US2898925A

US2898925A - Speed controller for impulse turbines

Info

Publication number: US2898925A
Authority: US
Inventors: Clarence L Avery
Original assignee: Woodward Governor Co
Current assignee: Woodward Inc
Priority date: 1955-09-14
Filing date: 1955-09-14
Publication date: 1959-08-11
Anticipated expiration: 1976-08-11

Description

Aug. 11, 1959 c. L. AVERY SPEED CONTROLLER FOR IMPULSE TURBINES Filed Sept. 14, 1955 /17/ 714 a v. Ill.

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\ ChT'TORMEYfi Unite States Patent SPEED CONTROLLER FOR IMPULSE TURBINES Clarence L. Avery, Rockford, 111., assignor to Woodward Governor Company, Rockford, 111., a corporation of Illinois Application September 14, 1955, Serial No. 534,356

4 Claims. (Cl. 137-35) This invention relates to the speed control of an impulse turbine having one or more free jets impinging on the buckets of a runner and each controlled primarily by a needle which governs the size of the jet and secondarily by a deflector for effecting quick diversion of all or part of the jet away from the buckets. The needles and the deflector of each jet are positioned by servos energized selectively by a single governor responsive to the turbine speed.

One object is to provide a dual control of the above character in which a detected speed deviation causes the correcting action of the servo for each of the several needles to be initiated more positively and at a time substantially earlier than has been possible heretofore.

Another object is to achieve the desired rapidity of response of the several needle servos without increasing the size or capacity of the speed governor.

A further object is to provide a system of the above character in which the reset cam for maintaining a predetermined positional relation between the deflectors and needles serves a plurality of jet units while providing the desired quick response of the individual needle servos.

Other objects and advantages of the invention will become apparent from the following detailed description taken in connection with the accompanying drawing which is a schematic view and circuit diagram of an impulse turbine control embodying the novel features of the present invention.

The invention is shown in the drawing as a modification of the standard system heretofore employed for regu lating the speed of an impulse turbine including a shaft 9 and a runner 10 with buckets 11 angularly spaced thereon against which are directed jets 12 of fluid controlled in size by needles 13 and 13 and varied in effectiveness by

associated deflectors

14 and 14. Two jets are shown in the present instance although a greater number is frequently employed.

The needle 13, which will be referred to as the master needle, is advanced and retracted by a servo 15 preferably of .the hydraulic type comprising a piston 16 slidable in a cylinder 17 to which the flow of fluid from the line 18 of a constant pressure source 19 is controlled by the usual relay valve 20. The plunger of the latter is actuated by

servos

22 and 23 to which pressure fluid from the source 19 is admitted under the control of a pilot valve 24 having a plunger 25 normally disposed in the centered position shown. When the plunger is moved downwardly, the servo 23 is energized to shift the valve and thus admit fluid to the right end of the cylinder 17 and advance the needle 13 to decrease the size of the jet 12. Reverse movement of the needle occurs in response to raising the pilot valve plunger from its normally centered position thus energizing the servo 22.

The servo 15 for the second needle 13' and any other that may be incorporated in the turbine are similarly and variably energized in response to changes in the position of a pilot valve 24' controlling similar servos 22 and 23' of associated relay valves 20.

ice

The deflectors 14 and 14' for the different jets 12 are preferably actuated by a common servo 28 comprising a piston 29 reciprocable in a cylinder 30 and joined by a connection 31 to a crank on one deflector '14 which is coupled through suitable connections 32 with the other deflector 14. Preferably, each deflector, when in the normal equilibrium position, is spaced outwardly from the edge of the associated jet so that the deflector does not intercept the stream until after the servo piston 29 has moved a short distance following the detection of an increase in the turbine speed.

The selective flow of pressure fluid from the source 19 to opposite ends of the cylinder 30 is controlled by a relay valve 33 actuated by a reversible hydraulic servo having a piston 35 and a cylinder 36 to which the flow of pressure fluid is controlled by a pilot valve 37. The plunger 38 of the latter valve is actuated directly by-a governor 39 driven in unison with the runner of the turbine and adapted to detect deviations in the turbine speed in either direction relative to a predetermined value manually adjustable in the usual way. The ball head 40 of the governor is driven by a synchronous motor 41 supplied with current from a generator 42 driven from the turbine shaft 9. Centrifugal forces acting on the governor flyballs 43 are opposed by a spring 44 so that the axial position of the flyball rod 45 varies in accordance with changes in the speed of the turbine.

Changes in the position of the rod 45 are communicated to the pilot valve 37 through a suitable linkage which usually includes a floating lever 47, and a link 48 joined to one end of the lever and pivotally connected to a floating lever 49 intermediate the ends thereof. One end of the lever 49 is supported by a pivot 50 positioned vertically by the usual speed and speed droop adjusting mechanisms indicated generally at 51 and 52. The other end of the lever is joined by a link 53 to the intermediate part of another floating lever 54 having one end pivotally joined to the stem of the pilot valve plunger 55. The usual follow-up motion is applied to the pilot valve and derived from the servo piston 35 through a member 56 pivotally connected to the other end 57 of the lever 54. By this action, the servo piston always follows the changes in the position of the control lever 49.

Isochronous operation of the turbine may be achieved through the use of the usual compensating mechanism 58. This includes the usual receiving piston 60 connected to the end of the floating lever 47 and urged by springs 59 toward a normally centered position. The piston 60 extends into a fluid filled chamber 61 closed by a transmitting piston 62. The latter is actuated through a lever 63 fulcrumed at 64 and joined to a link 65 which moves with the servo piston 29. Leakage of fluid into and out of the chamber is controlled by a needle valve 66.

In a manner well understood in the art, the mechanism 58 operates after each change in the position of the servo piston 29 to readjust the speed setting of the governor and provide a stabilizing drooping characteristic which is dissipated by' return of the speed setting to its original value at a slow rate determined by the setting of the needle valve. That is to say, in response to an increase in the turbine speed, the flyball rod 45 and the pilot valve plunger 55 will be lowered toadmit pressure fluid to the upper end of the servo cylinder 36. This lowers the plunger of the relay valve 33 to admit pressure fluid to the upper end of the servo cylinder 30 thus swinging the deflectors 14 toward the respective jets 12 and, after intercepting the streams, correspondingly reducing the speed of the runner. As a result of the servo movement, the piston 62 is raised and the piston 60 drawn into the chamber 61 thus adjusting the speeder spring 44 to cause the link 48 to be raised and thereby provide a drooping characteristic. The spring 59 then acts to slowly recenter the piston 60 thus returning the governor, the pilot valve 37, and the relay valve 33 to their equilibrium positions while the 'servo. 28 is permitted'to' remain in the. new and different load position. In the same manner, the parts inovereversely' in response to the detection of a speed decrease, the deflectors thus being retracted farther away from the paths of the jets 12.

.In the. system above described, the piston 35 of the relay valve servo 34 follows the changes in the position of the governor flyball rod 45. The present invention takes advantage of thischaracteristic to provide for direct and immediate response of the needleservos 15 and 15 to the detection of deviations in the turbine speed. For this purpose, the motionsof the servo piston 35 are transmitted. directly

topilot valves

24 and 24, this being accomplished herein by a linkage including a link 70, a bell crank 71, and a link 72 joined to one arm of a bell crank 73 pivoted at 74. The other arm supports a floating bell crank 75 and a lever 76 adapted to swing about a floating fulcrum 77 and connected intermediate its ends to the stem of a pilot valve plunger 25. A similar linkage, indicated by primed numbers, is extended to the pilot valve 24 by which the other needle servo 15 is controlled.

In. response to downward movement of the piston 35 of the relay valve servo 34 following detection of a turbine speed change, the linkage above described operates to lower the plunger of the pilot valve 24. Pressure fluid is thus admitted to the servo 23 shifting the relay valve 20 which is opened an amount proportional to the magnitude of the detectedv speed deviation by virtue of the follow-up or restoring motion transmitted back to the floating lever 76 through a link 110 movable in unison with the plunger 21 of the relay valve 20. As a result, pressure fluid is admitted to the rear end of the servo cylinder 17 thusadvancing the needle 13 to reduce the flow of liquid and the size of the jet 12 and therefore theturbine speed. Likewise, reverse or upward movement of the servo piston 35 in response to a speed decrease will result in upward movement of the valve plungor 25 and energization of the servo 22 to admit pressure fluid through the relay valve to the inner end of the servo 15. This retracts the needle 13 correspondingly increasing the size of the jet 12 and the turbine speed. .The other needle 13 is similarly actuated by its servo 15' and relay valve20 inresponse to the adjustment. of the pilot valve 24'. simultaneously with the valve 24.

In the operation of. an impulse turbine, it is desirable to. maintain a predetermined. relationship between the idle position of the deflector 14 and the edge of the associated jet 12 irrespective of the. size of the latter as it varies with the changing position of the associated needle 13. This relation is obtained by the use of cam and

follower elements

80 and 81 one moving in unison with the deflector, and the other being coupled to the plunger 25 of the needle servo pilot valve. Herein, the cam 80 is on a lever fulcrumed at 82 and rocked by an extension 83 of the cable 65 leading to the piston 29 of the deflector servo.

The follower 81 is on one end of a lever 84 fulcrumed at 85 and joined intermediate its ends to a lever 86 fulcrumed at 87, and, through a link 88, joined intermediate its ends to the fulcrum 77 of the lever 76. With this arrangement, the downward movement of the deflector 14 in response to a speed increase will result in counterclockwise turning of the cam 80 and downward movement of the pilot valve plunger 25. This movement supplements that resulting from a speed increase and transmitted to this plunger through the linkage 70, 71, 72 above described.

The cam motion is similarly transmitted to the pilot valve 24' which controls the second needle servo 15. The connection is through a rockshaft 90 having one arm '4 91 carrying the fulcrum 85 and a second arm 92 joined through a link 93 and bell .cranks 94 to one end of a floating lever 95 from which the pivot 77 of the lever 76' is suspended through a link 96. The valve plunger 25 is thus moved in unison with the plunger 25 in response to turning of the cam 80 by the servo 28.

To proportion the motions of the needles 13 and 13 in accordance with the cam motion, the needle motions 1ever 95. These connections operate in a direction to return the levers 76 and 76' to their former positions irrespective of whether the lever positions are changed directly by the action of the governor and the servo 34 or by the reset cam 80. By joining the two restoring

connections

97 and 97 together through the floating lever 95, the motions of the two needles 13 and 13' are equal ized irrespective of differences in the rates at which the servos 15 and 15 may operate during their corrective actions.

To prevent overtravcl of the needles 13 and 13 in response to wide speed deviations and large movements of the deflectors, a stabilizing mechanism 101 is associated with the resetting cam and its associated modifying mechanism. This mechanism may be of the same construction as the mechanism 58 above described including transmitting and receiving pistons 102 and 103 movable into and out of a fluid filled chamber 104 having a needle valve controlled outlet 105, the receiving piston being urged toward a centered position by springs 106. In the present instance, the receiving piston 102 is actuated by an arm 107 on the bell crank 90 and thus imparts to the needle servo control a drooping characteristic which is dissipated gradually by leakages of fluid through the needle valve under the action of the centering spring. Since the levers 76 and 76' are linked together as above described, the stabilizing eifect of the mechanism 101 is imposed on both of the needle servos 15 and 15'.

The entire system as above described operates as follows, it being first assumed that the governor 39 has detected a relatively small increase in the turbine speed from the desired value. In the manner above described, the downward movement of the governor rod 45 operates through the pilot valve 37 to energize the servo 28 and initiate movement of the

deflectors

14 and 14 toward the jets 12 and 12'. Because of the direct connection of the pilot valve 24 with the relay valve servo 34 as above described, the servos 15 and 15 are energized substantially simultaneously so that the advance of the needles 13 and 13' is initiated before the

deflectors

14 and 14, in view of the spacing thereof from the edge of the streams 12 and 12, actually enter the streams and become effective in diverting part of the same away from the buckets of the turbine. As a consequence, the speedof the turbine is resorted to the desired value by the adjustment of the. needles 13 rather than by the deflectors 14. This dc.-

sirable action is attributable to the rapid response of the needle servos to a speed change detected by the governor by virtue of the actuation of the pilot valves 24, 24' by the power actuated servo 34' which in turn is controlled directly from the governor.

Now, ifthe speed increase detected by the governor is of substantial magnitude, the corrective action of the deflector and needle servo will be long enough to bring the.

deflectors

14 and 14 into engagement with the jets 12. and 12 thus diverting part of the streams away from the turbine buckets to effect the desired reduction in the turbine speed well in advance of the time when the needles would be eifective to produce a similar speed reduction. The speed corrective operation then continues through the action ofthe compensating mechanism 58 and the reset cam as a result of which the deflectors are returned to. their equilibriumpositions and the size of thejetsand therefore the turbine is determined solely by the positions of the needles 13 and 13'. As a result, the deflectors are brought into play in controlling the turbine speed when ever it is necessary in order to avoid excessive pressure in the conduits leading to the runner casing. At the same time and in response to turbine speed changes, the needle servos are controlled more directly than has been possible heretofore. The ultimate result is a closer speed regulation of the turbine speed with a minimum burden of such control imposed on the secondary controllers or deflectors.

Throughout the entire operation and in spite of differences in the length and character of disturbances such as transient conditions as Well as speed deviations detected by the governor, the desired predetermined relationship is maintained by the action of the cam 80 between the deflectors and the edges of the jets 12 and 12. No additional burden is imposed on the governor by the addition of other needles and jets and as a result, the control mechanism as a Whole may be of minimum size and optimum sensitivity irrespective of the number of jets used in the turbine.

I claim as my invention:

1. For regulating the power delivered by a prime mover, the combination of, first and second regulating members, a first servo for moving said first member, a second servo for adjusting said second member, a governor for detecting deviations in speed from a predetermined value, a device controlled by said governor and having a normal equilibrium position, a third servo variably energized in response to changes in the position of said device and governing the selective energization of said first servo, compensating mechanism operable in response to the detection of a speed deviation by said governor to return said device to said equilibrium position, a controller for said second servo, first and second motion transmitting connections extending to said controller from the movable parts of said first and third servos respectively and movable independently of each other to adjust said controller differentially, and means including a cam interposed in said first connection for modifying the action of the latter to maintain a predetermined positional relation between said first and second members.

2. For regulating the power delivered by a prime mover, the combination of, first and second regulating members, a first servo for moving said first member, a second servo for adjusting said second member, a governor for detecting deviations in the prime mover speed from a predetermined value, a device controlled by said governor and having a normal equilibrium position, a third servo variably enengized in response to changes in the position of said device and governing the selective energization of said first servo, compensating mechanism operable in response to the detection of a speed deviation by said governor to return said device to said equilibrium position, a controller for said second servo, a connection for transmitting the motion of said first servo to said controller including a cam shaped to maintain a predetermined positional relationship between said first and second regulating members, and a separate connection for transmitting changes in the position of said third servo to said controller whereby to initiate corrective action of the latter in response to each speed deviation in advance of the response of the controller to said movement of said first servo.

3. For regulating the power output of a prime mover, the combination of, a plurality of first regulating members, a plurality of second regulating members, first servos for actuating the respective second members, first valves each selectively operable to vary the energization of said servos and each having an element movable in either direction away from a normally centered position, a second servo controlled by a relay valve and coupled to said first members for varying the positions of the latter in unison, a third reversible servo for actuating said relay valve and having a normally centered position, a second valve variably energizing said third servo and having a member movable in opposite directions away from a normally centered position, a governor responsive to speed changes, a coupling actuated by said governor and joined to said second valve to move said member in opposite directions out of said centered position in response to opposite deviations in speed away from a desired value, compensating mechanisms responsive to each speed deviation and operable to modify the action of said coupling, and connections transmitting the movements of said third servo to each of said first valves and operable in response to each speed deviation to actuate the first valves before substantial movement of said first members has occurred.

4. A prime mover regulating system as defined by claim 3 having a reset cam movable back and forth in unison with the movements of said second servo, a 01- lower riding said cam and coupled to each of said first valves, and stabilizing mechanism actuated in response to changes in the position of said first servos and operable to modify the length of said connections.

References Cited in the file of this patent UNITED STATES PATENTS 1,035,082 Cachin Aug. 6, 1912 1,106,434 Woodward Aug. 11, 1914 2,224,638 Ring et al. Dec. 10, 1940 2,491,059 Ring Dec. 13, 1949 2,606,533 Garde et al Aug. 12, 1952 2,635,847 Rued Apr. 21, 1953 2,715,892 Rodeck et al Aug. 23, 1955 FOREIGN PATENTS 186,613 Great Britain Aug. 9, 1923