Note: Descriptions are shown in the official language in which they were submitted.
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TRANSFORMER OIL CIRCULATING PUMP
This invention relates generally ~o luid-cooled
apparatus, such as power transformers, and, more particu-
larly, to an improved circulating pump for such apparatus.
In bearings made with the present state-of-the-
art for immersed applications, heat is dissipated byconduction through the metal of the bearing, and through
the journal and shaft, into the immersing fluid surround-
ing these masses, and by convection into the main stream
of the pumped 1uid. Fluid flow through the bearings is
so small as to be insignificant as a heat carrier. Metal
bearings with good heat conductivity through the metal can
be made with these limitations if the ambient fluid tem-
perature is maintained low enough so that the fluid film
is maintained. In some cases, such as with transformer
oil pumps, where the pumped fluid has very poor lubricat-
ing properties, and also where, despite good heat conduc-
tion, the temperature rise occurring in the oil ~ithin the
bearing area might limit the ambient of the oil permissi-
ble for safe operation to a value below that allowed in
the other functions of the oilj i.e., the insulating and
cooling fluid of the transformer. The reduced oil temper-
ature is a penalty on the transformer design which can
greatly increase cost. It has become apparent in present
designs Or transformer o.il pumps that some bearing fail-
ures (particularly in warmer climates) are ln fact aresult of lubricating film failure due to excessive tem-
perature.
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The foregoing problem i5 only magnified when
using electrically non-conducting bearing materials in
order to prevent contamination of pumped dielectric cool-
ant with particles of conduction bearing material. Such
non-conductive bearing materials are inherently poor heat
conductors which reduce heat dissipation through the
bearing to such an extent that the bearing and oil temper-
atures cannot be maintained at any acceptable level. This
is true even if the bearing size is increased to the
maximum practical, and even if a better lubricant is used.
Under these conditions, only the use of non-conductive
bearing materials capable of withstanding very high tem-
peratures could reduce-the risk of bearing failure.
It is the principal object of the invention to
provide a motor pump with means resulting in better lubri-
cation and cooling of the bearings, and the invention
accordingly resides in a motor pump comprising a housing
which contains a pumping elemenl: and an electric motor
including a rotor, said pumping element and said rotor
being secured to a common shaft rotatably supported in
bearings each having a cylindrical bearing surface and a
lubricant lntake region communicating with a space within
said housing which space contains a cooling liquid during
operation of the pump, characterized in that each bearing
has associated therewith (a) he:Lical groo~es formed in
said cyllndrical bearing surface and/or in the surface OL
the shaft portion journalled therein, said helical grooves
extending from said lubricant intake region to one e~d of
the bearing, and spiralling about the axis of rotation of
the shaft in such manner as to produce a flow of cooling
liquid from said intake region through said helical
grooves during normal rotation of the shaft; and (b) a
flow~inducing member which is disposed on the shaft for
rotation therewith adjacent said one end of the bearing
~S structure, and which cooperates with said helical grooves
to create therein suction aidiny said flow of cooling
liquid throu~h the bearing.
It will be appreciated that the above arrange-
ment re~ults in forced cooling o the bearings whereby the
heat is removed from the bearing surfaces by the induced
flow of cooling liquid through the helical groo~es. Thus,
the bearings of the novel motor pump do not depend for
proper heat dissipation upon radial heat flow through the
bearing material wherefore the designer has a much greater
latitude in selecting bearlng materials and, especially,
is not restricted in his choice to bearing metals which
are well heat-conductive but also electrically conductive
and, hence, undesirable in applications, for example,
where the pumped fluid is a dielectric that must not be
contaminated with conductive particles.
In pumps using bearings which include thrust
surfaces, at least some of the helical grooves preferably
are located on the shaft, and the above-mentioned flow-
inducing member preferably comprises a thrust collar on
the shaft which has generally radial grooves or channels
formed in its thrust surface cooperating with the thrust
surface of the respective bearin~, each of which grooves
commun.icates at its radially inner end with one of the
helical grooves in the shaft and communica-tes at its
radially outer end with the interior of the motor-pump
housing. Kotation of the shaft and, consequently, of the
thrust collar thereon will cause the liquid enteriny the
radial grooves from the helical grooves to be centrifuged,
so to say, through and out of the radial grooves which, of
course, creates suction at the discharge ends of the
helical grooves communicating therewith.
Prefarred embodiments of the invention will now
be described, by way of example only, with reference to
the accompanying drawings, in which:
Fi~ure 1 is a perspective view of a transformer,
partially cut away and partially in phantom;
Figure 2 is a vertical sectional view of a pump
suitable for use with a transformer such as shown in Fig.
1 ; .
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Figure 3 is an enlarged, vertical sectional view
of the shaft and one of the bearing structures of the
pump, constructed in accordance with the invention;
Figure 4 is a vertical sectional view taken on
the line IV-IV of Figure 3;
Figure 5 shows a portion of a shaft with a
modified groove configuration embodying the invention; and
Figure 6 is a schematic view of a bearing
sleeve portion having grooves formed therein.
The electric power transformer shown in Fig. 1
and given therein the reference numeral 10 includes a
magnetic core and winding assembly 12 disposed within a
tank 14. The tank is filled to a level 16 with a dielec-
tric insulating and cooling liquid, such as mineral oil,
in which the assembly 12 is immersed.
Heat exchangers 18, 20 are connected in fluid
flow communication with the tank 14 to permit the liquid
dielectric in the tank to be circulated through the heat
exchangers so as to dispose therein of heat removed from
the core and winding assembly 12 which comprises a mag
netic core 22 and phase windings 24, 26, 28 each consist-
ing of low- and high-voltage windings concentrically
disposed upon a leg of the magnetic core. The high-
voltage windings are connected to high-voltage bushings~
such as bushings 30 and 32 shown in Figure 1 (the third
high-voltaye bushing which would extend through opening 34
has been omitted from the drawing). The low-voltage
wi.ndings, assumed to be connected in wye, have their
neutral ends connected to a neutral bushirg 36, and have
their other ends connected to low-voltage bushings dis-
posed on the portion of the tank cover cut away in Figure
1.
The transformer 10 is cooled by circulating the
llquid dielectric upwardly through the tank 14 from below
a barrier 46 which directs the liquid dielectric through
ducts formed in the windings in a predetermined pattern.
The li~uid dielectric leaves the tank and enters the
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respective heat exchangers 18 and ~0 through openings,
such as opening 48, in the upper portion of the tan~,
flows downwardly through the heat exchangers 18 and 20,
giving up heat therein, and returns to the space in the
tank below the barrier 46. Each of the heat exchangers 18
and 20 includes a plurality of hollow, flat, fin-type
elements 40 which are in fluid communication with upper
and lower headers 4~ and 44, only some of the many fin-
type elements usually provided in this kind of heat ex~
changers being shown herein. Additional heat exchangers
(not shown) may be provided on one or more sides of the
transformar, depending upon the specific rating and cool
ing requirements of the apparatus.
The upper header 42 is connected directly to
tank 14 while the lower or collecting header a4 is con-
nected to the tank 14 through a conduit including a liquid
pump 50 having its inlet 52 connected to the header 44,
and having its outlet 54 connectsd to the tank 14.
Because transformers, such as transformer 10,
are relatively maintenance-free apparatus and are gener-
ally unattended, their pumps, such as pump 50, must be
designed so as not to detract from this condition of
relative freedom from maintenance. To this end, such
pumps are usually hermetically sealed motor pumps having a
pump impellor mounted directly on an extension of the
rotor shaft of an electric mot:or which is cooled and
lubricated with a portion o the pumped transformer oil
which is bled off and circulated through the motor. This
sealed design renders the motor pump itself rather main-
tenance-free and permits its physical size to be smaller
than would be the case otherwise.
In order to safeguard against contamination of
the pumped dielectric fluid with metallic or conductive
particles separated from the bearings, rotor and stator of
the motor and transported out into the main stream of the
dielectric being pumped, it has been proposed, in connec-
tion with pumps to be used for circulating fluid to be
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protected from such contamination, to form pump components
which are subject to frictional wear from suitable non-
metallic and electrically non-conductive materials
wherever possible, and to make provision for preventing
physical contact between metallic or electrically conduc-
tive components for which non-metallic and electrlcally
non-conductive materials cannot be used. It has also been
proposed to provide means for activating an alarm and/or
turning off the motor pump when a certain degree of bear-
ing wear is detected.
Referring now to Fig. 2, the pump 50 illustratedtherein comprises a housing 60 consisting of a motor
housing portion 62 and a pump housing portion 64. The
motor housing portion 62 defines a motor chamber 70 con-
taini.ng a rotor 66 and a stator 68, both of conventionaldesign.
The stator 68 is energized through electrical
wires 72 which extend through fluid-tight conduit 74 in
the motor housing wall and have terminals 76 enabling the
wires to be connected to an external power supply. The
pump housing portion 6~ defines an impeller chamber 80
containing an impeller 78, having passages 89 formed there-
in. The motor chamber 70 and the ilmpeller chamber 80 are
in fluid communication with each other through fluid
orifices 86 and ~nd-~ell ports 88.
Both the rotor 66 and the impeller 78 are
secured to a shaft 90 which extends into the motor and
impeller chambers, and is rotatably supported in electric-
ally non-conductive bearings 92 and 94 each having a
sleeve bearing surface 96 or 98 and a thrust bearing
surface 100 or 102, respectively, extending generally
radially from the adjacent sleeve bearing surface,
The bearings 92 and 94 can be made of suitable
resins, laminates or ceramic materials, either fired or
~rnfired. Glass silicon tubing, type G7, grade number
HY-1~06, a silicon laminate sold by Westinghouse Electric
Corporation, under its trademark MICARTA, has been used
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successfully in tests of a prototype of the pre~erred
ernbodiment of tl~e invention. Other non-conductive cer-
amics, resins and laminates with characteristics of good
oil resi.stance and temperature stability would also be
suitable.
Rigidly disposed on the shaft 90 so as to rotate
therewith are two thrust collars 104 and 106, made prefer-
ably of metal, which are located a~ially adjacent the
thrust surfaces 100 and 102, respectively, and which
cooperate with the latter so as to hold the shaft 90
against axial displacement thereof from its proper posi-
tion.
During operation of the pump 50, rotation of the
impeller 78 moves the fluid to be pumped from the suction
side 82 of the i.nlet 52 of the impeller chamber 80 to the
pressure side 84 thereof. Since the fluid orifices 86 in
the housing 60 communicate with the pressure side 84 of
the impeller chamber 80, there will be a small bleed-off
of oil into the motor chamber 70. This bled-off oil
passes through the motor chamber 70, cooling -the pump
motor therein and lubricating the bearings 92 and 94 and
then returns to the suction side 82 of the impeller cham-
ber 80 through the end-bell ports 88 and the impeller
passages 89.
As shown in Figure 2, the housing 60 includes
bearing blocks 108 and 110 supporting the bearings 92, 94,
respectively, each of which has its sleeve bearing portion
seated within the bore of the associated block 108 or 110
and has its radial thrust bearing portion or flange 112
(Fig. 3) in face-to-face contact with the associated
thrust collar 104 or 106, respectlvely.
Referring now to the detail showings of Figs. 3
and 4 which illustrate the outer bearing structure 94, 104
as generally representative also of the inner bearing
structure 92, 106, the shaft 90 is provided with helical
grooves 116, 118, 120, 121 which are formed in the shaft
portion journalled within the bearing 94, and which extend
helically from the outer end of the shaft 90 to the collar
104 thereon and spiral uniformly abou-t th shaft in a
direction opposite to the direction of normal rotation
thereof indicated by arrow 124. Furthermore, the collar 104
is provided with several generally radial grooves 122 which
are formed in the thrust surface of the collar 104 and which
extend from the shaft surface to the outer periphery of the
collar 104, the radial grooves 112 preferably corresponding
in number to the helical grooves in the shaft, and communicating
at their inner ends with the respective helical grooves.
Upon rotation of the shaft 90 in the direction
of the arrow 124, liquid coolant, such as transformer oil,
will flow from the motor chamber 70 (Fig. 2) ~hrough a
passage 128 (Fig. 3) in the bearing block 110 and into a
space 140 next to the end of the shaft, whence it will
enter the helical grooves 116, 118, 120, 12] in the shaft
and, due to the shaft rotation, be augered therein, so to
~ay, toward the opposite or thrust bearing end of the bearing
94 where the liquid will pass into the radial grooves 122 of
the collar 104 to be centrifuged therethrough and out of them
back into the motor chamber 70. In flowing through the helical
and radial grooves, the liquid performs two functions in that
it removes heat from the bearing surfaces and, at the same
time, forms a lubricating film between the shaft and the
bearing sleeve as well as between the rotating and stationary
thrust bearing surfaces. Of course, the desired mass flow of
cooling and lubricating liquid through the bearing is
obtained through a proper selection of the number and
cross~sectional size of the grooves formed in the shaft 90
and in the thrust collar 104.
In Fig. 4, the radial grooves or channels 122
are shown curved, from their radially inner ends toward
their outer ends, in a direction opposite to the normal
direction of shaft rotation. They could also be straight
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znd disposed, either in a perfectly radial orientation or
likewise inclined in said opposite direction, to provide
the desired centrifuging or pumping action during rotation
of the shaft 90.
Figure 5 illustrates an end or journal portion
of the shaft 90 with a somewhat modified groove pattern
formed therein, one that is suitable for use with a bear-
ing adapted to have liquid lubricant supplied thereto at a
location axially inboard from both of its opposite ends.
As seen from Fig. 5, the illustrated end portion of the
shaft has formed therein two sets of helical grooves 130
and 132, the grooves of the two sets extending from a
common lubricant~receiving location on the shaft axially
in opposite directions with respect to one another, and
15 with each set of grooves 130 or 132 spiralling, from said
lubricant-receiving location, about the shaft in a direc-
tion opposite to the normal direction of shaft rotation.
~ 1ith this arrangement, and with liquid lubricant
supplied to the shaft 90 at sai.d lubricant-receiving
location indicated in Fig. 5 by a broken line, rotation of
the shaft 90 in the direction of the arrow 134 will cause
some of the lubricant to enter the grooves 130 and some to
enter the grooves 132, so as to be auyerecl in the two sets
of groove~ in opposite directionra, as indicated by arrows
25 135 and 137. Unless the outer ends of the grooves are
intended, when in use, to communicate with regions of
sufficiently low pressure to sustain an adeguate lubricant
flow through the grooves and, hence, through the asso-
ciated sleeve bearing, the set or sets of yrooves requir-
ing a greater pressure differential thereacross has/have
associated therewith pumping means (not shown in Fig. 5)
which may take the form of a thrust bearing with radial
grooves formed therein, such as described above with
reference to Figs. 3 and 4, or, if no thrust bearing is
needed, such as, for example, at the outermost end of the
shaft 90 shown in Fig. S, of a disc-liks member (not
showr.) secured to the shaft and with radial passages
~ s 9,~5
formed therein and communicating with the outer ends of
the helical slots 130 or 132 in the shaft.
In Fig. 6, there is shown a half-section 136 of
a sleeve bearirlg which has helical grooves 138 formed in
the bearing surface thereof, and which grooves 138, as
viewed from their lubricant-intake ends toward their
lubricant-discharge ends, spiral about the longitudinal
sleeve axis in the same direction in which the shaft 90
normally rotates or, in other words, in the opposite
direction with regard to the helical grooves formed in the
shaft.
The embodiment which is most preferred, espec-
ially in connection with bearings made of poor heat con-
ductors, such as plastics materials, laminates or cer-
amics, is the one hereinbefore described with reference to
Figs. 3 and 4 or Fig. 5 wherein helical grooves in the
shaft communicate with radial grooves or passageways in a
flow-inducing rotor on the shaft, such as the thrust
collar 104, 114 in Figs. 3 and 4 or the disc-like member
mentioned above in connection with Fig. 5. The auger
action of the helical grooves in the shaft and the cen-
trifugal action derived from the radial grooves or pas-
sageways in the pumping rotor together will produce a
liquid flow through the bearing which will result not onl~l
in copious lubrication of the bearing surfaces but also in
a fair rate of heat dissipation from the bearing surfaces.
If desired, and where practicable, the above
features can be co~bined with a bearing sleeve whi~h
likewise is grooved, such as explained above in connection
with Fig. 6.
In a somewhat less efficient arrangement which
nevertheless might be deemed adequate for use in some
fields of applica-ion, a grooved bearing sleeve, such as
partially shown in Fig. 6, could be combined with a
smooth, that is, non-grooved shaft having thereon a pump-
ing rotor such as set forth above. Although there would
be no actual auger action in th.is arrangement, rotation of
ll
the shaft would tend to cause the liquid cooling andlubricating medium in the grooves of the sleeve to be
moved therealong due to the surface tension between the
liquid and the surface of the rotating shaft. And, of
course, this movement would be greatly aided 'oy the pump-
ing action of the radial grooves or passageways in the
rotor.
It will be appreciated, no doubt, that whilst
the invention has been shown herein as applied to a motor
pump used with a transformer, it is generally applicable
to motor pumps for use with fluid-cooled apparatus, in-
cluding electrical reactors, contactors, and the like.
