Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2001-07-20
2004-03-16
Le, Dang (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S071000, C310S055000
Reexamination Certificate
active
06707179
ABSTRACT:
FIELD OF THE INVENTION
This invention is related to seals for preventing fluid leakage and, more particularly, to seals used in power generators.
BACKGROUND OF THE INVENTION
Within the power generation industry, large-scale power generators convert mechanical energy, typically the energy output of a turbine, into electrical energy. The basic components of such power generators are a frame-supported stator core that provides a high permeability path for magnetism and a rotor assembly positioned to rotate continuously within the stator core so as to induce electrical current through rotor-borne conductors moving through magnetic fields set up within the stator. The resulting current is carried by high-current conductors through and out from a housing surrounding the power generator, to flex connectors that provide the current to a plant bus for power distribution to consumers, commercial establishments, and other users of electrical power.
According to the well-understood physics of electrical conduction through a conductor, current arises as a result of the flow of “free” electrons that move under the influence of an electric field through the conductor. In free space the electrons accelerate and continually increase their velocity (and energy), but within the crystalline material of a conductor the electrons are impeded by their continual collisions with thermally excited atoms arranged in a crystalline lattice structure in the conductor until a constant average “drift” velocity is attained. As a result of these collisions, heat is generated raising the temperature of the conductor and the surrounding environment. This effect can be especially pronounced within large scale power systems where large currents are generated and carried by the high-current conductors described above.
To deal with these temperature effects, various cooling systems are employed within large-scale power generators. For example, channels within the frame housing, the stator core and rotor assembly channel can be added to the power generator system to provide an avenue for a cooling fluid to flow into and out of the housing to cool the components therein. Frequently, hydrogen gas (H
2
) is used as a cooling fluid. These cooling devices, however, pose collateral challenges. In order to be effective in cooling the components of the power generator, the cooling fluid (i.e., hydrogen gas or other fluid) must be appropriately channeled or otherwise directed to the components. When flowing in such a channel, the cooling fluid must be maintained therein lest it escape into the air surrounding the frame thereby losing its cooling effect while inadvertently contaminating the surrounding environment.
In order to circulate the cooling fluid throughout the power generator, large blowers are usually employed to provide pressure differentials that disperse the cooling fluid within the frame housing the stator core and rotor assembly. The pressure so created can be quite high. Thus, to maintain the cooling fluid within the appropriate channel within the frame housing the stator core and rotor assembly, the channel must be sealed. The seal relied on to seal a channel must be able to withstand considerable pressure. In the typical power generation context, a sealing device intended to maintain the cooling fluid within the fluid channel must effectively accommodate pressures of as much as 75 pounds per square inch gauge (PSIG).
Of particular importance are the seals employed where the high-current conductors extend through the housing. For cooling purposes, the high-current conductor usually has a hollow channel or bore extending axially within the conductor and through which a cooling fluid such as hydrogen gas (H
2
) is pumped. The cooling fluid flows under pressure through the bore and exits the bore through vent holes formed through the conductor, flowing into a fluid channel extending along the conductor. Alternatively, a second bore can be disposed inside the channel or bore of the high-current conductor. Cooling fluid is then pumped into the inner bore where it flows out through vent holes and circulates within the channel formed by the high-current conductor.
Various sealing mechanisms have been used with varying degrees of success in attempting to effectively and efficiently seal cooling fluid within designated fluid channels in a power generator. U.S. Pat. No. 2,950,403 by Kilner et al., titled
Electrical Turbo Generators,
for example, describes the use of gas-tight shroud rings to contain gas surrounding the connection between a collector lead and collector ring. U.S. Pat. No. 4,682,064 by Crounse et al. titled
Coolant Gas Flow Separator Baffle For A Dynamoelectric Machine
describes a flexible flange that is urged into tighter abutment with the stator as surrounding gas pressure increases. U.S. Pat. No. 5,866,960 by Meier et al., titled
Gas
-
Cooled Electrical Machine
describes sealing cooling channels using a sealing cap and screw connection through which a tube extends. Finally, in the context of a non-cooling use, U.S. Pat. No. 6,121,708 by Muller titled Slot Sealing Arrangement describes sealing the winding slot in a stator core from an air gap using convex-surfaced wedges.
In other contexts, though, use of a sliding seal has been proposed. For example, U.S. Pat. No. 4,076,262 by Deventer titled Sliding Seal describes generally a seal comprising a rigid base (e.g., a metal or hard resin) that connects to an object and a flexible protrusion from the base that pliably bends with a foreign object as the foreign object contacts the outer portion of the protrusion in a moving fashion (See U.S. Pat. No. 4,076,262 FIGS.
2
and
6
). Thus, as illustrated therein, the seal does not so much slide relative to the foreign object as much as it bends therewith. U.S. Pat. No. 4,714,257 by Heinrich et al. titled Annular Sliding Body For A Sliding Seal And Process For Use Thereof describes a dual-piece device having a sliding ring and counter ring, wherein the former remains stationary while the later rotates annularly by sliding against the former.
These and other conventional seals, both in the context of power generation and in other situations, generally do not permit the seal to slide or otherwise move in response to thermal expansion, fluid pressure, or vibratory movements that occur during operation of the power generator. Conventional seal designs, at best, allow for thermal expansion on the high-pressure side of the seal during thermal cycling of the power generator. This is the case with the wedge-ring seal conventionally employed for sealing cooling fluid in a fluid channel surrounding a high-current conductor in a power generator.
FIGS. 1 and 2
illustrate a conventional wedge-ring seal
20
used to seal hydrogen gas or other cooling fluid within a fluid channel
22
surrounding a high-current conductor
24
of a power generator.
The conventional wedge-ring seal
20
poses several distinct problems. Among these is the inability of the wedge-ring seal
20
to smoothly slide relative to a sleeve
26
or other fluid channel forming member, thereby resulting in abrading degradation of a surface
21
of the wedge-ring seal
20
when the wedge-ring seal
20
movingly contact a surface
27
of the fluid channel forming member. The wedge-ring seal
20
is typically formed of a conductive material such as copper and is brazed to the high-current conductor
24
. The wedge-ring seal
20
is usually “wedged” against the channel-forming sleeve
26
, which is normally formed of fiberglass. The fiberglass sleeve
26
typically exhibits an abrading property, usually resulting from the machining of the fiberglass to form the dimensions of the sleeve
26
to accommodate the wedge-ring seal
20
. Machining removes any resin layer that would otherwise provide smooth contact between the fiberglass surface
27
of the sleeve
26
and the surface
21
of the wedge-ring seal
20
.
Instead of a smooth, resined layer on the surface
27
of the fiberglass sleeve
26
, the surface
27
has minute shards of glass particles extend
Guttromson Ross
Ryan Daniel J.
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