Metal working – Method of mechanical manufacture – Electrical device making
Reexamination Certificate
2002-01-17
2004-07-27
Arbes, Carl J. (Department: 3729)
Metal working
Method of mechanical manufacture
Electrical device making
C029S597000, C029S598000, C310S254100, C310S256000, C310S256000
Reexamination Certificate
active
06766572
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to electric power generators and, more particularly, to a stator core having pre-packaged stator core sections and manually stacked stator core sections.
A stator of an electric power generator generally includes a stator core and a stator frame. The stator core typically has a cylindrical shape and comprises of a stack of insulated steel laminations. Each lamination is a segment of a full circle that has slots on its inner diameter to accommodate a stator winding and dovetail slots on its outer diameter.
The stator frame has a plurality of key bars connected (e.g., welded) thereto, each key bar having a dovetail to provide structural support for the stator core. During the assembly of the stator core, each stator core lamination is manually installed into the stator frame by engaging a dovetail slot with a corresponding key bar dovetail.
This method for assembling stator cores is very time consuming and can only be done at a limited number of stacking stations. Additionally, this method requires that the key bars connected to the stator frame be located at very tight positional tolerances to ensure that the stator core can be assembled properly. To simplify the stator frame construction, key bars can be welded to the stator frame after a precise machining of the key bar dovetails. Unfortunately, this welding causes distortion that makes controlling the location of the key bars difficult. A significant amount of rework must therefore often be performed including the disassembly of the stator core and relocation of the key bars.
Manufacturing stator cores using pre-packaged stator core sections has been accomplished in the past under special circumstances. During these manufacturing processes, the key bar dovetails must be machined to very tight positional tolerances after they are welded onto the stator frame. This requires specialized equipment and increases the cost of the stator frame and cycle time. In other designs, the key bars and the stator flanges are assembled to form a completed stator core. This completed stator core is then welded or otherwise secured to the stator frame. An advantage of the pre-packaged stator core is that it can be used almost in any type of frame design.
Magnetic forces are imposed on a stator core of an electric power generator during the operation thereof. These magnetic forces will cause a relative vibration between the key bar dovetails and the dovetail slots of the laminations if a close fit therebetween is not established. This relative vibration will often result in the laminations impacting the key bars to thus generate an annoying noise.
It would thus be beneficial to increase stator core production capacity by reducing a lengthy stator core stacking cycle and eliminating lamination stacking difficulties and rework caused by the poor ability to provide an appropriate key bar location. It would also be beneficial to utilize standard low cost stator frame designs and to eliminate noise caused by a vibrating stator core impacting the key bars.
BRIEF SUMMARY OF THE INVENTION
In an exemplary embodiment of the invention, a stator comprises a stator frame, a plurality of key bars connected to the stator frame, each of the key bars having a dovetail, and a stator core. The stator core includes a first stator core section including at least one lamination having a first dovetail slot formed therein for engaging a first one of the dovetails. The stator core further includes a second stator core section including at least one lamination having a second dovetail slot formed therein for engaging a second one of the dovetails. The second dovetail slot has a cross-sectional area which is smaller than the cross-sectional area of the first dovetail slot.
The first one of the dovetails projects into the first dovetail slot such that no portion of the first dovetail directly contacts the lamination having the first dovetail slot formed therein. The second one of dovetails projects into the second dovetail slot such that the second dovetail directly contacts a portion of the lamination having the second dovetail slot formed therein.
The first stator core section is a pre-packaged stator core section, the second stator core section is a manually stacked stator core section and more of the stator core is formed by the first stator core section than the second stator core section. The first stator core section is held to the stator frame by a force caused by core stacking pressure of the stator core.
In a further exemplary embodiment of the invention, the stator comprises a stator frame, a plurality of key bars connected to the stator frame, each of the key bars having a dovetail, and a stator core. The stator core includes a pre-packaged stator core section including at least one lamination having a first dovetail slot for engaging a first one of the dovetails. The stator core further includes a manually stacked stator core section including at least one manually stacked lamination having a second dovetail slot for engaging a second one of the dovetails.
In the further exemplary embodiment, the second dovetail slot has a cross-sectional area which is smaller than the cross-sectional area of the first dovetail slot. The first one of dovetails projects into the first dovetail slot such that no portion of the first dovetail directly contacts the lamination having the first dovetail slot formed therein. The second one of dovetails projects into the second dovetail slot such that the second dovetail directly contacts a portion of the lamination which forms the second dovetail slot formed therein. More of the stator core is formed by the pre-packaged stator core section than the manually stacked stator core section. The pre-packaged stator core section is held to the stator frame by a force caused by core stacking pressure.
In a yet another exemplary embodiment of the invention, a method of assembling a stator comprises providing a stator frame, connecting a plurality of key bars to the stator frame, each of the key bars having a dovetail, and forming a stator core. Forming the stator core includes forming a pre-packaged stator core section including at least one first lamination having a first dovetail slot and coupling the pre-packaged stator section to the stator frame by engaging a first one of the dovetails into the first dovetail slot. Forming the stator core also includes forming at least one second lamination having a second dovetail slot, and coupling the second lamination to the stator frame by manually stacking the second lamination such that a second one of the dovetails engages into the second dovetail slot to form a manually stacked stator core section.
In the yet another exemplary embodiment, the first and second dovetail slots are formed such that a cross-sectional area of the first dovetail slot in the pre-packaged stator core section is larger than the cross-sectional area of the second dovetail slot in the manually stacked stator core section. The pre-packaged stator core section is coupled to the stator frame such that no portion of the first dovetail directly contacts the lamination having the first dovetail slot formed therein. The second stator core section is coupled to the stator frame such that the second dovetail directly contacts a portion of the lamination having the second dovetail slot formed therein. More of the stator core is formed by the pre-packaged stator core section than the manually stacked stator core section. The pre-packaged stator core section is held to the frame by a force caused by core stacking pressure of the stator core.
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Dawson Richard Nils
Nygard Robert J.
Petti John A.
Walko Steven C.
Nixon & Vanderhye P.C.
Phan Tim
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