Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
1999-04-07
2002-04-09
Tamai, Karl (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
Reexamination Certificate
active
06369476
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to high temperature superconductor bearings that can produce strong levitation forces. This kind of bearings can be utilized to support rotating machinery with no mechanical contact, including flywheel energy storage systems which can convert electrical energy into kinetic energy of a rotating member and re-convert the kinetic energy into electrical energy.
2. Description of the Background Art
Bearings are an integral part for all rotating devices. In order to reduce the energy loss caused by the friction of the rotating members of the devices, ball bearings or journal bearings with fluid are used. In this case, since a force is exerted owing to the mechanical contact, there is a limitation in reducing the friction.
Therefore, non-contact bearings have been introduced which use permanent magnets and electromagnets. In these bearings, a rotating member is levitated by an attractive or repulsive force produced by the magnet or the electromagnet for thereby implementing a non-contact rotation. In this case, an active control is used in order to stabilize the axle. This technique requires an expensive circuit and control devices, and the energy is continuously consumed by the system during the use of the bearings.
Recently, high temperature superconductors (HTS) which become perfectly diamagnetic under certain conditions, i.e. which exclude magnetic field from it, have been discovered. Using these materials, non-contact bearings which do not require an active control have been disclosed taking advantage of the property that once the magnetic field has penetrated the material, it is retained and pinned inside the material.
FIG. 1
illustrates an example of the magnetic flux pinning which is achieved using a permanent magnet
11
and a high temperature superconductor
12
.
As the magnetic field generated by the permanent magnet
11
is pinned inside the high temperature superconductor
12
, the magnet
11
is held close to the HTS with an elastic force below the critical temperature where superconductivity takes place. Since the magnet
11
does not receive a kinetic resistance in the direction in which there is no variation of the magnetic flux density, it is possible to make a rotation with no mechanical friction.
FIGS. 2A through 2C
illustrate the conventional thrust bearing.
FIG. 2A
shows a bottom view and a cross-sectional view illustrating a plurality of permanent magnets
21
. In this construction, the problem that the rotor magnet can not be made of single permanent magnet is overcome. In the rotor
22
, a plurality of permanent magnets
21
made of similar magnets having a predetermined characteristic are installed at a predetermined interval.
FIG. 2B
illustrates the magnetic flux density distribution by the rotor
22
including the permanent magnet
21
. As seen in the magnetic flux density curve
23
, a nonuniform magnetic flux density is formed in the rotational direction. Even if a plurality of circular-arc-shaped rotors tied together are used instead of the cylindrical magnets, the nonuniformity of the magnetic flux density does exist due to defects in the material and due to demagnetization, thereby causing rotational losses.
FIG. 2C
is a perspective view illustrating how the rotor
22
including a plurality of magnets
21
are held above the high temperature superconductor
12
.
FIG. 3
is a view illustrating a high temperature superconductor journal bearing using a permanent magnet according to the prior art. As shown in
FIG. 4
, the rotor
32
may be formed of a plurality of cylindrical magnets
31
or a plurality of ring shaped magnets
35
and is installed in a tubular high temperature superconductor
33
.
FIGS. 4A and 4B
illustrate the configuration of the rotors which may be adapted for the conventional high temperature superconductor journal bearing.
FIG. 4A
illustrates a magnet arrangement in which magnetic poles of the cylindrical magnets
31
contact opposite poles of the magnets.
FIG. 4B
is a view illustrating the magnet arrangement in which the same poles of the ring shaped magnet
35
contact each other around the rotor shaft
34
. The rotor shaft
34
is made of a non-magnetic material or a diamagnetic material.
As shown in
FIG. 4B
, in the construction in which the like poles face each other, the magnetic flux diverge radially outward between the poles of the magnets so that it is possible to obtain a strong force compared to the construction in which the opposite poles contact as shown in
FIG. 4A. A
high permeability material such as &mgr;-metal or a ferromagnetic material is preferred to lower the magnetic reluctance.
In the conventional construction, the journal bearing rotor is constructed by arranging magnets like (N-S)/(N-S)/(N-S)/(N-S) as shown in FIG.
4
A. In this case, however, the magnetic flux emerging from both ends of the rotor magnets only contribute to the magnetic force and it is impossible to effectively use the high temperature superconductor. Therefore, the ring shaped magnets
35
are stacked in opposing polarity, namely, in the configuration of (N-S)/(S-N)/(N-S)/(S-N) as shown in
FIG. 4B
, and the rotor shaft
34
is inserted into the hole.
In the case of the disc shaped thrust bearing as shown in
FIG. 2C
, the high temperature superconductor is inserted into the liquid nitrogen container, and the magnets are attached to the bottom of the rotor in such a manner that the pole surfaces of the magnets comprise the bottom surface of the rotor. Therefore, a force is generated between the rotor and the high temperature superconductor by the thusly generated magnetic field. In addition, in a thrust bearing, a superconductor magnet is placed lower as a stator instead of the high temperature superconductor, and then a high temperature superconductor is attached to the bottom of the rotor for thereby supporting the weight of the rotor. In this case, a predetermined shaped coil of superconductor film forms the superconductor magnet for thereby providing a straw hat-shaped magnetic density distribution, and then the high temperature superconductor of the rotor is inserted at the concave part.
In order to generate a strong magnetic force, a thrust bearing requires a strong magnet of large size. However, since it is difficult to fabricate a large size magnet having a uniform magnetization, a plurality of magnets are attached to the rotating plate. In this case, even when the magnets having the similar characteristics are attached, the nonuniformity of the magnetic flux density still exists due to defects in the material or due to the demagnetization, thereby causing a rotational loss.
In the prior art using a superconductor magnet for the stator, the magnetic flux density is uniformly formed in the rotational direction using the superconductor magnet, and there is an advantage in that it is possible to generate a very strong magnetic field compared to the regular magnets. However, in this case, diamagnetism in which the magnetic field is excluded from the superconductor is used, and it provides a stability only with the weight. When an asymmetrical magnetic flux pinning occurs in the high temperature superconductor attached to the rotor in the rotational direction, vibrational and rotational losses may occur.
In the case of the journal bearings, since a shaft is inserted at the center of the rotor magnet arrangement, the total volume of the magnets is reduced. When a strong force such as the weight, etc. is applied to the rotating member, the levitation force which is needed for the non-contact rotation of the rotating member is provided only based on the magnetic flux pinning of the high temperature superconductor and it is relatively weak.
In the case of the prior art thrust bearings, the rotational loss is large due to the nonuniformity of the magnetic flux density, and in the case of the journal bearings, it is very hard to obtain a strong levitation force.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide high tem
Han Sang Chul
Hyun Ok Bae
Kim Jin Joong
Lee Jun Sung
Sung Tae Hyun
Dykema Gossett PLLC
Korea Electric Power Corporation
Tamai Karl
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