US 3812377 A
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S United States Patent 11 1 1111 3,812,377 Malone May 21, 1974 SYSTEM FOR INDEPENDENT OR COMMON 3.391.539 7/l968 Dimitroff 60/67 CO O PRIME MOVERS 3,274,443 9/1966 Eggenberger et 290/40 X 3,233,412 2/1966 Wagner 415/17 X  Inventor: Paul E. Malone, Schenectady, NY.  Assignee: General Electric Company, Primary Examiner-G; Simmons Schenectady, Attorney, Agent, or F1rm-John F. Ahern; James W.
Mtchell 221 Filed: Dec. 4, 1972 I  Appl. No.: 311,942  ABSTRACT A system is provided for controlling the load settings 52 us. c1 290/4 290/2 290/40 0f a group of Prime movers Such as Steam turbines 60/102 ther independently or in a common mode. A master  Int. Cl. F0l d 15/10 load Setting for the group of prime movers is  Field of Search U 60/97 R 102 97 S 105 pared with an individual load setting for each of the 60/97 P 97 1 40 2 prime movers and the lowest load setting value is se lected as a load command signal. Isolation between  References Cited prime mover control systems is provided by load setting motors serving as memory devices in the event UNITED STATES PATENTS that power is lost to one of the control systems. Provi- 3,623,324 11/1971 Eggenberger 60/102 i i made f load removal either f individual 312131322 3/1325 5531171131:31:13:13::jiiiijijiiii'iiQ/i? Prime or from the entire group- 2,955,429 10/1960 Miller 60/102 X 5 Claims, 4 Drawing Figures 20 LOAD SET EXTERNAL SIGNAL l2 RUNBACK EXTERNAL 14 LOAD 17 I serrms rum ams LOAD SET LOGIC 1 l3 l6 LOAD SET 1 1 1 l9 1' MASTERI MODE I SELECTOR MASTER 32 1,2 LOGIC 1 33] OR common I I LOAD SET '5 MASTER 2 B 18 I LOAD SET LOGIC LOAD SET 23 21- RUNBACK *fiExrERNAu 25 SIGNAL FATENTEWMZT m4 $812.3,
SHEU 1 BF 2 FIG.| 20- LOAD SET la RUNBACK EXTERNAL |4 LOAD I? SETTING TUR?|NE l:v LOAD SET LOGIC 1 l3 LOAD SET f 1 '9 F MASTERl MODE MA TER 32 E R s SELI z LOGIC '1 33 35 37 GENERATOR OR COMMON I 7 1 k LOAD SET H lo '5 MASTER 2 L W T i 5 4[ LOAD SET GATE 7 4 LOGIC 2 1 27 2 -TURBINE LOAD LOAD SET 23 I RUNBACK (-fi 25 SIGNAL 1 LOAD -'o COMMAND SIGNAL MASTER LOAD SET TURBINE 2 SYSTEM FOR INDEPENDENT OR COMMON CONTROL OF PRIME MOVERS BACKGROUND OF THE INVENTION turbine-generator from damage and to ensure contin- 1 ued supply of service to the utility customers. An exam ple of such a control system is seen in US. Pat. No. 3,340,883 to Petemel issued Sept. 12, 1967 and assigned to the present assignee. In the Petemel patent, the steam turbine valve is controlled by means of a signal which is the lower of two signals compared in a gating device.
Although the capacities of steam turbines have'continued to increase over the years, the potential capacity of boilers or reactor steam generators now exceeds the capacity of the largest steam turbines. The use of two or more turbines with a single boiler or reactor is highly desirable and the present invention is directed toward an improved control system for two or more steam turbines operated from a single steam source, although the invention is not confined to a single steam source.
Suggestions have been made in the prior art for control systems to jointly control two o more prime movers. One example is found in US. at. No. 3,233,412 issued to J. B. Wagner on Feb. 8, 1966 describing a master-slave system, wherein a number of turbines with mechanical controls are slaved to a single master turbine with a more advanced electrical control. There the slaved turbines are controlled by reference settings representing adjustable fractions of a selected total signal. Similarly, US. Pat. No. 3,391,539 issued to V. T. Dimitroff et al. on July 9, 1968 provides integrated control of a plurality of steam turbines, wherein the flow from the turbines is maintained in accordance with selected fractions of flow from the various turbines. In these applications, there is a dividing up or sharing of a signal when the prime movers are being jointly controlled, as opposed to the present application, wherein the controlling signal is applied in full to the group during common control of the prime movers.
It is also known in the prior art that when prime movers are controlled as to load, the individual safety features, such as over-speed trips remain operative. However, the present application contemplates continuous control of the individual prime mover load settings as well as joint control thereof.
Accordingly, one object of the present invention is to provide an improved control system for operating two or more prime movers either individually or in a common mode.
Another object of the invention is to provide an improved control system combining the convenience of common load control of a plurality of prime movers together with the protective features of independent prime mover load controls such as start-up and load runback provisions.
Still another object of the invention is to provide a control system for common control of prime movers with provision for isolation between independent control systems and for shifting to separate controls in the event of failure of one or more prime movers.
DRAWING The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the concluding portion of the specification. The invention, however, both as to organization and method of practice, together with further objects and advantages thereof, may best be understood by reference to the following description, taken in connection with the ac- 5 companying drawing in which:
FIG. 1 is a simplified block diagram of a control system suitable for independent and/or common control of two steam turbines,
FIG. 2 is a simplified circuit diagram of one type of load setting and gating device, and
FIGS. 3 and 4 are graphs illustrating the principle of operation.
SUMMARY OF THE INVENTION Briefly stated, the control system provides means for generating a number of individual load setting signals for the individual prime movers and also a common load setting signal. The signals are applied through de vices which retain the previously set signal in the event of power failure. Each individual load setting signal is applied together with the common load setting signal, to a device which selects the lowest signal and uses it as a load command signal for the individual prime mover. Either the individual or the common load settings may be reduced or increased in accordance with the desired logic for prime mover operation.
DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1 of the drawing, a first prime mover such as a steam turbine 1 and a second independent prime mover such as steam turbine 2 each are connected to supply a respective load such as generators 3, 4. Generators 3 and 4 are electrically connected to a common power grid. Turbines 1, 2 are supplied with steam from a common steam generator 5, the steam flows to the respective turbines being controlled by the openings of valves 6, 7. It will be understood that the foregoing components are only a rudimentary representation of what can be an extremely complex power plant, each steam turbine l, 2 perhaps representing a number of separate turbine casings with reheating of the steam between casings and also it will be understood that many other types of controls and additional valves for emergency control and other purposes would normally be included. These are not shown since they are not material to the invention. The steam generator 5 can be either a conventional boiler fired by fossil fuel or can be a steam generator heated by a nuclear reactor. In its broader aspects, the steam valves 6, 7 are only representative of means to control the rate of energy released to any type of prime mover such as gas turbines, diesel engines and so forth. In this case, the valves 6, 7 would control fuel flow to the prime movers rather than steam.
Valve 6 is positioned by means of an electrohydraulic servomechanism 8 in response to an electrical load command signal entering at 9. A similar servomechanism positions valve 7, in accordance with an electrical load command signal at 11. In the illustrated arrangement, servomechanisms 8, 10 are each preferably an arrangement of solid-state analog circuits utilizing operational amplifiers and servo valves controlling high pressure hydraulic rams. They serve to translate the load command signals entering at 9, 11 into corresponding positions of the hydraulic rams to control the openings of valves 6, 7. The higher the load command signal, the wider the valve opening. Assuming that the main terminals of generators 3, 4 are connected into a power grid which keeps the speeds of the two units substantially constant, the respective valve positions therefore determine the respective loads carried by turbines l, 2.
A desired load setting for either or both of turbines l, 2 is communicated to the control system from an external source 12 connected to a mode selector panel 13. By means of switching circuits, selector panel 13 enables or disables a first load setting logic circuit 14 for turbine 1, a second load setting logic circuit 15 for turbine 2 and/or a master load setting logic circuit 16 for both turbines. Each logic circuit is arranged to drive a reversible motor, indicated at 17, 18 and 19. The motors drive position transducers, such as potentiometers, which raise or lower the desired'load settings on the turbines individually or in common.
Provision is also made to reduce the load'settings either for individual turbines or for both turbines, by means of load set runback circuits 20, 21. An example of such a runback circuit is described in a copending application Ser. No. 264,799 filed in the names of Barrigher et al. on June 21, 1972 and now issued as US. Pat. No. 3,748,491. The runbacks may be caused by external signals due to conditions in the electrical network as indicated at 22, 23, or may be to protect the steam turbine from overspeed. An example of the latter is a power load unbalance relay for each unit at 24, 25. An example of the same may be seen in US. Pat. No. 3,198,954 to M. A. Eggenberger et al. issued Aug. 3, 1965.
Electrical independence between the individual load setting channels for each turbine is maintained by means of a separate tachometer generator 26, 27 on each shaft giving both a separate speed signal and supplying power to mode selector panel 13.
The logic circuitry, by means of which the desired individual load settings on the turbines are increased or decreased, is very complex and beyond the scope of the present description. For example, the desired load setting of an individual turbine might be increased in accordance with constraints determined by stresses in the turbine rotor as exemplified in US. Pat. No. 3,446,224 to Zwicky issued May 27, 1969, or the load setting may be reduced under certain unbalanced conditions as exemplified in US. Pat. No. 3,601,617 to DeMello et al. issued Aug. 24, 1971. Some types of loading or unloading signals might be desirable for both turbines in common, while others might be desirable for individual turbines.
In accordance with the present invention, motor 17 drives a first device for generating an individual load setting signal for the first turbine which, in the embodiment shown, is a DC electrical potential appearing on line 29. In a similar manner, motor 18 drives a second device for generating a second individual load setting signal appearing at 31. Motor 19, on the other hand, drives a pair of similar devices 32, 33 through a common mechanical connection for generating a pair of electrically isolated load setting signals appearing at 34, 35, and representing a desired common load on turbines 1, 2. Signals 29, 34 are compared in a low load setting gating device 36 which selects the lowest load setting signal, this becoming the load command signal for turbine 1 at 9. A second low load setting gating device 37 performs the same comparison to provide a load command signal at 11.
An illustration of a simplified circuit for supplying an analog load command signal to turbine l is shown in FIG. 2. Reversible motor 17 drives a lead screw 40 which controls the setting of an adjustable potentiometer 41, thereby setting the magnitude of a DC potential on terminal 42.
Motor 19 drives a lead screw 43 controlling the settings on a pair of electrically isolated adjustable potentiometers 44, 45. This is only one of many possible ways known to those skilled in the art to obtain electrically isolated signals via a common mechanical drive device. A DC potential is thus set on terminal 46 and another DC potential on terminal 47. The signal at terminal 42 is a desired individual load setting on turbine l, as determined by the turbine l logic circuit 14 (FIG. 1); The load setting signals at terminals 46, 47 are the desired common load setting signals determined by the master logic circuit 16.
Amplification and selection of the lower of the two signals appearing at terminals 42, 46 are provided by means of a first operational amplifier 48, a second operational amplifier 49, each having its output connected via diodes 50, 51 to a common lead 52. An additional power amplification stage 53, which permits the gated output to go negative, connects lead 52 to a lead 53 supplying a terminal 54. The separate responses of amplifiers 48, 49 are controlled by selection of feedback impedances such as 55, 56. Provision is made for additional signals to enter the gating circuitry as indicated by a diode 57 connected to lead 52. For example, not only the load setting, but also the rate of increase in load for an individual turbine might be introduced via diode 57. An example of such an arrangement is seen in the aforementioned US. Pat. No. 3,340,883 to Petemel issued Sept. 12, 1967. The function of the circuit illustrated in FIG. 2 is to amplify the signals appearing at terminals 42, 46, to select the lower of the two signals by means of gating diodes 50, 51, and to further amplify the gated signal, which subsequently appears at terminal 54 as the load command signal.
Operation The operation of the invention is illustrated by the graphs of FIGS. 3 and 4. FIG. 3 represents a hypothetical time sequence of load settings provided by devices 28, 30, 32 and 33 as the inputs to the low load setting gates 36, 37. For example, the desired load setting of turbine l is increased along a time ramp 60 to a final load setting 61. Turbine 2, due to possible different constraints, is increased along a different ramp 62 to a load setting 63. Turbine 2 has its load setting decreased abruptly at 64 due to external conditions, recovers along a line 65 to a constant load setting 66.
The master load setting increases along a ramp 67 to a constant lesser load setting 68, is increased at 69 to a second setting 70, decreased at 71 to the original setting 72 and then reduced at 73.
FIG. 4 illustrates the load command signal appearing at the output of the respective low value gates 36, 37. Since the output from gate 36 will always be the lower of the master or the turbine 1 load settings, the load command signal 9 from device 36 will appear as shown in the graph 74. Similarly, the load command signal 11 for turbine 2 appearing at the output of gate 37 will appear as indicated by line 75 in FIG. 4. It should be noted that load setting reductions on individual turbines are reflected. This is indicated at 64 where the turbine 2 load setting was reduced below the master load setting.
While the invention herein has been described in terms of the preferred embodiment using analog signals, those skilled in the control art will recognize that it can easily be carried out within the scope of the present invention using digital techniques. Substitution of digital memory devices that retain their operating state, and therefore signal level, upon loss of power can be made for the reversible motors and load setting potentiometers. Comparison of the digital numbers in load setting registers can be made and the lower value selected as a load command signal in a manner similar to that of the gating devices 36, 37. These digitally derived load command signals may be converted to analog signals in a digital-to-analog converter for use in an analog electrohydraulic servomechanism or may be used directly in a digital electrohydraulic servomechanism.
While there has been described what is herein considered to be the preferred embodiment of the invention, other modifications will occur to those skilled in the art and it is desired to cover in the appended claims all such modifications which fall within the true spirit and scope of the invention.
What is claimed is:
1. A control system for a plurality of prime movers, each having individual servo means for setting the load level of the prime mover in response to a load command signal, said control system comprising:
first means for selectively generating a first individual load setting signal for a first prime mover, second means for selectively generating a second load setting signal for a second prime mover,
master means for selectively generating a common load setting signal for said plurality of prime movers,
first gating means comparing the first and master load setting signals and selecting the lowest load setting as a first load command signal for the first prime mover, and
second gating means comparing the second and master load setting signals and selecting the lowest load setting as a second load command signal for the second prime mover.
2. The combination according to claim 1, wherein said master means is arranged and adapted to provide a pair of substantially identical but electrically isolated master load setting signals to said first and second gating means respectively.
3. The combination according to claim 2, wherein said first means, said second means and said master means each comprise reversible electric motors driving transducers selectively providing said load setting signals.
4. The combination according to claim 1, wherein said master means is arranged to generate a pair of substantially identical but electrically isolated load signals via a common mechanical drive device.
5. The combination according to claim 1, wherein said first, second and master means comprise reversible electric motors driving adjustable potentiometer to provide DC signals for said load setting signals, and wherein said first and second gating means each include a plurality of operational amplifiers with diodes connected at their respective outputs to a common lead for selecting the lowest of said load setting signals applied to each of the gating means.