JP2018091224A - Control system, steam turbine, power-generating plant and control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a control device for reducing a peak value of a thrust force after blockage of load at a steam turbine.SOLUTION: A control system comprises a load blockage signal acquisition part for acquiring a load blockage signal during operation of a steam turbine; a revolution speed valve opening calculation part for calculating a valve opening of a steam regulating valve for adjusting inflow amount of steam into the steam turbine on the basis of the deviation between a target rotation speed and an actual rotation speed of the steam turbine; a thrust force valve opening calculation part for calculating a valve opening degree of the steam adjusting valve corresponding to the thrust force added to a rotor of the steam turbine; and a valve opening degree control part for controlling a valve opening degree of the steam adjusting valve on the basis of the valve opening degree calculated by the revolution speed valve opening calculation part and the valve opening degree calculated by the thrust force valve opening degree calculation part upon acquisition of the load blockage signal by the load blockage signal acquisition part.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a control system, a steam turbine, a power plant, and a control method.

  In a steam power plant or a combined cycle power plant that generates power using a steam turbine, when an emergency occurs during a load operation, there is a case where an operation called load interruption is performed to disconnect the load and continue the operation. When the load is shut off, the rotational speed of the steam turbine increases. However, the steam turbine has a function of automatically determining that the rotational speed exceeds a predetermined threshold (for example, 110% of the rated rotational speed) and automatically stopping it. Therefore, in order to prevent an automatic stop due to an increase in the rotational speed, the steam control valve is quickly closed immediately after the load is shut off, and then the actual rotational speed is fed back so that the rotational speed is settled in the vicinity of the predetermined rotational speed. There is a case where control is performed to adjust the valve opening degree according to the deviation from the target rotational speed.

  Regarding control at the time of load interruption, for example, Patent Document 1 describes a control method of closing a fuel stop valve of a gas turbine after a steam control valve of a steam turbine is closed at the time of load interruption in a combined plant.

JP 56-98510 A

  By the way, if the steam control valve is closed rapidly when the load is shut off, the balance of the steam pressure may be lost and a large thrust force may be generated in the rotor. Generation | occurrence | production of a big thrust force damages a rotor and a bearing, and causes the lifetime of those components to be reduced. There has been a demand for a control method that reduces the peak value of the thrust force while keeping the rotational speed below a predetermined threshold when the load is interrupted.

  Therefore, an object of the present invention is to provide a control system, a steam turbine, a power plant, and a control method that can solve the above-described problems.

  According to the first aspect of the present invention, the control system is based on a load cutoff signal acquisition unit that acquires a load cutoff signal during operation of the steam turbine, and a deviation between the target rotational speed and the actual rotational speed of the steam turbine. A rotation speed valve opening degree calculation unit for calculating a valve opening degree of a steam control valve that adjusts the amount of steam flowing into the steam turbine, and a valve of the steam control valve according to a thrust force applied to the rotor of the steam turbine When the thrust force valve opening calculation unit for calculating the opening and the load cutoff signal acquisition unit acquire the load cutoff signal, the valve opening calculated by the rotation speed valve opening calculation unit and the thrust force valve opening calculation A valve opening control unit that controls the valve opening of the steam control valve based on the valve opening calculated by the unit.

  Further, according to the second aspect of the present invention, the thrust force valve opening calculation unit includes a time function of the valve opening according to the thrust force applied to the rotor, and the load cutoff signal acquisition unit includes a load cutoff signal. The valve opening degree calculation unit calculates the valve opening degree based on the elapsed time since the acquisition of the valve, and the valve opening degree control unit calculates the valve opening degree calculated by the rotational speed valve opening degree calculation unit and the thrust force valve opening degree calculation unit. Is selected from among the calculated valve openings, and the opening of the steam control valve is controlled by the selected value.

  Further, according to the third aspect of the present invention, the thrust force valve opening calculation unit is configured to determine a valve opening based on a deviation between a target value of the thrust force applied to the rotor and a measured value of the thrust force applied to the rotor. The valve opening control unit selects a larger value from the valve opening calculated by the rotational speed valve opening calculating unit and the valve opening calculated by the thrust force valve opening calculating unit, and selects The valve opening degree of the steam control valve is controlled according to the obtained value.

  According to a fourth aspect of the present invention, the control system further includes a rotation speed determination unit that determines whether or not the rotation speed of the rotor has exceeded a predetermined limit value. When the rotational speed determination unit determines that the rotational speed exceeds a predetermined limit value, the degree calculation unit sets 0 to the calculated valve opening.

  According to a fifth aspect of the present invention, the control system further includes a preceding correction value calculation unit that calculates a preceding correction value of the valve opening degree according to the output value of the steam turbine, and the thrust The force valve opening calculation unit adds the preceding correction value calculated by the preceding correction value calculation unit to the calculated valve opening.

  According to the sixth aspect of the present invention, the valve opening degree control unit is configured such that the valve opening degree calculated by the rotational speed valve opening degree calculating unit and the valve opening degree calculated by the thrust force valve opening degree calculating unit are calculated. And the calculated weighted average is used as the valve opening degree of the steam control valve.

  Moreover, according to the 7th aspect of this invention, a steam turbine is provided with said control system.

  Moreover, according to the 8th aspect of this invention, a power plant is equipped with said control system.

  According to the ninth aspect of the present invention, a load cutoff signal is acquired during operation of the steam turbine, and the steam flow to the steam turbine is determined based on the deviation between the target rotational speed and the actual rotational speed of the steam turbine. Calculates the valve opening based on the number of rotations of the steam control valve that adjusts the inflow amount, calculates the valve opening of the steam control valve according to the thrust force applied to the rotor of the steam turbine, and obtains the load cutoff signal Then, the valve opening degree of the steam control valve is controlled by a value based on the valve opening degree based on the rotational speed and the valve opening degree corresponding to the thrust force.

  ADVANTAGE OF THE INVENTION According to this invention, the peak value of the thrust force added to a rotor, a bearing, etc. of a steam turbine at the time of load interruption can be reduced.

It is a systematic diagram of the gas turbine combined cycle plant in a first embodiment concerning the present invention. It is a block diagram of the control device in the first embodiment according to the present invention. It is a figure explaining the control method of the steam control valve in 1st embodiment which concerns on this invention. It is a flowchart of the valve opening degree control process of the steam control valve in 1st embodiment which concerns on this invention. It is a figure which shows the result of the valve opening degree control process in 1st embodiment which concerns on this invention. It is a 1st block diagram of the control apparatus in 2nd embodiment which concerns on this invention. It is a figure explaining the control method of the steam control valve in 2nd embodiment which concerns on this invention. It is a flowchart of the valve opening degree control process of the steam control valve in 2nd embodiment which concerns on this invention. It is a figure which shows the result of the valve opening degree control process in 2nd embodiment which concerns on this invention. It is a 2nd block diagram of the control apparatus in 2nd embodiment which concerns on this invention. It is a 1st block diagram of the control apparatus in 3rd embodiment which concerns on this invention. It is a figure explaining the control method of the steam control valve in 3rd embodiment concerning the present invention. It is a flowchart of the valve opening degree control process of the steam control valve in 3rd embodiment which concerns on this invention. It is a figure which shows the result of the valve opening degree control process in 3rd embodiment which concerns on this invention. It is a 2nd block diagram of the control apparatus in 3rd embodiment which concerns on this invention. It is a figure explaining the control method at the time of the conventional load interruption | blocking.

<First embodiment>
Hereinafter, the control method at the time of load interruption of the steam turbine according to the first embodiment of the present invention will be described with reference to FIGS.
FIG. 1 is a system diagram of a gas turbine combined cycle plant according to a first embodiment of the present invention.
As shown in FIG. 1, the gas turbine combined cycle plant (GTCC) of the present embodiment includes a gas turbine 10, an exhaust heat recovery boiler 20 that generates steam by the heat of exhaust gas exhausted from the gas turbine 10, and exhaust heat. A steam turbine 30 (high-pressure steam turbine 31, intermediate-pressure steam turbine 32, and low-pressure steam turbine 33) driven by steam from the recovery boiler 20, and a generator 34 that generates electric power by driving each turbine 10, 31, 32, 33; , A condenser 35 that returns the steam exhausted from the low-pressure steam turbine 33 to water, and a control device 100 that controls these devices.

  The gas turbine 10 includes a compressor 11 that compresses outside air to generate compressed air, a combustor 12 that mixes and burns compressed air with fuel gas to generate high-temperature combustion gas, and a turbine driven by the combustion gas. 13 and a fuel flow rate adjusting valve 14 for adjusting the flow rate of fuel supplied to the combustor 12. A fuel line for supplying fuel from a fuel supply source to the combustor 12 is connected to the combustor 12. A fuel flow rate control valve 14 is provided in this fuel line. The exhaust port of the turbine 13 is connected to the exhaust heat recovery boiler 20.

  The exhaust heat recovery boiler 20 includes a high-pressure steam generator 21 that generates high-pressure steam supplied to the high-pressure steam turbine 31, an intermediate-pressure steam generator 22 that generates intermediate-pressure steam supplied to the intermediate-pressure steam turbine 32, and low-pressure steam. A low-pressure steam generating unit 24 that generates low-pressure steam to be supplied to the turbine 33 and a reheating unit 23 that heats the steam exhausted from the high-pressure steam turbine 31 are provided.

  The high-pressure steam generator 21 of the exhaust heat recovery boiler 20 and the steam inlet of the high-pressure steam turbine 31 are connected by a high-pressure main steam line 41 that guides the high-pressure steam to the high-pressure steam turbine 31, and the steam outlet of the high-pressure steam turbine 31 and the medium pressure The steam inlet of the steam turbine 32 is connected by an intermediate pressure steam line 44 that guides the steam exhausted from the high pressure steam turbine 31 to the steam inlet of the intermediate pressure steam turbine 32 via the reheating unit 23 of the exhaust heat recovery boiler 20. The low pressure steam generator 24 of the exhaust heat recovery boiler 20 and the steam inlet of the low pressure steam turbine 33 are connected by a low pressure main steam line 51 that guides the low pressure steam to the low pressure steam turbine 33.

The steam outlet of the intermediate pressure steam turbine 32 and the steam inlet of the low pressure steam turbine 33 are connected by an intermediate pressure turbine exhaust line 54. A condenser 35 is connected to the steam outlet of the low-pressure steam turbine 33. The condenser 35 is connected to a water supply line 55 that guides the condensate to the exhaust heat recovery boiler 20.
An intermediate pressure main steam line 61 connects the intermediate pressure steam generation unit 22 of the exhaust heat recovery boiler 20 and the upstream side portion of the intermediate pressure steam line 44 from the reheating unit 23.

  The high-pressure main steam line 41 is provided with a high-pressure steam stop valve 42 and a high-pressure main steam control valve 43 that adjusts the amount of steam flowing into the high-pressure steam turbine 31. The intermediate pressure steam line 44 is provided with an intermediate pressure steam stop valve 45 and an intermediate pressure steam control valve 46 that adjusts the amount of steam flowing into the intermediate pressure steam turbine 32. The low-pressure main steam line 51 is provided with a low-pressure steam stop valve 52 and a low-pressure main steam control valve 53 that adjusts the amount of steam flowing into the low-pressure steam turbine 33.

  The control device 100 receives various operation data, instruction data, etc., controls the output of the gas turbine 10, controls the opening and closing of the high-pressure steam stop valve 42, controls the valve opening of the high-pressure main steam control valve 43, and medium-pressure steam. The output of the steam turbine 30 by controlling the opening / closing of the stop valve 45, controlling the valve opening of the intermediate pressure steam control valve 46, controlling the opening / closing of the low pressure steam stop valve 52, controlling the valve opening of the low pressure main steam control valve 53, etc. Power is generated by the generator 34 by control or the like. Moreover, when load interruption | blocking generate | occur | produces by some abnormality etc., the control apparatus 100 performs various control at the time of load interruption | blocking.

Next, the control with respect to the steam control valve (43, 46, 53) of the steam turbine 30 at the time of load interruption will be described with reference to FIG. For convenience of explanation, in the following explanation, valve opening control of the intermediate pressure steam control valve 46 will be explained.
FIG. 16 is a diagram for explaining a conventional control method at the time of load shedding.
The upper part of FIG. 16 is a graph showing the change over time of the valve opening degree of the intermediate pressure steam control valve 46. In FIG. 16, the vertical axis indicates the valve opening, and the horizontal axis indicates the passage of time. In the conventional control, the control device performs control to fully close the valve opening degree of the intermediate pressure steam control valve 46 when receiving the load cutoff instruction signal. The upper part of FIG. 16 shows a state in which the valve opening degree of the intermediate pressure steam control valve 46 is controlled to 0 immediately after receiving the load cutoff instruction signal at time T1.
The middle diagram of FIG. 16 is a graph showing the time change of the thrust force. In FIG. 16, the vertical axis represents the measured value of the thrust force applied to the rotor and bearing of the steam turbine 30, and the horizontal axis represents the passage of time. This graph shows that a large thrust force (peak value magnitude: N1) is applied to the rotor and the like when the valve opening degree of the intermediate pressure steam control valve 46 suddenly becomes zero at the time of load interruption. .
The lower diagram of FIG. 16 is a graph showing the change over time of the rotational speed of the steam turbine 30. In FIG. 16, the vertical axis indicates the number of rotations per minute of the steam turbine 30, and the horizontal axis indicates the passage of time. This graph shows how the rotational speed increases to R1 and then returns to the rated rotational speed when the opening degree of the intermediate pressure steam control valve 46 suddenly becomes 0 at the time of load interruption. A broken line indicates a rotation speed threshold value RX. When the rotation speed of the steam turbine 30 exceeds the threshold value RX, the steam turbine 30 (and the entire GTCC plant) automatically stops. By the conventional control, the rotation speed after the load is interrupted is suppressed with a margin below the threshold value RX.

  In the conventional control, when the load is shut off, the valve opening degree of the intermediate pressure steam control valve 46 is rapidly closed, and thereafter, the actual rotational speed is fed back so that the rotational speed of the steam turbine 30 is set near the rated value, so that the target rotational speed is obtained. The valve opening degree of the intermediate pressure steam control valve 46 is adjusted according to the deviation. Thus, in the conventional control, only the rotation speed of the steam turbine 30 is monitored and controlled, and the thrust force is not monitored. Then, as shown in the above middle diagram, a large thrust force (N1) is generated when the load is interrupted, resulting in a failure of the rotor and the bearing, a decrease in the service life, and an increase in maintenance costs as a result. It was. Therefore, in the present embodiment, a control method is provided in which the thrust force is further reduced while the increase in the rotational speed of the steam turbine 30 is suppressed by adjusting the valve opening degree of the steam control valve when the load is shut off.

FIG. 2 is a block diagram of the control device according to the first embodiment of the present invention.
As illustrated, the control device 100 includes a load cutoff signal acquisition unit 101, a first valve opening calculation unit 102, a second valve opening calculation unit 103, a valve opening control unit 104, and a storage unit 105. ing. The control device 100 is configured by a computer.
The load cutoff signal acquisition unit 101 acquires a load cutoff signal for disconnecting the load during operation of the GTCC.
The first valve opening calculation unit 102 acquires a target rotational speed (for example, a rated rotational speed) of the steam turbine 30 and an actual rotational speed, and based on a deviation between these two values, the intermediate pressure steam control valve 46. The valve opening (first valve opening) is calculated.

The second valve opening calculation unit 103 starts the time when the load cutoff signal acquisition unit 101 acquires the load cutoff signal, and starts the valve opening (second valve) of the intermediate pressure steam control valve 46 according to the elapsed time thereafter. Opening degree) is calculated.
The valve opening degree control unit 104 acquires the first valve opening degree and the second valve opening degree, selects a larger valve opening degree from these two values, and selects the valve corresponding to the selected valve opening degree. The opening command value is output to the intermediate pressure steam control valve 46.
The memory | storage part 105 memorize | stores various information, such as the correspondence table of the elapsed time after valve | bulb interruption | blocking, and valve opening degree.
Note that the control device 100 has various other functions related to GTCC control, but descriptions of functions not related to the present embodiment are omitted.

Next, with reference to FIG. 3, an example of valve opening control of the intermediate pressure steam control valve 46 at the time of load interruption by the first valve opening calculation unit 102, the second valve opening calculation unit 103, and the valve opening control unit 104 explain.
FIG. 3 is a diagram for explaining a control method of the steam control valve in the first embodiment according to the present invention.
The first valve opening calculation unit 102 includes a subtractor 102a and a controller 102b. The subtractor 102a subtracts the actual rotational speed from the target rotational speed to calculate the deviation between them. The target rotation speed is recorded in advance in the storage unit 105, for example. Further, the actual rotational speed is acquired from, for example, a rotational speed measurement sensor provided in the steam turbine 30 by the control device 100. The subtractor 102a outputs the calculated deviation to the controller 102b. The controller 102b calculates a valve opening command value (first valve opening) such that the deviation value acquired from the subtractor 102a becomes 0 using a technique such as feedback control. The controller 102b outputs the calculated first valve opening degree to the valve opening degree control unit 104.
In the control method at the time of load interruption described with reference to FIG. 16, the opening degree of the intermediate pressure steam control valve 46 is controlled by the valve opening degree calculated by the first valve opening degree calculation unit 102.

  On the other hand, the second valve opening calculation unit 103 includes a timer 103a and a time function 103b of the valve opening. When the load cutoff signal acquisition unit 101 acquires the load cutoff signal, the second valve opening degree calculation unit 103 starts the timer 103a and measures the elapsed time after acquiring the load cutoff signal. The time function 103b acquires elapsed time information from the timer 103a every predetermined time, and calculates a valve opening (second valve opening) corresponding to the elapsed time. A function may be used to calculate the valve opening, or a table in which elapsed time and valve opening are associated with each other may be used. For example, in the table, the correspondence between the elapsed time and the valve opening is determined in advance, such as the valve opening X1 if the elapsed time is 0.5 seconds, the valve opening X2 if the elapsed time is 1 second,. The time function 103b may calculate the valve opening degree by linearly interpolating the values registered in the table according to the elapsed time. The valve opening time function 103 b outputs the calculated second valve opening to the valve opening controller 104. Note that the function or table used by the time function 103b takes into account the thrust force applied to the rotor of the steam turbine 30 so that a large thrust force is not applied after the load is interrupted (for example, a rapid steam pressure such as rapid closing). The valve opening is set in association with the elapsed time after the load is interrupted.

The valve opening degree control unit 104 selects a large value from the first valve opening degree and the second valve opening degree, and performs control so that the opening degree of the intermediate pressure steam control valve 46 becomes the selected value.
The valve opening degree control unit 104 calculates a weighted average of the first valve opening degree and the second valve opening degree among the first valve opening degree and the second valve opening degree. The valve opening degree of the intermediate pressure steam control valve 46 may be controlled by the calculated weighted average value.

FIG. 4 is a flowchart of the valve opening degree control process of the steam control valve in the first embodiment according to the present invention.
First, it is assumed that load interruption occurs during operation of GTCC. Then, the load cutoff signal acquisition unit 101 acquires a load cutoff signal (step S11). The load cutoff signal acquisition unit 101 notifies the first valve opening degree calculation unit 102 and the second valve opening degree calculation unit 103 of the occurrence of load cutoff. Then, the first valve opening calculation unit 102 calculates the first valve opening from the deviation between the target value of the rotation speed of the steam turbine and the actual measurement value (step S12). The method for calculating the first valve opening is as described in FIG. The first valve opening calculation unit 102 calculates “0” as the first valve opening, for example, for several seconds to several tens of seconds immediately after the load is interrupted. The first valve opening calculation unit 102 outputs the calculated valve opening to the valve opening control unit 104.

  On the other hand, the second valve opening calculation unit 103 that has received the notification of occurrence of load interruption calculates the second valve opening according to the elapsed time after acquiring the load interruption signal (step S13). The method for calculating the second valve opening is as described in FIG. For example, the second valve opening calculation unit 103 calculates an opening for slightly opening the intermediate pressure steam control valve 46 as the second valve opening, for example, for several seconds to several tens of seconds immediately after the load is interrupted. Second valve opening calculation unit 103 outputs the calculated opening to valve opening control unit 104.

Next, the valve opening degree control unit 104 calculates the valve opening degree based on the first valve opening degree and the second valve opening degree (step S14). For example, the valve opening degree control unit 104 selects a larger valve opening degree from the first valve opening degree and the second valve opening degree. Alternatively, the valve opening control unit 104 calculates a weighted average of the first valve opening and the second valve opening. Next, the valve opening control unit 104 instructs the intermediate pressure steam control valve 46 to provide a valve opening command value corresponding to the selected (calculated) valve opening (step S15).
The control device 100 continuously performs the processing from step S11 to step S15 for several minutes (about 1 to 3 minutes) after the load is interrupted.

FIG. 5 is a diagram showing a result of the valve opening degree control process in the first embodiment according to the present invention.
The contents represented by the upper, middle, and lower diagrams in FIG. 5 are the same as those in FIG. That is, the upper graph of FIG. 5 shows the time change of the valve opening of the intermediate pressure steam control valve 46 when the valve opening control of the first embodiment is applied, and the middle graph shows the first embodiment. The time change of the thrust force after application is shown, and the graph in the lower diagram shows the time change of the rotational speed after application of the first embodiment.
From the upper diagram of FIG. 5, it can be seen that the valve opening degree of the intermediate pressure steam control valve 46 is controlled in a slightly opened state from time T1 when load interruption occurs to time T2 thereafter. Time T1 to T2 is several seconds.

  Next, referring to the middle diagram of FIG. 5, it can be seen that the peak value of the thrust force after the load is interrupted is reduced to N2, which is considerably smaller than the peak value N1 by the conventional control. This is because the valve opening of the intermediate pressure steam control valve 46 is not set to “0” (first valve opening) immediately after the load is cut off, but is slightly opened (second valve opening). This is considered to be because it is not as rapid as in the case of conventional control.

  Next, referring to the lower diagram of FIG. 5, the rotational speed of the steam turbine 30 is increased to R2, which is a larger value than R1 during conventional control. This is considered to be because the steam supply amount increased because the intermediate pressure steam control valve 46 was slightly opened. According to the result of FIG. 5, the rotational speed R2 after application of the present embodiment increases from the rated rotational speed to about half of the threshold RX. According to the present embodiment, it can be seen that the maximum rotational speed increases due to an increase in the amount of steam supplied by selecting a larger valve opening between the first valve opening and the second valve opening. When this embodiment is applied, the possibility that the maximum rotational speed increases and becomes equal to or higher than the threshold RX (overspeed trip) is higher than that in the conventional control.

  According to this embodiment, since the opening degree control of the steam control valve is performed at the time of load interruption by the valve opening considering a large value among the first valve opening and the second valve opening, the intermediate pressure steam control valve 46 is controlled. The valve opening degree can be slightly opened, and the peak value of the thrust force generated by the fluctuation of the steam pressure balance when the load is interrupted can be reduced. Thereby, damage to the rotor and the bearing of the rotor can be reduced, and the life can be extended.

<Second embodiment>
Hereinafter, the control method at the time of load interruption of the steam turbine according to the second embodiment of the present invention will be described with reference to FIGS.
Hereinafter, the control device 100A according to the second embodiment will be described. The control device 100A controls the intermediate pressure steam control valve 46 by a method different from the first embodiment. In the first embodiment, the second valve opening calculation unit 103 calculates the second valve opening using a time function. In the second embodiment, the third valve opening calculation unit 106 determines the valve opening (third valve opening) of the intermediate pressure steam control valve 46 according to the thrust force applied to the rotor or the like.

FIG. 6 is a first block diagram of a control device according to the second embodiment of the present invention.
Among the configurations according to the second embodiment of the present invention, the same components as those constituting the control device 100 according to the first embodiment are denoted by the same reference numerals, and description thereof will be omitted. As illustrated, the control device 100A includes a load cutoff signal acquisition unit 101, a first valve opening calculation unit 102, a third valve opening calculation unit 106, a valve opening control unit 104A, and a storage unit 105. ing. In addition, the third valve opening calculation unit 106 includes a preceding correction value calculation unit 107.

The third valve opening calculation unit 106 acquires the target value of the thrust force applied to the rotor of the steam turbine 30 and the measured value of the thrust force, and based on the deviation between these two values, the intermediate pressure steam control valve 46 The valve opening (third 3 ′ valve opening) is calculated. Further, the third valve opening calculation unit 106 adds the correction value calculated by the preceding correction value calculation unit 107 to the calculated valve opening, thereby opening the valve opening of the intermediate pressure steam control valve 46 (third valve opening). Is calculated.
The advance correction value calculation unit 107 acquires the output value of the steam turbine and calculates the advance correction value for the output value match.
The valve opening degree control unit 104A acquires the first valve opening degree and the third valve opening degree, and controls the valve opening degree of the intermediate pressure steam control valve 46 based on the two valve opening degrees. For example, the valve opening degree control unit 104A selects a larger valve opening degree from the first valve opening degree and the third valve opening degree, and sets the valve opening degree command value corresponding to the selected valve opening degree to the medium pressure. Output to the steam control valve 46.

Next, an example of the valve opening degree control of the intermediate pressure steam control valve 46 at the time of load interruption in the second embodiment will be described with reference to FIG.
FIG. 7 is a view for explaining a control method of the steam control valve in the second embodiment according to the present invention.
The first valve opening calculation unit 102 includes a subtractor 102a and a controller 102b. The subtractor 102a subtracts the actual rotational speed from the target rotational speed to calculate the deviation between them. The subtractor 102a outputs the calculated deviation to the controller 102b. The controller 102b calculates a valve opening command value (first valve opening) such that the deviation value acquired from the subtractor 102a becomes 0 using a technique such as feedback control. The controller 102b outputs the calculated first valve opening degree to the valve opening degree control unit 104A.

  On the other hand, the third valve opening calculation unit 106 includes a controller 106a. When the load cutoff signal acquisition unit 101 acquires the load cutoff signal, the controller 106a calculates a deviation between the two by subtracting the measured thrust force value from the target thrust force. Note that the target thrust force is recorded in the storage unit 105 in advance, for example. Further, the thrust force measurement value is acquired from, for example, a thrust force measurement sensor provided on the bearing or the like by the control device 100. The controller 106a calculates a valve opening command value (third 'valve opening) such that the calculated deviation becomes 0 using a technique such as feedback control. The controller 106a includes a correction value calculator 107a (preceding correction value calculator 107). The correction value calculator 107a acquires, for example, the output value (“ST output” in the figure) of the steam turbine 30 immediately before the load is cut off, and calculates the correction value of the valve opening degree of the intermediate pressure steam control valve 46 corresponding to this output value. To do. For example, the storage unit 105 stores a table, function, and the like that define the correspondence between the output value and the valve opening correction value, and the correction value calculator 107a calculates a correction value based on this table. Note that the output value of the steam turbine 30 immediately before the load is interrupted is recorded in the storage unit 105, for example. The controller 106a calculates the third valve opening by adding the correction value calculated by the correction value calculator 107a to the third 'valve opening. The controller 106a outputs the calculated third valve opening degree to the valve opening degree control unit 104A. By adding a correction value corresponding to the output value of the steam turbine 30 to the 3 ′ valve opening, it is possible to compensate in advance for a response delay due to feedback control based on the thrust force.

The valve opening degree control unit 104A selects a large value from the first valve opening degree and the third valve opening degree, and performs control so that the opening degree of the intermediate pressure steam control valve 46 becomes the selected value.
The valve opening degree control unit 104A calculates a weighted average of the first valve opening degree and the third valve opening degree among the first valve opening degree and the second valve opening degree. The opening degree of the intermediate pressure steam control valve 46 may be controlled by the calculated value.

FIG. 8 is a flowchart of the valve opening degree control process of the steam control valve in the second embodiment according to the present invention.
First, it is assumed that load interruption occurs during operation of GTCC. Then, the load cutoff signal acquisition unit 101 acquires a load cutoff signal (step S21). The load cutoff signal acquisition unit 101 notifies the first valve opening degree calculation unit 102 and the third valve opening degree calculation unit 106 that a load cutoff has occurred. Then, the first valve opening calculation unit 102 calculates the first valve opening from the deviation between the target value of the rotation speed of the steam turbine and the actual measurement value (step S22). The method for calculating the first valve opening is the same as in the first embodiment. For example, the first valve opening calculation unit 102 calculates “0” as the first valve opening for several tens of seconds immediately after the load is interrupted. The first valve opening calculation unit 102 outputs the calculated valve opening to the valve opening control unit 104.

  On the other hand, the third valve opening calculation unit 106 that has received the notification of the occurrence of load interruption calculates the third 'valve opening from the deviation between the target value of the thrust force and the measured value (step S23). The method for calculating the third 'valve opening is as described in FIG. In addition, a preceding correction value calculation unit 107 included in the third valve opening calculation unit 106 calculates a preceding correction value of the valve opening corresponding to the output value of the steam turbine 30. Then, the third valve opening degree calculation unit 106 calculates a third valve opening degree obtained by adding the preceding correction value to the 3 ′ valve opening degree (step S24). The third valve opening calculation unit 106 calculates, for example, an opening for slightly opening the intermediate pressure steam control valve 46 as the third valve opening for a few seconds immediately after the load interruption. The third valve opening calculation unit 106 outputs the calculated third valve opening to the valve opening control unit 104A.

Next, the valve opening degree control unit 104A calculates the valve opening degree based on the first valve opening degree and the third valve opening degree (step S25). For example, the valve opening degree control unit 104A selects a large value from the first valve opening degree and the third valve opening degree. Alternatively, the valve opening degree control unit 104A calculates a weighted average of the first valve opening degree and the third valve opening degree. Next, the valve opening degree control unit 104A instructs the intermediate pressure steam control valve 46 to provide a valve opening degree command value corresponding to the calculated valve opening degree (step S26).
The control device 100 continuously performs the processing from step S21 to step S26 for several minutes (about 1 to 3 minutes) after the load is interrupted.

FIG. 9 is a diagram showing a result of the valve opening degree control process in the second embodiment according to the present invention.
The upper graph of FIG. 9 shows the time change of the opening degree of the intermediate pressure steam control valve 46 when the valve opening degree control of the second embodiment is applied, and the middle graph shows the state after the second embodiment is applied. The time change of thrust force is shown, and the graph of the following figure shows the time change of the rotation speed after 2nd embodiment application.
As shown in the upper diagram of FIG. 9, from the time T1 when load interruption occurs to the subsequent time T3, the opening degree of the intermediate pressure steam control valve 46 was controlled in a slightly opened state using the thrust force as an index. I understand. The times T1 to T3 are several seconds.

  Next, referring to the middle diagram of FIG. 9, it can be seen that the peak value of the thrust force after the load is interrupted is reduced to N3 which is considerably smaller than the peak value N1 by the conventional control. This is because the opening of the intermediate pressure steam control valve 46 is not set to “0” (first valve opening) immediately after the load is cut off, but is slightly opened (second valve opening). This is thought to be because it is no longer as rapid as in the case of control. Further, the time until the thrust force is set to “0” is shorter than that in the first embodiment. This is probably because the second embodiment monitors the thrust force and considers the third valve opening calculated by feedback control based on the deviation between the target thrust force and the measured thrust force value.

  Next, referring to the lower diagram of FIG. 9, the rotational speed of the steam turbine 30 is increased to R3, which is a value larger than R1 during conventional control. This is considered to be because the steam supply amount increased because the intermediate pressure steam control valve 46 was slightly opened. According to the result of FIG. 9, the rotational speed R3 after application of the present embodiment has increased from the rated rotational speed to a rotational speed exceeding half of the threshold RX. This is because when the larger valve opening degree is selected from the first valve opening degree and the third valve opening degree, the steam supply amount of the third valve opening degree calculated according to the thrust force is selected. The increase is thought to be the cause. Similar to the first embodiment, the possibility of an overspeed trip is higher than in the conventional control.

According to this embodiment, since the control is performed with the valve opening considering a large value among the first valve opening and the third valve opening, the opening of the steam control valve can be slightly opened, and the load It is possible to reduce the peak value of the thrust force caused by the fluctuation of the steam pressure balance at the time of shutoff. Thereby, damage to the rotor and the bearing of the rotor can be reduced, and the life can be extended. Further, since the thrust force measurement value is brought close to the target thrust force (0 kN) by feedback control, the thrust force during load interruption can be reliably brought close to 0 (compared to the first embodiment). The life can be further extended.
Further, since the valve opening is automatically adjusted according to the magnitude of the thrust force, it is not necessary to design a time function each time.

FIG. 10 is a second block diagram of the control device according to the second embodiment of the present invention.
As shown in the figure, the control device 100A ′ includes a third valve opening degree calculation unit 106A instead of the third valve opening degree calculation unit 106. The third valve opening calculation unit 106A does not include the preceding correction value calculation unit 107. In the second embodiment, as shown in FIG. 10, a configuration in which the advance correction value calculation unit 107 is excluded may be employed. Control at the time of load interruption by the control device 100A ′ shown in FIG. 10 will be briefly described.
First, the load cutoff signal acquisition unit 101 acquires a load cutoff signal (step S21). Next, the first valve opening calculation unit 102 calculates the first valve opening (step S22). On the other hand, the third valve opening calculation unit 106 calculates the third valve opening from the deviation between the target value of thrust force and the actual measurement value (step S23). The third valve opening calculation unit 106 outputs the calculated 3 ′ valve opening to the valve opening control unit 104. Next, the valve opening degree control unit 104 calculates the valve opening degree based on the first valve opening degree and the third 'valve opening degree (step S25), and instructs the intermediate pressure steam control valve 46 about the valve opening degree. (Step S26).

  Even with the control device 100A ′, although the response delay is included in the third valve opening, the same effect as the control device 100A can be obtained.

<Third embodiment>
Hereinafter, the control method at the time of load interruption of the steam turbine according to the third embodiment of the present invention will be described with reference to FIGS.
Hereinafter, the control device 100B according to the third embodiment will be described. In the second embodiment, there is a possibility that the maximum rotational speed increases and an overspeed trip occurs. Therefore, in the control device 100B according to the third embodiment, a configuration for preventing an overspeed trip is added.

FIG. 11 is a first block diagram of a control device according to the third embodiment of the present invention.
Among the configurations according to the third embodiment of the present invention, the same components as those constituting the control device 100 according to the second embodiment are denoted by the same reference numerals, and description thereof is omitted. As illustrated, the control device 100B includes a load cutoff signal acquisition unit 101, a first valve opening calculation unit 102, a third valve opening calculation unit 106B, a valve opening control unit 104, and a storage unit 105. ing. The third valve opening calculation unit 106B includes a preceding correction value calculation unit 107 and a rotation speed determination unit 108.

The third valve opening calculation unit 106B calculates the valve opening (third ′ valve opening) based on the deviation between the target value of the thrust force and the measured value of the thrust force. Further, the third valve opening calculation unit 106 adds the correction value calculated by the preceding correction value calculation unit 107 to the calculated valve opening, thereby opening the valve opening of the intermediate pressure steam control valve 46 (third valve opening). Is calculated. In addition, when the rotation speed determination unit 108 determines that the rotation speed of the steam turbine 30 has exceeded a predetermined limit value, the third valve opening calculation unit 106B sets “0” to the third valve opening.
The advance correction value calculation unit 107 calculates a correction value for the output value of the steam turbine as in the second embodiment.
The rotation speed determination unit 108 acquires the actual rotation speed of the rotor of the steam turbine 30 and determines whether or not the actual rotation speed exceeds a predetermined limit value.
For example, the valve opening control unit 104A selects a larger valve opening from the first valve opening and the third valve opening, and sets the valve opening command value corresponding to the selected valve opening to the middle. It outputs to the pressure steam control valve 46.

Next, an example of the valve opening degree control of the intermediate pressure steam control valve 46 at the time of load interruption in the third embodiment will be described with reference to FIG.
FIG. 12 is a diagram for explaining a method of controlling the steam control valve in the third embodiment according to the present invention.
The first valve opening calculation unit 102 is the same as in the first and second embodiments. That is, the subtractor 102a calculates the deviation between the target rotational speed and the actual rotational speed, and the controller 102b calculates the first valve opening degree such that the deviation becomes 0 by a technique such as feedback control. The controller 102b outputs the calculated first valve opening degree to the valve opening degree control unit 104A.

On the other hand, the third valve opening calculation unit 106B includes a controller 106b. When the load cutoff signal acquisition unit 101 acquires the load cutoff signal, the controller 106b calculates a deviation between the target thrust force and the measured thrust force value. The controller 106b calculates the third 'valve opening so that the deviation becomes zero using a method such as feedback control. Further, the controller 106b calculates the third valve opening by adding the preceding correction value of the valve opening corresponding to the output value of the steam turbine 30 calculated by the correction value calculator 107a to the third 'valve opening. The controller 106b outputs the calculated third valve opening degree to the valve opening degree control unit 104A. The above processing is the same as in the second embodiment.
In addition to the target thrust force, the thrust force measurement value, and the output value of the steam turbine 30, the controller 106b according to the third embodiment acquires the actual rotational speed of the rotor detected by the sensor and monitors the rotational speed. When the number of rotations of the rotor exceeds a predetermined limit value, the controller 106b sets the third valve opening to 0 and outputs it to the valve opening controller 104A. Here, the predetermined limit value is a value for reliably preventing an overspeed trip set between the rated rotational speed and the threshold value RX. For example, if the threshold value RX is set to 110% of the rated speed, this limit value is set to 105%. When the actual rotational speed exceeds 105% of the rated rotational speed, the controller 106b sets “0” to the third valve opening degree.

The valve opening degree control unit 104A selects a large value from the first valve opening degree and the third valve opening degree, and performs control so that the opening degree of the intermediate pressure steam control valve 46 becomes the selected value. Here, according to the conventional control, the first valve opening set according to the rotational speed of the rotor is set to “0” for a while after the load is cut off (FIG. 16). Therefore, when “0” is output as the third valve opening during this time, the valve opening control unit 104A performs control to fully close the intermediate pressure steam control valve 46 (the first valve opening and the third valve opening). Both valve openings are “0”). When the intermediate pressure steam control valve 46 is fully closed, the steam supply amount becomes 0, and the increase in the rotational speed is suppressed. This control can prevent an overspeed trip.
In the present embodiment, the valve opening degree control unit 104A also includes the first valve opening degree and the third valve opening degree that give a greater weight to the third valve opening degree among the first valve opening degree and the second valve opening degree. A weighted average of the degrees may be calculated, and the valve opening degree of the intermediate pressure steam control valve 46 may be controlled by the calculated value.

FIG. 13 is a flowchart of the valve opening degree control process of the steam control valve in the third embodiment according to the present invention.
Processing similar to that of the second embodiment described in FIG. 9 will be briefly described.
First, the load cutoff signal acquisition unit 101 acquires a load cutoff signal (step S21). The load cutoff signal acquisition unit 101 notifies the first valve opening degree calculation unit 102 and the third valve opening degree calculation unit 106B that a load cutoff has occurred. Then, the first valve opening calculation unit 102 calculates the first valve opening from the deviation between the target value of the rotation speed of the steam turbine and the actual measurement value (step S22). The first valve opening calculation unit 102 outputs the calculated opening to the valve opening control unit 104A.

  On the other hand, the third valve opening calculation unit 106B that has received the notification of the occurrence of load interruption calculates the third 'valve opening from the deviation between the target value of the thrust force and the actual measurement value (step S23). In addition, the preceding correction value calculation unit 107 included in the third valve opening calculation unit 106B calculates the preceding correction value of the valve opening corresponding to the output value of the steam turbine 30. The third valve opening degree calculation unit 106B calculates a third valve opening degree obtained by adding the preceding correction value to the 3 ′ valve opening degree (step S24).

  Next, the rotation speed determination unit 108 included in the third valve opening calculation unit 106B acquires the measured value (actual rotation speed) of the steam turbine rotation speed, compares it with the limit value recorded in the storage unit 105, It is determined whether or not the actual rotational speed exceeds the limit value (step S241). The rotation speed determination unit 108 outputs the determination result to the third valve opening calculation unit 106B. When the actual rotational speed exceeds the limit value (step S241; Yes), the third valve opening calculation unit 106B sets 0 to the third valve opening (step S242). The third valve opening calculation unit 106B outputs the third valve opening (“0”) to the valve opening control unit 104A. When the actual rotational speed is equal to or less than the limit value (step S241; No), the third valve opening calculation unit 106B outputs the third valve opening calculated in step S24 to the valve opening control unit 104A.

  Next, the valve opening degree control unit 104A calculates the valve opening degree based on the first valve opening degree and the third valve opening degree (step S25). The valve opening control unit 104A instructs the valve opening command value corresponding to the calculated valve opening to the intermediate pressure steam control valve 46 (step S26). The control device 100 continuously performs the processing from step S21 to step S26 for several minutes (about 1 to 3 minutes) after the load is interrupted.

  As a modification, when the valve opening control unit 104A acquires the value “0” as the third valve opening, the valve opening that is unconditionally fully closed regardless of the size of the first valve opening. The degree command value may be instructed to the intermediate pressure steam control valve 46.

FIG. 14 is a diagram showing a result of the valve opening degree control process in the third embodiment according to the present invention.
The upper graph of FIG. 14 shows the time change of the valve opening of the intermediate pressure steam control valve 46 when the valve opening control of the third embodiment is applied, and the middle graph is after the third embodiment is applied. The graph shows the time variation of the rotational speed after application of the third embodiment.
As shown in the upper diagram of FIG. 14, the valve opening degree of the intermediate pressure steam control valve 46 is controlled in a slightly opened state using the thrust force as an index from time T1 when load interruption occurs to time T4 thereafter. I understand. The reason why the valve opening is 0 at time T4 is that the rotation speed determination unit 108 determines that the rotation speed exceeds the limit value at this time, and the third valve opening calculation unit 106B This is because the opening degree is set to 0.

  Next, looking at the middle diagram of FIG. 14, the magnitude of the peak value of the thrust force after the load is interrupted is reduced to N4, which is considerably smaller than the peak value N1 by the conventional control, as in the second embodiment. The time to settling is short. After that, a thrust force having a magnitude N4 ′ is generated at time T4. This is because the intermediate pressure steam control valve 46 was fully closed at time T4. However, the thrust force N4 ′ generated by changing from the slightly open state to the fully closed state is sufficiently smaller than N1 illustrated in FIG. 16 and the force applied to the bearings is relatively small. Can be suppressed.

  Next, referring to the lower diagram of FIG. 14, the rotational speed of the steam turbine 30 increases to R4, which is a larger value than R1 in the conventional control, but is lower than R3 of the second embodiment. It can be suppressed. This is because when the rotational speed exceeds the limit value, the intermediate pressure steam control valve 46 is fully closed so that the rotational speed does not increase any further. This can prevent an overspeed trip.

  According to the present embodiment, in addition to the effects of the second embodiment, the risk of an overspeed trip can be reduced.

FIG. 15 is a third block diagram of the control device according to the third embodiment of the present invention.
As illustrated, the control device 100B ′ includes a third valve opening calculation unit 106B ′ instead of the third valve opening calculation unit 106B. The third valve opening calculation unit 106B ′ does not include the preceding correction value calculation unit 107. The third embodiment may be configured without the advance correction value calculation unit 107 as shown in FIG. Control at the time of load interruption by the control device 100B ′ shown in FIG. 15 will be briefly described.
First, the load cutoff signal acquisition unit 101 acquires a load cutoff signal (step S21). Next, the first valve opening calculation unit 102 calculates the first valve opening (step S22). On the other hand, the third valve opening calculation unit 106 calculates the third valve opening from the deviation between the target value of thrust force and the actual measurement value (step S23).

  Next, the rotational speed determination unit 108 determines whether or not the actual rotational speed has exceeded a predetermined limit value (step S241). If the actual rotational speed exceeds the limit value (step S241; Yes), the third valve opening degree calculation unit 106B sets “0” to the third valve opening degree (step S242), and opens that value. Output to the degree control unit 104A. When the actual rotational speed is equal to or less than the limit value (step S241; No), the third valve opening calculation unit 106B outputs the third valve opening calculated in step S24 to the valve opening control unit 104A. Next, the valve opening degree control unit 104A calculates the valve opening degree based on the first valve opening degree and the third 'valve opening degree (step S25), and instructs the intermediate pressure steam control valve 46 about the valve opening degree. (Step S26).

  Even with the control device 100B ′, although the response delay is included in the third valve opening, the same effect as the control device 100B can be obtained.

  In the description of the first embodiment, the second embodiment, and the third embodiment described above, the case where the control device 100 or the like controls the valve opening degree of the intermediate pressure steam control valve 46 when the load is shut off has been described as an example. However, the control target is not limited to the intermediate pressure steam control valve 46. The control device 100 or the like may control one or a plurality of valve openings of the high-pressure main steam control valve 43, the medium-pressure steam control valve 46, and the low-pressure main steam control valve 53 by a similar control method.

  The control devices 100, 100A, 100A ′, 100B, and 100B ′ are examples of the control system. Load cutoff signal acquisition unit 101, first valve opening calculation unit 102, second valve opening calculation unit 103, third valve opening calculation unit 106, 106A, 106B, 106B ', valve opening control unit 104, advance correction At least a part of the value calculation unit 107 and the rotation speed determination unit 108 is a function provided by a processor included in the control device 100 or the like reading out and executing a program from the storage unit 105 such as a hard disk. Further, the load cutoff signal acquisition unit 101, the first valve opening calculation unit 102, the second valve opening calculation unit 103, the third valve opening calculation units 106, 106A, 106B, 106B ′, the valve opening control unit 104, The advance correction value calculation unit 107 and the rotation speed determination unit 108 are all or part of a microcomputer, an LSI (Large Scale Integration), an ASIC (Application Specific Integrated Circuit), a PLD (Programmable Logic Device), and an FPGA (Field-Programmable Gate). Array) or the like may be used.

In addition, it is possible to appropriately replace the components in the above-described embodiments with known components without departing from the spirit of the present invention. The technical scope of the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention.
Note that. The second valve opening calculator 103, the third valve opening calculators 106, 106A, and 106B are examples of thrust force valve opening calculators, and the first valve opening calculator is an example of a rotation speed valve opening calculator. is there. The gas turbine combined cycle plant shown in FIG. 1 is an example of a power plant. The thrust force applied to the rotor includes the thrust force applied to the bearing of the rotor.

DESCRIPTION OF SYMBOLS 10 ... Gas turbine 11 ... Compressor 12 ... Combustor 13 ... Turbine 14 ... Fuel flow control valve 20 ... Waste heat recovery boiler 21 ... High pressure steam generation part 22 ... Intermediate pressure steam generator 23 ... Reheating unit 24 ... Low pressure steam generator 30 ... Steam turbine 31 ... High pressure steam turbine 32 ... Medium pressure steam turbine 33 ... Low pressure steam turbine 34 ... Generator 35 ... Condenser 41 ... High pressure main steam line 42 ... High pressure steam stop valve 43 ... High pressure main steam control valve 44 ... Medium pressure steam line 45 ... Medium Pressure steam stop valve 46 ... Intermediate pressure steam control valve 51 ... Low pressure main steam line 52 ... Low pressure steam stop valve 53 ... Low pressure main steam control valve 54 ... Medium pressure turbine exhaust line 55 ...・ Water supply line 61: medium pressure main steam line 100, 100A, 1 0B ... Control device 101 ... Load cutoff signal acquisition unit 102 ... First valve opening calculation unit 102a ... Subtractor 102b ... Controller 103 ... Second valve opening calculation unit 103a ... Timer 103b ... Time functions 104, 104A ... Valve opening control unit 105 ... Storage units 106, 106A, 106B ... Third valve opening calculation unit 106a ... Controller 107 ..Previous correction value calculation unit 107a ... Correction value calculator 108 ... Number of revolutions determination unit

Claims (9)

A load cutoff signal acquisition unit for acquiring a load cutoff signal during operation of the steam turbine;
Based on the deviation between the target rotational speed of the steam turbine and the actual rotational speed, a rotational speed valve opening degree calculation unit that calculates the valve opening degree of the steam control valve that adjusts the amount of steam flowing into the steam turbine;
A thrust force valve opening calculation unit for calculating the valve opening of the steam control valve according to the thrust force applied to the rotor of the steam turbine;
When the load cutoff signal acquisition unit acquires the load cutoff signal, the steam is calculated based on the valve opening calculated by the rotational speed valve opening calculation unit and the valve opening calculated by the thrust force valve opening calculation unit. A valve opening degree control unit for controlling the valve opening degree of the adjusting valve;
Control system with. The thrust force valve opening calculation unit is a valve based on a time function of the valve opening according to the thrust force applied to the rotor and an elapsed time after the load cutoff signal acquisition unit acquires the load cutoff signal. Calculate the opening,
The valve opening control unit selects a larger value from the valve opening calculated by the rotational speed valve opening calculating unit and the valve opening calculated by the thrust force valve opening calculating unit, and the value is selected according to the selected value. Control the valve opening of the steam control valve,
The control system according to claim 1. The thrust force valve opening calculation unit calculates a valve opening based on a deviation between a target value of thrust force applied to the rotor and a measured value of thrust force applied to the rotor,
The valve opening control unit selects a larger value from the valve opening calculated by the rotational speed valve opening calculating unit and the valve opening calculated by the thrust force valve opening calculating unit, and the value is selected according to the selected value. Control the valve opening of the steam control valve,
The control system according to claim 1. A rotation speed determination unit that determines whether the rotation speed of the rotor exceeds a predetermined limit value;
Further comprising
The thrust force valve opening degree calculation unit sets the calculated valve opening degree to 0 when the rotation number determination unit determines that the rotation number exceeds a predetermined limit value.
The control system according to claim 3. A preceding correction value calculating unit that calculates a preceding correction value of the valve opening according to the output value of the steam turbine;
Further comprising
The thrust force valve opening calculation unit adds the preceding correction value calculated by the preceding correction value calculation unit to the calculated valve opening,
The control system according to claim 3 or claim 4. The valve opening control unit calculates a weighted average of the valve opening calculated by the rotational speed valve opening calculating unit and the valve opening calculated by the thrust force valve opening calculating unit, and calculates the calculated weighted average. The valve opening of the steam control valve,
The control system according to any one of claims 2 to 5.   A steam turbine comprising the control system according to any one of claims 1 to 5.   A power plant comprising the control system according to any one of claims 1 to 5. Obtain a load shedding signal during steam turbine operation,
Based on the deviation between the target rotational speed of the steam turbine and the actual rotational speed, calculate the valve opening based on the rotational speed of the steam control valve that adjusts the amount of steam flowing into the steam turbine;
Calculate the valve opening degree of the steam control valve according to the thrust force applied to the rotor of the steam turbine,
When the load cutoff signal is acquired, the valve opening degree of the steam control valve is controlled by a value based on the valve opening degree based on the rotational speed and the valve opening degree corresponding to the thrust force.
Control method.

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