Power generator

Details Power generator Power generator

2000-12-27

2002-08-06

Mullins, Burton S. (Department: 2834)

Electrical generator or motor structure

Dynamoelectric

Rotary

C310S256000, C310S256000, C310S064000

Reexamination Certificate

active

06429567

ABSTRACT:

BACKGROUND OF THE INVENTION
The invention relates generally to a power generator, and in particular to reduction of heat dissipation and undesirable voltage differentials in a power generator.
In order to improve generator efficiency and reduce generator size, high power electrical generator manufacturers are constantly endeavoring to improve generator thermal performance and efficiency. 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 power generator
100
from an isometric perspective.
FIG. 2
is a cut-away view of power generator
100
along axis
2
-
2
. As shown in
FIGS. 1 and 2
, power 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
(not shown in FIG.
1
). The multiple keybars
118
, together with the multiple flanges
204
, form a keybar cage around the 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 induced 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. A rotation of rotor
110
inside of stator
102
when a DC current is flowing in the multiple windings of rotor
110
induces electromagnetic fields in, and a passage of magnetic flux through, stator
102
and the loops of stator windings. The passage of magnetic flux through the stator windings induces a current in the stator windings and a power generator output voltage. The passage of magnetic flux through stator
102
induces eddy currents in the magnetically and electrically resistive stator. The eddy currents cause the dissipation of energy in stator
102
in the form of heat and impose a thermal constraint on the operation of generator
100
.
FIG. 3
is a partial perspective of generator of
100
and illustrates a typical technique of constructing stator core
104
. One known thermal management technique is the construction of stator core
104
from multiple ring-shaped laminations
302
. As shown in
FIG. 3
, the multiple ring-shaped laminations
302
are stacked one on top of another in order to build up stator core
104
. Each lamination
302
is divided into multiple lamination segments
304
. Each lamination segment
304
includes multiple slots
120
(not shown in FIG.
3
), wherein at least one slot
120
of each segment
304
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 one of the multiple slots
120
of a lamination segment
304
with a locking side
122
of a keybar
118
affixes each lamination segment
304
, and thereby each lamination
302
, in position in stator
102
. By building stator core
104
from stacked laminations
302
, as opposed to constructing a solid core, circulation of a current induced in stator
102
is limited to a lamination, thereby restricting current circulation and size and concomitantly reducing stator heating. However, the above thermal management technique does not fully address the thermal problems caused by the coupling of magnetic fields into stator
102
.
Furthermore, induced magnetic flux also passes through, and spills outside of, stator
102
, coupling into each of the multiple keybars
118
. The coupling of magnetic flux into a keybar
118
induces keybar voltages and keybar currents in the keybar, which current flows from the keybar 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, the 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
.
In addition, the induction of keybar voltage in each of the multiple keybars
118
can result in a voltage differential between keybar voltages induced in two of the multiple keybars
118
. When adjacent keybars
118
are coupled to adjacent lamination segments
304
, a keybar voltage differential appearing between the adjacent keybars
118
may also appear across the adjacent lamination segments
304
. The voltage differential between adjacent lamination segments
304
can cause arcing between the two segments, overheating in the stator core
104
, and reduced generator performance. The arcing can also create localized heating in the core, causing lamination segments
304
, and lamination rings
302
, to fuse together. Such fusing can spread quickly in generator
100
as the lamination segments
304
, and lamination rings
302
, short circuit to each other, resulting in damage to the generator.
Therefore, a need exists for a method and apparatus for further reducing the heat dissipated in the stator and for reducing keybar voltage differentials that may appear between keybars.
BRIEF SUMMARY OF THE INVENTION
Thus there is a particular need for a method and apparatus that reduces the heat dissipated in a generator stator and that reduces keybar voltage differentials that may appear between keybars. Briefly, in accordance with an embodiment of the present invention, a thermal control and keybar voltage reduction mechanism is provided for use in a power generator having multiple keybars. The thermal control and keybar voltage reduction mechanism includes a keybar coupler capable of being electrically coupled to each of a first keybar of the multiple keybars and a second keybar of the multiple keybars. When

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