CA1057065A - Control systems for steam turbine plants including turbine bypass systems - Google Patents
Control systems for steam turbine plants including turbine bypass systemsInfo
- Publication number
- CA1057065A CA1057065A CA264,219A CA264219A CA1057065A CA 1057065 A CA1057065 A CA 1057065A CA 264219 A CA264219 A CA 264219A CA 1057065 A CA1057065 A CA 1057065A
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- Canada
- Prior art keywords
- turbine
- signal
- pressure
- control system
- steam
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Abstract
Abstract of the Disclosure A control for a steam turbine plant having a boiler provided with a superheater and a reheater. A high pressure turbine is connected to receive stem generated by the boiler through first valve means and to supply exhaust steam to the reheater. A medium pressure turbine is connected to receive reheated steam from the reheater through second valve means. A high pressure bypass line connected between the first valve means and the reheater;
and a low pressure bypass line connected between the second valve means and a condenser. The control system comprises a first electric control system for the high pressure bypass line including means responsive to the temperature and pressure of the steam supplied to the high pressure turbine for controlling the quantity of steam circulating through the high pressure bypass line; a second electric control system for the low pressure bypass line including means responsive to the temperature and pressure of the steam supplied to the medium pressure turbine for controlling the quantity of the steam circulating through the low pressure bypass line; and a third electric control system responsive to the speed and load conditions of the turbine plant for control-ling said first and second valve means. There is an electrical connection between the first, second and third electric control systems so that the operation of the first and second electric control system is modified in accordance with the load of the turbine plant.
and a low pressure bypass line connected between the second valve means and a condenser. The control system comprises a first electric control system for the high pressure bypass line including means responsive to the temperature and pressure of the steam supplied to the high pressure turbine for controlling the quantity of steam circulating through the high pressure bypass line; a second electric control system for the low pressure bypass line including means responsive to the temperature and pressure of the steam supplied to the medium pressure turbine for controlling the quantity of the steam circulating through the low pressure bypass line; and a third electric control system responsive to the speed and load conditions of the turbine plant for control-ling said first and second valve means. There is an electrical connection between the first, second and third electric control systems so that the operation of the first and second electric control system is modified in accordance with the load of the turbine plant.
Description
057C~65 This invention relates to a control system for a steam turbine plant provided with turbine bypass systems.
The invention can be more fully understood from the following detailed description taken in conjunction with the accompanying drawings in which:
Figure 1 is a block diagram showing a prior art steam turbine plant provided with turbine bypass systems;
Figures 2 and 3 are block diagrams showing prior art control systems for a high pressure turbine bypass system and a low pressure turbine bypass system respectively;
Figure 4 i6 a block diagram showing the control system embodying the invention;
Figure 5 is a block diagram showing a combination of turbine bypass control systems and a turbine control system embodying the invention;
Figure 6 is a block diagram showlng the detail of the control system shown in Figure 4;
Figures 7 and 8 are graphs showing the manner of setting pressure for the turbine bypass systems embodying the invention, in which the ordinate shows the pressure in %, and the abscissa the turbine load in %; ant Figure 9 is a graph showing the operating characteristics of the main steam pressure, the steam flow quantity, the flow quantity through the high pressure bypass line, the turbine speed, the turbine load, the reheated steam pressure, and the flow quantity through the low pressure bypass line, respectively.
It ia a recent trend to provide a turbine bypass system for an electric power generating plant in the form of a combination of a sub-critical pressure natural circulation type boiler and a reheat turbine or a combination of a forced circulation type boiler and a reheat turbine. As shown in Figure 1 the turbine bypass system utilized in such power plant includes a hi8h pressure bypass line lO and a l~w pressure bypass line 11.
The high pressure bypass line 10 is connected to the inlet side of a main steam stop valve 13 for a high pressure turbine 12 and includes a --1-- .
pressure reducing valve 14 and a desuperheater 15. The lower end of the high pressure bypass line 10 is connected to a cold reheating line 16. The purpose of the high pressure bypass line is to decrease the temperature and pressure of the high temperature and high pressure steam generated by the superheater 18 of a boiler 17. Cooling water from a feedwater pump 19 is supplied to the desuperheater 15 through a temperature control valve 20.
This system permits the boiler to start and supply a certain load independ-ently of the turbine so that the pressure and temperature of the boiler are readily stabilized before starting the turbine. The steam passed through the high pressure bypass system flows back to the reheater 26 of i ~"~,~
-la-the boiler 17 is circulated through the boiler 17 The low pressure bypass line 11 is connected between the inlet side of a reheat stop valve 22 and a condenser 25 via a pressure reducing valve 23 and a desuperheater 24 and operates to reduce the temperature and pressure of the reheated steam. The cooling water from a conden-sate pump 27 is supplied to the desuperheater 24 through a temperature control valve 28 for the purpose of pre-venting thermal deformation of the medium pressure tur-bine 21 caused by the high pressure, high temperature steam from the reheater 26 during starting. ~he result-ing low temperature low pressure steam is circulated through the boiler 17 together with the condensate from condenser 25.
When the high pressure and low pressure bypass lines are provided for an electric power plant the steam generat-ed by boiler 17 flows, during starting, from superheater 18 through high pressure bypass line lO~ reheater 26, low pressure bypass line ll, condenser 25, ~eedwater pump 19, back to the boiler. However, the quantity of steam that flows through this circuit is about 3~/o of the rated ste~m flow of the boiler. During the bypass operation, the pressure of the main steam generated by the super-heater 18 of the boiler 17 and reheat steam 26 are controlled by pressure reducing valves 14 and 23 provided for the high pressure bypass line 10 and the low pressure byp~ss line 11, respectively. During the turbine startin~, both the main and reheated steams flow into high pressure, medium pressure and low pressure turbi~es through control ~o57065 valve 29, main stop valve 13 and intercept valve 30 and reheat stop valve 22, respectively.
As the load of the turbines increases gradually the quantity of the steam supplied to the turbines is in-creased and the quantity of the steam circulating through the high and low bypass lines 10 and 11 is decreased correspondingly. ~hereafter, the total quantity of the steam generated by the boiler flows through the turbines.
~hen pressure reducing valves 14 and 23 are fully closed to terminate the operation of the bypass lines.
During the normal running of the power plant the high and low bypass lines are not used, but when the quantity of the steam flowing into the turbines decreases rapidly due to the load reduction or turbine trip~ the turbine bypass systems described above operate to prevent pressure rise of steam and make it possible to continue the operation of the boiler without tripping and starting the turbine quickly.
~ he control system of the turbine bypass systems arè shown in ~I~S. 2 and 3. FIG. 2 shows a control system for the high pre6sure bypass system in which the pressure of the main steam is detected by a pressure detector 31. This pressure signal a is sent to a compara-tor 32 to be compared with a pressure reference signal d ;~
which is produced by correcting a set signal b produced by a manual se-tter 33 by an actually measured pressure signal c detected at a turbine stage by a pressure set-ter 34. Where there is a difference between signals a and d, a deviation signal is created which is sent to . .
pressure reducing valve 14 by a pressure controller 35 for opening or closing the pressure reducing valve 14.
The temperature of the steam leaving the desuper- `
heater 15 is sensed by a temperature detector 36 and a detection signal e produced b~ it is sent to a comprarator 37 where signal e is compared with a set signal f pro-duced by a temperature setter 38. When signals e and f are not equal a deviation or error signal is sent to the temperature control valve 20 through a temperature con-troller 39.
The control system for the low pressure bypass sys-tem is shown in FIG. 3. Since this control system is similar to that shown in ~IG. 2 it would be unnecessary to describe it in detail.
The control of the temperature and pressure has been made by the control systems described above. It is a recent tendency, however, to use electro-hydraulic control system (EHC) for controlling a turbine control valve because of its quick response characteristic.
Incorporation of EHC into the control system for the turbine bypass system results in such advanatges as a collective control of the turbine plant, cost saving due to common use of the hydraulic system, easiness of the maintainance and repair and improvement of the control characteristics due to interlocked control of the turbine system and the bypass system.
Accordingly,it is an object of this invention is to provide a novel control system for a steam turbine plant wherein the control system for the turbine bypass lines . ~. . ~ . : . .
~0570~65 described above is combined with an electro-hydraulic control system thereby enabling a collective control of the entire turbine plant.
Another object of this invention is to provide a~
improved steam turbine control system capable of decreas- ;
ing the starting time of a steam turbine plant, simpli-fying the control system, making easy the maintenance and inspection of the control system and improving the con-trol characteristic, According to this invention there is provided a control system for a steam turbine plant of the class comprising a boiler provided with a superheater and a reheater; a high pressure turbine co~nected to receive steam generated by the boiler through first valve means and to suppl~ exhaust stea~ to the reheater; a medium pressure turbine connected to receive reheated steam ~rom the reheater through second valve means; a high pressure bypass line connected between the first ~alve means and the reheater; and a low pressure bypass line connected between the second valve means and a condenser;
wherein said control system comprises a first electric control system for the high pressure bypass line including mea~s responsive to ~he temperature and pr~ssure of the steam supplied to the high pressure turbine for control-ling the quantity of steam circulating through the high pressure bypass line; a second electric control system for the low pressure bypass line including means respon-sive to the temperature and pressure of the ste~m supplied to the medium pressure turbine for controlling the quantity of the steam circulating through the low pressure bypass line; a ~
. , third electric control system responsive to the speed and load conditions of :~
the turbine plant for controlling the first and second valve means; an electrical connection between the first, second and the third electric control systems so that the operation of the first and second electric systems is modified in accordance with the load of the turbine plant.
The invention will now be described in detail with reference to a preferred embodiment illustrated in the accompanying drawings.
Figure 4 shows a block diagram of a control system wherein a novel control system for the turbine bypass system is incorporated into a prior ~`art electro-hydraulic control system (FHC) for controlling a turbine control valve. In Figure 4 the main control system 40 comprises a speed control circuit 41 and a load control circuit 42.
The speed control circuit 41 compares a speed setting signal g sent from a speed setter 43 with an acceleration signal h sent from an acceleration setter 44a and an actual turbine speed signal i and sends a deviation or error signal ~ to the load control circuit 42.
The load control circuit 42 is constructed to process and amplify -the deviation signal ~ from the speed control circuit 41, a load reference signal k from a load setter 44, a loading rate setting signal Q sent from a loading rate setter 45, a pressure signal m actually measured at the first stage of the turbine, a full arc-partial arc transfer signal n sent from a full arc-partial arc transfer circuit and a load : ''.
:, ~ -6-limiting signal p sent from a load limiter 47 for sending processed and amplified signals ~1~ q2~ q3 and q4 to the control circuit 48 of the main steam stop valvel the control circuit 49 for the steam control valve, the con-trol circuit 50 for the intercept valve, and the control cirucit 51 for the reheat stop valve, respectively, for controlling the degree of opening of these valves.
Above description relates to a well known main con- :
trol system 40 for controlling the turbine control valve.
According to this invention a control system designated by reference numerals 52 through 62 for controlling the turbine bypass system is added to the control system 40.
More particularly, in FIG. 4, the turbine bypass control system 52 for controlling the turbine bypass system 52 comprises a high pressure bypass control cir-cuit 5~ and a low pressure bypass control circuit 54.
~ he high pressure bypass control circuit 5~ is constructed to process and amplify a pressure settin~
signal rl sent from a pressure set-ter 55, a temperature setting signal sl sent from a temperature setter 56, an actual steam pressure signal tl and an actual steam temperature signal ul for producing output signals vl which are sent to a reducing valve control circuit 57 and a temperature control valve control circuit 58 which control the pressure reducing valve 14 and temperature control valve 20 respectively contained in the high pres-sure bypass line 10.
Similarly, the low pressure bypass control circuit 54 is constructed to process and amplify a pressure ~05706~ ;
setting signal r2 sent from a pressure setter 59, a temperature setting signal s2 sent from a temperature setter 60, an actual reheated steam pressure signal t2 and an actual reheated steam temperature signal u2 for producing output signals v2 which are sent to a reducing valve control circuit 61 and a temperature control valve control circuit 62 which control the pressure reducing ~:
valve 23 and the temperature control valve 28 respective-ly contained in the low pressure bypass line 11 shown in --j FIG. 1. The high pre6sure bypass control circuit 53 and the low pressure bypass control circuit 54 are electrical-ly connected to the load control circuit 42 so as to operate in accordance with the turbine load.
By combininK the control systems of turbine bypass lines with the control system for controlling the turbine control valve as above described, it is possible to commonly use an EHC circuit and a hydraulic power unit as shown in ~IG. 5.
~ IG. 6 is a block diagram ~howing the detail of a turbine bypass control circuit and a load control circuit when the control system for the turbine bypass lines is combined with an electro-hydraulic control system for controlling the turbine control valves shown in FIG. 4.
B More particularly in ~IG. 6, a deviation signal/~ent from speed control circuit 41 is passed through gain setters 70a and 70b which set a reciprocal of the turbine speed regulation and then added to a load setting signal k sent from load setter 44 by adders 71a and 71b to form valve opening setting signal~. ~uring the normal running -- 1~--~ .
~057065 of the turbine the output signal from adder 71a operates as a control signal for a control valve 73, whereas the output from the adder 71b operates as a control signal for an intercept valve 74.
During the turbine bypass operation, the output signal from adder 71a is sent to a low value priority circuit 76a which compares the output signal, a load ~-limiting signal p sent from load limiter 47, and a high pressure bypass pressure signal sent from a high pressure bypass control circuit 53 to be described later Por selecting a signal having the lowest value. A portion of the output signal from the low value priority circuit 76a is added to a bias signal sent from full arc - partial arc transfer circuit 46 by adders 77a and 77b, and the outputs of the adders are sent to main steam stop valve 72 and control valve 7~, respectively. The other portion oP the output of the low value priority circuit 76a is sent to another low value priority circuit 76b via a gain setter 78 and an adder 79 to be compared with a low pres-sure bypass pressure signal sent from a low pressure by-pass control circuit 54 so that a signal having lower value is selected by the low value priority circuit 76b.
The output oP this circuit is added to a bias signal sent from Pull arc - partial arc trans~er circuit 46 by adders77c and 77d to control intercept valve 74 and reheat stop valve 75. The gain setter 78 connected bet-ween the low value priority circuit 76a which interlocks the main stop valve 72 and the reheat stop valve 75, and the low value priority circuit 76b which produces a ~057065 cortrol signal for interlocking the control valve 73 and the intercept valve 74 determines the ratio of openings of the control valve 73 and the intercept valve 74 during the turbine bypass operation. A bias signal adder 80 is provided for the purpose of releasing the interlock bet-ween the main stop valve 72 and the reheat stop valve and the interlock between the control valve 73 and the intercept valve 74 during running.
The control system for the high pressure bypass line ,~, operates to decrease the opening of the pressure reducing valve 81a of the high pressure bypass line when the quan-tity of the steam flowing into the turbine increases during the bypass operation so that it operates as a pilot element for pressure control. Accordingly, the output signal from the high pressure bypass control circuit 58 is com-pared with the output signal from the low value priority circuit 76a by a comparator 82a and its deviation or error output signal is used for operating the high pressure bypass pressure reducing valve 83a. This deviation ~O signal and the temperature signal sent from a temperature control circuit 84a are compared by a high value priority circuit 85a~ and a signal having a higher value is sent to a high pressure bypass temperature control ~alve 81a from the high value priority circuit 85a. The pressure setting of the high pressure bypass line is effected in the following manner. Thus, the signal from a mc~nual setter 86a and the output signal sent from a pressure setter 87a and corresponding to the turbine l~ad are compared by a high value priority circuit 88a, and one 1 : ' ~ ~ ' ~ 057065 of the signals having higher value is sent to the high pressure b~pass co~trol circuit 53 to be compared with actual main steam pressure seignal xl. This relation is shown by the graph shown in ~IG.7. Accordingly, this high pressure bypass control system acts as a safety valve at the time of load interruption and to prevent decrease in the pressure of the main steam.
~ he control system for the low pressure line is similar to the control system for the high pressure by-pass line described aboveO Thus, during the bypass operation of the turbine, when the quantity of the steam flowing into the turbine increases the opening of the low pressure bypass pressure reducing valve 81b is decreased 80 that the control system acts as a pilot element.
Accordingly, the output signal from the low pressure by-pass control circuit 54 is compared with the output from the low value priority circuit 76b by a comparator 82b and its output deviation signal is used to control low pres~ure bypass pressure reducing valve 81b. ~urther,the deviation signal from comparator 82b is compared with a temperature signal from temperature control circuit by a high value priori-ty circuit 85b. The signal having a higher value is used to control a low pressure bypass temperative control valve 83b. The pressure setting of the low pressure bypass line is made in the following manner. More particularly, the output signal from a manual setter 86b is compared with the output sginal sent from a pressure setter 87b and corresponding to the tur-bine load b~ a high value priorit~ ciucuit 88b so that a ~/
-lOS706S
signal having a higher value is se~t to the low pressure bypass control circuit 54 to be compared with actual reheat steam pressure signal x2. ~his relationship is shown by a graph shown in ~IG. 8.
~ he operation of the control system of this inven-tion under normal running will now be described with reference to ~IGS. 6 and 9.
I. From boiler starting to pressure rise.
Since the turbine is at standstill, both output signals from the speed control circuit 41 and the load setter 44 are zero with the result that the main stop valve 72, the control valve 73, the intercept valve 74 and the reheat stop valve 75 are fully closed.
The high pressure bypass control system operates such t~at although the high pressure bypass pressure reducing valve 8~a is fully closed while the steam pres-sure is low as the pressure of the main steam generated by the boiler increases the output from the high pressure bypass control circuit is increased to gradually open the high pressure ~ypass pressure reducing valve 83a. ~he low pressure bypass control system operates in the same manner to gradually open the low pressure bypass pressure reducing valve 81b.
II. ~urbine starts As the turbine starts, the speed control circuit 41 functions and the output or valve opening signal produced by the low value priority circuit 76a increases gradually.
When the turbine is sarted with the all ~ull arc admission mode, the bias signal from the full arc -partial 1~ ' _ ~_ '~' .
arc transfer circuit 46 is applied to the steam adjust-ing valve 73 and the intercept valve 74 thus maintaining these valves in fully opened state.
~ he main steam stop valve 7~ and the reheat stop valve 7~ control the quantities of the main steam and the reheated steam respectively by a small internal bypass valve (not shown).
At this time, the control signal sent to the reheat stop valve 75 is sent from the low value priority circuit 76a through gain setter 78, adder 79 and low value priority circuit 76b thus interlocking each other the main stop valve 72 and the reheat stop valve 75, the ratio of the flow quantities of valves 72 and 75 being determined by the gain qetter 78.
III. Turbine loading As the turbine load increases the quantity of stec~m is increased by interlocked main stop valve 72 and the reheat stop valve 75 (the output from the low value priority circuit 76a increases) so that the deviation signals produced by adders 82a and 82b decrease whereby the degree of opening of the high pressure bypass pres-sure reducing valve 83a and the low pre~sure bypass pres-sure reducing valve 8~b is decreased thus limiting pres-sure variation.
IV. Full arc mode to partial arc mode transfer In this case control is transferred from the inter-locked control o~ the main stop valve 72 and the reheat r' stop valve 75 to the interlocked control of the control valve 73 and the intercept valve 74. The degree of 1~57065 ~ ~
openings of the control valve 73 and the intercept 74which have been maintained in their fully opened state is decreased by the bias signal from the full arc-partial arc control circuit 46. ~hereafter the main s-top valve and the reheat stop valve 75 are fully opened thus trans-ferri~g the control to the turbine control wherein the turbine is controlled by the steam control valve 73 and the intercept valve 74. However this control is not related directly to the invention.
V. ~urbine bypass running complete When the load increases under these conditions, as the openings of the control valve 73 and the intercept valve 74 increase, openings of the high pressure bypass pressure reducing valve 83a and the low pressure bypass pressure reducing valve 83b decrease. Finally,they are completely closed.
VI. Normal running The control of the turbine bypass systems becomes inoperative and the normal running of the turbine using reheated steam commences.
VII. Interruption of the turbine load Due to the rapid closure of the steam control valve 73 and the intercept valve 74 the pressures of the main steam and t~e reheat steam generated by the boiler in-crease so that the high pressure bypass pressure reducing valve 81 and the low pressure bypass pressure reducing valve 81b are opened quickly. At the same time,the high pressure bypass temperature control valve 83a and the low pressure bypass temperatur control valve 83b are 1~ .
.. , - - ... .. .
opened quicklythus controlling the pressure and temper_ ature of the turbine bypass systems.
Thus,according to this invention a turbine bypass -control system for controlling the turbine bgpass lines are incorporated to the conventional main control system which controls the main steam stop valve, steam control valve, interception valve and the reheat stop valve so that it is possible to provide an overall control of the turbine plant. Accordingly, it is possible to improve the control characteristics, to reduce the starting time and cost of maintenance and to make easy to mantain and inspect.
)S~
1.~ ` ;
- . . - - ~ -
The invention can be more fully understood from the following detailed description taken in conjunction with the accompanying drawings in which:
Figure 1 is a block diagram showing a prior art steam turbine plant provided with turbine bypass systems;
Figures 2 and 3 are block diagrams showing prior art control systems for a high pressure turbine bypass system and a low pressure turbine bypass system respectively;
Figure 4 i6 a block diagram showing the control system embodying the invention;
Figure 5 is a block diagram showing a combination of turbine bypass control systems and a turbine control system embodying the invention;
Figure 6 is a block diagram showlng the detail of the control system shown in Figure 4;
Figures 7 and 8 are graphs showing the manner of setting pressure for the turbine bypass systems embodying the invention, in which the ordinate shows the pressure in %, and the abscissa the turbine load in %; ant Figure 9 is a graph showing the operating characteristics of the main steam pressure, the steam flow quantity, the flow quantity through the high pressure bypass line, the turbine speed, the turbine load, the reheated steam pressure, and the flow quantity through the low pressure bypass line, respectively.
It ia a recent trend to provide a turbine bypass system for an electric power generating plant in the form of a combination of a sub-critical pressure natural circulation type boiler and a reheat turbine or a combination of a forced circulation type boiler and a reheat turbine. As shown in Figure 1 the turbine bypass system utilized in such power plant includes a hi8h pressure bypass line lO and a l~w pressure bypass line 11.
The high pressure bypass line 10 is connected to the inlet side of a main steam stop valve 13 for a high pressure turbine 12 and includes a --1-- .
pressure reducing valve 14 and a desuperheater 15. The lower end of the high pressure bypass line 10 is connected to a cold reheating line 16. The purpose of the high pressure bypass line is to decrease the temperature and pressure of the high temperature and high pressure steam generated by the superheater 18 of a boiler 17. Cooling water from a feedwater pump 19 is supplied to the desuperheater 15 through a temperature control valve 20.
This system permits the boiler to start and supply a certain load independ-ently of the turbine so that the pressure and temperature of the boiler are readily stabilized before starting the turbine. The steam passed through the high pressure bypass system flows back to the reheater 26 of i ~"~,~
-la-the boiler 17 is circulated through the boiler 17 The low pressure bypass line 11 is connected between the inlet side of a reheat stop valve 22 and a condenser 25 via a pressure reducing valve 23 and a desuperheater 24 and operates to reduce the temperature and pressure of the reheated steam. The cooling water from a conden-sate pump 27 is supplied to the desuperheater 24 through a temperature control valve 28 for the purpose of pre-venting thermal deformation of the medium pressure tur-bine 21 caused by the high pressure, high temperature steam from the reheater 26 during starting. ~he result-ing low temperature low pressure steam is circulated through the boiler 17 together with the condensate from condenser 25.
When the high pressure and low pressure bypass lines are provided for an electric power plant the steam generat-ed by boiler 17 flows, during starting, from superheater 18 through high pressure bypass line lO~ reheater 26, low pressure bypass line ll, condenser 25, ~eedwater pump 19, back to the boiler. However, the quantity of steam that flows through this circuit is about 3~/o of the rated ste~m flow of the boiler. During the bypass operation, the pressure of the main steam generated by the super-heater 18 of the boiler 17 and reheat steam 26 are controlled by pressure reducing valves 14 and 23 provided for the high pressure bypass line 10 and the low pressure byp~ss line 11, respectively. During the turbine startin~, both the main and reheated steams flow into high pressure, medium pressure and low pressure turbi~es through control ~o57065 valve 29, main stop valve 13 and intercept valve 30 and reheat stop valve 22, respectively.
As the load of the turbines increases gradually the quantity of the steam supplied to the turbines is in-creased and the quantity of the steam circulating through the high and low bypass lines 10 and 11 is decreased correspondingly. ~hereafter, the total quantity of the steam generated by the boiler flows through the turbines.
~hen pressure reducing valves 14 and 23 are fully closed to terminate the operation of the bypass lines.
During the normal running of the power plant the high and low bypass lines are not used, but when the quantity of the steam flowing into the turbines decreases rapidly due to the load reduction or turbine trip~ the turbine bypass systems described above operate to prevent pressure rise of steam and make it possible to continue the operation of the boiler without tripping and starting the turbine quickly.
~ he control system of the turbine bypass systems arè shown in ~I~S. 2 and 3. FIG. 2 shows a control system for the high pre6sure bypass system in which the pressure of the main steam is detected by a pressure detector 31. This pressure signal a is sent to a compara-tor 32 to be compared with a pressure reference signal d ;~
which is produced by correcting a set signal b produced by a manual se-tter 33 by an actually measured pressure signal c detected at a turbine stage by a pressure set-ter 34. Where there is a difference between signals a and d, a deviation signal is created which is sent to . .
pressure reducing valve 14 by a pressure controller 35 for opening or closing the pressure reducing valve 14.
The temperature of the steam leaving the desuper- `
heater 15 is sensed by a temperature detector 36 and a detection signal e produced b~ it is sent to a comprarator 37 where signal e is compared with a set signal f pro-duced by a temperature setter 38. When signals e and f are not equal a deviation or error signal is sent to the temperature control valve 20 through a temperature con-troller 39.
The control system for the low pressure bypass sys-tem is shown in FIG. 3. Since this control system is similar to that shown in ~IG. 2 it would be unnecessary to describe it in detail.
The control of the temperature and pressure has been made by the control systems described above. It is a recent tendency, however, to use electro-hydraulic control system (EHC) for controlling a turbine control valve because of its quick response characteristic.
Incorporation of EHC into the control system for the turbine bypass system results in such advanatges as a collective control of the turbine plant, cost saving due to common use of the hydraulic system, easiness of the maintainance and repair and improvement of the control characteristics due to interlocked control of the turbine system and the bypass system.
Accordingly,it is an object of this invention is to provide a novel control system for a steam turbine plant wherein the control system for the turbine bypass lines . ~. . ~ . : . .
~0570~65 described above is combined with an electro-hydraulic control system thereby enabling a collective control of the entire turbine plant.
Another object of this invention is to provide a~
improved steam turbine control system capable of decreas- ;
ing the starting time of a steam turbine plant, simpli-fying the control system, making easy the maintenance and inspection of the control system and improving the con-trol characteristic, According to this invention there is provided a control system for a steam turbine plant of the class comprising a boiler provided with a superheater and a reheater; a high pressure turbine co~nected to receive steam generated by the boiler through first valve means and to suppl~ exhaust stea~ to the reheater; a medium pressure turbine connected to receive reheated steam ~rom the reheater through second valve means; a high pressure bypass line connected between the first ~alve means and the reheater; and a low pressure bypass line connected between the second valve means and a condenser;
wherein said control system comprises a first electric control system for the high pressure bypass line including mea~s responsive to ~he temperature and pr~ssure of the steam supplied to the high pressure turbine for control-ling the quantity of steam circulating through the high pressure bypass line; a second electric control system for the low pressure bypass line including means respon-sive to the temperature and pressure of the ste~m supplied to the medium pressure turbine for controlling the quantity of the steam circulating through the low pressure bypass line; a ~
. , third electric control system responsive to the speed and load conditions of :~
the turbine plant for controlling the first and second valve means; an electrical connection between the first, second and the third electric control systems so that the operation of the first and second electric systems is modified in accordance with the load of the turbine plant.
The invention will now be described in detail with reference to a preferred embodiment illustrated in the accompanying drawings.
Figure 4 shows a block diagram of a control system wherein a novel control system for the turbine bypass system is incorporated into a prior ~`art electro-hydraulic control system (FHC) for controlling a turbine control valve. In Figure 4 the main control system 40 comprises a speed control circuit 41 and a load control circuit 42.
The speed control circuit 41 compares a speed setting signal g sent from a speed setter 43 with an acceleration signal h sent from an acceleration setter 44a and an actual turbine speed signal i and sends a deviation or error signal ~ to the load control circuit 42.
The load control circuit 42 is constructed to process and amplify -the deviation signal ~ from the speed control circuit 41, a load reference signal k from a load setter 44, a loading rate setting signal Q sent from a loading rate setter 45, a pressure signal m actually measured at the first stage of the turbine, a full arc-partial arc transfer signal n sent from a full arc-partial arc transfer circuit and a load : ''.
:, ~ -6-limiting signal p sent from a load limiter 47 for sending processed and amplified signals ~1~ q2~ q3 and q4 to the control circuit 48 of the main steam stop valvel the control circuit 49 for the steam control valve, the con-trol circuit 50 for the intercept valve, and the control cirucit 51 for the reheat stop valve, respectively, for controlling the degree of opening of these valves.
Above description relates to a well known main con- :
trol system 40 for controlling the turbine control valve.
According to this invention a control system designated by reference numerals 52 through 62 for controlling the turbine bypass system is added to the control system 40.
More particularly, in FIG. 4, the turbine bypass control system 52 for controlling the turbine bypass system 52 comprises a high pressure bypass control cir-cuit 5~ and a low pressure bypass control circuit 54.
~ he high pressure bypass control circuit 5~ is constructed to process and amplify a pressure settin~
signal rl sent from a pressure set-ter 55, a temperature setting signal sl sent from a temperature setter 56, an actual steam pressure signal tl and an actual steam temperature signal ul for producing output signals vl which are sent to a reducing valve control circuit 57 and a temperature control valve control circuit 58 which control the pressure reducing valve 14 and temperature control valve 20 respectively contained in the high pres-sure bypass line 10.
Similarly, the low pressure bypass control circuit 54 is constructed to process and amplify a pressure ~05706~ ;
setting signal r2 sent from a pressure setter 59, a temperature setting signal s2 sent from a temperature setter 60, an actual reheated steam pressure signal t2 and an actual reheated steam temperature signal u2 for producing output signals v2 which are sent to a reducing valve control circuit 61 and a temperature control valve control circuit 62 which control the pressure reducing ~:
valve 23 and the temperature control valve 28 respective-ly contained in the low pressure bypass line 11 shown in --j FIG. 1. The high pre6sure bypass control circuit 53 and the low pressure bypass control circuit 54 are electrical-ly connected to the load control circuit 42 so as to operate in accordance with the turbine load.
By combininK the control systems of turbine bypass lines with the control system for controlling the turbine control valve as above described, it is possible to commonly use an EHC circuit and a hydraulic power unit as shown in ~IG. 5.
~ IG. 6 is a block diagram ~howing the detail of a turbine bypass control circuit and a load control circuit when the control system for the turbine bypass lines is combined with an electro-hydraulic control system for controlling the turbine control valves shown in FIG. 4.
B More particularly in ~IG. 6, a deviation signal/~ent from speed control circuit 41 is passed through gain setters 70a and 70b which set a reciprocal of the turbine speed regulation and then added to a load setting signal k sent from load setter 44 by adders 71a and 71b to form valve opening setting signal~. ~uring the normal running -- 1~--~ .
~057065 of the turbine the output signal from adder 71a operates as a control signal for a control valve 73, whereas the output from the adder 71b operates as a control signal for an intercept valve 74.
During the turbine bypass operation, the output signal from adder 71a is sent to a low value priority circuit 76a which compares the output signal, a load ~-limiting signal p sent from load limiter 47, and a high pressure bypass pressure signal sent from a high pressure bypass control circuit 53 to be described later Por selecting a signal having the lowest value. A portion of the output signal from the low value priority circuit 76a is added to a bias signal sent from full arc - partial arc transfer circuit 46 by adders 77a and 77b, and the outputs of the adders are sent to main steam stop valve 72 and control valve 7~, respectively. The other portion oP the output of the low value priority circuit 76a is sent to another low value priority circuit 76b via a gain setter 78 and an adder 79 to be compared with a low pres-sure bypass pressure signal sent from a low pressure by-pass control circuit 54 so that a signal having lower value is selected by the low value priority circuit 76b.
The output oP this circuit is added to a bias signal sent from Pull arc - partial arc trans~er circuit 46 by adders77c and 77d to control intercept valve 74 and reheat stop valve 75. The gain setter 78 connected bet-ween the low value priority circuit 76a which interlocks the main stop valve 72 and the reheat stop valve 75, and the low value priority circuit 76b which produces a ~057065 cortrol signal for interlocking the control valve 73 and the intercept valve 74 determines the ratio of openings of the control valve 73 and the intercept valve 74 during the turbine bypass operation. A bias signal adder 80 is provided for the purpose of releasing the interlock bet-ween the main stop valve 72 and the reheat stop valve and the interlock between the control valve 73 and the intercept valve 74 during running.
The control system for the high pressure bypass line ,~, operates to decrease the opening of the pressure reducing valve 81a of the high pressure bypass line when the quan-tity of the steam flowing into the turbine increases during the bypass operation so that it operates as a pilot element for pressure control. Accordingly, the output signal from the high pressure bypass control circuit 58 is com-pared with the output signal from the low value priority circuit 76a by a comparator 82a and its deviation or error output signal is used for operating the high pressure bypass pressure reducing valve 83a. This deviation ~O signal and the temperature signal sent from a temperature control circuit 84a are compared by a high value priority circuit 85a~ and a signal having a higher value is sent to a high pressure bypass temperature control ~alve 81a from the high value priority circuit 85a. The pressure setting of the high pressure bypass line is effected in the following manner. Thus, the signal from a mc~nual setter 86a and the output signal sent from a pressure setter 87a and corresponding to the turbine l~ad are compared by a high value priority circuit 88a, and one 1 : ' ~ ~ ' ~ 057065 of the signals having higher value is sent to the high pressure b~pass co~trol circuit 53 to be compared with actual main steam pressure seignal xl. This relation is shown by the graph shown in ~IG.7. Accordingly, this high pressure bypass control system acts as a safety valve at the time of load interruption and to prevent decrease in the pressure of the main steam.
~ he control system for the low pressure line is similar to the control system for the high pressure by-pass line described aboveO Thus, during the bypass operation of the turbine, when the quantity of the steam flowing into the turbine increases the opening of the low pressure bypass pressure reducing valve 81b is decreased 80 that the control system acts as a pilot element.
Accordingly, the output signal from the low pressure by-pass control circuit 54 is compared with the output from the low value priority circuit 76b by a comparator 82b and its output deviation signal is used to control low pres~ure bypass pressure reducing valve 81b. ~urther,the deviation signal from comparator 82b is compared with a temperature signal from temperature control circuit by a high value priori-ty circuit 85b. The signal having a higher value is used to control a low pressure bypass temperative control valve 83b. The pressure setting of the low pressure bypass line is made in the following manner. More particularly, the output signal from a manual setter 86b is compared with the output sginal sent from a pressure setter 87b and corresponding to the tur-bine load b~ a high value priorit~ ciucuit 88b so that a ~/
-lOS706S
signal having a higher value is se~t to the low pressure bypass control circuit 54 to be compared with actual reheat steam pressure signal x2. ~his relationship is shown by a graph shown in ~IG. 8.
~ he operation of the control system of this inven-tion under normal running will now be described with reference to ~IGS. 6 and 9.
I. From boiler starting to pressure rise.
Since the turbine is at standstill, both output signals from the speed control circuit 41 and the load setter 44 are zero with the result that the main stop valve 72, the control valve 73, the intercept valve 74 and the reheat stop valve 75 are fully closed.
The high pressure bypass control system operates such t~at although the high pressure bypass pressure reducing valve 8~a is fully closed while the steam pres-sure is low as the pressure of the main steam generated by the boiler increases the output from the high pressure bypass control circuit is increased to gradually open the high pressure ~ypass pressure reducing valve 83a. ~he low pressure bypass control system operates in the same manner to gradually open the low pressure bypass pressure reducing valve 81b.
II. ~urbine starts As the turbine starts, the speed control circuit 41 functions and the output or valve opening signal produced by the low value priority circuit 76a increases gradually.
When the turbine is sarted with the all ~ull arc admission mode, the bias signal from the full arc -partial 1~ ' _ ~_ '~' .
arc transfer circuit 46 is applied to the steam adjust-ing valve 73 and the intercept valve 74 thus maintaining these valves in fully opened state.
~ he main steam stop valve 7~ and the reheat stop valve 7~ control the quantities of the main steam and the reheated steam respectively by a small internal bypass valve (not shown).
At this time, the control signal sent to the reheat stop valve 75 is sent from the low value priority circuit 76a through gain setter 78, adder 79 and low value priority circuit 76b thus interlocking each other the main stop valve 72 and the reheat stop valve 75, the ratio of the flow quantities of valves 72 and 75 being determined by the gain qetter 78.
III. Turbine loading As the turbine load increases the quantity of stec~m is increased by interlocked main stop valve 72 and the reheat stop valve 75 (the output from the low value priority circuit 76a increases) so that the deviation signals produced by adders 82a and 82b decrease whereby the degree of opening of the high pressure bypass pres-sure reducing valve 83a and the low pre~sure bypass pres-sure reducing valve 8~b is decreased thus limiting pres-sure variation.
IV. Full arc mode to partial arc mode transfer In this case control is transferred from the inter-locked control o~ the main stop valve 72 and the reheat r' stop valve 75 to the interlocked control of the control valve 73 and the intercept valve 74. The degree of 1~57065 ~ ~
openings of the control valve 73 and the intercept 74which have been maintained in their fully opened state is decreased by the bias signal from the full arc-partial arc control circuit 46. ~hereafter the main s-top valve and the reheat stop valve 75 are fully opened thus trans-ferri~g the control to the turbine control wherein the turbine is controlled by the steam control valve 73 and the intercept valve 74. However this control is not related directly to the invention.
V. ~urbine bypass running complete When the load increases under these conditions, as the openings of the control valve 73 and the intercept valve 74 increase, openings of the high pressure bypass pressure reducing valve 83a and the low pressure bypass pressure reducing valve 83b decrease. Finally,they are completely closed.
VI. Normal running The control of the turbine bypass systems becomes inoperative and the normal running of the turbine using reheated steam commences.
VII. Interruption of the turbine load Due to the rapid closure of the steam control valve 73 and the intercept valve 74 the pressures of the main steam and t~e reheat steam generated by the boiler in-crease so that the high pressure bypass pressure reducing valve 81 and the low pressure bypass pressure reducing valve 81b are opened quickly. At the same time,the high pressure bypass temperature control valve 83a and the low pressure bypass temperatur control valve 83b are 1~ .
.. , - - ... .. .
opened quicklythus controlling the pressure and temper_ ature of the turbine bypass systems.
Thus,according to this invention a turbine bypass -control system for controlling the turbine bgpass lines are incorporated to the conventional main control system which controls the main steam stop valve, steam control valve, interception valve and the reheat stop valve so that it is possible to provide an overall control of the turbine plant. Accordingly, it is possible to improve the control characteristics, to reduce the starting time and cost of maintenance and to make easy to mantain and inspect.
)S~
1.~ ` ;
- . . - - ~ -
Claims (6)
1. A control system for a steam turbine plant of the class comprising a boiler provided with a superheater and a reheater;
a high pressure turbine connected to receive steam generated by the boiler through first valve means and to supply exhaust steam to the reheater;
a medium pressure turbine connected to receive reheated steam from said reheater through second valve means;
a high pressure bypass line connected between the first valve means and the reheater; and a low pressure bypass line connected between the second valve means and a condenser;
said control system comprising a first electric control system for the high pressure bypass line including means responsive to the temperature and pressure of the steam supplied to the high pressure tubine for controlling the quantity of steam circulating through the high pressure bypass line;
a second electric control system for the low pressure bypass line including means responsive to the temperature and pressure of the steam supplied to the medium pres-sure turbine for controlling the quantity of the steam circulating through the low pressure bypass line;
a third electric control system responsive to the speed and load conditions of the turbine plant for con-trolling said first and second valve means; and an electrical connection between said first, second and third electric control systems so that the operation of said first and second electric control systems is modified in accordance with the load of the turbine plant.
a high pressure turbine connected to receive steam generated by the boiler through first valve means and to supply exhaust steam to the reheater;
a medium pressure turbine connected to receive reheated steam from said reheater through second valve means;
a high pressure bypass line connected between the first valve means and the reheater; and a low pressure bypass line connected between the second valve means and a condenser;
said control system comprising a first electric control system for the high pressure bypass line including means responsive to the temperature and pressure of the steam supplied to the high pressure tubine for controlling the quantity of steam circulating through the high pressure bypass line;
a second electric control system for the low pressure bypass line including means responsive to the temperature and pressure of the steam supplied to the medium pres-sure turbine for controlling the quantity of the steam circulating through the low pressure bypass line;
a third electric control system responsive to the speed and load conditions of the turbine plant for con-trolling said first and second valve means; and an electrical connection between said first, second and third electric control systems so that the operation of said first and second electric control systems is modified in accordance with the load of the turbine plant.
2. The control system according to claim 1 wherein said first electric control system comprises a pressure setter for producing a pressure setting signal for the high pressure turbine, a temperature setter for producing a temperature setting signal for the high pressure turbine, and a high pressure bypass control circuit responsive to said pressure setting signal, said temperature setting signal, and signals corresponding to the actual pressure and the actual temperature of the high pressure turbine for producing a signal for controlling the quantity of steam circulating through the high pressure bypass line.
3. The control system according to claim 1 wherein said second electric control system comprises a pressure setter for producing a pressure setting signal for the medium pressure turbine, a temperature setter for producing a temperature setting signal for the medium pressure tur-bine, and a low pressure bypass control circuit responsive to said temperature setting signal, said pressure setting signal and signals corresponding to the actual pressure and the actual temperature of the medium pressure turbine for producing a signal for controlling the quantity of steam circulating through the low pressure bypass line.
4. The control system according to claim 1 wherein said third electric control system comprises a speed control circuit responsive to a preset speed, a preset accelation rate and an actual speed of the turbine plant for producing a deviation signal, and a load control circuit responsive to said deviation signal, a preset load, a preset loading rate, a signal from a full arc-partial arc transfer circuit, a signal from a load limiter and a signal corresponding to the actual pressure of the turbine plant for gener-ating a signal for controlling said first and second valve means, said load control circuit being electrically connected to said first and second electric control systems.
5. The control system according to claim 1, wherein said control system comprises a load setter, a speed control circuit, a gain setter connected to receive the output signal from said speed control circuit for setting a reciprocal of the turbine speed regulation, a first adder for adding the output signal from said load setter to the output from said gain setter, a second adder for adding the output signal from said load setter to the output of said gain setter and a bias signal, a first low value priority circuit connected to receive the output from said first adder, the output from a load limiter, and the output from a control circuit for said high pressure bypass line for selecting one of the outputs having the lowest value as a control signal for controlling said first valve means of the high pressure turbine, a second low value priority circuit connected to receive the output from said second adder, the output from a control circuit for said low pressure bypass line, and the output from said first low value priority circuit passing through a second gain setter for selecting one of the outputs having the lowest value as a control signal for controlling said second valve means of the medium pressure turbine.
6. the control system according to claim 5 which further comprises a full arc-partial arc transfer circuit for producing an output which is added to the control signals produced by said first and second low value priority circuits.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP12833075A JPS5253105A (en) | 1975-10-27 | 1975-10-27 | Control device provided with steam turbine bypass system |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1057065A true CA1057065A (en) | 1979-06-26 |
Family
ID=14982108
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA264,219A Expired CA1057065A (en) | 1975-10-27 | 1976-10-26 | Control systems for steam turbine plants including turbine bypass systems |
Country Status (4)
| Country | Link |
|---|---|
| JP (1) | JPS5253105A (en) |
| AU (1) | AU512591B2 (en) |
| CA (1) | CA1057065A (en) |
| ZA (1) | ZA766292B (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN105201572B (en) * | 2015-09-25 | 2017-05-10 | 新会粤新热电联供有限公司 | Power generation system control method |
| CN111608753A (en) * | 2020-04-28 | 2020-09-01 | 沈阳工业大学 | Peak regulation system of combined solid electric heat storage device for high-low bypass modification of cogeneration unit |
-
1975
- 1975-10-27 JP JP12833075A patent/JPS5253105A/en active Granted
-
1976
- 1976-10-22 ZA ZA766292A patent/ZA766292B/en unknown
- 1976-10-26 CA CA264,219A patent/CA1057065A/en not_active Expired
- 1976-10-27 AU AU19071/76A patent/AU512591B2/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| AU512591B2 (en) | 1980-10-16 |
| JPS5253105A (en) | 1977-04-28 |
| ZA766292B (en) | 1977-09-28 |
| AU1907176A (en) | 1978-05-04 |
| JPS55564B2 (en) | 1980-01-09 |
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