ACTIVE MAGNETIC BEARING APPARATUS

Abstract

An active magnetic bearing apparatus for supporting a rotor of a rotary machine comprises an axial magnetic bearing unit and a radial magnetic bearing unit mounted directly to one another. One of the axial magnetic bearing unit and the radial magnetic bearing unit is mounted to a support for attachment to a housing of the rotary machine.

Claims

1-15. (canceled)

16. An active magnetic bearing apparatus for supporting a rotor of rotary machine, the apparatus comprising: an axial magnetic bearing unit for supporting an axial load of the rotor; a radial magnetic bearing unit for supporting a radial load of the rotor, the radial magnetic bearing unit including an inner radial magnetic bearing; and an auxiliary bearing unit for supporting loads exceeding a load capacity of one of the axial magnetic bearing unit or the radial magnetic bearing unit; wherein the radial magnetic bearing unit is mounted directly to the axial magnetic bearing unit, and wherein one of the auxiliary bearing unit, the axial magnetic bearing unit and the radial magnetic bearing unit are mounted to a support frame.

17. The active magnetic bearing apparatus of claim 16, wherein the axial magnetic bearing unit includes an inner axial magnetic bearing surrounded by an outer auxiliary coil, the inner axial bearing including a primary winding of wire wound a magnetic core, and the outer auxiliary coil including a secondary winding of wire.

18. The active magnetic bearing apparatus of claim 17, wherein the primary winding of wire and the secondary winding of wire are wound in opposing directions.

19. The active magnetic bearing apparatus of claim 17, wherein a shielding frame reduces leakage of magnetic flux from the inner radial magnetic bearing to the support frame and electromagnetic components of the axial magnetic bearing unit.

20. The active magnetic bearing apparatus according to claim 16, wherein the apparatus comprises a position sensor for determining one of an axial or a radial position of the rotor.

21. The active magnetic bearing apparatus according to claim 16, wherein the apparatus comprises a fluid cooling channel for cooling the axial magnetic bearing unit and the radial magnetic bearing unit, the fluid cooling channel extending transversely through the active magnetic bearing apparatus and extending between the axial magnetic bearing unit and the radial magnetic bearing unit.

22. The active magnetic bearing apparatus according to claim 21, wherein the fluid cooling channel extends from a cooling fluid inlet nozzle provided on a first side of the active magnetic bearing apparatus to a second side of the active magnetic bearing apparatus opposite the first side of the active magnetic bearing apparatus.

23. The active magnetic bearing apparatus according to claim 21, wherein the fluid cooling channel extends through or adjacent one of the axial magnetic bearing unit and the radial magnetic bearing unit.

24. The active magnetic bearing apparatus according to claim 21 further comprising a fluid mover for generating a flow of a cooling fluid through the cooling channel, wherein the fluid mover is connected to the cooling fluid inlet nozzle.

25. The active magnetic bearing apparatus according to claim 16, wherein the auxiliary bearing unit includes an angular contact auxiliary ball bearing and a damping ribbon.

26. The active magnetic bearing apparatus according to claim 16, wherein the auxiliary bearing unit includes a brush seal configured to inhibit back flow of fluid from the rotary machine into the active magnetic bearing apparatus.

27. A rotary machine comprising: a housing; an active magnetic bearing apparatus arranged in the housing and configured to support a rotor of the rotary machine, the active magnetic bearing apparatus including: a support frame fixedly connected to the housing; an axial magnetic bearing unit for supporting an axial load of the rotor; a radial magnetic bearing unit for supporting a radial load of the rotor, the radial magnetic bearing unit including an inner radial magnetic; and an auxiliary bearing unit for supporting loads exceeding a load capacity of one of the axial magnetic bearing unit or the radial magnetic bearing unit; wherein the radial magnetic bearing unit is mounted directly to the axial magnetic bearing unit, and wherein one of the auxiliary bearing unit, the axial magnetic bearing unit and the radial magnetic bearing unit are mounted to the support frame.

28. The rotary machine of claim 27, wherein the axial magnetic bearing unit includes an inner axial magnetic bearing surrounded by an outer auxiliary coil, the inner axial bearing including a primary winding of wire wound a magnetic core, and the outer auxiliary coil including a secondary winding of wire.

29. The rotary machine of claim 28, wherein the primary winding of wire and the secondary winding of wire are wound in opposing directions.

30. The rotary machine of claim 27, wherein a shielding frame reduces leakage of magnetic flux from the inner radial magnetic bearing to the support frame and electromagnetic components of the axial magnetic bearing unit.

31. The rotary machine of claim 27, wherein the apparatus comprises a position sensor for determining one of an axial or a radial position of the rotor.

32. The rotary machine of claim 27, wherein the apparatus comprises a fluid cooling channel for cooling the axial magnetic bearing unit and the radial magnetic bearing unit, the fluid cooling channel extending transversely through the active magnetic bearing apparatus and extending between the axial magnetic bearing unit and the radial magnetic bearing unit.

33. The rotary machine of claim 32, further comprising a fluid mover for generating a flow of a cooling fluid through the cooling channel.

34. The rotary machine of claim 27, wherein the auxiliary bearing unit includes an angular contact auxiliary ball bearing and a damping ribbon.

35. The rotary machine of claim 27, wherein the auxiliary bearing unit includes a brush seal configured to inhibit back flow of fluid from the rotary machine into the active magnetic bearing apparatus.

Description

FIGURES

[0051] Embodiments will now be described by way of example only, with reference to the Figures, in which:

[0052] FIG. 1 is an assembled active magnetic bearing module viewed in cross-section;

[0053] FIG. 2 is an inside view of the assembled active magnetic bearing module of FIG. 1;

[0054] FIG. 3 is a side view of the assembled active magnetic bearing module of FIG. 1;

[0055] FIG. 4 is an exploded view of the disassembled components of the active magnetic bearing module of FIG. 1;

[0056] FIG. 5 is a schematic cross-section through a portion of an active magnetic bearing system and a rotor;

[0057] FIG. 6 is a cross-section through the assembled active magnetic bearing module of FIG. 1 showing cooling air flow paths;

[0058] FIG. 7 is a schematic cross-section through a rotary machine having a rotor supported at first and second ends by active magnetic bearing modules;

[0059] FIG. 8 is a flow chart illustrating a method of assembling an active magnetic bearing module;

[0060] FIG. 9 is a flow chart illustrating a method of assembling an active magnetic bearing module; and

[0061] FIG. 10 is a flow chart illustrating a method of assembling a rotary machine.

DETAILED DESCRIPTION

[0062] With reference to FIGS. 1, 2, 3 and 4, an active magnetic bearing module 1 includes a steel support frame 2, a radial magnetic bearing unit 3 and an axial magnetic bearing unit 4.

[0063] When assembled, the radial and axial magnetic bearing units 3 and 4 are mounted to the steel support frame 2 by bolts 5A-5F (FIG. 4). A position sensor 6 is mounted between the radial magnetic bearing unit 3 and the steel support frame 2. In the embodiment shown in FIGS. 1 to 4, shims 7A and 7B are provided between the axial magnetic bearing unit 4 and the radial magnetic bearing unit 3. However, it will be appreciated that shims are not necessarily present in all possible embodiments of the invention. A cooling air inlet nozzle 8 is attached to a periphery of the radial magnetic bearing unit 3. The cooling air inlet nozzle 8, the position sensor 6, the radial magnetic bearing unit 3 and the axial magnetic bearing unit 4 are all provided on a first side of the generally disc-shaped steel support frame 2.

[0064] An auxiliary bearing unit 9, a brush seal 10, a power connector 11 and a sensor connector 12 are mounted on a second side of the steel support frame 2 opposite the first side.

[0065] A central aperture 13 extends through the steel support frame 2. All of the axial magnetic bearing unit 4, the radial magnetic bearing unit 3, the position sensor 6, the auxiliary bearing unit 9 and the brush seal 10 are generally annular in shape and therefore include a central aperture which aligns with the central aperture 13 of the steel support frame 2 when assembled. The active magnetic bearing module 1 is therefore designed to receive a rotor of a rotary machine, whereby one end of the rotor extends into and through central aperture 13 of the magnetic bearing module 1 in use.

[0066] The axial magnetic bearing unit 4 includes an inner axial magnetic bearing 14 surrounded by an outer auxiliary coil 15. The inner axial magnetic bearing 14 contains electromagnetic components configured to generate a controllable magnetic field for supporting the axial load of a rotor inserted into the active magnetic bearing module 1. The outer auxiliary coil 15 includes copper windings arranged to generate a magnetic field, when current flows through the outer auxiliary coil 15, which opposes the magnetic field generated by the electromagnetic components of the inner axial magnetic bearing 4, thereby reducing or preventing leakage of magnetic flux from the inner axial magnetic bearing 14 into surrounding components of the active magnetic bearing module 1.

[0067] For example, FIG. 5 illustrates schematically the structure and operation of the axial magnetic bearing unit 4. The inner axial magnetic bearing 14 includes a primary winding of copper wire 16 wound around a magnetic core 17, and the outer auxiliary coil 15 includes a secondary winding of copper wire 18. The primary and secondary windings 16 and 18 are wound in opposing directions so that, in use, an electric current flows through the primary and secondary windings in opposite directions. Both the primary and secondary windings 16 and 18 are wound through approximately the same number of turns. The inner axial magnetic bearing 4 is provided immediately adjacent a shoulder portion 19 of the rotor 20. In such a configuration, the majority of magnetic flux 21 (represented by spaced-apart, curved flux lines) generated by operation of the inner axial magnetic bearing 4 flows along a main magnetic flux path 22 through the shoulder portion 19 of the rotor 20. By controlling the current though the primary and secondary windings 16 and 18, the strength of the bearing thrust force acting on the rotor can be varied such that the axial displacement of the rotor can be controlled. The presence of the secondary winding 18 in the outer auxiliary coil 15 increases the density of magnetic flux along the main flux path 22, thereby increasing the load capacity of the axial magnetic bearing unit 4. In addition, because the currents in the primary and secondary windings 16 and 18 flow in opposing directions, leakage of magnetic flux from the primary electromagnetic components to the surrounding components of the active magnetic bearing module 1 is reduced. In fact, the net magneto-motive force (MMF) of the axial magnetic bearing unit 4 can be reduced to zero (or close to zero) by operation of the outer auxiliary coil 15.

[0068] The radial magnetic bearing unit 3 includes an inner radial magnetic bearing 24 surrounded by an aluminium shielding frame 25. The inner radial magnetic bearing 24 may contain any arrangement of electromagnetic components known in the art for supporting the radial load of the rotor. The aluminium shielding frame 25 reduces leakage of magnetic flux from the inner radial magnetic bearing 24 to surrounding components of the active magnetic bearing module 1.

[0069] The position sensor 6 and controller are configured to determine the position of the rotor relative to the locations of the axial and radial magnetic bearing units 3 and 4. This is achieved by sensing movements of the rotor along two different radial directions and along an axial direction. The position sensor 6 is connected to a controller (not shown) also in communication with the axial and radial magnetic units 3 and 4. The controller is programmed to detect, based on outputs from the position sensor 6, axial or radial displacements of the rotor from a neutral position and to control operation of the axial and radial magnetic units 3 and 4 to compensate for those axial or radial displacements. The position sensor may be of any suitable type known to a person of skill in the art. For example, the position sensor may be an inductive, eddy-current, capacitive or optical position sensor.

[0070] The auxiliary bearing unit 9 includes an angular contact auxiliary ball bearing 26, a damping ribbon 27 and a cover 28 with a volute seal 29 attached thereto. The angular contact auxiliary ball bearing 26 is arranged such that the rotor only comes into contact with ball bearings when subject to loads which exceed the bearing capacity of the axial and radial magnetic bearing units or when the active magnetic bearing module, and the associated rotary machine in which it is installed, are powered down.

[0071] In this embodiment, the volute seal 29 enables tight attachment of the active magnetic bearing module 1 to a volute of a turbo compressor. However, it will be appreciated that in alternative embodiments, for example where the active magnetic bearing module is used to support the rotor of a different type of rotary machine, the volute seal 29 may not be present.

[0072] The brush seal 10 inhibits back flow of fluid from the rotary machine (e.g. the compressor), in which the active magnetic bearing module 1 is installed, into the active magnetic module itself. It will be appreciated that, in alternative embodiments, the brush seal may not be present.

[0073] Power supply, measurement signal and control signal wiring for the axial magnetic bearing unit 4, the radial magnetic bearing unit 3 and the position sensor 6 extends through channels (i.e. cable feedthroughs) in the steel support frame 2 from the first side to the second side where the power and sensor connectors 11 and 12 are provided. The power supply, measurement signal and control signal wiring may be separated into different channels to reduce electromagnetic interactions between the wiring.

[0074] As shown in FIG. 6, radial air cooling channels 30 and 31 extend transversely through the active magnetic bearing module 1 from the cooling air inlet nozzle 8, provided on a lower side of the module, to an upper side of the module. Air cooling channel 30 extends transversely between the axial magnetic bearing unit 4 and the radial magnetic bearing unit 3, between the shims 7A and 7B. Air cooling channel 31 extends transversely between the radial magnetic bearing unit 3 and the position sensor, as well as through open portions of the position sensor itself. In use, the cooling air inlet nozzle 8 is connected to an air mover, such as a fan, for blowing cooling air through the air cooling channels 30 and 31.

[0075] The electromagnetic shielding between the axial magnetic bearing unit 4, the radial magnetic bearing unit 3 and the steel support frame 2 provided by the auxiliary coil 15 and the aluminium support frame 25 permits the axial and radial magnetic bearing units to be mounted closely together, and to the steel support frame, thereby enabling a particularly compact structure. This is also assisted by the cooling provided by the radial air cooling channels.

[0076] The compact active magnetic bearing module 1 can be readily integrated into a rotary machine, such as a compressor. For example, FIG. 7 illustrates schematically how a rotor 101 of a rotary machine 100 is supported at first and second ends by first and second active magnetic bearing modules 102A and 102B, each module containing respective axial magnetic bearing units 103A,103B and radial magnetic units 104A,104B.

[0077] The active magnetic bearing modules are typically installed such that the first side of each steel support frame faces towards the centre of the rotor while the second side of each steel support frame faces away from the centre of the rotor. Accordingly, the first side of the support frame is an “inwards-facing” or “inner” side of the support frame and the second side of the support frame is an “outwards-facing” or “outer” side of the support frame. Since power supply and sensor connectors are provided on the second side of each steel support frame, connecting the axial magnetic bearing units, the radial magnetic bearing units and the position sensors to a power supply or to a controller is relatively simple and fast. It is also easy to carry out maintenance on these electrical connectors without disassembling the entire active magnetic bearing modules. Similarly, providing the auxiliary bearing units on the second, externally-facing sides of the steel support frames simplifies maintenance or replacement without disassembly of the active magnetic bearing modules.

[0078] A simplified method of assembling an active magnetic bearing module 1 is illustrated in a flow diagram in FIG. 8. In block 201, an axial magnetic bearing unit and a radial magnetic bearing unit are mounted directly together, for example by way of bolts. In block 202, one of the axial magnetic bearing unit and the radial magnetic bearing unit is mounted to a steel support frame, for example by way of bolts. As can be seen in FIG. 9, the method steps 201 and 202 may also be carried out in the opposite order. In fact, the order in which the steps is carried out is not important. For example, the method steps may be carried out concurrently, for example by stacking the axial magnetic bearing unit, the radial magnetic bearing unit and steel support frame, and mounting all three components to one another at the same time, for example by way of bolts.

[0079] A simplified method of assembling a rotary machine 100 is illustrated in a flow diagram in FIG. 10. In block 301, a first active magnetic bearing module is provided or assembled. In block 302, a first end of a rotor is inserted into the first magnetic bearing module such that a first axial bearing region of the rotor aligns with the axial magnetic bearing unit of the first active magnetic bearing module and a first radial bearing region of the rotor aligns with the radial magnetic bearing unit of the first active magnetic bearing module. In block 303, a second active magnetic bearing module is provided or assembled. In block 304, a second end of the rotor is inserted into the second active magnetic bearing module such that a second axial bearing region of the rotor aligns with the axial magnetic bearing unit of the second active magnetic bearing module and a second radial bearing region of the rotor aligns with the radial magnetic bearing unit of the second active magnetic bearing module.

[0080] It will be understood that the invention is not limited to the embodiments described above and various modifications and improvements can be made without departing from the concepts described herein. Except where mutually exclusive, any of the features may be employed separately or in combination with any other features and the disclosure extends to and includes all combinations and sub-combinations of one or more features described herein.