Abstract:
The object of the invention is to provide a generator easy to assemble even if there is an obstacle such as a turbine in the axial direction of the rotor of the generator. A generator comprising; a rotor having a permanent magnet placed therein and supported to be rotatable, and a stator having a field coil wound thereon, characterized in that; the rotor is provided with a seating made of a magnetic material for supporting the permanent magnet and a pole shoe made of a magnetic material placed in the outward radial direction of the permanent magnet.

Description:
CLAIM OF PRIORITY  
       [0001]     The present application claims priority from Japanese application serial No. 2005-087482, filed on Mar. 25, 2005, the contents of which is hereby incorporated by references into this application.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     This invention relates to a generator employing permanent magnets for its excitation.  
         [0004]     2. Description of Related Art  
         [0005]     An example of a conventional generator having field permanent magnets inserted into slots is described in the official gazette, Japanese Application Patent Laid-Open Publication No. Hei 05-146103.  
         [0006]     [Patent Document 1] Japanese Application Patent Laid-Open Publication No. Hei 05-146103  
       SUMMARY OF THE INVENTION  
       [0007]     With such a generator employing permanent magnets for its magnetic field as described in Patent Document 1 above, it is inevitable that the permanent magnets need to be inserted into its rotor of the generator in the axial direction. In this case, there is an obstacle such as a turbine for the electric generating system in the axial direction of the rotor of the generator, the problem arises that it is difficult to insert permanent magnets to the generator.  
         [0008]     The object of the invention is to provide a generator easy to assemble even if there is an obstacle such as a turbine in the axial direction of the rotor of the generator.  
         [0009]     A feature of this invention is a generator which is provide with a rotor having a permanent magnet placed between a seating and a pole shoe.  
         [0010]     Another feature of this invention is a generator which is provide with the above-mentioned permanent magnet of which width is greater than that of the seating.  
         [0011]     Still another feature of this invention is a generator which is provide with a rotor having permanent magnets and being supported to be rotatable, and a stator having field windings wound on it, wherein the rotor is provided with seatings for supporting the permanent magnets, and the radius of the pole shoe arc part is smaller than that of the rotor.  
         [0012]     Yet another feature of this invention is a generator which is provide with a rotor having permanent magnets and being supportedto be rotatable, and a stator having field windings wound on it, wherein the stator is so constructed in portions that the number of stator portions equals that of the parallel circuits in the field windings wound on the stator.  
         [0013]     Further features of this invention will be described in the Preferable Embodiments of the Invention section.  
         [0014]     According to the present invention, a permanent magnet is placed between a seating and a pole shoe, thus it is possible to provide a generator and/or an electric generating system which is easily assembled. 
     
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0015]      FIG. 1  is a sectional view in the circumferential direction of a part of the generator in the second embodiment of this invention.  
         [0016]      FIG. 2  is a sectional view in the axial direction of a part of the generator in the second embodiment of this invention.  
         [0017]      FIG. 3  is a sectional view of in the circumferential direction of a part of the generator in the third embodiment of this invention.  
         [0018]      FIG. 4  is a sectional view in the circumferential direction of a part of the generator in the fourth embodiment of this invention.  
         [0019]      FIG. 5  is a sectional view in the circumferential direction of a part of the generator in the fifth embodiment of this invention.  
         [0020]      FIG. 6  is a sectional view in the axial direction of a part of the generator in the fifth embodiment of this invention.  
         [0021]      FIG. 7  is a sectional view in the circumferential direction of a part of the generator in the sixth embodiment of this invention.  
         [0022]      FIG. 8  is a graph showing the relation between Gmax/Gmin and the distortion factor in a sixth embodiment of this invention.  
         [0023]      FIG. 9  is a vertical sectional view of the stator in the seventh embodiment of this invention.  
         [0024]      FIG. 10  is a sectional view of a comparative example of a turbine generator.  
         [0025]      FIG. 11  is a diagram showing the circuit in a comparative example of a turbine generator.  
         [0026]      FIG. 12  is a sectional view of the turbine generating system in the first embodiment of this invention.  
         [0027]      FIG. 13  is a sectional view in the circumferehtial direction of a part of the generator in the first embodiment of this invention.  
         [0028]      FIG. 14  is a sectional view in the circumferential direction of a part of the generator in the eighth embodiment of this invention.  
         [0029]      FIG. 15  is a sectional view in the vertical direction of a part of the generator in the eighth embodiment of this invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0030]     In  FIG. 10 , to explain the effects of the invention, a comparative example of a turbine generator having a brushless excitation system is shown. The turbine generator has an alternating-current exciter  4  and a sub-exciter  5  both in the overhang part located at an end of its rotor shaft  1 . The sub-exciter  5  has a permanent magnet  13  in the rotor poles, and the permanent magnet  13  produces magnetic fields at right angles to armature windings  8  of the sub-exciter.  
         [0031]     On the other hand, to a rotor shaft  1 , a rotational force is applied by the turbine through a coupling  3 , thus the rotor shaft is rotated. In this way, the armature coils  8  of the sub-exciter  5  has an alternating current I a1  induced in them owing to electromagnetic induction. An auto voltage regulator  16  capable of rectification detects the voltage of the generator, changes this alternating current I a1  into a direct current I d1 , and supplies it to the field coils  18  of the alternating-current exciter  4 .  
         [0032]     The armature coils  19  of the alternating-current exciter  4  are placed on the rotor  20  of the alternating-current exciter  4 , thus the rotation of the rotor shaft  1  induces an alternating current I a2  in the armature coils  19 . The alternating current I a2  is converted into a direct current through a rotating rectifier  17 , and is supplied to turbine generator field coils  22 . The rotation of the rotor shaft  1  induces an alternating current in turbine generator armature coils  21 , making it possible to supply electric power outwards.  
         [0033]     In  FIG. 11 , an example of a circuit diagram showing a comparative example of a brushless excitation system. The magnitude of the alternating voltage arising from a sub-exciter  1201  is regulated by an auto voltage regulator  1203 . This alternating voltage is converted by a rectifier into a direct voltage, resulting in a direct current flow on the output side of the sub-exciter  1201 . This direct current gives off direct current magnetic fields, the electromagnetic induction of which produces an alternating current in an alternating-current exciter  1202  of a rotating part  1205 . This alternating current is converted by the rectifier of the rotating part into a direct current, which is then supplied to the field coils of the rotating part.  
         [0034]     When the rotating part rotates owing to the mechanical force of the turbine, the electromagnetic induction of the magnetic field given off by the direct current made to flow in the field coils gives rise to an alternating voltage in the armature windings on the side of the turbine generator stator (not shown in the figure). In the construction shown in  FIG. 10 , the overhang part has the sub-exciter  4  and the alternating-current exciter  5 , which results in the problem of the overhang part being long.  
       Embodiment 1  
       [0035]     In the first embodiment of this invention, therefore, as shown in  FIG. 12 , using the space between a coupling  3  and a rotor shaft  1  of the generator, a sub-exciter  5  is installed. According to this embodiment, the sub-exciter installed in the overhang part in the comparative example is absent from the overhang part, thus it is possible to shorten the overhang part of the rotor shaft  1 .  
         [0036]     Here, if the rotor of the sub-exciter  5  is, as shown in Patent Document 1, so constructed that a magnet is inserted into a slot, it turns out that the magnet needs to be inserted in the direction represented by an arrow  23 , but the coupling  3  obstructs the insertion of the magnet. This is why in the embodiment, as shown in  FIG. 13 , a permanent magnet  1102  is sandwiched by a pole shoe  1109  and a seating  1104  fitting the permanent magnet  1102 . This construction allows the permanent magnet  1102  to be placed on the seating  1104  in the radial direction  31 , thus even if a presence such as a turbine in the axial direction of the rotor shaft makes it impossible to insert a permanent magnet in the axial direction, a generator for excitation can be installed.  
         [0037]     A more detailed description will be given of the construction shown in  FIG. 13 . The seating  1104  is made of a magnetic material, is placed in the inward radius direction of the permanent magnet  1102  (toward the rotor shaft), and supports the permanent magnet  1102 . The pole shoe  1109  is placed in the outward direction of the permanent magnet  1102 , and is made of a magnetic material. The numeral  1106  represents a stator, and  1107  a rotor carried so as to be rotatable. The stator  1106  has coils  1105  wound on it, and the rotor  1107  has the permanent magnet  1102  placed on it. The rotation of the rotor  1107  in the circumferential direction  1108  allows the magnetic flux produced by the permanent magnet  1102  to cross the coils  1105  and thereby a voltage to occur in the coils  1105  owing to electromagnetic induction.  
         [0038]     In this embodiment, the pole shoe  1109  and a rotor  1107  are secured together with a bolt or a binding, but it is understood that the pole shoe  1109 , the permanent magnet  1102 , and the seating  1104  and the rotor  1107  may be fixed solidly with a bolt. And in this embodiment the pole shoe  1109 , the permanent magnet  1102  and the seating  1104  are rectangular in shape radially, but it is understood that their shape may be circular or elliptic in order to raise their mechanical strength.  
         [0039]     In this embodiment, there is a big advantage that a generator can easily be assembled. However, the problem arises that, among the magnetic fluxes given off by the permanent magnet  1102 , a magnetic flux  1103  passes effectively the stator  1106 , but a magnetic flux  1204  given off by an end of the permanent magnet  1102  goes beside the permanent magnet  1102 , and without passing the stator  1106  returns to the permanent magnet  1102 , ending up being ineffective for electric generating.  
       Embodiment 2  
       [0040]     In a second embodiment, therefore, as shown in  FIGS. 1 and 2 , the width Wm in the circumferential direction of the permanent magnet  13  is greater than the width Wb in the circumferential direction of a seating  24 . According to this construction, the magnetic flux given off by an end of a permanent magnet  13  goes beside the permanent magnet  13  and enters the seating  24  by way of a path  32 , whose magnetic resistance is so great that there are hardly any fluxes going on this path, and that it is possible to reduce flux leakage. With reference to  FIGS. 1 and 2 , a more detailed description will be given of the second embodiments of this invention.  
         [0041]      FIG. 1  shows a circumferential section of a part of a gererator pole placed in a generator in this embodiment. On a rotor shaft  1  in any given circumferential position is mounted the seating  24  for placing the permanent magnet  13 . The seating  24  is formed uniformly with the rotor shaft  1  by machining or formed separately out of a magnetic material, and is located on the rotor shaft  1 . The permanent magnet  13  is covered with a cover  14  made of a non-magnetic material in order to prevent scattering. The distance Wm in the circumferential direction of the permanent magnet  13  is greater than the distance Wb in the circumferential direction of the seating  24 , thus a pole shoe  12  is farther apart so as to prevent the flux leakage from the pole shoe  12  to the seating  24 . This prevents generated voltage from reducing.  
         [0042]      FIG. 2  is a axial sectional view of a part of a generator pole placed in a generator in this embodiment. The length Wm in the axial direction of the permanent magnet  13  is greater than the length Wb in the axial direction of the seating  24 , thus the flux leakage from the pole shoe  12  to the seating  24  is prevented.  
       Embodiment 3  
       [0043]      FIG. 3  shows a third embodiment of this invention. It shows a circumferential section of a part of a pole of the sub-exciter mounted in a turbine generator according to this invention. There is placed a permanent magnet  13  between the rotor shaft  1  and a pole shoe  12 , the permanent magnet being covered with a cover  14  made of a non-magnetic material in order to prevent scattering. The cover  14  has a convex part on it, and the pole shoe  12  a concave part. Fitting these convex part and concave part into each other on placing the magnet allows the permanent magnet  13  to be held during rotation, and also allows the positioning in the circumferential direction of the permanent magnet  13  and the pole shoe  12  to be easier on assembling and disassembling them.  
         [0044]     Borh of the pole shoe  12  and the seating  24  have a concave part  25 , respectively which is not fitted on the convex part of the covering  14 , thus the disassembly of the permanent magnet  13  is made easier.  
         [0045]     Note that in the figures the convex and concave parts are represented by rectangles, but they may take shapes whose section is triangular or circular.  
       Embodiment 4  
       [0046]      FIG. 4  shows a fourth embodiment of this invention. It shows a circumferential section of a part of a pole placed in a generator in this embodiment. There is placed a permanent magnet  13  between a rotor shaft  1  and a pole shoe  12 , the permanent magnet being covered with a cover  14  made of a non-magnetic material in order to prevent scattering. In addition to the convex parts of the cover  14  and the concave parts of the pole shoe  12  shown in reference to Embodiment 3, the permanent magnet  13  has a convex part, and a seating  24  has a concave part. Fitting these convex part and concave part into each other on placing the magnet allows the permanent magnet  13  to be held during rotation, and also to be assembled and disassembled with more ease.  
         [0047]     Borh of the pole shoe  12  and the seating  24  have a concave part  25 , respectively which is not fitted on the convex part of the covering  14 , thus the disassembly of the permanent magnet  13  is made easier. To remove the pole shoe  12  from the permanent magnet  13  during maintenance, the concave part  25  has only to be picked with a nail.  
         [0048]     Note that in the figures the convex and concave parts are represented by rectangles, but they may take shapes whose section is triangular or circular.  
       Embodiment 5  
       [0049]      FIGS. 5 and 6  show a fifth embodiment of this invention.  FIG. 5  shows a circumferential section of a part of a generator pole placed in a generator in this embodiment. The pole shoe  12  has its concave parts, which in the fifth embodiment are in contact with the permanent magnet  13 , brought circumferentially to the edges, and has its overall circumferential section made convex, with the result that the length Wm in the circumferential direction of the permanent magnet  13  is greater than the length Wp in the circumferential direction of the convex part of the pole shoe  12 . This pole shoe  12  with the concave parts is fitted into convex parts formed in a cover  14  to hold the permanent magnet  13  and to have the pole shoe  12  and a seating  24  located far from each other so as to reduce the flux leakage from the pole shoe  12  to the seating  24  and to prevent the generated voltage of the generator from falling.  
         [0050]      FIG. 6  is a axial sectional view of a part of a generator pole placed in a generator in this embodiment. The pole shoe  12  has its concave parts, which are in contact with the permanent magnet  13 , brought axially to the edges and has its overall axial section made convex, with the result that the length Wm′ in the axial direction of the permanent magnet  13  is greater than the length Wp′ in the axial direction of the convex part of the pole shoe  12 . This allows the pole shoe  12  and a seating  24  to be located far from each other to reduce the flux leakage from the pole shoe  12  to the seating  24  and prevents the generated voltage of the generator from falling.  
       Embodiment 6  
       [0051]      FIG. 7  shows a sixth embodiment of this invention. It shows a circumferential section of a part of a generator pole placed in a turbine generator of this invention. The radius R 2  of the arc part of a pole shoe  12  is smaller than the radius R 1  of the rotor  1 , thus the outer edge of the rotor  1  and the inner surface of the stator  7  have their maximum gap Gmax and their minimum gap Gmin the ratio Gmax/Gmin of which is given as 1.33 or more.  
         [0052]      FIG. 8  is a graphs a result of assuming that Gmin is 10 mm and then analyzing the relation between Gmax/Gmin and the distortion factor of a voltage induced in the windings of the armature of the generator. Judging from  FIG. 8 , giving Gmax/Gmin as 1.2 or more allows the voltage distortion factor to remarkably fall, and giving Gmax/Gmin as 1.33 or more allows the voltage distortion factor to be as small as 5 percent or less.  
       Embodiment 7  
       [0053]      FIG. 9  shows a vertical sectional view of the seventh embodiment of this invention. It shows a generator in this embodiment, detailedly a single-phase, two-parallel-circuit stator. Slots  11  contain coils C 1  to C 24  wound on each tooth  10 , respectively. Series winding is applied to coils C 1  to C 12 . Coils not having a tooth in between, for example, C 2  and C 3 , are connected to each other on an overhead part. In the same way, coils C 13  to C 24  have series winding applied to them. The joints of the windings are only at the single location between C 1  and C 24  so as to facilitate the jointing of wires and the assembly and disassembly of parts.  
         [0054]     According to this embodiment, dividing the stator into two divisions and providing two parallel circuits allows the stator, while kept parted and after each set of parallel-circuit coils is wound on each parted stator, to be assembled. The effect of this embodiment can be obtained by giving the coils as concentrated windings and by giving the number of the phases multiplied by that of the parallel circuits equals to number of the stator divisions.  
         [0055]     Note that the iron core  26  of the stator  7  has core parts  27  each of which is located between two slots not having a tooth  10  in between and that two of them are divided along lines a-a′ and b-b′. Designating core parts  27  as these divisions allows the windings to be kept intact when parting them. This makes it possible to assemble and disassemble the stator of a sub-exciter  5  without its coils and insulators being damaged by such accidents as hitting.  
       Embodiment 8  
       [0056]      FIGS. 14 and 15  show an eighth embodiment of this invention.  FIG. 14  is a circumferential sectional view of a part of a generator pole in this embodiment, and  FIG. 15 a  vertical sectional view of it, where between a seating  1424  mounted on a rotor shaft  1401  and a circular-cone-shaped pole shoe  1412  there is inserted a ring-shaped permanent magnet  1413 . The pole shoe  1412  has an end-enlarged hole formed radially-centered so as to be secured by a non-magnetic bolt  1426 . And the permanent magnet  1413  also has a hole formed radially-centered so as to receive the non-magnetic bolt  1426 . The non-magnetic bolt  1426  is fastened into the tapped holes formed in the rotor shaft  1401  and the seating  1424  so as to secure the pole shoe  1412  and the permanent magnet  1413  together.  
         [0057]     Using a plurality of bolts to keep the pole shoe  1412  and the permanent magnet  1413  in place has a possibility that a certain bolt has their load biased toward it and that the bolt itself or its hole breaks. In this embodiment, one non-magnetic bolt  1426  is used to secure the pole shoe  1412  and the permanent magnet  1413  together, thus such an imbalance of load can be avoided.  
         [0058]     Note that using one bolt to secure a pole shoe and a permanent magnet which have a rectangular horizontal section leads to a pronounced warping up at a corner of the rectangle far from the location of fixing. In addition, a pole shoe radially having a uniform thickness leads to a pronounced warping up at its ends during assembly or during operation. In this embodiment, to prevent these, there are a circular-cone-shaped pole shoe  1412  and a ring-shaped permanent magnet  1413 . This can prevent excessive warping up at ends.