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 INVENTION
Improved totally enclosed fan cooled AC induction motor
INVENTOR
Pandya Avnish Datt, Design Department, Motor Division (Ml), Crompton Greaves Ltd,
D-5 Industrial Area, Mandideep, Bhopal - 462 046, Madhya Pradesh, India, Indian
national
APPLICANTS
Name : CROMPTON GREAVES LIMITED
Nationality : Indian Company
Address : CG House, Dr Annie Besant Road, Worli, Mumbai 400025, Maharashtra, India
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 INVENTION
This invention relates to an improved totally enclosed fan cooled AC induction motor.
BACKGROUND OF INVENTION
During operation of electric motors substantial heat is generated in the motors because of the resistance to the flow of electric current through the windings of the stator of the motors and friction between the components of the motors like the shaft and bearings. In order to improve motor output and durability (life), it is essential that the heat being generated in the motor is efficiently removed. Basically based on the cooling arrangement, the AC induction motors are generally classified into various types as totally enclosed fan cooled (TEFC), totally enclosed tube ventilated (TETV), closed air cool air (CACA) and closed air cooled water (CACW).
A totally enclosed fan cooled AC induction motor comprises a stator located within the stator frame in close contact therewith. The motor shaft with the rotor mounted on it, is disposed within the stator and rotatably supported in the end shields at the drive end and non-drive end of the motor using bearings. The motor further comprises a drive end cover and a non-drive end cover supported on the frame of the motor. An external fan is located within the drive end cover or non-drive end cover and mounted on the respective end of the motor shaft. Air pockets are provided externally along the length of the stator frame in spaced apart relationship and fins are provided on the stator frame externally between the air pockets. The stator frame is provided with openings at the ends communicating with the air pockets which are otherwise air tight. The motor further comprises an internal fan disposed within the motor at one end thereof and mounted on
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the motor shaft and axial air vents provided in the rotor along the length thereof. During operation of the motor, both the internal fan and external fan rotate with the motor shaft. Air getting heated up in the motor during operation of the motor is blown into the air pockets by the internal fan through the openings in the stator frame at the respective end. While passing through the air pockets, heat of the air is conducted and radiated away to the surroundings by the walls of the air pockets and the cooled air returns into the motor through the openings in the stator frame at the opposite end thereof. The air in the motor is thus recirculated in the motor by the internal fan via the clearance between the rotor and stator, axial air vents in the rotor, openings at the ends of the stator frame and the air pockets thereby cooling the motor. Simultaneously heat being generated in the motor is also conducted to the fins between the air pockets and the fins in turn radiate the heat to the surroundings. The external fan rotating with the motor shaft blows cold air (atmospheric air) onto the fins and the air pockets so as accelerate radiation of the heat and cooling of the motor. There is scope for improving the cooling efficiency of the motor so as to increase its output and life and the invention addresses this problem.
OBJECTS OF INVENTION
An object of the invention is to provide an improved totally enclosed fan cooled AC induction motor which has increased cooling efficiency so as to increase the motor output and life.
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Another object of the invention is to provide an improved totally enclosed fan cooled AC induction motor, which is simple in construction and is cost effective.
Another object of the invention is to provide an improved totally enclosed fan cooled AC induction motor which is without any basic alterations or constructional changes in a totally enclosed fan cooled AC induction motor or without any size increase of the motor.
DETAILED DESCRIPTION OF INVENTION
According to the invention there is provided an improved totally enclosed fan cooled AC induction motor comprising a plurality of open ended heat transfer tubes located spacedly within each of the air pockets along the length thereof, the heat transfer tubes opening into the drive end cover and non-drive end cover of the motor at the ends thereof, the stator frame being provided with openings at the ends for communication with the air pockets which are otherwise air tight.
The following is a detailed description of the invention with reference to the accompanying drawings, in which
Figs 1 is elevation of the improved totally enclosed fan cooled AC induction motor according to an embodiment of the invention;
Fig 2 is drive end side view of the induction motor of Fig 1; and
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Fig 3 is section at A-A in Fig 2.
The improved totally enclosed fan cooled AC induction motor 1 as illustrated in Figs 1 to 3 of the accompanying drawings comprises a stator 2 located within the stator frame 3 in close contact therewith. The stator windings are marked 4. The motor shaft 5 with the rotor 6 mounted on it, is disposed within the stator and rotatably supported in the end shields 7 and 8 motor at the drive end and non-drive end of the motor using bearings 9a and 9b, respectively. The motor is provided with a drive end cover 10 and a non-drive end cover 11 supported on the frame of the motor. An external fan 12 is located within the drive end cover and is mounted on the drive end of the motor shaft. Air pockets 13 are provided externally along the length of the stator frame in spaced apart relationship. Fins 14 are provided on the stator frame externally between the air pockets. The stator frame is provided with openings 15 at the ends communicating with the air pockets which are otherwise air tight. The motor further comprises an internal fan 16 disposed within the motor at the drive end thereof and mounted on the motor shaft. Axial air vents provided in the rotor along the length thereof are marked 17. A plurality of open ended heat transfer tubes 18 are located spacedly within each of the air pockets along the length thereof. The heat transfer tubes open into the drive end cover and non-drive end cover of the motor at the ends thereof. The heat transfer tubes are made of good thermal conductor materials such as copper, stainless steel, ERW (electric resistance weld) steel or aluminum.
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During operation of the motor both the internal fan and external fan rotate with the motor shaft. The internal fan throws the air in the motor into the air pockets via the openings in the stator frame at the drive end and the air returns to the motor via the openings in the stator frame at the non drive end. The internal fan thus recirculates the air in the motor via the clearance between the rotor and stator, axial air vents in the rotor, openings at the ends of the stator frame and the air pockets. The external fan blows cold air (atmospheric air) over the fins and the air pockets and also through the heat transfer tubes located within the air pockets. While the air getting heated up in the motor during operation of the motor passes through the air pockets the heat of the air is transferred to the cold air passing through the heat transfer tubes located within the air pockets. The air passing through the heat transfer tubes in turn gets heated up and flows out into the surroundings via the non-drive end cover thereby taking away the heat being generated in the motor. Simultaneously the walls of the air pockets also conduct and radiate away the heat of the hot air passing through the air pockets. Cooled air returns to the motor via the openings in the stator frame at the non-drive end of the motor. The heat being generator in the motor is also conducted to the fins between the air pockets and the fins in turn radiate the heat to the surroundings. Cold air (atmospheric air) being blown on to the fins and the air pockets by the external fan help to accelerate radiation of the heat and cooling of the motor.
According to the invention the heat transfer tubes spacedly located within the air pockets provide considerably increased additional surface area of contact between the hot air travelling through the air pockets and the cold air (atmospheric air) passing through the
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heat conductor tubes so as to increase substantially the heat transfer from the hot air to the cold air and increase the cooling efficiency of the motor considerably. The additional cooling provided by the provision of the heat transfer tubes in addition to the fins and walls of the air pockets is substantial. The improved cooling efficiency of the motor is achieved by the judicious utilisation of the spaces in the air pockets with the provision of the heat transfer tubes and without any basic alterations or constructional changes in the configuration of the totally enclosed fan cool AC induction motor. The heat transfer tubes do not significantly increase the cost of the motor. Therefore, realization of increased cooling efficiency of the motor is without any increase in the size of the motor and without any significant increase in the cost of the motor. Because of the increased cooling efficiency achieved by the invention, the output and life of the motor are increased.
Comparative studies were carried out with totally enclosed fan cooled (TEFC) AC induction motor and improved TEFC AC induction motor of the invention and the results were as shown in the following Table 1. The rating of the motors was 690 V, 4P, 500KW and the heat conductor tubes used in the improved motor were made of copper.
Table 1

AC induction motor Stator Temperature rise in °C
Conventional TEFC AC induction motor 92.73
Improved TEFC AC induction motor 71.96
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It is quite clear from the Table 1 that the cooling efficiency of the improved motor of the invention increased considerably for the same power output of 500KW.
It was also found that the temperature rise in the stator of 600KW improved motor of the invention was only 86.71°C, less than that of the 500KW conventional induction motor.
It is to be clearly understood that the number of air pockets and the number of heat transfer tubes within the air pockets can vary. The external fan and the internal fan can be mounted at the non-drive end of the motor in which case the forward flow of air within the motor and through the air pockets will be in the direction of the drive end of the motor. There can be two internal fans each mounted at the drive and non-drive end of the motor shaft. Such variations of the invention are obvious to those skilled in the art and are to the construed and understood to be within the scope of the invention.
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We Claim
1. An improved totally enclosed fan cooled AC induction motor comprising a plurality of open ended heat transfer tubes located spacedly within each of the air pockets along the length thereof, the heat transfer tubes opening into the drive end cover and non-drive end cover of the motor at the ends thereof, the stator frame being provided with openings at the ends for communication with the air pockets which are otherwise air tight.
2. An improved AC induction motor as claimed in claim 1, wherein the heat transfer tubes are made of good thermal conductor materials like copper, stainless steel, electric resistance weld steel or aluminium.
Dated this 14th day of March 2007.

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Abstract
An improved totally enclosed fan cooled AC induction motor (1) comprising a plurality of open ended heat transfer tubes (18) located spacedly within each of the air pockets (13) along the length thereof The heat transfer tubes open into the drive end cover (10) and non-drive end cover (11) of the motor at the ends thereof The stator frame (3) is provided with openings (15) at the ends for communication with the air pockets which are otherwise air tight (Fig 3).