FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
As amended by the Patents (Amendment) Act, 2005
AND
The Patents Rules, 2003
As amended by the Patents (Amendment) Rules, 2006
COMPLETE SPECIFICATION
(See section 10 and rule 13)
TITLE OF THE INVENTION
An improved squirrel cage rotor and induction motor, thereof.
APPLICANTS:
Crompton Greaves Limited, CG House, Dr. Annie Besant Road, Worli, Mumbai -400030, Maharashtra, India, an Indian Company
INVENTORS:
Choudhury Chhavi and Pangal Sarvesh; both of Crompton Greaves Ltd, Machines 7 Division, D-5, Industrial Area MPAKVN, Mandideep - 462046, Madhya Pradesh, India; both Indian Nationals.
PREAMBLE TO THE DESCRIPTION:
The following specification particularly describes the nature of this invention and the manner in which it is to be performed:

FIELD OF THE INVENTION:
The invention relates to the field of motors.
Particularly, this invention relates to rotors.
Specifically, this invention relates to an improved squirrel cage rotor and induction motor, thereof.
BACKGROUND OF THE INVENTION:
An 'electrical rotating machine' or a 'rotating electrical machine' is any form of apparatus, equipment, or system which has a rotating member and generates, converts, transforms, or modifies electric power. These include apparatus such as a motor, generator, or synchronous converter.
Essentially all of the world's electric power is produced by rotating electrical generators, and about 70% of this energy is consumed in driving electric motors. Electric machines are electromechanical energy converters; generators convert mechanical energy into electrical energy and motors convert electrical energy into mechanical energy.
An electric machine can be constructed on the principle that a magnet will attract a piece of permeable magnetic material such as iron or magnetic steel. For example, a pole structure along with a magnetic block is allowed to rotate. The magnetic block will experience a torque tending to rotate it counterclockwise to the vertical direction.
One type of an 'electrical rotating machine' or a 'rotating electrical machine' is a motor. A motor for electrical purposes, i.e. an electric motor, is a device which converts electrical energy to mechanical energy. For industrial use, the ratings of motor may typically be very high. They may be placed in housings or frames. It contains two main components; stator and rotor. The rotor is the non-stationary part of a rotary motor, which rotates because the wires and magnetic field of the motor are arranged so that a torque is developed about the rotor's axis. The stator is the stationary part of a rotor system. The rotor has a fanning action.
AC induction motors are generally classified into squirrel cage induction motors and wound-rotor induction motors based on the type of rotor construction. Induction motors have a variety of industrial applications as prime movers, for example, in pumps, crushers, compressors, fans or mills. A squirrel cage induction motor comprises a cylindrical rotor rotatably disposed within a stator having stator windings.
The rotor comprises a rotor body having a plurality of electrical grade steel laminations press formed

together. The rotor body is mounted on a shaft with end plates pressed against the ends of the rotor body. The end plates each comprises a plurality of spaced apart upwardly directed straight teeth at the outer circumference thereof. A rotor includes two types of stampings; 1) core or central stampings which essentially form the central body of a rotor and 2) bunch of stacked end stampings which form the end portions of a rotor. A rotor essentially consists of a core assembly with rotor bars (12) (defined in a plurality of longitudinal conductor slots extending axially along the inner circumference of the rotor body in radially spaced apart relationship with one another) protruding out from the ends of the rotor and resistance rings (14) as shown in Figures 1 and 2 of the accompanying drawings. The rotor bars are brazed (assembled) to the resistance ring, which forms a shorted connection for all bars in the rotor. The rotor further comprises a pair of short circuiting rings, each ring being disposed at each end of the rotor body and comprising a plurality of slits transversely extending through the circumference thereof matching with the protruding ends of the rotor conductors. Each of the short circuiting rings is engaged to the protruding ends of the rotor conductors at each end of the rotor through the slits and welded and short circuited to the respective protruding ends of the rotor conductors.
During operation of the motor, a current is passed through the stator windings to induce a current in the rotor and create a magnetic field around the rotor to cause the rotor to rotate. Induced current in the rotor flows through the rotor conductors and short circuiting rings. The rotor rotates at high speeds and develops high centrifugal forces. High current also passes through the rotor conductors and short circuiting rings generating excess heat at the surface area of contact or joint between the short circuiting rings and rotor conductors. Unless the joint between the conductor ends and short circuiting rings is mechanically strong and electrically enduring, it will easily fail under the high centrifugal forces and excess heat development.
The short circuiting rings are generally welded to the conductor ends by induction brazing using induction brazing, because of the good thermal and mechanical properties of copper, the copper conductors and rings can be welded together by induction brazing. However, induction brazing is expensive and time consuming and cumbersome to carry out. Fabrication of large diameter short circuiting rings for induction motors of heavy rating is also expensive, time consuming and cumbersome from handling and labour requirement points of view. Besides, although the surface area of contact or joint between the conductor ends and rings is narrow and limited, because of the good thermal and mechanical properties of copper, the narrow and limited surface area of contact between the rotor conductors and short circuiting rings serves as a mechanically strong and electrically enduring joint between the rotor conductors and short circuiting rings to withstand the adverse effects of high centrifugal forces and excess heat development.

Copper is an expensive metal and is becoming scarce day by day. Although aluminium is known as an alternative to copper as a cheap conductor material, to the best of our knowledge and information, squirrel cage induction motor rotors comprising aluminium rotor conductors and aluminium short circuiting rings are not known to be used probably because of the low mechanical strength, low resistivity and low melting properties of aluminium and unsuitability of aluminium for induction brazing at high temperatures. Aluminium will melt and fuse at such high temperatures. Furthermore, because of the low mechanical strength, resistivity and melting properties of aluminium, a narrow and limited joint between aluminium short circuiting rings and rotor conductors would not be mechanically strong enough and electrically enduring to withstand the adverse effects of high centrifugal forces and excessive heat development at the surface area of contact between the rings and conductor ends during operation of the motor. Therefore there is a need for squirrel cage AC induction motors based on aluminium rotors.
The performance of an 'electrical rotating machine' or a 'rotating electrical machine' is defined by many characteristics. One such characteristic is its geometry of more specifically, the geometry of the rotor. These motors are subject to heavy vibrations throughout its lifespan for example high speed traction applications. The mismatched geometry also results in increased shaft voltage.
A squirrel cage rotor is the rotating part used in the most common form of AC induction motor. An electric motor with a squirrel cage rotor is termed a squirrel cage motor. The rotor converts the flux generated from the stator into mechanical energy. The rotor essentially consists of a core assembly with rotor bars (12) and resistance rings (14) as shown in Figures 1 and 2 of the accompanying drawings. The rotor bars are brazed (assembled) to the resistance ring, which forms a shorted connection for all bars in the rotor.
The resistance ring is just a connecting point for all the bars and hence not an essential requirement. The connections can be made in any other form of shorting and hence can be eliminated if another way of connection is available.
These motors are subject to heavy vibrations throughout its lifespan for example high speed traction applications.
PRIOR ART:
GB477693 refers to improvements in the rotors of squirrel cage induction motors wherein end portions of adjacent rotor bars are twisted at right angles to meet or connect by means of welding, brazing or

otherwise. However, this 'connection' is not a stable assembly as temperature variations or vibrations may lead to stresses in the connecting joint and even result in breakage at the connecting joint.
US2011241473 refers to a rotor of an electric machine is disclosed that resists expansion of the rotor components even at high rotational speed. It further describe a support disk, into which the rotor bars are slid, restrains the rotor bars from bending outwardly at high rotational speeds of the rotor.
JP2009011067 describes a high output rotary electric machine with a stator and a rotor. The rotor core is formed by laminating a plurality of steel plates, which steel plates are chamfered.
According to US20120091850, a rotating electric machine that can improve the efficiency in a rated operation by reducing a loss generated in a rotor due to a carrier harmonic component during the driving by an inverter and suppressing a current generated in armature windings by improving a power factor. A rotating electric machine, comprising: a stator that includes a stator iron core having a plurality of stator slots, which are formed on the inner diameter side of the stator iron core, are spaced in a circumferential direction at predetermined intervals, and extend in an axial direction, and an armature winding provided in the stator slots; and a rotor disposed opposite to the stator with a predetermined gap there between, the rotor including a rotor iron core having a plurality of rotor slots, which are formed on the outer diameter side of the rotor iron core, are spaced in the circumferential direction at predetermined intervals, and extend in the axial direction, rotor bars, each of which is provided in one rotor slot, and end rings connected to the ends of the rotor bars; wherein each rotor slot is asymmetrically shaped in the circumferential direction with respect to a straight line drawn from a central axis of rotation of the rotor in a radial direction; and wherein a slot opening is provided at the top of each rotor slot, the width of the slot opening being smaller in the circumferential direction than the width of the rotor slot.
According to EP1158644, an electric motor and a generator which is constituted using the electric motor as a power source and is used in an electric power line, characterized in that an electric drive generator is provided integrally or is provided separately, thereby a power generation function is obtained.
According to "Selection of Copper vs. Aluminum Rotors for Induction Motors" (NPL) Paper No. PCIC-2000-19 on squirrel cage induction motors, there is an important choice between utilizing a lower cost die cast or fabricated aluminum rotor versus the more expensive copper bar rotor. Utilizing the wrong rotor construction for the application can either increase costs unnecessarily or lead to catastrophic failure. This paper provides the background necessary to assist in making the proper

choice. The fundamentals of rotor construction and basic information on how the induction motor works will be discussed. Additionally, the effects of various materials and types of rotor construction on motor performance will be analyzed.
According to Indian patent application 1210/MUM/2013, a squirrel cage AC induction motor comprising a cylindrical rotor rotatably disposed within a stator, wherein the rotor comprises a rotor body having a plurality of electrical grade steel laminations press formed together and mounted on a shaft with end plates pressed against the ends of the rotor body, the.end plates each comprising a plurality of spaced apart upwardly directed straight teeth at the outer circumference thereof and wherein the rotor further comprises a plurality of longitudinal conductor slots extending axially along the inner circumference of the rotor body in radially spaced apart relationship with one another and a plurality of rotor conductors extending through the conductor slots in the rotor body and protruding out from the ends of the rotor and a pair of short circuiting rings, each ring being disposed at each end of the rotor body and being engaged to the respective protruding ends of the rotor conductors and short circuited to the respective protruding ends of the rotor conductors and wherein the rotor conductors and short circuiting rings are made of aluminium and each of the short circuiting rings is two piece construction and is short circuited to the respective protruding ends of the rotor conductors by metal inert gas welding with aluminium as the weld material.
OBJECTS OF THE INVENTION:
An object of the invention is to provide a rotor which prevents insertion bars from flying off under centrifugal force.
Another object of the invention is to provide a rotor assembly which facilitates provisioning of a good weldingjoint.
Yet another object of the invention is to provide a structurally stable rotor.
SUMMARY OF THE INVENTION:
According to this invention, there is provided an improved squirrel cage rotor comprising a rotor core having a plurality of laminations press formed together and mounted on a shaft with end plates pressed against ends of said rotor core, each of said end plates comprising a plurality of spaced apart outwardly directed teeth at the outer circumference thereof and wherein said rotor further comprising a plurality of longitudinal conductor slots extending axially along the inner circumference of said rotor core in radially spaced apart relationship with one another and a plurality of rotor conductor bars extending through said longitudinal conductor slots in said rotor core, said rotor conductor bars

protruding out from the ends of said rotor core and wherein said rotor further comprising at least a short circuit outer ring and at least a short circuit inner ring, each ring being disposed at each end of said rotor core, said rings being engaged to respective protruding ends of said rotor conductor bars and short circuited to respective protruding ends of said rotor conductor bars, characterised in that:
a. said end plate being a chamfered end plate;
b. said outer short circuit ring being a chamfered outer short circuit ring;
c. said bars being machined on its outer and inner side; and
d. a groove is provided between said chamfered outer ring and said inner short circuit ring; said
groove being filled with molten metal.
According to this invention, there is also provided a squirrel cage induction motor comprising an improved squirrel cage rotor rotatably disposed within a stator, said improved squirrel cage rotor comprising a rotor core having a plurality of laminations press formed together and mounted on a shaft with end plates pressed against ends of said rotor core, each of said end plates comprising a plurality of spaced apart outwardly directed teeth at the outer circumference thereof and wherein said rotor further comprising a plurality of longitudinal conductor slots extending axially along the inner circumference of said rotor core in radially spaced apart relationship with one another and a plurality of rotor conductor bars extending through said longitudinal conductor slots in said rotor core, said rotor conductor bars protruding out from the ends of said rotor core and wherein said rotor further comprising at least a short circuit outer ring and at least a short circuit inner ring, each ring being disposed at each end of said rotor core, said rings being engaged to respective protruding ends of said rotor conductor bars and short circuited to respective protruding ends of said rotor conductor bars, characterised in that:
a. said end plate being a chamfered end plate;
b. said outer short circuit ring being a chamfered outer short circuit ring;
c. said bars being machined on its outer and inner side; and
d. a groove is provided between said chamfered outer ring and said inner short circuit ring, said
groove being filled with molten metal.
Typically, said laminations are electrical grade steel laminations.
Typically, said bars are lathe turned bars or machines bars.
Typically, said bars are Aluminum bars.

Typically, said outer short circuit ring is a ring with spaced apart teeth disposed on the inner side of said ring with slots occurring due to the spaced apart nature of the teeth, said slots accommodating inserted bars while said chamfered outer short circuit ring is being fitted.
Typically, said outer short circuit ring is a lateral edge chamfered ring.
Typically, said chamfered end plate and said chamfered outer short circuit ring create spigot where the two touch.
Typically, said outer short circuit ring is of a relatively lower mass as compared to said inner short circuit ring.
Typically, said inner short circuit ring is a gear-like ring with protruding spaced apart teeth located on a ring with slots occurring due to the spaced apart nature of the teeth, said slots accommodating inserted bars while this chamfered outer short circuit ring is being fitted.
Typically, teeth of said chamfered short circuit ring sit on teeth of said inner short circuit ring, with corresponding slots forming a complete slot for receiving bars.
Typically, said molten metal is Aluminum.
Typically, groove is provided between said chamfered outer ring and said inner short circuit ring, said groove being filled with molten metal by metal inert gas welding.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
Figure 1 illustrates an existing arrangement of a rotor;
Figure 2 illustrates an exploded view of the existing rotor;
The invention will now be described in relation to the accompanying drawings, in which:
Figure 3 illustrates a pressed rotor core;
Figure 4 illustrates a chamfered end plate;
Figure 5 illustrates bars, preferably aluminum bars, being inserted in a pressed rotor core;

Figure 6 illustrates lathe turning on bars;
Figure 7 illustrates trimetric view of lathe turning on bars;
Figure 8 illustrates a chamfered outer short circuit ring;
Figure 9 illustrates an isometric view of an inner short circuit ring;
Figure 10 illustrates the inner short circuit ring inserted in the pressed rotor core;
Figure 11 illustrates the outer short circuit ring inserted in the pressed rotor core;
Figure 12 illustrates a sectional view of the inner short circuit ring and the outer short circuit ring inserted in the pressed rotor core;
Figure 13 illustrates turning for cutting out groove for welding; and
Figure 14 illustrates a step of welding where a welding joint is seen.
DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
Figure 1 illustrates existing arrangement of a rotor. Figure 2 illustrates an exploded view of the existing rotor.
The existing rotor (100) essentially consists of a core assembly with rotor bars (12) and resistance rings (14) as shown in Figures 1 and 2 of the accompanying drawings. The rotor bars are brazed (assembled) to the resistance ring, which forms a shorted connection for all bars in the rotor. The resistance rings are also known as short circuit rings (SCR).
Copper bars (12) are inserted into rotor slots and short circuit ring (SCR) (14) is fitted with the bars.
The ring (14) comprises slots, typically, rectangular slots disposed radially. These slots receive the
rotor bars (12). The SCR and the bars are brazed to provide contact. Brazing of the joints is done
keeping the rotor in vertical position.
According to this invention, there is provided an improved squirrel cage rotor and induction motor,
thereof.
Figure 3 illustrates a pressed rotor core.
In accordance with an embodiment of this invention, there is provided a pressed rotor core (22).

Typically, a pressed rotor core is made of laminations, preferably steel laminations, press formed together and mounted on a shaft with end plates pressed against the ends of the rotor body. The rotor core is secured by end plates (24), located, axially, at lateral sides of the pressed rotor core.
Figure 4 illustrates a chamfered end plate.
In at least one embodiment, the end plate is a chamfered end plate (24) provided in order to help secure a chamfered outer short circuit ring. Typically, there are two end plates located axially at the end of the pressed rotor core.
Each of the end plates each comprises a plurality of spaced apart, upwardly directed, teeth at the outer circumference thereof. The spaced apart nature of the teeth provides rings' slot. The chamfering of the end plate renders these spaced apart teeth, bent in a pre-defined configuration, at their distal open ends. Figure 5 illustrates bars, preferably aluminum bars, being inserted in a pressed rotor core.
Bars (28), preferably Aluminum bars, are inserted into the rotor core from an axial direction through one of the ends of the rotor core. The rotor bars have a tendency to fly off due to centrifugal force under running condition of rotor core. Lathe turning of bars, is performed, on the outer and inner side of the bars in order to ensure proper insertion of the bar in the rings' slot. Reference numeral 30 refers to lathe turned bars.
Figure 6 illustrates lathe turning on bars. Figure 7 illustrates trimetric view of lathe turning on bars.
Lathe turning is performed on the outer and inner side of bars to ensure proper insertion of the bar in the rings' slots. Thus, the bars are machined from the outer and inner sides of its protrusions outside the pressed rotor core.
Figure 8 illustrates a chamfered outer short circuit ring.
In accordance with another embodiment of this invention, there is provided a chamfered outer short circuit ring (32). Bar machining is performed in order to enable short circuit ring insertion. The outer short circuit ring is a ring with spaced apart teeth disposed on the inner side of the ring. Reference numeral 34 refers to slots occurring due to the spaced apart nature of the teeth. These slots accommodate inserted bars while this chamfered outer short circuit ring is being fitted. The lateral edge of this ring is chamfered. Only outer ring is provided with the chamfer. The chamfer will get located against the chamfer of the end plate. Together, the two chamfered portions i.e. the chamfered

portion of the outer short circuit ring and the chamfered portion of the end plate help bars of the rotor core and the short circuit ring to overcome the centrifugal forces acting on the rotor due to its angular displacement. The two chamfers help to create a spigot where the two touch. Preferably, outer short circuit ring is given lower mass as compared to the inner short circuit ring in order to reduce overall weight and hence to reduce the centrifugal force.
Figure 9 illustrates an isometric view of an inner short circuit ring.
In accordance with another embodiment of this invention, there is provided an inner short circuit ring (36). Typically, the inner short circuit ring is a gear-like ring with protruding spaced apart teeth located on a ring. Reference numeral 38 refers to slots occurring due to the spaced apart nature of the teeth. These slots accommodate inserted bars while this chamfered outer short circuit ring is being fitted. After the bars (28) are inserted, first, end plate is axially slipped on; one at each end of the pressed rotor core. Then, the inner short circuit ring (36) is axially located; one at each end of the pressed rotor core with bars inserted. Further, the chamfered outer short circuit ring (32) is located; one at each end of the pressed rotor core. The teeth of the chamfered short circuit ring (32) sit on the teeth of the inner short circuit ring (36). The corresponding slots form a complete slot for receiving bars (28).
Figure 10 illustrates the inner short circuit ring inserted in the pressed rotor core.
Figure 11 illustrates the outer short circuit ring inserted in the pressed rotor core.
It can be seen that the bars end at a depth in the slots provided by the outer ring and inner ring, i.e. the bars do not protrude till the edge of the slot, axially.
Figure 13 illustrates turning for cutting out groove for welding. A groove is formed between the chamfered outer ring and the inner short circuit ring. This groove should be wide enough such that the nozzle is able to touch the inner most point of the groove. This is critical to ensure a good welding joint (40).
Figure 14 illustrates a step of welding where a welding joint is seen.
The groove is then filled with molten aluminum by MIG welding (Metal Inert gas) to ensure a proper joint. The fill ensures that the inner short circuit ring (36) is flush with the chamfered outer short circuit ring (32).

The technical advancement of this invention lies in providing a squirrel cage rotor and motor, thereof, wherein the chamfered outer short circuit ring and the chamfered end plate form a unique assembly in order to prevent rotor bars from flying off. The chamfers of the outer short circuit ring and end plate helps to give a spigot in the top portion. The matching of the outer short circuit ring, inner short circuit ring, and bars provide for a groove such that it may be filled in order to provide an effective assembly. The short circuit rings have through slots. This makes the process of short circuit ring manufacturing easy. A profile cutter can be used to perform the machining instead of a CNC cutting machine. This reduces the cost of machining the short circuit ring greatly. The short circuit rings and bars are welded together. This construction allows a wide enough grove for appropriate welding and filling.
While this detailed description has disclosed certain specific embodiments of the present invention for illustrative purposes, various modifications will be apparent to those skilled in the art which do not constitute departures from the spirit and scope of the invention as defined in the following claims, and it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the invention and not as a limitation.

We claim,
1. An improved squirrel cage rotor comprising a rotor core having a plurality of laminations press
formed together and mounted on a shaft with end plates pressed against ends of said rotor core,
each of said end plates comprising a plurality of spaced apart outwardly directed teeth at the
outer circumference thereof and wherein said rotor further comprising a plurality of longitudinal
conductor slots extending axially along the inner circumference of said rotor core in radially
spaced apart relationship with one another and a plurality of rotor conductor bars extending
through said longitudinal conductor slots in said rotor core, said rotor conductor bars protruding
out from the ends of said rotor core and wherein said rotor further comprising at least a short
circuit outer ring and at least a short circuit inner ring, each ring being disposed at each end of
said rotor core, said rings being engaged to respective protruding ends of said rotor conductor
bars and short circuited to respective protruding ends of said rotor conductor bars, characterised
in that:
a. said end plate being a chamfered end plate;
b. said outer short circuit ring being a chamfered outer short circuit ring;
c. said bars being machined on its outer and inner side; and
d. a groove is provided between said chamfered outer ring and said inner short circuit ring, said
groove being filled with molten metal.
2. The improved squirrel cage rotor as claimed in claim 1, wherein said laminations are electrical grade steel laminations.
3. The improved squirrel cage rotor as claimed in claim 1, wherein said bars are lathe turned bars or machines bars.
4. The improved squirrel cage rotor as claimed in claim 1, wherein said bars are Aluminum bars.
5. The improved squirrel cage rotor as claimed in claim 1, wherein said outer short circuit ring is a ring'with spaced apart teeth disposed on the inner side of said ring with slots occurring due to the spaced apart nature of the teeth, said slots accommodating inserted bars while said chamfered outer short circuit ring is being fitted.
6. The improved squirrel cage rotor as claimed in claim 1, wherein said outer short circuit ring is a lateral edge chamfered ring.
7. The improved squirrel cage rotor as claimed in claim 1, wherein said chamfered end plate and said chamfered outer short circuit ring create spigot where the two touch.

8. The improved squirrel cage rotor as claimed in claim 1, wherein said outer short circuit ring is of a relatively lower mass as compared to said inner short circuit ring.
9. The improved squirrel cage rotor as claimed in claim 1. wherein said inner short circuit ring is a gear-like ring with protruding spaced apart teeth located on a ring with slots occurring due to the spaced apart nature of the teeth, said slots accommodating inserted bars while this chamfered outer short circuit ring is being fitted.
10. The improved squirrel cage rotor as claimed in claim 1, wherein teeth of said chamfered short circuit ring sit on teeth of said inner short circuit ring, with corresponding slots forming a complete slot for receiving bars.
11. The improved squirrel cage rotor as claimed in claim 1, wherein said molten metal is Aluminum.
12. The improved squirrel cage rotor as claimed in claim 1, wherein a groove provided between said chamfered outer ring and said inner short circuit ring said groove being filled with molten metal by metal inert gas welding.
13. A squirrel cage induction motor comprising an improved squirrel cage rotor rotatably disposed within a stator, said improved squirrel cage rotor comprising a rotor core having a plurality of laminations press formed together and mounted on a shaft with end plates pressed against ends of said rotor core, each of said end plates comprising a plurality of spaced apart outwardly directed teeth at the outer circumference thereof and wherein said rotor further comprising a plurality of longitudinal conductor slots extending axially along the inner circumference of said rotor core in radially spaced apart relationship with one another and a plurality of rotor conductor bars extending through said longitudinal conductor slots in said rotor core, said rotor conductor bars protruding out from the ends of said rotor core and wherein said rotor further comprising at least a short circuit outer ring and at least a short circuit inner ring, each ring being disposed at each end of said rotor core, said rings being engaged to respective protruding ends of said rotor conductor bars and short circuited to respective protruding ends of said rotor conductor bars, characterised in that:
a. said end plate being a chamfered end plate;
b. said outer short circuit ring being a chamfered outer short circuit ring;
c. said bars being machined on its outer and inner side; and
d. a groove is provided between said chamfered outer ring and said inner short circuit ring, said
groove being filled with molten metal.

14. The squirrel cage induction motor as claimed in claim 1, wherein said laminations are electrical grade steel laminations.
15. The squirrel cage induction motor as claimed in claim 1, wherein said bars are lathe turned bars or machines bars.
16. The squirrel cage induction motor as claimed in claim 1, wherein said bars are Aluminum bars.
17. The squirrel cage induction motor as claimed in claim I, wherein said outer short circuit ring is a ring with spaced apart teeth disposed on the inner side of said ring with slots occurring due to the spaced apart nature of the teeth, said slots accommodating inserted bars while said chamfered outer short circuit ring is being fitted.
18. The squirrel cage induction motor as claimed in claim 1, wherein said outer short circuit ring is a lateral edge chamfered ring.
19. The squirrel cage induction motor as claimed in claim 1, wherein said chamfered end plate and said chamfered outer short circuit ring create spigot where the two touch.
20. The squirrel cage induction motor as claimed in claim 1, wherein said outer short circuit ring is of a relatively lower mass as compared to said inner short circuit ring.
21. The squirrel cage induction motor as claimed in claim 1, wherein said inner short circuit ring is a gear-like ring with protruding spaced apart teeth located on a ring with slots occurring due to the spaced apart nature of the teeth, said slots accommodating inserted bars while this chamfered outer short circuit ring is being fitted.
22. The squirrel cage induction motor as claimed in claim 1, wherein teeth of said chamfered short circuit ring sit on teeth of said inner short circuit ring, with corresponding slots forming a complete slot for receiving bars.
23. The squirrel cage induction motor as claimed in claim 1, wherein said molten metal is Aluminum.
24. The squirrel cage induction motor as claimed in claim 1, wherein a groove provided between said chamfered outer ring and said inner short circuit ring said groove being filled with molten metal by metal inert gas welding.