US3718837A

US3718837A - Control system for an extraction turbine system

Info

Publication number: US3718837A
Application number: US00244796A
Authority: US
Inventors: M Yokota; H Sato
Original assignee: Tokyo Shibaura Electric Co Ltd
Current assignee: Toshiba Corp
Priority date: 1971-04-19
Filing date: 1972-04-17
Publication date: 1973-02-27
Anticipated expiration: 1990-02-27
Also published as: AU4120572A; GB1347934A; JPS4943732B1; AU462753B2

Abstract

A control system for an elastic fluid turbine having a high pressure turbine stage and a motive fluid flow thereto regulated by a main control valve, and a low pressure turbine stage to which the flow of motive fluid is controlled by an interstage control valve. A speed/load control arrangement controls the main and interstage control valves in the same directions responsive to rotational speed of the turbine and a pressure control arrangement controls the valves respectively in opposite directions responsive to the pressure of extracted motive fluid. The control of the main control valve by the pressure control arrangement is interrupted when the load of the turbine system is lost, to prevent overspeed upon such occurrence.

Description

' United States Patent 1 Yokota et al. 1 Feb. 27, 1973 54] CONTROL SYSTEM FORAN 3,244,898 4/1966 Hickox ..290/2 RACTION TURBINE SYSTEM 3,421,014 l/l969 Moorganov ....290/2 X 3,643,437 2/1972 Birnbaum et al. ..60/105 X [75] Inventors: Mitsuhisa Yokota, Hiroya Sato, both Of YOROham LJ' P Primary Examiner-James D. Trammell' [73] Assignee: Tokyo Shibaura Electric Company Atmmey Nrman p'oblon et Limited, Kawasaki-shi, Japan ABSTRACT 'l 17 1972 [22] Flled A control system for an elastic fluid turbine having a [21] Appl. No.: 244,796 high pressure turbine stage and a motive fluid flow thereto regulated by a main control valve, and a low P D pressure turbine stage to which the flow of motive [30] Forelgn Apphcanon nomy am fluid is controlled by an interstage control valve. A April 19, 1971 Japan ..46/25l33 peed/load control arrangement controls the main and interstage control valves in the same directions 1 .290/2, responsive to rotational speed of the turbine and a 19 pressure control arrangement controls the valves [51] Int. Cl. ..H02h 7/06 respectively in opposite directions responsive to the [58] Field of Search ..290/2, 40; 60/105; 307/86; pressure of extracted motive fluid. The control of the 317/13 R, 19 main control valve by the pressure control arrangement is interrupted when the load of the turbine [56] References Cited system is lost, to prevent overspeed upon such occurrence. UNITED STATES'PATENTS 2 Claims, 2 Drawing Figures 3,097,490

7/1963 Callan et al. ..60/l05 CONTROL SYSTEM FOR AN EXTRACTION TURBINE SYSTEM BACKGROUND OF THE INVENTION I Field Of The Invention:

This invention relates generally to a control system for an elastic fluid turbine and more particularly to a control system for a turbine having at least one extraction stage.

2. Description Of The Prior Art:

In turbine control systems for elastic fluid turbines of the types such as, for example, extraction noncondensing, extraction condensing, two-stage extraction condensing, and the like, there are provided speed/load control arrangements and extraction pressure control arrangements. These control arrangements regulate a main control .valve unit and an interstage or integral control valve unit, the main control valve unit controlling the flow rate of the motive fluid from a motive fluid generator to a high pressure turbine, and the interstage control valve unit controlling the flow rate of the motive fluid from the high pressure turbine to a low pressure turbine. Increasing or decreasing the opening of the main control valve unit results in the output power of the turbine, and also the pressure or quantity of the extracted fluid in the extraction stage, being increased or decreased, whereas increasing and decreasing the opening of the interstage control valve unit results in the output power of the turbine being respectively increased and decreased, while the pressure or quantity of the extracted fluid is in turn decreased and increased.

Accordingly, the speed/load control arrangement'is adapted to regulate the main control valve unit and the interstage control valve unit so as to control the turbine speed without adverse effect on the extraction stage and the extraction pressure control arrangement is adapted to regulate the main control valve unit and the interstage control valve unit in a reverse direction of each other so as to controlv the extraction of fluid without causing a variation of the output power of the turbine. Also, the speed/load control and the extraction control arrangements'are adapted tooperate independently of each other, so that the desired speed of the turbine and the desired pressure of-' the extracted fluid may be achieved under a turbine operation having a load larger than a predetermined value such as, for example,ahalf-load. v

Under the condition where there is no variation in the desired quantity of extracted fluid, the main control valve unit is generally adapted to be operated to open and close against a speed variation of the turbine at such a rate that the main control valve unit isclosed from the full load opening thereof to an opening thereof at which the turbine operates at the rated speed under no load, hereinafter referred to as the no-load opening, when the turbine speed rises above its rated speed by a predetermined value such as, for example, 5 percent of its rated speed, thus characterized as 5 percent speed regulation. In other words, the output power of the turbine is caused to change from its rated value to null when the speed reaches 105. percent of the rated speed. Where a turbine system operated as described above drives an electric'generator, it is necessary to rapidly close the, main control valve unit to the noload opening" in order to prevent an undesirable or dangerous speed rise when the generator load is lost due to a fault in the electric power system to which the output of the generator is supplied. However, the decrease in the opening of the main control valve unit caused by the speed/load control arrangement also tends to cause the quantity of the extracted fluid to decrease, whereby the pressure controlarrangement tends to cause the main control valve to open. The turbine speed is then liable to rise a relatively large amount.

In a turbine system wherein thequantity of the extracted fluid is relatively large when compared with the total flow quantity of the motive fluid being supplied to the turbine, the opening of the main control valve is largely affected by the pressure control arrangement. In these turbine systems, there is not only a'fear that the speed of the turbine is liable to reach 108 to 109 percent of the rated speed but also a most perplexing problem of the speed reaching a set speed, in Japan being usually I 10 percent of the rated speed, at which an over-speed trip device operates to stop the operation of the turbine system. It is desirable to make the over-speed as low as possible, and yet, once the overspeed trip device operates to halt the operation of the system, .it is troublesome and time consuming to restart the turbine system.

SUMMARY OF THE INVENTION Accordingly, it is an object of this invention is to provide a turbine control system for a turbine system having one or more extraction stages capable of preventing dangerous or undesirable over-speed upon loss of load.

Briefly stated, according to this invention, the foregoing object is attained by a control system for an extraction turbine system having a'high pressure turbine stage and a motive fluid flowing thereto being regulated by a main control valve means, and a low pressure turbine stage,lthe flow to which of a motive fluid is controlled by an interstagecontrol valve means. There are.provided a speed/load control arrangement and a pressure control arrangement, the former controlling the main and interstage control valve means in the same directions in response'to rotational speed of the turbine and the latter controlling the main and interstage control/valves in opposite directions of each other in response to the pressure of the extracted mo-' tive fluid. Additionally, means are incorporated for interrupting control of the main control valve means by the pressure control arrangement .when the load of the turbine system is removed, thereby to prevent an undesirable over-speed from occurring upon loss of the turbine load.

BRIEF DESCRIPTION OF THE DRAWING Various other objects, features and attendant advantages of the present invention will be more fully appreciatedas the same becomes better understood from the following detailed description when considered in connection with the accompanying drawing, wherein:

I FIG. 1 shows a schematic circuit diagram of one embodiment according to this invention; and FIG. 2 is a diagram to explain the operation of the embodiment shown in FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1, the embodiment shown therein is a control system adapted for use with a turbine system which, generally being indicated by the reference numeral 10, comprises a high pressure turbine 11 and a low pressure turbine 12, which drive an electric generator 13. A motive fluid, such as a steam generated by a motive fluid generator, as for example, a steam boiler 14, flows through a main control valve 15 to the high pressure turbine and expands therein, whereupon one part of the steam flows through an interstage or integral extraction control valve 16 to the low pressure turbine 12 and the residual part of the steam flows out to an extraction line 17. The steam flowing to the low pressure turbine 12 expands therein, then finally flows to a condenser 18. The main control valve 15 regulates the flow rate of the steam from the steam generator 14 to the high pressure turbine 11, while the interstage control valve 16 regulates the flow rate of the steam from the high pressure turbine 11 to the low pressure turbine 12. Although the actual system usually employs a plurality of main control valves and a plurality of interstage control valves, as is well known to those skilled in the art, for the sake of brevity, only one control valve and one interstage valve are shown. The extraction line is connected to a thermal load, not shown. Electric power generated by the generator 13 is supplied through a main circuit breaker 19 to electric loads 20, or supplied to an electric power system 21 through a circuit breaker 22.

In order to detect the turbine speed, a pair of electromagnetic pick-up devices 23 and 24 are provided, and the output signals of each are applied to

speed detectors

25 and 26, respectively. The speed signals from the

detectors

25 and 26 are supplied to a high value gate 27, which is arranged to transmit the higher speed signal of the two speed signals applied thereto, whereby a speed signal of fail safe is obtained at an output ter-. minal thereof. A sensor 28 and a pressure detecting device 29 are disposed in the extraction line 17, whereby to provide an electric signal representing the pressure of the extracted steam.

There is provided a speed/load controller, generally indicated by the reference numeral 30, comprising a main device 31 and a speed regulation setting device 32. The main S/L control device 31 compares the actual speed represented by the speed signal from the high value gate 27 with a reference speed represented by a reference signal from a speed setting device 33 to produce an output signal. The maximum value of the output signal of the device 31 is limited in accordance with a reference signal from a load setting device 34, thereby to limit the maximum load which the turbine can share. The output of the device3l is treated in a speed regulation setting device 32 for providing a speed control signal. The speed regulation setting device 32 may be an operational amplifying device having an input resistor, a high gain amplifier and a feedback resistor. The amount of the speed regulation can be adjusted by variation of the ratio between the input and feedback resistors The speed control signal is responsively operable for opening of the main control valve to obtain the desired speed of the turbine 10 under the condition that the turbine 10 has a load equal to or lower than that set by the load setting device 34.

The speed control signal is applied to an adder 35 which may comprise an operational amplifier 36, a pair of input resistors 37 and 38 and a feedback resistor 39. Also applied to the adder 35 is a pressure control signal through the resistor 38, hereinafter described. An output of the adder 35 is amplified by a power amplifier 40, then applied to an electric-mechanical convertor 41. A hydraulic servo mechanism 42 is provided to actuate the main control valve 15 in accordance with the mechanical output of the convertor 41.

The pressure signal from the pressure detector 29 is supplied to a pressure controller, generally indicated by the reference numeral 43, to obtain a pressure control signal in a similar manner to the treatment of the speed/load controller 30. The pressure controller comprises a main device 44 and a pressure regulation setting device 45. The main pressure control device 44 compares the actual pressure of the extracted steam represented by the pressure signal from the detector 29 with a desired pressure represented by a reference signal from a pressure setting device 46 to produce an output signal, the maximum value thereof being limited by a signal being applied from a setting device 47 of a limiter. The output signal of the device 44 is applied to the pressure regulation setting device 45 which may be an operational amplifier having input and feedback resistors, to thereby provide a pressure control signal. The amount of the pressure regulation can be adjusted by adjustment of the ratio between the input and output resistors.

This pressure control signal is applied to an inverter or polarity changer 48, which may also be an operational amplifier, and is further applied to an adder 49. The adder 49 comprises a high-gain amplifier 50, a pair of input resistors 51 and 52, and a feedback resistor 53. The output of the adder 49 is amplified by a power amplifier 54 and is then supplied to an electric-mechanical convertor 55, and the mechanical output thereof in turn is given to I a hydraulic servo mechanism 56 to drive the interstage control valve 16.

The pressure control signal from the pressure controller 43 is also supplied through a contact 57b of a relay 57 to the adder 35 through the input resistor 38 thereof, while the speed control signal from the speed/load controller 30 is applied to the adder 49 through the input resistor 52 thereof.

In order to detect any loss of load of the generator 13, there is provided a relay 58 which is connected in series with a contact 19b which'takes a closed position when the main circuit breaker 19 is open and which takes an open position when the circuit breaker 19 is closed. The contact 19!; may be an auxiliary contact associated with the main circuit breaker 19. Thus, when the main circuit breaker 19 is opened, the relay 58 is energized by power supply busses P and N for the control operation, whereby the normally open contract 58a of the relay 58 is operated to close. One terminal of a relay 57 is connected to the control supply bus P while the other terminal thereof is connected through a diode 59 of indicated polarity and the contact 58a to the control supply bus N. There is further provided a relay 60 connected in parallel with the relay 57. Provided across the lower terminal of the relay 60 and the bus N are a normally open contact 60a of the relay 60 and a contact 61 in series relation. The contact 61 is an output contact of a detector 62 which operates in response to the pressure control signal from the pres sure controller 43 in such a manner that the contact 61 is open only when the pressure control signal takes a value which represents that the pressure or the quantity of the extracted steam is at a zero level. Thus when the main circuit breaker 19 is open, and the contact 19b is closed, the relay 58 is energized to cause the contact 5812 thereof to close, whereby the

relays

57 and 60 are energized to cause the contacts 57b and 60a respectively open and close. If the contact 58a becomes open, the closure of the contact 60a keeps the energization of the

relays

57 and 60 under a condition such that the contact '61 remains closed.

There is further'provided a contact 57a which is also one of the related contacts of the relay 57 and takes a closed position only when the relay 57 is energized. One terminal of the contact 57a is connected to the lower input terminal in the drawing of the adder 35, and the other terminal is connected to an appropriate potential supply P which corresponds to a value of the pressure control signal representing that the pressure of the extracted steam is zero. In other words, the level P is equal to that at which the detector 62 operates to open the contact 61 thereof.

As is well known by those skilled in the art, in an actual system many other devices are provided, such as, for example, control means for partial arc operation, an over-speed trip device, and so on, such devices being omitted herein because the description of such devices is not essential for an understanding of this invention.

The operation of this embodiment will now be explained with reference-to FIG.- 1.

1n the normal operation, the turbine 10 or the generator 13 bears a load over the predetermined value, such as a half-load, which is determined by the design of the system, and the desired quantity of the steam is extracted from the high pressure turbine l l.

The main circuit breaker 19 is closed, so that the contact 1% is open, and in turn, the relay 58 is de-energized so that the contact 580 is open, and the detector 62 detects the pressure control signal to make the contact 61 thereof open, hence the

relay

57 and 60 are in the de-energized state, whereby the

contacts

57b and 57a are closed and opened, respectively. I

When the rotational speed of the turbine 10 tends to decrease as is the case when there is no variation in the quantity of the extracted steam, the speed control signal from the speed/load controller increases so that the main and interstage control valves 15 and 16 are actuated toward more open positions until the speed of the turbine 10 becomes consistent with the desired speed set by the setter 33. Thus, the load which the turbine 10 bears increases. The ratio between the shift quantities of the main and interstage control valves 15 and 16 is adjusted to cause no adverse affection to the pressure of the extracted steam line 17. This adjustment is achieved by adjusting the ratio between input and

feedback resistors

37 and 39 of the adder and adjusting the ratio between input and feedback resistors 52 and 53 of the adder 49.

In the above description, if the speed control signal is restricted by the load limitation set by the load setting device 34, the actual rotational speed of the turbine 10 can not increase up to the desired speed, while the limitation of the load which the turbine 10 bears can be obtained. This feature is also obtained where the generator 13 is connected to the electric power system which is also supplied with electric power by one other or more generators. That is, the load which the turbine 10 bears is controllable by adjusting the set value of the load limiting setter 34 although the generator 13 rotates in synchronism with the frequency of the power system.

When the speed of the turbine 10 increases, the speed/load control arrangement operates to compensate for the speed rise. The operation in such case will be easily understood and the further description is omitted.

When the pressure of the extracted steam decreases under the condition that no variation in the speed of the turbine 10 exists, the pressure control signal increases in response thereto. This pressure control signal is transmitted through the contact 57b of closed state to the adder 35, then the main control valve 15 is actuated towards an open state. On the other hand, an inverted pressure control signal from the inverter 48 is supplied to the adder 49, then the interstage control valve 16 is actuated towards a closed state. Thus the pressure of the extracted steam increases until the same reaches the desired value set by the pressure setter 46. It is noted that the appropriate adjustment of the ratio of the input and feedback resistors 38 and 39 and of the ratio of the input and feedback resistors 51 and 53 is required in order to cause the turbine speed to have no variation.

In the above pressure control operation, there is also achieved a limiting function for the quantityof the extracted steam by adjusting the setting device 47, whereby the amount of the extracted steam can be restricted below the rated value, which is defined by the design of the turbine system.

Next, the operation upon the removal of a load will be explained. When the main circuit breaker 19 is tripped due to a fault in the loads 20, or in the power system 21 orv the like, vthecontact 19b is closed to energize the relay 58 and in turn to close the contact 58a. Therelays '57 and 60 are thus energized so that the contact 57b is opened and contacts 57a and 60a are closed. As'thecontaetfl of the detector 62 keeps a closed state because the pressure control signal exists, the

relays

57 and 60 are in a self-hold state. Together with the above behavior, the speed of the turbine 10 increases because of the loss of its load.

The speed control signal from the speed/load con troller 30 decreases rapidlyto the value corresponding to the no-load opening of the main control valve 15, thus the main control valve 15 is operated toward its no-load opening. Accordingly, the pressure of the extracted steam decreases so that the pressure control signal increases. However, the contact 57b has already been opened while the contact 57a has been closed substantially simultaneously with the trip of the main circuit breaker 19 to supply the zero level signal P to the adder 35 with the result that the output signal from the adder 35 has been suddenly decreased thereby. Hence, the main control valve is operated in response only to the speed control signal from the speed/load controller 30. On the other hand, the inverted pressure control signal from the inverter 48 is supplied to the adder 49 and this signal promotes the closing operation of the interstage control valve 16. Thus, the speed of the turbine which has been increasing due to the loss of load decreases rapidly.

The system is reset by adjusting the set value of the setting device 46 to zero level, when the pressure control signal from the circuit 45 is also brought to zero and contacts 61 of detector 62 open. Relays 57 and 60 then become de-energized, assuming that circuit breaker 19 has been reset and the contacts 19b reopened, and the

contacts

57b, 57a returned to their closed and open positions, respectively.

Referring now to FIG. 2, in the graph shown therein, the ordinate represents the opening of the main control valve, and the abscissa the speed control signal and the percentage of speed rise of the turbine.

Assume at first that the contact 571) is always closed. When the turbine speed rises over 100 percent of the rated speed thereof due to the tripping of the main circuit breaker 19, the opening of the main control valve 15 takes a value along the line A if the quantity of the extracted steam is zero. In this case, the'main control valve is actuated towards a no-load condition opening when the turbine speed reaches 105 percent of its rated speed. However, if the quantity of the extracted steam is a maximum value, the main control valve is operated in accordance with the line B. Then the main control valve cannot take its no-load" opening unless the speed of the turbine reaches a value more than b percent of the rated speed. Accordingly, it becomes difficult to restrict the speed rise of the turbine less than percent. As is easily understood, if the quantity of the extracted steam takes a value between the maximum and zero, the main control valve is controlled along a line parallel to the line A and B existing therebetween, such as shown as a dotted line C in FIG. 2.

According to this embodiment, the contact 57b is opened upon the tripping of the main circuit breaker 19 and also the contact 57a is closed, and the'main control valve is controlled along the line A whenever the load of the turbine is lost. Further, the closure of the contact 57a serves to suddenly decrease the output of the adder35 byfa value corresponding'to the pressure control signalfrom the device 45, whereby the load is effectively restricted and the usual fears involving the operation of an over-speed trip device are eliminated.

While there is shown what is considered to be the preferred embodiment of the invention, it is, of course, understood that various other modifications, such as, for example, employing transisterized circuitry instead of the

relay

57, 58 and 60, are possible, and it is understood thereforc that within the scope of the appended clalms, the invention may be practiced otherwise than as specifically described herein.

Accordingly what is claimed as new and desired to be secured by letters patent of the United States is:

1. A control system for an extraction turbine system having a high and low pressure turbine stages and driving a mechanical load comprising:

main control valve means for regulating the flow rate of a motive fluid from a motive fluid generator to said high pressure turbine stage; interstage control valve means for regulating the flow rate of the motive fluid from said high pressure turbine stage to said low pressure turbine stage; a speed/load control arrangement for controlling said main and said interstage control valve means in the same direction to each other in response to the rotational speed of said turbine; a pressure control arrangement for controlling said main and said interstage control valve means in opposite directions to each other. in response to a pressure of the extracted steam; and means for interruptingthe control of said main control valve means by said pressure control arrangement when said mechanical load of the turbine is removed. 2. A control system as claimed in claim 1 wherein: said mechanical load is an electric generator; and said interrupting means is actuated when a circuit breaker which connects said electric generator to an electric load thereof is opened.

Claims

1. A control system for an extraction turbine system having a high and low pressure turbine stages and driving a mechanical load comprising: main control valve means for regulating the flow rate of a motive fluid from a motive fluid generator to said high pressure turbine stage; interstage control valve means for regulating the flow rate of the motive fluid from said high pressure turbine stage to said low pressure turbine stage; a speed/load control arrangement for controlling said main and said interstage control valve means in the same direction to each other in response to the rotational speed of said turbine; a pressure control arrangement for controlling said main and said interstage control valve means in opposite directions to each other in response to a pressure of the extracted steam; and means for interrupting the control of said main control valve means by said pressure control arrangement when said mechanical load of the turbine is removed.

2. A control system as claimed in claim 1 wherein: said mechanical load is an electric generator; and said interrupting means is actuated when a circuit breaker which connects said electric generator to an electric load thereof is opened.