Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
1999-05-05
2001-07-17
Enad, Elvin (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S179000, C310S180000, C310S184000, C318S254100, C318S288000
Reexamination Certificate
active
06262506
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to rotating electrical machines having auxiliary windings in the stator of the machines for providing multiplanar rotor balancing, mechanical stiffening and rotor levitation/centering independent of machine orientation or axis of rotation.
2. Related Art
Electrical machines, such as motors and generators, may use auxiliary or control windings for rotor levitation/centering and rotor balancing. A typical rotor can have a slight amount of mass imbalance. As the rotor rotates, the mass imbalance leads to an unwanted vibrational force appearing at the motors bearings. Such vibrational forces reduce the lifetime of bearings and degrade the performance of the machine. The electromagnetics associated with the machine can also cause undesired forces which appear at the motor casing due to deflection of the stator core. Prior attempts have been made to cancel the forces created by a mass imbalance and/or electromagnetics by forming a magnetic field with auxiliary control windings in a manner which creates a force on the rotor to cancel the undesired forces.
In conventional electrical machines which incorporate auxiliary windings, the control windings are provided along the entire active length of the machine which provides a uniform force distribution. A single sensor measures the effect of undesired forces at a single point and feeds the information to a controller. The controller then drives the control windings with a controlled voltage or current determined from the measurements made by the sensor. With this winding arrangement, optimizing the performance at one axial location along the rotor based on sensor measurements may make the performance at other locations worse.
Some prior art machines also include radial magnetic bearings. Magnetic bearings cause the rotor to levitate/center and eliminate the need for mechanical contacts. Conventional magnetic bearings are placed only on the spindle, which has a relatively smaller diameter. Such placement necessitates the use of a high magnetic field per unit area or use of axially longer bearing surface (since the magnetic field may be limited by material characteristics) in order to levitate/center the rotor.
SUMMARY OF THE INVENTION
According to the invention, there is provided an electrical machine with multiple independent control windings placed at different axial locations along the stator independent of rotor type. The control windings optimize the performance of the machine by canceling undesired forces produced by 1) mass imbalances of the rotor, 2) variations in rotor position or 3) electromagnetics, and, in one embodiment, also act as magnetic bearings to provide a bearingless, globally balanced machine.
In accordance with a first embodiment of the invention, a rotating electrical machine is provided which comprises: a stator; a rotor adapted for rotation relative to the stator and having a longitudinal axis; a first set of control windings mounted on the stator for producing a magnetic field to oppose an undesired force at a first location along the longitudinal axis of the rotor, and a second set of control windings mounted on the stator for producing a magnetic field to oppose an undesired force at a second location (which may overlap the first location) along the longitudinal axis of the rotor spaced from the first location.
The first set of control windings preferably has a different distribution than the second set of control windings. It is also preferred that the first set of control windings has an axial length different from that of the axial length of the second set of control windings.
In a preferred embodiment, the first and the second sets of control windings produce magnetic fields for levitating, balancing or centering the rotor.
In another preferred embodiment, the machine further includes a third set of control windings mounted on the stator for producing a magnetic field to oppose other undesired forces at a third location along the longitudinal axis of the rotor spaced from the first location and the second location.
In a first preferred implementation of the first preferred embodiment, the machine also includes: a first set of lead wires connected to the first set of control windings at an edge of the stator; a second set of lead wires connected to the second set of control windings at an edge of the stator; and a third set of lead wires connected to the third set of control windings and placed between or alongside the first set of control windings and arranged to exit at an edge of the stator.
In a second preferred implementation of the first preferred embodiment, the machine includes: a first set of lead wires connected to the first set of control windings at an edge of the stators a second set of lead wires connected to the second set of control windings at an edge of the stator; and a third set of lead wires connected to the third set of control windings and arranged to exit radially through a hole in the stator.
In another preferred embodiment, the machine further includes a means for providing axial spacings of the first set of control winding end turns and the second set of control winding end turns. In a first preferred implementation of this embodiment, the means for providing axial spacing comprises beams mounted on at least one side of a stator lamination and having regions between the beams for mounting the first set of control winding end turns and the second set of control winding end turns. In a second preferred implementation of this embodiment, the means for providing axial spacing comprises toothless laminations having recessed regions for mounting said first set of control winding end turns and said second set of control winding end turns therein. In a third preferred implementation of this embodiment, the means for providing axial spacing comprises stepped laminations having recessed regions for mounting said first set of control winding end turns and said second set of control winding end turns therein.
In accordance with a second preferred embodiment of the invention, a rotating electrical machine is provided which comprises: a stator; a rotor adapted for rotation relative to the stator; a first set of control windings attached to the stator for producing a first magnetic field to apply a force to the rotor at a first axial location of the rotor; a second set of control windings attached to the stator and overlapping and extending beyond the first set of control windings for producing a second magnetic field for opposing undesired forces at a second axial location of the rotor and for, in combination with the first magnetic field, opposing undesired forces at the first axial location of the rotor.
The machine preferably includes a third set of control windings attached to the stator and overlapping and extending beyond the first and the second sets of control windings for producing a third magnetic field for opposing undesired forces at a third axial location of the rotor and for, in combination with the first and the second magnetic field, opposing undesired forces at the first axial location of the rotor and for, in combination with the second magnetic field, opposing undesired forces at the second axial location of the rotor.
Other features and advantages of the invention will be set forth in, or apparent from, the following detailed description of the preferred embodiments of the invention.
REFERENCES:
patent: 3888553 (1975-06-01), Wehde
patent: 4286180 (1981-08-01), Langley
patent: 4434389 (1984-02-01), Langley et al.
patent: 4630013 (1986-12-01), Takada
Lewandowski Chad R.
Shah Manoj R.
Caress Virginia B.
Enad Elvin
Gottlieb Paul A.
Lam Thanh
Lucas John T.
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