US2747373A

US2747373A - Quick-starting governing system for reheat turbine

Info

Publication number: US2747373A
Application number: US311248A
Authority: US
Inventors: Markus A Eggenberger; Peter G Ipsen
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1952-09-24
Filing date: 1952-09-24
Publication date: 1956-05-29
Anticipated expiration: 1973-05-29

Description

May 29, 1956 M. A. EGGENBERGER ETAL Filed Sept. 24, 1.952

SHAFT 69a QUICK-STARTING GOVERNING SYSTEM FOR REHEAT TURBINE Mr'k us Amen henger; peter @hosen nitecl States Patent AQUICKSSTARTING GOVERNING SYSTEM 'FR 'REHEAT 'TU-RBINE Markus AA. Eggenberger and Peter JG. lpsen, Schenectady,

N. Y., assignors to AGeneral Electric Company, a corporation ofNew .York

Application September 24, 11952, Serial No. 311,24

,11,Clain1s. (CLAW-73) This vinvention relates to elastic tluid Yturbine powerplants, particularly fto a l:governing lsystem :for a large `reheat .type steam turbine gplant especially 1adapted to permitquick .restarting of the plant vafter :a short `shutdown.

When a very large steam turbine powerplant `is shut down, the hotrnetal parts, :particularly those around'the inlet'ends ofthe high pressure and intermediate ipressure turbines, cool down `at a very slow rate, perhaps only about F. per hour. Thus after 'eighthours Vof 'shutdown, the inlet ends of these turbines vmay still beat a .temperature of ,perhaps i800 to 900 2F. AIf then it is desired to restart the turbine by again tiring athe boiler which Afurnishes the :motive liuid, the steam entering .the still hot turbine might initially be at a comparatively lowrtemperature,.perhaps .on the yorder of 600 rto V706" FF. This would .produce .a Ithermal shock .by reason of :the temperature differential of 200 lto 300, :which :would seriously endanger the structure .unless some .special starting procedure is employed to make .sure the `temperature of the hot turbine Aparts .changesata safe rate. Such a procedure, with conventional turbine ygoverning systems, would require v.from l .to 1.1/2 'hours :to :bring the turbines back `up :to .rated speed so :the .generators could be re-connected with the network "to `.which they deliver power, whileran'otheriull hour would "be required to bring the load on the turbines up to :full icapacity.

In a power distribution .system .fora large `metropolitan area, where .the electricaliload fluctuates -greatly'over a twenty-four lhour period, such procedure would -make it impracticable to :shut down a large turbine at might, because the shutting-down process `and the restarting process would occupy substantially vthe entire v down :period. On the other hand, operating `the nplant at low load during the night yhours is `not desirable because -ol the poor thermal eiiciency of 'the=plant in `this'conditicn. It therefore becomes desirable to tind ways .to shorten therestarting cycle, so that a large generating plantfcan be put back on the line in substantially yless than l hour after an overnight shutdown.

Accordingly, the object of `the present invention is to provide an improved-governing system for a large Areheat type steam turbine powerplant which l-makes possible the safe restarting of the plant `within a'comp'aratively short .time vafter a 'temporary shutdown period.

Another object is -to provide a high temperature tur-l bine .governing system of "the type described `which `is comparatively simple and provided with full safeguards against overspeed conditions.

Other objects and advantages will become apparent from the following description, taken in connection with the accompanying drawing, in which the single figure represents diagrammatically -a large high temperature cross-compound turbine powerplant `with -a governing 'system for effecting quick restarting in accordance with the invention.

Generally stated, `the invention Ais practiced by ipro- -viding a steam :bypass conduit around the turbine rtothe mais ICE

condenser whereby the boiler may be red and l'brought up to ,normal .pressure and ,temperature conditions, -at a `rate .of llow about one-quarter its normal rated `ilow, before any steam is Iadmitted tothe comparatively hot turbines, with special control valves-incorporated in 'the turbines for admitting h igh temperature steam at a yery restricted -rate to 4both `the high y,pressure and -intermedate lpressure turbines simultaneously during the restarting procedure.

Referring now more `particularly to the drawing, the invention Vis disclosed as applied to a cross-compound steam :turbine Apowe'rplant having -in series a :boiler -1, a superheater 2, a-main 'emergency stop valve 3,-a high l.pressure turbine 4, areheaterfB, an `intercept valve -,6,.an intermediate pressure turbine'?, Va Flow pressure turbine 8, a condenser 9, .and .conventional condensate and :boiler feed pumps 210, 111, for .returning the duid .to the boiler. The conduits `connecting these components have for con venience vbeen `labeled with ,reference numerals corres pending to the component immediately upstream from the =respective 1'conduit sections. 'The high pressure turbinerexhaust 4.conduit 4a is :provided 4with a non-return" check-valve 4b.

It willbe seen from the :drawing that the :high pressure :turbine 4 and vintermediate pressure 4turbine 7 are actually built as .an integral unit, :having `two 'rotors on a :common shaft .housed in a Vcommon casing. Thezh'gh pressure steam is admitted to an inletichaniber i2 disposed adjacent `.the :middle of the turbine casing, :whence the `motive fluid flows Ito the left through :the hi'gh pressure 'turbine frotor Vand exhausts .to lconduit 4a at ythe extreme .leftehand end of vthe turbine casing. Likewise, the reheated .motive fluid from :intercept -valve 6 lpasses through :conduit 6a fand Yenters the lintermediate pressure Aturbine '7 `adjacent the midpoint ro'f the casing, -owing to Ithe .right through =the intermediate Ipressure :turbine rotor and leaving at the-extreme right-hand end of the 'casing through conduit '7a. In low pressure `turbine `-8, the nnotive iluid enters adjacent fthe midpoint/ofthe casing `and flows lboth Ito .the right and to lthe lett vthrough the :low pressure :turbine rotors, -and through the 'condenser :neck 8a to 'the condenser 9. Cooling water for the condenser is supplied by an inlet conduit 9a and a discharge conduit 9b, V4through which cooling water is circulated by suit-able :pumps (not shown). A pressure switch indicated diagrammaticlly at 9c is arranged to signal l'the failure `ot cooling Waterfow.

The primary 'means for regulating the rate of ilow `of motive liuid through the turbines is thehighpre'ssure inlet governing valvesystem indicated diagrammatically 'at 13 ars-comprising amainowfcontrol member lafcontaining a pilotcontrol'member 13b, which forms a .lost'moti'on connection with the =main llow control member v13a so that, as the `valve stem i rises, `the pilot member 13b first fopens to .admit a limited quantity o'f steam to ithe high-'pressure turbine rotor, and, after apreselected travel, the=pilot 13b engages'themainiiowcontrol member '13a so as to position itin/'the opening direction. The governing valve members 13a, 13b are 'biased downwardly to closed position "by a spring 13d engaging the 'upper end of Avalvestern'lc. The inlet valves are positioned in the opening directionfby arot-ata'ble cam 141engaging a-cam follower roller 15a carried -at -the extreme vlett-band 'end of :an operating lever 15, `the mid-portion of which is fulcrumedat 1115b-on the turbine casing. Cam 14 is positioned 'by a rack and Ipinion 16,na mannerwhich'will be'obvious Afrom 'the'drawing :Itis to be notedthatemovement of the rack to the right-in 'the drawing `causesthe cam v414'to position valve ystern 13C `upwardly in the valveopening direction Actually, iin-such large capacity Asteam turbines, onthe order of 160,000 .kw., fthe admission of fnrotive tiuid :to

the high pressure turbine will ordinarily be controlled by a plurality of valves similar to that shown at 13, each having a main operating lever 13 and a cam keyed to the camshaft 14 but so shaped and oriented that the respective valves open in a preselected sequence. The inlet valve mechanism shown at 13 in the drawing is intended to represent that governing valve which opens rst as the rack 16 moves to the right.

The means for actuating these multiple governing valves comprises a hydraulic motor 17 having a piston 17a slidably disposed in a housing 17b and connected by a bellcrank 17C to position the rack and pinion 16. Motor 17 is controlled by a hydraulic pilot 18 having a slidable spindle member 18a connected to admit high pressure operating liquid to the upper end of cylinder 17h when the pilot spindle moves downwardly, and to the lower end of cylinder 17b when the pilot moves upwardly. The manner in which this is effected will be obvious from the drawing. It will, of course, be appreciated by those skilled in the art that the hydraulic pressure lluid for actuating the governing system is supplied by a suitable pump (not shown) which may for instance be driven from the turbine rotor.

Pilot 18 is positioned by a floating lever 19, the righthand end of which is connected by a link 20 to a threearmed lever 21, one arm 21a being connected to link 20 with a second arm 2lb connected by another link 22 to piston 17a. Those familiar with the art will appreciate that motion of the main operating piston 17a produces a restoring etfect on the pilot 18 by way of the

followup linkage

22, 21, 20, 19.

In normal operation, pilot 18 is positioned by an operating governor shown generally at 23 as comprising a conventional centrifugal flyball governor connected to position a pivot 24a connected to the mid-portion of a lever 2S, the right-hand end of which is connected by link 26 to the left-hand end of oating lever 19. The left-hand end of lever is carried by an adjustable fulcrum mernber in the form of a nut 25a carried on a threaded synchronizing screw 27, the position of nut 25a being determined by suitable manual or remotely controlled motor means, represented diagrammatically by the hand-wheel 27a. The flyball governor 23 positions pilot 18 to move the piston 17a in order to hold a pre-selected speed or load, the value of which is determined by the position of the synchronizing screw 27.

For shutting down the turbine in the event of an emergency overspeed condition, conventional emergency governors 2S and 28a are associated with the high and low pressure turbine rotors respectively, and are arranged to furnish a signal in the event the speed of either of the rotors reaches a preselected maximum permissible value, which signal trips closed the main emergency stop valve 3 and certain other valves described hereinafter. These emergency governors 2S and 28a may be of any suitable mechanical or electrical type, the precise details of which are not material to an understanding of the present invention. The dot-dash line 2811 in the drawing is intended to indicate that the emergency governors 28, 2da are suitably connected to stop valve 3 and other valves so as to close them upon attainment of a preselected overspeed.

In the event of an emergency overspeed condition, it is also necessary in a reheat type turbine powerplant to stop the tlow to the intermediate pressure turbine 7 of the steam remaining in the high pressure turbine 4 and the comparatively .long interconnecting conduit 4a, reheater 5, and conduit 5a. The volume of the high pressure steam trapped in these components can be suicient that it would create a dangerous overspeed in the turbines if permitted to expand through the intermediate and low pressure turbines. To prevent this, the intercept valve 6 is provided with a tlow control member 6b positioned by a hydraulic motor 6c under the control of a pilot valve 6d. Pilot spindle 6j is connected to be positioned by a lever 6e, the right-hand end of which is connected through suitable linkage to the piston rod so as to effect restoring -motion of the pilot f. The left-hand end of intercept pilot lever 6e is connected to a link 29 arranged to be positioned by a pre-emergency governor shown at 30 as being a second conventional ilyball governor similar to governor 23 but set to become effective at a certain speed somewhat higher than the rated speed of the machine. As shown in the drawing, governor 30 positions a lever 31 supported on a fixed fulcrum at its left-hand end and connected at the right-hand end to link 29. It'will be seen that an increase in speed will cause governor 30 to pull lever 31 downwardly, causing link 29 to lower pilot f so that hydraulic liquid is bled from the motor 6c, whereupon the heavy coil spring 6g causes the tlow control member 6b to move downwardly to closed position. Thus it will be seen that, as the speed rises toward a preselected value, the pre-emergency governor 30 iirst closes the intercept valve 6, and at an appreciably higher speed, the emergency governor 28 strips the stop valve 3. In the drawing, pilot f is shown below the aligned or neutral position which the pilot would occupy in quick starting operation. The reason for this will appear hereinafter.

For providing direct manual control of the turbine governing valves 13, as in starting the turbines, a manual starting member represented by hand-wheel 32 is provided. This manual control is represented diagrammatically as comprising a threaded screw 32a carried in a stationary nut and having a lower end adapted to engage lever 19, so that by turning the hand-wheel 32 pilot 18a can be forced downwardly to admit operating liquid to the upper end of cylinder 17 so as to move piston 17a downwardly in the valve-closing direction. In normal operation, the manually positioned screw 32a is backed completely away from the lever 19 so that the pilot 18a is under the sole control of speed governor 23. In preparation for starting the turbine, the hand-wheel is turned to cause screw 32a to force pilot spindle 18a to its loWermost position, so that motor 17 will close the governing valves 13. Then, when it is desired to admit steam through valves 13, the screw 32a is gradually backed off, permitting pilot to risc and cause motor 17 to open the control valves.

To permit quick-starting the plant with high temperature steam at temperatures on the same order of magnitude as that of the still hot turbine inlet parts, a bypass arrangement is provided permitting operation of: a steam generating equipment at part load, without passing any steam through the turbines, until the pressure and temperature of the motive tluid rise to values which the turbine can safely handle. Generally this means that the motive luid must be within about 5G F. oi" the temperature of the turbine parts.

This bypass arrangement comprises a turbine bypass conduit 5b for taking steam from the discharge side oi reheater 5 and passing it directly to the condenser 9. For preventing excessive pressures and temperatures in the condenser, which might otherwise damage the heat exchange tubes therein, a pressure-reducing desupcrheater is provided as shown at 33. This comprises a plurality of pressure reducingk orifices 'i series, shown at 33a, 33b, 33C, with a plurality of Water spray noi;- zles 33d, 33e interposedl between the respective orifices. The effect of the orifices is to reduce the steam pressure in progressive steps, while the water sprays reduce the temperature of the steam admitted to the condenser. The supply and control of this desu-perheating Water will be noted'hereinatter.

lf the steam delivered by the boiler were taken directly from the superheater 2, ywhen bypassec to the condenser as described above, the heat exchange tubes in the reheater 5 would be burned out. Therefore it is necessary to provide a second high pressure bypass conduit 2b, which takes steam fromthe outlet side of superheater 2 and supplies it to the inlet side of reheater 5. Thus the bypassed steam maintains at normal safeoperating-` temperatures the' heat exchange tubes inthe boiler 15, superheater 2, andfreheater To control the pressure and temperature conditions in the superheater and reheater during this process, several regulatingdevices are associated with the high pressure bypass conduit 2b. These include a high pressure bypass pressure regulating valve shown diagrammatically at 34 as having flow control means adaptedv to hold ata'preselccted value' the pressure of the steaml inl the superheater 2, in4 accordance. with a pressure signal derived from a suit-A able detector 35", responsive to the superhcater discharge pressure. Pressure detectenl 35 transmits an" appropriate signal: toi the regulating valve 3:4?- asl indicated' by the dot-dash line 35a.

The temperature of the reileater 5 is prevented from rising'to a dangerous: level by temperature control' means comprising a desuperheater4 inE the form of a water injection spray 36, the water supply to which is controlled' by a valve 37 inl accordance with a' signal received from a temperature detector 38f responsive to the temperature atV the discharge side ofireheater 5", as indicatedE bythe dot-dash line 38u; The' temperature detector 38 is` arranged toincrease the ilowy ofdesuperheater water when the temperature rises, so as to hold-` a preselectedreheater outlet temperature; InY normal operation, when the discharge temperature of reheater 5 is maintained at its rated value by thel normal flow of steamtherethrough, detector 3`8` automatically discontinues` the supply of water.

The precise nature and mechanical detailsl of the con-

l trol devices

34, 35 and 36', 3'7 are not' material to an understanding of the presenti invention; sincei they mayf obviously take the form of' anyoff numerous pneumatic, hydraulic, orelectrical temperature and pressure controlling devices known' to'- the art.

It remains to note that thehighA pressure bypass conduit Zb contains a manualI highpressure` bypass shutott. valve 39, ay high pressure' bypass emergency stopA valve 40, actuatedby the emergency governor 28= by the' signal transmitted as indicated by line 28h, and a pressure reducing oriiice' 4I disposed between theV regulating valve. 3'4 and the desuperheater 36. Thev function of orifice 41` is to reduce thepressure of the bypassed steam to' a value otV the same order of magnitude as that' occurring. in the reheater in normali opt-.raucht` The reheater outlet pressure and` the temperature o the' steam bypassed to the condenser through` conduit Sby are controtted: in the following'.I manner.V A. manuali turbine bypass stop valve 421 is opened to place' the bypass' Sb under control of an automatic valve shown at 43:. Thisi's-actua'llyV a multiple: valve having a.. steam ow control componentlta anda seconddesuperh'eating water flow control valve 431)', the latter" regulating the supply of Water to the pressure-reducing desuperhe'at'er 33' through the water supply conduit 44. lt will be apparent-from the. drawing'v that conduit 44 is connected to theV dischargeV conduit 11a of the boiler' feedi pumpf and supplies' desuperheating water toV the respective: sprays 3321, 33e. Thevalves 43a, 43h are positively linkedl together and controlled by asignal from" a pressure detector` 45 responsive to reheater outlet. pressure, as. indicated by the. dot-dash'l line 45a. It mayl be. noted'- that' valve 431 and pressure detector 45: are arranged sov` the valve 43` opens atlabout435 p; s. i; and: maintains. rehieater dis.'- charge pressure constant ate. about' 450 p. s; il, closing: whenever the. pressure'. at` the reheater discharge tends to fallv below 450. p. s'. i.

As noted above, the turbine governing valve 13 represents that one of the multiple: inlet valves: which'. opens first whenoperation ofl the high pressure turbine 4' is initiated. In restarting theV turbine after a; short shutdown period, with the turbine parts still hot from previous operation, it is-d'esired-th'at steam be admitted simultaneously to both the high pressure turbine 4 and intermediate pressure turbine 7 at temperatures which do not vary by more than a preselectedl differential from the' temperature' oftheV inlet parts ofthe respective turbines. To this'- end, the intercept valve bypassy conduit 5c takessteam from the reheater outlet by way of conduit 5a and supplies it to anv intercept bypass controlvalve 46. It will be seenV that valve 46 has aflow control member 46a biased Ito closed position by aspring 4Gb and arranged toI move in the opening direction by a lever 46c connected' by a link 46d to the point 15C on the main operating lever 15. By proper selection of the sizes of the pilot valve 13b and the intercept bypass tlow control member 46a, and by proper design of the actuatingy levers 1'5, 46c, the relative sizes of the ow control openings admittingl steam to the high pressure turbine 4 andintermediate p'ressure' turbine 7 can be determined. The arrangement is so selected that the rate of steam ow through the turbines 4; 7` will just bring them to normali speed and other operating conditions when operating at no load. It is also tofbe noted that the positive me` chanical interconnection between the main governing pilot valve 13b and the intercept bypass control valve 46u insures that they will open simultaneously. On the other hand, the main intercept valve 6 is not opened by the' governor untilvalves 13b, 46a have been opened wide sol as to bring the machine up to speed and apply a small load: More load can then be applied to the turbine byopening additional inlet valves 13 and the interceptvalve. This constitutes the reason for the displacement of pilot of belowthe aligned: condition. The amount of this displacement is identitiedat 6h, and is so selected that valves 13b, 46aget wide open before the intercept valve'6 be'- gins to` open. The intercept valve bypass conduit Se is provided with' a'n intercept bypass emergency stop valve 47, which is also connected'to'b'e closed by the emergency governor 28- throughinterconnection with the dot-dash overspeed signal line 28b.

It' remains tonote that the turbine governing system is provided with specialv means for overpowering` the preemergency governor 30- in such a manner as to` close the intercept valve 6 during the quick-starting cycle; This means comprisesV amanual control member shown as a hand-wheel- 481 arranged to= position-a nut 48a by rotation of a lead-screwV 48h. Pivoted to the nut 43u is a lever 49; the other end of which is' connected by a link 50 to a bell-crank 51T, the other arm of which is pivoted to the intercept valve control' link 29. The intermediate portionofV lever 49l is provided with apivot 49a disposed inl aufelongatedsloti 51a in' a link SIb, the other end of which isp'ivoted to" the third arm 21e of thethree-arm lever 2l.

The normal operating position of the nut 48a and' lever 49 are-shown in dotted lines in the drawing'. In such condition, the pivot pin 49a ioats` freely in the elongatedv slot 51a, so as to have no effect on the governing-` mechanism.

The-operation ofthe entire system is as follows.

First', it is to be" noted' that the governing system as shown in the drawing represents the quick-starting condition with' the boiler just about tobe red. As indicated by the legendon the drawing, solid arrows indicate fluid'flow'as' it;` occurs in normalV operation, dotted arrows represent the flow during the quick-starting cycle, and' thefdot-dasl'xVv lines represent the paths ot' the various condition-sensing signals.

Now; let it beassumedthat the entireplant; including the steam-generating apparatus 1`-, 2f, 5I is shut down. The manual hand-wheel 32V will be screwed down to depress' lever 159andV the main operating piston 17u willbeatthe bottom of its' stroke so that; both valves 13b and 46a will be closed, as shown. Since the preemergency governor 301is notrunning, lever'3'1l will tend to assume its uppermost position, so-tliat'pil'ot f'is raised to effect communication of operating liquid'to` the motor 6c. (In the drawing, pilot 6f-'isshown lowered, for av reason to be seen shortly.)

If now it is desired to start the plant, supply of cooling water to the condenser by way of conduits 9a, 9b will be initiated. Other turbine auxiliaries such as a separately driven pump for supplying lubricating oil to the bearings and hydraulic actuating liquid to the governor will be put into operation. These are conventional components and are therefore not shown in the drawing.

To condition the governing mechanism for the quickstarting cycle, the hand-wheel 48 is rotated so that nut 48a travels to the left on lead-screw 481;. whereup pivot 49a engages the left-hand end of slot 51a and pulls link 50 to the right so as to cause bellcrank 5l to rotate counterclockwise and thereby move link 2.9 downwardly, overpowering the pre-emergency speed governor 30. This causes pilot 6i to drain the operating liquid from motor 6c, and the intercept valve member 6b descends to closed position, as shown. Next it is necessary to open the manual high pressure bypass shutoff valve 39 and the manual turbine bypass shutolf valve 42.

Now with the condensate pump 10 and boiler feed pump 1l operating, the boiler 1 may be fired, and the temperature and pressure of the steam in the superheater discharge conduit 2a begins to rise. When the superheater discharge pressure reaches a value slightly higher than rated pressure, the pressure detector 35 causes the pressure regulating valve 34 to open, and thereafter holds the superheater discharge pressure constant at that value. The pressure of the steam flowing from the superheater to the reheater is reduced at the pressure-reducing orifice 41 to the reheater pressure which may be around 400 to 500 p. s. i. Specicaiiy, when the reheater discharge pressure rises to a preselected value, the pressure detector 45 causes steam bypass valve 43a to open, and steam begins to flow from the reheater to the condenser 9 by way of conduit 5b and the pressure-reducing desuperheater 33. Simultaneously, the water supply valve 4311 is opened and the water sprays 33d, 33e, effect an appropriate reduction of temperature of the steam entering the condenser so that the condenser tubes will not be damaged.

increasing the firing rate of the boiler will now cause the discharge temperature of the superheater and reheater to progressively rise and the rate of flow through the turbine bypass conduit 5b to increase, With pressure regulating valve 43a maintaining a constant pressure in the discharge conduits Sa, 5b of reheater 5. The boiler tiring rate is gradually brought up to a value which will produce conditions of 1850 p. s. i. and 900 F. in the superheater discharge conduit 2a. Control of the tiring rate determines the superheater discharge temperature, and the pressure detector 35 controlling the high pressure bypass valve 34 holds the superheater discharge pressure at the desired value. The orifice 41 reduces this pressure, and the temperature detector 38 controlling the desuperheater water valve 37 maintains the temperature at the discharge side of the reheater at a value of perhaps about 900 F., which value is carefully selected to be no more than a safe differential from the temperature of the still-hot turbine parts during the quick-starting cycle.

As noted above, the turbine bypass regulating valve 43a maintains the reheater discharge pressure in conduits 5a, 5b at a preselected value between 400 and 500 p. s. i. The capacity of the high pressure bypass 2b and the turbine bypass conduit Sb is adequate to permit the

steam generator

1, 2, 5 to operate at about one-quarter of its normal rated capacity, this rate being whatever is just sutlicient to permit the boiler to be brought up to the desired discharge conditions, which rate is of course a function of the boiler operating characteristics. It is necessary here to note only that the capacity of the bypass conduits must be suicient to permit the steam generator to develop the desired operating conditions With its entire output going through the bypass to the condenser 9, none passing through the turbines.

It will be seen that now there is available steam at apefr-173% propriate pressuresl and temperatures for operating both the high pressure turbine 4 and the intermediate pressure turbine 7. Therefore, the turbines may be started by rotating the hand-wheel 32 so pilot 18a is permitted to move upwardly and operating liquid is supplied to the lower end of hydraulic cylinder 17b to move piston 17a up and begin to open the governing valve pilot 13b and the intercept bypass valve 46a. Thus steam at substantially the temperature of the hot inlet parts of the turbine is caused to flow simultaneously through both high pressure turbine 4 and intermediate pressure turbine 7. Since the intercept valve 6 is still closed, steam discharged from the high pressure turbine 4 through conduit 4a goes to the reheater 5 and, if the ow through valve 13b is larger than that through valve 46a, a part of the steam passing the high pressure turbine will ilow through the bypass conduit 5b directly to the condenser.

When valves 13b and 46a are about 3i open, the rate of flow is sucient to drive the turbine rotors at normal operating speeds. This of course means that the main operating governor 23 and the pre-emergency governor 30 are rotating at normal speed. The manual starting hand-wheel 32 can now be backed away from lever 19 so governor 23 controls the speed of the turbine; but nut 48a of the quick-starting hand-wheel 48 is still in the fullline position so it overpowers the pre-emergency governor 30 and holds the intercept valve 6 closed.

The turbines are now operating at normal rated speed. The electric generator driven by the turbines may now be interconnected with the power distributing network (not shown). With load thus applied to the turbines, the operating governor 23 causes hydraulic motor 17 to begin to open the main governing valve 13a. Continued upward movement of piston 17a causes the three-arm lever 21 to rotate counterclockwise so that link 51 moves to the left relative to pivot 48a. Thus, the overpowering mechanism releases link 29 of the pre-emergency governor, gradually causing pilot 6J' to lift and open the intercept valve in proportion to further control valve movement.

Meanwhile the turbine bypass valve 43a and the high pressure bypass valve 34 have progressively closed, in the following manner. As noted above,

valves

34 and 43 are arranged to maintain a preselected superheater and reheater discharge pressure respectively. When the turbine governing valves are opened and steam is admitted to the turbines, the superheater and reheater pressure tend to drop, thus both pressure controlling valves progressively close in attempting to keep the respective pressures constant.

In this way the automatic

pressure regulating valves

34 and 43a automatically reduce progressively, and then stop entirely, the ow through the high pressure bypass 2b and the turbine bypass 5b when motive fluid is admitted to the turbine.

The invention provides a comparatively simple addition to the governing systems known to the prior art, by which the boiler can be operated at a reduced rate, with no ow through the turbines, until the proper steam conditions are obtained. This is eiected by a bypass system which maintains all portions of the steam generating equipment at safe temperatures and pressures and discharges the bypassed steam safely into the condenser. The specially arranged turbine inlet valves 13b, 46a eiect supply of motive fluid to the high pressure and intermediate turbines at an easily controllable rate suicient to keep the turbines at an adequate temperature and drive the rotors at normal operating speed at no load. The main intercept valve 6 remains closed until the electrical generators are synchronized, after which the intercept valve gradually opens so that a high reheater pressure is maintained through the low load range of the unit, This is necessary to allow the boiler to keep the temperature of the reheat steam at 900 F. or above, which is necessary to start the hot turbine safely. As the load is increased to rated load, the intercept valve will be opened wide and normall operating conditions are resumed. Once' in normal operation, theV quick-startingl hand-Wheel 48 may be' rotated so nut 48a assumes the dotted line position shown in the drawing, in which condition pivot 49a merely lioats freely in the slot Sla so as to have no effect on the governing mechanism.

With this arrangement, it is possible to start safely a high temperature reheat type turbine in a period of 15 or minutes, as compared with several hours required Without the invention. Thus it becomes feasible to shut down a large reheat turbine plant promptly when' the load falls at night, shutting down the associated boiler entirely and retiring the boiler and restarting the turbine in the morning' when the load' on the power system begins to increase.

The special emergency stop valves 40', 47, in addition' to the conventional main stop valve 3, are under the control of the emergency governor 28 to provide full emergency overspeed protection both during the quick-starting cycle and during normal. operation.

An additional advantageA of the system is that if, during normal operation, theload is suddenly removed from the turbines, so the governing valves 13' suddenly close, the pressure in conduit 2a will rise and pressure detector 3'5 will cause valve 34 to open and motive fluid to be diverted through bypass 2b, whereupon the bypass valve 43 opens and the steam is discharged directly to the condenser, until the boiler controls canreact to reduce the firing rate to the no-load condition. This provides an additional safety feature and operation convenience.

While only one specific embodiment has been describedv herein,. and that in quite diagrammatic fashion, it will be apparent that many changes and substitutions of equivalents may be made without departingfrom the invention. it is, of course, intended to cover by the ap.- pended claims all such modifications as fall Within the true spirit and scope of thev invention.

What we claim as new and desire to secure by Letters Patent of the United States is:

l'. In a reheat turbine pow'erplantl having in series a boiler, superheater, high pressure turbine, reheater, main intercept valve, intermediate pressure turbine, and c'on.- denser, the combination of a first steam conduit cornmunicating between the superheater discharge and the high pressure turbineV inlet andy having first governing valve means, a second steam conduit in parallel with the intercept valve and communicating between the reheater discharge and the intermediate pressure turbine inlet, an intercept bypass valve in saidA second conduit, a third high pressure bypass steam conduit communicating between the superheater outlet and the reheater inlet, means for maintaining the pressure of the steam discharged'from the superheater at a rst preselected high value, means for maintaining the temperature of the steam delivered from the reheater at a first preselected value, al fourth steam conduit communicating between the reheater outlet' and the condenser, means for maintaining the pressure at the outlet of the reheater at a value below said: first pressure, means for reducing the pressure and; temperature of steam entering the condenser through said fourth conduit, and means for opening both the first governing-valve means and the intercept bypass valve whilel the-mainlintercept valve remains closed, whereby comparativelyco'olY steam may be bypassed: around'` the turbinesv directly to the condenser in starting and Warming up theboiler.

2'. In a reheat turbine p'o'werplant having inl series a boiler, superheater, high pressure turbine, reheater, main' interceptJ valve, intermediate pressure turbine, and: condenser, the combinationV of' a1 first steamA conduit communieatingfbetween the superheater and thehigh pressure turbine inlet and having first governing valve means, asecond conduit in parallel with the main intercept' valve and communicating between the reheater and the intermediate pressure turbine and having an intercept bypass valve, a third bypass steam conduit communicating between the superheater and the reheater inlet, autonlatic valve means for maintaining' the pressure of the steamv discharged from thesuperheater4 at a' firstv preselected' high value, means for maintaining the temperature of steam delivered from the reheater at a preselected value, a fourth bypass steam conduit communicating between the reheater and the condenser and' having automatic valvel means for maintaining at the outlet of the reheater` a pressure below said first pressure, means` for reducing the pressure and temperature of the steam entering the condenser through said fourth conduit, whereby the boiler may be fired and brought up to normal operating conditions with4 said governing and intercept bypassV valves closed, and means for opening said governing valve and intercept bypass valve while the main intercept valve remains closed, whereby steam may be admitted to the high pressure and intermediate pressure turbines to bring the" rotors thereof up to normal speed while the main intercept valve remains closed and excess steam is bypassed through said fourth conduit to the condenser.

3. In a reheat turbine powerplant having in series a boiler, superheater, high pressure turbine, reheater, main intercept valve, intermediate pressure turbine, and condenser, the combination of a first steam conduit communicating between the superheater and the high pressure turbine and having first governing valve means, a second conduit in paralleli with the main intercept valve and communicating between the reheater and the intermediate pressure turbine, an intercept bypass valve in said second conduit, a third high pressure bypassconduit communicating4 between the superheater and the reheater inlet, automatic pressure-regulating valve means for maintaining the pressure ofthe steam discharged from the superheater at a first preselected high value, automatic desuperheater means for injecting water into the bypassed steam entering the reheater through said third conduit for maintaining the temperature of the steam leavingl the reheater at a preselected value, a fourth conduit communicating between the reheater outlet and the condenser, automatic pressure-regulating valve means for maintaining at the outlet of the reheater a pressure below said firstpressureorifice means in, said fourth. conduit for reducing the pressure of the steam entering the condenser through said fourth conduit, automatic desuperheater means for injecting water into theV bypassed steam for reducing the temperature of the steam enteringA the condenser through said fourth conduit,- whereby the boiler may be operated ata limited rate. toA establish* normal operating. conditionstherein with the steam flowing through said` fourth. bypassY conduit direct to the condenser while said governing valve, main intercept valve, and intercept bypass. valve remainclosed,l and means for opening said governing' valve and intercept bypass valve substantially simultaneously while the main intercept valve remains closed, r whereby steam may be admitted to the high pressure and intermediate pressure turbines for bringing the rotors thereof up to normal speed while excess steam is bypassed to thecondenser.

4. In a reheat turbine Powerplant having in series a boiler, superheater, high pressure turbine, reheater, main intercept valve,l intermediate pressure turbine and condenser, the combination-of a first conduit-f communicating between. the. superheaterdischarge and the high pressure turbineand having first governing Valvemeans for admitting a limited flow of steam-tothe high pressure turbine adequate to establish. no1-.mal speedthereof at no load, a second.-4 conduit in parallel with the main intercept valve and communicatingbetween the reheater andV the intermediate pressure turbine, second valve means for admitting steam through said second conduit at a limited rate to the intermediate pressure turbine adequate to establish normal operating conditions therein,A a third high pressure bypass conduit connecting., between the superheater andthe reheater inlet, automatic pressure regulating valve means for maintaining the pressure of the steam discharged from the superheater at a first preselected high value, automatic desuperheater means for maintaining the temperature of the steam discharged from the reheater at a preselected value, a fourth conduit communicating between the reheater and the condenser, orice means for reducing the pressure of the bypassed steam admitted through said fourth conduit to the condenser, second automatic desuperheater means for injecting water for limiting the temperature of the steam entering the condenser, whereby the boiler may be brought up to normal operating conditions with all the steam generated therein flowing directly to the condenser, and means for opening said first and second valves to admit steam to the high pressure and intermediate pressure turbines and bring the rotors thereof up to normal speed while excess steam is bypassed from the reheater through said fourth conduit to the condenser.

5. In governing mechanism for a reheat turbine power'- plant having conduits connecting in series a boiler, superl heater, high pressure turbine, reheater, main intercept valve, intermediate pressure turbine, and condenser, the combination of first governing valve means controlling the admission of steam to the high pressure turbine, bypass conduit means communicating between the reheater and the intermediate pressure turbine, second intercept valve means controlling the admission of steam to the intermediate pressure turbine through said bypass conduit means, first motor means controlled by a main operating governor for opening said first and second valves simultaneously, second motor means actuating the main intercept valve, pre-emergency speed governor means connected to said second motor means and adapted to open the main intercept valve only after said first and second valve means are opened a preselected amount, and means for disabling the second motor means whereby the first and second valve means may be opened to admit motive iiuid simultaneously to the high pressure and intermediate pressure turbines while the main intercept valve remains closed.

6. Governing mechanism in accordance with claim in which the mechanism for disabling the second motor means comprises an overriding lever member for positively maintaining the intercept valve closed, adjustable fulcrum means adapted to move one end of said lever from a starting position to a normal operating position, first linkage means connecting the opposite end of said lever to position the intercept valve in the closing direction, and second linkage means including a member positioned in accordance with the motion of the first and second valves and having a lost-motion connection with an intermediate portion of said lever, said lost-motion connection constituting an operative fulcrum for said lever when the first and second valves are closedy whereby the main intercept valve may be closed by moving said adjustable fulcrum to the starting position, said lost motion connection permitting free motion of said lever without effect on the main intercept valve after movement of said fulcrum to normal operating position.

7. Governing mechanism in accordance with claim 5 in which the mechanism for disabling the second motor means comprises an overriding lever member for maintaining the main intercept valve closed during a preselected initial movement of the first motor means in the direction to open the first and second valves and for positioning the main intercept valve proportional to further movement of said first motor means, adjustable fulcrum means for moving one end of the lever from a starting position to a normal operating position, first linkage means connecting the opposite end of said lever to the second motor means, and second linkage means including a member positioned in accordance with motion of the first motor means and having a lost motion connection with an intermediate portion of said overriding lever member, whereby the main intercept valve is sub- 12 ject to the control of the pre-emergency governor when said adjustable fulcrum is in normal operating position, said second linkage means serving to override the preemergency governor and maintain the main intercept valve closed while the first and second valve means move said preselected initial portion of their travel.

8. In governing mechanism for a reheat turbine powerplant having conduits connecting in series a boiler, superheater, high pressure turbine, reheater, main intercept valve, intermediate pressure turbine, and condenser, the combination of first governing valve means regulating the admission of steam to the high pressure turbine, other conduit means with second intercept bypass valve means and communicating between the reheater and the intermediate pressure turbine, first motor means for opening said first and second valves simultaneously and including a motor controlled by a main operating governor, second motor means for opening the main intercept valve and including a motor controlled by a pre-emergency speed governor', means for disabling said second motor means whereby the main intercept valve remains closed while the first motor means moves the first and second valve means in the opening direction up to a preselected limit, and means for positively positioning the main intercept valve proportional to movement of the first and second valve means above said limit whereby a higher than normal reheater pressure is maintained during part load operation of the turbine.

9. In a reheat turbine powerplant having steam generating means for supplying motive fluid at a first preselected high pressure to a high pressure turbine, steam reheating means, main intercept valve means for controlling the liow of motive fiuid from the reheater to an intermediate pressure turbine, and a condenser, the combination of first governing valve means for controlling the flow of motive fluid from the steam generator to the high pressure turbine, means defining a bypass passage with first bypass valve means for admitting motive fluid to the intermediate pressure turbine independently of said main intercept valve means, second bypass conduit means with pressure reducing means for supplying motive fluid from the steam generator to the reheater inlet at a pressure substantially below said first pressure, and third bypass conduit means communicating between the reheater outlet and the condenser and having valve means for determining the tiow therethrough, means for reducing the pressure and temperature of steam entering the condenser through said third bypass conduit, and means for opening the first governing valve means and the first bypass valve means while the main intercept valve remains closed, whereby steam may be bypassed from said generating means to the condenser during the starting cycle of the powerplant.

l0. ln a reheat turbine powerplant having in series steam generating means, a high pressure turbine, steam reheating means, main intercept valve means, an intermediate pressure turbine, and a condenser, the combination of first governing valve means for admitting a limited iiow of steam to the high pressure turbine adequate to establish normal operating conditions therein at no load, first bypass conduit means in parallel with said main intercept valve and communicating between the reheater and the intermediate pressure turbine, second valve means for admitting steam through said first bypass conduit at a limited rate to the intermediate pressure turbine adequate to establish normal operating conditions therein at no load, second high pressure bypass conduit means cornmunicating between the steam generator outlet and the reheater inlet, means for maintaining the pressure of the steam at the outlet of the steam generator at a first preselected high value, means for maintaining the temperature of the steam discharged from the reheater at a preselected value, third bypass conduit means communicating between the reheater outlet and the condenser, means for limiting to preselected safe values the pressure and temperature of the steam entering the condenser through said third bypass conduit, whereby the steam generating means may be operated to establish normal steam operating conditions with all the steam from the generator flowing to the condenser without passing through the turbines, and means for opening said iirst and second valve means to admit steam simultaneously to the high pressure and intermediate pressure turbines and establish normal operating conditions therein while said main intercept valve means remains closed and any excess steam produced by the generator is bypassed from the reheater through said third conduit to the condenser.

11. In governing mechanism for a reheat turbine powerplant having conduits connecting in series a steam generator, high pressure turbine, reheater, mainintercept valve, intermediate pressure turbine, and condenser, the combination of iirst governing valve means regulating the admission of steam to the high pressure turbine, bypass conduit means with second bypass valve means commu- 14 nicating between the reheater and the intermediate pressure turbine, rst motor means connected to open said first and second valves substantially simultaneously, second motor means connected to open the main intercept valve, means for disabling said second motor means whereby the main intercept valve will remain closed while the first motor means causes the irst and second valve means to open to a preselected position, and linkage means connecting the first motor means to the second motor means to open the main intercept valve proportional to movement of said first and second valve means in the opening direction beyond said preseleted position.

1,726,561 Hodgkinson et al Sept. 3, 1929 Rice Sept. 21, 1915 y