Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2001-09-07
2004-09-14
Nguyen, Tran (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S057000, C310S061000, C310S261100, C310S219000, C310S262000
Reexamination Certificate
active
06791230
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to high speed generators and, more particularly, to the structure of the rotors on such generators.
BACKGROUND OF THE INVENTION
Generator systems that are installed in aircraft may include three separate brushless generators, namely, a permanent magnet generator (PMG), an exciter, and a main generator. The PMG includes permanent magnets on its rotor. When the PMG rotates, AC currents are induced in stator windings of the PMG. These AC currents are typically fed to a regulator or a control device, which in turn outputs a DC current. This DC current next is provided to stator windings of the exciter. As the rotor of the exciter rotates, three phases of AC current are typically induced in the rotor windings. Rectifier circuits that rotate with the rotor of the exciter rectify this three-phase AC current, and the resulting DC currents are provided to the rotor windings of the main generator. Finally, as the rotor of the main generator rotates, three phases of AC current are typically induced in its stator windings, and this three-phase AC output can then be provided to a load such as, for example, electrical aircraft systems.
Because the generators installed in aircraft will often be variable frequency generators that rotate in the speed range of 12,000 rpm to 24,000 rpm, large centrifugal forces are imposed upon the rotors of the generators. Given these stressful operating conditions, the rotors of the generators must be carefully designed and manufactured, both so that the rotors are reliable and also so that the rotors are precisely balanced. Improper balancing in particular not only can result in inefficiencies in the operation of the generators, but also potentially risk failures in the generators.
Among the important components in rotors that must be carefully designed and manufactured in order to guarantee reliability and proper balancing of the rotors are the wire coils of the rotors. The centrifugal forces experienced by the rotors are sufficiently strong as to cause bending of the wires of these coils, which over time can result in mechanical breakdown of the wires. Additionally, because the coils are assemblies of individual wires that can move to some extent with respect to one another and with respect to the remaining portions of the rotors, the coils constitute one of the significant potential sources of imbalance within the rotors. Even asymmetrical movements of these coils on the order of only a few thousandths of an inch can be significant.
In order to improve the strength and reliability of the wire coils and to minimize the amount of imbalance in the rotors that occurs due to the wire coils, wedges may be inserted in between neighboring poles of the rotors. The wedges in particular serve as physical barriers beyond which the wires of the coils cannot bend or move, and in many embodiments provide some pressure onto the coils that helps to maintain the physical arrangement of the coils.
Although the wedges employed in conventional rotors are capable of providing these benefits to some extent, the design of these conventional rotors and wedges limits the wedges' effectiveness. Just as the wires of the coils of a rotor experience high centrifugal forces as the rotor rotates at high speeds, the wedges also experience high centrifugal forces. These forces tend to cause the wedges to spread radially outward away from the shaft of the rotor during operation, thus limiting the wedges ability to confine and place pressure upon the wire coils. Particularly, insofar as the axial lengths of conventional rotors are often relatively large in comparison with the diameters of the rotors, the centrifugal forces often tend to cause significant radial deflection or flexure of the wedges near their axial midpoints.
In order to prevent the wedges from spreading radially outward, many conventional rotors employ bands around the circumferences of the rotors to retain the wedges. In other conventional rotors, an “underwedge” system is employed in which the wedges extend in their arc length all of the way between neighboring pole tips on the rotors, and snap rings are then employed to hold the wedges in place relative to the poles.
Yet these conventional structures for retaining wedges in place on rotors are limited in their effectiveness. Both the bands used to retain the wedges and the components of the underwedge systems (particularly the snap rings) also can suffer from bending during operation of the rotors. Because these devices suffer bending, the devices can only provide a limited amount of counteracting force to keep the wedges in place, and further can create additional imbalance in the rotors. Additionally, because it is difficult to accurately control the positioning of, and the amount of pressure applied by, the bands and underwedge componentry, it is difficult to accurately set and maintain the positioning of the wedges and to control the concentricity of the various wedges around the rotors.
Hence, there is a need for a new system and method for retaining wedges in a rotor. In particular, there is a need for a new system and method that allows for sufficient radial retention of the wedges of the rotor even at high speeds of operation, so that the wedges continue to provide support for and direct pressure towards the wire coils throughout operation of the generator. Further, it would be advantageous if the new system and method did not require components that had a tendency to bend in such a way as to create imbalance in the rotor. It would additionally be advantageous if the system and method allowed for the accurate positioning of wedges onto the rotor so as to provide concentricity of the rotor and its wedges. It would further be advantageous if the system was designed so as to allow the wedges to conduct heat away from the coils. It would additionally be advantageous if the system and method were relatively simple and inexpensive to implement.
SUMMARY OF THE INVENTION
The present inventors have recognized that conventional rotor wedges that are supported by bands or underwedge componentry near the circumference of a rotor can be replaced by two-wedge sets that each include an outer wedge and an inner wedge, where the inner wedges retain the outer wedges in their positions relative to the central axis of the rotor. The outer wedges, like conventional rotor wedges, expand in cross section as one moves radially outward from the shaft of the rotor. The outer wedges extend between neighboring poles of the rotor, and thereby provide support for, and direct pressure towards, the wire coils of those poles. The inner wedges are positioned radially inward from the corresponding outer wedges and are coupled to the outer wedges. The inner wedges expand in cross section as one moves radially inward toward the shaft of the rotor and rest upon the sides of the wire coils of neighboring poles. Consequently, the inner wedges are blocked from moving radially outward by the sides of the wire coils, and the sides of the wire coils provide the centripetal force necessary for restraining the inner and outer wedges in place. To the extent that any radial movement of the wedges does occur, the movement can only occur when accompanied by increased pressure applied on the coils. Further, the inner wedges and outer wedges can be coupled to one another by fastening devices that allow for variation in the relative positioning of the inner and outer wedges, and therefore allow for concentricity control.
In particular, the present invention relates to a rotor including a shaft extending along an axis through the rotor, first and second poles extending radially from the shaft, and first and second coils of wire windings respectively wrapped around the first and second poles. Each coil includes a respective outer face including two end turn portions and two side portions, and a respective inward-facing edge including two end turn sections and two side sections. The rotor further includes a first outer wedge positioned between a first of the sid
Borden Raymond W.
Chen WuenFar L.
Doherty Kieran P. J.
Lengel James D.
McDowall Gregor J. S.
Honeywell International , Inc.
Mullen, Esq. Douglas A.
Nguyen Tran
LandOfFree
System and method for retaining wedges in a rotor does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with System and method for retaining wedges in a rotor, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and System and method for retaining wedges in a rotor will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3206168