High power generator with enhanced heat removal

A high speed, high power generator has its main stator and main rotor configured to provide enhanced cooling capability. The generator includes a generator housing, a stator, a shaft, and a rotor. The stator is mounted within the generator housing. The shaft is rotationally mounted within the generator housing, and includes an inner surface that defines an internal fluid flow passage, an outer surface, and a plurality of interlamination cooling supply orifices extending between the shaft inner and outer surfaces. The rotor is mounted on the shaft and includes a plurality of poles formed from laminations, and one or more interlamination disks. Each interlamination disk is disposed between at least two of the laminations and includes a plurality of interlamination flow passages that receive a cooling medium from the shaft and direct the cooling medium, via centrifugal force, through the rotor and onto the stator.

TECHNICAL FIELD

The present invention relates to relatively high power generators and, more particularly, to high power generators that are used with gas turbine engines such as those used in aircraft, tanks, ships, terrestrial vehicles, or other applications.

BACKGROUND

Many vehicles, including aircraft, ships, and some terrestrial vehicles, include AC generator systems to supply relatively constant frequency AC power. Many of the AC generator systems installed in these vehicles include three separate brushless generators, namely, a permanent magnet generator (PMG), an exciter, and a main generator. The PMG includes a rotor having permanent magnets mounted thereon, and a stator having a plurality of windings. When the PMG rotor rotates, the permanent magnets induce AC currents in PMG stator windings. These AC currents are typically fed to a regulator or a control device, which in turn outputs a DC current to the exciter.

The exciter typically includes single-phase (e.g., DC) stator windings and multi-phase (e.g., three-phase) rotor windings. The DC current from the regulator or control device is supplied to exciter stator windings, and as the exciter rotor rotates, three phases of AC current are typically induced in the rotor windings. Rectifier circuits that rotate with the exciter rotor rectify this three-phase AC current, and the resulting DC currents are provided to the main generator. The main generator additionally includes a rotor and a stator having single-phase (e.g., DC) and multi-phase (e.g., three-phase) windings, respectively. The DC currents from the rectifier circuits are supplied to the rotor windings. Thus, as the main generator rotor rotates, three phases of AC current are induced in main generator stator windings. This three-phase AC current can then be provided to a load such as, for example, electrical aircraft systems.

In recent years, vehicles are being designed that rely more and more on electrical power. Thus, there is an ever-increasing demand for enhanced electrical generators, such as the one described above. One way of meeting these demands is through manipulation of the length and diameter ratio of a generator. For a given rotational speed, increasing the diameter of the generator increases the stress levels in the rotating components. Because some electrical generators rotate at relatively high speeds, with potential rotational speeds up to and in excess of 24,000 rpm, the stress levels in rotating components can, upon increasing the generator diameter, reach material limits. Thus, for many vehicles, the increased power demand can only be met by increasing the length of the generator.

As is generally known, some of the electrical components within the generator may generate heat due to electrical losses, and may thus be supplied with a cooling medium. For example, in some generators the main rotor windings and main stator windings are cooled using a cooling medium, such as a lubricant, that flows in and through the generator. In particular, the main rotor and main stator windings are cooled by spraying the cooling medium, via orifices in the main rotor shaft, onto end turns of the main rotor and main stator windings. The cooling medium flow through the main rotor shaft also provides conduction cooling of the main rotor along its axial length. Conduction cooling along the axial length of the main stator is provided via a stator back iron cooling flow path. More specifically, a portion of the cooling medium is directed through a flow path formed in or on the stator back iron.

Although the above described generator cooling configuration provides sufficient cooling for many generators, as the length of the generator is increased the cooling scheme can present certain drawbacks. In particular, the cooling scheme can result in insufficient cooling of the main rotor and main stator near the axially positioned centers, causing relatively high temperature hot spots at or near these locations, which can be detrimental to overall generator performance.

Hence, there is a need for a high speed, high power generator that addresses the above-noted drawback. Namely, a high speed, high power generator that supplies sufficient cooling to its main rotor and main stator even if the length to diameter ratio is increased. The present invention addresses at least this need.

BRIEF SUMMARY

The present invention provides a high speed, high power generator that provides enhanced cooling of the main rotor and main stator near the axially positioned centers thereof.

In one embodiment, and by way of example only, a high power generator includes a generator housing, a stator, a shaft, and a rotor. The stator is mounted within the generator housing. The shaft is rotationally mounted within the generator housing, and includes an inner surface that defines an internal fluid flow passage, an outer surface, and a plurality of interlamination cooling supply orifices extending between the shaft inner and outer surfaces. The internal fluid flow passage is configured to receive a flow of a cooling medium, and each interlamination cooling supply orifice is in fluid communication with the internal fluid flow passage. The rotor is mounted on the shaft and is disposed at least partially within and is spaced apart from the stator to form an air gap there-between. The rotor includes a plurality of poles, and one or more interlamination disks. Each pole extends radially outwardly from the shaft and is formed of at least a plurality of laminations. Each interlamination disk is disposed between at least two of the laminations and includes a plurality of fluid inlets, a plurality of fluid outlets, and a plurality of interlamination flow passages. Each fluid inlet is in fluid communication with one of the shaft interlamination cooling supply orifices, each fluid outlet is in fluid communication with the air gap, and each interlamination flow passage extends between one of the fluid inlets and one of the fluid outlets.

In another exemplary embodiment, a high power generator includes a generator housing, a stator, a shaft, and a rotor. The stator is mounted within the generator housing and includes a plurality of stator core subassemblies and a plurality of main stator windings. Each stator core subassembly is coupled to the generator housing and is spaced apart from at least one other adjacent stator core subassembly to form an inter-stator gap there-between. Each stator winding has at least one end turn and extending into an inter-stator gap. The shaft is rotationally mounted within the generator housing, and includes an inner surface that defines an internal fluid flow passage, an outer surface, and a plurality of interlamination cooling supply orifices. extending between the shaft inner and outer surfaces. The internal fluid flow passage is configured to receive a flow of a cooling medium, and each interlamination cooling supply orifice is in fluid communication with the internal fluid flow passage. The rotor is mounted on the shaft and is disposed at least partially within and is spaced apart from the stator to form an air gap there-between. The rotor includes a plurality of poles, and one or more interlamination disks. Each pole extends radially outwardly from the shaft and is formed of at least a plurality of laminations. Each interlamination disk is disposed between at least two of the laminations and includes a plurality of fluid inlets, a plurality of fluid outlets, and a plurality of interlamination flow passages. Each fluid inlet is in fluid communication with one of the shaft interlamination cooling supply orifices, each fluid outlet is in fluid communication with the air gap, and each interlamination flow passage extends between one of the fluid inlets and one of the fluid outlets.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

Before proceeding with the detailed description, it is to be appreciated that for convenience of explanation the present embodiment is depicted and described as being implemented in a brushless AC (alternating current) generator. However, the present invention is not limited to a brushless AC generator environment, but may be implemented in other AC generator designs needed in specific applications.

Turning now toFIG. 1, a functional schematic block diagram of an exemplary high speed generator system100for use with a gas turbine engine such as that in an aircraft is depicted. This exemplary generator system100, which is commonly known as a brushless AC generator, includes a permanent magnet generator (PMG)110, an exciter120, a main generator130, a generator control unit140, and one or more rectifier assemblies150. During operation, a rotor112of the PMG110, a rotor124of the exciter120, and a rotor132of the main generator130all rotate. The rotational speed of these components may vary. In one embodiment, the rotational speed may be, for example, in the range of about 12,000 to about 24,000 r.p.m., or greater. As the PMG rotor112rotates, the PMG110generates and supplies, via a PMG stator114, AC power to the generator control unit140. The generator control unit140supplies direct current (DC) power to a stator122of the exciter120. The exciter rotor124in turn supplies AC power to the rectifier assemblies150. The output from the rectifier assemblies150is DC power and is supplied to the main rotor132, which in turn outputs AC power from a main stator134.

The generator system100is capable of providing output power at a variety of frequencies and over a variety of frequency ranges. Further, typically the output power from the main generator stator134is three-phase AC power. The generator control unit140can regulate the power output based upon monitoring signals provided to it from monitoring devices195. In the depicted embodiment, the PMG rotor112, the exciter rotor124, and the main rotor132are all mounted on a common shaft136, and thus all rotate along a single axis198at the same rotational speed. It will be appreciated, however, that this is merely exemplary of a particular preferred embodiment. It will additionally be appreciated that the generator system100, or at least portions of the system100, may be housed within a generator housing202, a perspective view of which is illustrated inFIG. 2.

Turning now toFIG. 3, which is a simplified cross section side view representative of the schematic and physical high power generators described above, it is seen that the shaft136includes an inner surface302that defines an internal fluid flow passage304, and an outer surface306. The shaft136receives a supply of cooling fluid such as, for example, oil or other lubricant, via an opening308in a first end312thereof. The supplied cooling fluid flows through the opening308and into and through the internal fluid flow passage304toward a closed second end314of the shaft136.

AsFIG. 3also depicts, the shaft136additionally includes a plurality of end turn cooling supply orifices316, and a plurality of interlamination cooling supply orifices318. The end turn cooling supply orifices316and the interlamination disk cooling supply orifices318each extend between the shaft inner302and outer306surfaces, and are thus in fluid communication with the internal fluid flow passage304. In the depicted embodiment, the end turn cooling supply orifices316and the interlamination cooling supply orifices318are both preferably circumferentially disposed on, and evenly spaced about, the shaft136. The end turn cooling supply orifices316, however, are disposed near both ends of the main rotor132, whereas the interlamination cooling supply orifices318are preferably disposed substantially midway between the end turn cooling supply orifices316. It will be appreciated that the end turn cooling supply orifices316may alternatively be provided near only one end of the main rotor132. Moreover, while the interlamination cooling supply orifices318are preferably disposed near an axial center of the main rotor132, it will be appreciated that these orifices318may be otherwise disposed, if so needed or desired.

The main rotor132, as was noted above, is mounted on the shaft136, and includes a plurality of poles322, and a plurality of coils324(for clarity, only one shown). The poles322extend radially away from the shaft136and, as is generally known, are preferably spaced evenly apart from one another. The poles322are formed of a plurality of laminations326and an interlamination disk328, both of which are shrunk fit onto, or otherwise coupled to, the shaft136. The rotor laminations326, as is generally known, are continuous stacks of a magnetically permeable material. The particular material may be any one of numerous magnetically permeable materials. In a particular preferred embodiment, the laminations326are formed of a magnetic alloy material such as, for example, vanadium permendur. It will be appreciated that this material is only exemplary, and that other suitable materials can be used for the rotor laminations326.

The interlamination disk328is disposed between at least two of the rotor laminations326, and includes a plurality of fluid inlets332, a plurality of fluid outlets334, and a plurality of interlamination flow passages336. It will be appreciated, however, that for clarity and ease of illustration, only two fluid inlets332, one fluid outlet334, and two interlamination flow passages336are depicted inFIG. 3. Preferably, each interlamination disk fluid inlet332is collocated with at least one of the interlamination cooling supply orifices318formed in the shaft136. As such, each interlamination flow passage336, which extends between one of the fluid inlets332and one of the fluid outlets334, is in fluid communication with the shaft internal fluid flow passage304. The interlamination disk328is formed of a high-strength material such as, for example, magnetic iron or other magnetically permeable metal or metal alloy. It will be appreciated that this material is merely exemplary, and that other suitable materials may be used to form the interlamination disk328. It will additionally be appreciated that the main rotor132may be implemented with more than one interlamination disk328, if needed or desired.

The rotor coils324are wrapped, one each, around a pole322, and are preferably formed by wrapping numerous individual wire windings around one of the poles322. In the depicted embodiment, each rotor coil324includes two end turns332(e.g.,332-1,332-2), each of which is made up of wire segments that loop around ends of the pole322. During generator operation, cooling fluid supplied to the shaft internal fluid flow passage304is directed, via centrifugal force, through the end turn cooling supply orifices316and the interlamination cooling supply orifices318. The cooling fluid that is directed through the end turn cooling supply orifices316is sprayed onto, among other things, the rotor coil end turns332, as depicted by flow lines360. This cooling fluid spray provides cooling to the rotor coil end turns332and, as will be described further below, to portions of the main stator134.

The cooling fluid that is directed through the interlamination cooling supply orifices318flows into and through the interlamination disk fluid inlets332, into and through the interlamination disk flow passages336, and out the interlamination disk fluid outlets334. Thus, the cooling fluid flowing through the interlamination disk flow passages336, together with the cooling fluid flowing through the shaft internal fluid flow passage304, provides conduction cooling for the main rotor laminations326. It will thus be appreciated that if the main rotor132is implemented with a plurality of interlamination disks328, a more uniform temperature throughout the main rotor132can be achieved. In addition to providing conduction cooling for the main rotor132, and as will also be described in more detail further below, the cooling fluid that flows out the interlamination disk fluid outlets334is directed onto, and provides cooling for, the main stator134, an embodiment of which will now be described in more detail.

The main stator134is also mounted within the generator housing202, and is positioned such that it is spaced apart from, and surrounds at least a portion of, the main rotor132to form an air gap340there-between. The main stator134includes a stator core338and a plurality of stator coils342, and is coupled to the generator housing202. The stator core338is preferably implemented using a plurality of spaced apart stator core sub-assemblies. In the depicted embodiment, the stator core338is implemented using two stator core subassemblies344-1,344-2, which are spaced apart from each other to form an inter-stator gap346there-between. It will be appreciated, however, that the stator core338could be implemented with more than this number of stator core subassemblies344and inter-stator gaps346. For example, the stator core338could be implemented with “N” stator core subassemblies (e.g.,344-1,344-2,344-3, . . .344-N), and with “N−1” inter-stator gaps (e.g.,346-1,346-2,346-3, . . .346-(N−1)) formed between adjacent stator core subassemblies344. Although the particular number of stator core subassemblies344may vary, preferably the number of stator core subassemblies344is selected such that the number of inter-stator gaps346formed between adjacent stator core subassemblies344matches the number of interlamination disks328in the main rotor132.

No matter the particular number of stator core subassemblies344that are used, each is preferably formed of a plurality of laminations349. The stator core subassembly laminations349, much like the main rotor laminations326, are stacks of a magnetically permeable material, which may be any one of numerous magnetically permeable materials such as, for example, vanadium permendur or silicon iron.

The stator coils342are wrapped around each of the stator core subassemblies344, preferably within non-illustrated slots formed in the stator core stator core subassemblies344. Similar to the rotor coils324, the stator coils342include a pair of end turns348(e.g.,348-1,348-2). It will thus be appreciated that a portion of the cooling fluid spray that is directed onto the rotor coil end turns332is also directed onto the stator coil end turns348, and provides cooling thereto. In addition to this, the stator coils342extend across the inter-stator gap346formed between the stator core subassemblies338. As such, and as was previously alluded to, a portion of the cooling fluid that flows out the interlamination disk fluid outlets334is directed into the inter-stator gap346. The cooling fluid directed into the inter-stator gap346is directed onto, and flows over, the stator coils342within the gap346and a portion of the stator core subassembly laminations349, providing additional conduction cooling for both the stator core338and the stator coils342.

The cooling fluid may be directed into the inter-stator gap346at a relatively high velocity, which may lead to erosion of the stator coils342within the inter-stator gap346. Thus, the velocity of the cooling fluid in the interlamination disk flow passages336is preferably reduced prior to being discharged from the main rotor132. In the depicted embodiment this velocity reduction is implemented by directing a portion of the cooling fluid toward the rotor laminations326on one or both sides of the interlamination disk328. It will be appreciated that this may be accomplished in any one, or combination, of numerous ways. For example, and as shown inFIGS. 4 and 5, the interlamination disk328may be configured such that the interlamination flow passages336and at least portions of the interlamination disk328have radii that are less than the rotor laminations326between which it is disposed. With these configurations, the interlamination disk328may additionally include one or more velocity reduction flow passages402(seeFIG. 4) or502(seeFIG. 5) in fluid communication with each interlamination flow passage336. Thus, upon exiting the interlamination disk fluid outlet334, at least a portion of the cooling fluid is directed against the rotor laminations326, causing a reduction in velocity. It will be appreciated that with the configuration depicted inFIG. 4, the interlamination disk328is preferably configured such that the velocity reduction flow passages402cause the cooling medium to be sprayed in a direction404that is generally opposite the direction406in which the rotor132is rotating. Although the velocity reduction flow passages402,502are each shown disposed substantially perpendicular to its associated interlamination flow passage336, it will be appreciated that one or more of the velocity reduction flow passages402,502may be disposed at another predetermined angle relative to its associated interlamination flow passage336.

Returning once again toFIG. 3, it is additionally seen that the generator housing202includes a collection cavity352. The collection cavity352, which may be integrally formed as part of the housing202or separately formed and coupled to the housing202, is in fluid communication with the inter-stator gap346via a collection flow passage354. Although not depicted inFIG. 3, it will be appreciated that the collection cavity352is additionally in fluid communication with a collection reservoir, such as a non-illustrated sump disposed within the generator housing202. With this arrangement, the cooling fluid that is directed into the inter-stator gap346is directed into the collection cavity352, and is in turn directed into the non-illustrated sump. It will be appreciated that the generator housing202may include more than one collection cavity352and collection flow passage354, if needed or desired. For example, the generator housing202is preferably implemented with one collection cavity352and one collection flow passage354per inter-stator gap346. Thus, if the stator core338is implemented to include more than one inter-stator gap346, the generator housing202will concomitantly be implemented with more than one collection cavity352and one collection flow passage354.

The high speed, high power generator described herein provides enhanced cooling of the main rotor and main stator, most notably near axially positioned centers thereof. The generator also provides enhanced cooling of the stator coils, again most notably near the center of the main stator. As a result, the axial length of the generator can be increased, if needed to meet increase power generation demands, without adversely impacting thermal management of the generator. Although the efficiency of the generator may be adversely affected by directing cooling fluid into the air gap between the main rotor and main stator, the reduction in temperature that is realized mitigates this potential drawback.