AU715929B2 - An energy storage and conversion apparatus - Google Patents

Description

P/00/0011 Regulation 3.2

AUSTRALIA

Patents Act 1990 COMPLETE

SPECIFICATION

FOR A STANDARD

PATENT

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ORIGINAL

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rotor is driven by a stator within the rotor to store energy as kinetic energy of the rotor and wherein energy can be withdrawn from the rotor when the stator and rotor act as a generator.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 0 0• and conversion apparatus and, as a result thereof, has designed an apparatus according to the present invention.

According to the present invention, there is provided an energy storage and 0.o conversion apparatus comprising a plurality of stators, a corresponding plurality of cylindrical rotors arranged to rotate about the stators and means for containing the stators and rotors, .0 the stators in use driving the rotors to store energy as kinetic energy of the rotors and interacting with the rotors to act as generators to release energy, wherein the containment means defines a plurality of chambers within a unitary structure in which the stators and rotors are accommodated.

As far as the applicant is aware, a single structure accommodating a plurality of energy storage and conversion apparatus units has never before been suggested.

SThe unitary structure preferably comprises a honeycomb-type structure in which a plurality of cylindrical chambers are regularly arranged.

Preferably each chamber accommodates a single stator and corresponding O 25 rotor. However, a single chamber may accommodate more than one stator/rotor unit in some circumstances.

The advantages of such a honeycomb arrangement in a single unit are that a greater number of rotors can be accommodated in the smallest area possible since the rotors share common containment walls, and those walls internal to the structure do not need to be as thick as would be required in a single machine since a breech from one rotor chamber to another would not endanger personnel. Further, the TNB:JL:#29916SPE 11 December 1998 common mass of a unitary structure of this size is sufficient to absorb the kinetic energy of a crashing rotor without any special bolting down arrangements.

The unitary structure may be fabricated to include any number of rotors depending on the total energy storage requirements of the application. The arrangement shown for illustration purposes contains 37 chambers.

The unitary structure may be formed from a plurality of extrusions cut to length and welded together. If the unitary structure is formed in this way, preferably a minimum number of different shaped extrusions are used to produce the complete unitary structure. By way of example a structure is illustrated 10 which employs only three different extrusion types.

Preferably, each chamber is closed by an end flange incorporating a non- 0o* return valve. Although each chamber may be provided with a separate vacuum pump, it is preferable that the unitary structure be encased in a common vacuum chamber so that the common vacuum chamber can be pumped out, thereby resulting S 15 in a vacuum being produced in each rotor chamber. In the event of a crash of any

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single rotor in the unitary structure, the instantaneous release of light gases from the rotor material and subsequent pressure rise in the rotor chamber will cause the nonreturn valve to close thus isolating that chamber from the other chambers in the structure and preserving the integrity of the remaining rotors.

Although the unitary structure may be manufactured from aluminium, any 4 other appropriate material can, of course, alternatively be used.

-A common cooling system may be provided for all the stators and rotors of the complete apparatus. This is clearly preferable to having separate cooling systems for each stator/rotor unit.

Preferably the containment means includes a getter for removing gas from the chambers to improve the vacuum. Silicon or carbon based getters are the preferred choice for this.

Each stator and rotor unit can preferably store up to 20 kWhr, more preferably about 5 kWhr, of energy.

Although not specifically stated to date, it should be appreciated that any of the features of the various aspects of the present invention described herein may be TNB:JL:#29916SPE 11 December 1998 combined with any other aspect to produce an energy storage and conversion apparatus which is both novel and inventive over the known prior art.

Furthermore, in an energy storage and conversion apparatus according to the present invention, an external circuit may be 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.

Moreover, the speed of a rotor may be measured to provide an output indicative of the energy stored in the rotor. More preferably, a visual output is provided giving the energy available from the apparatus in real time.

10 In a particular embodiment, the speed of the rotor may be measured by 9*e* monitoring the switching frequency of the motor/generator power electronics. o..

•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 4 magnetising fixture for magnetising the rotor are shown; 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 apparatus according to the present invention incorporating an external circuit for removing gas from the vacuum chamber of the apparatus.

TNB:JL:#29916SPE 11 December 1998 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 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 stator 11 (for energising the stator 11 to drive the rotor 13) are not shown in the enclosed drawings, but may pass along the hollow bore 9a of the shaft 9.

0The stator 11 is not shown in any detail in Figure 1, but may be of any 10 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 Sstrength. 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 Oprevented 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 that torque forces and energy imparted by the rotor 13 during a failure of the apparatus 1 will be transferred to the base member 3, and hence the solid support 19, via the shaft 9.

TNB:JL:#29916SPE 11 December 1998 It should also be noted that the rotor 13 has a length which is at least twice its 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.

S•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 owe: 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.

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 Aspherical 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 which acts to dampen the radial and axial motion of the cup 37 as the rotor 13 moves, thereby resulting in damping of the complete energy storage and conversion apparatus 1. The oil in the damper 39 also acts as a lubricant for the pin bearing 31 TNB:JL:#29916SPE 11 December 1998 between the head 35 of the bearing 31 and the surface of the cup 37. As will be 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 Sowith the stator 11. More particularly, a permanent magnet 45 is mounted on the 6 shaft 9 with, in this case, a north pole of the magnet 45 facing the inside surface of 10 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 too: 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.

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 Minvention is shown. In Figure 2, however, the rotor 13 is shown significantly shortened. As can be seen, a radial multi-polar rnagnetisation 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 only one north pole 47 and one south pole 49 are shown on of the rotor 13, additional poles and additional permanent magnets/electromagents could be utilised TNB:JL:#29916SPE 11 December 1998 8 to strengthen the interaction between the rotor 13 and the magnets/electro magnets mounted on the shaft 9, depending upon the forces required.

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 rotor 13 during manufacture of the rotor 13. Although it is possible to introduce pre-magnetised material into the rotor 13 and to align the material as required 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 10 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 o•(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.

c 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 nwinvention further provides an energy storage and conversion apparatus comprising a Itplurality 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 neat and compact by virtue of the arrangement of cylindrical chambers 102 in the 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 TNB:JL:#29916SPE 11 December 1998 requiring an unreasonable amount of space. As will be seen from Figure 5, adjacent 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 shown in Figure 5. It will be understood however, that the choice of extrusion shape, and number of different shapes used to fabricate the unitary structure are

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1 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 d 20 individual chambers 102 being drawn out through the non-return valves to be removed by the main vacuum pump. Further, if an individual stator 1 1/rotor 13 unit OOfails, 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 the vacuum within the vacuum chambers 7, 102. In this regard, as will be appreciated, the better the vacuum within the vacuum chamber 7, 102, the less friction will result and, accordingly, less energy will be lost from the rotor 13.

TNB:JL:#29916SPE 11 December 1998 Hence, a higher vacuum is essential for successful running of an energy storage and 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 is attached to the containment 5 of an energy storage and conversion apparatus 1.

Seals 71 are provided between the getter housing 61 and the containment and between 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) 10 is used. This incorporates a wall 73 for encasing the getter housing 61, an access E g.

g 75 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.

SAnother form of apparatus for removing gases present in the vacuum Schamber 7 of an energy storage and conversion apparatus 1 according to the present Sinvention is shown in Figure 7. In this Figure, a molecular pump 79, comprising a Splurality 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.

An external pipe circuit 83 is shown incorporating a gas remover device which may be an ionisation pump or a getter material. Hence, due to the pressure TNB:JL:#29916SPE 11 December 1998 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.

To assist in servicing of the remover device 85, valves 87 are provided on 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 device 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

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*10 to the valves 87 being reopened. Hence, a very simple and user friendly *0W@ o arrangement is provided for improving the vacuum within the vacuum chamber 7 of o* 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 S 15 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:#29916SPE 11 December 1998 'ZNB:JL:#29916SPE I IDecember 1998

Claims (16)

1. An energy storage and conversion apparatus comprising a plurality of stators, a corresponding plurality of cylindrical rotors arranged to rotate about the stators and means for containing the stators and rotors, the stators in use driving the rotors to store energy as kinetic energy of the rotors and interacting with the rotors to act as generators to release energy, "wherein the containment means defines a plurality of chambers within a •I b o 0 10 unitary structure in which the stators and rotors are accommodated.

2. An apparatus as claimed in claim 1, wherein each chamber accommodates a single stator and corresponding rotor.

3. An apparatus as claimed in claim 1 or claim 2, wherein the unitary structure comprises a honeycomb-type structure in which a plurality of cylindrical 15 chambers are regularly arranged.

4. An apparatus as claimed in any one of claims 1-3, wherein the unitary structure is formed from a plurality of extrusions cut to length and welded together.

An apparatus as claimed in claim 4, wherein only three different shaped extrusions are used to produce the complete unitary structure.

6. An apparatus as claimed in any one of claims 1-5, wherein each chamber is closed by an end flange incorporating a non-return valve to protect adjacent rotors in the event of a crash occurring in any one chamber.

7. An apparatus as claimed in any one of claims 1-6, wherein the unitary structure is encased within a vacuum chamber.

8. An apparatus as claimed in any one of claims 1-7, wherein the unitary structure is manufactured from aluminium.

9. An apparatus as claimed in any one of claims 1-8, wherein a common cooling system is provided for all the stators and rotors of the complete apparatus. An apparatus as claimed in any one of claims 1-9, wherein the containment means include a getter for removing gas from the chambers to improve the vacuum.

TNB:JL:#29916SPE 11 December 1998 0e 0O* a a 00*6

11. An apparatus as claimed in any one of claims 1-10, wherein each stator and rotor unit can store up to 10 kWhr, preferably 5 kWhr, of energy.

12. An apparatus as claimed in any one of claims 1-11, wherein the unitary structure includes between 30 and 40, preferably 37, chambers.

13. 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.

14. An apparatus as claimed in any preceding claim, wherein the speed of 0 the rotor is measured to provide an output indicative of the energy stored in the rotor.

15. An apparatus as claimed in claim 14, wherein a visual output is provided giving the energy available from the apparatus in real time.

16. An apparatus as claimed in claim 14 or claim 15, wherein the speed of 5 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 1: S. 000 2( TNB:JL:#29916SPE 11 December 1998