Rotating electrical machine and drive system of cage induction motor

1. A rotating electrical machine comprising:

a rotor core,

a plurality of rotor slots radially provided at predetermined spaces in a circumferential direction of the rotor core, and

a plurality of rotor conductors, respectively, received in the plurality of rotor slots, wherein the plurality of rotor conductors comprise:

a rotor conductor upper portion, which is positioned near to an outer periphery of a rotor, and has a trapezoidal cross sectional shape which tapers continuously toward the outer periphery of the rotor, and

a rotor conductor lower portion, which is contiguous to the rotor conductor upper portion to be positioned nearer to a center of the rotor than the rotor conductor upper portion, and a cross sectional shape of which has substantially the same width as that of a bottom of the rotor conductor upper portion.

2. The rotating electrical machine according to claim 1 , wherein the rotor conductor upper portion tapers linearly toward the outer periphery of the rotor.

3. The rotating electrical machine according to claim 1 , wherein brass is used to make the plurality of rotor conductors, and the rotor conductor upper portion has a height of not less than 27 mm.

4. The rotating electrical machine according to claim 1 , wherein brass is used to make the plurality of rotor conductors, and the rotor conductor upper portion has a height of 27 to 46 mm.

5. The rotating electrical machine according to claim 1 , wherein copper is used to make the plurality of rotor conductors, and the rotor conductor upper portion has a height of not less than 7 mm.

6. The rotating electrical machine according to claim 1 , wherein copper is used to make the plurality of rotor conductors, and wherein the plurality of rotor conductors have a total height of not less than 60 mm, and the rotor conductor upper portion has a height of 7 to 44 mm.

7. The rotating electrical machine according to claim 1 , wherein copper is used to make the plurality of rotor conductors, and wherein the plurality of rotor conductors have a total height of not less than 30 mm, and the rotor conductor upper portion has a height of 7 to 17.5 mm.

8. A rotating electrical machine comprising a rotor core, a plurality of rotor slots radially provided at predetermined spaces in a circumferential direction of the rotor core, and a plurality of rotor conductors, respectively, received in the plurality of rotor slots;

wherein the plurality of rotor conductors comprise a rotor conductor upper portion made of brass and positioned near to an outer periphery of a rotor, and a rotor conductor lower portion made of copper contiguous to a bottom of the rotor conductor upper portion to be positioned nearer to a center of the rotor than the rotor conductor upper portion; and

wherein the rotor conductor upper portion has a trapezoidal cross sectional shape tapering continuously toward the outer periphery of the rotor, and the rotor conductor lower portion has a rectangular cross sectional shape having substantially the same width as that of the bottom of the rotor conductor upper portion.

9. The rotating electrical machine according to claim 8 , wherein the rotor conductor upper portion tapers linearly toward the outer periphery of the rotor.

10. The rotating electrical machine according to claim 8 , wherein the rotor conductor upper portion is made of brass, and has a height of not less than 27 mm.

11. The rotating electrical machine according to claim 8 , wherein the rotor conductor upper portion is made of brass, and has a height of 27 to 46 mm.

12. A drive system of a cage induction motor comprising a stator core, a plurality of stator slots radially provided at predetermined spaces and around an inner periphery of the stator core, a stator comprising stator coils received in the stator slots, a rotor core, a plurality of rotor slots radially provided at predetermined spaces in a circumferential direction of the rotor core, a cage induction motor comprising rotor conductors received in the rotor slots, a power supply for supplying three-phase alternating current to the cage induction motor,

wherein the rotor conductors comprise at least one rotor conductor upper portion, which is positioned near to an outer periphery of a rotor, and has a trapezoidal cross sectional shape which tapers continuously toward the outer periphery of the rotor, and a corresponding rotor conductor lower portion, which is contiguous to the rotor conductor upper portion and is positioned nearer to a center of the rotor than the rotor conductor upper portion, and a cross sectional shape of which has substantially the same width as that of a bottom of the rotor conductor upper portion, and

a switch for applying to the stator coils voltage of a commercial three-phase AC power supply.

13. The drive system according to claim 12 , wherein the rotor conductor upper portion tapers linearly toward the outer periphery of the rotor.

14. The drive system according to claim 12 , wherein brass is used to make the rotor conductors, and the rotor conductor upper portion has a height of not less than 27 mm.

15. The drive system according to claim 12 , wherein copper is used to make the rotor conductors, and the rotor conductor upper portion has a height of not less than 7 mm.

16. The drive system according to claim 12 , wherein the rotor conductor upper portion is made of brass, and the rotor conductor lower portion is made of copper.

17. The drive system according to claim 12 , wherein the rotor conductor upper portion is made of brass and tapers linearly toward the outer periphery of the rotor and has a trapezoidal cross sectional shape.

18. The drive system according to claim 12 , wherein the rotor conductor upper portion made of brass, and has a height of not less than 27 mm.

19. The drive system according to claim 12 , wherein the switch applies to the stator coil voltage a commercial three-phase AC power supply with a commercial frequency remaining intact.