Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2003-04-09
2004-08-17
Mullins, Burton (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S064000, C505S166000
Reexamination Certificate
active
06777841
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a device having at least one rotor which rotates or can rotate about a rotation axis, and having at least one magnetic bearing in which the rotor is borne or can be borne in a contactless manner.
U.S. Pat. No. 5,482,919 A discloses a device which has a rotor which can rotate about a rotation axis and has at least one superconducting winding (field coil) for an electric motor, and has a cryogenic cooler for cooling the superconducting winding. The superconducting winding may be formed from a known, metallic superconductor material (low-temperature superconductor) with a low critical temperature of T
c
, below 35 K, such as a niobium-tin alloy or a ceramic metal-oxide superconductor material (high-temperature superconductor) with a high critical temperature T
c
above 35 K, such as bismuth strontium calcium copper oxide, an yttrium barium copper oxide or a mercury or thallium compound. The cryogenic cooler makes use of rapid expansion of a working fluid (which is compressed by a compressor) such as helium, neon, nitrogen, hydrogen or oxygen for cooling in thermodynamic cycles (processes) such as a Gifford-McMahon cycle, a Stirling cycle or a pulse tube cycle. The superconducting winding is thermally conductively connected to a cold head, which rotates with the rotor, of the cryogenic cooler via two or more annular supporting elements composed of a material with a high thermal conductivity coefficient, and which are connected via heat pipes or thermally conductive rods. In this way, heat is dissipated from the superconducting winding by thermal conduction through a solid body to the cold head. There is no need for a liquid coolant such as liquid helium or liquid nitrogen in this known cooling system, so that there is also no influence on the rotation of the rotor from a cold liquid. The compressor of the cryogenic cooler can rotate with the rotor or may be in a fixed position with respect to the rotor, and may be connected to the cold head via a rotating coupling. U.S. Pat. No. 5,482,919 A states nothing more with regard to the bearing of the rotor.
Magnetic bearings are generally known for bearings for rotors, and allow the rotors to be borne in a contactless bearing, which is thus free of wear. Both active magnetic bearings with electromagnets and position control as well as passive magnetic bearings with automatic position stabilization are known.
DE 44 36 831 C2 discloses a passive magnetic bearing for bearing a rotor shaft with respect to a stator, which has a first bearing part which is connected to the rotor shaft, and a second bearing part which is arranged on the stator and surrounds the first bearing part. One of the two bearing parts has a high-temperature superconductor. The other bearing part has an arrangement of permanent-magnet elements arranged alongside one another and composed of a neodymium (Nd), Iron (Fe) boron (B) alloy or of a samarium (Sm) cobalt (Co) alloy. Adjacent permanent-magnet elements are magnetized with opposite polarity to one another. When a position change occurs, the permanent-magnet elements induce shielding currents in the superconductor, as a result of field changes. The resultant forces may be repulsive or attractive, but are always directed such that they counteract the deflection from the nominal position. In contrast to known active magnetic bearings, an inherently stable bearing can be achieved in this case, and there is no need for a complex control system that is subject to defects. The intermediate spaces between in each case two permanent-magnet elements are filled with ferromagnetic material in order to concentrate the magnetic flux, which emerges from the permanent-magnet elements, on the side facing the other bearing part. This results in a high level of bearing stiffness (stability, robustness). The permanent-magnet elements together with the ferromagnetic intermediate elements may be arranged axially with respect to the rotor shaft axis one behind the other in the form of thin rings, or else may be axially elongated and arranged one behind the other in the circumferential direction.
In a refinement of this known magnetic bearing, the permanent magnets are provided in a hollow-cylindrical arrangement on the inner bearing part, and the superconductor is arranged as a hollow-cylindrical structure on the inside of a hollow-cylindrical supporting body for the outer bearing part. Cooling channels are formed in the supporting body for passing liquid nitrogen through in order to cool the superconductor.
In another refinement according to DE 44 36 831 C2, the high-temperature superconductor on the inner bearing part is arranged on the rotor shaft, with a coolant channel being provided for the liquid nitrogen in the rotor shaft, in order to cool the high-temperature superconductor. This embodiment with a cold rotor body is proposed as part of a generator or of a motor with a cryogenic normally conductive or superconducting winding.
The document U.S. Pat. No. 5,214,981 A discloses a device for storing energy. This device has a rotating flywheel which has permanent magnets (which interact with stationary electromagnets) on its circumference for power transmission. The flywheel is borne in each case one magnetic bearing on opposite sides via two rotor shafts. In one embodiment (FIG.
1
), one or more permanent magnets are provided in a cylindrical arrangement at each of the ends of the two rotor shafts. These ends project as first bearing parts into in each case one superconductor, in the form of a pot, as the second bearing part for the respective magnetic bearing. For cooling, the superconductors are each arranged in a cold bath of liquid nitrogen. In another embodiment (FIG.
3
), each rotor shaft has a recess as the first magnetic bearing part on its end face facing away from the flywheel, with this recess being clad with a superconductor. The superconductor is cooled exclusively by the thermal radiation from the superconductor to the vacuum vessel, which is kept in a liquid bath filled with liquid nitrogen. Furthermore, the magnetic bearings have cylindrical second bearing parts, whose ends project into the recesses in the rotor shafts and have one or more permanent magnets in a cylindrical arrangement. The flywheel is enclosed together with the two magnetic bearings in a vacuum vessel which is evacuated to a pressure of less than 10
−4
Torr, in order to avoid friction of the rotating parts and the energy losses associated with such friction. The bearing gaps of the two magnetic bearings form continuous connections between the adjacent evacuated areas of the vacuum vessel.
JP 04370417 A and the associated abstract from Patent Abstracts of Japan disclose a further device for storing energy by a flywheel which is borne in two magnetic bearings and is arranged together with the magnetic bearings in a common evacuated vacuum chamber. Each magnetic bearing has a central permanent-magnet ring on the flywheel and two superconductor rings at an axial distance from it, which are arranged on stationary supporting disks, through which liquid coolant flows.
Finally, DE 197 10 501 A1 discloses an electrical machine having a stator with a polyphase winding for producing a rotating magnetic field, and with a rotor which rotates with the rotating field. The stator has a magnetic return path yoke, which forms a housing for the rotor. The rotor has a shaft which is passed through an opening, which is not sealed, in the housing and magnetic return path yoke. The rotor is composed entirely, or at least on its outside, of a high-temperature superconductor. Magnetic bearings for contactless bearing of the rotor are formed by the superconductor and by annular permanent magnets which are provided at two points. In order to cool the superconductor on the rotor, the entire machine is designed to have a small physical size and is operated completely in a cryogenic bath formed from liquid nitrogen.
Owing to the contactless bearing, the known magnetic bearings always have a continuous bearing gap, and g
Mullins Burton
Siemens Aktiengesellschaft
Staas & Halsey , LLP
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