Patent Publication Number: US-2012038230-A1

Title: Rotating electric machine and production method for rotating electric machine

Description:
TECHNICAL FIELD 
     The present invention relates to a rotating electric machine and a production method for the rotating electric machine. 
     BACKGROUND ART 
     In a conventional stator for a rotating electric machine, an insulation paper is used to insulate between a stator core and a stator coil. In addition, a stator coil extending outside of a slot exit, i.e., so-called coil end, is provided with a straight section so as to reduce mechanical stress in the slot exit section and ensure a creepage distance and a spatial distance between the stator core and the stator coil. 
     The rotating electric machine is effectively reduced in size by reducing the coil end of the stator. However, bending the stator coil without providing the straight section of the coil end may result in mechanical stress or the like tearing the insulation paper insulating between the stator core and the stator coil, thereby causing insulation failure. Then, a method is proposed to reduce stress on the stator coil and the insulation paper at the slot exit section by forming a step section around the slot of the stator core and folding the insulation paper at this step section to form a dual structure (refer to patent literature 1 for example).
     Patent literature 1: Japanese Laid Open Patent Publication No. H4-210744   

     SUMMARY OF INVENTION 
     Technical Problem 
     However, since in the conventional method as described above, the stator coil is bent from inside the slot, the creepage distance and the spatial distance between the stator coil and the end face of the stator core can not be sufficiently ensured. In addition, mechanical stress generated at the step section formed around the slot may result in reduction in the thickness of the insulation paper, thereby causing insulation failure. 
     Solution to Problem 
     A rotating electric machine according to claim  1  is characterized by comprising: a stator in which a stator coil is mounted to a plurality of slots formed on a stator core; and a rotor that is rotatably disposed inside the stator, wherein: a slot groove, having a predetermined depth and a predetermined width from an end face of the stator core and forming a space between the stator coil and the stator core, is formed around each of the plurality of slots; and the stator coil includes a straight-shaped straight section which is inserted into the slot and is provided with an insulating material, and a coil end section which extends outside of the slot and is bent at a same height as the end face of the stator core. 
     A production method, according to claim  9 , for a rotating electric machine including a stator in which a stator coil is mounted to a plurality of slots formed on a stator core and a rotor rotatably disposed inside the stator, is characterized by comprising: forming a slot groove, having a predetermined depth and a predetermined width from an end face of the stator core around each of the plurality of slots, that forms a space between the stator coil and the stator core; inserting the stator coil, having been provided with an insulating material, into the slot; inserting a coil bending jig into the slot groove to fix the stator coil; and bending the stator coil at a same height as the end face of the stator core with the coil bending jig as a fulcrum. 
     A production method, according to claim  10 , for a rotating electric machine including a stator in which a stator coil is mounted to a plurality of slots formed on a stator core and a rotor rotatably disposed inside the stator, is characterized by comprising: forming a slot groove, having a predetermined depth and a predetermined width from an end face of the stator core around each of the plurality of slots, that forms a space between the stator coil and the stator core; inserting the stator coil that has been provided with an insulating material and bent in advance, into the slot; and a bent portion of the stator coil is arranged to be level with the end face of the stator core. 
     Advantageous Effect of the Invention 
     According to the present invention, dielectric breakdown at an insulating material or the stator coil is prevented, the rotating electric machine is reduced in size, and the creepage distance and the spatial distance are ensured. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  A side sectional view of a rotating electric machine according to the first embodiment of the present invention. 
         FIG. 2  A sectional view of a stator of the rotating electric machine shown in  FIG. 1 . 
         FIG. 3  A sectional perspective view of a rotor of the rotating electric machine shown in  FIG. 1 . 
         FIG. 4  A perspective view showing a stator including a winding configuration with lap winding. 
         FIG. 5  An enlarged partial sectional view of the stator shown in  FIG. 2 . 
         FIG. 6  A partial sectional view of a slot formed in the stator core. 
         FIG. 7  A characteristic profile showing a relationship between the creepage distance and the spatial distance between the stator core and the stator coil, and the dielectric breakdown distance. 
         FIG. 8  A view of the stator core seen axially, illustrating a production method for the stator coil. 
         FIG. 9  An axial partial sectional view of the stator core, illustrating a production method for the stator coil. 
         FIG. 10  ( a ) to ( c ) Views illustrating a production method for the stator coil in the second embodiment of the present invention. 
         FIG. 11  A view showing a state in which the pre-bent stator coil is inserted into the slot. 
         FIG. 12  A view illustrating a production method for the stator according to the third embodiment of the present invention. 
         FIG. 13  A view illustrating a production method for the stator according to the fourth embodiment of the present invention. 
         FIG. 14  A view illustrating a production method for the stator according to the fifth embodiment of the present invention. 
         FIG. 15  A view illustrating a production method for the stator according to the sixth embodiment of the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     First Embodiment 
     A rotating electric machine in the first embodiment of the present invention will now be explained in detail with reference to the drawings. 
       FIG. 1  is a side sectional view of an induction rotating electric machine in the first embodiment,  FIG. 2  is a view showing a cross section of the stator, and  FIG. 3  is a perspective view showing a cross section of the rotor. The induction rotating electric machine includes a bottomed cylindrical housing  1  having an opening at one axial end side and a cover  2  sealing the opening end of the housing  1 . The housing  1  and the cover  2  are fastened with a plurality of, for instance, six bolts  3 . The housing  1  is provided with a water path forming member  22  inside thereof, and a stator  4  is fixed to the inside of the water path forming member  22  by shrink fitting or the like. A flange of the water path forming member  22 , shown on the left of the figure, is sandwiched between and fixed to the housing  1  and the cover  2 , so that a water path  24  is formed between the water path forming member  22  and the housing  1 . Coolant which cools the rotating electric machine is inlet to the water path  24  through an inlet  32  formed on the housing  1  and discharged from an outlet  34  of the housing  1 . 
     The stator  4  is constituted with a stator core  412  in which a plurality of slots  411  are provided and spaced equally circumferentially and a three-phase stator coil  413  inserted into each of the slots  411 . The stator core  412  in which the stator coil  413  is inserted has 24 slots  411  formed therein. The stator core  412  is formed with laminated steel plates prepared by punching or etching, for example, a magnetic steel plate of 0.05 to 0.35 mm thick and laminating the shaped magnetic steel plates, and the equally circumferentially spaced plurality of slots  411  are arranged radially in the stator core. 
     A rotor  5  is rotatably arranged in the inner circumference of the stator core  412  so as to oppose the stator core  412  through a tiny gap. The rotor  5  is fixed to a shaft  6  and rotates together with the shaft  6 . The shaft  6  is rotatably supported by a pair of ball bearings  7   a  and  7   b  provided on the housing  1  and the cover  2 , respectively. Of those bearings  7   a  and  7   b , the bearing  7   a , on the cover  2  side, is fixed to the cover  2  with a fixing plate not shown in the figures and the bearing  7   b , on the bottom side of the housing  1 , is fixed to a recess provided on the bottom of the housing  1 . 
     A pulley  12  is attached to the left end of the shaft  6  with a nut  11 . A sleeve  9  and a spacer  10  are provided at the shaft  6  between the pulley  12  and the bearing  7   a . The outer circumference of the sleeve  9  and the inner circumference of the pulley  12  have a slightly conical shape. The pulley  12  and the shaft  6  are firmly integrated on tightening force by the nut  11 , so that those can rotate together. When the rotor  5  is rotationally driven relative to the stator  4 , rotational force of the shaft  6  is output externally through the pulley  12 . In addition, when working as an electric generator, rotational force from the pulley  12  is input into the shaft  6 . 
     As shown in  FIG. 3 , a rotor core  513  of the rotor  5 , which is a squirrel-cage rotor, is embedded with a plurality of conductor bars  511  extending in the rotation axis over the whole circumference at regular intervals. The rotor core  513  is made of a magnetic material, and each of the axial ends of the rotor core  513  is provided with a shorting ring  512  shorting each of the conductor bars  511 . It is to be noted that the perspective view of  FIG. 3  shows the cross-sectional structure of a cross-sectional surface perpendicular to the rotation axis so as to manifest the relationship between the rotor core  513  and the conductor bars  511 , and thus the shorting ring  512  and the shaft  6  on the pulley  12  side are not illustrated. 
     The rotor core  513  is constituted with laminated steel plates prepared by punching or etching a magnetic steel plate of 0.05 to 0.35 mm thick and laminating the shaped magnetic steel plates. As shown in  FIG. 3 , substantially fan-shaped hollow sections  514  are provided and spaced equally circumferentially in the inner circumference side of the rotor core  513  for weight reduction. The conductor bars  511 , described above, are embedded in the outer circumference side of the rotor core  513 , i.e., in the stator side, and a magnetic circuit is formed on a rotor yoke  530  inward of the conductor bars  511 . Each of the conductor bars  511  and the shorting ring  512  are made of aluminium and integrated with the rotor core  513  by die casting. The shorting ring  512  disposed at the both ends of the rotor core is arranged to protrude from the rotor core  513  to the axial ends. It is to be noted that although not illustrated in  FIG. 1 , the bottom side of the housing  1  is provided with a detecting rotor for detecting rotation of the rotor  5 . A rotation sensor  13  detects teeth of the rotating detecting rotor and outputs an electrical signal for detecting the position of the rotor  5  and the rotational speed of the rotor  5 . 
     As a comparison example of the stator  4  according to the first embodiment,  FIG. 4  shows a perspective view of a stator  4 A which includes 48 slots and in which the stator coil  413  is wound in each of the slots by lap winding. The stator coil  413  is wound around a pair of slots across a predetermined number of slots therebetween. A coil end  414  is formed on each end face of the stator core  412  by the stator coil  413  protruding outwardly from each of the slots. 
     As shown in  FIG. 4 , a straight section where the stator coil  413  extends straight is provided at the coil end  414  in the vicinity of the exit section of each of the slots, and an insulation paper  13  is wound around it so as to ensure a creepage distance and a spatial distance between the stator core  412  and the stator coil  413 . In order to reduce the stator  4 A in size while maintaining the output of the rotating electric machine, the coil end  414  is required to be reduced in the rotation axis direction of the rotating electric machine. However, bending the stator coil  413  without providing a straight section for reducing the coil end  414  may cause the insulation paper  13  wound around the stator coil  413  or enamel coating to be broken due to an effect of electrical stress or mechanical stress at the exit section of each of the slots. Otherwise, there is a problem that the bending of the stator coil  413  causes the insulation paper  13  to be opened and the stator coil  413  and the stator core  412  to come into contact with each other, thereby causing insulation failure. 
     Then, in the first embodiment, the stator  4  is configured so as to reduce the coil end  414  while preventing electrical breakdown in the insulation paper  13  or enamel coating caused by mechanical stress generated in the stator coil  413  at the exit section of each of the slots and securing the creepage distance and the spatial distance between the stator coil  413  and the stator core  412 . 
     The configuration of the stator  4  in the first embodiment will now be explained in detail.  FIG. 5  shows an enlarged partial sectional view of the stator  4  shown in  FIG. 2 .  FIG. 6  shows an A-A sectional view of the slot  411  shown in  FIG. 5 . As shown in  FIG. 5  and  FIG. 6 , a slot groove  415  is provided around each of the slots  411  of the stator core  412 . The slot groove  415  is provided surrounding the slot  411  so as to form a space between the stator coil  413  and the exit section of the slot  411 . The slot groove  415  can be formed by preparing the stator core  412  by, for instance, laminating magnetic steel plates which have been punched and shaped corresponding to the position and the size of the slot groove  415 . 
     An axial depth D 1  and radial and circumferential widths D 2  from a core end face  416  of the slot groove  415  are each appropriately set based upon electrical breakdown voltage at the rotating electric machine so as to sufficiently ensure the creepage distance and the spatial distance between the stator core  412  and the stator coil  413 . It is to be noted that the dashed line in  FIG. 5  denotes an inside end of the slot groove  415 . 
     As shown in  FIG. 6 , the stator coil  413  is not provided with a straight section at the coil end  414  described above and is bent at a slot exit section  417 , i.e., at the height of the core end face  416  of the stator core  412 . In addition, the insulation paper  13  insulating between the stator core  412  and the stator coil  413  is provided inside the slot  411 , at least up to the core end face  416 . In other words, the stator coil  413  is constituted with a straight section  413   a  inserted into the slot  411  and covered with the insulation paper  13  and a coil end section  413   b  extending outside of the slot  411 , bent, and not covered with the insulation paper  13 . It is to be noted that the coil end  414  described above is formed by the coil end section  413   b  of the stator coil  413 . 
     Here, the spatial distance is a minimum distance in the space between the stator core  412  and the stator coil  413 , which corresponds to the minimum distance from the slot exit section  417  of the stator core  412  to the coil end section  413   b  of the stator coil  413  in  FIG. 6 . The creepage distance is a minimum distance along the insulation paper  13  between the stator core  412  and the stator coil  413 , which corresponds to the axial depth D 1  of the slot groove  415  in  FIG. 6 . 
       FIG. 7  shows a characteristic profile showing a relationship between the creepage distance and the spatial distance between the stator core  412  and the stator coil  413  and electrical breakdown voltage at the rotating electric machine. IEC60034 (standard for general information on motors) issued by IEC (International Electrotechnical Commission) specifies that a dielectric strength test for a motor exceeding 150 V is to be conducted with the test voltage at least 1500 V for one minute. It is to be noted that voltage 1.2 times higher than that of the standard is accepted if a one-minute voltage withstand test is substituted with a one-second voltage withstand test in a mass production line or the like. Thus, if the rotating electric machine according to the first embodiment is a low voltage rotating electric machine of between 150 V and 600 V, this rotating electric machine is required to withstand the voltage withstand test of 1.5 kV×1.2=1.8 kV. 
     As shown in  FIG. 7 , the creepage distance or the spatial distance corresponding to 1.8 kV, which is a short-time electrical breakdown voltage, is 1.5 mm. Accordingly, the stator  4  is required to be configured with the creepage distance and the spatial distance between the stator core  412  and the stator coil  413  each ensured to be at least 1.5 mm. Then, in the first embodiment, if the rotating electric machine is a low voltage rotating electric machine of equal to or less than 600 V, the axial depth D 1  of the slot groove  415  is set to 1.5 mm or greater and the radial and circumferential widths D 2  is set to 1.5 mm or greater. It is to be noted that the axial depth D 1  and the radial and circumferential widths D 2  of the slot groove is preferably set to as minimum as possible so as not to reduce the output of the rotating electric machine. 
     Next, a production method for the rotating electric machine according to the first embodiment will be explained. The rotor  5  and the stator core  412  can be produced by adopting a known method. A production method for the stator coil  413  will be mainly explained now.  FIG. 8  shows a view in which one slot  411  of the stator core  412  is viewed axially, and  FIG. 9  shows an axial sectional view of the slot  411  of the stator core  412 . 
     At first, if the stator coil  413  has a winding configuration in a wave winding method, a straight conductor (the stator coil  413 ) around which the insulation paper  13  is wound is insert axially into the slot  411  of the stator core  412 . Here, a rectangular wire is used as the conductor. Next, as shown in  FIG. 8 , a U-shaped coil bending jig  14  is inserted into the slot groove  415 . The axial height of the coil bending jig  14  is substantially the same as the axial depth D 1  of the slot groove  415  as shown in  FIG. 9 . In a state in which the conductor is fixed with the coil bending jig  14 , the conductor is bent at a desired angle with the coil bending jig  14  inserted into the slot groove  415  as a fulcrum. Then, the coil bending jig  14  is removed from the slot groove  415 . This can realize the stator coil  413  which is bent at the same height as the core end face  416  as shown in  FIG. 6 , i.e., has a bent portion at the same height as the core end face  416 . The stator coil  413  is not bent at the straight section  413   a  inserted into the slot  411  and it is bent from the core end face  416 . The coil end section  413   b  of the stator coil  413  corresponds to a portion which extends outside from the slot  411  and is bent from the core end face  416  without a straight section. 
     The coil bending jig  14  has a sufficient strength to bend the stator coil  413  and is made of an appropriate material that does not cause damage to the stator coil  413 . It is to be noted that if the coil bending jig  14  is an insulator, the coil bending jig  14  may remain in the slot groove  415 . If the stator coil  413  has a winding configuration in a distributed winding method, the conductor is inserted into the slot  411  from the inner diameter side of the stator core  412 . 
     The following operations and advantageous effects can be achieved in the first embodiment explained above. 
     (1) The rotating electric machine includes the stator  4  in which the stator coil  413  is inserted into the plurality of slots  411  formed on the stator core  412  and the rotor  5  rotatably provided inside the stator  4 . Around each of the plurality of slots  411 , the slot groove  415 , having a predetermined depth and a predetermined width from the end face  416  of the stator core  412  and forming a space between the stator coil  413  and the stator core  412 , is formed. The stator coil  413  includes the straight section  413   a , having a straight shape and being inserted into the slot  411  and provided with an insulating material (the insulation paper  13 ), and the coil end section  413   b , extending outside of the slot  411  and being bent at the same height as the end face  416  of the stator core  412 . This prevents electrical breakdown of enamel coating of the insulation paper  13  and the stator coil  413  and allows the coil end  414  to be reduced axially while ensuring the creepage distance and the spatial distance, thereby enabling the entire rotating electric machine to be reduced in size.
 
(2) The slot groove  415  has the predetermined depth D 1  in the rotation axis direction of the rotating electric machine and the predetermined width D 2  in the circumferential and radial directions of the stator core  412 , and the predetermined depth D 1  and the predetermined width D 2  are each set based upon electrical breakdown voltage of the rotating electric machine. More specifically, if the rotating electric machine is a low voltage rotating electric machine of equal to or less than 600 V, the depth and the width of the slot groove  415  is each equal to or greater than 1.5 mm. This allows the slot groove  415  to have an appropriate size in view of electrical breakdown voltage of the rotating electric machine and can effectively prevent electrical breakdown and insulation failure of the insulation paper  13  and the like.
 
(3) The insulating material (the insulation paper  13 ) is provided on the stator coil  413  in the slot  411  at least up to the height of the end face  416  of the stator core  412 . Since the insulation paper  13  does not protrude outside the slot  411 , the bending of the stator coil  413  can prevent the insulation paper  13  from becoming thin or broken.
 
(4) When producing the stator  4  to be included in the rotating electric machine, at first the slot groove  415 , having the predetermined depth D 1  and the predetermined width D 2  from the end face  416  of the stator core  412  and forming a space between the stator coil  413  and the stator core  412 , is formed around each of the plurality of slots  411 . Then, the stator coil  413  provided with the insulation paper  13  is inserted into the slot  411  and the coil bending jig  14  is inserted into the slot groove  415  so as to fix the stator coil  413 , and the stator coil  413  is bent at the same height as the end face  416  of the stator core  412  with the coil bending jig  14  as a fulcrum.
 
     Second Embodiment 
     The rotating electric machine according to the second embodiment of the present invention will now be explained. The overall structure of the rotating electric machine in the second embodiment is the same as that of the first embodiment described above. The following explanation will mainly focus upon the difference from the first embodiment. 
     In the production method for the stator coil  413  in the first embodiment described above, the conductor which constitutes the stator coil  413  is inserted into the slot  411  before the conductor is bent at a predetermined angle so as to form the stator coil  413 . However, if the slot  411  of the stator core  412  is a so-called open slot as shown in  FIG. 2 , a conductor bent in advance at a predetermined angle may be inserted into the slot  411  so as to form the stator coil  413 . The production method for the stator coil  413  according to the second embodiment will now be explained in detail. 
     At first, as shown in  FIG. 10(   a ), a rectangular wire conductor constituting the stator coil  413  is inserted into and fixed to a metal coil bending jig  15 . At this time, the coil bending jig  15  and the conductor are fixed so that a bent portion  413   c  of the stator coil  413 , i.e., a boundary between the straight section  413   a  and the coil end section  413   b  of the stator coil  413 , is level with the upper end of the coil bending jig  15 . In a state in which the conductor is fixed to the coil bending jig  15 , the conductor is bent at a desired angle and the coil bending jig  15  is then removed. This allows the stator coil  413  having the bent portion  413   c  to be formed as shown in  FIG. 10(   b ). It is to be noted that the insulation paper  13  may be wound around the straight section  413   a  of the stator coil  413  before bending the stator coil  413  or may be wound around the straight section  413   a  after bending the stator coil  413 . 
     The stator coil  413  bent as shown in  FIG. 10(   b ) is inserted into the slot  411  from the inner diameter side of the stator core  412 . The bent portion  413   c  of the stator coil  413  is arranged to be level with the core end face  416  of the stator core  412 .  FIG. 11  shows a partial perspective view of a state in which two pre-bent stator coils  413  are inserted into the slot  411 , viewed from the inner diameter side of the stator core  412 . As shown in  FIG. 11 , in the stator coil  413 , the straight section  413   a  around which the insulation paper  13  is wound is inserted into the slot  411  and the coil end section  413   b  without the insulation paper  13  is bent at the same height as the core end face  416  of the stator core  412 . 
     The stator coil  413  inserted into the slot  411  as shown in  FIG. 11  is connected with the stator coil  413  inserted into another slot  411  corresponding thereto (refer to  FIG. 10(   c )). The stator coils  413  are connected with each other by a method, for instance, TIG welding, fusing, fusing brazing, resistance brazing, or the like. 
     As explained above, also in the second embodiment, similarly to the first embodiment described above, the coil end  414  can be reduced axially while preventing electrical breakdown of enamel coating of the insulation paper  13  and the stator coil  413  and ensuring the creepage distance and the spatial distance. This allows the entire rotating electric machine to be reduced in size. 
     When producing the stator  4  to be included in the rotating electric machine, at first, the slot groove  415 , having the predetermined depth D 1  and the predetermined width D 2  from the end face  416  of the stator core  412  and forming a space between the stator coil  413  and the stator core  412 , is formed around each of the plurality of slots  411 . Then, the pre-bent stator coil  413  on which the insulation paper  13  is provided is inserted into the slot  411  and the bent portion  413   c  of the stator coil  413  is arranged to be level with the end face  416  of the stator core  412 . 
     Third Embodiment 
     The rotating electric machine according to the third embodiment of the present invention will now be explained. The overall structure of the rotating electric machine in the third embodiment is the same as that of the first embodiment described above. The following explanation will mainly focus upon the difference from the first embodiment. 
     As described earlier, in a low voltage rotating electric machine of, for example, equal to or less than 600 V, it is necessary to ensure each of the creepage distance and the spatial distance between the stator core  412  and the stator coil  413  to be at least 1.5 mm. However, it may be difficult to ensure each of the creepage distance and the spatial distance to be at least 1.5 mm in a small rotating electric machine for instance. Then, in the third embodiment, even if it is difficult to form the slot groove  415  with the depth and the width of at least 1.5 mm, insulation failure due to insufficient creepage distance and spatial distance can be prevented. 
     More specifically, as shown in  FIG. 12 , an insulation tape  16  is wound around from a portion inside the slot groove  415  of the stator coil  413  to a portion outside the slot  411 . The insulation tape  16  is a thin insulator for insulating between the stator core  412  and the stator coil  413 . As shown in  FIG. 12 , the insulation tape  16  is attached inside the slot groove  415  so as to cover the insulation paper  13 . 
     For winding the insulation tape  16  around the stator coil  413 , the axial depth D 1  and the radial and circumferential widths D 2  of the slot groove  415  may have at least an enough size for the insulation tape  16  to be wound around the stator coil  413 . The stator coil  413  may be bent before inserted into the slot  411  or may be bent after inserted into the slot  411 . 
     As explained above, also in the third embodiment, similarly to the first and the second embodiments described above, the coil end  414  can be reduced axially while preventing electrical breakdown of the insulation paper  13  and enamel coating of the stator coil  413  and ensuring the creepage distance and the spatial distance. This allows the entire rotating electric machine to be reduced in size. In addition, even if the creepage distance and the spatial distance required based upon electrical breakdown voltage at the rotating electric machine can not be ensured by the slot groove  415 , the insulation tape  16  is provided on the stator coil  413  so as to prevent well electrical breakdown of the insulation paper  13  and the enamel coating and to prevent insulation failure of the stator core  412  and the stator coil  413 . 
     Fourth Embodiment 
     The rotating electric machine according to the fourth embodiment of the present invention will now be explained. The overall structure of the rotating electric machine in the fourth embodiment is the same as that of the first embodiment described above. The following explanation will mainly focus upon the difference from the first to the third embodiments. 
     The stator coil  413  may be provided with an insulation powder resin coat  17  as shown in  FIG. 13  if, for instance, the stator coils  413  provided on the stator core  412  are narrowly spaced with each other and it is thus difficult to wind the insulation tape  16  used in the third embodiment described above around the stator coil  413 . The insulation powder resin coat  17  is applied from a portion inside the slot groove  415  of the stator coil  413  to a portion outside the slot  411 . The stator coil  413  may be bent before inserted into the slot  411  or may be bent after inserted into the slot  411 . 
     Thus, a similar effect to that of the third embodiment can be achieved by forming an insulation layer on the stator coil  413  by the insulation powder resin coat  17 . 
     Fifth Embodiment 
     The rotating electric machine according to the fifth embodiment of the present invention will now be explained. The overall structure of the rotating electric machine in the fifth embodiment is the same as that of the first embodiment described above. The following explanation will mainly focus upon the difference from the first to the fourth embodiments. 
     In the fifth embodiment, an insulation layer is formed on the core end face  416  of the stator core  412 . This allows electrical breakdown and insulation failure of the insulation paper  13  to be prevented well even if, for instance, it is difficult to ensure the creepage distance and the spatial distance by the slot groove  415  as explained in the first and the second embodiments and it is difficult to form an insulation layer on the stator coil  413  as explained in the third and the fourth embodiment. 
     More specifically, as shown in  FIG. 14 , in the stator core  412 , the insulation powder resin coat  17  is applied from the inside of the slot groove  415  to the core end face  416 . The insulation powder resin coat  17  may be applied to a range from inside the slot groove  415  to around the slot  411 , which may secure sufficient creepage distance and the spatial distance between the stator core  412  and the stator coil  413 . 
     In addition, for applying the insulation powder resin coat  17  onto the stator core  412 , the axial depth D 1  and the radial and circumferential widths D 2  of the slot groove  415  may have an enough size to apply the insulation powder resin coat  17  at least. The stator coil  413  may be bent before inserted into the slot  411  or may be bent after inserted into the slot  411 . 
     As explained above, also in the fifth embodiment, similarly to the first to the fourth embodiments described above, electrical breakdown of the insulation paper  13  and the enamel coating and insulation failure of the stator core  412  with the stator coil  413  can be prevented well. 
     Sixth Embodiment 
     The rotating electric machine according to the sixth embodiment of the present invention will now be explained. The overall structure of the rotating electric machine in the sixth embodiment is the same as that of the first embodiment described above. The following explanation will mainly focus upon the difference from the first to the fifth embodiments. 
     The slot exit section  417  of the stator core  412  may be chamfered if, for example, it is difficult to ensure the creepage distance and the spatial distance by the slot groove  415  as explained in the first and the second embodiments. 
       FIG. 15  shows an enlarged partial sectional view of the vicinity of the slot exit section  417 . More specifically, as shown in  FIG. 15 , the slot exit section  417  at which the slot groove  415  and the core end face  416  are to cross or meet is chamfered with a curved surface. This can ensure the spatial distance between the stator core  412  and the coil end section  413   b  of the stator coil  413 . 
     It is to be noted that although  FIG. 15  merely shows a part of the slot groove  415 , a chamfer is provided all around the slot groove  415 . The chamfer is not limited to that with a curved surface as shown in  FIG. 15 , and it may be planar or polyhedron. The stator coil  413  may be bent before inserted into the slot  411  or may be bent after inserted into the slot  411 . 
     As explained above, also in the sixth embodiment, similarly to the first to the fifth embodiments described above, electrical breakdown of the insulation paper  13  and the enamel coating and insulation failure of the stator core  412  with the stator coil  413  can be prevented well. 
     While in the first to the sixth embodiments explained above, the insulation paper  13  is used to insulate between the stator coil  413  and the stator core  412 , the present invention is not limited thereto and an insulating material other than the insulation paper may be used to insulate between the stator coil  413  and the stator core  412 . In other words, it is acceptable as long as the straight section  413   a  of the stator coil  413  inserted into the slot  411  is covered with an insulating material. 
     It is to be noted that the rotating electric machine in the first to the sixth embodiments can be modified as follows. 
     (1) While in the first to the sixth embodiments, an induction rotating electric machine is explained as an example, the present invention can be applied also to a stator coil of, for instance, a permanent magnet type rotating electric machine or the like.
 
(2) The conductor used for the stator coil  413  is not limited to have a rectangular cross-section, and the present invention can be applied to that using a circular round wire.
 
(3) The winding method of the stator coil  413  may be a distributed winding or a wave winding.
 
(4) The stator core  412  may assume a structure other than that of a laminated core.
 
     It is to be noted that the present invention may be embodied in any way other than those described in reference to the embodiments, as long as the features characterizing the present invention remain intact. 
     The disclosure of the following priority application is herein incorporated by reference: Japanese Patent Application No. 2008-297608 (filed on Nov. 21, 2008).