US3176142A - Prime mover dynamo plant having a speed droop characteristic - Google Patents

Description

Mardl 1965 F. E. VANDAVEER, JR 3,176,142

PRIME MOVER DYNAMO PLANT HAVING A SPEED DROOP CHARACTERISTIC Filed 001;. 11, 1960 SPEED NORMAL SPEED IN V EN TOR.

%NORMAL FREDERICK E. VANDAVEER, JR.

0 5 0% 160% 50 LOAD BY F/G.

United States Patent 3,176,142 PRIME MOVER DYNAMO PLANT HAVING A SPEED DROOP CHARACTERISTIC Frederick E. Vandaveer, In, North Chili, N.Y., assignor to Taylor Instrument Companies, Rochester, N.Y., a

corporation of New York Filed Oct. 11, 1960, Ser. No. 62,017 7 Claims. (Cl. 290-40) This invention relates to the art of automatically controlling a system or process of the type wherein it is desirable that system or process response to control efforts have a drooping characteristic.

For example, in an electrical power generating system, wherein a plurality of motor-generator units supply in parallel a common, varying load, it is necessary to assure that each unit maintains its proper share of the load.

In a typical unit, such as a gas turbine driving an AC. generator, the frequency and power output is a function of turbine speed, and the basic control effect of the usual control system is to automatically resist changes in turbine speed. While it is possible to exercise automatic speed control such as to make the unit to operate very closely at the same speed for different loads, i.e., isochronously, this may create load sharing problems. For example, if one unit of a system tends to respond to load changes faster than its fellows, it will tend to take more than its share of the load, upon load increase, or less than its share of the load, upon load decrease. In the past, this problem of load sharing has been dealt with by taking advantage of the phenomenon known as droop.

In a typical system, turbine speed is controlled by a fuel valve positioned by a servo motor. The servo motor is, in turn, controlled by a hydraulic pilot having an element the position of which depends on the position of a governor fly-weight element relative to the position of some linkage which may be set to various positions depending on the turbine speed desired at a given load. The said linkage is also arranged so that, upon speed changes, the speed control effect is fed back to the linkage in such a way as to make the effective speed setting of the linkage closer to the actual speed of the turbine then obtaining. Thus, if turbine speed drops due to load increase, the speed set point is effectively dropped so that turbine stabilizes out at a speed less than the original setting of the said linkage.

Hydraulic controllers of the type described above have reached a high degree of perfection in function and structure. In particular, being hydraulic, they are inherently fast-acting devices, and, moreover, are self-contained packages including centrifugal governor and hydraulic power supply. However, they are also precise, complex devices which require a high degree of skill and elaborate facilities in manufacturing, repair and maintenance. Hence, the user, upon malfunction of the package, seldom has any recourse but to return the unit to the manufacturer or turn it over to a specialist for repair or servicing.

Furthermore, in present day generator systems, the

individual speed controls of the motor-generator units are small parts of a much larger overall control system, and the speed controls are necessarily integrated with the other parts of the overall control system.

However, hydraulic speed controls are not well-suited for such service, because such service would require considerable length of connecting hydraulic piping and interconnection of hydraulic circuitry. Moreover, except for small units which can go from full load to no load in a matter of seconds, the speed of hydraulic action is not important. The possibilities of leakage, and the design problems inherent in designing hydraulic circuitry involving hundreds of feet of liquid-carrying pipe to be used in anenvironment having a varying heterogeneous tem- 3,176,142 Patented Mar. 30, 1965 perature distribution and incorporating the compact, carefully designed hydraulic circuitry of individual speed control units, more or less rule out a larger, overall hydraulic system.

On the other hand, in extensive control systems, the trend is to use pneumatic apparatus, and, hence, it would be convenient to the system designer if hydraulic speed control units were replaced by pneumatic versions thereof.

According to my invention, I provide a pneumatic speed control apparatus with droop, that does all that its hydraulic counterpart can do. In addition, my novel control apparatus is cheaper in initial cost, modular in nature, can be serviced and repaired by the user, and in general, has all the advantages of pneumatic apparatus in respect of the consequences of leakage, environmental temperature, and so on, as compared to hydraulic apparatus.

By modular in nature, I refer to thefacts that pneumatic systems are generally a collection of relays strung together with appropriate piping, and that a few basic relay types can provide a much larger number of functions, are interchangeable, and can be stocked with the view in mind of being able to use them in different parts of the overall control system. This is to be contrasted with the selfcontained hydraulic speed control package, which is an individual in itself and in general, must be so treated when it comes to service, repair and adjustment.

Turning now to the drawings:

FIGURE 1 is a graph of actual speed versus actual load in percent relative to a given load to be driven at a predetermined speed;

FIGURE 2 is schematic diagram of a plural unit electrical power generating system; and

FIGURE 3 illustrates my novel control system as ap plied to one of the units of the system shown in FIGURE 2.

Droop, or offset, as it often is termed in control theory, is an inherent characteristic of simple proportional control of a process having a certain amount of inertia, capacity, lag, or other characteristic, the end result of which is to cause the process to stabilize out at a point that is a function of the load represented by process behavior. For example, in a simple governor controlled turbine system wherein a governor tends to open or close the fuel or steam valve of the turbine in proportion to its speed, the speed of the turbine will be a function of the load on the turbine, a characteristic often expressed as the regulation of the turbine, i.e., the percentage change in speed for a range of percentages of a given load relative to a given speed at said given load.

This characteristic is illustrated in FIGURE 1, from which it will be seen from the said figure, that at more than of load, the turbine stabilizes out a speed less than that for 100% of load. Since the power generated into a load is a function of speed, the regulation of the turbine opposesthe tendency to pick-up and drop load upon load changes, as compared to isochronous action (which would be represented by the horizontal Normal Speed line in FIGURE 1).

FIGURE 1 also illustrates how the turbine goes from one stabliization point to another by means of an Actual Speed line (which may be curved, but is here shown as straight, for convenience) representing the lows of the stabilization points of the system for different loads. For example, to get from point A, Normal Load, to point B, 50% of Normal Load, the turbine speed varies along the dashed line running from A to B during the time it takes the turbine to stabilize out at the speed corresponding to point A.

Again, as the turbine goes from 50% of Normal Load to of Normal Load, turbine speed varies as indicated by the dashed line from point B to point C.

The speed fluctuation indicated by the dashed line curves is generally controlled so as to keep the area between them and the Actual Speed line at a minimum, hence, one finds that the typical speed controller is desirably a so-called multi-response device, i.e., one that not only measures out its control elfectin proportion to the deviation of actual speed from normal speed, but also in accordance with the rate of change of deviation and the time integral of deviation. This last characteristic of the controller, known as reset action, has the characteristic of tending to prevent droop or olfset and, therefore, where reset action is involved, the necessary droop is obtained by varying the set point of the speed control system.

Turning again to FIGURE 1, the Actual Speed line represents the result of droop in a speed control system under varying load. Supposing some Normal Load to be chosen at which the generator unit will require to be run at a speed given by the Normal Speed line in FIGURE 1, if the load varies in a range from 50% of normal to 150% of normal, the regulation of the system is represented by the difference in the 50%of-Normal-Load speed and the 150%-of-Normal-Load speed, i.e., the speed difference given by the vertical distance between points B and C on the Actual Speed line. As is known in the art, it such regulation or droop is adjusted to suit the load-following characteristic of each motor-generator unit in a system of units in parallel driving a common variable electrical load, each unit will carry its share of the varying load at all times. In typical cases, the amount of droop needed ranges up to about 10% of Normal Speed.

As indicated by what was described initially of FIG- URE l, the speed-load picture in this figure is somewhat idealized. Nevertheless, given the particular speed-load characteristic of a particular unit, it is possible to establish the amount of droop in the speed control system of that unit such as will enable the unit to follow load changes in the proper proportion along with its fellows, each of which has been provided with the appropriate droop calculated to make it cooperate likewise in the generating system.

FIGURE 2 shows schematically the sort of generating system envisaged herein. Such systems comprise a plurality of generators, of number n, say, i.e., G G as indicated in the figure.

Generator G is driven by a motor T, say a gas turbine, having a fuel intake 1 controlled by a flow control valve V, the exhaust of the turbine being shown at 2. Turbine T has a shaft 3 that rotates the armature (not shown) of generator G and the generator has output terminals 4 and 5 at which electric power is fed into lines L, connected to one or sundry electrical power consuming means (not shown) of such nature that the electrical demand on the generating system varies from time to time,

To control the output of generator 6,, a control system is provided including speed sensing device S, connected to shaft 3 and emitting a signal in proportion to turbine speed, which signal is transmitted via a connection 6 to a controller C.

Controller C receives the speed signal and emits a control signal which is relayed via override controls 0 and connections 7, 8, and 9 to valve V.

Override controls 0, for purposes of this application, are relay devices that normally repeat the control signal emitted by controller C into the connections 8 and 9, and hence, do not exist except in special circumstances. In this case, these special circumstances may include temperature, pressure, and other conditions such as would signify dangerous or otherwise undesirable operating conditions. Merely by way of example, override controls 0 are illustrated as connected to inlet 1 and exhaust 2 of turbine T by connections 10 and 11 for the purpose of sensing temperatures and responding to critical values of temperature to shut down the fuel flow. Assuming a biased-closed, signal-to-open valve V, override controls 0 will be constructed to cut-off the signal connection between valve V and controller C upon occurrence of an improper temperature. Otherwise, override controls 0 merely relay the control signal on to valve V. Since such overriding of the controller C is known in the art, it is of no concern to this application to indicate the exact manner of operation and construction of override controls O.

Generator G would likewise be fitted out as is generator G and is connected to lines L, and, therefore, neither it nor its control system need be described any further, and so on for each of whatever number of generators may be connected to lines L. It is to be noted, however, that the generators involved (and their motors, etc.) need not be identical as to structure, capacity, etc. Each motor generator unit must be capable of being drooped, however, in order to assure proper load sharing in the face of varying load.

FIGURE 3 shows one embodiment of my novel pneumatic speed control system with droop. In the figure, the main components of the system are shown to be pneumatic relay devices 20 and 40.

Relay device 20 is a conventional controller having proportional, rate and reset action, and comprises bellows 21, 22, 23 and 24, the near ends of which are connected together by means of a cross bar 25, the lengths of the bellows being parallel and their far ends being fixed to a common support (not shown). The said bellows are substantially identical and are equispaced about a circle divided into four quadrants by the arms of cross bars 25. Bellows 21 to 24 are so arranged (as by providing suitable adjustable biasing springs, not shown, between crossbar and said common support), that with equal pressure in opposite bellows the crossbar 25 lies in a predetermined reference plane with each bellows substantially equally extended. A flexible, inextensible element 25A, such as a wire connected between said common support and the center of crossbar 25, allows crossbar 25 to be deflected by said bellows without being displaced bodily away from the said common support.

A pipe 60, corresponding to connection 6, FIGURE 2, connects bellows 21 to speed transmitter S, adapted to measure the rate of rotation of shaft 3, FIGURE 1, and to establish an air pressure in pipe 6%} and bellows 21, the value of which corresponds to the measured rate of rotation. Such devices are well known in the art, hence, transmitter S needs no further description.

Bellows 23 and 24 are connected together by piping 26 and adjustable restrictors 27 and 28, and pipe 70 connects piping 26, between restrictors 27 and 28, to an override control 0. A further pipe connects the last said override control 0 to a further override control 0, and this latter is connected to valve V by means of a pipe 96. Piping '70, 8t and 90, obviously corresponds to connections 7, 8 and 9 of FIGURE 2. Likewise, valve V is in the fuel intake 1 of the turbine T.

To provide a control air pressure for pipe 70, there is provided a booster relay 30 connected at its output by pipe 29 to pipe 70. As shown by the symbol A.S., air under pressure is supplied via pipe 31 to relay 3%) and, via a restrictor 32, to piping 33 and to a pipe 34 which is connected between piping 33 and relay 3%). It is not necessary to describe booster relay 3G in detail, since in accordance with prior art practice, it is merely a pressure amplifier that responds to the level of pressure in pipe 34 to establish a pressure in piping 29, 70, 26 and bellows 23 and 24 corresponding to the pressure in pipe 34. The output pressure of the booster will be some definite multiple or fraction of the pressure in pipe 34, generally 121, since the booster relay is used mainly for its characteristic of being able to establish its output pressures in terms of air volume output much greater than the corresponding air volume change at its input, i.e., in pipe 34. Such relays are well known in the art and need not be further described or illustrated.

To establish a control pressure in line 7% of the desired sort, there are provided a nozzle 35 connected to pipe 33,,

and a circular cross section baffle rod 36. Baffle rod 36 is mounted at the center of crossbar 25, with its length normal to the plane of crossbar 25.

Nozzle 35 is supported at the side of rod 36 with its opening (not shown) facing the side of the rod. Hence, within a certain spacing range, rod 36 will obstruct flow through nozzle 35 in accordance with the separation between nozzle opening. and the next adjacent rod surface. Therefore, change in bafile-nozzle spacing will vary the pressure in pipes 33, 34 and 26.

A plate 37 supports nozzle 35 in the attitude described, and is itself supported by a rotatable shaft 38, said shaft being rotatably mounted by a supporting element (not shown) that is fixed relative to whatever supports the fixed ends of bellows 21-24. To permit adjustment of nozzle 35 by rotation of shaft 38, a knob 39 is provided on shaft 38 for turning the plate 37 and, hence nozzle 35. Also, piping is coiled and flexible, as shown, in order to permit the nozzle 35 to be deflected about the axis of shaft 38.

The parts of the nozzle mechanism are so positioned that when crossbar is in the aforesaid predetermined plane, the axis of the circular-section rod 36 is coextensive with the axis of rotation of nozzle 35 about shaft 38. This orientation of parts defines a neutral position, in which, if knob 39 is turned, the nozzle opening moves about the circular contour of rod 36 without the flow obstructing efifect of rod 36 changing, due to the fact that the spacing between nozzle opening and the rod-surface stays constant.

As thus far described, controller 20 is old in the art, insofar as this application is concerned, although in practice the adjustable baflle and nozzle mechanism are otherwise realized (to give however, the same results envisaged here). Controllers and relay devices of this type are described and claimed in the prior copending application of H. R. Jaquith, Ser. No. 626,537, filed December 5, 1956, and assigned to the Taylor Instrument Companies, now US. Letters Patent No. 3,047,002, issued July 31, 1962.

Taking the parts in the position shown as defining the aforesaid neutral position with the pressures in each of bellows 21 to 24 at 9 p.s.i. gauge, increase in the pressure in bellows 21 would throttle nozzle 35. Supposing the booster relay St? to be direct acting, the pressure in line 70 would be increased by the relay 30 and, supposing valve V to be of biased-closed and air-to-open type, it would increase its opening from whatever it was at the 9 psi. gauge position, (remembering that override controls 0 are supposed to be relays that repeat the signals applied to them, in this case, air pressure).

Therefore, if transmitter S is designed so that it increases the pressure in bellows 21 in response to decrease in speed, (and vice versa for increase in speed) the result is that more fuel is fed to turbine T and it attempts to restore its generator to a speed corresponding to 9 p.s.i. gauge in bellows 21.

Considerations of load-sharing aside, for control purposes in general, bellows 23 and 24 and restrictions 27 and 23 are normally arranged to vary the control pressure applied to valve V in such a way as to restore the original speed as stably and quickly as possible. That is, restrictors 27 and 28 respectively provide for reset and rate effects, as is well known in the art. In brief, a deflection of crossbar 25' out of the aforesaid reference plane, due, say, to pressure increase in bellows 21, increases the pressure in the motor of valve V and in bellows 23 and 24, the end result being increase in turbine speed. Hence, the pressures in bellows 21, 23 and 24 change in a manner determined by, respectively, the time constant of the connections between relay 30 and bellows 23, the time constant of the connections between relay 30 and bellows 24, and the time constant involved in making a change in the output pressure of relay 30 result in a change in output of transmitter S into bellows 21.

By adjusting the values of restrictions 27 and 28, and the fluid capacity involved in bellows 23 and 24 and their connections to relay 30 to suit the process characteristics, namely: the manner in which the turbogenerator responds to electrical load changes, it is possible to make turbine speed follow closely the Normal Load line (which corresponds to the pressure in bellows 22) and to cause the curvature by which turbine speed restabilizes upon change in load (i.e., the transient characteristic of the system exemplified by the dashed line curves in FIGURE 1) to conform to a known criterion of control quality not relevant here. This, however, is a typical approximation to control without droop, i.e., isochronous governing of turbine speed, or offset-less control. Hence, it is necessary to introduce the desired droop somehow.

The prior art application of pneumatic control principles involves providing a pressure regulator, which can be set to produce a set point pressure corresponding to the desired value of whatever process variable is being controlled. In this case, the process variable is turbine speed, hence, the set point pressure in bellows 22 would be maintained at a value corresponding to Normal Speed.

According to my invention, rather than connecting a set point transmitter or regulator directly to bellows 22, I connect a set point transmitter to a biasing or droop relay and the biasing relay to set point bellows 22. Such biasing relay must be of the type which can be adjustable to modify the value of the set point pressure by an amount corresponding to the necessary droop and which retransmits the set point pressure, thus modified, to bellows 22.

In FIGURE 3, reference numeral 12 denotes a set point transmitter connected by pipe 17 to the relay 40. Transmitter 12 is supplied with air as indicated at A.S., and includes a knob 13 and structure (not shown) which responds to turning of knob 13 to produce from the supply air, a set point pressure in pipe 17 that has a magnitude corresponding to the setting of knob 13. Suitable means in the nature of a set point pressure gauge or knob position indicating means, and having a scale and pointer indicating means 14, is provided to permit setting the pressure in pipe 17 at the desired value. Conveniently the indications of means 14 may be in terms. of turbine speed and, in this case, the speed scale readings would be inversely proportional to the pressure in pipe 17. (Normally, a pressure gauge 15 having scale and pointer means 16 would also be connected to pipe 60 to indicate actual turbine speed, as measured by transmitter S.) Under the circumstances outlined here, the means 16 would be scaled off in turbine speed, the readings of which would be inversely proportional to the pressure in line 60.

The basic structure of [relay 40, which is the aforementioned biasing or droop relay, is identical to that of controller 20. Specifically, bellows 41-44, crossbar 45 and flexible, inextensible element 45A are provided and arranged exactly as their counterparts in controller 20, except for pressure connections. Likewise, the identical adjustable bafiie and nozzle mechanism is provided (omitting in FIGURE 3 all but bafile rod 46 and nozzle 47, for the sake of clarity). Also, a booster relay 50 supplied with air via a pipe 51 (which air is also applied via orifice 52 and a pipe 53 to nozzle 47) is connected by a pipe 54 to pipe 53 to allow relay 50 to sense nozzle back pressure and to produce a corresponding output pressure in a pipe 59 connected into a pipe 58 connecting set point bellows 22 of controller 20 with a bellows 42 of bias relay 40. Set point transmitter 12 having its out put pressure connected via pipe 17 to bellows 41 direct- 1y opopsite bellows 42, it is evident that the pressure in bellows 41 will be reflected by a pressure in bellows 42 that acts on crossbar 45 opposite to the pressure in bellows 41.

The bellows 44 is connected to atmosphere via a vent 19, and bellows 43 is connected by pipe 18 to pipe 90,

7 in which reigns the control pressure which operates valve V.

Thus, as will be obvious from the foregoing, the pressures in bellows 41 and 43 will determine, for a given angular position of nozzle 47 relative to rod 46, the pressure in bellows 42 and 22, and, hence, the speed set point or Normal Speed of the turbine T.

When the turbine T is 100% loaded by its generator, i.e., when the generator is taking its full share of the Normal Load, and the load is unchanging, fuel supply control valve V must be opened to a predetermined extent which in turn determines the control pressure in line 96 and bellows 43. At the same time, the setting of set point transmitter 12 will be such as toprovide a pressure in bellows 41 corresponding to Normal Speed, and equal to the output pressure of transmitter S which will be measuring actual speed.

Accordingly, the pressure in each bellows 22 and 42 must also be equal to the pressure in each of bellows 41 and 21, hence, under these circumstances, the crossbar and bellows structure of both controller 20 and bias relay 40 are adjusted so that their crossbars 25 and 45 are in the neutral position described, supra, in the case of controller 20, namely, such that the nozzles 35 and 47 can be deflected about their respective rods without changing the output of the respective booster relays.

Accordingly, with the turbo-generator running at Normal Speed under 100% of load, bias relay 46 simply repeats the set point pressure in bellows 41 into set point bellows 22 of controller 20. However, if the electrical load on the generator then changes, obviously booster relay 30 will establish a new output pressure in pipe 29, which will be repeated via override controls in pipe 9%) and therefore into bellows 43 as well as the motor of valve V. As a result, crossbar 45 will deflect and alter the position of rod 46 relative to nozzle 4'7. Nozzle 47, therefore, is initially set at such an angle relative to the long axis of rod 46, that deflection of crossbar 45 disturbs the spacing between rod 46 and the opening of nozzle 47. As a result, when the pressure in bellows 43 changes from the value corresponding to Normal Speed of the turbine, the pressure in bellows 42 will change in an amount and sense depending on the angular setting of nozzle 47 and the sense and amount of such pressure change. This phenomenon supplies the droop.

In the angular position shown for nozzle 47, if the generator load increases from 100% of Normal Load, turbine speed will drop and controller 2% will increase its output pressure, thereby increasing the pressure in bellows 43, and rod 46 is therefore tilted toward the opening of nozzle 47. The resulting increase in nozzle back pressure is sensed by booster relay $0, which in turn increases the pressure in bellows 22 and 42. Accordingly, rod is forced to move away from the nozzle opening, the eventual result being that the pressure in bellows 42 increases just sufliciently to counterbalance the increase in pressure in bellows 43.

Since the pressure in bellows 22 also increases, rod 36 moves away from the opening of nozzle 35 and therefore opposes the original change in the pressure in bellows 21 that began the events just described. That is, the back pressure of nozzle 35 decreases, booster relay 3%) senses the decrease, and decreases its output pressure into line 2s, and as a result, valve V decreases the rate at which fuel is being supplied to the turbine, thereby drooping the turbo-generator. The effect is some What as if knob 13 had been turned to establish a lower Normal Speed value, that is to increase the pressure in line 17, although of course, transmitter 12 still continues to establish in bellows 41 a pressure corresponding to the Normal Speed for 100% of Normal Load.

The amount of pressure droop or bias required is normally a small fraction of the set point pressure in bellows 41. Hence, the angular position of nozzle 47 would be such that tilting of crossbar 45 by bellows 43 (which would be about an axis defined, in effect, by the crossbar connections to bellows 41 and 42), varies net rod-nozzle spacing less than the same amount of tilt, applied by bellows 42 about the axis determined by the crossbar connections to bellows 43 and 44, would vary net rod-nozzle spacing.

It will be noted, of course, that if load decreases from 100% of normal, the converse effect occurs, i.e., the pressure in bellows 22 decreases below the value corresponding to Normal Speed for 100% of Normal Load, which prevents the generator from dropping load upon decrease of the total load from 100% of Normal Load. Obviously, too, if load returns to 100% of Normal Load, the bias relay 40 restores the pressure in bellows 22 to a value equal to that established in pipe 17 by set point transmitter 12.

Although I have gone into great detail as to the relays 20 and 40, etc., I have done so mainly by way of example, and in order to indicate clearly the advantages of pneumatic instrumentation in the specific control situa tion involved here.

Note, for example, that relays 20 and 40 are identical except for piping. Likewise, relays 31B and 50 may be identical with each other. Indeed, override control 0 and transmitter S may have the same basic structure as relays 20 and 40, although in practice it is not customary to go so far for the sake of uniformity. Again, with reference to the overall system, i.e., the generators 1 to n and the apparatus directly appurtenant thereto: speed control system, override controls 0, turbine, etc., such system may be part of an even larger system wherein other control functions are exercised by means of pneumatic controllers and relays such as relays 20 and 40. It is easy to see that as a matter of maintenance, service, etc., it is within the province of my invention to use structurally quite diflerent (but functionally similar) types of pneumatic relays than those illustrated in FIGURE 3. Again, it is not absolutely necessary that the full complement of proportioning, reset and rate actions be applied. Normally, however, at least proportioning plus reset action, or equivalent would be provided, since although the inherent droop of a proportional-only control ler would tend to alleviate load sharing difflculties, it is more convenient to: introduce droop for the purpose in the manner disclosed herein, namely, by adding it to a system that would otherwise tend to control isochronously.

The purpose of controlling the bias action of droop relay 46 in response to what amounts to output pressure of relay 3% is to make such bias action reflect load changes in the electrical load. That is, variations in the electrical load are reflected by variations in turbine speed, hence, measurement of turbine speed serves as a measurement of load change. It would also be possible to measure load changes otherwise than indicated, so long as the measurement eventually results in a pressure which can be supplied to bellows 43 to do what the control pressure in pipe does in FIGURE 3.

The override controls 0 form no part of the invention and may or may not be used, as desired. It is to be noted that whereas with a typical hydraulic system, overrides are designed (to order, more or less), into the control package, on the other hand, with pneumatic control components, no such package is involved, and the control system for a particular turbo-generator unit is more or less built up ad lib by piping together the sundry relays as shown. In practice, it is usual to integrate booster relay, baifle nozzle mechanism and the basic relay unit together, likewise, some sort of easing structure housing gauges and indicating or recording mechanisms such as speed indicator 15 and set point transmitter 12 may be provided, to which casing may be attached to the controller Zil.

Such integration is done on a plugin basis or quickdetach and attach basis, however, not feasible with liquid type systems, hence, structural unity of a pneumatic control system, lends itself to service and repair practices that would be infeasible in the case of a hydraulic speed control unit, unless an expert mechanic and special tools were available. Thus, a faulty bias relay 40 or controller 20 need merely be replaced bodily by breaking a few air connections and installing a new unit. In a hydraulic system, equivalent practices are far more tedious and troublesome, e.g., replacement of droop linkage is a task for an expert and replacement of the controller corresponds to replacing elements corresponding to everything shown in FIGURE 3 but the valve V, that is, in short, the entire speed control unit.

I believe the foregoing demonstrates a considerable advance in the art and one that is worthy of patent protection. While the foregoing is a clear and fullydetailed description of the best mode of practicing my invention, it is evident that modifications may be made therein without departing from the spirit orf the invention. Therefore, I have framed the claims appended hereto accordingly and intend that they, rather than the details I have disclosed, supra, set the patentable bounds of my invention.

I claim:

1. In combination, a generator and: a motor for driving said generator at a given rate when said generator is generating into a given load; said generator being connected to a varying load; whereby said motor tends to drive said generator at a varying rate inversely related to variation in generator loading; relay means constructed and arranged for comparison of. first and second signals and for producing a control signal corresponding to the difference between said first and second signals; measuring means responsive to the said varying rate for providing said first signal in accordance with said varying rate; set point means settable to provide said second signal in accordance with said given rate; first signal transmitting means being connected between said relay means and said measuring means for transmitting said first signal to said relay means; second signal transmitting means being connected between said relay means and said set point means for transmitting said second signal to said relay means; all the aforesaid means being so arranged as to produce said control signal as aforesaid; motor control means responsive to said control signal for causing said motor to change said varying rate of drive in a sense tending to reduce said difference between said first and second control signals; whereby said varying rate of drive tends to maintain a value corresponding to the setting of said set point means; settable signal biasing means constructed and arranged to receive a signal and to retransmit such signal with a bias corresponding to the setting of said settable signal biasing means; said settable signal biasing means being arranged in said second signal transmitting connection for receiving and retransmitting said second signal, as aforesaid, to said relay means; said settable signal biasing means being responsive to said varying load to adjust said bias in accordance with the difference between said given load and said varying load; said settable signal biasing means being so constructed and arranged that for varying load difference from said given load, said second signal is so biased as to be retransmitted with such value that the difference between said first signal and said second signal retransmitted is less than the dilierence between said first signal and said second signal received by said settable signal biasing means.

2. In combination, means responsive to actual frequency of generation in a motor-generator set for producing a variable pressure varying with actual frequency; means settable to produce a fixed pressure corresponding to a desired frequency of generation in said motorgenerator set; a bias responsive to said fixed pressure to produce a modified pressure equal to the sum of said fixed pressure and a bias pressure; relay means responsive to said variable pressure and said modified pressure to produce a control signal varying in accordance with the relation between said modified pressure and said variable pressure; control means responsive to said control signal such as to tend to cause said motor-generator set to generate at said desired frequency; the arrangement being that said control signal varies in a sense such as to tend to cause said actual frequency to change in a sense opposing changes of actual frequency causing said control signal to vary; said bias relay also being responsive to said control signal so as to add said bias pressure to said fixed pressure in such sense as to reduce the tendency of said control signal to cause said actual frequency to assume the value of said fixed frequency.

3. In combination, a process variable transmitter for producing a process variable signal in accordance with a process variable; a set point transmitter settable to produce a set point signal in accordance with its setting; a controller; a first connection means connecting said process variable transmitter to said controller; a second connection means connecting said set point transmitter to said controller; said first and second connection means providing said controller with, respectively, said process variable signal from said process variable transmitter and said set point signal from said set point transmitter; said controller being constructed and arranged to produce a control signal variable in sense and magnitude according with the difference between a signal provided it by said first connection means and a signal provided it by said second connection means; bias means in said second connection means, said bias means being settable to add a bias to said set point signal; whereby said control signal varies in sense and magnitude in accordance with the difference between said process variable signal and said set point signal biased by said bias means.

4. A droop-type relay system including, a controller constructed and arranged to have an input for receiving a process variable input signal, an input for receiving a set point input signal, and an output at which to produce an output signal; said controller being responsive to the difference between said input signals such as to change its said output signal in an amount and sense determined by the amount and sense of the difference between the said input signals; and a droop relay having an input connected to said output of said controller for receiving said output signal; an input for receiving said set point signal, and an output at which to produce a modified set point input signal, said droop relay being constructed and arranged to be responsive to deviation of said output signal from a given value to produce at its said output a said modified set point input signal as a function both of the first said set point input signal and of said deviation of said output signal; said output of said droop relay bemg connected to said controllers second said input for providing said second said input with said modified set point input signal. 5. The invention of claim 4, wherein said controller includes a pneumatic means responsive to the signals applied to said controllers said inputs to produce said output signal in the form of an equivalent pneumatic output signal; said droop relay includes pneumatic means responsive to a pneumatic signal applied to the first said input of said droop relay to produce at its said output the said modified set point input signal, and there being a pneumatic connection connecting said output of said controller to the said first said input of said droop relay for applying said pneumatic output signal to said first said input of said droop relay.

6. A power-generating system including: a power generator; a variable speed motor for driving said generator; control means for exerting a speed adjusting efiect on said motor; measuring means for measuring the speed of said motor and producing a first effect corresponding to actual motor speed; set point means for setting the speed of said motor and for producing a second effect in accordance with its setting; said measuring means and said set point means being automatically operative to cause said control means to exert said speed-adjusting effect on said motor in such fashion as to oppose change in motor speed, said speed-adjusting efiect corresponding to the difference between said first and second effect; said measuring means being constructed and arranged to produce said first effect in the form of a pneumatic signal corresponding to the said speed of said motor, and said control means being constructed and arranged to respond to said pneumatic signal and to said second efiect in order to produce said speed-adjusting effect; droop means responsive to said speed-adjusting effect for modifying said second effect so as to oppose the tendency of said speed-adjusting effect to oppose said changes in motor 5 speed.

7. The invention of claim 6, said droop means being responsive to said set point means to produce said second efiect, and said droop means also being responsive to deviate from accordance with said setting of said set point means; said droop means being constructed and arranged so that such deviation of said second effect from accordance with said setting is in accordance with difierence between actual motor speed and the motor speed corresponding to said setting, but has a sense such as to make the diiference between said first effect and said second effect less than the said difference between actual motor speed and the motor speed corresponding to said 10 setting.

References Cited by the Examiner UNITED STATES PATENTS 2,273,407 2/42 Lilja 29040.1 2,811,651 10/57 Lepley 29040 FOREIGN PATENTS 583,247 9/59 Canada.

to said speed-adjusting effect to cause said second effect 20 ORIS L. RADER, Primary Examiner.

Claims (1)

1. 6. A POWER-GENERATING SYSTEM INCLUDING: A POWER GENERATOR; A VARIABLE SPEED MOTOR FOR DRIVING SAID GENERATOR; CONTROL MEANS FOR EXERTING A SPEED ADJUSTING EFFECT ON SAID MOTOR; MEASURING MEANS FOR MEASURING THE SPEED OF SAID MOTOR AND PRODUCING A FIRST EFFECT CORRESPONDING TO ACTUAL MOTOR SPEED; SET POINT MEANS FOR SETTING THE SPEED OF SAID MOTOR AND FOR PRODUCING A SECOND EFFECT IN ACCORDANCE WITH ITS SETTING; SAID MEASURING MEANS AND SAID SET POINT MEANS BEING AUTOMATICALLY OPERATIVE TO CAUSE SAID CONTROL MEANS TO EXERT SAID SPEED-ADJUSTING EFFECT ON SAID MOTOR IN SUCH FASHION AS TO OPPOSED CHANGE IN MOTOR SPEED, SAID SPEED-ADJUSTING EFFECT CORRESPONDING TO THE DIFFERENCE BETWEEN SAID FIRST AND SECOND EFFECT; SAID MEASURING MEANS BEING CONSTRUCTED AND ARRANGED TO PRODUCE SAID FIRST EFFECT IN THE FORM OF A PNEUMATIC SIGNAL CORRESPONDING TO THE SAID SPEED OF SAID MOTOR, AND SAID CONTROL MEANS BEING CONSTRUCTED AND ARRANGED TO RESPOND TO SAID PNEUMATIC SIGNAL AND TO SAID SECOND EFFECT IN ORDER TO PRODUCE SAID SPEED-ADJUSTING EFFECT; DROOP MEANS RESPONSIVE TO SAID SPEED-ADJUSTING EFFECT FOR MODIFYING SAID SECOND EFFECT SO AS TO OPPOSE THE TENDENCY OF SAID SPEED-ADJUSTING EFFECT TO OPPOSE SAID CHANGES IN MOTOR SPEED.

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