CA1183721A

CA1183721A - Transformer oil circulating pump

Info

Publication number: CA1183721A
Application number: CA000394645A
Authority: CA
Inventors: Clifford J. Bell
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1981-01-23
Filing date: 1982-01-21
Publication date: 1985-03-12
Also published as: KR830009392A; JPS57143192A; FR2498696B1; BE891880A; JPS61175596U; FR2498696A1

Abstract

A B S T R A C T
TRANSFORMER OIL CIRCULATING PUMP
The invention relates to a motor pump including means for improving the lubrication and cooling of the bearings supporting the pump shaft.
At each bearing, helical grooves are formed in the cylindrical bearing surface and/or in the surface of the shaft portion journalled therein, and a flow-inducing member disposed on the shaft for rotation therewith is located adjacent one end of the bearing, the arrangement being such that rotation of the shaft causes lubricating liquid coolant from a space within the pump housing to flow into and through the helical grooves, and causes the flow-inducing member to produce suction aiding the flow of liquid through the helical grooves. Preferably, the flow-inducing member is a thrust collar having radial grooves formed in its thrust surface cooperating with a thrust surface of the bearing, and each of which radial grooves communicates at its inner end with a helical groove formed in the shaft.
The invention is particularly useful in connec-tion with bearings made of materials which are poor heat conductors.

Description

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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 3~7~

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 ~ 3 ~

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 ~ ~3~t~ ~

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 ~3~

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.

Claims

What we Claim is:

1. A pump for circulating a cooling fluid within electrical apparatus, comprising:
(a) a housing having a motor portion and a pump portion;
(b) a rotatable shaft extending between the motor portion and the pump portion;
(c) first and second bearings mounting the shaft for rotation in the housing;
(d) a stator-rotor assembly within the housing with the rotor mounted on the shaft to effect rotation of the shaft when the stator is energized;
(e) an impeller mounted on the shaft within the pump portion to cause circulation of a cooling fluid when the shaft rotates;
(f) each first and second bearings having a radial end flange;
(g) first and second thrust collars fixedly mounted on the shaft adjacent to and in surface-to-surface contact with corresponding first and second bearings;
(h) the shaft bearings having surface-groove means for spreading a coolant fluid over the interfaces of the shaft and the bearings as a lubricant therefor;
(i) the surface-groove means including at least one spiral groove extending substantially longitudinally between ends of the bearings;
(j) the surface of each thrust collar having an arcuate channel extending outwardly from the shaft to the periphery of the collar;
(k) the surface-groove means communicating with the channels; and (1) conduit means in the housing for conducting cooling fluid to the ends of said bearings so that the fluid enters the surface-groove means from where the fluid flows to the respective arcuate channels and flows radially outwardly to the periphery of the collars.

2. The pump of claim 1 in which the grooves are spiral and extend around the shaft in a direction opposite the shaft rotation.

3. The pump of claim 2 in which the channel has a spiral configuration with an outer and extending to the direction of rotation.

4. The pump of claim 1 in which the contacting surfaces of the flange and collar are comprised of bearing material.

5. The pump of claim 1 in which the first and second bearing are comprised of a non-metallic material, and the surface-groove means are disposed in the shaft.