US2124339A - Steam turbine and speed controlling mechanism therefor - Google Patents

Description

July-19,1938; c. A. scHELLENs 2,124,339

STEAM TURBINE AND SPEED CONTROLLING MECHANISM THEREFOR Filed Nov. 19. 1955 Patented July 19, 1938 UNITED STATES PAre'N-fr operee- Application November 19, 1935, Serial No; 50,572

22 Claims;

This invention relates to steam lturbines and to speed governing devices therefor, and particularly tof-safety devices for preventing excessive rotative speeds of the turbine.

A steam turbine is commonly provided with a device for preventing the turbine wheel from rotating ata dangerously high speed at times When there is not sufficient loadkon the turbine to keep the speed down to a safe value orwhen the speed governing deviceassociated with the turbine fails to operate properly to adjust the high pressure steam supply of the turbine to the load on the turbine. 4

It will Ioefappreciated` that the turbine speed, When the turbine is insufficiently loaded and is supplied with unthrottled steam, can be high enough to cause the bursting of the turbine Wheel or` other damage due to the high centrifugal forces created. i

'IheV over-speed protective, or speed limiting,V device of the turbine, at the present time, consists essentially of speed responsive means associated with the turbine shaft andop'erable upf on excessive rotative speed ofthe wheel to actate a `valve in the high pressure steam'supply tothe turbine to shut oifthe'supply of steam. This arrangement necessitates a shaft or some other movable part which projects outwardly through a .high-pressure steamfchamber of rthe turbine, o1"

upon to operatefor long periods of time, and

hence the operating shaft or part thatextends through the high pressure casing is liable to become stuckin the casingpdue tothe depositing vof Scaleon the rod at the packing, corrosion ofthe rod` outside the packing, and the like. This is especially true on turbineV driven centrifugal `pumps onalocomotives usedl for supplying the vboilers thereofwith feed Water, wherein the locomotive, at times, necessarily has/to use hard water, and wherein the pumps are sometimes neglected. Thus the over-speed preventing device may be' rendered inoperative.

An object of the present` invention is the kprovision of a device for controlling the speed and particularly 'for preventing the over-speeding of a steam turbine, wherein the necessity for the location of parts thereof inchambers of diiferent `-steam pressures `and theV use of steam packings is avoided.`

A afurther object vof :the invention is the provision ofa device for controlling or limitingthe 55,,1speed of vasteam turbine wherein the device is arrangedto controlthe escape of exhaust steam from theyturbine rather than to control the sup-r plyof high pressure steamto the turbine, as has been Vthe practice heretofore.

, A-yet'furtherobject'of the invention is the provision of -a turbine speed controlling or limiting devicethat is locatedin the exhaust'steam chamber of the turbine 4casing and acts to control the fiowiof exhaustA steam from the casing so as to eliminate the necessity for extending parts of the device through steam tight packings, whereby to'provide a devicer that Vcan remain indefinitely in operative condition. .i

Another object is the provision of a turbine speed controlling or over-speedpreventing devicethat` is not deleteriously' affected by scale deposits.,

A further object is generally to improve the construction and`operation of speed vregulating and, over-speed preventing devices for steamturbinesg Fig.` 1 isa sectional elevation through a steam turbinek embodying the present invention.

- Fig. 2 isapdetail' of the speed limiting mechanism of Fig. l in an operated position thereof.

Fig. 3' isan end view of thespeed responsive weights of Figs. 1 and2.

Fig. 4 is a section taken along line 4--4 of V1=ig.,3.

The turbineembodying the present invention is particularly adapted for'driving a centrifugal pump `for supplying feed Vwater to a locomotive boiler, although the invention is applicable to other turbines.

The'tuibine includes a bearing bracket IIJ hav ing' in; one end a bearing I2 which rotatably supports-the turbine shaft I4. The bracketis provided integrally with a wheel casing I6 that is open at thefront end and is closed by a removable cover I8. A turbine Wheel 20 is mounted on and secured to the'turbine shaft Within the cas,` ing by` means including a nut 22 screwed ontothe shaft. The turbine wheel is provided with a rovvl of buckets 24 which receive steam from a series of nozzlesr26 in a nozzle plate 28 carried internally by the casing part I6 and receiving high pressure steam fromy a chamber o r inlet passage 3uV haust steam has free access to the front and rear faces of the post. The post is hollow or is provided with an exhaust steam passage 34 which communicates with an exhaust steam passage 36 in the casing part I6. Said passage 36 communicates with an outlet opening 38. The front and rear walls i8 and 42, respectively, of the post are apertured to snugly receive a valve casing 44 therein, the valve casing consisting of a circular front plate @l and a circular rear plate 158A connected together and spaced apart by a series of peripherally spaced bridges 58. The plates 48 and 48 are provided with circular exhaust steam openings or ports 52 and 54, respectively, therethrough. Said openings are disposed concentrically with the axis of the turbine shaft I4 and preferably, although not necessarily, the opening 52 is larger than the opening 54, for a purpose that will presently appear. Y

The turbine shaft is provided with an extension 58 which extends coaxially through the openings 52 and 54 and at its end, beyond the rear Wall 42 of the exhaust steam post, has a nut 58 screw-threaded thereon, the nut having a circular periphery. A valve sleeve 60 encircles said shaft extension t8 and said nut andv is slidable axially on saidV nut and is connected thereto against rotation independently thereof by pins 62 that are carried by said nut and extend loosely into axially elongated slots 64 formed in the end of the sleeve 68. The sleeve at the end adjacent the turbine wheel is provided with an inwardly directed radial flange 66 that encircles and is supported for axial motion upon the shaft extension 58, the flange having a hub 68 that bears upon'an enlargement 'i8 of the shaft. A compression spring 12 is located within the sleeve 68 and bears at one end against the ilange 86 and at the other end against the nut 58 and thereby tends to urge the sleeve constantly in an axial direction toward the turbine wheel and to maintain the inner end ofthe sleeve in engagement with internal radial anges 'lll of speed-responsive weights 78. l

Said weights, as shown clearly in Figs. 3v and 4, have semi-cylindrical bodies 718 which surround theinner end of the sleeve 68 and have outstanding semi-circular flanges 88 at their inner ends which are located within a recess of a collar 82 screw-threaded upon the hub 84 of the turbine wheel. The spring "i2 under conditions of normal speed of the turbine wheel serves to maintain the flanges 'M and 88 against the flat radial face of the collar 82. The collar is provided with an annulai` shoulder or ledge 8B which closely surrounds the il'anges 8! of the weights to retain them in cooperative relation with said collar 82. When the turbine speed becomes excessive the weights due to centrifugal force tend to become displaced into some position as indicated by the dotted lines and thereby pivot on the edges of the ilanges against the` collar 82 at the inner edge of the annular ledge 8B thereof, thereby displacing the sleeve 68 toward the left and effecting the throttling of the exhaust steam outlet.

Thesleeve 6i) is provided with two annular outstanding axially spaced valve discs or flanges 88 and 98, respectively, each of which cooperates respectively with a separate oneof valve ports or openings 52 and 54 in the valve casing 44 of' the exhaust steam post. The discs 88 and 9U are but slightly smaller in diameter than the ports 52 and 54 so that they canenter and substantially close said ports although there is suicient clearance between the valve discs and the walls of the ports to permit the discs to rotate with the turbine without any rubbing contact between the discs and the valve casing. Y

When the turbine is rotating at normal speed the parts are in the position illustrated in the full lines of Fig. l.` When, however, the turbine rotates at an excessive speed the weightsv 'I8 become displaced outwardly into some position as illustrated in Fig. 2, and hence force the sleeve 6U axially towards the right against the action of the spring l2 and thereby position the valve discs 88 and 9B within the valve ports 52 and 54. In this position the exhaust steam passage of the turbine is substantially closed and hence the flow of steam through the turbine buckets is reduced Vat least to such an extent that the no-load speed of the turbine is held down to a safe value.

It will be appreciated that the discs 88 and 90 do not make an absolutely steam tight fit within the ports 52 and 54 as the small clearance is desirable to prevent wear on the valve casing due to the rotation of the turbine. Thus a small amount o steam can pass from the turbine casing into the exhaust passage even when the valve dis-cs are within the ports. It will also be appreciated that steam can escape from the turbine casing through the shaft packing gland 92 and also through the condensate drain 94 passing through the bottom wall of the casing part I6 and opening into the exhaust passage 36. Nevertheless, the mechanism above described throttles the exhaust steam outflow to such an extent that the amount of steam that can pass through the turbine buckets is so little that the turbine speed'is held down to a safe value. The turbine casing is, of course, made strong enough to withstand the high pressure steam that exists therein at such time. The windage losses are greatly increased by the high pressure and cooperate in holding the turbine speed down to a safe value.

It is desirable to provide an attendant with a warning signal that the over-speed device has operated. This warning signal is conveniently in the form of a steam whistle 96 which is connected through a spring loaded valve 98 with the wheel chamber. `The valve is maintained closed under normal low pressures of exhaust steam in the chamber but opens automatically upon the occurrence of high steam pressure caused by the operation of the over-speed preventing device and thereby allows steam to pass into the whistle to sound the warning signal. The steam capacity of the whistle is made small enough not to deleteriously influence the speed of the turbine wheel.

Ii the valve discs 88 and S, instead of being of different diameters, are made of the same diameter the over-speed device is then balanced against movement in any direction by the exhaust steam pressure within the casing so'that the device is then responsive only to movements of the centrifugal Weights. It is preferred, however, to have the disc 88 larger than the disc 90 for the following reason. When the discs are within the valve ports and the exhaust steam passage is then substantially closed, there is a relatively high stearn pressure within the wheel casing and hence there is a corresponding high axial thrust on the turbine shaft since the turbine wheel is an outboard wheel and one end of the shaft is terminated within the wheel casing. However, by having the disc 88 sufficiently larger in diameter than the disc 98 there is provided an axial thrust on the shaft through the larger valve disc operating in the opposite direction to the direct thrust, on the shaft, when the discs are within theirA corresponding valve ports and the sleeve 6!)-` is bearing against the pins 62', as illustrated in Fig. 2. oppositely directed thrust can beY made tooffset the thrust on the shaft sothat there is no substantial axially directed shaft displacing force.

The increased'diameter of the disc 88 over the disc 90v is also desirable in providing a rapid or snap closing of the exhaustports; It will be appreciated-that while the sleeve60=is substantially balanced so farl as. its .movementin response to-exhaust steam pressure `is-coneerned when the discs are remote from the-'exhaust steam ports, when, however, thediscs are-close enough to the ports-to exert. a throttling ehi-ect on the steam passing therethrough, there will be a considerably greaterl pressure toward the rightonA the disc 88-than towardv the left on the disc 901 and hence the sleeve wil-lv be moved rapidly into a port closing position. Furthermore withthe sleeve in this position'it- Will tend to -be held there by the steam pressure untillthesteam supply to the turbine is shut off by an attendant, and the tendency to periodic open-ing and. closing of the ports by the sleeve, or hunting, will be minimized. Obviously'however, if these advantages are -not desired the discs 88 and 9|)` can be 4made the'same diameter so as to provide astruc-ture that is balanced again-st movement due to the steam `pressures thereon.

` The spring 'l2 is preferablyfso adjusted as to be unstable in an outwardly displaced position of the centrifugal weigh-ts so that when these weights have become-substantially displaced the spring is unable to maintain the weights in lthe `displacedr position but will yield and permit' the Weights to be further ldisplaced into theirl maxi;- muni and exhaust valve closing position.

It will be appreciated that by throttling the `exhaust steam rather than by-throttling the high pressure inlet steam, as has been the case heretofore, a speed limiting device Vis obtained wherein all the operative parts arein the'same body of steam so that steam tight pack-ings and other closely fitting 'partsl canv be eliminated and thus ther device can remain inoperative for long periods `of time and yet operate surelyf'when required.

Itwill also be notedl that since all movi-ng parts ofthe device are carried by the turbine shaft and hence are subjected to centrifugal force, that water of condensation is thrown there-from sov that there is little'li'kelihood of scale being deposited onthe partsto hinder the free operation thereof. Where considered necessary passages, such as the passages Hill formed in the cylindrical Wallv 1'8' of the centrifugal weights, have been provided to permit the ready'escape of water oi condensation andthe 'structure has otherwise been designedl to render it immune from impairment of operation due tosca-le deposit.

While the invention has herein been explained vin its adaption forr use primarily as an overspeed Apreventing device it can also beused as a speed regulating device to maintain a constant speed of the steam turbine wheel. `For such use the valve discs 88 and Sil preferably will be of 'the same diameter andthe spring- 112; will be so adjusted that it tends to maintainthe centrifugal `weights stablyl inv any displaced positionthereof,

corresponding with certainwspeeds, thereby to hold the discs88zland Sil-in-lthrottlingr positions with respect to the exhaust.'ports.` as determined by the displaced positionsofftheweights. The

use of theA device as a speed: governor may be valuable for certain purposes but in generalis-not recommended Where the pressure of the incoming steam lis suiiiciently highto necessitate the' use of an expansion nozzle in directing the, steam into the turbine buckets, since the speed contro-1- ling effect obtained by throttling the exhaust steam outlet is relatively small under such condition, until relatively high exhaust steam pres.- sures are obtained, as compared with throttling the high pressure inlet steam. Where extreme uniformity of speed is not necessary, however, or where the pressure of the inlet steam does not demand an expansion nozzle, the device is useful for maintaining an approximately uniform turbine speed.

I claim:

`1. In a turbine, a turbine Wheel, means providing an inlet passage for steam to the Wheel, means providing an outlet passage for exhaust steam from the wheel, said outlet passage having an entrance port that is co-axial with the wheel, and speed responsive means carried by and rotatable with said wheel and including a valve member on said shaft movable in response to the speed of the wheel into throttling relation with said port.

2. In a steam turbine, a turbine casing, a turbine Wheel therein, a shaft on which said wheel is mounted, said casing having an inlet passage for guiding steam to said turbine wheel, said casing also having a passage for exhaust steam therefrom, means providing said exhaust passage with an entrance port that is co-axial with said shaft, and port controlling means comprising a member movable axially cn said shaft toward and away from throttling relation with said port, and means responsive to the speed of said wheel for moving said member into throttling relation with said port.

3. In a steam turbine, a turbine casing, a turbine wheel therein, a shaft on whichA said wheel is mounted, said casing having an entrance passage guiding steam to said wheel, said casing also having means providing an outlet passage for the exhaust steam therein and a pair of opposed exhaust steam entrance ports open to the exhaust steam space of said casing and axially aligned with said wheel shaft, a valve member carried by and movable axially on said shaft having a pair of valve members each controlling a separate port, and means responsive to the speed of said wheel for moving said valve members into throttling relation with said ports.`

4. In a steam turbine, a turbinecasing, a turbine wheel therein, a shaft on which said wheel is mounted,.said casing having an inlet passage guiding steam to. said wheel, said casing also having a hollow exhaust post confronting the axis of said wheel and provided with co-axial ports that are co-axial with said wheel and open to the interior of said post, said casing having an outlet passage for'exhaust steam communicating with the interior of said post, a valve member carried by and movable axially on said shaft and having valve elements eachl confronting a separate port, and means responsive to the speed of said shaft for moving said valve memberaxially to position said elements into throttling relation with said ports.

5. Inga steam turbine, a turbine casi-ng comprising an open-ended body part and a cover for theopen end` thereof, a turbine wheel within the wheel chamber of said easing, a shaft o n which said wheel isvm0unted said casing'ihaving an entrance passage guiding steam to said wheel, said casing also having an exhaust steam passage conducting steam from the interior of said casing, said exhaust steam passage being located both in said body part and in'said cover, said cover having a port co-axial with said shaft and opening into said exhaust passage, andv wheel-speed responsive means carried by said shaft controlling the flow of exhaust steam through said port.

6. In a steam turbine, a turbine casing comprising an open-ended body part and a cover for the open end thereof, a turbine wheel within the wheel chamber of said casing, a shaft on which said wheel is mounted, said casing having an entrance passage guiding steam to said wheel, said casing also having an exhaust steam passage conducting steam from the interior of said casing, said exhaust steam passage being located both in said body part and in said cover, said cover having a port co-axial with said shaft and opening'into said exhaust passage, wheel-speed responsive means carried by said shaft controlling the flow of exhaust steam through said port, said exhaust steam passage of said bcdy part being located in part below said wheel chamber, and said casing having a bl-eed passage extended from the bottom of said wheel chamber into said part of said exhaust steam passage.

7. In a steam turbine, a turbine casing comprising an open-ended body, a cover therefor, a turbine wheel in said casing, a shaft on which said wheel is mounted, said casing having an inlet passage conducting steam to said wheel and also having an exhaust passage conducting exhaust steam from the interior of said casing, said cover having an upstanding hollow post therein the interior of which post forms a part of said exhaust passage, said post being disposed in the axis of said shaft and having opposed entrance ports in its opposite walls, a sleeve movable axially on said shaft having a pair of valve elements each of which is disposed in throttling relation with a separate port, and wheel-speed responsive means carried by said shaft and wheel and operable to move said sleeve axially into throttling relation with said exhaust steam ports in response to excessive wheel speeds.

8. In a steam turbine, a turbine wheel, a shaft on which said wheel is mounted, means providing an entrance for guiding steam into said wheel, means providing an outlet passage for exhaust steam from said wheel including an entrance port for said exhaust steam passage disposed co-axially with said shaft, a port-throttling valve member mounted on said shaft and movable axially thereof into and away from throttling relation with said port, said valve member being arran-ged to fit closely within said port in the throttling position thereof but to be free from contact with the wall of said port so that it can rotate without rubbing against the wall of said port, and means responsive to the speed of said wheel for controlling the axial movements of said valve member.

9. In a turbine, a turbine casing, a turbine wheel therein, a shaft on which said wheel is mounted, said casing having an inlet passage guiding steam to said Wheel, said casing also having a hollow part surrounding said shaft and provided with a pair of opposed circular ports coaxial with each other and with said shaft and opening to the interior of said casing and to said hollow part, a valve sleeve mounted on said shaft for conjoint rotation therewith but free for axial movement thereon extended through said ports and having annular outstanding fianges constituting valvediscs each disposed to throttle a separate port, a' compression spring encircling said shaft within said sleeve and arranged to urge said sleeve for axial movement along said shaft away from said ports, and centrifugal means responsive to the speed of said wheel for moving said sleeve axially in a port throttling direction.

10. In a steam turbine, a turbine wheel, a shaft on which said wheel is mounted, means providing an inlet passage guiding steam to said wheel, means providing an exit passage for exhaust steam from said wheel, said exit passage having an entrance port, and means responsive t0 the speed of said wheel for throttling said exhaust steam entrance port and including means responsive to the difference in exhaust steam pressures in and in front of said entrance port for actuating said speed responsive means rapidly into full port throttling position..

11. In a steam turbine, a turbine wheel, a shaft on which said Wheel is mounted, means providing an inlet passage guiding steam to said wheel, means providing an exit passage for exhaust steam from said Wheel, said exit passage having an entrance port, and means responsive to the speed of said Wheel for throttling said exhaust steam entrance port and including means for actuating said speed responsive means rapidly into full port throttling position, said last named means being responsive to exhaust steam pressure.

l2. In a steam turbine, a turbine casing, a turbine wheel therein, a shaft on which said Wheel is mounted, said casing having an inlet passage guiding steam to said wheel, said casing also having an exhaust steam duct provided with opposed entrance ports for the exhaust steam to flow out of said casing, one of said ports being larger than the other, a valve member having large and small discs respectively confronting said large and small ports, means guiding said valve member for movement toward and away from said ports, and means responsive to the speed of said wheel for moving said valve member in a port throttling direction, said large valve member being responsive to exhaust steam pressure within said casing and operable thereby to move rapidly into port throttling position independently of the action of said speed responsive means.

13. In a steam turbine, a turbine casing, a turbine wheel therein, a shaft on which said wheel is mounted, said casing having an inlet passage guiding steam to said wheel, said casing also having an exhaust steam duct provided with opposed entrance ports for the exhaust steam to flow out of said casing, one of said ports being larger than the other, a valve member having large and small discs respectively confronting said large and small ports, means guiding said valve member for movement toward and laway from said ports, means responsive to the speed of said wheel for moving said valve member in a port throttling direction, said large valve member being responsive to exhaust steam pressure within said casing and operable thereby to move rapidly into port throttling position independently of the action of said speed responsive means, and spring means acting on said sleeve to move it away from port controlling position upon a suflicient reduction of wheel speed and steam pressure within said casing.

14. In a steam turbine, a turbine wheel, a shaft .on which said wheel is mounted, means providing an inlet passage guiding steam to said wheel,

means providing anoutlet passage for exhaust steam, and means actuated by a predetermined increase of wheel speed with said outlet passage and additionally influenced by the exhaust steam pressure for rapidly throttling said outlet passage.

15. In a steam turbine, a shaft, a turbine wheel mounted on said shaft, a casing providing a wheel chamber in which said Wheel is rotatable and an exhaust steam duct under said chamber, said duct having an entrance to said chamber above the bottom thereof, means for governing the flow of exhaust steam through said duct, and means providing a bleed passage from the bottom of said wheel chamber into saidduct.

16. In a turbine, a shaft, a turbine wheel on said shaft, a wheel casing having an exhaust steam outlet concentric with said shaft, a valve on and rotatable with said shaft and movable axially thereof into throttling relation with said outlet and being free from rotating engagement with the outlet wall, means normally holding said valve away from said outlet, and centrifugal means responsive to the speed of said wheel for moving said valve toward said outlet.

17. In a turbine, a shaft, a turbine wheel on said shaft, a wheel casing having an exhaust steam outlet concentric with said shaft, a valve on and rotatable with said shaft and movable axially thereof into throttling relation with said outlet and being free from rotating engagement with the outlet wall, means normally holding said valve away from said outlet, and centrifugal `means responsive to the speed o-f said Wheel for moving said Valve toward said outlet, said centrifugal means being carried by said shaft and rotatable with it and said valve.

18. In a turbine, a shaft, a turbine wheel on said shaft, a wheel casing having an exhaust steam outlet concentric with said shaft, outletthrottling valve means on and rotatable with said shaft and movable axially thereof toward and away from said outlet, and centrifugally-controlled means carried by said shaft to operate said valve means.

19. In a steam turbine, a shaft bearing, a shaft in said bearing having an end overhanging said bearing,l an over-hung turbine wheel on said overhanging shaft end, a casing providing a wheel chamber in which said wheel is rotatable, means providing an exhaust steam duct having an entrance to said wheel chamber on the side of said wheel opposite said bearing and aligned coaxially with said shaft, valve means controlling said entrance mounted on and rotatable with said shaft and movable axially thereof toward and away from said entrance, and shaft speed responsivemeans mounted on and rotatable with said shaft having an operative connection with said valve means.

20. In a steam turbine, a shaft, a turbine wheel mounted on said shaft, a casing providing a Wheel chamber in which said wheel is rotatable and an exhaust steam duct a part of which is below the wheel, said duct having an `entrance to said chamber above the bottom thereof, means for governing the passage of exhaust' steam into said entrance, and means providing a bleed passage from said chamber into said duct, said bleed passage having an entrance intoy said wheel chamber below said wheel and an outlet into said exhaust steam duct part below said wheel.

21. In a turbine, a rotatable Wheel structure, a housing about said structure having an exhaust steam outlet, a speed responsive valve supported by said structure and located adjacent the axis thereof for movement into throttling relation with said outlet, and speed-responsive mechanism separate from said valve supported by and rotatable with said wheel structure and Valve having connection with said valve operative to move it into throttling -relationwith said outlet.

22. In combination in a turbine, a turbine wheel and shaft structure, a'wheel casing having an exhaust steam outlet co-axial therewith, outlet throttling valve means on and rotatable with said structure and movable axially thereof toward and away from said outlet, and centrifugally controlled means carried by said structure to operate said valve means.

CHRISTOPHER A. SCHELLENS.

Images