Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
1997-09-08
2001-03-27
Tamai, Karl (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S043000, C310S071000
Reexamination Certificate
active
06208056
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to armature windings for direct and alternating current electric machines. More particularly, this invention relates to the use, configuration, and manufacturing process for improved smooth air-gap armature windings.
Rotating electric machines convert mechanical energy into electrical energy (e.g., an electric generator) and electrical energy into mechanical energy (e.g., an electric motor) by moving a magnetic field with respect to an electric circuit. The magnetic field is produced by electrons in motion, and the electric circuit is typically a set of electrical conductor windings or coils.
Rotating electric machines have two basic components, a rotor and a stator. The rotor is usually the moving part that contains electrical conductors for producing a magnetic field. The stator is usually the stationary part that contains an electric circuit (e.g., armature windings) for also producing a magnetic field that interacts with the magnetic field produced by the rotor. The interaction between the moving and stationary magnetic fields produces torque (i.e., a twisting force) in a motor or voltage in a generator.
FIG. 1A
is a simplified diagram illustrating a rotating electric machine with a slot wound armature geometry. A primary magnetic field is developed on rotor
101
a
that rotates relative to fixed windings
102
a
on stator
103
a
. Often, the windings are wound on iron cores to maximize magnetic flux between the rotor and stator. Magnetic flux is analogous to current and can be thought of as the lines of force of a magnetic field. When currents flow in the stator windings, electromechanical torque develops as a result of the interaction of the rotor and stator magnetic fields. By installing the stator windings in slots
104
, the resultant torque is generated between the stronger iron core materials of stator
103
a
rather than on the lower strength conductors of windings
102
a.
Alternatively, the armature conductors may be arranged on a smooth bore stator as shown in FIG.
1
B. The terms “smooth bore windings” or “air-gap windings” are often used to describe this geometry. An advantage of this geometry is the elimination of azimuthal variation in the iron circuit. In other words, the total flux in the air gap between the rotor and the stator does not change as a function of rotor angular position. This advantage is particularly important in high speed, multi-pole machines that operate at high electrical frequency, because these variations in total flux contribute to rotor and stator heating through the development of eddy currents. Heating can damage the windings and other components.
The standard method of minimizing eddy currents is to laminate the iron core components (most often the stator is laminated). Lamination thickness is a function of operating frequency. However, as the frequency of operation increases to several hundred hertz and beyond, the required lamination thickness becomes extremely thin and thus difficult to assemble into bulk components. Moreover, the laminations must be insulated from one another and the finite thickness of the non-ferrous insulation reduces the effective cross section of iron, which ultimately decreases a given machine's peak power output due to field saturation.
Applications particularly well suited to air-gap windings are machines requiring high power output. By placing the conductors in the air gap, some of the iron (e.g., teeth
105
) from the armature circuit is eliminated, reducing the armature circuit inductance and thus the reactive impedance. Thus, for a given machine voltage, maximum power output may be obtained. However, unlike slot wound stator windings, the air-gap windings transfer torque through the lower strength conductors themselves. To facilitate transfer of torque loads from the conductors to the stronger iron core stator, several machines have been built where the conductors are bonded to the smooth bore of the stator using adhesives. The strength of this bond is a function of surface cleanliness and other factors that are difficult to control prior to assembly and difficult to inspect in service.
Machines such as the flywheel motor-generator described in U.S. patent application Ser. No. 08/597,008, which is assigned to Active Power, Inc. of Austin, Tex., operate in a vacuum to reduce rotor windage losses (i.e., energy losses caused by air drag). However, several complications result from this environment. First, the armature conductors must penetrate the stator that provides the vacuum enclosure. These penetrations must be vacuum tight to minimize the size of the vacuum pump. Furthermore, conductors or conductor connections exposed to the vacuum environment should be insulated to reduce the risk of corona discharge (i.e., electrical discharge through an ionized gas). The likelihood of a corona discharge depends on the pressure and composition of residual gases within the vacuum. A vacuum environment also requires that heat transfer from the windings to the stator be by radiation or conduction; the latter advantageously resulting in a lower temperature rise within the armature, which increases service life.
Finally, loss of armature dielectric integrity because of mechanical damage, heating damage, and other causes of internal shorting requires that the armature be replaced. With either slot wound armatures or bonded air-gap windings, the entire rotating electric machine must be sent to a service facility to machine-out the old windings and either rewind or bond-in new windings. The labor costs of this process are so significant that many smaller machines are discarded and replaced.
In view of the foregoing, it would be desirable to provide an improved armature winding for rotating electric machines that can be easily and economically serviced in the field.
It would also be desirable to provide an improved armature winding that provides a low inductance air-gap winding to increase machine power density.
It would further be desirable to provide an improved armature winding that transfers torque to a stator during high power operation.
It would still further be desirable to provide an improved armature winding that provides conduction heat transfer from the armature conductors to a stator.
It would yet further be desirable to provide an improved armature winding that provides electrically insulated, vacuum tight penetrations of a stator for electrical feed-throughs.
It would also be desirable to provide an improved armature winding that provides armature conductor isolation in vacuum environments to reduce the risk of corona discharge.
It would further be desirable to provide an improved armature winding that provides compact coil connections to reduce the volume of the armature winding.
Finally, it would be desirable to provide an improved armature winding that provides coil-to-coil electrical isolation.
SUMMARY OF THE INVENTION
It is an object of this invention to provide an improved armature winding for rotating electric machines that can be easily and economically serviced in the field.
It is also an object of this invention to provide an improved armature winding that provides a low inductance air-gap winding to increase machine power density.
It is a further object of this invention to provide an improved armature winding that transfers torque to a stator during high power operation.
It is a still further object of this invention to provide an improved armature winding that provides conduction heat transfer from the armature conductors to a stator.
It is yet a further object of this invention to provide an improved armature winding that provides electrically insulated, vacuum tight penetrations of a stator for electrical feed-throughs.
It is also an object of this invention to provide an improved armature winding that provides armature conductor isolation in vacuum environments to reduce the risk of corona discharge.
It is a further object of this invention to provide an improved armature winding that provides compact coil connections to reduce the
Active Power Inc.
Arons Edward M.
Fish & Neave
Morris Robert W.
Tamai Karl
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