US2933301A - Steam turbine control - Google Patents

Description

April 19, 1960 o. N. BRYANT 2,933,301

STEAM TURBINE CONTROL Filed April 30, 1958 INVENTOR OZRO N. BRYANT BY y C ...control signal to close the admission valves.

trapped steam once the valves do close. acceleration of the turbine dueto the time delay between .Nalves are closing, an undesirable result.

United States Patent STEAM TURBINE CONTROL 1.02m N. Bryant, Chester, Pa., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application April 30, 1958, Serial No. 731,973

6 Claims. (Cl. 264-7) This invention relates to a control for a prime mover and more particularly to a control responsive to acceleration of the prime mover. "illustrated by Patent No. 2,548,072 to A. F. Schwendner This type of apparatus is and assigned to the same assignee as that of the present application. It is an object of the invention to provide improved control structure of this type.

When a major portion of the load which a steam turbine is carrying is suddenly lost, a hydraulic control that is responsive solely to speed will only be operative .to close the valves that admit steam to the turbine after a period of time has elapsed. Consequently, there is a significant time delay between the loss of load and the time at which the admission valves are closed, during which the admission valves to the turbine remain open, steam is supplied thereto, and the turbine accelerates in speed. This time delay can be significantly reduced by a hydraulic control that is responsive to acceleration in speed.

Itis another object of the present invention to provide improved hydraulic control apparatus responsive to' acceleration in speed of the prime mover.

Furthermore, in present day high temperature and high pressure steam turbines, the hydraulically operated ad- ...mission valves have long hydraulic piping connecting them n10, the source of the hydraulic control signal. The foregoing induces a further time delay in transmitting the Therefore, it is a further object of the present invention to provide can improved control for reducing the time delay'due to .the connecting piping between the admission valves and the source of the control signal.

. Also, there is a large volume downstream'of the' admission valves which makes for a large volume of en- Hence, any

loss of load and closing of the admission valves will be augmented by the entrapped steam. Thus, with a speed responsive. control, it. has been found that it is possible .for the speed of the turbine to increase as much after all. the admission valves are closed as it does while the Thus, it is another object of this invention to maintain the rise in speed f the turbine above the normal speed to a minimum.

In the above-mentioned Schwendner patent, a steam turbine having fluid admission valves is provided with a pressure-responsive servo-motor relay device for controlling. the admission valves. "There is further provided, a governor driven by the turbine for pressurizing a primary .liquid at a pressure varying as a function of the speed of the turbine. The primary liquid is supplied to a control device which provides a regulated secondary liquid proportional in pressure to the primary liquid for controlling the servo-motor relay. The servo-motor relay is of the type which will open or close the admission valves upon a decrease or increase, respectively, in secondary liquid pressure.

In accordance with the invention, there is provideda control device for transforming a primary pressure signal iatented Apr. 1,9, ,rseo

to-a secondary pressure signal of increased magnitude 'andemployingthe secondary signal to actuate the servo motor relay. However, the servo-motor relay closes. the ,admission valves upon a decrease in secondary liquid pressure, and vice versa. The control .has ,a movable abutment subject to the primary liquid pressure and connected to a regulating valve which regulates the secondary liquid pressure in a space formed adjacent thereto. The

"movable abutment controls the regulating valve to vary the secondary liquid pressure in a manner to maintain "the latter in reverse proportional relation to the primary liquid pressure and turbine speed up to a predetermined Irate of acceleration inspeed. A diaphragm is provided to and the lower surface are in fluid communication, through diaphragm instead .of the movable abutment.

a variable capacity chamber and a viscous orifice resistance with the space in which the secondary liquid ,is

disposed, so that when a change in secondary liquid pressure takes place, a corresponding, but delayed, change in pressure of secondary liquid takes place within the lower chamber. Thus, upon a predetermined rate of decrease in secondary liquid pressure, a pressure difference will arise across the diaphragm flexing the diaphragm and placing the regulating valve under the control of the Thus, upon. a loss in load on the steam turbine and a consequent acceleration in speed thereof, the primary liquid pressurewill increase, moving the movable abutment which, in turn, opens the regulating valve, and decreases the secondary liquid pressure in the space and the upper chamber. The secondary liquid in the lower chamber is momentarily trapped therein and is gradually decreased to the pressure in the upperchamber. This momentary delay creates an unbalance across the diaphragm, which is indicative of the acceleration, and the diaphragm is operative to move the regulating valve in the opening direction over and beyond the amount imparted thereto by the movable abutment. The more the pressure of the primary liquid increases, the larger will the decrease, in

secondary liquid pressure be and thegreater will be the unbalance across the diaphragm, which, in turn, will result in a larger-tendency-of the-regulating valve to open.

Once thediaphragm operates to open the regulating valve, ithe secondary liquid will be further reduced, resulting in .a greater unbalance across the diaphragm and a greater tendency to openthe regulating valve.

Thus, the body of secondary. liquid within the space and conduit com- .municating with the servo-motor relay is rapidly accelerated toward'a decreasing pressure, an importantfeature wherea large body of secondary liquid is disposed wwithin the space, and servo-motor relay, insuring that the admission valves. of the turbine will be promptly closed andremain sountil the speed of the turbine returns to approximately normal, by which time the secondary liquid has been drained out of the lower chamber and the regulating valve-returned to the primary control of the movable abutment.

The foregoing andothenobjects are effected by the..in-

vention as will be apparent from the'following description and claims taken-in connection with the accom- *panying drawings, forming a-partof this application, in

which:

The single-drawing illustrates'a. portion of a. typical steamturbine, partly; in elevation and partly in sectiontin conjunction with a control the present invention.

formed in The steam turbine is illustrated as having steam admission valves 12 and a pressure-responsive servomotor relay device 14 for regulating the valves 12, these elements being shownjin elevation since they may be of suitable well-known types. v The turbine 10 is provided with a governor 16, suchas disclosed in the patents-to Bryant 2,035,689 and to Schmidt 2,256,963, comprising a reverse flow impeller 17, cooperating with a control mechanism or transformer 18 formed in accordance with the invention to provide accordance with p bellows 54 for varying the capacity of the chamber 53, as well known in the art. The chamber 53 is in communication with the lower chamber 52 through a passage 56 and in communication with the space 28 through a vertical passage 57 and a horizontal passage 58. Flow through the passage 56 may be controlled by a check valve 59. Within the horizontal passage 58, there is placed 7 a viscous orifice resistance device 69 operative to provide, upon a change in secondary liquid pressure in the space 28, a change in the lower chamber 52. Since the capacity chamber 53 communicates with the passages a hydraulic control signal to the servo-motor relay device 14 for regulating the admission of steam to the turbine by the admission valves 12.

. The governor'16 includes a passage 19 supplied with high pressure liquid through an orifice 21 from a suitable source such as the turbine driven impeller 22. The pressure. in the passage 19 is varied by means of the centrifugal resistance to escape "of liquid afforded by the reverse flow impeller 17. Hence, the pressure in the passage 19 increases with increase in speed and vice versa,

' the pressure varying substantially as the square of the speed of the turbine. The primary liquid in the passage 19 is applied to a movable abutment or bellows 26 provided in the transformer 18 by a conduit27 and operates to change the pressure of a secondary liquid (in the opposite sense relative to the primary liquid pressure) in wall structure I defining aspace 28 irrproportion tothe change in primary liquid pressure in the passage 19. The space 28 com municates with the servo-motor relay device 14 through a conduit 29 for supplying to the. servo-motor 1 4, the hydraulic or control signal of secondary liquid that controls the position of the admission valves 12. In installations of this type, it is current practice to place the transformer .18 remotely from theturbine .unit. Accordingfly, the conduit 29 mayassurne a length of a relatively large order, for exampleupto 90 feet. The servo-motor relay device 14 is" of the'type that will. tend to close the ,admissionvalves 12 upon a decrease in secondary liquid pressure and to open them upon an increase in secondary liquid pressure. Movement of the bellows 26 is transmitted to a regulating valve 30 of the cup type through a pivoted arm 31 that is biased by anadjustable spring 32 in the direction to close the cup valve 30. The pressure of the secondary liquid is varied by moving the cup valve 30, thus varying the quantity of secondary liquid fiow through a conduit 37 to a suitable drain (not shown)? The secondary liquid may be provided by any suitable high pressure source. In the' example illustrated, it is r supplied by the turbine impeller 22 through an orifice and conduit 36 communicating with the conduit 29.

i The cup valve 30 is slidably connected to a vertically extending reciprocable rod 41 disposed within wall structure defining a vertical passage 42 that communicates directly with the space 2,8 andwith the drain conduit 37 through the cupvalve. The rod 41 is secured at one 45 and 46 of the transformer 18. The other end of the rod 41 is connected tothe cup valve 30 by a slidable joint 47 that provides complete freedom in downward direction but limited freedom in upward direction, so that continued movement in the upward direction will tend to open the cup valve. g

* The diaphragm 43 is disposedv within a chamber formed in the wall structures 45 and 46 and'divides the former into an upper chamber 50 and. a lower chamber 52. The upper chamber 50 is in communication. with the space 28 through the passage .42 and, thereby, exposes at all times the' upper surface of the diaphragm 43 to the pressure of the secondary liquid in the space 28.

' Disposed below the lower chamber 52 is a variable Ycap'acity chamber 53 in whichis disposed a spring biased 57 and 58, this change in pressure in the lower chamber 52 and on the lower surface of the diaphragm 43 is delayed, in a manner which will subsequently be described.

Thus, when the pressure of the secondary liquid in the space 28 and upper chamber 59 decreases, a pressure difference will exist across the diaphragm 43 for a period of time,'due;to the resistance 69 and the capacity chamber 53, During this time, an upward force will beexerted by the diaphragm 43 upon the rod 41 and the cup valve 3t tending to open the latter. The pressure of the secliquid within the space 28, the conduit 29 and the servoondary liquid in the space 28 is accelerated toward a lower pressure because, as this upward force opens the cup valve 30, the secondary liquid pressure further decreases, further increasing the pressure difference across the diaphragm and further creating an upward opening force on the cup valve 30. Thus, the pressure of the motor relay device 14 decreases rapidly, permitting the servo-motor relay device to close the valves 12 rapidly. The check valve 59 is provided to insure that the diaphragm 43 will hold the cup valve in a raised position pacity chamber 53 drops suddenly and permits the check valve 59 to close.

The liquid trapped in the chamber 52 by the closing of the check valve 59, is allowed to leakaway through a lateral passage 72, another viscous orifice resistance 76,

' a central passage 78 formed therein and in communicatiOn'With the horizontal passage 58, and the viscous orifice resistance 60, thus gradually permitting the diaphragm 43 and the cup valve 30 to fall at a slow rate.

Furthermore, by proper selection of the weight of the rod and diaphragm and the size of the resistance 60, a preselected diiference in pressure value across the diaphragm-may be balanced by the weight of the rod and diaphragm so that small pressure difierences below the preselected value, occasioned by turbine rate of acceleraend to a horizontally disposed diaphragm 43 fixedly secured at its peripheral portionbetween wall structures tion below a predetermined level, will not actuate the rod 41. Also, by varying the resistance value of the viscous resistance 76, the time duration of .the upward force on the rod or the time in which the secondaryliquid is at its lowest pressure may be varied. I

In operation, theimpeller 17 produces a liquid pressure-proportional to the turbine speed. .As the turbine speed rises, the primary liquid pressure P in the passage 19 and the conduit 27 will rise accordingly. This rise in pressure will cause the cup valve 30 to open, there fby decreasing the secondary liquid pressure P within the space 28. The secondary liquid pressure P in the servo-motor relay device 14 and adjacent the portion of v the conduit 29, will lag behind the pressure P because of the resistance to flow ofiered by the walls of the conduit 29 and the inertia of the mass of the secondary liquid within. the conduit 29 and-the servo-motor, relay device 14. The pressureof the secondaryliquid within the passage 42 and the upperchamber 50 will be the same as the pressure P: within the space 28 due to their proximity to the drain conduit 37. The pressures of the secondary liquid within the capacity chamber 53 and within the lower chamber 52 indicated as R; and P respectively, will lag'behind P Thus, P is momentarily larger than F: andan upward force will be exerted on the diaphragm'and' rod, tending to open the cup valve 30. This upward force, can be balanced by the weight of the rod and diaphragm so that, for rates of acceleration up to a predetermined level, substantially no movement of the rod and diaphragm will occur. For rates of acceleration beyond this level, the rod and diaphragm willmove upwardly, causing the cup valve 30 to open over and beyond any opening of the latter caused by the bellows 26. Once the cup valve is further opened by the rod 41 a further decrease in the pressure P of the secondary liquid takes place. This resultsin an increased upward force on the rod 41, tending to further open the cup valve 30 and to. further reduce the pressure P of the secondary liquid, Thus, a cumulative efiect takes place'in which once movement of1the rod 41 is started upward, the pressure P ofthe secondary liquid will rapidly decrease. In this manner, the pressure P of the liquid within the conduit and the servo-motor relay device 14 -is rapidly decreased. Since the servo-motor relay device 14 is of the type thattends to close the valves 12 upon a decrease in secondary liquid pressure, it ;will promptly, upon a decrease in secondary liquid pressure occasioned by turbine rate of acceleration beyond the predetermined level, close the valves 12, and prevent the turbine from accelerating in speed to a dangerous level.

Although in the embodiment shown, the diaphragm and rod are disposed for vertical actuation, it will be obvious that-they may be disposed for actuation in other directions. For such actuation, thebias on the diaphragm due to gravity may be substituted by a suitable spring (not shown).

While the invention has been shown in but one form, it will be obvious to those skilled in the art that it is not so limited, but is susceptible of various changes and modifications without departing, from the spirit thereof.

What is claimed is:

1, For use with. elastic fluid utilizing apparatus having a fluid admission valve, pressure-responsive means for controlling said valve, and means, driven by said fluid utilizing apparatus for pressurizing a primary liquid at a pressure varying as a function of the speed thereof, a control comprising wall structure defining a space for secondary liquid under pressure which is supplied to said pressure-responsive means, a regulating valve for regulating the pressure of said secondary liquid and subject to secondary liquid pressure for urging the regulating valve in-the opening direction, biasing means for urging said regulating valve. to the, closed position, a movable abutment connected to said regulatingvalve and subject to said primary liquid pressure for opposing said biasing means, whereby the regulating valve isoperative to vary the secondary liquid pressure to, maintain the latter in proportional relation to the primary liquid pressure, wall structure defining a chamber, a second'movable abutment disposed within saidchamber and having opposed surfaces, means connecting said last-mentioned abutment, to said regulating valve, said last-mentioned abutment having one of said surfaces in fluid communication with said space wall structure defining -a variable capacity chamber, said last-mentioned abutment having the other of said surfaces in fluid communication with said variable capacity chamber, means defining a passage including a restriction placing said space in communication wtih said variable capacity.chamber,- whereby upon a decrease in secondary liquid pressure the pressure difference. across said second movable abutment due to said restriction will move the latter. inadirectionto open said regulating valve, further decreasingsaid secondary liquid pressure.

2. For use with elastic fluid utilizing apparatus having a fluid admission valve, pressure-responsive means for controlling said valve, and means driven by said fluid utilizing apparatus for pressurizing a primary liquid at a pressure varying as a function of the speed thereof, a control comprising wall structure defining a space for secondary liquid under pressure which is supplied to said pressure-responsive means, a regulating valve for regulating the pressure of said secondary liquid and subject to secondary liquid pressure for urging the regulatingvalve in the opening direction, biasing'means for urging said regulating valve to the closed position, a movable abutment connected to said regulating valve and subject to said primary liquid pressurefor opposing said biasing means, whereby the regulating valve is operative to vary the secondary liquid pressure-to maintain the latter in pro: portional relation to the primary liquid pressure, wall structure defining a chamber, a diaphragm disposed within said chamber and having opposed surfaces, means connecting said diaphragm to said regulating valve, said diaphragm having one of said surfaces in fluid communication with said space, wall structure defining a variable capacity chamber, said diaphragm having the other of said surfaces in fluid communication with said variable capacity chamber, means defining a passage including a restriction placing said space in communication with said variable capacity chamber, whereby upon a decrease in secondary liquid pressure the pressure difference across said diaphragm due to said restriction will flex the latter in a direction to open saidregulating valve, further de creasing said secondary liquid pressure and further opening said regulating valve.

3. The combination with a prime mover having a motive fluid admission valve, pressure-responsive means for controlling the valve, and a hydraulic governor comprising means driven by the prime mover for developing primary liquid at a pressure varying as a function of prime mover speed, of control apparatus including means providing a space for secondary liquid under pressure which is supplied to the pressure-responsive means, a regulating valvecooperating with said space to regulate the pressure of said secondary liquid including a surface connected to said regulating valve and subject to said secondary pressure, a biasing device for urging said regulating valve to the closed position, a movable abutment connected to said regulating valve and subject to said primary liquid for counteracting said biasing device, where by the regulating valve is operative to vary the secondary liquid pressure to maintain the latter in proportional relation to the primary pressure, and means responsive to the rate of change of speed of said prime mover to vary the admission of motive fluid to the latter to limit the change in speed incident to sudden load change, said rate of change responsive means comprising a second movable abutment having equal and opposed areas, means defining a chamber in which said last-mentioned abutment is disposed, said last-mentioned abutment dividing said chamber into a first chamber and a second chamber, a reciprocable rod connecting said last-mentioned abutment to said regulating valve for moving said regulating valve in the opening direction, a first passage for supplying secondary liquid to said first chamber, a secondpassage for supplying secondary liquid to said second chamber, means associated with said second passage for restricting flow therethrough, a variable capacity chamber interposed in said second passage, a check valve for separatingsaid variable capacity chamber from said second chamber and preventing flow from said second chamber to said variable capacity chamber but permitting flow from said variable. capacity chamber to said second chamber, and means defining a third passage and a restriction providing a continuously open communication betweensaid second chamber and said space.

reagent "7 I 4. The combination with a prime mover having a motive fluid admissionvalve,pressure-responsive means for controlling the valve, and a hydraulic governor comprising means driven by the prime mover for developing primary liquid at a pressure varying as a function of prime mover speed, of control apparatus including means providing a space for secondary liquid under pressure which is supplied to the pressure-responsive means, a cup valve cooperating with said space to regulate the pressure of said secondary liquid including a surface connected to said cup valve and subject to said secondary pressure, a biasing device for urging said cup valve to the closed position, a movable abutment connected to said cup valve and subject to said primary liquid for counteracting said biasing device, whereby the cup valve is operative to vary the secondary'liquid pressure to maintain the latter in proportional relation to the primary pressure, and means responsive to the rate of increase of speed of said prime mover to reduce the admission of motive fluid to the latter to limit the increase in speed incident to sudden reduction in load, said rate of change responsive means comprising a diaphragm having equal and opposed areas,

means defining a chamber in which said diaphragm is disposed, said diaphragm dividing said chamber into a first chamber and a second chamber, a reciprocable rod connecting said diaphragm to said cup valve for moving said cup valve in the opening direction, a first passage for supplying secondary liquid to said first chamber, a second passage for supplying secondary liquid to said second chamber, means associated with said second passage for restricting flow therethrough, a variable capacity chamber in communication with said second passage, a check valve interposed between said variable capacity chamber and said second'chamber and preventing flow from said second chamber to said variable capacity chamber, and means defining a third passage and a restriction providing communication between said second chamber and said space, whereby during substantially steady state speed of the prime mover said secondary liquid within the second chamber attains substantially the pressure of the secondary liquid within said space to render the diaphragm ineffective to actuate said cup valve, said secondary liquid within the first chamber decreasing at a more rapid rate than the secondary liquid in said second chamber during acceleration of the prime mover and said diaphragm being effective to move said cup valve in opening direction, thereby further reducing the secondary pressure in said space to actuate the admission valve control means in admission valve closing direction.

5. For use with an elastic motive fluid utilizing prime mover having a motive fluid admission valve, pressureresponsive means for controlling the valve, and an impeller driven by said prime mover for pressurizing a primary liquid at a pressure varying as a function of prime mover speed; a control comprising wall structure defining a space for secondary liquid under pressure which is supplied to said pressure-responsive means, a regulating valve for regulating the pressure of said secondary liquid,

a movable arm to which said regulating valve isconnected, a spring cooperating with said arm for biasing said regulating valve toward the closed position, a movable abutment secured to said movable arm and subject to said primary liquid pressure for urging the arm in the opposite direction to that of the bias on said arm, said regulating valve having a surface subject to secondary liquid pressure for urging the regulating valve in the opening direction, whereby the regulating valve is operative to vary the pressure of the secondary liquid to maintain the latter in proportional relation to the primary liquid pressure, wall structure defining a chamber, a second movable abutment dividing said chamber into an upper chamber and a lower chamber, a rod secured to said last-mentioned abutment at one end and connected at the other end to said regulating valve so that movement of saidrod in one direction tends to open said regulating valve, said upper chamber being in communication with said space, wall structure defining a variable capacity chamber, saidlower chamber'bei ng in communication with said variable capacity chamber, a check valve between said lower chamber and said variable capacity chamber for preventing flow of liquid from said lower chamber to said variable capacity chamber, means defining a'first passage including a viscous resistance placing said space in communication with said variable capacity chamber, means defining a second passage including a viscous resistance placing said lower chamber in communication with said space, said last-mentioned abutment and rod having a predetermined weight and "said first-mentioned viscous resistance having a predetermined resistance such that upon a predetermined rate'offdecrease in secondary liquid pressure in said upper chamber the weight of said last-mentioned abutment and rod will substantially balance the'difierence in pressure across said last-mentioned abutment, but above said predetermined rate of decrease in pressure, the pressure difference across the last-mentioned abutment will move the latter and move the rod in the direction tending'to open the regulating valve, further decreasing said secondary liquid pressure. 7 p

6; For use with an elastic motive fluid utilizing prime mover having a motive fluid admission valve, pressureresponsive means for controlling the 'valve,'-and an impeller driven by said prime mover for pressurizing aprimary liquid at a pressure varying as a function of prime mover speed; a control comprising wall structure de fining a space for secondary liquid under pressure which is supplied to said pressure-responsive means, 'acup valve for regulating the pressure of said secondary liquid, a drain conduit in communication with said cup valve, a pivotable arm to which said cup valve is connected, a spring cooperating with said arm for biasing said cup valve to the closed position, a movable abutment secured to said pivotable arm and subject to said primary liquid pressure for urging the arm in the opposite direction to that of the bias on said arm, said cup valve having a surface subject to secondary liquid pressure for urging the cup valve in the opening direction, whereby the cup valve is operative to permit flow of secondary liquid to said drain conduit and thereby vary the pressure of the secondary liquid to maintain the latter in proportional relation to the primary liquid pressure, 'wall structure defining a chamber, a diaphragm dividing said chamber into an upper chamber and a lower'chamber, a rod con} necting said diaphragm to said'cup valve so that movement of said rod in one direction tends to open said cup valve, said upperchamber being in unrestricted communication with said space, wall structure defininga variable capacity chamber, means defining a passage between said lower chamber and said variable capacity chamber, a check valve disposed in said passage for preventing flow of liquid from said lower chamber to said variable capacity chamber, means defining a second passage including a viscous resistance placing said space in communication with said variable capacity chamber, means defining a third passage including a viscous. re-

sistance placing said lower chamber in communication with said space, said diaphragm and rod having a prede termined weight and said first-mentioned viscous: resistance having a predetermined resistance such that, upon a predetermined rate of decrease in secondary liquid pressure incident to a preselected rate of acceleration of the prime mover, the pressure in said-lower chamber will be higher than the pressurein said upper chamber and the weight of said diaphragm and rod will substantially balance the difference in pressure across said diaphragm and render the diaphragm inefiective to actuate said cup valve, but upon increase in pressure difference across the diaphragm, incident to'excessive rate of ac,- celeration of the prime mover, the diaphragm is rendered 9 efi'eetive to move the rod in the direction tending to open the cup valve, further decreasing said secondary liquid pressure and further tending to open the cup valve, accelerating the flow of the secondary liquid from said space to said drain conduit.

References Cited in the file of this patent UNITED STATES PATENTS Schwendner Apr. 10, 1951 Wheeler July 14, 1953 Engel Dec. 25, 1956

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