Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2002-10-25
2004-04-13
Le, Dang (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S182000
Reexamination Certificate
active
06720699
ABSTRACT:
FIELD OF THE INVENTION
The invention relates generally to a power generator, and in particular to reduction of keybar voltages in a power generator.
BACKGROUND OF THE INVENTION
In order to improve generator efficiency and reduce generator size, generator manufacturers are constantly endeavoring to improve the thermal performance of the generator. For example, a prior art design of a high power electrical generator
100
is illustrated in
FIGS. 1 and 2
.
FIG. 1
is an end view of a cross-section of generator
100
from an isometric perspective.
FIG. 2
is a cut-away view of generator
100
along axis
2
—
2
. As shown in
FIGS. 1 and 2
, electrical generator
100
includes a substantially cylindrical stator
102
housing a substantially cylindrical rotor
110
. Power generator
100
further includes multiple axially oriented keybars
118
that are circumferentially distributed around an outer surface of the stator
102
. Each keybar
118
is mechanically coupled to the outer surface of stator
102
. Each keybar
118
is further mechanically coupled at each of a proximal end and a distal end to one of multiple flanges
204
. The multiple keybars
118
, together with the multiple flanges
204
, form a keybar cage around stator
102
.
An inner surface of stator
102
includes multiple stator slots
106
that are circumferentially distributed around an inner surface of stator
102
. Each stator slot
106
is radially oriented and longitudinally extends approximately a full length of stator
102
. Each stator slot
106
receives an electrically conductive stator winding (not shown).
Rotor
110
is rotatably disposed inside of stator
102
. An outer surface of rotor
110
includes multiple rotor slots
114
that are circumferentially distributed around the outer surface of rotor
110
. Each rotor slot
114
is radially oriented and longitudinally extends approximately a full length of rotor
110
. An air gap exists between stator
102
and rotor
110
and allows for a peripheral rotation of rotor
110
about axis
130
.
Each rotor slot
114
receives an electrically conductive rotor winding (not shown). Each rotor winding typically extends from a proximal end of rotor
110
to a distal end of the rotor in a first rotor slot
114
, and then returns from the distal end to the proximal end in a second rotor slot
114
, thereby forming a loop around a portion of the rotor. When a direct current (DC) voltage differential is applied across a rotor winding at the proximal end of rotor
110
, an electrical DC current is established in the winding. Similar to the rotor windings, each stator winding typically extends from a proximal end of stator
102
to a distal end of the stator in a first stator slot
106
, and then returns from the distal end of the stator to the proximal of the stator in a second stator slot
106
, thereby forming a stator winding loop.
FIG. 3
is a partial perspective of generator of
100
and illustrates a typical technique of constructing a stator core
104
. As shown in
FIG. 3
, stator core
104
includes multiple ring-shaped lamination packets
302
that are stacked one on top of another in order to build up the core. A gap
303
between adjacent packets allows for ventilation to cool rotor
110
and stator core
104
. One design of stator core
104
further includes subdividing each lamination packet
302
into multiple lamination segments
304
. A radially outer surface of each lamination segment
304
includes at least one slot
120
(not shown in
FIG. 3
) that aligns with one of the multiple keybars
118
. Each keybar in turn includes an outer side
124
and an inner, or locking, side
122
that mechanically mates with one of the multiple slots
120
. Stator core
104
is then constructed by sliding each lamination segment
304
, via one of the multiple slots
120
, into the keybar cage formed by the multiple keybars
118
. The coupling of each slot of the multiple slots
120
of a lamination segment
304
with a locking side
122
of a keybar
118
affixes each lamination segment in position in stator
102
.
A rotation of rotor
110
inside of stator
102
with a DC current in the multiple windings of rotor
110
establishes a magnetic flux in the generator. A portion of the magnetic flux that passes through stator
102
, spills outside of the outer surface of stator
102
coupling into each of the multiple keybars
118
. The coupling of magnetic flux into each of multiple keybars
118
can induce keybar voltages and thus setup keybar currents in each keybar. One possible result is a development of a voltage differential between keybar voltages produced in each of two different keybars
118
. When adjacent keybars
118
are coupled to adjacent lamination segments, a voltage differential between the adjacent keybars
118
may also appear across the adjacent lamination segments. The voltage differential between adjacent lamination segments can cause arcing between the two segments; overheating in the stator core
104
, and reduced generator performance.
Furthermore, the keybar currents induced in each keybar
118
flow from the keybar
118
to a flange
204
coupled to the keybar. A mechanical joint by which a keybar
118
is coupled to a flange
204
can be a poor electrical conductor that provides a high resistance path for the current. As a result, the joint can be a source of undesirable energy dissipation and heat generation in power generator
100
, and is also a potential source of arcing and pitting in the power generator. Furthermore, a flow of keybar current in a magnetically and electrically resistive flange
204
results in undesirable energy and heat dissipation in the flange. To avoid overheating the joint and the flange
204
and potential arcing and pitting, a power generator such as power generator
100
sometimes must be operated at backed off levels of magnetic flux and output voltage, reducing the efficiency and rated power level of the power generator
100
.
Therefore, a need exists for a method and apparatus for reducing keybar currents and keybar voltage differentials induced in each of the multiple keybars.
BRIEF SUMMARY OF THE INVENTION
Thus there is a particular need for a method and apparatus that reduces keybar currents and that reduces any voltage differential that may appear between keybars. Briefly, in accordance with an embodiment of the present invention, a keybar shield is provided for insertion adjacent to an outer surface of a stator and that extends approximately an axial length of the stator. The keybar shield reduces the amount of flux coupling into a keybar during operation of a power generator, reducing a keybar voltage and a voltage differential that may appear between keybars. Also, by reducing the amount of flux coupling into a keybar, the keybar shield also reduces keybar currents and flange currents and their associated energy losses.
REFERENCES:
patent: 3987325 (1976-10-01), Wilson et al.
patent: 5796191 (1998-08-01), Schwanda
patent: 5869912 (1999-02-01), Andrew et al.
patent: 6025666 (2000-02-01), Kliman
patent: 6104116 (2000-08-01), Fuller et al.
patent: 6127761 (2000-10-01), Shen et al.
patent: 6429567 (2002-08-01), Shah et al.
patent: 6462457 (2002-10-01), Shah et al.
patent: 57-78334 (1982-05-01), None
Salem Sameh R.
Shah Manoj R.
Banner & Witcoff , Ltd.
Le Dang
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