Generator assembly

An electric machine, such as a generator, providing for the generation of electricity and includes a rotor generating a magnetic field and a stator having stator windings. The interaction of the magnetic field with the stator windings generates current in the windings. The generator may provide the generated current to a power output of the generator, where it may be further transmitted to an electrical load to power the load.

BACKGROUND OF THE INVENTION

Electric machines, such as generators, provide for the generation of electricity from a mechanical force. The generation of the electricity occurs due to the interaction of a rotating magnetic field in relation to a set of conductive windings. In one generator example, a rotor rotated by a mechanical force may generate the rotating magnetic field relative to a stationary stator having a set of conductive windings. The interaction generates a current in the stator windings, which may be provided to the power output of the generator, where it may be further transmitted to power an electrical load.

BRIEF DESCRIPTION OF THE INVENTION

In one aspect, a generator assembly includes a stator having a core with multiple poles, stator windings wound about the poles to define winding end turns at an end of the poles, a heat transfer element having a body defining a face confronting the end turns and comprising an aluminum alloy including a predetermined amount of Silicon Carbide (SiC) providing the body with a first coefficient of thermal expansion, and a thermally conductive, dielectric coating deposited on at least a portion of the face of the heat transfer element and in physical contact with the stator windings, and having a second coefficient of thermal expansion. The predetermined amount of SiC is selected such that the first and second coefficients of thermal expansion are close enough that the thermal expansion of the heat transfer element and the dielectric coating in response to exposure to heat from the end turns will not result in through cracking of the dielectric coating during normal operation of the generator.

DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The invention may be implemented in any environment using an electric motor regardless of whether the electric motor provides a driving force and/or generates electricity. For purposes of this description, such an electric motor will be generally referred to as an electric machine, electric machine assembly, or similar language, which is meant to make clear that one or more stator/rotor combinations may be included in the machine. While this description is primarily directed toward an electric machine providing power generation, it is also applicable to an electric machine providing a driving force and/or an electric machine providing both a driving force and power generation. Further, the invention is applicable in any environment using an electric machine.

FIG. 1illustrates an electric machine assembly, such as a generator1, comprising a first machine2having an exciter rotor3and an exciter stator4, and a synchronous second machine5having a main machine rotor6and a main machine stator10. At least one power connection is provided on the exterior of the generator1to provide for the transfer of electrical power to and from the generator1. Power is transmitted by this power connection, shown as an electrical power cable7, directly or indirectly, to the electrical load and may provide for a three phase with a ground reference output from the generator1.

The generator1further comprises a rotatable shaft8mechanically coupled to a source of axial rotation, which may be a gas turbine engine, about an axis of rotation9. The rotatable shaft8is supported by spaced bearings11. The exciter rotor3and main machine rotor6are mounted to the rotatable shaft8for rotation relative to the stators4,10, which are rotationally fixed within the generator1. The stators4,10may be mounted to any suitable part of a housing portion of the generator1. The rotatable shaft8is configured such that mechanical force from a running turbine engine provides rotation to the shaft8. Alternatively, in the example of a starter/generator, rotation of the rotatable shaft8of the generator1during a starting mode produces a mechanical force that is transferred through the shaft8to provide rotation to the turbine engine.

FIG. 2illustrates the stator10in greater detail. The stator10, as shown, comprises a generally cylindrical core12, a plurality of posts14, at least one winding slot16, and may optionally include at least one slot liner18provided for at least some of the winding slots16. The surface at the inner perimeter of the core12faces the rotor6and has a plurality of spaced posts14defining a corresponding plurality of spaced winding slots16therebetween, radially arranged at a predetermined spacing in the circumferential direction. Each of the plurality of winding slots16are configured with an open top facing the circumferential center point of the core12and may terminate in opposing open ends spaced axially along the core12. For instance, the ends of the winding slot16may axially terminate at the same length as the core12. A slot liner18is placed along the inner perimeter of the winding slot16defining an open top facing the circumferential center point of the core12and terminating in opposing ends which are shown extending beyond the winding slot16open ends. Alternatively, the slot liner18terminating ends may not extend beyond the winding slot16open ends. The core12may be formed from a plurality of laminations, but alternate forming or machining of materials is envisioned.

FIG. 3illustrates a sectional view of a configuration of a single winding slot16assembled stator10having stator windings20according to one embodiment of the invention. The stator windings20comprise conductive wires (only a few are shown, not to scale, for illustrative purposes) that are wound about the core12within the winding slot16such that individual sets of windings20may be separated from other sets of windings20found in adjacent slots16. Additionally shown, the slot liner18isolates the plurality of stator windings20from the plurality of posts14and the stator core12. While only one set of stator windings20are shown, it is envisioned that at least one set of windings20is wound around the axial ends of at least two posts14(henceforth, “end turns”) and through at least two adjacent winding slots16such that the energization of the windings20form a magnetic pole22at the intervening post14. The rotation of a magnetic field at the rotor6generates a corresponding voltage in the stator windings20at the corresponding poles22.

FIG. 4illustrates an exploded view of the stator10of the generator1taken from the longitudinal axis of the stator10. As shown, the stator10may further comprise a stator assembly24having a heat transfer element in physical contact with the stator10such that heat may be transferred from the core12to the stator assembly24. In the illustrated example, the heat transfer element may comprise a first body element26configured in a ring to encircle and receive the stator core12, and a second body element28also configured in a ring, and encircled and received by the first body element26. Each of the first and second body elements26,28further define at least one abutting face30configured to abut a respective axial terminating end32of the core12.

Each of the first and second body elements26,28may comprise a thermally conductive material, for example, an aluminum alloy having a predetermined amount of silicon carbide having a first coefficient of thermal expansion (CTE) according to the material properties. In one example, an aluminum alloy having a 30% reinforcement of SiC (by volume) may have a CTE of 14.0 ppm/° Celsius (° C.) between an operating temperature of 21-100° C. This example may further include a thermal conductivity of 165 Watts per meter-Kelvin at 21° C. While one example of an aluminum alloy having a 30% SiC is provided, alternative heat transfer elements, such as aluminum alloys having different predetermined amounts of SiC, are envisioned.

The stator assembly24is configured such that the first body element26, stator core12, and second body element28may be fixedly or removably assembled, for example, by axially aligning each component26,12,28along a common axis34, and inserting the core12into the first body element26, followed by inserting the second body element28into the first body element26, such that the abutting face30of each first and second body elements26,28abuts the core ends32of the core12.

FIG. 5illustrates a cross-sectional view of an assembled stator assembly24. As shown, the stator assembly24may further comprise a thermally conductive, dielectric coating36deposited on at least a portion of a face of the first and/or second body elements26,28. The coating36may be applied prior to or after assembling the stator assembly24. Additionally shown are at least a portion of the stator windings20end turns38axially extending outside the core12and slot liner18as they wind about the poles22. It is envisioned that the stator windings20and/or end turns38are in physical and/or thermal contact with the first and/or second body elements26,28, via the coating36, such that the elements26,28and coating36provide heat transfer between the materials and/or layers. Additionally, the dielectric properties of the coating36electrically isolate the stator windings20from the stator core12and the first and/or second body elements26,28.

The coating36may be adhered or deposited on to the first and second body elements26,28through a number of techniques, for example, by including adhesives, plasma coating, or spray-on coating. Additional coating36adhesion or depositing techniques are envisioned. One example of the coating36may include a ceramics-based material, such as aluminum oxide, which has a second CTE, such as 6.3 ppm/° C. between 21-100° C., however alternative conductive, dielectric materials or coatings are envisioned.

During operation of the generator1, the interaction of the rotating magnetic field with the stator windings20of the stator assembly24generates a current through the windings20, which may ultimately be delivered to a generator output or electrical load for operating the load. The current generated in the stator windings20generates heat in the windings20, for example, at the end turns38. The physical and/or thermal contact between the stator windings20and/or end turns38, the coating36, and the body elements26,28allows the heat generated in the windings20to be thermally conducted through the coating36to the body elements26,28, where it may be further dissipated, for example, via heat fins, air cooling, or through coolant traversing through a coolant passage in physical and/or thermal contact with the body elements26,28. Additional cooling techniques are envisioned.

It is envisioned that the predetermined amount of the SiC of the aluminum alloy is selected such that the first and second coefficients of thermal expansion are close enough that the difference between the thermal expansion of the body elements26,28and the coating36will not result in through-cracking of the coating36in response to exposure to the heat generated by the end turns38of the stator windings20during normal operation of the generator1. Stated another way, the relationship of the SiC of the aluminum alloy is selected so that the thermal expansion of the aluminum alloy is more aligned to the thermal expansion of the coating36so that the coating36does not crack during thermal expansion. For example, the CTE of the body elements26,28may be higher or lower than the CTE of the coating36. In the example provided above, the first and second CTE may be within 7.7 units of each other, however any first and second CTE within 10 units of each other are envisioned. In this example, the difference between the first and second CTE is within 55 percent of the first CTE. The descriptions provided are non-limiting examples of possible relationships between the CTE of the body elements26,28and the coating36, and other relational percentages and/or relational coefficient limits are envisions.

Many other possible embodiments and configurations in addition to that shown in the above figures are contemplated by the present disclosure. For example, one embodiment of the invention contemplates a heat transfer element having additional or fewer body elements configured to abut the stator core12. Another embodiment envisions configuring the coating36on alternative heat transfer element faces, yet still in physical and/or thermal contact with the stator windings20or end turns38. Additionally, the design and placement of the various components may be rearranged such that a number of different in-line configurations could be realized.

The embodiments disclosed herein provide a generator assembly with improved heat dissipation at the stator winding end turns. One advantage that may be realized in the above embodiments is that the above described embodiments have superior thermal and electrical operation over the conventional generator configurations. With the proposed configurations, a high thermal conductivity between the end turns of the stator windings and the heat transfer element can be achieved due to the high thermal conductivity of the heat transfer element and the coating as described above. The higher thermal conductivity allows for a generator that can dissipate higher levels of heat. Since the amount of heat generated in the stator windings is related to the amount of electricity generated, the above-described embodiments allows for an electric machine capable of generating more power than conventional machines.

Additionally, the dielectric strength of the coating layer reduces or eliminates the likelihood of an electrical short between the stator windings and heat transfer element, even at higher current and voltage generation by the electric machine. The combination of higher thermal conductivity and dielectric strength of the embodiments described herein result in a stator assembly which can be used in higher thermal class applications due the improved ability to dissipate heat away from the stator windings. Thus, another advantage of the above described embodiments is that electric machines having the described generator assembly may be driven to generate more power and at higher temperatures than the conventional electric machines.

Furthermore, by providing the heat transfer element with a predetermined amount of silicon carbide, the generator assembly may be configured to provide a closer matching coefficient of thermal expansion between the heat transfer element and the coating. Thus, when the heat transfer element and the coating are heated during the heat dissipation, they may be configured to expand at a similar or closer rate, reducing the likely hood that a disparity in expansion rate may crack the coating. By reducing the likelihood of developing cracks in the coating, the likelihood of developing electrical shorts between the stator windings and the heat transfer element is reduced as well.

In even yet another advantage of the above-described embodiments is that by providing improved heat dissipation of the stator windings, and thus allowing the windings to operate at a lower temperature, as well as including a coating material such as ceramic, which may require less maintenance and a higher mean time between failures, the overall operating life of the generator is improved, and/or the maintenance time and costs of the generator are reduced. When designing electric machine systems, an important factor to address is reliability. Improved operating life, and reduced maintenance time and costs result in competitive advantages.

To the extent not already described, the different features and structures of the various embodiments may be used in combination with each other as desired. That one feature may not be illustrated in all of the embodiments is not meant to be construed that it may not be, but is done for brevity of description. Thus, the various features of the different embodiments may be mixed and matched as desired to form new embodiments, whether or not the new embodiments are expressly described. All combinations or permutations of features described herein are covered by this disclosure.