Patent Application
20100237723
The invention relates generally to rotating electrical machines, such as electric generators and/or electric motors. Particularly, this invention relates to cooling in such electrical machines.
Electrical machines are commonly cooled by various techniques. Low power density machines, including endwinding regions are often air-cooled. Another type of cooling includes natural convection, wherein a casing of the electrical machine has a finned surface and heat is dissipated via buoyancy driven cooling. In an alternative example, large generators for utilities are gas cooled using forced convection. In general, low power density machines use gas for cooling, whereas high power density machines use liquid cooling since it results in a higher heat removal efficiency.
In comparison to air cooling systems, liquid cooling systems are significantly more efficient and make it possible to discharge a large amount of heat. However, a specific issue with liquid cooled machines is cooling the endwindings. One method of cooling the endwinding in a liquid cooled electrical machine is to conduct the heat back into a stator core and remove heat via liquid cooling in the stator core. However, the cooling is limited by size of the electrical machine and amount of heat that can be effectively conducted back into the stator core.
An alternate method of endwinding cooling that is effective includes spraying a non-conductive fluid on the endwindings. However, the method is complicated and commonly results in the fluid entering an air gap, which is undesirable.
Accordingly, there is a need for an improved cooling system for electrical machines.
In accordance with an embodiment of the invention, a cooling system for an electrical machine is provided. The cooling system includes at least one baffle enclosing multiple endwindings, wherein the at least one baffle is configured to guide a cooling fluid flow to multiple regions of interest in the machine.
In accordance with another embodiment of the invention, a method for cooling regions of interest in a machine is provided. The method includes enclosing a multiple endwindings with a respective plurality of baffles, each of the baffles being configured to guide a cooling fluid flow to multiple regions of interest in the machine.
In accordance with another embodiment of the invention, an electrical machine is provided. The electrical machine includes a stator having a stator core. The stator also includes multiple endwindings wound around multiple stator teeth. The stator further includes at least one baffle enclosing at least one of the multiple windings, wherein the at least one baffle is configured to guide a cooling fluid flow to multiple regions of interest in the machine. The baffle includes one or more partitions comprising at least one inlet and at least one outlet for the cooling fluid flow. The electrical machine also includes a rotor comprising a rotor core, wherein the rotor disposed concentrically either inside or outside of the stator.
These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:
As discussed in detail below, embodiments of the invention are directed to a system and method for thermal management in electrical machines. The system and method include a cooling technique employing one or more baffles arranged such that an optimal cooling path is provided around endwindings.
At least one slot wedge 22 closes an opening of a respective one of the step-shaped stator slots 16. This enables adjusting the leakage inductance in the PM machine 10. In an example, the leakage inductance is in a range between about 100 μH to about 110 μH. In one embodiment, the slot wedge includes an iron epoxy resin. Other suitable slot wedge materials, include without limitation, nonmagnetic materials, ceramics, and epoxy.
In the illustrated example, a rotor 24 including a rotor core is disposed outside and concentric with the stator 12. In one embodiment, the rotor core includes multiple axial segments that are electrically insulated from each other to reduce eddy current losses. For the illustrated example, the rotor core includes a laminated back iron structure 28 disposed around multiple magnets 30. The magnets are also axially-segmented to reduce eddy current losses. In one non-limiting example, each magnet includes one hundred (100) segments. For the illustrated example, the back iron structure 28 is laminated in order to reduce the eddy current losses due to undesirable harmonic components of magnetic flux generated in the stator 12.
A cooling fluid is circulated through cooling tubes (not shown) at locations 31 through the stator core 14 to the endwindings 18. A non-limiting example of the cooling fluid includes a non-conductive fluid. In one embodiment, the cooling fluid is circulated via means of a pump (not shown). In a particular embodiment, the PM machine 10 includes at least one retaining ring 32 disposed around the back iron structure 28 to retain the magnets 30. In a non-limiting example, the retaining ring 32 comprises carbon fiber. Other suitable retaining ring materials, include without limitation, Inconel, and carbon steel. In another embodiment, the retaining ring 32 is preloaded to minimize fatigue effects and extend life of the rotor 24. In the illustrated embodiment, the PM machine 10 includes 2 retaining rings 32. It should be noted that one or more retaining rings may be employed. In yet another embodiment, the PM machine 10 has a power density in a range between about 1.46 kW/Kg to about 1.6 kW/Kg. In the illustrated embodiment, the PM machine 10 is an inside out configuration, wherein the rotor 24 rotates outside the stator 12. In other embodiments, the rotor 24 may be disposed inside the stator 12. In yet other embodiments, the machine 10 may include multiple number of phases.
The PM machine 10 may or may not include a baffle. An enclosure on one end of the machine 10, with a fluid inlet, forces the fluid through cooling slots to the other end of the machine. An enclosure is also installed at that end, along with a fluid outlet. In another embodiment, as illustrated herein, the improved cooling system includes at least one baffle 38 enclosing multiple endwindings 18. The baffle 38 is configured to guide a flow of the cooling fluid 31 to multiple regions of interest in the machine 10. In different embodiments, the baffle 38 may be disposed at different angular locations to introduce the cooling fluid 31 in specific angles and then guide the cooling fluid to circulate circumferentially around so that it flows around the endwindings 18. In one embodiment, partitions are formed by the baffle 38 at an angle of 45 degrees relative to a horizontal axis of the electrical machine 10. In another embodiment, the baffle is torroidal. In yet another embodiment, the endwindings include stator endwindings. In other embodiments, the stator endwindings include concentrated or distributed windings. Multiple inlets and outlets (not shown) may be disposed within a region enclosed by the baffle 38.
In another embodiment, wherein the side 160 includes two baffles as in
Electrical machines including a cooling system, as described above, may be employed in a variety of applications. One of them includes aviation applications, such as in aircraft engines. Particularly, the electrical machines may be a generator used for generating supplemental electrical power from a rotating member, such as a low pressure (LP) turbine spool, of a turbofan engine mounted on an aircraft. The electrical machines can also be used for other non-limiting examples such as traction applications, wind and gas turbines, starter-generators for aerospace applications, industrial applications and appliances.
The various embodiments of an electrical machine including a cooling system described above thus provide a way to provide efficient cooling that allows for an electrical machine with high power density, reliability and fault tolerance. The electrical machine also allows for a less complicated, cost-effective cooling system that enables improved power density. Furthermore, the techniques and systems provide an innovative thermal management arrangement and also allow for highly efficient electrical machines.
Of course, it is to be understood that not necessarily all such objects or advantages described above may be achieved in accordance with any particular embodiment. Thus, for example, those skilled in the art will recognize that the systems and techniques described herein may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other objects or advantages as may be taught or suggested herein.
Furthermore, the skilled artisan will recognize the interchangeability of various features from different embodiments. For example, the use of a quad baffle configuration described with respect to one embodiment can be adapted for use with a two-step stator slot configuration described with respect to another. Similarly, the various features described, as well as other known equivalents for each feature, can be mixed and matched by one of ordinary skill in this art to construct additional systems and techniques in accordance with principles of this disclosure.
While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.
