Patent Application
20150207365
The invention relates generally to electric power generation systems, and, more particularly, to a superconducting bulb hydro machine used for generating electric power.
A direct drive generator driven by a plurality of blades of a hydro turbine is efficient and has minimal losses due to transmission of torque from the plurality of turbine blades to the generator. However, conventional direct drive generators typically have low torque density and are too heavy for the hydro turbine. Use of indirect drive generators, which usually include a gearbox and a shaft, results in a compact high speed generator. However, such gear boxes tend to be unreliable and not suitable in a hydro application.
There is a need for an enhanced direct drive generator for hydro turbines that is reliable, light weight, and capable of generating electrical power.
In accordance with one exemplary embodiment, a system is disclosed. The system includes a generator unit coupleable to a hydro turbine. The generator unit includes a casing having a first stationary support coupleable to a base disposed within water and a superconducting generator disposed within the casing. The superconducting generator includes an annular armature and an annular field winding including a plurality of superconducting magnets disposed coaxial with the annular armature and separated by a gap. One of the annular armature and the annular field winding is rotatable by the hydro turbine and other of the annular armature and the annular field winding is stationary.
In accordance with another exemplary embodiment, a method for generating electric power is disclosed. The method involves generating a magnetic field in a superconducting generator. The superconducting generator is disposed within a casing having a first stationary support coupleable to a base disposed within water. The method further involves generating electric current by rotating one of an annular armature and an annular field winding of the superconducting generator via a hydro turbine. The method further involves transmitting the generated electric current to a power converter.
These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:
Embodiments of the present invention disclose a superconducting bulb hydro machine and a method of generating electric power via the superconducting bulb hydro machine. The superconducting bulb hydro machine includes a generator unit coupled to a hydro turbine. The generator unit includes a superconducting generator disposed within a casing. The casing has a first stationary support coupleable to a base disposed within water. The superconducting generator includes an annular field winding having a plurality of superconducting magnets disposed coaxial with an annular armature and separated by a gap. One of the annular armature and the annular field winding is rotatable by the hydro turbine and other of the annular armature and the annular field winding is stationary.
Typical hydro power systems includes two cost components i.e. cost associated with civil construction of the hydropower system and cost related to electro-mechanical equipment in the hydropower system. The electro-mechanical equipment includes turbines, generators, transformers, cabling and associated control systems. In relatively smaller hydropower systems, the electromechanical equipment constitutes a larger proportion of the overall size and cost. The exemplary system 10 overcomes the drawbacks associated with the conventional hydro power systems.
The exemplary system 10 used to generate electrical power, is employed in run-of-the-river hydro and tidal schemes, where water heads are considered to be relatively lower, for example in a range of 10 to 12 meters. Flowing water 24 turns the hydro turbine 14 which then drives the superconducting generator 18 to produce electric power. Conventional direct drive machines are usually very large in diameter (for example, up to 8 meters) and very heavy (for example, 160 tons). Substantial foundations are required to support such large conventional machines. The typical electrical efficiencies of such conventional machines are also relatively low. Replacing the conventional generator with the exemplary generator unit 12 results in a light weight system having a relatively higher efficiency.
The armature 24 further includes a cylindrical yoke 32 that support the conductive windings 28. An outer surface of the cylindrical yoke 32 is fixed to a cylindrical housing 34. The cylindrical housing 34 rotates along with the armature 24. The cylindrical housing 34 is fitted to a circular disc 36 having a central circular aperture mounted to an annular bracket 38. The annular bracket 38 is coupled to a hub of the hydro turbine. The circular disc 36 additionally includes openings 40 for reducing weight.
The annular bracket 38 is mounted on an end of a rotatable cylindrical support tube 42 disposed radially inward from the conductive windings 28. Reinforcement gussets 43 are disposed between the circular disk 36 and the support tube 42. A reinforcing ring 44 is coupled to an inner corner between the bracket 38 and the support tube 42. A slip ring assembly 46 is provided on an outer surface of the support tube 42 and rotatable with the support tube 42. The slip ring assembly 46 is further electrically coupled to the conductive windings 28.
The support tube 42 is rotatably supported on a stationary base tube 48 via a pair of annular bearings 50. The stationary base tube 48 is attached to a mount 52. The mount 52 is attached to a bracket 54 via a ring bracket 56. The brackets 54, 56 may be secured together via bolts.
A disc brake 58 is coupled to an annular lip 60 provided at an end of the housing 34. The base tube 48 supports a support disc 64 (also referred to as a second stationary support) used for mounting the super-conducting field winding 26. The support disc 64 includes one or more holes 66 for reducing weight. A plurality of reinforcement gussets 62 extend from the base tube 48 to the support disc 64. The support disc 64 is coupled to one end of a cryostat housing 68 containing a plurality of superconducting coils of the super-conducting field winding 26. The housing 68 and a plurality of cooling components form a cryostat.
The housing 68 includes a plurality of insulated conduits 70 for receiving a cryogenic liquid, for example liquid helium, from a two-stage re-condenser 72. The cryogenic liquid is fed around a plurality of superconducting magnets of the super-conducting field winding 26 so as to cool the superconducting magnets to achieve a superconducting condition. Cryogen vapor generated after cooling is fed through the conduits 70 to the re-condenser 72, where the cryogen vapor is again cooled, liquefied and then returned via the conduits 70 to the superconducting magnets.
In the illustrated embodiment, another re-condenser 74 may be optionally provided provides a cooling liquid, for example liquid nitrogen, neon or nitrogen, to an inner thermal shield 76 of the housing 68. The cooling liquid is used to cool the thermal shield 76 to a temperature in a range of 30 Kelvin to 80 Kelvin. Cooling the thermal shield assists in cooling the super-conducting field winding 26 by reducing the thermal radiation adsorbed by the helium. The re-condenser 74 receives the vaporized liquid from the thermal shield 76, liquefies the vapor, and then again feeds the cooling liquid to the thermal shield 76 via a plurality of insulated conduits 78. The re-condenser 74 is mounted at a location higher than the housing 68. In another embodiment, instead of the re-condenser 74, the re-condenser 72 has a first cooling stage for cooling the thermal shield 76. In one example, warm helium vapor fed from the superconducting coils to the re-condenser 72, may be redirected to cool the thermal shield 76.
Torque is applied by the hydro turbine to rotate the armature 24 around the super-conducting field winding 26. Torque is applied from the armature 24 to the super-conducting field winding 26 due to electromagnetic force coupling. The torque applied to the super-conducting field winding 26, is transmitted by the housing 68 to the support disc 64 and the mount 52.
In another embodiment, the annular armature 24 is stationary and the field winding 26 is rotatable. In such an embodiment, a rotatable helium coupling 79 may be optionally provided in the conduit 70. Further, in such an embodiment, a rotatable helium coupling 81 may be optionally provided in the insulated conduit 78.
One end of a torque tube 90 is supported by the flange 86 against an inner wall of the thermal shield 76. The torque tube 90 is used to thermally insulate and suspend the annular casing 88 from the thermal shield 76. Further, the torque tube 90 transmits torque from the superconducting coils/magnets 80 to the torque tube 82.
In accordance with the embodiments discussed herein, use of the exemplary superconducting generator results in a smaller, lighter superconducting bulb hydro machine for a hydro or tidal scheme. Use of the exemplary superconducting generator also improves the efficiency of the superconducting bulb hydro machine.
The efficiency is enhanced in the superconducting generator because there is reduced electric dissipation. The efficiency is further enhanced in the superconducting generator under partial load conditions, due to features such as air gap winding, higher magnetic flux, higher density super-conducting field windings. The exemplary superconducting generator has reduced size and weight, which facilitates retrofitting to an existing hydropower station facility.
A curve 114 is representative of variation of machine weight of an exemplary synchronous low temperature superconducting generator operated at a speed of 100 rpm, for example, with respect to machine rating employed for a hydro application in accordance with an exemplary embodiment of the present invention. A curve 116 is representative of variation of machine weight of an exemplary synchronous low temperature superconducting generator operated at a speed of 200 rpm, for example, with respect to machine rating employed for a hydro application in accordance with an exemplary embodiment of the present invention.
A curve 126 is representative of variation of torque density of an exemplary synchronous low temperature superconducting generator operated at a speed of 100 rpm, for example, with respect to machine rating employed for a hydro application in accordance with an exemplary embodiment of the present invention. A curve 116 is representative of variation of torque density of an exemplary synchronous low temperature superconducting generator operated at a speed of 200 rpm, for example, with respect to machine rating employed for a hydro application in accordance with an exemplary embodiment of the present invention.
In accordance with the embodiments of the present invention, an exemplary superconducting generator has higher torque density and relatively light weight. The superconducting generator is directly driven by blades of the hydro turbine. The exemplary superconducting bulb hydro machine may also be applicable for marine propulsion systems applied to marine ships, oceanographic vessels, cable layers, or the like due to advantages associated with fuel savings, reduced size, reduced noise, and cost.
While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.
