Abstract
The present inventions include a rotating electromagnetic machine such as a motor or generator wherein changes of flux direction adjacent the air gap are avoided. The disclosed improvements apply to permanent magnet alternators, induction motors and generators, doubly fed induction generators, and the like. Adaptation of coils to and fixation within the required slot geometries are disclosed. Excitation systems co-located within the primary rotor core and primary stator core are also disclosed. The use of rubber vulcanized to the rotor in conjunction with a stainless steel rotor sleeve is also disclosed.
Claims
1. A rotating electrical machine comprising an alternating current stator with stator slots, a rotor that rotates relative to said alternating current stator, an air gap between said stator and said rotor, and a magnetic flux that crosses said air gap, wherein the stator slots are substantially aligned with said magnetic flux at rated load conditions.
2. A rotating electrical machine comprising an alternating current stator, a rotor that rotates relative to said alternating current stator, a gap between said stator and said rotor, and a magnetic flux that crosses said gap, wherein the rotor magnetization is substantially aligned with said magnetic flux at rated load.
3. A rotating electrical machine comprising an alternating current stator with stator slots, a rotor that rotates relative to said alternating current stator, an air gap between said stator and said rotor, and a magnetic flux that crosses said air gap, wherein said stator slots are substantially aligned with said magnetic flux that crosses the air gap at rated load conditions and wherein the rotor magnetization is substantially aligned with said magnetic flux that crosses the air gap at said rated load conditions.
4. The rotating electrical machine as described in claim 3 further comprising a rotor field coil.
5. A rotating electrical machine excitation system co-located with a rotating electrical machine, comprising a stator with at least one AC coil and at least one DC coil, and a rotor, wherein said DC coil in the otherwise AC stator generates AC power in the rotor that is otherwise of non-alternating magnetic flux, wherein said AC power in the rotor is rectified to DC power within the rotor and used to excite a rotor field coil.
6. The rotating electrical machine as described in claim 5 wherein rectification is controlled through an optical link between a excitation controller and an optically controlled rectifier.
7. The rotating machine as described in claim 5 wherein a portion of the rotor field is supplied by one or more permanent magnet segments.
8. A coil fixation system for rotating electrical machines comprising electrical coils and elastomeric packers, wherein said coils are secured with the aid of said elastomeric packers, wherein said packers are stretched thin for assembly and positioning of said coils, then allowed to return to an unstretched condition for a tight fit after said coils are assembled and positioned.
9. A submersible rotating electrical machine including a rotor, a stainless steel sleeve fitted to said rotor, a gap aside said sleeve, a layer of rubber aside said gap, and a stator, wherein said layer of rubber is bonded to said stator.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 is prior art.
[0019] FIG. 2 is prior art.
[0020] FIG. 3 is prior art.
[0021] FIGS. 4a, 4b, and 4c illustrate a cross section of a permanent magnet machine incorporating form wound Roebel bar coils adapted to the present invention. FIG. 4b shows detail of circled region B within and indicated in FIG. 4a. FIG. 4c shows detail of region E within and indicated in FIG. 4b.
[0022] FIGS. 5a, 5b, 5c, 5d, 5e, and 5f illustrate a cross section of a permanent magnet machine with formed coils in accordance with one aspect of the present invention. FIG. 5b shows detail of region A within and indicated in FIG. 5a. FIG. 5c shows detail of region D within and indicated in FIG. 5a. FIG. 5d shows detail of region E within and indicated in FIG. 5a. FIG. 5e shows detail of region B within and indicated in FIG. 5b. FIG. 5f shows detail of region C within and indicated in FIG. 5a.
[0023] FIGS. 6a and 6b illustrate a cross section of a random wound permanent magnet machine in accordance with one aspect of the present invention. FIG. 6b shows detail of region A within and indicated in FIG. 6a.
[0024] FIG. 7 illustrates a cross section of a permanent magnet machine in accordance with one aspect of the present invention wherein slots in the rotor laminations are provided to allow conductors to be inserted should the permanent magnets magnet segments ever have to be re-magnetized.
[0025] FIG. 8a illustrates a cross section of a machine with an external permanent magnet rotor (rotatable in directions 64 and 65) in accordance with one aspect of the present invention. FIG. 8b shows detail of circled region B within and indicated in FIG. 8a.
[0026] FIGS. 9a and 9b depict an external rotor permanent magnet machine. FIG. 9b shows detail of circled region A within and indicated in FIG. 9a.
[0027] FIG. 10 is a hybrid permanent magnet machine with an excitation coil.
[0028] FIG. 11a shows a prior art high voltage rotating electrical machine coil. FIGS. 11b-e depict a coil fixing method. FIGS. 11b and 11d show detail of circular region C as appears in embodiments of the inventive technology.
[0029] FIG. 12 is a schematic of brushless excitation system in conjunction with the present invention.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0030] FIGS. 1, 2, and 3 illustrate prior art configurations of magnets and slots in motors and generators.
[0031] Referring to FIGS. 4a, 4b, and 4c, a cross section of a rotating electric machine with an alternating current stator, which could operate in either motor or generator mode, is illustrated. Stator core 30 carries sinusoidally varying magnetic flux illustrated by flux lines 21a, 21b, 21c, 21d, 21e 21f, 21g and 21h. This machine is asymmetric and does not function the same in all four quadrants. It is optimized for two-quadrant operation such as is required for raising and lowering an elevator or for use in conjunction with a reversible pump turbine, for example. Generating and motoring occur in these two examples with torque in the same direction but with rotation in opposite directions. In each of these two quadrants the flux lines cross the air gap 49 with the same sign of angle. For maximum power the angle of the flux lines crossing the air gap may be in the range of 30 to 45 degrees from the radial direction. Flux angles greater than 45 degrees may result in slippage or loss of synchronization between the permanent magnet poles and the coil generated poles in the stator. In accordance with one aspect of the present invention, the coil current phase angle may be adjusted to prevent loss of synchronization. Referring now also to FIG. 5f, the uni-directionally tapered stator slots 51 shown (as shown, tapered in one direction) prior to coil insertion are aligned with this angle in order to minimize flux concentrations at the tips 55 of the stator teeth 56. Likewise, the permanent magnet segments 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, and 19 are magnetized such that the flux may leave the magnets, cross the air gap and enter the stator core without unnecessary changes in direction. The orientation of magnetization of the permanent magnet segments may be uniform across discrete magnet segments, or, in the case of a single magnet per pole, may preferably be magnetized in a continuum of directions to maintain the design angle of air gap crossing. The required field strength varies with angular position and the magnet thickness should be varied accordingly in order to achieve economic use of expensive magnetic materials. Changes in flux direction within the air gap in prior art machines result in a greater effective air gap. The longer indirect flux path across the air gap of prior art machines results in either lower magnetic field strength or the requirement for larger magnets. The coils 60 illustrated may be similar to Roebel bars, except that the conductor cross section shape changes with each pass through the slot in order that the assembled bar fit the uni-directionally tapered stator slots 51.
[0032] Referring to FIGS. 5a, 5b, 5c, 5d, 5e, and 5f, a variation of the rotating electrical machine of FIGS. 4a, 4b, and 4c is shown. Windings 28 (e.g., 28a through 28ab) are comprised of wire flattened according to its placement order in each slot. Flattening is preferably done with automated equipment configured to establish the required thicknesses over the length of each individual wire. This allows the coil to assume a tapered shape that matches the shape of the uni-directionally tapered stator slots 51 that provide for a constant core cross sectional area and flux density as a function of radius. This constant flux density configuration minimizes hysteresis losses while optimizing the use of both iron and copper. The uni-directionally tapered stator slots 51 also allow for coil insertion from one end of the slot with generous clearances. Once the coil is fully inserted an elastomeric stretched packer 25 is threaded under tension through the back-iron end 54 of the slot. Back iron 57 is identified in FIG. 6a. The tension results in the stretched “packer” 25 assuming a reduced cross section compared to unstretched packer 26. Once the stretched packer 25 is in place the tension is released and the tensioning means may be disconnected. This results in the unstretched packer 26 fully occupying the available space and exerting a positioning preload against the back edge of the coil. Coil removal may be accomplished by tensioning again packer 26. The preload provided suppresses coil vibration. The resulting tight contact between coil and slot improves heat transfer. Permanent magnet segments 4 through 19 may be secured with carbon fiber winding 27.
[0033] Referring to FIGS. 6a and 6b, an example arrangement of random wound coils 58 and 59 in a slot is illustrated. Coil insulation 62 separates the coils 58 and 59. Slot insulation 63 insulates the coils from the stator core 30.
[0034] Referring to FIG. 7, re-magnetizing slots 31 are provided in rotor core 20 for the purpose of re-magnetizing the permanent segments 4 through 19 should demagnetization occur due to an external short circuit or overheating the magnets for any reason. Conductors placed in such slots for remagnetization would preferably be used in conjunction with conductors positioned and secured outside of the rotor, removed from the stator.
[0035] Referring to FIGS. 8a and 8b, a cross section of an exterior magnet rotating electrical machine, similar to those used for permanent magnet UAV motors, is shown. Splined shaft 22 prevents rotation of stator core 30. Splined shaft 22 is preferably non-magnetic in order to minimize eddy current losses that would otherwise be caused by alternating flux passing through splined shaft 22. Splined shaft 22 may include hole 23 which may be used to augment cooling, as part of a heat pipe for example. In the two-pole configuration shown, flux must pass across the diameter of stator core 30. The splined connection between splined shaft 22 and stator core 30 minimizes the required diameter of splined shaft 22 and thereby minimizes the reluctance of the diametral flux path through the assembly comprised of splined shaft 22 and stator core 30. Permanent magnet segments 4 through 19 are each magnetized with a flux orientation aligned with the nominal rated load flux orientation crossing the air gap. Again, flux lines that do not change direction as they cross the air gap result in a shorter effective air gap, minimize the reluctance of the magnetic circuit and allow the use of minimal magnetic materials, such as rare earths. FIG. 8b illustrates example coils 58, 59 in a slot (e.g., non-tapered slot 50) designed to guide the magnetic flux lines between the rated torque orientation in the air gap and the diametral flux path across the two-pole machine illustrated. It should be noted that differing numbers of poles require different flux paths through the rotor.
[0036] Referring to FIGS. 9a and 9b, a variation of the machine of FIGS. 8a and 8b is shown. In this case bi-directionally tapered slots 24 are shaped (as shown, tapered in two different directions) to avoid magnetic flux concentrations at either end of the slots 24.
[0037] Referring to FIG. 10, a hybrid synchronous machine is illustrated in cross section. This machine combines permanent magnet segments 4 through 19 with a rotor field coil 29 in order to provide control of Voltage and power factor while retaining some of the efficiency advantage of the permanent magnet field. The rotor field coil 29 may be energized in either direction so as to either add to or subtract from the field provided by the permanent magnet segments. The rotor field coil 29 may be energized through conventional slip rings, through a conventional (prior art) brushless exciter), or, in accordance with a further aspect of this invention, excited through a brushless exciter co-located with and superimposed upon the primary synchronous alternator illustrated.
[0038] Referring to FIGS. 11a, 11b, 11c, 11d, and 11e, unstretched packers 26 may take the shape of flat rubber bands. Stretched packers 25 may be threaded through circular portion of high voltage stator slot 52 while stretched. By this means a circular coil 61 may be secured in a circular portion of high voltage stator slot 52 in the stator core 30. This may be used in conjunction with high Voltage rotating electrical machine coils such as are incorporated into the ABB Powerformer® high Voltage generators (see FIG. 11a).
[0039] Referring to FIG. 12, the excitation system may comprise an auxiliary winding (stator DC excitation coil) 41 co-located with the AC power stator windings 48 to produce a non-rotating magnetic field with a magnetic circuit passing through both stator 72 and rotor 45. This results in AC power being generated in an auxiliary winding 44 in the rotor 45. This AC power, available in the rotor 45, is rectified to provide DC power to the rotor field coil 29. Optical rectifier controller 46 controls optically controlled rectifiers 70 through optical link 71. Optically controlled rectifiers 70 may switch the polarity of and adjust the rotor field coil 29. Optically controlled rectifiers 70 may be substituted with functionally similar means such as small photodiodes controlling conventional silicon-controlled rectifiers or the functional equivalent. This configuration overcomes the complexity of mounting a separate exciter onto a larger alternator wherein the larger alternator may have large air gaps and large bearing clearances not compatible with those of the exciter. The present invention in this regard provides a cheaper, more robust, and more compact excitor configuration. The exciter magnetic circuit is superimposed on, i.e., co-located with, the primary magnetic circuit of the motor or generator. This configuration eliminates the need for a separate excitation generator. Separate excitation generators tend to be smaller and may require smaller air gaps and have smaller positioning tolerances for the rotor within the stator. Elimination of the separate magnetic circuit for the rotor reduces parts count, machine weight, machine size and machine cost.
[0040] Referring to FIG. 12, excitation controller 40 supplies DC current to auxiliary winding 41 (stator DC excitation coil). This results in an alternating current power being delivering to auxiliary winding 44 in rotor 45. The resulting AC power is rectified with optically controlled rectifier 46. The resulting DC power can be of either polarity depending upon which optical rectifier control is activated. This DC power is applied to rotor field coil 29. This power can be used to create a field by itself or can be used to create a rotor magnetic field in conjunction with permanent magnet segments in the rotor. The output power is drawn from the generator through the AC power stator windings 48. Note that this system may be configured as a generator, as a synchronous motor, or as a synchronous condenser.
[0041] In accordance with a further aspect of the invention, the machine may be designed for submersible use. Its end coils may be embedded in rubber. Its stator pole face surfaces may likewise be embedded in rubber. The rubber is preferably vulcanized to the surface of the stator core laminations using a bonding agent such as Lord Chemical Company ChemLok® Furthermore, a stainless steel sleeve fitted to the rotor can slide on the rubber bonded to the stator with water lubrication with very little wear. The assembly acts as a rubber bearing similar to those used for ship stern tubes. This is superior to covering the pole face surface in stainless steel because, unlike stainless steel, the rubber does not incur eddy current losses. The rubber covered stator in conjunction with a stainless steel covered rotor may also be used in the case of a configuration wherein the rotor is on the outside of the stator.
[0042] It should be noted that the improvements disclosed herein apply to rotating electromagnetic machines of varying pole numbers and phases. The 2 pole machines herein illustrated are but examples.
