Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
1999-06-21
2001-10-16
Waks, Joseph (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S058000
Reexamination Certificate
active
06304011
ABSTRACT:
The present invention relates to rotary electrical machines such as electrical generators and electric motors and to a method of cooling the components of such machines.
UK Patent Specification GB-A-2 222 031 describes an axial field generator capable of operation at very high speeds. However certain features of this known design have been perceived to have some drawbacks. In response to this, our UK Patent Specification No. GB-A-2 261 327 describes and claims certain improvements in rotary electrical machines. Both of these known designs employ rotors having substantially equi-angularly spaced magnets retained by a retention ring and stators provided with respective electrical windings.
The generator described in GB-A-2 222 031 employs air cooling for the stators. The air is directed by means of radial channels entering at the rim. The channels conduct air towards the centre of the stators and back again to the rim. As a result, on the return path the air is already hot and so performs little cooling. At the same time, the multiplicity of channels detracts from the strength of the stators.
On the other hand, GB-A-2 261 327 discloses a stator comprising at least one radial channel for ducting of cooling air. The channel has an entrance at or substantially near the rim of the stator and an exit at or substantially near the centre of the stator. Also, spaces are provided between each stator and an adjacent rotor. In use, air is drawn into the stator, and is conducted through the channel from the rim to the centre. At the same time, air is conducted through the channels formed by the stator-rotor spaces, from the rim to the centre. The machine comprises a central drive shaft, having a hollow core which communicates with the radial channel and the stator-rotor spaces. The air enters the hollow core of the drive shaft after conduction through the stator and is conducted away from the stators.
The cooling arrangement described in GB-A-2 261 327 provides adequate cooling in electrical machines for many applications. However, the power or speed output of such machines is limited because the air in the stator reaches a maximum temperature above which the machine overheats.
We have now devised an arrangement which overcomes the disadvantage of the above prior art arrangements. In accordance with a first aspect of the present invention, there is provided a rotary electrical machine comprising at least one generally disc-shaped stator stage and at least one generally disc-shaped rotor stage, the electrical machine further comprising cooling means for cooling the stator by causing a liquid to pass thereover.
The liquid cooling is preferably but not necessarily supplemented by a gas cooling arrangement.
By supplementing or replacing gas cooling of a disc-type rotary electrical machine of a particular size with liquid cooling, it is possible to achieve a power or speed output which is substantially greater than the available output from known machines of the same size. However, the gas cooling may be replaced entirely if the machine is required to operate in vacuum conditions, so as to be suitable for operation as a flywheel motor-generator.
The stator stage is preferably provided with at least two stator windings defining a passage therebetween. The cooling means may then be arranged to cause cooling liquid to pass through the passage. The stator stage may be provided with three or more stator windings, a passage being provided between each. The cooling means may then be arranged to cause cooling liquid to pass through each passage.
The cooling means may comprise a pump. Furthermore, a fluid cooler may be provided which receives liquid after it has passed through the at least one radial channel, and cools the liquid. The cooled liquid can then be re-used.
The electrical machine according to the present invention preferably comprises a channel disposed in the or each passage between the stator windings for conducting the cooling liquid. The channel may comprise a separate entity, for example a pipe, or it may be formed integrally with one or both of the walls of the respective passage, for example, by means of moulding. In either case, the channel is preferably in substantially in the same plane as the stator. In one embodiment of the present invention, the channel may be coiled to form a generally disc shaped arrangement
In another arrangement, the or each channel is arranged to conduct cooling liquid radially within the passage.
In either of the embodiments described above, if a plurality of passages are provided in the or each stator stage, then the outlet of a channel disposed in one passage is preferably coupled with the inlet of the channel disposed in an adjacent passage. Thus, the cooling liquid is circulated around each channel, before exiting the stator stage through the outlet of the last channel.
In a third embodiment, cooling liquid is conducted from a first position at the periphery of the passage to a second position which is substantially diametrically opposite the first position, preferably by means of a plurality of parallel channels. In this case, the channel or channels disposed in each passage preferably have a common inlet and a common outlet.
The channel preferably comprises a non-conducting or poorly electrically conducting material, so as to avoid eddy currents.
The cooling liquid may be, for example, water or oil.
The at least one rotor stage is preferably adjacent the at least one stator stage, and a space is preferably provided between them. Cooling means may provided which causes cooling gas, if required, to pass through the stator-rotor space. The electrical machine of the present invention preferably comprises at least two rotor stages, having a stator stage disposed therebetween, the rotor stages being connected together by means of a coupling arrangement. The coupling arrangement may comprise a respective set of teeth provided on or formed integrally with each rotor stage. In use, the rotor stages are coupled together by inserting a set of teeth on one of the rotor stages into the spaces between the teeth of the other rotor stage. Each tooth and each respective space is generally V-shaped, the apex each tooth and each space being flattened out. In use, when the rotor stages are connected together, the apex of the tooth does not contact the apex of the respective space, such that an air gap is provided.
Alternatively, coupling of the discs may be achieved using a spigot fit between the discs. Communication of the air through such a coupling is achieved by, drillings or slots which are substantially radial.
In a preferred embodiment, the rotary electrical machine of the present invention comprises a generally central hollow core which communicates with the stator-rotor space. In this case, cooling means may be provided which causes cooling gas to pass through the hollow core before entering the stator-rotor space. The cooling means in this case may be arranged to provide pressurised cooling air to the hollows core to blow the cooling air through the hollow core and into the stator-rotor space. Alternatively, the cooling means mast be arranged to subject the stator-rotor space to a reduced pressure to suck the cooling air through the stator-rotor space from the hollow core.
The hollow core is formed by means of a generally cylindrical housing which is mounted around a generally central drive shaft. The housing may be provided with one gas inlet, but is preferably provided with at least two gas inlets at opposite ends thereof.
More preferably, a plurality of equi-angularly spaced gas inlets are provided, at each end of the cylindrical housing defining the hollow core.
The cooling gas, if required, may be, for example, air, preferably at close to atmospheric pressure or partial vacuum to reduce windage losses. Alternatively, helium may be used, which reduces density and therefore windage of the machine.
In accordance with a second aspect of the present invention there is provided a rotary electrical machine comprising a stator stage, at least one rotor stage, a s
Etemad Mohammad Reza
Fenocchi Arnold
Hall Justin Arthur
Pullen Keith Robert
Kaplan & Gilman, L.L.P.
The Turbo Genset Company Limited
Waks Joseph
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