Note: Descriptions are shown in the official language in which they were submitted.
Case 2967
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SPIDER BAFFLE FOR DOUBLE END VENTILATION
IN DYNAMOELECTRIC ~ACHINE
Background of the Invention
This invention relates to the ventilation of
dynamoelectric machines, and in particular it relates
to an improvement in the ventilation of a double end
ventilation machine by use of a spider baffle.
In a double end ventilation machine, air or
other cooling gas enters at both ends of the machine
and at least a portion of the air passes axially into
the spider of the rotor from both ends. There are
several spaced apart, radially extending, air passages
through the rotor core and the air which has entered
at both ends of the rotor passes through these
radially extending passages into th~e air gap and may
continue through radially extending passages in the
stator. Because the air passages are usually not
precisely uniform and may have different flow
resistances, the air flow may not be balanced. That
~0 is, more air may flow into the rotor spider from one
end than from the other, and air entering from one end
may flow through more of the radially extending air
passages than air entering from the other end. This
imbalance is often more pronounced in series flow
machines and tends to be particularly so in series
flow machines that do not have fans and therefore tend
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to move air at slower speeds. The result of this
unbalance is that portions of the rotor and stator
cores tend to be hotter on one end than on the other
end.
In addition, when the cooling air enters
from both ends, the air flow meets in the central
region where there is turbulence. This turbulence
tends to decrease the air flow in the radial ducts and
to decrease cooling.
The present invention overcomes some of
these problems by using a baffle between the spider
arms of the rotor. This baffle is positioned axially
to equalize or balance the air flow from both ends.
It is known to use various baffles in
certain types of dynamoelectric machines. For
example, in totally enclosed, fan cooled, explosion
proof motors, it is known to use a vertical baffle
between the spider arms to provide isolation between
the two ends. This provides a seal which, if an
explosion should occur~ isolates one end from the
other end and keeps the trapped gas in the end where
it was generated. There are no radially extending
passages or ducts in this type of motor.
As another example, in a mixed flow, single
end ventilation motorl it is known to use a vertical
baffle (i.e. a bafEle at right angles to the axis of
the motor shaft) at one end of the rotor to prevent
air entering the spider from the baffled end. In
other words the baffle is used to direct air flow
which enters the spider at the opposite or un-bafEled
end and then flows radially outwards through radial
ducts to join a parallel flow moving behind the stator
core.
There is no flow from opposite ends in these
examples and consequently there is no need to balance
or equalize the air flow. The baffles in the examples
do not equalize cooling.
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Summary of the Invention
The present invention is for use with double
end ventilation dynamoelectric machinesO It provides
a vertical baffle, that is a baffle extending
substantially at right angles to the motor shaft,
positioned between the spider arms, at an axial
location which provides a balanced flow of air from
both ends. The axial position of the baffle may be at
the mid-point of the rotor or approximately at the
mid-point, but not necessarily. Because the air flow
paths from each end are not always symmetrical and
identical, the location for the bafEle, in order to
balance the flow, may be displaced from the
mid-point. While the use of a plain vertical baffle
will also reduce pressure drop which would otherwise
occur where the oppositely directed air streams meet,
the baffle may be shaped on both sides to further
reduce pressure drop.
It is therefore an object of the invention
to provide an arrangement for improved cooling in a
double end ventilation dynamoelectric machine which
balances the air flow from each end.
It is another object of the invention to
provide a baffle between the arms of the spider of a
rotor in a double end ventilation dynamoelectric
machine for balancing or equalizing the flow of
cooling gas.
~ ccordingly there is provided in a double
end ventilation dynamoelectric machine having a rotor
comprising a rotor shaft, a spider mounted on said
rotor shaft and supporting rotor laminations forming a
rotor core, said laminations being spaced apart in
groups to provide radially extending ventilation
passages between adjacent groups, and axially
extending passages in said spider communicating at
each end with an air inlet and communicating with said
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radially extending ventilation passages, the
improvement comprising a baffle extending in a radial
direction between said shaft and said core and located
axially at a position providing a substantially equal
flow of air from each air inlet.
Brief Description of the Drawin _
The invention will be described with
reference to the drawings in which,
Figure 1 is a sectional view of a prior art
motor showing an unhalanced flow of air,
Figure 2 is a sectional view of a similar
electric motor having a vertical baffle according to
the invention,
Figure 3 is a plan view of one section of a
vertical baffle, and
Figures 4A and 4B are cross-sectional views
of two embodiments or forms of baffle taken along
line 4-4 of Figure 3.
Description of the Preferred Embodiment
Referring first to Figure 1, there is shown
a sectional view of a double end ventilated electric
motor having a stator 10 and a rotor 11. Rotor 11
comprises a shaft 12 having a spider 14 which
comprises a plurality of axially extending arms fixed
to shaft 12. The spider arms extend in a radial
direction from shaft 12 to support a plurality of
rotor laminations 15 which form the rotor core. The
spider 14 provides axially extending passages between
the shaft 12 and the rotor laminations 15 for the
circulation of cooling gas. The rotor laminations 15
are spaced apart in groups with radially extending
ventilation passages 16 between adjacent groups. The
laminations 15 have spaced peripheral slots to receive
conductor bars 17 which extend axially from end to end
and project beyond the laminations 15 where they are
joined to end rings 18 and 20. Rotor flanges 21
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and 22 hold laminations 15 in place on shaft 12
between a shoulder 19 on spider arms 14 and a rotor
ring l9A welded to the spider arms 14.
The stator 10 comprises stator
laminations 23 spaced apart in groups with radially
extending ventilation passages 24 between adjacent
groups. The ventilation passages 24 are shown aligned
with the ventilation passages 16, however the passages
24 and 16 can be offset with one another to reduce the
noise generated by the air passages or ducts when the
motor is running. Offset passages reduce the noise
level but this also tends to reduce air flow.
The stator laminations 23 are held in
position on stator frame 25 by outside space blocks 26
and 27 and stator flanges 28 and 30. The stator
laminations 23 have radially spaced slots at their
radially inner edge to receive stator windings 31
which have end turns shown as 32 and 33. The stator
winding connections are shown at 34. The stator frame
25 includes bracket covers 35 and 36, brackets 37 and
38 and bearings 40 and 41.
Air inlet passages 42 and 43 are formed
generally by frame 25 with bracket cover 35 and
intermediate frame plate 44 on one side and by frame
25 with bracket cover 36 and intermediate frame plate
45 on the other side. The outlet ventilation passages
for air moving out of radial air passages 24 is
between intermediate frame plates 44 and 45.
In Figure 1 the airflow, or flow of cooling
gas, is indicated by arrows for a very unbalanced flow
condition for purpose of illustration. In Figure 1
the major air flow is shown entering through air inlet
passage 43. In this instance the flow ls so
unbalanced that air from inlet 43 passes through all
of the ventilation passages 16 and 24 thereby
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virtually excluding the air entering a:ir inlet passage
42 from cooling the rotor or stator. ~hile this
condition would be extreme, the effects of unbalanced
conditions which are not so extreme will be
indicated in subsequent examples.
Referring now to Figure 2, where like parts
have the same designation numbers, a vertical baffle
46 has been added between the arms of spider 14. The
baffle 46 is not necessarily located axially at the
mid-point of the rotor core, but is located at an
axial position where the air flow at air inlet
passages 42 and 43 is balanced or equal. This
achieves a more even cooling of the rotor and stator
cores. It also prevents the mixing of the air flowing
from either end and helps to reduce turbulence.
The use of a baffle 46 results in many cases
in an increase in air flow. For example, on a large,
series ventilated, high speed motor (4500 H.P. and
1800 RPM) the measured air flow through the motor
before a baffle was installed was 7520 cubic ft./min.
or cfm. After a baffle was installed the measured air
flow increased to 9478 cfm. The windage losses
dropped by approximately one kilowatt after the baffle
was installed.
As another exampie, on a smaller, slower
speed motor having no rotor fans (350 Il.P. and 450
RPM) the measured airflow through the motor without a
baffle was 927 cfm. After a baffle was installed the
air flow increased to 988 cEm. While the airflow
increased with improved cooling, the windage losses
also showed a slight increase which appears to be
because of the increased air flow.
It is believed that the increase in air flow
when a baffle is installed as described, may be
explained as follows. The air flowing axially from
both ends meets and mixes in the annular air spaces
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between the spider arms. As the two air streams meet
they try to pass each other and create a turbu]ent
region with possibly secondary flows. This causes
higher friction losses. The baffle prevents any
mixing action and reduces turbulence. It is also
believed to provide a pumping action to move the air
outwards in a radial direction.
Tests were also carried out on series type,
double end ventilated motors with rotor mounted fans
to assist air flow. Motors with fans develop a high
pressure which apparently tends to overcome the small
variations in pressure and in resistance to air flow,
and consequently the unbalances in flow from the two
ends is usually not as great. Consequently the use of
a baffle does not result in as great an improvement.
Referring now to Figures 3 and 4~, Figure 3
is an elevation view of a section of vertical baffle
46. It was previously mentioned that the sides of the
baffle could be shaped to further reduce turbulence.
In Figure 4A there is a baffle 46A, shown in section,
with curved walls 47. The base portion of baffle 46A
is at the shaft, and the curved walls 47 very
generally direct a portion of the axially moving air
in a radial direction. Similarly, in Figure 4B there
is a cross-sectional view of baffle 46B which has flat
sloping sides 48, also intended to reduce turbulence
and pressure loss in turning the axial flow to radial
flow.
In conclusion, in any doubled end ventialted
machine, air flow from either end can be balanced by a
baffle placed between the spider arms at an
appropriate axial location. The improvement in
cooling that is achieved with a baffle tends to be
greatest in series flow machines that do not have a
rotor fan. However there may still be a significant
improvement in series flow machines with rotor mounted
fans and in parallel flow machines.
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