FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
As amended by the Patents (Amendment) Act, 2005
&
The Patents Rules, 2003
As amended by the Patents (Amendment) Rules, 2006
COMPLETE SPECIFICATION
(See section 10 and rule 13)
TITLE OF THE INVENTION
Air cooled AC induction motor
APPLICANTS
Crompton Greaves Limited, CG House, Dr Annie Besant Road, Worli, Mumbai 400 030, Maharashtra, India, an Indian Company
INVENTOR
Chatterjee Chayan, Crompton Greaves Limited, Machines 7 Division, D-5, Industrial Area MPAKVN, Mandideep - 462 046, Madhya Pradesh, India, an Indian national
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
This invention relates to an air cooled AC induction motor
BACKGROUND OF THE INVENTION
Air cooled AC induction motors are generally totally enclosed heavy duty motors rugged and robust in construction. They are also very versatile in their use and are used for a variety of applications. For example, they are used in different kinds of heavy duty pumps like boiler feed pumps, recirculating pumps or condensate extraction pumps or in heavy duty fans like induced draft fans or forced draft fans or in crushers, grinders, compressors, cutters or shredders, conveyors, mixers or agitators or rolling mills.
An air cooled AC induction motor comprises a stator and a rotor mounted on a shaft and rotatably disposed within the stator. The stator is located within a stator frame having a pair of circular openings, one at each end of the stator frame. The stator frame also comprises a plurality of spaced reinforcing inner plates arranged within the stator frame along the length thereof. The reinforcing plates each is provided with a circular opening. The openings in the reinforcing plates and the openings at the ends of the stator frame match with one another and are aligned. The stator comprises a cylindrical stator body and a stator winding inserted within the stator body. The stator winding comprises a pair of overhangs protruding out of the stator body, one overhang protruding out towards the drive end of the motor and the other overhang protruding out towards the non-drive end of the motor. Air vents or air ducts are provided in the stator body and in the overhangs in order to facilitate air circulation in the stator and to keep the stator cooled.

It is very essential that the temperature rise in the stator winding is kept within the permissible limits so as to prevent burning of and damage to the winding due to excessive heat generated in the winding and to ensure efficient and trouble free performance of the motor. In order to sense the temperature in the winding, a plurality resistance temperature detectors (RTDs) are located in the winding and the lead wires of the RTDs are terminated on a common terminal which is located at the inner face of the overhang of the stator winding at the drive end of the motor at the Outer diameter of the overhang. The common terminal is also connected to a resistance temperature measuring device located at the drive end of the motor by lead wires. The lead wires connecting the common terminal to the resistance temperature measuring device extend to the resistance temperature measuring device over the overhang at the drive end of the stator.
As the lead wires connecting the common terminal to the resistance temperature device are extending over the overhang at the drive end of the motor, they block the air vents in the overhang at the drive end of the motor thereby reducing the air flow through the overhang at the drive end of the motor and the cooling efficiency of the stator and the motor. Further the outer diameter of the overhangs of the stator winding and the diameter of the circular openings in the reinforcing plates and at the ends of the stator frame are almost equal and matching. As the common terminal is located at the inner face of the overhang at the drive end of the motor at the outer diameter of the overhang, while inserting the stator in the stator frame with the overhang at the drive end of the motor as the leading edge or front edge of the stator as is always required and as is always the case, there are chances for the common terminal to hit against the sidewalls of the circular openings in the reinforcing plates and at the ends of the stator frame and get damaged. In case of damage to the common terminal, a fresh common terminal is

required to be fixed in position at the inner face of the overhang at the drive end of the stator resulting in wastage of material and increasing the cost of manufacture of the stator and also assembly time of the stator.
DETAILED DESCRIPTION OF THE INVENTION
According to the invention there is provided an air cooled AC induction motor comprising a stator and a rotor mounted on a shaft and rotatably disposed within the stator, the stator being located within a stator frame having a pair of circular openings, one at each end thereof, the stator frame further having a plurality of spaced reinforcing inner plates arranged within the stator frame along the length thereof, each of the reinforcing inner plates having a circular opening, the circular openings in the reinforcing inner plates and at the ends of the stator frame matching with one another and being aligned, the stator comprising a cylindrical body and a stator winding inserted within the stator body, the stator winding comprising a pair of overhangs protruding out of the stator body, one overhang protruding out towards the drive end of the motor and the other overhang protruding out towards the non-drive end of the motor and a plurality of resistance temperature detectors (RTDs) located in the winding and connected to a common terminal by lead wires, wherein the common terminal is located at the outer face of the overhang at the drive end of the motor close to the inner diameter of the overhang at the drive end of the motor and the common terminal is also connected to a resistance temperature measuring device located at the drive end of the motor by lead wires which extend directly to the resistance temperature measuring device without passing over the overhang at the drive end of the motor.

The following is a detailed description of the invention with reference to the accompanying drawings, in which the sole Fig 1 is an exploded isometric view of a stator and stator frame of an air cooled AC induction motor according to an embodiment of the invention. The stator 1 of the motor comprises a cylindrical stator body 2 and a stator winding 3 inserted within the stator body. The stator winding comprises a pair of overhangs 4, 5 protruding out of the stator body, one overhang 4 protruding out towards the drive end of the motor (not shown) and the other overhang 5 protruding out towards the non-drive end of the motor. Air vents or air ducts provided in the stator body are marked 6. Air vents or air ducts provided in the overhangs are marked 7. The stator also comprises a plurality of resistance temperature detectors or RTDs (not shown) located in the winding. The lead wires (not shown) of the RTDs are terminated on a common terminal 8 which is located at the outer face of the overhang 4 at the drive end of the motor close to the inner diameter of the overhang. The stator is located in a stator frame 9 having circular openings 10 and 11 at the ends thereof and a plurality of spaced reinforcing inner plates 12 arranged within the stator frame along the length thereof. Each of the reinforcing plates is provided with a circular opening 13. The circular openings in the reinforcing plates and at the ends of the stator frame are matching and aligned. The common terminal is also connected to a resistance temperature measuring device (not shown) by lead wires 14. The RTDs and the resistance temperature measuring device and the lead wires interconnecting the common terminal and RTDs are not shown as they are not necessary for understanding the invention. The other parts of the stator frame are also not marked and described as they are not necessary for understanding the invention.

According to the invention the common terminal is located at the outer face of the overhang at the drive end of the motor close to the inner diameter of the overhang and is connected to the resistance temperature measuring device by lead wires. The lead wires interconnecting the common terminal and resistance temperature measuring device do not pass or extend over the overhang at the drive end of the motor. Therefore, there are no chances for blockage of the air vents in the overhang at the drive end of the motor by the lead wires interconnecting the common terminal and the resistance temperature measuring device. As a result, the cooling efficiency of the stator and motor is improved. Further, since the common terminal is located at the outer face of the overhang at the drive end of the rotor close to the inner diameter of the overhang, chances for the common terminal to hit against the sidewalls of the circular openings in the reinforcing plates and at the ends of the stator frame and get damaged while being inserted in the stator frame with the overhang at the drive end of the motor as the leading edge or front edge of the stator, are avoided as there is no possibility for the common terminal to touch the side walls of the openings in the reinforcing plates and at the ends of the stator frame. As a result need for replacement of the common terminal by fresh one is avoided. No material wastage occurs and cost for fresh common terminal is avoided. Assembly time of the stator is also improved.

We Claim:
1. An air cooled AC induction motor comprising a stator and a rotor mounted on a shaft and rotatably disposed within the stator, the stator being located within a stator frame having a pair of circular openings, one at each end thereof, the stator frame further having a plurality of spaced reinforcing inner plates arranged within the stator frame along the length thereof, each of the reinforcing inner plates having a circular opening, the circular openings in the reinforcing inner plates and at the ends of the stator frame matching with one another and being aligned, the stator comprising a cylindrical body and a stator winding inserted within the stator body, the stator winding comprising a pair of overhangs protruding out of the stator body, one overhang protruding out towards the drive end of the motor and the other overhang protruding out towards the non-drive end of the.motor and a plurality of resistance temperature detectors (RTDs) located in the winding and connected to a common terminal by lead wires, wherein the common terminal is located at the outer face of the overhang at the drive end of the motor close to the inner diameter of the overhang at the drive end of the motor and the common terminal is also connected to a resistance temperature measuring device located at the drive end of the motor by lead wires which extend directly to the resistance temperature measuring device without passing over the overhang at the drive end of the motor.