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
Flame proof totally enclosed fan cooled AC induction motor
APPLICANTS
Crompton Greaves Limited, CG House, Dr Annie Besant Road, Worli, Mumbai - 400 030, Maharashtra, India, an Indian Company
INVENTORS
Desale Rajgopal and Dhokane Prakash, Technology Department, LT Motors, (M3) Crompton Greaves Ltd A6/2 MIDC Area, Ahmednagar, Maharashtra, 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
This invention relates to a flame proof totally enclosed fan cooled AC induction motor.
BACKGROUND OF THE INVENTION
Flame proof totally enclosed fan cooled (TEFC) AC inductor motors are generally used, especially in areas prone to fire hazards like coal mines. A flame proof TEFC AC induction motor comprises a rotor mounted on a shaft and rotatably disposed in a stator which is located within a motor housing. The rotor shaft is rotatably mounted in a pair of endshields fitted at the ends of the motor housing. A cooling fan is mounted at the non-drive end of the motor and enclosed in a fan cover fitted to the motor housing at the non-drive end of the motor. The motor also comprises a terminal box mounted on the motor housing. The terminal box communicates with the motor housing through an opening in the motor housing. Lead wires from the stator windings are connected to a set of terminal studs in the terminal box. Because of the totally enclosed nature of the motor, vapours being generated in the motor during working thereof get condensed when the motor is non-operative. The condensate can damage the stator and rotor windings and the insulation thereof thereby reducing the life of the stator and rotor windings. Due to presence of the condensate in the windings, shorting may also take place in the windings in case there is damage to the insulation and this can lead to explosion and accidents. In order to evaporate the condensate and maintain dry atmosphere within the motor housing, a heater coil is provided with the stator winding and the lead wires of the heater coil are connected to another set of terminal studs provided in the terminal box. The terminals corresponding to the stator and rotor windings are connected to a three phase 415 Volts 50 Hz supply. The terminals of the heater coil are connected to a single phase 230 Volts 50 Hz supply. Because of the terminals of the stator and rotor windings and the heater coil being in the same terminal box there is possibility of wrong connection of 230

Volts supply to the stator and rotor windings terminals and 415 Volts supply to the heater coil terminals. In case of wrong connections, high currents will flow through the heater coil and burn the heater coil. This will not only reduce the life of the heater coil but may also lead to explosion and accidents.
OBJECTS OF THE INVENTION
An object of the invention is to provide a flame proof totally enclosed fan cooled AC
induction motor which prevents accidents and has improved safety.
Another object of the invention is to provide a flame proof totally enclosed fan cooled AC induction motor which increases the life of the heater coil.
DETAILED DESCRIPTION OF THE INVENTION
According to the invention there is provided a flame proof totally enclosed fan cooled AC induction motor comprising a rotor mounted on a shaft and rotatably disposed in a stator which is located in a motor housing, the rotor shaft being rotatably mounted in a pair of endshields fitted at the ends of the motor housing, the stator including a heater coil, a cooling fan mounted on the rotor shaft at the non-drive end thereof and enclosed in a fan cover fixed to the non-drive end of the motor housing, a main terminal box mounted on the motor housing and communicating with the motor housing through an opening in the motor housing and an auxiliary terminal box mounted at one side of the main terminal box and communicating with the main terminal box through an opening at the said one side of the main terminal box, the main terminal box comprising main terminal studs with the lead wires of the rotor and stator windings being connected to the main terminal studs and the auxiliary terminal box comprising auxiliary terminal studs with the lead wires of the heater coil

extending through the opening in the motor housing and the opening at the said one side of the main terminal box and connected to the auxiliary terminals of the auxiliary terminal box.
The following is a detailed description of the invention with reference to the accompanying drawings, in which :
Fig 1 is a partly sectional elevation of the flame proof totally enclosed fan cooled AC induction motor according to an embodiment of the invention;
Fig 2 is a plan view of the motor of Fig 1;
Fig 3 is a crosssectional view of the auxiliary terminal box of the motor of Fig 1; and
Fig 4 is an end view of the auxiliary terminal box of the motor of Fig 1.
The flame proof totally enclosed fan cooled (TEFC) AC induction motor 1 as illustrated in Figs 1 to 4 of the accompanying drawings comprises a rotor 2 mounted on a shaft 3 and rotatably disposed within a stator 4 which is located within a motor housing 5. The stator includes a heater coil 6. The rotor shaft is rotatably held in a pair of endshields 7,7 using bearings 8,8. The endshields are fitted at the ends of the motor housing. 9 is a cooling fan mounted on the shaft at the non-drive end 10 of the motor and enclosed in a fan cover 11 fitted at the non-drive end of the motor housing. Eye bolts of the motor are marked 12 which provide a grip for lifting or otherwise handling the motor. Drive end of the motor is marked 12a. 13 is a main terminal box comprising main terminal studs 14. The main terminal box communicates with the motor housing through an opening 15 in the motor housing. Lead

wires 16 of the stator and rotor windings are connected to the main terminal studs in the main terminal box. An auxiliary terminal box 17 comprising a cupshaped chamber 17a is fitted at one side of the main terminal box. The auxiliary terminal box communicates with the main terminal box through opening 18 at the said one side of the main terminal box. The auxiliary terminal box comprises auxiliary terminal studs 18a and a mounting flange 9 laterally extending from the outer surface of the open end thereof. Lead wires 20 of the heater coil are connected to the auxiliary terminals in the auxiliary terminal box via connector terminal 21. The lead wires 20 extend into the auxiliary terminal box via the opening 15 in the motor housing and opening 18 at the said one side of the main terminal box. 22 is cover for the cup shaped chamber fitted at the open end thereof by bolts 23 tightened in mounting holes in the cover and corresponding mounting holes in the mounting flange. The mounting holes in the cover and mounting flange have not been shown in the drawings but can be very well visualized in the figures. During tightening of the bolts 23 against the cover and the mounting flange, a clearance is provided between the mounting flange and the cover to describe a flame path for the auxiliary terminal box. Shrouds 24 are formed on the cover around the bolts 23 so as to prevent accidental loosening of the bolts in case lumpy material like coals (not shown) happen to hit the bolts and tend to loosen the bolts accidentally. The bolts 23 are tightened or loosened with a tool like box spanner or alien key, which can access the bolts within the shrouds. 25 is the foot of the motor.
According to the invention lead wires of the stator and rotor windings are separately terminated in the main terminal box and a three phase 415 Volts Supply (not shown) is given to the stator and rotor windings. The lead wires of the heater coil are separately terminated in the auxiliary terminal box and a single phase 230 Volts Supply (not shown) is given to the heater coil. Therefore, possibility of any wrong connections between the 415 Volts supply

and 230 Volts supply is completely eliminated. Possibility of high currents passing through the heater coil due to the wrong connection and consequent damage to the heater coil and accidents are avoided and the life of the heater coil is increased. The clearance between the cover and the mounting flange provides increased flame path for the auxiliary terminal box. In case of any minor explosion within the auxiliary terminal box due to arcing or the like, such flame will die down by the time it reaches the end of the flame path. The shrouds will hold the bolts in position even if some lumpy materials like coal happen to hit the bolts accidently and prevent loosening of the bolts. As a result of all this, the motor of the invention has increased level of safety and prevents accidents and increases the life of the heater coil. It is understood that the auxiliary terminal box can be mounted on the motor housing separately and the lead wires 20 can be taken to the auxiliary terminal box through a separate opening in the motor housing. This will require a separate opening in the motor housing instead of the opening at the said one side of the main terminal box. Such a variation in the construction of the invention is obvious to a person skilled in the art and is to be construed and understood to be within the scope of the invention.

We claim :
1) A flame proof totally enclosed fan cooled AC induction motor comprising a rotor mounted on a shaft and rotatably disposed in a stator which is located in a motor housing, the rotor shaft being rotatably mounted in a pair of endshields fitted at the ends of the motor housing, the stator including a heater coil, a cooling fan mounted on the rotor shaft at the non-drive end thereof and enclosed in a fan cover fixed to the non-drive end of the motor housing, a main terminal box mounted on the motor housing and communicating with the motor housing through an opening in the motor housing and an auxiliary terminal box mounted at one side of the main terminal box and communicating with the main terminal box through an opening at the said one side of the main terminal box, the main terminal box comprising main terminal studs with the lead wires of the rotor and stator windings being connected to the main terminal studs and the auxiliary terminal box comprising auxiliary terminal studs with the lead wires of the heater coil extending through the opening in the motor housing and the opening at the said one side of the main terminal box and connected to the auxiliary terminals of the auxiliary terminal box.
2) The AC induction motor as claimed in claim 1, wherein the auxiliary terminal box comprises a cup shaped chamber fitted at the said one side of the main terminal box and having the auxiliary terminals studs and a cover fitted at the mouth of the cup shaped chamber.

3) The AC induction motor as claimed in claim 2, wherein the cup shaped chamber comprises a mounting flange laterally extending from the outer surface of the open end thereof and the cover is fitted to the mounting flange with bolts describing a clearance between the cover and the mounting flange to provide a flame path for the auxiliary terminal box.
4) The AC induction motor as claimed in claim 3, wherein the cover comprises a shroud formed around each of the bolts.