Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2000-01-03
2001-07-31
Enad, Elvin (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
Reexamination Certificate
active
06268668
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to gas cooled generator stators and, more particularly, to a structure and method for impingement cooling of generator stator coils.
During the process of producing electricity, power generators also create heat that must be dissipated away from the generator. Generators are typically gas-cooled by ventilated cooling systems that circulate cooling gasesthrough ducts in the rotor and stator.
By way of example,
FIG. 1
shows a cross-section of one-half of a generator
10
, (see axial center line
12
and longitudinal center-line
14
) havinga reverse flow ventilated cooling system. In this example, a portion
16
of the flow of cooling gases is directed to the rotor
18
. The cooling gases are drawn through ventilation ducts
20
in the rotor by centrifugal forces created by the spinning rotor. As the gases flow through the rotor, heat in the rotor is transferred to the gases. Thus, heated gas exits the rotor ducts
20
at the surface of the rotor
18
and enters an air gap
22
between the rotor
18
and stator
24
. Fans
26
mounted at the ends of the rotor
18
(only one of which is shown in
FIG. 1
) draw these heated gases through the annular gap
22
and direct the same via an external duct
28
to a heat exchanger
30
for cooling the gas.
The stator
24
is cooled by ventilation flow path(s) that are separate from the flow paths in the rotor
18
. Gas
32
cooled by the heat exchanger
30
enters a plenum chamber
34
surrounding the stator
24
. Cooling gas tends to flow in greater volume and velocity through stator ducts near the ends of the stator because the end sections of the stator are closest to the exhaust fans
26
. This potential imbalance in the flow of cooling gas through the stator is preferably compensated for by varying the spacing and cross-sectional area of stator cooling ducts along the length of the stator to optimize the distribution of cooling gases through the stator and minimize the necessary pressure head needed for the cooling gases. The cooled gas flows to the stator outer circumferential surface
38
and into the cooling ducts
40
defined between the packets
42
of stator core laminations.
Referring to
FIG. 2
, the armature bars
44
,
46
are secured in the stator coil slot
48
with filler
50
, top-ripple spring(s)
52
, and stator wedge
53
to restrain the bars radially, and with side-ripple spring(s)
54
to increase friction between the bars
44
,
46
and the side walls of the slot
48
. Referring to the lower armature bar
44
for convenience, the heat that is generated in the copper strands
56
of the armature bar
44
is thermally conducted along a heat flow path
58
from the strands
56
, through a layer of insulation
60
to the side walls of the slot
48
.
As noted above, cooling ducts
40
are incorporated into the stacks of laminations defining the stator core
24
. Referring to
FIG. 3
, space blocks
62
,
64
are provided axially between adjacent stator core packets
42
for defining the axial dimensions of the ducts
40
and for directing the cooling air flow radially through the stator
24
. As the gas flows radially inwardly through the stator
24
, heat from the stator coils
44
,
46
is transferred to the gas. In conventional systems, the cooling gas ducts
40
are open ended so that the cooling gas flows radially directly into the annular gap
22
between the rotor
18
and stator
24
and then flows axially along that gap under the influence of the fans
26
for return to the heat exchanger
30
.
As is apparent from the foregoing, the current-carrying copper conductors
56
of the typical stator coil/armature bar
44
are indirectly cooled. That is, in systems of the type described above, the coolant does not directly contact the current-carrying copper conductors
56
of the armature bar
44
, nor indeed most of the bar
44
. Instead, there is a thermal conduction path
58
from the armature bar
44
to the walls of the stator slot(s)
48
. Thereafter the heat must be conducted through the lamination packet
42
to the adjacent cooling duct(s)
40
.
This thermal conduction path
58
, however, includes regions of imperfect contact between, e.g., the armature bar
44
and the side walls of the slot
48
. The imperfect contact is inherent in the assembly of the multiple components. For example, because of the nature of the armature bar
44
, it is not perfectly flat. Moreover, because of the assembly tolerance of the laminations that define the packets
42
, the stack of laminations from which the core
24
is made may not align perfectly, so the slots
48
are not perfectly straight. More specifically, laminations may be slightly rotated clockwise or counterclockwise relative to a next adjacent lamination. Dead-air spaces are formed when individual adjacent laminations are slightly offset from each other in the peripheral direction. As a result, there are voids in the thermal conduction path, referred to as lamination stagger. Voids and imperfect contact of the type described above cause increased thermal resistance between the bar, which is the source of heat, and the cooling duct which is where the heat is taken away. High thermal resistance results in a higher operating temperature of the armature bar, which limits the output performance of the generator, since there is an imposed limit on the bar operating temperature.
In addition to the aforementioned imperfect thermal conduction paths in/along the stator slot, there is a further thermal resistance conduction path through the stack of stator core laminations. More specifically, once the heat is conducted through the thermal-contact resistance in the slot, heat needs to flow peripherally, radially and/or axially through the stack of iron laminations eventually to the cooling duct surface. The axial conduction path in particular presents a high resistance to heat flow since there is thermal contact resistance and often an enamel layer in between individual laminations in the stack.
BRIEF SUMMARY OF THE INVENTION
In view of the problems and inefficiencies observed with the traditional methods of heat removal, a more effective heat removal path would be highly desirable. The end result of a more effective heat removal path would be a lower operating temperature for the stator armature bar. In that regard, the power output for a generator is limited by how hot the armature bar can get. Indeed, the stator RTD temperature is monitored by the customer and will limit the output of the machine. If the stator bar can be cooled more effectively, the machine can produce more output for the same size unit. This in turn results in an increase in power density which realizes a cost reduction because more power can be made onto the grid with a smaller size machine.
The invention is embodied in a new stator core cooling concept that can be implemented with the basic core structure described above, having cooling ducts interspersed at intervals along the axial length of the stator core. More particularly, the concept of the invention is embodied in a stator core in which cooling ducts are radially closed off. Thus, cooling air is forced to flow circumferentially preferably through small holes, channels, or slots to impinge directly on the armature bar surface. Thus, rather than flowing cooling gas through the cooling ducts and immediately discharging it, cooling gas flows radially through the cooling duct and then must flow circumferentially whereupon it impinges directly on the armature bar surface itself.
In a preferred embodiment of the invention, once the cooling gas impinges on the armature bar surface, it is directed to flow axially, along at least a portion of the length of the armature bar. Advantageously, the axial flow extends into the lamination packet. The cooling gas flow may then be directed, for example, into the gap between the stator and rotor and through aperture(s) in the stator wedge.
Accordingly, the invention is embodied in an electromagnetic generator that comprises a stator structure concentri
Glynn Christopher Charles
Jarczynski Emil Donald
Mercer Gary
Seitzer Kenneth E.
Vandervort Christian Lee
Enad Elvin
General Electric Co.
Nixon & Vanderhye
Perez Guillermo
LandOfFree
Gas cooled generator stator structure and method for... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Gas cooled generator stator structure and method for..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Gas cooled generator stator structure and method for... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2471008