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
Closed air circuit air cooled high voltage electric motor
APPLICANTS
Crompton Greaves Limited, CG House, Dr Annie Besant Road, Worli, Mumbai - 400 030, Maharashtra, India, an Indian Company
INVENTOR
Singh Pravin Rajendra, Crompton Greaves Limited, Machine 7 Division, D-5, Industrial Area, Mandideep, Bhopal 462046, 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 a closed air circuit air cooled high voltage electric motor.
BACKGROUND OF THE INVENTION
A closed air circuit air cooled high voltage or high tension electric motor includes a forced ventilation or cooling arrangement comprising a shell and tube heat exchanger mounted on the enclosure of the electric motor. The shell of the heat exchanger is connected to the enclosure of the electric motor through openings provided in the enclosure. An fan is mounted on the non-drive end of the motor shaft and disposed within a fan cover fitted to the corresponding end of the shell of the heat exchanger. The fan cover comprises an inner chamber and an outer chamber separated by a partition wall extending radially along the fan. The inner chamber communicates with the tubes of the heat exchanger and is connected to the outer chamber through an air inflow opening provided in the partition wall. The outer chamber is provided with an air inlet opening at the top of the end wall thereof extending in a spaced apart relationship with the partition wall. The air inlet opening is provided with a wire mesh filter or screen. During operation of the electric motor, hot air being generated within the enclosure of the electric motor is circulated through the shell of the heat exchanger. The fan rotates with the motor shaft and sucks in atmospheric air axially through the air inlet opening at the top of the end wall of the outer chamber and the air inflow opening in the partition wall of the fan cover and throws up the cooling air radially into the tubes of the heat exchanger. Cooling air passing through the tubes takes away the heat of the hot air being circulated in the shell of the heat exchanger so as to keep the motor cooled. The amount of atmospheric air entering the fan cover through the air inlet opening is limited. Besides, the air entering

the outer chamber of the fan cover has to travel a distance in the space between the end wall of the outer chamber and the partition wall before entering the inner chamber because of which there is a pressure drop. As a result of all this, the cooling efficiency of the motor is reduced. During operation of the fan, noise is generated due to air cutting by the fan blades. This noise travels out into the atmosphere through the air inflow opening in the partition wall and the air inlet opening in the end wall of the outer chamber creating a lot of noise during operation of the electric motor.
OBJECTS OF THE INVENTION
An object of the invention is to provide a closed air circuit air cooled high voltage
electric motor, which has increased cooling efficiency.
Another object of the invention is to provide a closed air circuit air cooled high voltage electric motor, which has reduced noise level.
DETAILED DESCRIPTION OF THE INVENTION
According to the invention there is provided a closed air circuit air cooled high voltage electric motor including a forced ventilation arrangement comprising a shell and tube heat exchanger mounted on the enclosure of the motor, the shell of the heat exchanger being connected to the enclosure of the motor through openings provided in the enclosure, a fan mounted on the motor shaft at the non-drive end thereof and disposed in a fan cover mounted to the corresponding end of the shell of the heat exchanger and communicating with the tubes of the heat exchanger, the outer wall of the fan cover comprising an air inflow opening concentrically with the motor shaft, the air inflow opening being provided with a cylindrical baffle compnsing an inner portion extending

inwardly and an outer portion extending outwardly and a muffler chamber comprising an end wall and a side wall mounted to the outer wall of the fan cover, a first air inlet opening provided in the end wall of the muffler chamber at the top thereof, an outer baffle inwardly extending from the end wall at the bottom of the first air inlet opening spaced apart from the outer portion of the cylindrical inner baffle, the outer surface of the outer wall of the fan cover facing the first air inlet opening being provided with a first noise absorbent material pad, the sidewall of the muffler chamber being provided with a second air inlet opening, the outer surface of the outer portion of the inner baffle facing the second air inlet opening being provided with a second noise absorbent material pad, the first and second air inlet openings being provided with a wire mesh filter.
The following is a detailed description of the invention with reference to the accompanying drawings, in which the sole Fig 1 comprises a schematic view of a closed air circuit air cooled high voltage electric motor according to an embodiment of the invention. The closed air circuit air cooled motor 1 as illustrated in Fig 1 of the accompanying drawings includes a forced ventilation or cooling arrangement 2 comprising a shell and tube heat exchanger 3 mounted on the enclosure 4 of the motor. The shell 5 of the heat exchanger is connected to the enclosure of the motor through openings 6 provided in the enclosure. A fan 7 is mounted on the motor shaft 8 at the non-drive end thereof and is disposed in a fan cover 9 mounted to the shell of the heat exchanger at the corresponding end thereof. The fan cover communicates with the tubes 10 of the heat exchanger and comprises an air inflow opening 11 in the outer wall thereof concentrically with the motor shaft. 12 is a cylindrical inner baffle provided in the air inflow opening and comprising an inner portion 12a extending inwardly and an outer portion 12b extending outwardly. 13 is a muffler chamber comprising an end wall 13a

and a sidewall 13b fitted to the outer wall of the fan cover. 14 is a first air inlet opening provided at the top of the end wall of the muffler chamber and provided with a wire mesh filter or screen 14a. 15 is an outer baffle extending inwardly from the end wall of the muffler chamber at the bottom of the air inlet opening 14. The outer surface of the outer wall of the fan cover facing the air inlet opening 14 is provided with a noise absorbent material pad 16 which is made of a noise absorbent material like foam. The outer baffle is in spaced apart relationship with the outer portion of the inner baffle. The sidewall of the muffler chamber is provided with a second air inlet opening 17 at the bottom thereof. The second air inlet opening is provided with a wire mesh filter or screen 17a. The outer surface of the outer portion of the inner baffle facing the second air inlet opening is provided with a noise absorbent material pad 18 which is made of a noise absorbent material like foam. 19 is an inspection opening in the end wall of the muffler chamber provided with the end wall of the muffler chamber and having an inspection cover 20 bolted to the end wall.
During operation of the electric motor, hot air being generated within the enclosure of the electric motor is circulated in the shell of the heat exchanger over the tubes extending along the length of the shell of the heat exchanger. The fan rotates with the motor shaft and sucks in atmospheric air axially through the air inlet opening 14 and radially through the air inlet opening 17. Atmospheric air enters the fan cover via the air inflow opening 11 in the outer wall of the fan cover and the atmospheric air is thrown up radially into the tubes of the heat exchanger. Atmospheric air flows through the tubes of the heat exchanger and takes away the heat of the hot air being circulated in the shell of the heat exchanger. According to the invention cooling atmospheric air is sucked into the fan cover axially and radially through the respective air inlet openings. A larger volume of

atmospheric air is sucked into the fan cover and thrown up radially into the tubes of the heat exchanger by the fan so as to increase the cooling efficiency of the motor of the invention. The flow of the incoming air is dampened by the noise absorbent material pads and regulated by the outer baffle and inner baffle. The air inflow opening 11 in the outer wall of the fan cover is very large and the distance that the incoming air has to travel to enter the fan cover is very limited. As a result of this also air inflow is high so as to increase the cooling efficiency of the motor of the invention. The wire mesh filters or screens prevent foreign particles in the incoming air like dust particles entering the muffler chamber and fan cover. Noise created by the fan due to air cutting travels out through both the air inlet openings. The noise is split and let out in the axial direction and in the radial direction through the respective inlet openings and is dampened by the inner baffle and outer baffle. Noise is also absorbed by the noise absorbent material pads. Therefore, noise of operation of the motor is considerably reduced. Because of the inspection opening access into the fan cover is possible without dismantling the muffler chamber. The inspection opening and cover are, however, optional and the end wall of the muffler chamber may be without the inspection opening and inspection cover.
Noise level and pressure drop of a conventional closed air circuit air cooled motor and a closed air circuit air cooled motor of the invention of 350 kW, 11000 V and synchronised speed of 3000 RPM were measured and the results were as shown in the following Table

Table

Conventional motor Motor of the invention
Noise level at distance of lm from motor and at shaft centre height of motor 90dBA 87dBA
Pressure drop from air inlet opening to fan blade 5mm of water gauge 2.5mm of water gauge
The Table clearly shows the reduced noise level and pressure drop of the motor of the invention.

We claim :
1) A closed air circuit air cooled high voltage electric motor including a forced ventilation arrangement comprising a shell and tube heat exchanger mounted on the enclosure of the motor, the shell of the heat exchanger being connected to the enclosure of the motor through openings provided in the enclosure, a fan mounted on the motor shaft at the non-drive end thereof and disposed in a fan cover mounted to the corresponding end of the shell of the heat exchanger and communicating with the tubes of the heat exchanger, the outer wall of the fan cover comprising an air inflow opening concentrically with the motor shaft, the air inflow opening being provided with a cylindrical baffle comprising an inner portion extending inwardly and an outer portion extending outwardly and a muffler chamber comprising an end wall and a side wall mounted to the outer wall of the fan cover, a first air inlet opening provided in the end wall of the muffler chamber at the top thereof, an outer baffle inwardly extending from the end wall at the bottom of the first air inlet opening spaced apart from the outer portion of the cylindrical inner baffle, the outer surface of the outer wall of the fan cover facing the first air inlet opening being provided with a first noise absorbent material pad, the sidewall of the muffler chamber being provided with a second air inlet opening, the outer surface of the outer portion of the inner baffle facing the second air inlet opening being provided with a second noise absorbent material pad, the first and second air inlet openings being provided with a wire mesh filter.
2) The motor as claimed in claim 1, wherein the end wall of the muffler chamber comprises an inspection cover fitted over an inspection opening provided in the end wall.

3) The motor as claimed in claim 1 or 2, wherein the noise absorbent material pad comprises foam.
Dated this 5th day of March 2009