US2727523A - Compensating speed governor, especially for hydraulic turbines - Google Patents

Description

T. W. BROWN Dec. 20, 1955 COMPENSATING SPEED GOVERNOR, ESPECIALLY FOR HYDRAULIC TURBINE-S Filed May 27, 1950 m (j P. M O

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c 5 a a 2 a 0 w 22 2 2 4 6 2 g 2 1 l i a g a Patented Dec. 20, 1955 COMPENSATHNG SPEED GGVERNOR, ESPECIAL- LY FUR HYDRAULIC TURBINES Thomas W. Brown, Ashiand, Mass, assignor to Lombard Governor Corporation, Ashland, Mass, a corporation of Massachusetts Appiication May 27, 1950, Serial No. 164,774 Qlaims. (Cl. 137-34) My present invention relates to governing, regulating and control systems and apparatus generally, and especially as related to governing the speed of prime movers, as for example, hydraulic turbines. More particularly it aims to provide improved controlling means having secondary compensating or follow-up means in association with a primary servo and pilot or other main controlling device.

It is the general practice in hydraulic turbine governor design to provide a primary means acting back from the supply regulating or gate-operating element for modifying the action of the prime mover speed measuring device upon the primary pilot or main motor controlling device, to prevent overtravel of the gates with consequent instability. It is also not unusual to employ some secondary means to overcome gradually the larger speed changing effect of such primary means, in an effort to produce approximately iscchronous governing yet without objectionable instability. However, the provision of such secondary compensating means presents various problems and heretofore has not been accomplished with entire satisfaction.

capable of accomplishing substantially isochronous governing with adequate stability, while avoiding difiicult mechanical fits, use of critical springs and the like, or the requirement of extended periods for adjustment.

The invention will be more fully understood from the following description taken in con'unction with the accompanying drawings illustrative of one embodiment thereof, in which:

Fig. l is a schematic view of a fluid-pressure operated hydraulic turbine governor novelly incorporating secondary compensator means; and

Fig. 2 is a schematic view of an alternative form for the compensator throttle.

In the selected example the novel governor system and compensator means is illustrated in association with an hydraulic turbine indicated generally at 10, having an l closes the turbine gate to reduce output speed; coversely, counter-clockwise turning of shaft 28 will open the gate and increase the speed.

H In the illustrated application of the invention to govern ing hydraulic turbines, it will be understood that the final control or regulating element is the gate shaft 28 of the turbine whereby the control agent, in this instance the hydraulic driving energy supplied to the turbine, is varied by the automatic governor means here concerned f6 give to the variable and regulated quantity the desired value, namely, a substantially constant speed for the turbine out- 2 put regardless of changes, and particularly step changes, in the load.

The governor system comprises first a metering and force relaying element shown as a tachometer of the centrifugal type, of known or preferred construction, designated generally at 16. It has a spindle 17 driven from the turbine pulley 12 as by a belt 13 passing over a guide pulley 14 to a pulley 15. The latter is held from axial movement while the spindle 17 is slidably splined or otherwise angularly fixed coaxially in it, with capacity to shift axially, vertically in the diagram, under output speed change at the turbine.

The centrifugal action of the revolvable masses or flyballs 18a, 18a hung on the spindle 17 and their attendant radial movement is converted to axial movement of the spindle, downward in the drawing under turbine speed increase, and vertically upward under speed decrease. A

end of the lever 20 as at 20a. The slidable valving spool element 22a of the three-Way pilot valve 22 cooperates with upper and lower ports to close both in the neutral or equilibrium position, and to open one while closing the other in upper and in lower positions, reversely, thereby placing the opened port in communication with the comcrank arm 27 on the gate shaft 23 and connected to the servo piston 26a as by a rod 26b. Piston movement to the right turns the gate shaft 28 clockwise, in the gate pilot valve 22. It is normally, as during periods 'of no change'in the turbine load, balanced between the operating fluid pressure from the tank 25 through a branch line 250 to the smaller piston face, and the remaining pressure at the larger piston face, at the left in the diagram, under the closed-off neutral position of the pilot valve 22. 7 t

In this neutral position both the pressure tank 25 and movement, port either the upper or the lower pipe 230 brZS'a throughthe valvetoth'e line 24 to the larger face of the servomotor piston --26a. -In the diagram down movement of the tachometer spindle 17 and of valve spool 22a opens thelower valve port and thus through lines "25a Land-24 subjects said larger piston "face to the oil pressure from the supply tank, thereby moving the pistonfifia toward'the'right on'the drawing,'-to close the gate. Conversely, opposite upward movement of the spindle 17' and val-vespool 22a subjects said larger face of' 'the servo piston' 26a-to the lower pressure side of the system, through the line 24, the then open upper port of valve 22 an'dthe'upper pipe 23a leading to the sump '2'3, with resu'ltantpistontravelto the left onthe' drawing, in the gate opening direction.

"'By way-"of summary tothispoinnthe desired constant output speed for the turbine over a range of loads requires corrective variation of the turbine input energy at' thegate directly with theload 'and'inversely with the output speed. The described'primary control accordingly Closes the gate under speed'increase (load decrease) and opensit under'speedreduction (load increase). With descent ofthe spindle 17 under speed increase the servo piston'26a'movesto theright and'turns'the gate shaft'23 clockwise-to close the gate in-the speed decreasing direction. And with rise of the spindle 17 under speed decrease the servo piston 26a goes to the left and the gate shaft-28 is turned counter-clockwise in the gate opening and speed increasing direction.

Topreventovertravel'of the gate and consequent instability in the governing action it is common practice to employ a primarycomp'ensatingmeans or follow-up. Herein such primary compensating meansto modify the action oftherelay'governor 16"on the primary control valve-orpilot 22 comprises a'verticallink 31connected as zit- 201; totheendof the lever '20 distal 'to' theprimary valve 22. This-link 31is intermediately connected as at 31 a toa secondhorizontal'lever 30. The right .end of the latter is pivoted as at 3'0bto the upper end of a' followup=link29 the lower end of which is pivoted to a short lever-arm 27a angularly fixed with the lever 27 on the gate shaft 28 previously described. As will be more fully apparent hereinafter, action of this primary compensating means 270:, 29, 31, b is to return the primary pilot or control valve 22 to neutral, as illustrated in Fig. l, in-response to regulating movement of the gate shaft 28, and thus reestablish an equilibrium.

'Butwith such primary compensation if alone and unmodified such equilibrium is restored at a substantially differentturbine speed-than was in effect before the load change. Accordingly a secondary compensating means, which is-itself susceptible of appropriate regulation, is herein novelly provided. The'purpose of'this secondary compensating means is to overcome the stated turbine speed'ch'ange or deviation from original speed before the load change, by maintaining an imbalance in the governor-until the turbine speed has been returned to approximately its initial value, thereby producing such isochronous governing as is consistent with stability.

As herein illustrated such secondary compensating means of-my present invention is'indicated generally at 32, centrally of Fig. 1. It comprises a three-way secondary control or pilot valve 33 which may'besimilar in type toprimary pilot 22. Operatively associated with it is a secondary se1vomotor'34. The secondary compensating means further comprises a lever connection between the secondary pilot andservo, andwith'the follow-up means, together with piping-connections as indicated. The slidable valve 'spool 33a of the secondary pilot 33 is reciprocable by a link 35Iwhich maybe an extension of vertical link 31 of the follow-up or primary compensator means. it ispivoted at -31a intermediary of the second horizontal-lever 30 already mentioned.

' The-secondary pilot or-control valve 33 is connected to the sump 23 through an upper pipe branch' 23b from the sump line 23a,.and to thepressure tank 25 "through a lower pipe branch 25b from the pressure line 25a. This secondary pilot 33 is adapted to place the lower andlarge face of the piston 34a of the secondary servo 34 alternatively in communication with the low-pressure or sump side of the system or with the pressure side. This is accomplished through the pipe connection 36 between the common intermediate port of the secondary pilot 33 and said lower'end of the secondary servo 34. The upper end of the latter, and upper and smaller face of the secondary servo piston 34a have a pipe connectiorr 25d to the pressure fluid line 2511.

An adjustable flow restrictor or throttle 36a limits the rate of flow through the pipe 36 between the secondary servo and its pilot. Under equilibrium conditions piston 34a is balanced in the secondary servo 34 by a constant pressure supply from tank 25 through pipe 25d. It is coupled by its rod 37 to the adjacent end of the second horizontal lever 3b as at 30a, opposite to the primary compensator arm connection 3012. It will be seen that the secondary pilot or control valve 33 will be shifted through lever 30 under the combined influence of thezprimary compensator or follow-up arm 29 and of the secondary servo 34. This secondary pilot 33, like main pilot valve 22, will have upper, intermediate, and lower positions in which it supplies variously sump, equilibrium or system, and pressure tank pressures to the larger-area face of piston 34a of the secondary servomotor 34. The linkage 37, 30, 35 in a sense provides a follow-up action between this secondary servo 34 and its pilot 33.

Itwill'be obvious that in the operation of the described system and means the similar sequence of events will occur in response either to a decrease or to an increase in the turbine load, but with the various motions having opposite directions. For purposes of the present discussionit will be assumed that the system has been in operation at the desired speed under some fixed load in .the turbine, and that this load decreases suddenly in a step change to another fixed load. The resultant increase in the regulated quantity or turbine speed will effect a corresponding increase at the tachometer 16 and the governing apparatus proceeds in effect to cut ofi the necessary amount of hydraulic energy from the turbine to suit the new load and to operate the turbine at the same speed as formerly.

Under such load drop and speed increase the attendant radial outward movement of the tachometer masses 18a will drop the spindle 17 and the valve spool 22a of the primary pilot 22. The distal or right end 20b of horizontal lever 20 initially remains fixed. Oil from the pressure tank 25 is thus admitted to the primary servomotor 26, forcing its piston 26a to the right and rotating gate shaft 28 clockwise to close the turbine gate. Closing of the gate tends to reduce the speed; the speed measuring force of masses 18a is accordingly reduced and the tachometer spindle 17 is permitted to return upward.

Coincident to this, the primary follow-up arm 29 is urged downwardly by the clockwise rotation of the gate shaft, drawing down with it end 20b of lever 20. The secondary servo piston 34a may be regarded as stationary for the moment. These two results of the gate shaft movement combine to raise lever end 2011 and primary valve spool 22a to an equilibrium or neutral position, cutting off the oil to servo 26 and so halting movementof the gate. Assuming suitable adjustments throughout, and supposing the secondary compensating means were inoperative or not present, the sequence of events started 'by the initial load change is thus ended. But equilibrium is thus reestablished at a higher turbine speed than .formerly, due to the fact that a lower position of tachometer spindle '17 will suflice to hold valve 22 closed, in view of the lowered position of the end 2012 of lever 20.

Now consider the secondary compensator means including the secondary servo 34 and its pilot valve 33. With'these present and operative, the above mentioned otherwise operatable flow restrictor downmovement of the lever end b eifects a like down movement of the secondary valve spool 33a, admitting oil from pressure tank to the larger under face of the piston 34a of the secondary servo 34. This forces said piston 34a and the adjacent end a of the second horizontal lever 30 upward. The opposite end 3% of said lever being momentarily fixed, the secondary valve spool 33a and the overlying end 20b of the first horizontal lever 20 are likewise raised, thus simultaneously tending to return the secondary valve 33 to its neutral position and the end 20b of lever 20 to its original position. This will initially force main valve 22 from its momentarily established neutral position, in the speed reducing direction. The result is that the turbine speed is required to return through a rapid series of approximations to its desired initial value preliminary tore-establishing equilibrium in the governor system. It will be observed that the secondary compensation is mechanically opposite to the primary follow-up lever action, thereby tending to prolong the total unbalance until the original speed value is reached. At the same time the secondary compensation aflects the primary pilot in the same directional sense as did the load change, thereby overcoming the deviation otherwise resulting as between the regulated speed and the set point or original speed.

The flow of oil from the secondary valve 33 to its associated servo connection 36, which provides the minimum damping or drag necessary for appropriate governor stability.

same resultant of exact same speed maintenance. In the case of a continuously changing load the same events will take place, but will overlap in accordance with the particular form of the load variations, the net eflect of the governing system being to cause the speed deviations to be minimized.

For certain installations, for example those involving higher turbine loads, having higher inertia and requiring less damping for governor stability, the modified cona secondary compensator corresponding to that of Fig. 1, other parts of the system being understood as the same. The similar pressure fluid connection between the secondary pilot 33 and the associated servo 34 is indicated at 36 and the adjusting throttle at 36a. In this instance the system further includes a second connecting line 38 between the secondary pilot and servo 33, 34. This may generally parallel the line 36 and forms a shunt or alternate therefor. In it are incorporated a remote-control on-and-ofl valve 38a herein shown as solenoid operated, and a manually or or throttle 38b. This latter corresponds in general function to the throttle 36a and has a predeterminedly settable and in assumed higher-load example a smaller throttling effect than the other throttle 36a. The solenoid of the on-ofl valve 38a is suitably connected for actuation, preferably automatically, when the turbine such as 10 is placed under known heavy-load condition on the power line. The solenoid is thereby energized to open valve 38a, the eflect of which is to by-pass throttle 36a and permit a higher velocity flow through throttle 38b as consistent with the lesser requirement of damping under the higher inertia conditions.

It will be understood that for any particular application of the system, the amount of hunting or oscillation which must be removed by the above mentioned throttling for purposes of stability can be predetermined, as well as whether alternatively selectable speeds of response are desirable or necessary under given operating loads.

It will be understood that my invention, either as to system, means or method, is not limited to the exemplary or described, and I set forth its scope in my following claims.

I claim:

1. In combination with a prime mover having a supply regulating element, a main motor connected to and positioning said element, a pilot controlling said motor and having a neutral position when the speed of the prime mover is at set point value, a prime mover speed sensing device, a first floating lever connected at one end point to said ondary motor govern said primary pilot directly and also independently one of the other.

3. In combination with a prime mover having a supply regulating element, a primary pilot having a neutral position when the speed of the prime mover is at set point value, a main motor controlled by said pilot and connected to and for positioning said supply regulating element, follow up means comprising a floating lever connecting said regulating element to said primary pilot, a prime mover speed sensing device connected to said follow up means and to move the primary pilot in one direction from said neutral position upon departure of the prime mover speed from said set point value, movement of said regnlatingelement efiecting tlirough-said iollow up means returnlmovementnoi said primarytpilot tintatdireetionppgositetojsaid one direetiontand totthet-neutraltposition, and secondary compensator meansl'includinga-lmotor and. a.

device connected-:toz-saidpilot:andior. moving. the pilot'in' one .tdirection,-. from said neutrabposition (upon. departure ofjthe prime rnover speed-from saidzsetpoint,value,.fol1ow up: meanseconnenting-r said snpplyregulating .elernentgto said primary pilot andw forcopposit returnamovement of the pilot to the.nentral positiom..a secondary motor and pilot, said secondary pilot connected; to saidnfollow :up meanszand moving-fromwneutral: position upon said primary-.ipilotz return :movement, said secondary motonconnected to rand for: movingthe primary pilot-z fromthe neutra'l'position and in the same-sense as initially by'thespeed sensing device; means 'for selectively varying the rate of movement of said secondary "motor comprising parallel fluid. tlines between said. ,rnotQr; and ;1 i.1,0t,v adjustable thl'QifliIlg; elements :in both; said dines, ,andr on-ofi valve means in one said. line.

5 In combinations-with, a. prime. movgarhaving a supply regulatinglelement; ,a mainnmotor-tconnected to and positioning said element; .al pi-lot controlling said motor and having agneutral positiou; when. the .speedof the prim mover ;is= ,at -se,t -point value,;aspeed-sensing device connected :to. saidzpilotandrvfor movimgthe pilot inone direction ,firom said, ,neutral position; upon departure of the prime, mover speedlfrom said point value,,fc llctvvv up means connectingsaid .supply regulating element to said primary pilQt;andfor. op osite:returnlm v ment-ofthelpilotto h neutral. position, .a. secondaryv .Inotor andv pil t, aid secondary pilot connected.to,saidf01low.;up,means and moving from. neutral. position .upon .said primary pilot return movement, saidsecondary motor vconnected.to and for moving the pIllIl8Ify..Pi10t from the. neutral position and in the same senseasinitiallyrbylthespeed sensing device,

parallel .fluid'linesthetweensaid s econdarymotorand pilot,

throttling; elementsin .eachtof said lines. and adapted to fford difier-ent degrees .of-ithrot lin and rem y c011- trollable valve means.nornntlly, .elosingthe lesser-throttled line and. automaticallylqperableto openthe same during predetermined load conditions.

References Citedfin the file of thispatent UNITED ST TES.- BAEENTS

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