FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
COMPLETE SPECIFICATION
(See Section 10 and Rule 13)
TITLE OF THE INVENTION
Interior Magnet Rotors With Special Geometry For Improving The Efficiency Of The Line Start Permanent Magnet Synchronous Motors.
APPLICANT:

a. NAME: Bharat Bijlee Limited
b. NATIONALITY An Existing Indian Company incorporated under the Companies Act, 1913.
c. ADDRESS Electric Mansion, 6th Floor, Appasaheb Marathe Marg, Prabhadevi, Mumbai-400 025.
PREAMBLE TO THE DESCRIPTION:
The following specification particularly describes the invention and the manner in which it is to be performed.

DESCRIPTION
i'
INTERIOR MAGNET ROTORS WITH SPECIAL GEOMETRY FOR IMPROVING EFFICIENCY OF LINE START PERMANENT MAGNET SYNCHRONOUS MOTORS
FIELD OF THE INVENTION
The present invention relates in general to line start permanent magnet motors, and in particular to interior magnet rotors with special geometry for improving efficiency of line start permanent magnet synchronous motors.
BACKGROUND AND PRIOR ART
The Line Start Permanent Magnet Synchronous Motor (LSPMSM) combines a permanent magnet rotor that allows higher motor efficiency during synchronous operation, and an induction motor squirrel cage rotor for starting the motor by connecting it directly to an a.c. source.
The fact that the magnetizing field is generated by the permanent magnets means that no magnetizing current is drawn from the line finally leading to a much higher power "factor in full load operation and lower losses in the stator winding. The LSPMSM can replace the common induction motor in many applications, including variable torque applications (fans and pumps driving) and constant torque applications, due to their known torque-speed characteristic.
Although there are continuous efforts in improving the design of these motors, there is need in the industry for LSPMSM motors that have higher running efficiency combined with increased starting torque. The present invention seeks to fulfill this drawback of the prior art.
OBJECTS OF THE INVENTION
Accordingly, the primary object of the invention is to provide a Line Start Permanent Magnet Synchronous Motor with improved efficiency.

Another object of the invention is to provide a Line Start Permanent Magnet Synchronous Motor having improved starting torque.
Yet another object of the invention is to provide a Line Start Permanent Magnet Synchronous Motor which offers savings in materials and costs.
A further object of the invention is to provide a Line Start Permanent Magnet Synchronous Motor in the same frame size as a standard induction motor, making replacement of old inefficient motors very easy.
How the foregoing objects are achieved will be clear from the following description. In this context it is clarified that the description provided is non-limiting and is only by way of explanation.
SUMMARY OF THE INVENTION
An improved rotor of an LSPMS motor is made of aluminium die casting. It is provided with four interior permanent magnets positioned on the rotor body symmetrically around a shaft in specified slots made on the rotor body. Additional slots are incorporated in the rotor body to create high reluctance paths which improve the efficiency of the motor, by which the efficiency of the motor increases by 0.5 to 1.5 percentage points.
The rotor saves about 10-14 % copper and steel laminations in its manufacture.
The rotor fits frame sizes from 100L to 200L of standard induction motors, making replacement of old inefficient motors very easy.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The nature and scope of the present invention will be better understood from the accompanying drawings, which are by way of illustration of a preferred embodiment and not by way of any sort of limitation. In the accompanying drawings:-
Figure 1 is a perspective view of the rotor of an LSPMS motor according to the present invention.
Figure 2 is a photographic end view of the rotor shown in figure 1.

Figure 3 is a photographic perspective view of the rotor shown in figure 1.
DETAILED DESCRIPTION OF THE INVENTION
Having described the main features of the invention above, a more detailed and non-limiting description of a preferred embodiment will be given in the following paragraphs with reference to the accompanying drawings.
In all the figures, like reference numerals represent like features. Further, the shape, size and number of the devices shown are by way of example only and it is within the scope of the present invention to change their shape, size and number without departing from the basic principle of the invention.
Further, when in the following it is referred to "top", "bottom", "upward", "downward", "above" or "below", "right hand side", "left hand side" and similar terms, this is strictly referring to an orientation with reference to the apparatus , where the base of the apparatus is horizontal and is at the bottom portion of the figures. The number of components shown is exemplary and not restrictive and it is within the scope of the invention to vary the shape and size of the apparatus as well as the number of its components, without departing from the principle of the present invention.
All through the specification including the claims, the technical terms and abbreviations are to be interpreted in the broadest sense of the respective terms, and include all similar items in the field known by other terms, as may be clear to persons skilled in art. Restriction or limitation if any referred to in the specification, is solely by way of example and understanding the present invention.
The new motors have permanent magnets, embedded in a rotor. The stator three-phase winding is similar to that of standard induction motor, but modified to upgrade torques.
Referring to figure 1, the improved rotor (A) of an LSPMS motor is made of aluminium die casting. Four interior permanent magnets (1) are positioned on the rotor body symmetrically around a shaft (2) in specified slots made on the rotor body.
The improved rotor (A) has additional slots (3) incorporated in the rotor body which create high reluctance paths, the effect of which is to improve the efficiency of the

motor by 0.5 to 1.5 percentage points, depending upon the output rating. Due to this improvement, 1E4 levels of efficiency as per IEC 60034-30 are achieved. These slots are also distributed symmetrically around the axis of the rotor.
The invention also leads to material and cost savings. In order to achieve similar increase in efficiency, about 10-14 % more copper and steel laminations would have had to be added in its manufacture according to prior art practices.
Figure 2 shows in particular the innovative slots (3) in red colour.
This invention makes it possible to achieve high motor efficiencies in the same frame size as a standard induction motor of the prior art, making replacement of old inefficient motors very easy.
Motors according to the present invention have been designed and made in the output range from 1.5 kW to 30 kW in frame sizes from 100L to 200L.
ADVANTAGES:
The main non-limiting advantages of the invention are listed below.
It improves the efficiency of the LSPMS motors by 0.5 to 1.5 percentage points,
depending upon the output rating.
IE4 levels of efficiency as per IEC 60034-30 are achieved by these motors.
It leads to material and cost savings, by about 10-14 % of copper and steel
laminations.
- This invention makes it possible to achieve high motor efficiencies in the same frame sizes as standard induction motors available in the market, making replacement of old inefficient motors very easy.
- These motors can be made in the output range from 1.5 kW to 30 kW in frame sizes from 100L to200L.
The present invention has been described with reference to some drawings and a preferred embodiment purely for the sake of understanding and not by way of any

limitation and the present invention includes all legitimate developments within the scope of what has been described herein before and claimed in the appended claims.

CLAIMS We claim:
1. An improved rotor (A) of an LSPMS motor made of aluminium die casting is provided with four interior permanent magnets (1) positioned on the rotor body symmetrically around a shaft (2) in specified slots made on the rotor body, characterized in that additional slots (3) are provided in the rotor body to create high reluctance paths which improve the efficiency of the motor.
2. The improved rotor as claimed in claim 1, wherein said additional slots (3) are distributed symmetrically around said shaft (2).
3. The improved rotor as claimed in claim 1, wherein the efficiency of said motor increases by 0.5 to 1.5 percentage points.
4. The improved rotor as claimed in claim 1, wherein said rotor (A) is adapted to save about 10-14 % copper and steel laminations in its manufacture.
5. The improved rotor as claimed in claim 1, wherein said rotor (A) is adapted to fit frame sizes from 100L to 200L of standard induction motors, making replacement of old inefficient motors very easy.