Note: Descriptions are shown in the official language in which they were submitted.
1 164032
1 CWL1076
TOTALLY ENCLOSED FAN COOLED MOTOR
BACKGROUND OF THE INVENTION
Field of the Invention:
The invention relates to improved cooling of
dynamoelectric machines, particularly those of the totally
enclosed fan cooled type.
Description of the Prior Art:
Totally enclosed machines are used where isolation
between internal parts and the environment is desirable or
necessary. Since there is no flow of external air through
the machine, such machines, particularly in larger sizes such
as several hundred horsepower and above, are in most cases
temperature limited in their rating~ This is so even with
external fan cooling.
Active machine parts of copper and magnetic steel
are capable of developing much higher power than -the power
that can be prod~ced continuously and still be cooled to a
safe temperature. The maximum safe temperature is usually
d0termined by the type of insulation in the machine. Notwith-
stand~ng improvement in insulation, it is still desirable to
improve the heat transfer from the acti~e parts to the exte~ior.
One of the most important heat transfer paths is
that from the stator copper to the core, from the core to the
1 16~0:}~
frame, and from the frame to the outside air. The effectiYe-
ness of this ~ath depends upon transfer of heat from the frame
to the outside air.
SUMMARY OF THE~ NTION
An object of this invention is to provide an improYed
exterior fan configuration, to improve transfer of heat from
the frame to the outside air and also desirable for lowering
the temperature of the rear bearing which is important for
large motors.
Briefly, the improvements in accordance w~th this
invention include a pair of similar exterior fans which move
external air axially over the machine from both ends through
hoods to cause an essentially equal flow over the machine from
each end to the midpoint of the machine.
BRIEF DESCRIPTION OF THE DRA~INGS
_
Figure 1 is a longitudinal view, partly in elevation
and partly in section, of a dynamoelectric machine in accordance
with one embodiment of the invention; and
Figure 2 is an en& view, partly in section of the
machine of Fig. 1.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The invention will be described with reference to an
embodiment that is an ac motor of the totally enclosed fan
cooled type. The embodiment described is one that has been
made in ~arious sizes for operation in the range of from about
200 horsepower to about 600 horsepower.
Referring to Figs. 1 and 2, the motor in accordance
with ~his invention includes a frame 10 that has a generally
cylindrical configuration and within which is affixed the stator
1 ~64()~
core 12, such as one made of a plurali~y of stacked lamina-
tions, with a winding 13 therearound. A rotor 1~, such as
one also made of a stack of laminations, is mounted on a
shaLft 16. End brackets 1~ and 19 (sometimes called end
bells) cooperate with the cylindrical frame portion 10 to
tot;ally enclose the rotor and stator. The shaft 16 extends
through the end brackets 1~ and 19 and is rotatably supported
by suitable bearings.
The frame 10 is characterized by a cylindrical wall
22 that is essentially unbroken and makes direct contact ~ith
essentially all of the outer surface of the stator core 12.
The frame 10 is also characterized by a plurality of axially
extending heat dissipating fins 23 extending radially there-
from.
The machine in accordance with this invention
comprises front and rear external fans 25 and 26, respectively,
substantially identical but smaller than the normal single fan
mounted on the shaft 16 each driving air axially over the end
brackets and frame. The front external fan 25 is conventional
in totally enclosed fan cooled motors. In accordance with
this invention, a rear external fan 26 is added to assist motor
cooling and is also helpful for cooling the rear bearing. The
external fans 25 and 26 are partially enclosed within hoods
27 and 2~ which have vented end faces. The hoods 27 and 2~
engage the end portions of fins 23 but retain openings between
them and the ~rame exterior for air flow as shown by arrows
42 and 44. The air from the fans 25 and 26 will therefore
flow over and between the fins 23 on the frame outer surface
providing improved heat transfer. The means for joining the
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It
various members are not in themselves a part of ~his invention
and are not shown in detail.
In an alternative arrangement, a barrier ~2 at the
ce!ntre of frame 10, shown in dotted lines, prevents the can-
ce!llation of air velocity at the centre of the frame 10 by
deflecting both air streams radially outwards.
On a conventional totally enclosed fan cooled motor
with a single external blower 25, the velocity of the external
cooling air between the fins 23 decreases as the air moYes
towards the rear end of the frame 10. This reduces heat
dissipation at the rear end. The external blower 26 on the
rear end of the motor effectively increases the heat dissipa-
tion at the rear end by virtue of the high air velocity at
this end. Thus, with equal heat dissipation at each end, a
more even temperature distribution and higher horsepower
rating is obtained. The construction has the additional
advantage of permitting an equal cooling with reduced noise
because of the smaller fan required or increased cooling with
no increase of noise.
~hile the invention has been described in a single
form only, it will be apparent that numerous changes may be
made without departing from its true scope. Preferably,
construction is such as to permit identical components such
as fans and hoods at each end and also to conform to standard
motor frame sizes.
