JPS6149481B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control system for a steam turbine,
In particular, the present invention relates to a control system that suppresses stress in the rotor that occurs due to speed increase and load change to below an allowable value, and enables safe and rapid start-up and rapid load change.

When starting a steam turbine and changing load, it is necessary to suppress fatigue, that is, life consumption, due to thermal stress generated in the thick portion of the turbine to within an allowable value.
Therefore, in order to achieve safe and rapid startup and load changes, it is important to accurately determine and control the generated thermal stress.

During operation of the turbine, stress generation points that should be noted are the rotor surface and bore (center hole) of the first stage rear labyrinth packing, which are exposed to high-temperature, high-velocity leaked steam from the high-pressure and intermediate-pressure turbines. However, the rotor is a rotating body, and it is difficult to actually measure the stress or the temperature distribution that is the basis for stress calculation. Conventionally, methods have been used in which the actually measured inner wall metal temperature of the casing after the first stage is regarded as the rotor surface temperature, or the stress is calculated from the actually measured values of steam temperature and pressure after the first stage. However, the former has a problem with the correlation between the casing and the rotor, and the latter has a problem with measurement accuracy during no-load operation and low load when the flow rate is small. As another method, a method has conventionally been proposed in which the startup schedule is determined according to the main steam conditions immediately before ventilation to the turbine and the turbine metal temperature. However, this method creates a startup schedule with a margin that takes into account that the main steam conditions will deviate from the scheduled values during the startup process.
The startup time tended to be longer than necessary. Therefore, with conventional methods, it has been difficult to achieve rapid startup that effectively utilizes the life consumption allowed for one startup and rapid load changes that faithfully adhere to allowable stress.

In addition, in the conventional system, the boiler generated steam conditions, that is, the main steam temperature, pressure, and reheat steam temperature are controlled independently of the turbine stress control.
The stress generated was not fed back to the boiler control. Therefore, when stress exceeding the stress limit value occurs, the turbine copes with the problem by maintaining speed or maintaining load. However, if the rate of increase in the temperature of the steam actually flowing into the turbine at this time is large, the stress increases even though the speed or load is maintained, often leading to turbine tripping.

The purpose of the present invention is to maintain the conditions of the steam flowing into the turbine when the stress generated in the turbine due to the state changes of the power generation equipment such as load changes and speed increases exceeds the limit value, even if these state changes are stopped or restricted. It is an object of the present invention to provide a control method for a steam turbine that makes it possible to prevent excessive stress from occurring due to changes.

Another object of the present invention is to always optimally determine the rate of change of load change and speed increase to effectively utilize the life consumption of the turbine allowed for one startup, and to reduce the stress generated in the turbine to a limit value. To provide a control system for a steam turbine that makes it possible to set the rate of change as large as possible after that by suppressing the generation of excessive stress as much as possible when the stress exceeds the limit, thereby enabling rapid startup. .

One feature of the present invention is that when the stress generated in the turbine exceeds a limit value, a command is given to the boiler control system to correct target values such as temperature and pressure in accordance with this excess amount. .

Another feature of the present invention is to predict the stress occurring in the turbine while determining the maximum speed and load change rate within a range that does not exceed limit values, and to estimate the stress currently occurring in the turbine. When a limit value is exceeded, a command is given to the boiler control system to correct target values such as temperature and pressure in accordance with the amount of excess.

FIG. 1 shows the relationship of input and output signals between a thermal stress prediction turbine control system 100 and related control systems and plants when a digital computer is used as an embodiment of the present invention. This figure shows the first-stage rear labyrinth packing part 1 of the high-pressure turbine 200 and the first-stage rear labyrinth packing part 2 of the intermediate-pressure turbine 300. In both turbines, high-temperature, high-pressure steam leaks through this area at high speed, so this is the location where the heat transfer between the steam and the metal is most intense. Due to this heat exchange, the rotor in this area produces a temperature distribution in the radial direction, and the rotor surface and bore (center hole)
3, large thermal stress occurs. The basic function of the control system 100 of the present invention is that the thermal stress generated at startup or load change is below a limit value, and the governor 100 determines the optimum acceleration rate 4 allowed under that condition.
or optimal load change rate 6 to ALR
(Automatic Load Regulator) 7 as a setting value. For example, the first stage post-pressure signal P _H1 is fed back to the ALR as a signal that substitutes for the output. An instantaneous target load 9 is applied to the governor 10 from the ALR 7. A speed signal N is fed back to the governor 10. This governor ultimately provides a valve position command 13 to the actuator 12 for controlling the position of the regulating valve 11. The control system 100 of the present invention determines the possibility of load addition from the viewpoint of thermal stress, and issues an addition permission command 15 to the synchronous addition function 14 .

Furthermore, a main steam temperature modification command 113 and a reheat steam temperature modification command 114 are given to the boiler control system 60 in accordance with the amount of generated stress exceeding the limit value.

The present invention realizes rapid start-up and rapid load follow-up performance of the turbine using the method described below based on the heat transfer characteristics of the labyrinth packing parts 1 and 2 and predictive calculation of the thermal stress generated in the rotor.

FIG. 2 shows a processing procedure in the thermal stress prediction turbine control system 100 of the present invention.

First, before turbine ventilation, there is an initial temperature distribution determining function (hereinafter, for simplicity, the display of "function" will be omitted).
The same applies to other calculation prediction and decision functions. )10
1, the initial temperature distribution of the rotor is estimated. Here, the part where the rotor and metal wall thickness are about the same and the temperature distribution tends to be similar, for example, in a high pressure turbine, the first
For the post-stage casing and intermediate pressure turbine, the temperature distribution is estimated from the actual measured values of the metal temperatures of the inner and outer walls of the steam chamber.

In the next stress limit value determination step 102, a stress limit value determined from the allowable life consumption of the rotor corresponding to the startup mode (startup in very hot, hot, warm, cold, etc.) is determined. The stress limit value determined here is a low value at the beginning of startup in order to compensate for the error in estimating the initial value of temperature distribution when the computer is immediately brought online during a rapid restart or during use of computer control, as will be described later. Set.

In prediction time determination 103, it is determined how far in advance stress should be predicted and controlled. This predicted time is determined to be an appropriate value depending on the steam conditions generated by the boiler and the turbine startup sequence.

Steam condition change rate learning 104 is a function for grasping the state of the current boiler dynamic characteristics relative to the operating state of the turbine. Specifically, it is to understand from actual measurements at what rate the turbine inlet steam conditions (main steam temperature, pressure, and reheat steam temperature) change with respect to changes in turbine speed or load. This learning result is used in steam condition prediction 106, which will be described later.

In operation mode determination 105, whether the circuit breaker 16
It is determined whether the mode is speed control mode or load control mode based on the ON/OFF state, and if it is the former, it is sent to the speed control system 160, and if it is the latter, it is sent to the load control system 140.
Switch the processing flow to

In the speed control system 160, the current stress estimation 16
1 estimates the current value of rotor stress. This function has the following functions: first stage post steam condition calculation 107, rotor surface heat transfer coefficient calculation 108, rotor temperature distribution calculation 109, rotor thermal stress calculation 110, and rotor stress calculation 111 considering centrifugal stress.

In the current stress level check 162, it is determined whether the estimated current stress is below a limit value. At this time, if the stress exceeds the limit value at even one point, the speed is maintained as a general rule.

In the next calculation mode judgment 163, it is judged whether the current calculation is the time to search for the maximum acceleration rate based on the predicted calculation, and if it is the time, the process is passed to the maximum acceleration rate search 170; This processing function is bypassed and the processing is passed to the next critical speed judgment 164. In this case, the processing cycle of the current stress estimation 161 is τ ₁ , the processing cycle of the maximum acceleration rate search 170 is τ ₂ , and there is a relationship of τ ₂ =n _T τ ₁ (n _T : integer).

Maximum acceleration rate search 170 includes acceleration rate assumption 171, stress prediction 172, predicted stress level check 173,
It is composed of each processing function of prediction time arrival judgment 174. Furthermore, the stress prediction 172 is the steam condition prediction 1.
06, Steam condition calculation after first stage 107, Rotor surface heat transfer coefficient calculation 108, Rotor temperature distribution calculation 10
9. Rotor thermal stress calculation 110, Rotor stress calculation 1
It consists of 11 processing functions. This maximum acceleration rate search 170 is performed using the acceleration rate [N ₁ ,
N ₂ , . . . _. . . _N first,
The stress after τ ₁ is predicted, including the steam conditions after the first stage. If this predicted stress is less than the limit value, further τ ₁
Predict what will happen next. By repeating this, if all the stresses do not exceed the limit values until the predicted time that has already been determined, the assumed speed increase rate is set as the maximum possible speed increase rate based on the stress. However, in the process of predicting stress in τ ₁ increments, if the predicted value exceeds the limit value before reaching the prediction time, a one rank lower acceleration rate is assumed, and the prediction calculation is performed again in τ ₁ increments from the current point. Proceed. As a result, if the predicted stress does not exceed the limit value, this acceleration rate is adopted.

The dangerous speed judgment 164 is a function that judges whether the current speed is in the dangerous speed region.

Optimum acceleration rate determination 165 is maximum acceleration rate search 170
It has a function to set the maximum speed increase rate found by . Furthermore, if the current stress estimate exceeds the limit value, the speed will be maintained regardless of the search result for the maximum acceleration rate, but if the current speed is in the critical speed range, the speed will be increased at the same acceleration rate as before. Continue speed.

The subsequent steam temperature correction 50 will be explained after the next explanation of the load control system 140.

When the speed increase is completed, the circuit breaker 16 is closed, and a load is added, the operation mode is transferred from the speed control system 160 to the load control system 140.

Current stress estimation 141 in load control system 140
is a function to estimate the current value of rotor stress. This function includes first stage steam condition calculation 107, rotor surface heat transfer coefficient calculation 108, rotor temperature distribution calculation 10
9. Rotor thermal stress calculation 110, Rotor stress calculation 1
It is composed of eleven functions, all of which are shared with the speed control system 160.

In the current stress level check 142, it is determined whether the estimated current stress is below a limit value. At this time, if the stress exceeds the limit value at even one point, the load is maintained.

In the calculation mode judgment 143, it is judged whether the current calculation is the time to search for the maximum load change rate based on the predicted calculation, and if this is the time, the process is passed to the maximum load change rate search 150; otherwise, Bias this processing function to determine the next optimal load change rate 14
Pass the processing to 4. In this case, the current stress estimation 141
The processing period is τ ₁ , and the maximum load change rate search 1
The processing period of 50 is τ ₂ , and τ ₂ = n _T τ ₁
( _nT : integer).

Maximum load change rate search 150 is based on load change rate assumption 1
51, stress prediction 152, predicted stress level check 153, and predicted time arrival judgment 154. Furthermore, the stress prediction 152 is composed of the following processing functions: steam condition prediction 106, first stage post-steam condition calculation 107, rotor surface heat transfer coefficient calculation 108, rotor temperature distribution calculation 109, rotor thermal stress calculation 110, and rotor stress calculation 111. All of these functions are shared with the speed control system. This maximum load change rate search 150 is performed using load change rates prepared in advance [±L ₁ , ±L ₂ , ......±L _X ......±L _P
(%/min)], load change rate assumption 1 in descending order
51, and predict the future value of stress that will occur in this case. The procedure for searching for this maximum load change rate is similar to the procedure for searching for the maximum acceleration rate described above.

The optimum load change rate determination 144 determines the maximum load change rate found by the maximum load change rate search 150.
It has a function to set ALR7, but if the main steam temperature or reheat steam temperature is below the specified value, the signal for load holding, that is, the load change rate of zero, is set to ALR.
Set to 7. This function also has the function of holding the load regardless of the maximum load change rate search result if the current stress estimate exceeds the limit value.

The search signal generation 145 is performed during the load increase control at the time of turbine startup.
This is a function to add flexibility to the learning function of the system and quickly increase the load.

The next steam temperature correction 50 is a function that operates in common during speed increase and load operation. This function controls the main steam temperature for high-pressure turbine rotor stress and the reheat steam temperature for intermediate-pressure turbine rotor stress, depending on the amount of stress generated, that is, the current stress value, which exceeds the limit value. In order to temporarily lower
These are for giving a main steam temperature modification command 113 and a reheat steam temperature modification command 114 to the boiler control system, respectively.

As outlined above, if each function of stress limit value determination 102, prediction time determination 103, speed control system 160, or load control system 140 is operated at a cycle of τ ₁ , control of turbine startup and normal load operation is executed. . This repeated operation is system stop judgment 1
The process continues until a request is made to stop the system at 12.

Next, the details of each of the above functions will be explained in order.

First, the determination 101 of the initial temperature distribution of the rotor will be explained with reference to FIGS. 3 and 4. FIG. 3 is a sectional view of the rotor 40 and casing 41 of the labyrinth packing portion 1 viewed from the axial direction. However, for the intermediate pressure turbine, we will focus on the steam chamber wall instead of the casing 41, but the concept is the same;
Only the high-pressure turbine will be described here.

T _HCO , T _HCI , T _S , T _b , T shown in FIG.
_j (j=1 to m) is the casing outer wall metal temperature, the casing inner wall metal temperature, the rotor surface temperature, the rotor bore temperature, and the temperature of each cylinder when the rotor is divided into m virtual coaxial cylinders. Although it is difficult to actually measure the temperature distribution of the rotor,
Accurately determining the initial value is particularly important for this system, which aims at rapid startup and rapid load changes.

FIG. 4 shows the specific processing contents of this initial temperature distribution determination 101.

When this system starts operating, it estimates the radial temperature distribution inside the rotor from the actually measured casing inner and outer wall temperatures T _HCI and T _HCO . In this case, T
_S and T _b are considered as T _S = T _HCI …………(1) T _b = T _HCI +k _T ( _THCO − T _HCI ) …………(2). k _T in the above equation (2) is a constant determined by the shape of the turbine. The internal temperature distribution is T _S and T _b
is regarded as a value obtained by linear interpolation, and is expressed by the following equation.

T _j =T _S -(T _S -T _b )2j-1/2 m (3) In addition, B in the figure is a variable indicating the magnitude of the temperature gradient in the radial direction inside the rotor. If the gradient is large, the error in estimating the temperature distribution will also be large. When the temperature difference between the inner and outer walls of the casing is larger than the specified value ΔT, B=1, and when it is smaller, B=0. Furthermore, if the current speed N _a is larger than the specified value N _S , the estimation error may become large even if the temperature difference is small, so B=1. This value of B is for reference in the next processing function, stress limit value determination 102.

Stress limit value determination 102 is a function to determine limit values for rotor surface stress and bore stress.
This function will be explained using FIG.

Suppose that the turbine is started at time t ₁ . If the slope of the rotor initial temperature distribution at t ₁ is small,
In other words, when B=0, the stress limit value is the value set by the plant operator (for the rotor surface,
±σ _LS and ±σ _LB for the rotor bore). However, when the slope is large, that is, when B = 1, the stress limit value is set by subtracting the maximum △σ from the value set by the plant operator, as shown in Figure 5, to ensure safety, taking into account the estimation error of the initial temperature distribution. I hope. As this Δσ, a value necessary to compensate for the estimation error of the initial stress is selected. Since the estimation error of the temperature distribution becomes smaller as time passes after startup, Δσ is gradually decreased until Δσ=0 at time t ₂ .

Next, prediction time determination 103 will be explained. What is important in determining the predicted time T _P is the behavior of the reheat steam temperature T _RH immediately after the injection. At the time of merging, the amount of fuel in the boiler increases in steps, so the reheat steam temperature in particular rises rapidly, as shown in Figure 6, and tends to follow the main steam temperature T _MS with almost a first-order lag. . Therefore, even if the initial load is maintained after joining,
Rotor stresses in intermediate-pressure turbines may continue to rise for some time. Therefore, before annexation, this phenomenon should be quantitatively predicted, and after confirming that the resulting stress does not exceed the limit value, annexation permission order 1.
5 will be given to the synchronous join function 14. To do this, as shown in the same figure, the shortest prediction time required is the time t _P at which the stress generated when the initial load is held after insertion reaches its peak, and predictions must be made at least up to this point. When this t _P is determined from the boiler and turbine dynamic characteristics, it can be expressed by the following equation.

t _P =a log _e d/b T _MSA -T _RHA +c……
…(4) Here, a, b, c, d: Constant T _MSA : Current value of main steam temperature T _RHA : Current value of reheat steam temperature In addition, △T _MR = T _MSA − T _RHA …………(5) Then, the relationship between t _P and ΔT _MR is as shown in FIG.

The predicted time after merging will be explained using FIG. 8. It is thought that the change in reheated steam temperature after incorporation shows the dynamic characteristics predicted before incorporation. Therefore, as shown in FIG. 8, the predicted time t _P is also decreased as time passes, using the predicted time t _PO determined immediately before merging. At time t _PO after addition, the predicted time is reduced to t _PL , which is the same as during normal load operation.

Next, the steam condition change rate learning 104 will be explained. What is studied here is the amount of change in three state quantities: main steam temperature T _MS , main steam pressure P _MS , and reheat steam temperature T _RH with respect to the amount of change in speed or load. Since both methods are learned in the same way, the case of main steam temperature will be explained as an example in FIG. 9. Further, this learning method is carried out in exactly the same manner when the speed is increased, but here, the case when the load is increased will be explained.
Accurate stress prediction begins with highly accurate prediction of turbine inlet steam conditions. However, this steam condition is closely related to the operating status of the turbine.
It is not easy to uniquely express this correlation as a dynamic characteristic model. Therefore, as shown in Fig. 9, the ratio of the load △L and the main steam temperature △T _MS that changed between the current time t and the past nτ ₁ (n: integer) is defined as the rate of change, △T _MS /△L = T _MS ( t)-T _MS (t-nτ ₁ )/L(t)-
L(t-nτ ₁ )...(6) is learned. This makes it possible to predict the rate of change in main steam temperature for any rate of load change.

Next, each processing function of the speed control system 160 when the circuit breaker 16 is in the OFF state will be specifically explained.

First, the current stress estimation 161 will be explained. As mentioned above, this processing function includes the first stage post-steam condition calculation 107, rotor surface heat transfer coefficient calculation 108, rotor temperature distribution calculation 109, which is also used in the load control system.
Rotor thermal stress calculation 110, rotor stress calculation 111
It consists of each processing function. A step-by-step explanation will be given below.

The first-stage post-steam condition calculation 107 is a function that calculates the first-stage post-steam temperature and pressure of the high-pressure and intermediate-pressure turbines from arbitrary main steam conditions, turbine speed, speed increase rate, load, and reheat steam temperature. It is difficult to measure the steam temperature and pressure after the first stage of high-pressure and intermediate-pressure turbines with high accuracy in operating conditions where the steam flow rate is small, such as during speed increase and low load. Also, if you rely on actual measurements, you cannot expect highly accurate predictions.
FIG. 10 shows a calculation procedure for uniquely estimating from the steam conditions generated by the boiler and the operating state of the turbine to solve this problem. This estimation method can be used consistently from startup to normal load operation by using main steam temperature T _MS , pressure P _MS , reheat steam temperature T _RH , speed N, speed increase rate N〓, and load L as input variables. can. However, for safety reasons, the steam temperature after the first stage of the intermediate pressure turbine is assumed to be the actual value of the reheated steam temperature assuming that there is no temperature drop due to the first stage. The meanings of the symbols used in FIG. 10 are as follows.

N: Speed (rpm) N _O : Rated speed (rpm) N〓: Speed increase rate (rpm/min) L: Load (%) L': Equivalent load under rated steam conditions (%) L ₁ : All-round injection and mixed injection boundary load (%) L ₂ : Boundary load (%) between partial injection and mixed injection T _MS : Main steam temperature (°C) T _RH : Reheat steam temperature (°C) T _MSR : Rated main steam temperature ( ℃) T ₁ ′: Steam temperature after the first stage of the high-pressure turbine relative to L′ (℃) △T ₀ : Temperature drop between the main steam temperature and the steam temperature in the high-pressure turbine bowl (℃) △T _R0 : Temperature drop at the rated steam condition △T ₀ (°C) T _H1 : Steam temperature after the first stage of the high pressure turbine (°C) T _I1 : Steam temperature after the first stage of the intermediate pressure turbine (°C) P _MS : Main steam pressure (ata) P _I0 : No-load operation Equivalent steam pressure after the first stage of the high pressure turbine (ata) P _H1R : Steam pressure after the first stage of the high pressure turbine at rated load (ata) P _I1R : Steam pressure after the first stage of the intermediate pressure turbine at rated load (ata) P _H1 : Steam pressure after the first stage of the high pressure turbine (ata) P _I1 : Steam pressure after the first stage of the intermediate pressure turbine (ata) K ₁ : Control valve throttling rate (k ₁ = 0 at all times during partial injection) K ₂ : Temperature reduction coefficient due to the first stage of the high-pressure turbine K _NL : Steam pressure after the first stage of the high-pressure turbine equivalent to no-load loss at rated speed (ata) K _AC : Steam pressure after the first stage of the high-pressure turbine equivalent to acceleration (ata/(rpm) ) ² /min) k: No-load loss index The processing contents of rotor surface heat transfer calculation 108 are as follows.
As shown in Figure 1, we will focus on turbulent heat transfer from steam leaking through the labyrinth packing section 1 after the first stage.
However, although FIG. 11 shows the high-pressure turbine, the heat transfer coefficient is also determined using the same procedure for the intermediate-pressure turbine. The meanings of the symbols used in this figure are as follows.

N: Speed (rpm) T _H1 : Steam temperature after the first stage of the high pressure turbine (℃) P _H1 : Steam pressure after the first stage of the high pressure turbine (ata) λ _1ST : Steam thermal conductivity after the first stage of the high pressure turbine (kca)
l/m・℃・sec) ν _1ST : Steam kinematic viscosity coefficient after the first stage of the high-pressure turbine (m ² /sec) γ _1ST : Specific weight of the steam after the first stage of the high-pressure turbine (Kg/
m ³ ) F _SL : Labyrinth packing part leakage flow rate (Kg/sec) F _SLV : Labyrinth packing part volumetric leakage flow rate (m ³ /
sec) U _AX : Axial leakage flow velocity at the labyrinth seal (m/sec) U _RD : Rotor surface speed at the labyrinth seal (m/sec) U: Synthetic leakage flow velocity at the labyrinth seal (m/sec)
c) R _e : Reynolds number N _u : Nutsselt number K : Rotor surface heat transfer coefficient (kcal/m ²・℃・sec) K ₀ : Constant determined by turbine shape δ : Gap between labyrinth packing (m) d : Rotor Surface diameter (m) Z: Number of fins of labyrinth packing A: Gap area of labyrinth packing (m ² ) r _S : Rotor surface radius (m) P _H2 : Pressure after second stage of high pressure turbine (ata) However, Fig. 11 The pressure ratio (P ₂ /P ₁ ) after the first stage and after the second stage is obtained by assuming that it is almost constant even if the operating state of the turbine, that is, the speed, acceleration rate, and load change, so it is actually a constant. Calculate as.

Next, regarding the rotor temperature distribution calculation 109, the first
This will be explained using Figure 2. Since heat transfer inside the rotor can be considered as a one-dimensional flow consisting only of the radial direction,
As shown in FIG. 12, the rotor is divided into m virtual cylinders, and the temperature distribution is determined by focusing on the heat balance between each cylinder. If the step width for heat balance calculation is τ ₁ , then Q _f , _S is the amount of heat transferred from the steam to the rotor surface during τ ₁ , and Q _S , ₁ is the amount of heat transferred from the rotor surface to the outermost cylinder center. The amount of heat, Q _j , _j+1 is the amount of heat conducted from the j-th cylinder to the j+1-th cylinder.
However, since the bore is in an adiabatic state, Q _n and _n+1 are always 0. Now, assuming that the current time is t, the amount of heat transfer that occurs between each cylinder during τ ₁ from time t-τ ₁ to t is expressed as follows.

Q _f , _S (t) = 2πr _S K (t) (T _H1 (t) - T _S (t - τ ₁ )) τ ₁ ...... (7) Q _S , ₁ (t) = 2π (r _S +3/4△r)λ _M T _S (t-τ ₁ )-T ₁ (t-τ ₁ )/△r/2τ ₁ ......
(8) Q ₁ , ₂ (t)=2πr ₂ λ _M T ₁ (t−τ ₁ )−T ₂ (t−τ ₁ )/△rτ ₁ ………(9) Q _j , _j+1 ( t)=2πr _j+1 λ _M T _j (t−τ ₁ )−T _j+1 (t−τ ₁ )/△rτ ₁ ………(10) Q _n , _n+1 (t)=0…… ...(11) Here, λ _M is the thermal conductivity of the rotor material.

From the relationship Q _f , _S (t)=Q _S , ₁ (t), T _S (t
−τ) is expressed by the following equation.

T _S (t-τ ₁ ) = r'T ₁ (t-τ ₁ )+2r _S W (t) T _H1 (t
)/r+2r _S W(t)…………(12) Here, r'=4r ₂ +3△r W(t)=△rK(t)/λ _M Amount of heat accumulated in the j-th cylinder △Q _j (t) is △Q _j (t)=Q _j-1 , _j (t)-Q _j , _j+1 (t)
......(13) Therefore, the temperature T _j of the j-th cylinder is expressed by the following equation.

T _j (t)=T _j (t-τ ₁ ) +△Q _j (t)/v _j ρ _M c _M …………(14) where v _j :J-th middle cylinder per unit length Volume ρ _M : Density of rotor material c _M : Comparison of rotor materials Further, the rotor bore temperature T _b (t) is expressed by the following equation by approximating the temperature distribution by a quadratic equation.

T _b (t) = 1/8 (9T _n (t) - T _n-1 (t))...
(15) FIG. 13 shows the detailed procedure of this processing function described above.

Next, rotor thermal stress calculation 110 will be explained.

Rotor thermal stress, i.e. rotor surface thermal stress σ _ST
The rotor bore thermal stress σ _BT is expressed by the following equation based on the temperature distribution obtained by the rotor temperature distribution calculation 109 described above.

σ _ST =Eα/1−ν(T _M −T _S )…………(16) σ _BT =Eα/1−ν(T _M −T _b )…………(17) Here, E: Rotor material Young's modulus α: Coefficient of linear expansion of rotor material ν: Poisson's ratio of rotor material T _S : Rotor surface temperature T _b : Rotor bore temperature T _M : Rotor volume average temperature Note that the rotor volume average temperature T _M is expressed by the following formula. .

Next, rotor stress calculation 11 considering centrifugal stress
1 will be explained. The centrifugal stress is the turbine speed N
Since it is proportional to the square of , if the rated speed is N ₀ and the bore centrifugal stress at the rated speed is σ _BCR , the centrifugal stress σ _BC acting on the bore at the speed N is expressed by the following equation.

σ _BC =σ _BCR (N/N ₀ ) ² ………(19) Therefore, the bore stress σ _B is σ _B =σ _BT +σ _BC ………(20). Note that stress concentration occurs on the rotor surface due to the surface shape, and the direction of action of thermal stress is the axial direction. Considering that the centrifugal stress is in the circumferential direction, both act in directions perpendicular to each other. Therefore,
Regarding the rotor surface stress, it is only necessary to consider the thermal stress for which life consumption is a problem, and the rotor surface stress σ
_S is σ _S =σ _ST …………(21).

This completes the explanation regarding the current stress estimation 161.

The next current stress level check 162 is a function of determining whether or not the above-mentioned σ _S and σ _B exceed the stress limit value set in the stress limit value determination 102 described above.

The next calculation mode determination 163 is a function of determining whether or not the current calculation is the time to perform a search for the maximum acceleration rate based on the predicted calculation. In other words, if you specify to perform predictive calculation once every n times,
This processing function 163 has the function of bypassing the maximum acceleration rate search 170 n-1 times out of the times.

Next, the maximum acceleration rate search 170 will be explained.
This processing function uses the current time as a reference to predict the stress that will occur on the rotor surface and rotor bore until after the prediction time t _P determined in the prediction time determination 103 in time steps (τ ₁ ), and each time, This function compares the stress limit value and searches for the maximum acceleration rate at which the stress during this period does not exceed the limit value. The acceleration rate here is selected from a plurality of acceleration rates prepared in advance based on the acceleration rate assumption 171. The plurality of acceleration rates are passed to the stress prediction 172 in order from the largest one based on the acceleration rate assumption 171. The processing function of this stress prediction 172 first predicts the stress on the rotor surface and bore after τ ₁ from the current time, and the predicted stress level check 173 compares it with the stress limit value. As a result of this comparison, if both stresses are less than the limit value, the process returns to stress prediction 172 and further predicts the stress after _τ1 . In this way, stress is predicted at _intervals of _{τ until after t P for} a given acceleration rate assumption N If the value is exceeded, the process is returned to the acceleration rate assumption 171, the assumed acceleration rate value is changed, and stress is similarly predicted. In this case, the assumption of the acceleration rate is made in ascending order, and in the predicted time arrival judgment 174, the stress predicted value for the assumed acceleration rate value is
If the limit value is not exceeded over _P , the assumed acceleration rate at this time is determined as the maximum acceleration rate, and the search is completed. If the stress exceeds the limit value for all the assumed values of the acceleration rate, the acceleration rate is set to zero as the maximum acceleration rate search result. Note that the processing content of the stress prediction 172 is similar to that of the current stress estimation 161 described above. The difference is that the turbine inlet steam condition uses a predicted value instead of the current value, and the speed uses the predicted value corresponding to the assumed speed increase rate instead of the current value. In order to predict this turbine inlet steam condition, the result of learning the ratio of the amount of change in steam condition to the amount of load change is used, as explained in FIG. 9 and equation (6). In other words, the rate of change over time of the main steam temperature with respect to the assumed value _NX of the speed increase rate is expressed by the following equation.

(dT _{MS / dt} ) _NX = △T _MS / _{△ NN〓}
τ ₁ ) _N 〓
This judgment result has an important meaning in the next optimum acceleration rate determination 165. Note that this optimum acceleration rate determination 165 has already been described.

As explained above, the setting of the optimal acceleration rate is nτ
However, the current value of the stress is monitored every ₁ period τ ₁ , and if this value exceeds the limit value, the speed is maintained, so the turbine inlet may be affected by disturbances etc. that were not taken into account at the time of prediction. Turbine speed increase control is performed safely even when steam conditions fluctuate.

Next, each processing function of the load control system 140 when the circuit breaker 16 is in the ON state will be specifically explained.

Current stress estimation 14 in load control system 140
1. The processing methods of current stress level check 142, calculation mode judgment 143, and maximum load change rate search 150 are basically the same as the respective processing functions 161, 162, 163, and 170 of the speed control system 160. However, while the speed control system 140 searches for the maximum speed increase rate, the load control system 16
When the value is 0, the only difference is that the load change rate is the target of the maximum value search.

The load change rate assumption 151 in the maximum load change rate search 150 is such that if the load request L _R is a load increase request for the current load, it is assumed in descending order of the load change rates prepared in advance, and vice versa. If it is a load drop request, the requests are assumed in descending order of magnitude (larger negative rate of change).

Next, the optimum load change rate determination 144 will be explained. This processing function 144 has the following two functions. One is to set the load change rate searched at a cycle of τ ₁ in the maximum load change rate search 150 in ALR7, and modify this, and if the current stress exceeds the stress limit value during nτ ₁ . Another is the load limiting function, which sets an upper limit on the load depending on the main steam conditions, when a large load is applied when the main steam temperature or reheat steam temperature is low. This function is to prevent erosion of the final stage blades of the low pressure turbine. This load limiting method is as shown in Figures 14 and 15.
In this method, the lower limit values of the main steam temperature and the reheat steam temperature are determined from the limit value of the final stage humidity of the low-pressure turbine, and if both limit values cannot be satisfied, the load is maintained. That is, FIG. 14 shows the load limitation based on the main steam temperature, and the load is maintained unless the main steam temperature exceeds the lower limit T _MSL that meets the main steam pressure P _MS . Further, Fig. 15 shows load limitation based on the reheat steam temperature, and if there is no reheat steam temperature equal to or higher than the lower limit value T _PHL that meets the load L, the load is maintained.

Next, search signal generation 145 will be explained. As a method for predicting the rate of change in steam conditions, see Figure 9 and (6).
Learn the rate of change in steam conditions using the method shown in the formula,
Based on this, a method is used to predict future values. However, if some kind of disturbance occurs in the boiler and the steam conditions suddenly rise, as is clear from equation (6), the rate of change in the steam conditions will be learned and stored at a greater rate than in normal times. In such a case,
The stress will be predicted to be larger than the actual stress, and even though the actual stress is sufficiently smaller than the limit value, a long-term load retention phenomenon may occur, and there is a risk that the load cannot be increased. The search signal generation 145 is
This function prevents this phenomenon. In this specific method, a search signal ΔL _EX as shown in FIG. 16 is superimposed on the load, and changes in steam conditions at that time are learned in the same manner as in equation (6). In this case, the already learned rate of change (ΔT _MS /ΔL) is corrected by the newly learned rate of change (ΔT _MS /ΔL _EX ) using the search signal. The correction method uses a weighting coefficient β as shown in the following equation.

△ _TMS /△L≡β(△ _TMS /△ _LEX )+(1-β
) (△T _MS /△L) (23) Next, this search signal △L _EX is generated at the same period as the maximum load change rate search period nτ ₁ , but the change rate L _EXR = △L _EX / τ ₁ ......(24) is determined as follows and set in ALR7.
Now, among the values obtained by normalizing the current pressure on the rotor surface and bore of the high/intermediate pressure turbine by the limit value, the value with the maximum absolute value is defined as σ _MN . That is, it is expressed by the following equation.

σ _MN ≡M _aX (|σ _HS /σ _LS |, |σ _IS /σ _LS |, |σ _HB /σ _LB |, |σ _IB /σ _LB |) (25) Here, σ _LS : Rotor surface stress limit Value σ _LB : Rotor bore stress limit value σ _HS : High pressure turbine rotor surface stress σ _IS : Intermediate pressure turbine rotor surface stress σ _HB : High pressure turbine rotor bore stress σ _IB : Intermediate pressure turbine rotor bore stress Depending on this σ _MN , The rate of change L _EXR of the search signal as shown in FIG. 17 is determined.

The steam condition change rate learning 104 has a learned value correction function using a search signal as described above;
In addition, it has a so-called forgetting property, which means that the learned value is forgotten over time. That is, until new learning is performed, the learned value of the steam condition is forgotten according to the forgetting characteristic shown by the following equation.

△T _MS /△N≡ (1-τ ₁ /τ _F ) (△T _MS /△N
)……(26) △T _MS /△L≡(1-τ ₁ /τ _F ) (△T _MS /△L
)...(27) If the learning results are corrected at a period of τ ₁ according to equations (26) and (27), a forgetting characteristic with a time constant τ _F is obtained.

From the time of joining at turbine startup to the low load range,
Response of turbine inlet steam conditions to load increase;
In particular, the temperature increase characteristics of the reheat steam temperature change significantly.
Specifically, the time constant of temperature rise changes significantly. In order to effectively utilize the steam condition change rate learning function in such cases, it is necessary to modify the operating cycle, that is, the setting cycle of the optimal load change rate for ALR, in response to changes in the time constant. . In order to realize this, the calculation mode determination 143 of the load control system 140 is provided with the function shown in FIG. That is, in a low load region, the maximum load change rate search period is made larger than nτ ₁ to ensure that the response of steam conditions with a large time constant is learned, and then the maximum load change rate search 150 is operated. .

Next, the steam temperature correction 50 will be explained using FIGS. 19 and 20. FIG. 19 shows the process state behavior in a case where the current stress value exceeds the limit value due to a large rate of increase in the turbine inlet steam temperature despite the turbine speed or load being maintained. The figure particularly shows the load operation. Curves -a, b, and c in the figure are the process states without this function, that is, the steam temperature correction 50, where -a is the stress normalized to the stress limit value, -b is the steam temperature, and -c is the process state without the steam temperature correction 50. Indicates load. However, for convenience, -a indicates the stress at a specific stress point. Moreover, -b also indicates the main steam temperature or the reheat steam temperature for convenience. The curve shows the stress limit value. Curves - a, b, c are the process conditions when the steam temperature correction 50 is activated;
They correspond to -a, b, and c, respectively. The curve shows the steam temperature correction width when the current stress value exceeds the limit value, and this correction width ΔT is given as a negative bias to the basic setting value of the steam temperature by the boiler control system 60 shown in the curve. This is for modifying the steam temperature set value in a curve-like manner. This is to quickly eliminate the excess amount of stress Δσ and prevent the occurrence of excessive stress. In this way, t+ when the stress becomes less than the limit value
After τ ₂ , the steam temperature correction width △T is set to t+2τ ₁
Decrease from the value of time with a predetermined time constant,
Gradually return to the basic settings. FIG. 20 specifically shows the contents of the processing described below. First, the amount in excess of each limit value of the current value of stress occurring on the rotor surface and rotor bore of the high-pressure and intermediate-pressure turbines is normalized and expressed by the following equation.

△σ ^* _HS (t)=|σ _HS (t)/σ _LS (t)|-
1…………(28− a) △σ ^* _HB (t)=｜σ _HB (t)/σ _LB (t)｜−
1…………(28− b) △σ ^* _IS (t)=｜σ _IS (t)/σ _LS (t)｜−
1…………(28− c) △σ ^* _IB (t) = |σ _{IB (t)} /σ _LB (t) | −
1…………(28-d) Next, by selecting the larger excess amount of surface stress and bore stress, △σ _H (t) and △σ _I (t) for the high-pressure turbine and the intermediate-pressure turbine are It is expressed by the following formula.

△σ _H (t)=M _aX (△σ ^* _HS (t), △σ ^* _HB (t), 0) …………(29-a) △σ _I (t)=M _aX (△σ ^* _IS (t), △σ ^* _IB (t), 0) …………(29-b) In order to eliminate this excess stress, _the main steam temperature is , the reheat steam temperature is lowered for Δσ _I (t) of the intermediate pressure turbine. In other words, the rotor surface temperature after the first stage quickly responds to changes in the steam temperature in contact with it, and the change in steam temperature after the first stage is approximately equal to the amount of change in the turbine inlet steam temperature, and the rotor temperature and stress This is because the relationship is shown by equation (16). Therefore, the main steam temperature correction range △T _MS
Set (t) and reheat steam temperature correction range △T _{RH S
et} (t) has a size expressed by the following equation.

△T _{MS Set} (t)=1−ν/Eασ _H (t)…………(3
0 −a) △T _{RH Set} (t)=1−ν/Eα△σ _I (t) ………… (30−b) However, as shown after t+τ ₂ in the example shown in Fig. 19, the stress If it is below the limit value, it is returned to zero using an exponential function with a time constant τ _S shown by the following equation.

△T _{MS Set} (t) = △T _{MS Set} (t - _{τ 1} ) (1-τ ₁ /τ _S ) ...... (31-a) △T _{RH Set} (t) = △T _{RH Set} (t -τ ₁ ) (1-τ ₁ /τ _S ) ...... (31-b) Although the above temperature correction width was made proportional to the amount of excess stress, this method does not necessarily have to be used. For example, when the stress exceeds a limit value, a method may be adopted in which the temperature correction range is made proportional to the time integral value of the amount of excess force. In this case as well, if the stress falls below the limit value, equation (31) is applied to return it to the basic setting value.

Further, in the above embodiment, it is assumed that the fluctuation range of the turbine inlet steam temperature and the fluctuation range of the steam temperature after the first stage are approximately equal, but especially in a high-pressure turbine, the temperature drop at the control valve is large. As a more strict method, the following may be used. In other words, as already explained in Fig. 10, the steam conditions after the first stage can be determined from the turbine operating state and the main steam temperature and pressure, so if this relationship is used inversely, the desired main steam temperature can be determined. The correction width can be determined. An example of a method of using this inversely is, for example, a method of convergence calculation that utilizes the calculation procedure shown in FIG. 10 as it is.

All of the above methods aim to suppress excessive stress by modifying the steam temperature at the turbine inlet.
For high-pressure turbines, the same effect can be obtained by modifying the main steam pressure. That is, this is a method that utilizes the temperature drop caused by the throttle of the control valve. This is done by taking advantage of the fact that when the main steam pressure is increased, the control valve is throttled to keep the turbine load constant, and the turbine inflow steam temperature decreases accordingly. The correction width of the main steam pressure in this case can also be determined using the calculation procedure shown in FIG.

In the various embodiments described above, the following effects can be expected. In other words, in each of these examples, the maximum load change rate that is allowed by predicting the stress that will occur in the turbine in the future,
Alternatively, the rate of speed increase may be determined periodically, and when the currently occurring stress exceeds the limit value, the target value of the steam conditions applied to the boiler control system may be corrected to prevent future excessive stress from occurring. is possible. Therefore, even if the stress once exceeds the limit value, the next time the load change rate or speed increase rate is determined, it can be set to a somewhat larger value again, making it possible to start up quickly as a whole, and to improve the turbine speed. This makes it possible to avoid situations that may lead to trips.

By the way, the present invention is not applied only to a control system having a stress prediction function as described above. For example, assume that the load change rate and speed increase rate are given predetermined values in some way (it may be one type of load change rate or speed increase rate), and this estimated value is limited by only having the function of estimating the current stress. When the stress exceeds the stress, the load and speed may be maintained, and the target values of the steam temperature, pressure, etc. of the boiler control system may be corrected in accordance with the amount of excess stress. Even in this case, it is possible to prevent excessive stress from occurring subsequently due to a change in the steam conditions flowing into the turbine, and the effect of preventing a situation leading to a turbine trip can be expected.

[Brief explanation of the drawing]

FIG. 1 shows the input/output signal relationship between the thermal stress prediction turbine control system of the present invention, the related control system, and the plant, FIG. 2 shows the processing procedure in the control system of the present invention, and FIG. 3 shows the cross-section of the rotor and casing after the first stage of the turbine and their temperature conditions. Fig. 4 shows the method for determining the initial temperature distribution of the rotor. Fig. 5 shows the stress limit values for the rotor surface and bore. Figure 6 shows the relationship between the dynamic characteristics of turbine inlet steam temperature and thermal stress immediately after loading is added. Figure 7 shows the predicted time before loading. Figure 8 shows the predicted time after loading. Figure 9. Figure 10 shows the method of estimating the steam condition after the first stage, Figure 11 shows the method of calculating the heat transfer coefficient of the labyrinth packing, and Figure 12 shows the method of learning the rate of change of steam conditions. Figure 13 shows the concept of heat balance between virtual divided cylinders. Figure 13 shows the specific calculation procedure for rotor temperature distribution. Figure 14 shows the lower limit of main steam temperature for load limitation. Figure 15 shows the load limit. No. 16 indicating the lower limit of reheat steam temperature for restriction.
The figure shows the search signal, Figure 17 shows the method for determining the rate of change of the search signal, Figure 18 shows the method for determining the operation cycle, and Figure 19 shows the effect of stress control by the steam temperature correction function in the present invention. FIG. 20 shows the processing procedure of the steam temperature correction function. 100...Thermal stress prediction turbine control system,
200... High pressure turbine, 300... Intermediate pressure turbine, 400... Low pressure turbine, 500... Generator, 1... High pressure first stage rear labyrinth packing part,
2... Intermediate pressure first stage rear labyrinth packing part, 3...
...Bore (center hole), 4...Optimum speed increase rate, 6...Optimum load change rate, 7...ALR, 9...Momentary target load, 10...Governor, 11...Adjustment valve, 12...
Actuator, 13... Valve position command, 14...
Synchronous annexation function, 15... annexation permission command, 16...
Circuit breaker, 17... Circuit breaker ON/OFF status, 18...
... Load requirement value, 19 ... Speed, 20 ... Main steam,
21...Reheat steam, 22...Adjustment valve position, 23...
...Main steam pressure, 24...Main steam temperature, 25...Reheat steam temperature, 26...Casing outer wall temperature after high pressure first stage, 27...Casing inner wall temperature after high pressure first stage, 28...High pressure first stage Post-stage steam pressure, 29...Intermediate pressure steam chamber outer wall temperature, 30...Intermediate pressure steam chamber inner wall temperature, 50...Steam temperature correction, 60...Boiler control system, 140...Load control system, 160...Speed Control system, 150... Maximum load change rate search, 170...
Maximum acceleration rate search, 101... initial temperature distribution determination,
102... Stress limit value determination, 103... Prediction time determination, 104... Steam condition change rate learning, 105...
...Operation mode judgment, 106...Steam condition prediction, 1
07... First stage post-steam condition calculation, 108... Rotor surface heat transfer coefficient calculation, 109... Rotor temperature distribution calculation, 110... Rotor thermal stress calculation, 111...
Rotor stress calculation, 112... System stop judgment,
141...Current stress estimation, 142...Current stress level check, 143...Calculation mode judgment, 14
4...Optimum load change rate determination, 145...Search signal generation, 151...Load change rate assumption, 152...Stress prediction, 153...Predicted stress level check, 1
54... Judgment of arrival of predicted time, 161... Current stress estimation, 162... Current stress level check, 16
3...Calculation mode judgment, 164...Critical speed judgment, 165...Optimum acceleration rate determination, 171...Acceleration rate assumption, 172...Stress prediction, 173...Predicted stress level check, 174...Predicted time arrival judgment .

Claims (1)

[Claims] 1. A boiler that generates main steam for driving a turbine;
A boiler control device that controls the steam pressure of main steam generated in the boiler to a predetermined target value, a turbine driven by the main steam from the boiler, a turbine control valve that controls the flow rate of steam flowing into the turbine, the turbine and the machine. In a control system for a power plant comprising a generator and a generator coupled to each other, a first controller for estimating stress generated in the turbine;
A control device for a power plant, comprising: means for correcting a target value of steam pressure of the boiler control device according to an amount in excess of the estimated stress with respect to a stress limit value.