John Hillesdon
Original assignee: British Nuclear Fuels Plc
Priority date: 1995-10-03
Filing date: 1996-10-01
Publication date: 1997-04-10
Also published as: GB9520128D0; GB2305992A; AU7138296A

Abstract

An energy storage and conversion apparatus (1) comprising a containment (5, 7) defining a vacuum chamber (9), a support shaft (13) within the vacuum chamber (9), a stator (11) on the shaft (13), a cylindrical rotor (15) which, in use, is driven by the stator (11) to store energy as kinetic energy of the rotor (15) and acts with the stator (11) as a generator to release energy and a movable energy absorbing structure (37, 43) between the rotor (15) and the containment (5) which, in the event of failure of the rotor (15), limits the amount of torque transmitted by the rotor (15) to the containment (5) and thus to the machine mountings. As a result, a safer apparatus (1) is produced which can handle the energy stored in the rotor (15) in the event of failure of the apparatus (1).

Description

AN ENERGY STORAGE AND CONVERSION APPARATUS

This invention relates to energy storage and conversion apparatus (or machine) , and in particular to an apparatus wherein a cylindrical rotor is driven by a stator within the rotor to store energy as kinetic energy of the rotor and wherein energy can be withdrawn from the rotor when the stator and rotor act as a generator.

Energy storage and conversion apparatus of the aforementioned type have already been described in some of the present applicant's earlier patent specifications. The applicant has, however, continued to develop its energy storage and conversion apparatus and, as a result thereof, has invented an apparatus as herein described. As will be appreciated, an apparatus of the kind described above requires an outer casing or containment to serve two main functions. Firstly, it forms a gas tight barrier around the rotor which allows the volume around the rotor to be evacuated to a high degree of vacuum. And secondly, it serves to contain crash debris in the event of a failure of the rotor during operation.

The provision of a high vacuum is vital for efficient operation of the machine, and the high operating speeds of the rotor could not be achieved without a high quality vacuum. The containment as crash protection is vital to the machine operation since, without it, it is doubtful that the machine would be allowed to operate at all. A failure of an unguarded or inadequately protected rotor could result in injury or death to nearby personnel and/or serious damage to other equipment.

The containment serves a further function. Together with its end flanges it forms a modular structure in which all the components of the machine may be located together as an assembly and the complete assembly may then be mounted to a rigid structure (the floor for example) using suitable fixings. As previously described, the containment must be able to contain all debris in the event of a rotor failure. A further consideration must be to ensure that the machine does not break away from its mountings which could be equally as dangerous to personnel or equipment. As a consequence of a rotor failure in which the rotor bursts apart at full operating speed (normally considered to be the worst case failure) , there will be a rapid deceleration of the rotor fragments against the inner wall of the containment which transfers a high torque to the containment and machine mountings. In a conventional, rigid type containment system this transfer of torque from the failed rotor to the body of the containment may wrench the machine from its mountings, if no other precautions have been taken. The aim of the present invention is to provide a fail¬ safe containment system which will fully contain all crash debris from a worst case rotor failure, and will limit the effects of the high torque generated on the containment to ensure that the machine remains firmly fixed to its mountings.

The rotor is made up of a large mass of material in order to fill its task of storing kinetic energy. In a conventional system, the containment would be designed to have sufficient thickness and strength to ensure total containment of crash debris in the event of a rotor failure. However, there would still remain the problem of machine mounting failure due to high torque loads imparted on the containment by the failing rotor. Hence, the present invention aims to improve upon such containment by providing an energy storage and conversion apparatus which incorporates a relatively thin outer containment wall with means within the containment wall for limiting the effects of the generated torque imparted on the containment by a failing rotor, thus minimising the transfer of that energy to the machine mountings.

In the light of the foregoing, the present invention provides an energy storage and conversion apparatus comprising a containment defining a vacuum chamber, a support shaft within the vacuum chamber, a stator on the shaft, a cylindrical rotor which, in use, is driven by the stator to store energy as kinetic energy of the rotor and acts with the stator as a generator to release energy and a movable energy absorbing structure between the rotor and the containment which, in the event of failure of the rotor, limits the torque transfer to the containment and machine mountings and, combined with the outer containment, provides sufficient strength and thickness to prevent the containment from being breached by crash debris.

In a preferred embodiment, the movable energy absorbing structure comprises a cylindrical mantle which can rotate about the rotor.

Preferably, the cylindrical mantle is supported internally by bearing pads. In the event of a rotor failure, the cylindrical mantle can rotate, thereby producing friction between the mantle and the bearing pads to absorb energy.

The bearing pads preferably support both ends of the cylindrical mantle.

The movable energy absorbing structure may also comprise an axial end bearing. If such an end bearing is included, this may rotate around the support shaft upon interaction with the rotor. Once again, energy can be absorbed by this action.

The axial end bearing preferably sits on a bearing pad which supports the cylindrical mantle. However, any other appropriate arrangement could, of course, alternatively be used.

The apparatus preferably also includes at least one radial catcher bearing mounted on the support shaft for engaging the rotor in the event of a failure of the apparatus. By including a radial catcher bearing, the rotor can be held in position about the stator and support shaft, in the event that the rotor remains largely intact (i.e. it has not burst apart). This arrangement helps to prevent the rotor from moving excessively about its axis and thus prevents unacceptable bending moments from being imparted onto the stationary components of the machine.

In a particular embodiment, the or each radial catcher bearing may comprise a ball bearing race mounted on the support shaft.

Preferably the rotor is carried by an end cap and pin bearing supported by the support shaft. In such an embodiment, a top axial catcher bearing may be provided which catches the end cap in the event of failure of the pin bearing.

A specific embodiment of the present invention is now described, by way of example only, with reference to the accompanying drawings, in which:-

Figure 1 is a sectional side view of an energy storage and conversion apparatus according to the present invention; and

Figure 2 is an enlarged portion of Figure 1 showing the top catcher bearing.

With reference to the drawings, an energy storage and conversion apparatus 1 comprises a base member 3, a cylindrical containment wall 5 mounted on the base member 3 and a top flange 7 for defining, with the containment wall 5 and base member 3, a vacuum chamber 9. A stator 11 is mounted on a substantially vertical support shaft 13 within the vacuum chamber 9 and a rotor 15 is positioned around the stator 11. The rotor 15, which is preferably made from fibre reinforced composite material, carries an end cap 17 supported by a pin bearing 19 positioned at the top of the support shaft 13.

The stator 11 is not shown in any detail in Figure 1, but may be of any appropriate type incorporating a core defining a plurality of poles, such as four poles, about which coils are wound to produce magnetic flux. The rotor 15 is fitted with magnets, or contains a material which is magnetised to form a multipolar magnetisation for interaction with the stator 11 during use. Flux from one pole of the rotor magnets crosses the air gap, flows through the stator teeth and around the yoke, and then re-crosses the air gap into an opposite pole of the rotor magnets. The flux path therefore flows through the centre of one of the stator coils, thus creating a flux linkage with the coil. When the coil is carrying a current, a force will result which causes the rotor 15 to rotate. In this way, electrical energy can be stored as kinetic energy of the rotor. Conversely, if energy is to be withdrawn from the apparatus 1, the rotor 15 and stator 11 can act as a generator to produce an electrical output via the power electronics (not shown) of the apparatus 1.

The base member 3 of the apparatus 1 has significant strength by virtue of its thickness and the material from which it is made, which may be aluminium, for example. Holes 21, one of which is shown, through the base member 3 receive bolts (not shown) for securing the base member 3 to a floor or the like of considerable mass and strength. As a result, the energy storage and conversion apparatus 1 will be held firmly in position, even if the apparatus 1 fails.

A magnetic bearing 23 is provided towards the lower end of the support shaft 13 under the stator 11. The magnet of the bearing 23, which may be a permanent magnet or an electromagnet, interacts with the magnetic material embedded in the rotor 15 to position the lower end of the rotor 15 radially about the stator 11. In theory, the magnet 23 could be used to support some of the weight of the rotor 15. As can be seen in the drawings, the end cap 17, which may engage the rotor 15 with a friction fit or may be attached thereto with some form of glue, carries a pin 25 of the pin bearing 19. The pin bearing 19 is threadedly received at the top of the support shaft 13, as shown in Figure 1. As can be seen in Figure 2, the pin 25 of the pin bearing 19 is actually carried by a support block 27 in the centre of the end cap 17. Further, a cover 29 of the pin bearing 19 defines a recess 31 which accommodates the support block 27 and acts as a top catcher bearing 32 in the event of failure of the pin 25 of the pin bearing 19.

The support shaft 13 also carries upper and lower radial catcher bearings 33,35 which comprise ball bearing races for centering the rotor 15 in the event that the end cap 17, pin bearing 19 or magnetic bearing 23 fail to control the position of the rotor 15 during use. If a failure of this kind does occur, the ball bearing races of the upper and lower radial catcher bearings 33,35 can rotate and guide the rotor 15.

A cylindrical mantle 37 is positioned between the rotor 15 and the containment wall 5 of the apparatus 1. This cylindrical mantle 37 is supported at its upper and lower ends by annular stepped internal bearing pads 39,41. The cylindrical mantle 37 acts as an energy absorbing structure by rotating on the friction bearing pads 39,41 in the event of a failure of the rotor 15, thereby limiting the amount of torque transmitted to the containment 5 and ultimately to the machine mountings. A lower axial end bearing 43 is provided mounted on the lower bearing pad 41, as shown in Figure 1. This axial end bearing 43 is designed to carry the rotor 15 in the event of the end cap 17 disengaging from the rotor 15 and allowing the rotor 15 to drop. If this occurs, friction between the rotor 15 and the end bearing 43 will cause the end bearing 43 to rotate about the support shaft 13, thereby producing friction between the end bearing 43 and the bearing pad 41. In this way, energy of the rotor is absorbed by the apparatus without the apparatus 1 failing completely and becoming dangerous.

The way in which the component parts of the apparatus 1 interact and operate depends to a large extent on the nature of the rotor 15 failure of which there are two main scenarios. These will now be described. The first scenario is by far the most threatening to containment integrity and may be regarded as the worst case scenario. In this event, there is an instantaneous bursting apart of the rotor 15 at full operating speed (say 1200 Hz) . The debris is flung outwards by the action of centrifugal forces until it comes to bear up against the inner surface of the cylindrical mantle 37. This position may occur only a fraction of a millisecond into the crash sequence and the debris is still rotating at almost full operating speed. As friction begins to build up between the inner surface of the mantle 37 and the crash debris, the mantle 37 begins to rotate on the bearing pads 39,41. In the prior art devices, where the containment vessel is a rigid tube, this initial contact between the debris and the containment wall would result in a massive torque load being transmitted directly to the body of the containment vessel. The mantle 37 prevents this occurrence since it is not rigidly fixed to the containment wall 5 or base member 3. Accordingly, friction is generated between the debris and the mantle inner surface and at the mantle bearing surfaces.

The mantle 37 may expand in diameter due to the pressure of the debris on the inner surface. The mantle bearing pads 39,41 are designed such that the expansion of the mantle 37 will not cause the ends of the mantle 37 to tighten up into the bearing surfaces, since the bearing surfaces are on the inner and end faces of the mantle 37. This ensures that the mantle 37 continues to remain free to rotate as pressure and friction between the debris and the mantle inner surface continue to build up. As friction continues to be generated, the debris rotation slows down rapidly. The mantle 37 has prevented the transmission of massive torque loads to the containment 5 and has thus prevented high torque loads on the machine mountings. Any remaining rotational energy is now within safe limits and provides no danger to the containment system.

In a second scenario, the rotor 15 may remain largely intact and the apparatus failure is brought on by failure of one of the other apparatus components. This may be one of a number of different items. If a failure is in the bearing pin 25 or ball or bearing cup, the rotor 15 and end cap 17 will drop down under the effect of gravity. The first line of crash control is the top axial catcher bearing 32 which catches the dropping rotor 15 by the block 27 of the end cap 17 in the shaped recess 31. The recess 31 serves to keep the rotor 15 centered for a short time as the rotor 15 begins its initial deceleration. As mentioned above, radial positioning of the bottom end of the rotor 15 is achieved by means of the lower radial catcher bearing 35 mounted on the support shaft 13.

As the top axial catcher bearing 32 rapidly wears away, the upper radial catcher bearing 33 takes over to centre the upper end of the rotor 15. Further deterioration of the rotor end cap 17 and top axial catcher bearing 32 causes the rotor 15 (if still intact at this stage) to bear down against the bottom axial catcher ring bearing 43 where friction between the rotor 15 and bearing 43 and between the bearing surfaces themselves continues to decelerate the rotor 15 down to safe limits. During the crash sequence, should the radial catcher bearings 33, 35 fail to hold the rotor 15 concentric with the support shaft 13, the inside surface of the rotor 15 will proceed to decelerate against the stator 11 which is anchored to the support shaft 13. Additionally, should the rotor 15 disintegrate at any point during this crash sequence, the mantle 37 will provide torque management as previously described.

Failure of the end cap 17 or the joint between the end cap 17 and the rotor 15 may cause the rotor 15 to drop without acting on the top axial catcher bearing 32. In this scenario, the rotor 15 drops directly onto the bottom axial catcher ring 43 and energy of the rotor is absorbed by friction between the rotor 15 and the ring 43 and between the ring 43 and the bearing pad 41, as described above.

As will be appreciated, the materials from which the apparatus is manufactured will have an effect on the friction produced between the various component parts during failure of the apparatus 1 in the scenarios described above. Hence, some control of a crash sequence can be predetermined by choosing carefully the materials to be used.

Although not shown in the drawings, skid rings may be carried by the inner surface on the containment wall 5. The skid rings may be free to rotate inside the containment wall 5 and to carry the central region of the cylindrical mantle 37 if the mantle expands and contacts the skid rings.

It will of course be understood that the present invention has been described above purely by way of example, and that modifications of detail can be made within the scope of the invention.

Claims

10CLAIMS

1. An energy storage and conversion apparatus comprising: a containment defining a vacuum chamber, a support shaft within the vacuum chamber, a stator on the shaft, a cylindrical rotor which, in use, is driven by the stator to store energy as kinetic energy of the rotor and acts with the stator as a generator to release energy and a movable energy absorbing structure between the rotor and the containment which, in the event of failure of the rotor, limits the amount of torque transmitted by the rotor to the containment.

2. An apparatus as claimed in claim 1, wherein the movable energy absorbing structure comprises a cylindrical mantle which can rotate about the rotor.

3. An apparatus as claimed in claim 2, wherein the cylindrical mantle is supported internally by bearing pads.

4. An apparatus as claimed in claim 3, wherein the bearing pads support both ends of the cylindrical mantle.

5. An apparatus as claimed in any preceding claim, wherein the movable energy absorbing structure includes an axial end bearing.

6. An apparatus as claimed in claim 5 when dependent upon claim 4, wherein the axial end bearing sits on a bearing pad which supports the cylindrical mantle.

7. An apparatus as claimed in claim 5, wherein the axial end bearing is an annular ring.

8. An apparatus as claimed in any preceding claim, further comprising at least one radial catcher bearing mounted on the support shaft for engaging the rotor in the event of a failure of the apparatus.

9. An apparatus as claimed in any preceding claim, wherein the rotor is carried by an end cap and a pin bearing supported by the support shaft.

10. An apparatus as claimed in claim 9, further comprising a top axial catcher bearing which catches the end cap in the event of failure of the pin bearing.

11. An apparatus as claimed in any preceding claim, wherein skid rings are carried by the containment, the skid rings being free to rotate relative to the containment in the event of failure of the apparatus.

12. An energy storage and conversion apparatus substantially as hereinbefore described with reference to and as shown in the accompanying drawings.