FIELD OF THE INVENTION
This invention relates to an improved process for flow circulation of Pre-start
purging air in cast iron enclosure of TEFC (Totally Enclosed Fan Cooled) A.C.
Induction Motor installed on hazardous zones.
BACKGROUND OF THE INVENTION
Totally enclosed fan cooled (TEFC) type H-Compact A.C .Induction Motors having
Cast-iron enclosures including cooling Ribs are known as opposed to Fabricated
enclosures of conventional A.C. Induction Motors.
As per technical specification of the newly introduced Safety Standard, TEFC
Motors must be suitable for gas group IIA/IIC, zone-2 and temperature class T-
3. Apart from other statutory stipulations, it is further mandatory that enclosures
of such motors (having Cage Rotors), should not contain any explosive gas, at
the time of starting. Such guidelines emanates from the provisions of recently-
revised standards IS-6381:2004 & IEC-60079-7 (2001). The revised standards
further require that either provision for Pre-Start purging OR means for fixed gas
detection inside the motor enclosure should be arranged.
During development of a testing process, it was recognized that because of basic
chemical composition and mechanical properties, cast iron is not suitable for any
type of welding process. Therefore, prior art technique of air purging
arrangement used for welding of conventional motors can not be employed on
TEFC Motor having cast iron enclosure.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose an improved process for
flow-circulation of Pre-start purging air in cast iron enclosure of TEFC (Totally
Enclosed Fan Cooled) A.C. Induction Motor installed on hazardous zone which
satisfies increased safety norms stipulated by revised standards.
Another object of the invention is to propose an improved process for flow
circulation of Pre-start purging air in cast iron enclosure TEFC (Totally Enclosed
Fan Cooled) A.C. Induction Motor installed on hazardous zones, which eliminates
sparking during starting of the motor.
A further object of the invention is to propose an improved process for flow
circulation of Pre-start purging air in cast iron enclosure of TEFC (Totally
Enclosed Fan Cooled) A.C Induction motor installed on hazardous zones which is
provided with an inlet for purging air at Drive End side and an outlet at Non
Drive End side of the motor respectively.
SUMMARY OF THE INVENTION
According to the invention there is provided an improved process for flow
circulation of Pre-start purging air in cast iron enclosure TEFC (Totally Enclosed
Fan Cooled) A.C Induction Motor on hazardous zones. According to the
invention, a pre-start air purging device is configured with inlet/outlet purging air
selected at a location on the "End-Shield" at Drive End Side, and on the
'Terminal Box Opening Cover Plate" at Non-Drive End side respectively, for fixing
Inlet and outlet Pipe-Flange.
In order to achieve a complete purging of Hazardous gases from the motor
enclosure, said locations identified on the Motor constitute the strategic locations
for fixing Pipe-Flange connections. Thus, the inlet is provided at bottom on any
side (Drive End or Non-Drive End) and Outlet is provided at top of the motor
diagonally opposite to the Inlet. TEFC Motors are having Cast Iron enclosure with
cooling ribs over it. These cooling ribs make it difficult to provide any size of
tapped hole on Motor body for connecting the Pipe-Flange. Thus, the invention
selects said strategic locations for providing tapped holes to fix inlet and outlet
pipe flanges.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 - shows side and front elevational views of TETV type conventional
Motor with inlet and outlet Pipe-Flanges for Purging air.
Figure 2 - shows side and front elevational views of TEFC type Increased Safety
Motor with improved pre-start air purging device according to the invention.
Figure 3 - shows a Drive End side "End-Shield" with a provision for fixing Inlet
Pipe-Flange according to the invention.
Figure 4 - shows schematic of a "terminal box opening cover plate" with a
provision for fixing outlet Pipe-Flange according to the invention.
Figure 5 - shows schematic of a "Pipe-Flange" to be fixed at DE side "End-
Shield" and NDE side "Terminal Box Opening Cover Plate" for purging air
according to the invention.
DETAIL DESCRIPTION OF THE INVENTION
Figure 1 shows a typical TETV conventional Motor with fabricated type enclosure.
Motor enclosure (Stator Frame) is covered with End-Shields (2) at both ends, in
order to make Totally Enclosed Tube Ventilated (TETV) enclosure with degree of
protection as per IP-55 standards.
Figure 1 also shows locations of the Purging Pipe-Flanges (3, 4). An inlet Pipe-
Flange (3) is fitted at (Bottom) Non-Drive End side and an Outlet Pipe-Flange (4)
is fitted at (Top) Drive-End side.
These Inlet and Outlet Pipe-Flanges (3, 4) are welded on the Motor body at
strategic locations, so as to achieve complete Purging of hazardous gases from
motor enclosure as per prior art.
Figure 2 shows a typical TEFC Motor with Cast iron Frame (6) having ribs over it.
Motor body in this case, is covered by Cast iron End-Shields (7) at both ends. It
is known that ribs always obstruct any type of drilling and tapping operation on
the Motor enclosure.
Figure 2 also shows, Drive-End side "End-Shield" (7) and Non-Drive End side
"Terminal Box Opening Cover" (8), wherein tapped holes of desired size at
strategic locations (5, 9), are provided, for fixing an inlet and outlet Pipe-Flange
(10) according to the invention to achieve protection level as stipulated in
revised standards IS-6381-2004 & IEC-60079-7 (2001).
As per the invention, a provision (5) for fixing the Inlet Pipe-Flange (10) is
provided at the bottom of the End-Shield (7) and that for the Outlet Pipe-Flange
(10) is provided at top (9) of the enclosure, in order to ensure zero accumulation
of hazardous gases and complete purging of the Motor enclosure.
WE CLAIM:
1. An improved process for flow circulation of Pre-start purging air in cast
iron enclosure TEFC (Totally Enclosed Fan Cooled) A.C. Induction
Motor installed on hazardous zones, the improvement is characterized
by the steps of:
selecting a first strategic location of first tapped hole (5) on drive end
side End-Shield (7) of the cast iron stator frame (6), for fixing a first
end of Pipe-Flange (10); and
selecting a second strategic location of a second tapped hole (9) on
non-drive end side Terminal Box Opening Cover plate (8) of the motor
body for fixing a first end of the another Pipe-Flange (10), wherein
the inlet (5) for purging air is provided at bottom of both side "End-
Shields" (7) and the outlet (9) is provided at top on the "Terminal
Box Opening cover plate" (8), for smooth removal of hazardous
gases from the motor enclosure by the purging air.
2. The process as claimed in claim 1, wherein a single pipe member (10) is
configured with two flanges exhibiting a "J" shape.

ABSTARCT

The invention relates to an improved process for flow circulation of Pre-start
purging air in cast iron enclosure TEFC (Totally Enclosed Fan Cooled) A.C
Induction Motor installed on hazardous zones, the improvement is characterized
by the steps of selecting a first strategic location of a first tapped hole (5) on
drive end side End-Shield (7) of cast iron stator frame (6) for fixing a first end of
Pipe-Flange (10); and selecting a second strategic location of a second tapped
hole (9) on non-drive end side Terminal Box Opening Cover plate (8) of the
motor body for fixing first end of the another Pipe-Flange (10), wherein the inlet
(5) for purging air is provided at bottom of both side "End-Shields' (7) and the
outlet (9) is provided at top and on the "Terminal Box Opening Cover plate" (8)
for smooth removal of hazardous gases from the motor enclosure by the purging
air.