Method and Apparatus for Permanent Magnet Attachment in an Electromechanical Machine
An apparatus and method for the installation and removal of permanent magnets in a permanent magnet electromechanical machine, for example a wind turbine power unit generator. A magnet holder is mounted on a magnet carrying structure such as a rotor. Permanent magnets may be inserted into and removed from the magnet holder after the electromechanical machine is assembled. The magnet holders define passages for airflow between the inside top and magnet surface. In this manner, permanent magnets may be installed on the magnet carrying structure and provided with additional cooling via said passages. Further, the holders may be configured to secure the magnets by an interference fit, without using bolts or adhesives, to facilitate both assembly and removal for maintenance and repair.
The present application is a divisional of U.S. patent application Ser. No. 13/837,358, filed Mar. 15, 2013, which is a continuation-in-part of U.S. patent application Ser. No. 12/543,153, filed Aug. 18, 2009, now U.S. Pat. No. 8,664,819, issued Mar. 4, 2014. Each of these applications is incorporated by reference in its entirety herein.
TECHNICAL FIELDThe present invention generally relates to the field of permanent magnet machines, for example, wind power generators. In particular, embodiments of the present invention are directed to a holder for installing, containing and cooling permanent magnets within the rotor structure of a permanent magnet motor or generator.
BACKGROUNDPermanent magnet (“PM”) electromechanical machines utilize permanent magnets to convert rotational inputs into electricity or electrical inputs into rotational motion. One example is wind power units (WPUs) that generate electricity from the energy in wind. Generally, a PM generator or motor has three components. A first component, a stator, is a cylindrical housing that contains electrical windings that remain immobile during electricity generation. A second component, a rotor, is a rotatable assembly containing permanent magnets that spin with respect to the stator. The relative movement between the rotor and the stator produces a moving magnetic field, which induces an electrical current in the stator electrical windings, thereby producing electricity. A third component, such as an axle, rotationally supports the rotor with respect to the stator, enabling the two to rotate relative to each other.
As with other electromechanical machines that use permanent magnets, the permanent magnets in WPUs are typically installed relatively early in the assembly process. While it may be convenient to install magnets early in the assembly process, the presence of high strength permanent magnets can make later stages of assembly and installation inconvenient and even dangerous. This situation arises because subsequent assembly and installation steps require use of, and transportation near, ferromagnetic materials that are strongly attracted to the permanent magnets. Further, the process of assembling the stator and the rotor can be more difficult because of the tight spacing at the machine airgap, and the high magnetic forces between the rotor and the stator. Such assembly of magnets can especially complicate field repair and service of WPUs due to remote locations and positioning at the top of high towers.
Permanent magnets are often fastened within PM machines using bolts or other similar mechanical means directly secured to the magnets. While bolting the magnet to the rotor does securely fasten the magnet, bolting also makes removal of the magnet during maintenance difficult by, for example, requiring disassembly of the generator in order to remove the bolts. Directly bolting the magnets may also remove magnetic material. Removal of magnetic material can change the magnetic flux characteristics, thereby altering electricity generation. Furthermore, removing magnetic material and using bolts risks damaging the magnet during generator assembly or maintenance because of the stresses exerted on the magnet. These factors increase the effort and expense required to maintain a PM electromechanical machine, especially a WPU located in the field.
Another challenge in the design of PM machines is temperature control. As is well known in the art, managing magnet temperature is important, among other reasons, to protect against demagnetization during machine operation, and to allow the use of lower cost magnets. For example, a ten degree Celsius decrease in magnet operating temperature may provide a reduction in magnet cost in the range of about $25,000 for a large, permanent magnet machine utilizing rare earth alloy magnets. While many cooling schemes have been proposed, often they are complex or ineffective in practice. But even when a cooling scheme is effective to an extent, further efficiencies still can be achieved by additional temperature control means if such means can be cost effectively incorporated into the design without adding undue complexity.
SUMMARY OF THE DISCLOSUREExemplary embodiments of the present invention include methods, systems, and apparatus for securing magnets within a PM electromechanical machine, and assembling a generator, including securing the permanent magnet within the generator assembly after it is otherwise completed. When a magnet is secured according to embodiments of the present invention, the magnet can be removed and replaced as needed, thereby simplifying maintenance. In one exemplary embodiment, a magnet holder mounted in a PM machine is configured and dimensioned in combination with a magnet mounting surface and the magnet to produce an interference fit with the magnet.
In one implementation, the present disclosure is directed to an apparatus. The apparatus includes: a rotor assembly in a permanent magnet electromechanical machine including: a rotor having plural magnet mounting surfaces; a plurality of magnet holders, one at each magnet mounting surface on the rotor, each magnet holder having a top inside surface; a plurality of magnets, one each retained on the magnet mounting surfaces within a magnet holder, each magnet having a top surface opposite the magnet mounting surface; and at least one void defined between the holder top inside surface and the magnet top surface, the at least one void occupying about 90% to 100% of the space between the surfaces.
In another implementation, the present disclosure is directed to a method. The method includes: mounting permanent magnets to a magnet carrying structure in an electromechanical machine, including: providing a magnet holder having a top portion and sides defining at least a first open end, the top portion having an inside surface; sizing the magnet holder and configuring the top portion inside surface in combination with the magnet to provide an interference fit between the magnet holder and the magnet along facing surfaces thereof when the magnet is retained by the magnet holder on the magnet carrying structure, the interference fit being configured to maintain at least about 90% of the facing surfaces in a spaced apart relationship defining void space there between; mounting the magnet holder on the magnet carrying structure; and sliding the magnet into the magnet holder through the first open end to secure the magnet on the magnet carrying structure by the interference fit.
In still another implementation, the present disclosure is directed to an apparatus. The apparatus includes: a magnet holder for securing permanent magnets to a magnet mounting surface on a rotor in an electromechanical machine, wherein the magnets have a height and width, the magnet holder including a body having side walls joined by a closed top to define at least a first open end and open bottom, wherein the sides and closed top together define a magnet holder inside height configured and dimensioned in combination with the magnet height and magnet mounting surface to define at least one void between the closed top and the magnet, the at least one void occupying about 90% to 100% of the space between the surfaces when the magnet is retained on the magnet mounting surface within the magnet holder.
For the purpose of illustrating the invention, the drawings show aspects of one or more embodiments of the invention. However, it should be understood that the present invention is not limited to the precise arrangements and instrumentalities shown in the drawings, wherein:
As will be seen, the exemplary embodiments of methods, systems, and apparatus implementing the present disclosure are varied in terms of where and how permanent magnets may be inserted into an electromechanical machine after the machine has been assembled. While a number of particular examples are presented below to illustrate the breadth of the disclosure, those skilled in the art will appreciate the large number of variations.
For illustration purposes only, embodiments of the invention are described herein with reference to WPU embodiments. As depicted in
As shown in
Permanent magnets 216, as mounted on rotor 208, may be divided into sections 216′ for ease of installation and handling as shown in
According to embodiments of the present invention, magnet holders are used to secure the magnets via an interference fit between an inside surface of the top of magnet holder and the top surface of the magnet. The interference fit into the magnet holder provides a biasing force to secure the magnet within the holder. In one exemplary embodiment of the present invention as illustrated in
As shown, for example, in
In one non-limiting example, with reference to
As can be seen, for example, in
Analysis of computer models based on embodiments such as shown in
In order to increase the thermal barrier provided by voids 434, the voids themselves may be increased in size as will be appreciated by persons of ordinary skill in the art based on the teachings set forth herein. In one alternative exemplary embodiment, as shown in
In embodiments with conforming-shaped top 406′, as in the exemplary embodiments of
Other alternative embodiments may be configured for use with a magnet having a rectangular cross-section as shown, for example, in
In a further embodiment, shown in
Based on the teachings herein, persons of ordinary skill in the art will appreciate that the amount of void space as compared to areas of contact for interference fit purposes will vary according to particular design requirements. In general, the amount of contact area between the top surface of the magnet and the magnet holder inside the top surface will be minimized to the extent that the heat transfer characteristics of the boundary between the magnet and magnet holder are at least substantially determined by the heat transfer characteristics of the void space. In an exemplary embodiment, at least about 90% of the top surface, or more preferably at least about 95% of the top surface of the magnet should be in communication with voids forming air channels. In some embodiments the area of the top surface of the magnet in communication with voids may be as large as between about 99-100% of the total surface.
In another alternative embodiment, a reflective, low emissivity outer surface may be provided on magnet holders 400 to add a radiation barrier between the stator across the machine air gap to the magnet holders, reducing the temperature rise of both the holders and the magnets. This property can be attained by using a smooth or polished surface with no paint or anodizing on the outer surface of the magnet holder facing the air gap. A further alternative would be to metallize the outer surface of a nonmetallic magnet holder, increasing its reflectivity and decreasing its emissivity.
As will be apparent to those of skill in the art, other arrangements of geometries, dimensions and interference fits between the magnet holders 400 and magnets 216 or magnet sections 216′ may be selected based on the teachings contained herein without departing from the scope of the present invention. For example, rather than having a closed top, the magnet holder may be formed with an open top, in other words essentially as two inverted L-shaped sides 400A, 400B with inwardly directed flanges separated by a gap defining a top surface. These inwardly directed flanges maintain the magnets by interference along the base of each inverted L (line contact indicated at points Z) as shown in
An exemplary embodiment of a method for inserting magnets into an electromechanical machine such as a WPU generator according to the present invention will now be described in connection with
Exemplary embodiments have been disclosed above and illustrated in the accompanying drawings. It will be understood by those skilled in the art that various changes, omissions and additions may be made to that which is specifically disclosed herein without departing from the spirit and scope of the present invention.
Claims
1. A method for mounting permanent magnets to a magnet carrying structure in an electromechanical machine, comprising:
- providing a magnet holder having a top portion and sides defining at least a first open end, said top portion having an inside surface;
- sizing the magnet holder and configuring said top portion inside surface in combination with the magnet to provide an interference fit between the magnet holder and the magnet along facing surfaces thereof when the magnet is retained by the magnet holder on the magnet carrying structure, said interference fit being configured to maintain at least about 90% of the facing surfaces in a spaced apart relationship defining void space there between;
- mounting the magnet holder on the magnet carrying structure; and
- sliding the magnet into the magnet holder through said first open end to secure the magnet on the magnet carrying structure by said interference fit.
2. The method of claim 1, wherein said top portion inside surface is configured to form said interference fit along a line contact with said magnet.
3. The method of claim 1, wherein said top portion inside surface includes dimples configured to form said interference fit with said magnet.
4. The method of claim 1, wherein said top portion inside surface is configured to form plural ridges forming said interference fit with said magnet.
5. The method of claim 1, further comprising positioning a porous spacer between the magnet holder inside top surface and the magnet.
6. The method of claim 1, wherein said mounting comprises at least one of welding, bolting, or clamping the magnet holder to the magnet carrying structure or mounting the magnet holder to the magnet carrying structure within slots in the magnet carrying structure.
7. The method of claim 1, wherein the magnet carrying structure comprises a rotor.
8. The method of claim 7, wherein the electromechanical machine comprises a wind power unit.
9. The method of claim 8, wherein said wind power unit is mounted on a tower and said sliding and securing steps are performed on said tower.
10. The method of claim 9, wherein said sliding comprises securing a loading fixture to the rotor, placing a magnet into the loading fixture, and forcing the magnet into the magnet holder from said loading fixture.
11. The method of claim 10, wherein the loading fixture comprises a plunger to force the magnet into the magnet holder.
12. The method of claim 10, wherein said sliding further comprises aligning the loading fixture with the magnet holder prior to said forcing.
13. The method of claim 9, wherein the magnet holder has an open second end, said method further comprising removing the magnets through the magnet holder open second end for maintenance or replacement.
14. The method of claim 1, wherein:
- the permanent magnets to be mounted have a height and width;
- the magnet holder comprises a body having side walls joined by a closed top to define at least said first open end and an open bottom;
- the sides and closed top together define a magnet holder inside height configured and dimensioned in combination with the magnet height and a magnet mounting surface on the magnet carrying structure to define said void space between said closed top and said magnet, said void space occupying about 90% to 100% of the space between said surfaces when the magnet is retained on the magnet mounting surface within said magnet holder.
15. A magnet holder for securing permanent magnets to a magnet mounting surface on a rotor in an electromechanical machine, wherein the magnets have a height and width, said magnet holder comprising a body having side walls joined by a closed top to define at least a first open end and open bottom, wherein said sides and closed top together define a magnet holder inside height configured and dimensioned in combination with the magnet height and a magnet mounting surface to define at least one void between said closed top and said magnet, said at least one void occupying about 90% to 100% of the space between said surfaces when the magnet is retained on the magnet mounting surface within said magnet holder.
16. The magnet holder of claim 15, further comprising flanges disposed along bottom edges of said sides, said flanges being configured for attachment to the magnet mounting surface.
17. The magnet holder of claim 15, wherein said closed top has an inside surface configured and dimensioned to be spaced from the magnet mounting surface by a predetermined height wherein said predetermined height is less than the height of the magnet to form an interference fit between said closed top inside surface and the magnet.
18. The magnet holder of claim 17, wherein said closed top inside surface and said magnet height configured in combination to form said interference fit as a line contact there between.
19. The magnet holder of claim 18, wherein said at least one void comprises two voids formed on opposite sides of a single line contact, said voids occupying between about 99% and 100% of the space between said surfaces.
20. The magnet holder of claim 18, wherein said closed top and magnet height are configured in combination to form interference fits along plural lines of contact.
21. The magnet holder of claim 20, wherein said closed top is configured to form plural ridges forming said interference fit with said magnet, with plural said voids defined by said ridges.
22. The magnet holder of claim 17, wherein the magnet holder inside height is configured and dimensioned so as to not exceed an elastic deformation limit of the magnet holder body in said interference fit.
Type: Application
Filed: Dec 2, 2016
Publication Date: Mar 23, 2017
Inventors: Jonathan A. Lynch (St. Johnsbury, VT), Mark S. Piercey (Sudbury, MA), Peter P. Mongeau (Westborough, MA)
Application Number: 15/367,769