AU715669B2 - An energy storage and conversion apparatus - Google Patents

Description

-1- P/00/0011 Regulation 3.2

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT 9@

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ORIGINAL

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Name of Applicant: Actual Inventors: Address for service in Australia: Invention Title: BRITISH NUCLEAR FUELS PLC Roger Eric HORNER; Colin David TARRANT; Ian CROMBIE; Geoffrey Martin BARKER and David Stephen HAYWARD CARTER SMITH BEADLE 2 Railway Parade Camberwell Victoria 3124 Australia AN ENERGY STORAGE AND CONVERSION APPARATUS The following statement is a full description of this invention, including the best method of performing it known to us This invention relates to energy storage and conversion apparatus, 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rotor is driven by a stator within the rotor to store energy as kinetic energy of the rotor and wherein energy can be withdrawn from the rotor when the stator and rotor act as a generator.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 designed an apparatus **so °00;0 according to the present invention.

10 According to the present invention, there is provided an energy storage and 6066 6conversion apparatus comprising *6 a base member, °o o •a containment mounted on the base member defining a vacuum chamber, a substantially vertical shaft within the vacuum chamber, a stator on the shaft and 6 66a cylindrical rotor which, in use, is driven by the stator to store energy as 6666 Skinetic energy of the rotor and acts with the stator as a generator to release energy, °66 characterised in that the shaft is mounted to the base member such that, in the event r of a failure of the apparatus, the energy stored in the rotor is preferentially transferred to the shaft rather than to the containment.

By providing an apparatus of this kind, torque forces resulting from a crashing rotor will not all impact themselves on the machine containment as is the case in many prior art flywheel energy storage and conversion systems. Instead the torque forces will be transmitted via the stator to the central shaft and from the shaft either directly to the machine base plate or be dissipated in a friction joint on the shaft (for example between the motor/generator and the shaft). The containment may therefore have a reduced wall thickness than is normally required to withstand such high energy dissipation.

Preferably the spacing between the rotor and the stator on the shaft is substantially less than the spacing between the rotor and the containment. This arrangement ensures that, if a rotor does fail, it will crash initially into the TNB:JL:#29914SPE 11 December 1998 stator/shaft unit rather than the containment wall. Energy will, therefore, be transferred to the base member immediately upon failing of the apparatus or be dissipated in the friction joint on the shaft.

The base member may include a recess for receiving an end of the shaft, the shaft being received in the recess with a tight fit. Other ways of engaging the shaft with the base member can, of course, alternatively be used (for example, a friction joint for energy dissipation).

Preferably the shaft is formed of high strength aluminium. Any other suitable *0oo .000 material could alternatively be used.

*e10 Preferably the shaft is hollow to accommodate a pin bearing for supporting bODO the rotor. The shaft may, however, simply have a recess at its upper end for r •receiving the pin bearing, rather than being completely hollow.

•The base member is preferably adapted to be attached to a support having significant mass which safely disperses energy from the rotor, if necessary.

Although not essential for the implementation of the present invention, the length of the rotor is preferably at least twice the external diameter of the rotor. If this requirement is satisfied, however, a tall relatively thin unit is provided which includes a significant length of shaft per mass of rotor. Hence, a safer apparatus may result. Furthermore, by forming a tall, relatively thin unit, a larger number of units can be accommodated in any given floor area than is the case with the known prior art apparatus.

Specific embodiments of the present invention are now described, by ways of example only, with reference to the accompanying drawings in which: Figure 1 is sectional side view of an energy storage and conversion apparatus according to the present invention; Figure 2 is a schematic cross-sectional side view of the inner layer of a rotor, somewhat shortened, which could be used in an apparatus as shown in Figure 1; Figure 3 is a view in the direction A-A of the rotor of Figure 2; Figure 4 is the same view as in Figure 3, but wherein windings of a magnetising fixture for magnetising the rotor are shown; TNB:JL:#29914SPE 11 December 1998 Figure 5 is a plan view of a containment for accommodating a plurality of stator/rotor units; Figure 6A is a schematic side view of a maintenance bell for a, getter housing assembly mounted on a side of an energy storage and conversion apparatus containment wall; Figure 6B is an enlarged side view of the getter housing assembly shown in the maintenance bell of Figure 6A; and Figure 7 is a schematic side view of an energy storage and conversion *e0* apparatus according to the present invention incorporating an external circuit for 10 removing gas from the vacuum chamber of the apparatus.

With reference to Figure 1, an energy storage and conversion apparatus 1 comprises a base member 3, a containment 5 mounted on the base member 3 0 defining a vacuum chamber 7, a substantially vertical shaft 9 within the vacuum chamber 7, a stator 11, mounted on the shaft 9 and a cylindrical rotor 13 which, in use, is driven by the stator 11 to store energy as kinetic energy of the rotor 13 and acts with the stator 11 as a generator to release energy. The electrical contacts to the O. stator 11 (for energising the stator 11 to drive the rotor 13) are not shown in the O*:B •enclosed drawings, but may pass along the hollow bore 9a of the shaft 9.

6.0..0 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 4 poles, about which coils are wound to produce magnetic flux which is directed by the pole faces towards the rotor 13 to cause the rotor 13 to rotate. In this way, energy can be stored as kinetic energy of the rotor 13. Conversely, if energy is to be withdrawn from the apparatus 1, the rotor 13 and stator 11 can act as a generator or generator to produce an electrical output via the power electronics (not shown) of the apparatus.

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 15 through the base member 3 are shown for receiving bolts 17 for securing the base member 3 to a floor 19 or the like of considerable mass and TNB:JL:#29914SPE 11 December 1998 strength. As a result, the energy storage and conversion apparatus 1 will be held firmly in position, even if the apparatus 1 fails.

In the event of a failure of the apparatus 1, the energy stored in the rotor 13 is prevented from destroying the containment 5 by virtue of the shaft 9 being solidly mounted to the base member 3. More particularly, the lower end 21 of the shaft 9 is received in a recess 23 in the base member 3 with a tight fit. Means (not shown) for strengthening the joint between the shaft 9 and the base member 3 can also be used. Further, the shaft 9 is made of a high strength material, such as aluminium, so 9**9 0..r.e that torque forces and energy imparted by the rotor 13 during a failure of the 10 apparatus 1 will be transferred to the base member 3, and hence the solid support 009.

19, via the shaft 9.

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It should also be noted that the rotor 13 has a length which is at least twice its 0S90 external diameter so that a tall, relatively thin apparatus 1 results. This arrangement also means that there is a significant length of shaft 9 for absorbing torque forces and energy from the rotor 13 in the event of a failure of the apparatus 1. A safer apparatus 1 is, therefore, provided and the containment 5 does not need to have a particularly large wall thickness. In practice, of course, the containment 5 would be designed to provide significant shielding against a rotor failure.

0 As can be seen from Figure 1, the rotor 13 is formed with an inner layer of E-glass and an outer layer 27 of carbon fibre composite. Other suitable materials could, however, alternatively be used, provided that they provide the required properties for the rotor. In this regard, the inner layer 25 of E-glass is relatively cheap and provides a reasonable amount of mass to the rotor 13. The E-glass is also able to receive magnetisable material, in the form of particles or powder, between the fibres or tows of the glass fibre in the E-glass. As can be seen from Figure 2 which only shows the inner layer 25 of the rotor 13, the magnetisable material is preferably only entered into the inner half 25a of the inner layer 25 of the rotor 13.

The outer layer 27 of the rotor 13 is included primarily to support the inner layer and is, therefore, formed of a material having significant strength when spinning at high speed, such as 1,200-1,800 Hz. Carbon fibre composites are particularly suitable for this.

TNB:JL:#29914SPE 11 December 1998 The rotor 13 includes an end cap 29 made of maraging steel, aluminium or carbon fibre composite which mounts a pin bearing 31 as shown in Figure 1. The pin bearing comprises a shaft 33 carrying a spherical ball 35 at its free end. The spherical ball 35 is etched, during manufacture, such that spiral grooves are formed in the surface thereof. The spherical ball 35, or head, of the pin bearing 31 is received in a cup 37 mounted in a damper 39 positioned at the end of the shaft 9.

The damper 39 extends into the bore 9a of the shaft and is retained therein by means of side flanges 41 abutting the upper end of the shaft 9. The damper 39 carries oil *Oa.

which acts to dampen the radial and axial motion of the cup 37 as the rotor 13 .10 moves, thereby resulting in damping of the complete energy storage and conversion o° apparatus 1. The oil in the damper 39 also acts as a lubricant for the pin bearing 31 0S between the head 35 of the bearing 31 and the surface of the cup 37. As will be O appreciated, as the rotor 13 spins, the spiral grooves in the head of the pin bearing 31 drive oil between the head 35 and the cup 37 to lift slightly the rotor 13 onto a film of oil. The rotor 13 is, therefore, free to spin with negligible friction, resulting in minimal energy being lost through the bearing. This is clearly desirable.

At the lower end of the rotor 13 a permanent magnet bearing 43 is provided to ensure, in combination with the pin bearing 31, that the rotor 13 does not clash with the stator 11. More particularly, a permanent magnet 45 is mounted on the

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shaft 9 with, in this case, a north pole of the magnet 45 facing the inside surface of the rotor 13. As can be seen in Figure 2, the magnetisable material within the inner layer 25 of the rotor 13 is magnetised with a north pole 47 and a south pole 49 formed annularly. The north pole of the magnet 45 and the north pole 47 of the rotor 13 face each other and hence provide a repelling force and the south pole 49 of the rotor 13 is attracted towards the north pole of the magnet 45. By virtue of this arrangement, the rotor 13 is kept clear from the stator 11 and the rotor 13 is provided with a little lift to assist in reducing friction between the pin bearing 31 and the cup 37.

An additional axial bearing may also be provided comprising another permanent magnet 51 (see Figure 1) for acting in conjunction with a magnetised region on the end of the rotor 13 to repel the rotor 13 and thereby lift the rotor 13.

TNB:JL:#29914SPE 11 December 1998 With reference to Figures 2-4, an inner layer 25 of the rotor 13 which could be used in an energy storage and conversion apparatus according to the present invention is shown. In Figure 2, however, the rotor 13 is shown significantly shortened. As can be seen, a radial multi-polar magnetisation 51, to enable the rotor to act as a motor/generator, is shown in the central region of the rotor 13. At the lower end of the rotor 13, homo-polar radial magnetisation is shown which can interact with a permanent magnet (as described above) or an electromagnet mounted on the shaft 9 to assist in suspension of the rotor 13 about the stator 11. Although 1 only one north pole 47 and one south pole 49 are shown on of the rotor 13, 10 additional poles and additional permanent magnets/electromagents could be utilised 0000 to strengthen the interaction between the rotor 13 and the magnets/electro magnets @0 mounted on the shaft 9, depending upon the forces required.

0000 The magnetised regions 47, 49, 51 of the rotor 13 are produced by acting on virgin magnet material included in the inner half 25a of the inner layer 25 of the 15 rotor 13 during manufacture of the rotor 13. Although it is possible to introduce 0* pre-magnetised material into the rotor 13 and to align the material as required 0000 e° during manufacture of the rotor 13, a rotor 13 as described herein preferably has the magnetisation applied to the rotor 13 after the composite materials of the rotor 13 have cured. This is achieved by impressing on the virgin magnet material within the rotor 13 a magnetisation using a fixture which consists of a series of coils 53 which, when excited, produce a magnetic field of the form required in the magnet (see Figure The field required to magnetise the magnetic material, which may be ferrite, NdFeB or any other appropriate material, depends on the material type. For example, 1.5 Tesla is required for ferrite, whereas 4 Tesla is required for NdFeB.

The field is produced by a single, high current pulse from a capacitor discharge unit, which current may be in the region of 30,000 amps. Once the field has been applied to the rotor 13, the fixture is removed leaving the permanent magnetisation as shown in Figures 2 and 3, for example. As will be appreciated, it is simply necessary to design a fixture for a particular application to achieve a desired magnetisation in the rotor 13.

TNB:JL:#29914SPE 11 December 1998 Although to date an energy storage and conversion apparatus 1 has been described which incorporates a single stator 11 with a single rotor 13, the present invention further provides an energy storage and conversion apparatus comprising a plurality of stators 11, a corresponding plurality of cylindrical rotors 13 arranged to rotate about the stators 11 and containment means 100 defining a plurality of chambers 102 within a unitary structure in which the stators 11 and rotors 13 are accommodated. Such a containment 100 is shown in Figure The energy storage and conversion apparatus shown in Figure 5 is extremely 9040 neat and compact by virtue of the arrangement of cylindrical chambers 102 in the 10 unitary structure. As a result, an apparatus having the power storage and conversion capability of 37 apparatus as shown in Figure 1 is provided without 9.

requiring an unreasonable amount of space. As will be seen from Figure 5, adjacent 9*9e vacuum chambers 102 share common containment walls 104.

The honeycomb-type structure shown in Figure 5 is formed from three different shaped extrusions 106, 108, 110 (cf. the shaded area in Figure The extrusions are made of aluminium or any other appropriate material and are simply cut to length. Adjacent extrusions are then welded together by weld joints 112, as 0. shown in Figure 5. It will be understood however, that the choice of extrusion 00 0. shape, and number of different shapes used to fabricate the unitary structure are based purely on commercial reasons to minimise fabrication costs and the choice of extrusion shapes and numbers of different shapes used does not affect the validity of the final structure.

Although in theory each chamber 102 could have an end flange at either end and a separate means for preserving the vacuum in the chamber 102, an apparatus according to the present invention ideally has either an external casing (not shown) around the complete unitary structure or an end capping covering at least one end of the unitary structure. In either event, each chamber 102 should still have its own end flanges (not shown); a non-return valve may then be provided in each end cap protected by the outer capping or casing. In such an arrangement, a single vacuum pumping device can be provided for the complete unitary structure, gas within the individual chambers 102 being drawn out through the non-return valves to be TNB:JL:#29914SPE 11 December 1998 removed by the main vacuum pump. Further, if an individual stator 1 /rotor 13 unit fails, resulting in molecules being released to the rotor chamber, the remaining units will not be affected due to the protection provided by the closing of the non-return valve.

Moving on now to Figures 6A and 6B, a getter housing assembly 61 and maintenance bell 63 are shown. The getter housing assembly 61 provides a mount for a getter material 65, such as silica gel, activated charcoal (possibly in the form of a cloth or fabric formed by pyrolysis), which absorbs gas molecules to improve 0046 o; the vacuum within the vacuum chambers 7, 102. In this regard, as will be :o 10 appreciated, the better the vacuum within the vacuum chamber 7, 102, the less •00e friction will result and, accordingly, less energy will be lost from the rotor 13.

a Hence, a higher vacuum is essential for successful running of an energy storage and 0000 conversion apparatus according to the present invention.

With specific reference to Figure 6B, the getter material 65 is mounted on an end cap 67 of the getter housing assembly 61 such that the getter material 65 is positioned adjacent to the rotor 13. A cylindrical wall 69 of the getter housing 61 °o 0 is attached to the containment 5 of an energy storage and conversion apparatus 1.

o~o Seals 71 are provided between the getter housing 61 and the containment au ULW-eeii the end cap 67 and the cylindrical wall 69 of the housing 61. To enable the getter 65 to be serviced or replaced, the maintenance bell 63 (Figure 6A) is used. This incorporates a wall 73 for encasing the getter housing 61, an access to a vacuum pump for producing a high vacuum within the maintenance bell 63 and robotic or other maintenance tools 77 for interacting with the getter housing 61.

Hence, when the maintenance bell 63 has been attached to the containment 5 and a vacuum has been produced within the maintenance bell 63, the tools 77 can be used to remove the end cap 67 and attached getter material 65 from the getter housing 61.

Replacements of the getter material 65 can then be achieved without spoiling the vacuum around the rotor 13 within the vacuum chambers 7, 102 of the energy storage and conversion apparatus 1. Once replacement of the getter material 65 has been achieved, the end cap 67 of the getter housing 61 is replaced prior to the maintenance bell 63 being removed.

TNB:JL:#29914SPE 11 December 1998 Another form of apparatus for removing gases present in the vacuum chamber 7 of an energy storage and conversion apparatus 1 according to the present invention is shown in Figure 7. In this Figure, a molecular pump 79, comprising a plurality of helical grooves 81, faces the outside of the rotor 13. As the rotor 13 rotates, gases produced by off-gasing from the rotor, or other gases within the containment 5, are driven by the molecular pump 79 upwards in Figure 7. This results in a low pressure region being formed towards the bottom of the vacuum chamber 7 and a high pressure region being formed towards the top of the vacuum chamber 7.

10 An external pipe circuit 83 is shown incorporating a gas remover device

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which may be an ionisation pump or a getter material. Hence, due to the pressure differential between the high pressure region and the low pressure region in the vacuum chamber 7, gas is driven through the remover device 85 and is thereby removed from the system. An improved vacuum can therefore be achieved within the vacuum chamber 7.

d To assist in servicing of the remover device 85, valves 87 are provided on S either side of the remover device 85. When these valves 87 are closed, the remover device 85 can be disconnected from the pipe circuit 83 for servicing. The remover udevice 85 then simply needs to be reinstated into the circuit 83 and that part of circuit 83 between the valves 87 needs to be pumped out to produce a vacuum prior to the valves 87 being reopened. Hence, a very simple and user friendly arrangement is provided for improving the vacuum within the vacuum chamber 7 of the energy storage and conversion, apparatus 1.

Although not shown in the drawings, the speed of the rotor 13 can be measured, such as by monitoring the switching frequency of the motor/generator power electronics, to provide an output indicative of the energy stored in the rotor 13 at any particular time. More preferably, a visual output is provided giving the energy available from the energy storage and conversion apparatus 1 in real time.

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, as defined by the appended claims.

TNB:JL:#29914SPE 11 December 1998

Claims (13)

1. An energy storage and conversion apparatus comprising a base member, a containment mounted on the base member defining a vacuum chamber, a substantially vertical shaft within the vacuum chamber, *a stator on the shaft and 10 a cylindrical rotor which, in use, is driven by the stator to store energy #*to as kinetic energy of the rotor and acts with the stator as a generator to release .4 4 O° Fenergy, characterised in that the shaft is mounted to the base member such that, in o •the event of a failure of the apparatus, the energy stored in the rotor is preferentially transferred to the shaft rather than to the containment.

2. An apparatus as claimed in claim 1, wherein the spacing between the rotor and the stator on the shaft is substantially less than the spacing O0 between the rotor and the containment.

3. An apparatus as claimed in claim 1 or claim 2, wherein the .0 abase member includes a recess for receiving an end of the shaft, the shaft being received in the recess with a tight fit.

4. An apparatus as claimed in any one of claims 1-3, wherein the shaft is formed of high strength aluminium.

An apparatus as claimed in any one of claims 1-4, wherein the shaft is hollow to accommodate a pin bearing and damper for supporting the rotor.

6. An apparatus as claimed in any one of claims 1-5, wherein the base member is adapted to be attached to a support of significant mass which can safely disperse energy from the rotor, if necessary.

7. An apparatus as claimed in any one of claims 1-6, wherein the length of the rotor is at least twice the external diameter of the rotor.

8. An apparatus as claimed in any one of claims 1-7, wherein the rotor comprises an inner layer of glass fibre and an outer layer of carbon fibre, the TNB:JL:#29914SPE I1 December 1998 em.. 0O*0 a *6 C 00C 0S q C t 0 e g. 0S 0 12 thickness of the inner layer being about two thirds of the thickness of the complete rotor.

9. An apparatus as claimed in any one of claims 1-8, wherein the containment means defines a plurality of chambers within a unitary structure in which the stators and rotors are accommodated. An apparatus as claimed in any preceding claim, wherein an external circuit is provided through which gases in the containment are driven by a pressure difference, the external circuit including a device for removing gas thereby improving the vacuum within the containment.

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11. An apparatus as claimed in any preceding claim, wherein the speed of the rotor is measured to provide an output indicative of the energy stored in the rotor.

12. An apparatus as claimed in claim 11, wherein a visual output is provided giving the energy available from the apparatus in real time.

13. An apparatus as claimed in claim 11 or claim 12, wherein the speed of the rotor is measured by monitoring the switching frequency of the motor/generator power electronics. DATED: 11 December, 1998 CATER SMITH BEADLE Patent Attorneys for the Applicant: BRITISH NUCLEAR FUELS PLC TNB:JL:#29914SPE I1 December 1998