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, 2005
COMPLETE SPECIFICATION
(See section 10 and rule 13)
TITLE OF THE INVENTION
Rotor with unified O-bar shorting assembly
APPLICANTS :
Crompton Greaves Limited, CG House, Dr Annie Besant Road, Worli, Mumbai 400 030, Maharashtra, India, an Indian Company
INVENTOR (S):
Pandya Ankit and Upadhyay Amarendra; both of Crompton Greaves Limited, Machine (M7) Division, 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 the field of squirrels cage of induction motors.
More particularly, this invention relates to a unified O-bar shorting assembly for rotor bars, and rotors thereof.
BACKGROUND OF THE INVENTION:
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, 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.
An induction or asynchronous motor is a type of AC motor where power is supplied to the rotor by means of electromagnetic induction. These motors are widely used in industrial drives, particularly polyphase induction motors, because they are robust and have no brushes. Their speed can be controlled with a variable frequency drive.

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.
A squirrel cage rotor is the rotating part used in an 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. A 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
Rotor bar cracking is a very common failure in induction traction motors. A crack in the rotor bar drastically brings down the current carrying capability of that bar; in turn, it reduces overall capability of the rotor. There are two major reasons which lead to generation of cracks in the rotor bars in the induction traction motors; one is structural and the other is thermal problem.

Structural Problem:
The short circuiting rings (SC rings) are supported only on the bars, due to which the bars have to bear complete weight of the SC rings. The phenomenon gets even worse with the heavy vibration from the axle of the locomotive during normal running of the traction motors.
Thermal Problem:
The rotor bars, which are rectangular or trapezoidal in cross section, are directly brazed to the short circuiting rings which have a ring shaped construction. As the temperature of the rotor goes up to 200°C or more, the rotor bars try to expand outwards in the axial direction. However, the SC rings being ring shaped, tries to expand radially outwards. As the bars are brazed to the SC rings, they also get pulled radially along with the SC rings. This leads to generation of excess stress in the portions near the brazing joints of the bars and the SC rings may eventually lead to rotor bar crack.
The above mentioned two problems (structural problem and thermal problem) of rotor bar cracking need to be addressed.
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.
Hence, there is a need for a rotor which eliminates these 'connections'.

OBJECTS OF THE INVENTION:
An object of the invention is to eliminate short circuiting rings in the squirrel cage rotor.
Another object of the invention is to provide a structurally stable squirrel cage rotor.
Yet another object of the invention is to provide a thermally stable squirrel cage rotor.
Still another object of the invention is to eliminate rotor bar breakage in a squirrel cage rotor.
An additional object of the invention is to eliminate resistance ring in a squirrel cage rotor.
SUMMARY OF THE INVENTION:
According to this invention, there is provided a rotor comprising a rotor body with longitudinal slots which open at its axial ends, said rotor comprises: a plurality of substantially rectangular strips, having two side arms (bars), of metal with rounded corners to provide unified O-bars, each of said arms being fitted into said slots, such that, each slot receives two arms corresponding to adjacent O-bars.

Typically, each of said unified O-bar have a pre-defined thickness and are fitted into said slots, in a longitudinal direction, on the rotor body, such that the ends of the O-bars extend beyond the axial ends of the rotor body, thereby providing a spaced apart region between the widthwise arm of said O-bar and said axial end at each side of said rotor body.
Typically, each longitudinal slot has a thickness to receive two sides of adjacent unified rotor O-bars.
Typically, the distance between two adjacent slots is equal to the width of each unified O-bar, thus, each two adjacent slots receiving one complete unified O-bar, consecutively.
Typically, said slots are circumferentially equi-distantly located throughout said rotor body.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 illustrates an isometric view of the squirrel cage rotor of the prior art; and
Figure 2 illustrates an exploded view of the squirrel cage rotor of Figure 1 (prior art).
The invention will now be described in relation to the accompanying drawings, in which:
Figure 3 illustrates an isometric view of a rotor body;

Figure 4 illustrates an isometric view of the rotor body (of Figure 3) with unified O-bar shorting assembly; and
Figure 5 illustrates an isometric close-up view of the rotor body (of Figure 3) with unified O-bar shorting assembly.
DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
Figure 1 illustrates an isometric view of the squirrel cage rotor of the prior art,
Figure 2 illustrates an exploded view of the squirrel cage rotor of Figure 1 (prior art).
A rotor, of the prior art, 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 rings (14) are at both the axial ends of the rotor bar (12) ends of the rotor of the prior art.
The resistance ring (14), at both ends, is a connecting point for all the bars (12).
According to this invention, there is provided a unified O-bar shorting assembly for rotor bars, and rotors thereof.
Figure 3 illustrates an isometric view of a rotor body;

Figure 4 illustrates an isometric view of the rotor body (of Figure 3) with unified O-bar shorting assembly.
Figure 5 illustrates an isometric close-up view of the rotor body (of Figure 3) with unified O-bar shorting assembly.
In accordance with an embodiment of this invention, the rotor body comprises longitudinal slots (22) which open at the axial ends of the rotor body. The slots are circumferentially equi-distantly located throughout the rotor body.
In accordance with an embodiment of this invention, there is provided a plurality of substantially rectangular strips (24), having two side arms (bars), of metal with rounded corners to provide unified O-bars. These unified O-bar have a pre-defined thickness and are fitted into the slots provided, in a longitudinal direction, on the rotor body, such that the ends of the O-bars extend beyond the axial ends of the rotor body, thereby providing a spaced apart region between the widthwise arm of the O-bar and the axial end at each side of the rotor body. Each longitudinal slot has a thickness to receive two sides of adjacent unified rotor O-bar. The distance between two adjacent slots is equal to the width of each unified O-bar. Thus, each two adjacent slots receive one complete unified O-bar, consecutively. And each slot receives two sides of adjacently located unified O-bar.
This design eliminates the need of using short circuiting rings. The design has been proposed in order to feed the needs of application where motors are subjected to heavy vibrations throughout its lifespan for example high speed traction applications. These unified O-bars, essentially, are continuous rings without any connections.

Since, the design eliminated the short circuit ring, of the prior art, itself, the excessive weight of the short circuit rings during normal operating condition of the traction motor which actually the rotor bars had to bear gets nullified. Also, the thermal problem in which the rotor bars were expanding in the axial direction and the short circuit ring in the radial direction gets eliminated as the expansion of the proposed bars will only be in axial direction. This expansion can be tolerated without any consequence to the working of the rotor.
The rotor bars are short circuited in the slot portions as shown in figures 4 and 5, of the accompanying drawings, and hence, there is no need of using short circuiting rings at the periphery. With this design, the probability of rotor bar crack is very less, but even if a crack if observed in the rotor bar, the path of the current is not obstructed as the other adjacent shorted O-bar of that same slot will provide the necessary path to the current to complete its circuit.
The technical advance is provided by the elimination of resistance ring and by the following advantages:
a. reducing load and vibrations in rotor;
b. problem of rotor bar crack is reduced drastically;
c. inertia between resistance ring and rotor bar is not present, reducing bar
breakage;
d. reduction in manufacturing time and cost;
e. reduction of material cost of motor;
f. brazing process is faster as heating of resistance ring is not a requirement
in the process;
g. no overhang portion;

h. no external stress;
i. additional components eliminated; and
j. more reliable system
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. A rotor comprising a rotor body with longitudinal slots which open at its
axial ends, said rotor comprising:
a plurality of substantially rectangular strips, having two side arms (bars), of metal with rounded corners to provide unified O-bars, each of said arms being fitted into said slots, such that, each slot receives two arms corresponding to adjacent O-bars.
2. A rotor as claimed in claim 1 wherein, each of said unified O-bar have a predefined thickness and are fitted into said slots, in a longitudinal direction, on the rotor body, such that the ends of the O-bars extend beyond the axial ends of the rotor body, thereby providing a spaced apart region between the widthwise arm of said O-bar and said axial end at each side of said rotor body.
3. A rotor as claimed in claim 1 wherein, each longitudinal slot has a thickness to receive two sides of adjacent unified rotor O-bars.
4. A rotor as claimed in claim 1 wherein, the distance between two adjacent slots is equal to the width of each unified O-bar, thus, each two adjacent slots receiving one complete unified O-bar, consecutively.
5. A rotor as claimed in claim 1 wherein, said slots are circumferentially equi-distantly located throughout said rotor body.