JPS586041B2 - Load addition method for turbine power plant - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control system for a steam turbine, and in particular, suppresses stress in the rotor that occurs due to speed increases and load changes to below an allowable value, and enables safe and rapid load addition. This article relates to a load merging method.

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 turbine operation, stress generation points should be noted at the first point of the high-pressure and intermediate-pressure turbine, which is exposed to high-temperature, high-speed leakage steam.
These are the rotor surface and bore (center hole) of the post-stage labyrinth packing.

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, the actually measured inner wall metal temperature of the casing after the first stage has been regarded as the rotor surface temperature, or the stress has been calculated from the actually measured values of the 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, in this method, the startup time tends to be longer than necessary because the startup schedule is created with a margin that takes into account that the main steam conditions may deviate from the scheduled values during the startup process.

Therefore, with conventional methods, it has been difficult to achieve a rapid start-up that effectively utilizes the life consumption allowed for one start-up or a rapid load change that faithfully adheres to the allowable stress.

Therefore, even under changing main steam conditions, we have made effective use of the life consumption allowed for one startup, enabled safe and rapid startup, and achieved rapid load changes that faithfully adhere to the allowable stress. In order to make this possible, we use the speed increase rate at startup and the load change rate at load operation as control parameters, predict the thermal stress in a given part of the turbine in accordance with the assumed values of these control parameters, and compare this with the allowable stress. It was proposed to determine the optimal control parameters.

By the way, when a load is added to a turbine power plant, the boiler combustion charge changes in a stepwise manner, so the turbine inlet steam conditions change significantly after the load is added, and in particular, the rise in reheat steam temperature is large.

Therefore, depending on the conditions at the time of adding a load, there is a risk that multiple stresses may be generated. It is desirable to allow.

However, the rise in resteaming steam temperature tends to follow the main steam temperature with a first-order lag, and therefore the stress generated due to the addition of a load reaches its maximum value quite late after the addition of the load, and even reaches its maximum value. The time it takes to reach this point varies depending on the steam conditions at the time of load addition.

Therefore, even if stress is to be predicted, the problem is how far into the future should the prediction be made to determine whether or not to add a load.If the prediction time is taken too long to allow for a margin, it will put a burden on the computer for stress prediction calculations. This increases the size of the load, and as a result, there is a delay in determining whether or not load can be added, resulting in a disadvantage that rapid startup is not possible.

On the other hand, if the prediction time is set short, load addition may be performed based on incorrect judgment, which may end up consuming the life of the turbine.

The present invention was made in view of these problems, and its purpose is to reduce the burden on the computer for stress prediction calculations, perform sufficient stress prediction, and effectively utilize the life consumption of the bin. An object of the present invention is to provide a turbine control method that allows rapid startup.

The first feature of the present invention is the time taken from the current value of the main steam temperature and the current value of the reheat steam temperature until the peak value of stress appears when the load is added at the current moment and the initial load is maintained. is predicted in advance, future values of stress are sequentially predicted after the elapse of this predicted time, and when these predicted values are within the stress limit value, load addition to the turbine generator is allowed.

The second feature of the present invention is that when adding a load, the stress after adding the load is sequentially predicted at a predetermined time interval when the load is added at the current time and the initial load is maintained, and This is repeated until the stress appears, and when this extreme value is within the stress limit value, the load is allowed to be added.

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.

This is the location where the heat transfer between the steam and the metal is most intense, as high-temperature, high-pressure steam leaks from both turbines at high speed.

This heat transfer causes a temperature distribution in the radial direction of the rotor in this vicinity, and a large thermal stress is generated in the rotor surface and bore (center hole) 3.

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,
The optimal speed increase rate 4 allowed under those conditions is determined by the governor 10.
or by setting the optimum load change rate 6 to ALR (Automatic
ticLoad Regulator) 7 as a setting value.

For example, the first stage post-pressure signal PHt is fed back to the ALR as a signal for changing the output.

An instantaneous target load 9 is applied to the governor 10 from the ALD 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 point of view of thermal stress, and sends the synchronous addition permission command 1 to the synchronous addition function 14.
Give 5.

This embodiment 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 a thermal stress prediction turbine control system 100 that is an embodiment of the present invention.

First, the initial temperature distribution determination function (hereinafter referred to as
For simplicity, the display of "functions" is omitted.

The same applies to other calculation prediction and decision functions.

) 101, the initial temperature distribution of the rotor is estimated.

Here, the temperature distribution is determined from the actual measured values of the temperature of the inner and outer wall metals of the steam chamber in the casing after the first stage in a high-pressure turbine, and the inner and outer walls of the steam chamber in a φ-pressure turbine. Estimate.

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.) states 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.

Prediction time determination 103 determines how far in advance the 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, and is set to a value that will be described in detail later, especially after the turbine speeds up and when load is added.

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

In the speed control system 160, the current stress estimation 161 estimates the current value of the 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 or not the current calculation is the time to search for the maximum speed increase rate based on the predicted calculation or to perform the annex permission judgment. If not, this processing function is bypassed and the process is passed to the next critical speed judgment 164.

In this case, the processing cycle of the current stress estimation 161 is τ, and the processing cycle of the best dog acceleration rate search 170 is τ2.
-nTτ1 (nT: integer).

Next, in the rated speed attainment determination 180, the turbine speed N is the rated speed N.

It is determined whether or not the vehicle has reached the vicinity, and if it has, the processing is passed to the annexation permission judgment 190, and if not, the process is passed to the maximum acceleration rate search 170 since the vehicle is still being promoted.

Maximum acceleration rate search 170 uses acceleration rate assumption 171 and stress prediction 1
72, predicted stress level check 173, and predicted time arrival judgment 174.

Further, the stress prediction 172 includes a steam condition prediction 106, a first stage post-steam condition calculation 101, a rotor surface heat transfer coefficient calculation 108,
Rotor temperature distribution calculation 109, mouth-evening heat stress calculation 110,
It is composed of each processing function of rotor stress calculation 111.

This maximum acceleration rate search 170 is performed using a previously prepared acceleration rate [N1
, N2, . . . Nx, .

First, the stress after τ1 is predicted, including the steam conditions after the first stage.

If this predicted stress is less than the limit value, further prediction is made after τ1.

By repeating this process, if all stresses do not exceed the limit values until the predetermined predicted time, 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 τ1 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 proceeds again in τ1 increments from the current time.

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.

The optimal speed increase rate determination 165 has a function of setting the maximum speed increase rate found by the widest speed increase rate search 170 to the governor 10, but if the current speed of the turbine is in the critical speed region, the speed increase rate is not changed. , has the function of continuing the speed increase at the previous speed increase rate.

Furthermore, if the current stress estimate exceeds the limit value, this function will maintain the speed regardless of the search result for the maximum acceleration rate, but if the current speed is in the critical speed area, the same acceleration rate as the previous one will be maintained. Continue accelerating.

In the annexation permission determination 190, it is first assumed that the initial load annexation has been carried out at the present time in the initial load annexation assumption 191, and then the future value of stress after annexation is predicted.

First, the stress prediction 192 predicts the stress after τ1 has elapsed using steps similar to the stress prediction 172 described above, and then the predicted stress level check 193 checks whether the predicted stress exceeds the stress limit value. If it exceeds the limit, the initial load addition judgment process is terminated and the next processing synchronization is waited for.

If the predicted time has not been exceeded, it is determined whether the predicted time has been reached in the predicted time arrival judgment 194, and if the predicted time has not been reached, the stress prediction and predicted stress level check processes described above are repeated, and the stress is predicted in τ1 increments. I do.

If the predicted stress reaches the predicted time without exceeding the stress limit value, the merging permission command 15 is issued by the merging permission 195, and the synchronous merging function 14 activates the breaker 16 when the merging conditions are met. Closed.

Therefore, in the next processing cycle, the processing is transferred to the load control system 140.

In the load control system 140, the current stress estimation 141 is a function of estimating the current value of rotor stress.

This function consists of 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, all of which are used to control speed. This is a function shared with the 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 it is the time, the process is passed to the maximum load change rate search 150; otherwise, This processing function is bypassed and processing is passed to the next optimum load change rate determination 144.

In this case, the processing cycle of the current stress estimation 141 is τ1, the processing cycle of the maximum load change rate search 150 is τ2,
The relationship is τ2=nTτ1 (T: integer).

The maximum load change rate search 150 is composed of the following processing functions: load change rate assumption 151, stress prediction 152, predicted stress level check 153, and predicted time arrival determination 154.

Furthermore, the stress prediction 152 includes a steam condition prediction 106, a first stage post-steam condition calculation 107, a rotor surface heat transfer coefficient calculation 108,
Rotor temperature distribution calculation 109, rotor thermal stress calculation 110,
It consists of each processing function of rotor stress calculation 111,
These are all functions shared with the speed control system.

This maximum load change rate search 150 assumes a load change rate assumption 151 in descending order of load change rates [+Lt, ±L2, ...±Lx...Lp (%/O))] prepared in advance, and occurs in this case. Predict future values of stress.

This maximum load change rate search procedure is similar to the maximum speed increase rate search procedure 7 described above.

Optimum load change rate determination 144 is maximum load change rate search 150
It has a function to set the maximum load change rate found by .

This function also has the function of holding the load regardless of the maximum load change rate search result if the current stress estimate value exceeds the limit value.

The search signal generation 145 is a function for quickly increasing the load by giving flexibility to the learning function in the steam condition change rate learning 104 in the load increase control at the time of turbine startup.

As outlined above, stress limit value determination 102, prediction time determination 103, speed control system 160 or load control system 140
If each function is operated at the period τ1, control of turbine startup and normal load operation is executed.

This repetitive operation continues until the system stop judgment 112 requests a system stop.

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

First, regarding the initial temperature distribution determination 101 of the rotor, FIG.
This will be explained with reference to FIG.

FIG. 3 is a sectional view of the rotor 40 and casing 41 of the labyrinth packing section 1 viewed from the axial direction.

However, regarding the intermediate pressure turbine, attention will be paid to the steam chamber wall instead of the casing 41, but since the concept is the same, only the high pressure turbine will be described here.

THoO, THOI, T5, TbtT shown in FIG.
i (J=1 to m) is the casing outer wall metal temperature, the casing inner wall metal temperature, the rotor surface cleanliness, the rotor bore temperature, and the temperature of each cylinder when the rotor is divided into m virtual coaxial F cylinders.

Although it is difficult to actually measure the temperature distribution of the rotor, it is particularly important to accurately determine its initial value 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 temperature distribution in the radial direction inside the rotor from the actually measured casing inner and outer wall temperatures THeIpTHOO.

In this case, TsTb is Ts-THcI ・・・・・・・・・・・・・・・・・・
・・・・・・・・・・・・・・・(1) Tb=THaI+k
T(THao-THOI)...(2) is considered.

kT in the above equation (2) is a constant determined by the shape of the turbine.

The internal temperature distribution is regarded as a value determined by linear interpolation of T8 and Tb, and is expressed by the following equation.

Further, 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, it is set as B-1, and when it is smaller, it is set as B=O.

Furthermore, if the current speed Na is greater than the specified value Ns, B=1 because there is a possibility that the estimation error will become large even if the temperature difference is small.

This value of B is determined by the next processing function, stress limit value determination 102.
This is for reference only.

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.

Assume that the turbine is started at time t1.

If the slope of the initial rotor temperature distribution at 1 is small,
That is, when B=O, the stress limit value is constant at the value set by the plant operator (±σLS for the rotor surface, ±σLB for the rotor bore).

However, if the slope is large, νD or B = 1, the stress limit value can be safely determined by subtracting the maximum thickness Δσ from the value set by the plant operator, as shown in Figure 5, 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 temperature distribution becomes smaller as time passes after startup, Δσ gradually decreases until Δσ becomes smaller at time t2.
Let it be ten.

Next, prediction time determination 103 will be explained.

This predictive time determination is the main part of the invention.

What is important in determining the predicted time tp is the behavior of the reheat steam temperature TRH immediately after the addition.

Since the amount of fuel in the boiler increases in a stepwise manner at the time of joining, the reheat steam temperature particularly rises rapidly as shown in FIG. 6, and tends to follow the main steam temperature TMS with approximately a first-order lag.

Therefore, even if the initial load is maintained after joining, the rotor stress of the intermediate pressure turbine may continue to increase for a while.

Therefore, before joining, this phenomenon is quantitatively predicted, and after confirming that the resulting stress does not exceed the limit value, the joining permission command 15 is given to the synchronous joining function 14.

For this purpose, as shown in the figure, the shortest prediction time required is the time point tp at which the stress generated when the initial load is maintained after joining is at its peak, and predictions must be made at least up to this point.

When this tp is determined from the dynamic characteristics of the boiler and turbine, it can be expressed by the following equation.

Here, a, b, c, d: Constants TMSA: Current value of main steam temperature TRHA: Current value of reheat steam temperature In addition, ΔTMR=TMSA-TRHA………………(5) If we set ΔTMR, tp for ΔTMR. The relationship is shown in FIG.

That is, according to this embodiment, when adding a load to the turbine generator, first calculate the time tp until the generated stress reaches an extremely thick value when the load is added at the current moment and the initial load is maintained by calculating the main steam temperature and the reheat steam. Temperature is predicted, and the generated thermal stress is sequentially predicted by using this time tp as the prediction time until after the elapse of this time, and when the predicted stress is within the stress limit value, the annexation permission command 15 is given and synchronous annexation is performed. Function 14 performs a synchronous join.

Therefore, is it necessary to accurately determine permission for annexation by calculating the minimum necessary stress prediction? This makes it possible to start up the turbine quickly and effectively conserve turbine life.

The predicted time after merging will be explained using FIG. 8.

The change in reheated steam temperature after the addition is considered to be indicative of the dynamic characteristics measured before the addition.

Therefore, as shown in FIG. 8, the predicted time tp determined for the annexed territory is used and is decreased as time passes.

At the time tPo after the combination, the predicted time is shortened to tPL, which is the same as during continuous 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 variables, main steam temperature TMS, main steam pressure PMS, and reheat steam temperature TBH, 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 state of the turbine, and it is not easy to uniquely express this correlation as a dynamic characteristic model.

Therefore, as shown in Fig. 9, the current time t and the past nτ1(n:
The ratio of the load ΔL and the main steam temperature ΔTMS that changed during the period (integer) is learned as a rate of change.

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 is also used in the load control system: first stage steam condition calculation 10γ, rotor surface heat transfer coefficient calculation 108, rotor temperature distribution calculation 109, mouth-evening heat 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 TMS, pressure PMS, reheat steam temperature TRH, speed N, speed increase factor, and load L as input variables.

However, for safety reasons, the steam temperature after the first stage of the intermediate pressure turbine is 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
: Increase rate (rpm/min) L
: Load (%) Lr: Equivalent load under rated steam conditions (%) L1: Boundary load between full-circle injection and mixed injection (%) L2: Boundary load between partial injection and mixed injection (%) TMS: Main steam temperature
(℃)TRH: Reheat steam temperature
(℃) TMsa: Rated main steam temperature
('C) T1': Steam temperature after the first stage of the high pressure turbine (°C) relative to L' ΔTo: Temperature drop between main steam temperature and steam temperature in the high pressure turbine bowl (°C) ΔTRo: ΔTo at rated steam conditions (°C) ) THI: Steam temperature after the first stage of the high-pressure turbine (°C) TI1: Steam temperature after the first stage of the intermediate-pressure turbine (°C) PMS: Main steam pressure
(ata) PIO: Steam pressure after the first stage of high pressure turbine equivalent to no-load operation
(ata)PHt: Steam pressure after the first stage of the high-pressure turbine at rated load (
ATA) PIIR: Steam pressure after the first stage of the intermediate pressure turbine at rated load (ATA
)PH+: Steam pressure after the first stage of the high-pressure turbine (at
a) PIt: Steam pressure after the first stage of the intermediate pressure turbine (a
ta) K1: Adjustment valve throttling rate (K1 = 0 at all times during partial injection)
) (ata)K2:
Temperature reduction coefficient KNL due to the first stage of the high pressure turbine: Steam pressure after the first stage of the high pressure turbine equivalent to no-load loss at rated speed
(ata) KAO: Steam pressure after the first stage of high-pressure turbine equivalent to acceleration (ata
/(rpm)2/min)k: No-load loss index The processing content of the rotor surface heat transfer calculation 108 is as shown in Fig. 11. Pay attention.

However, although Fig. 11 shows a high-pressure turbine,
The heat transfer coefficient for the intermediate pressure turbine is determined using the same procedure.

The meanings of the symbols used in this figure are as follows.

N: Speed (rpm) TH1
: Steam temperature after first stage of high pressure turbine (℃) PH1: Steam pressure after first stage of high pressure turbine (ata) λ1sT: Steam heat transfer coefficient after first stage of high pressure turbine (kCa4/m・℃・
SeC) ν, sT: Steam kinematic viscosity coefficient after the first stage of the high-pressure turbine (m2
/sec) γIST: Steam specific weight after the first stage of the high-pressure turbine (kg/m
3) FSL: Labyrinth packing leakage flow rate (kg/s
ec) FSLV: Labyrinth packing volume leakage flow rate (
m3/sec) UAX: Labyrinth packing axial leakage flow rate (m
/SeC) URD: Labyrinth packing rotor surface speed (m
/SeC) U: Labyrinth packing composite leakage flow velocity (m/se
c) Re: Reynolds number Nu: Nutsselt number K: Rotor surface heat transfer coefficient (kcat/m2・℃・s
ec) KO: Constant determined by turbine shape δ: Labyrinth packing gap (m) d
: Rotor surface diameter (m)2 :
Number of fins A of labyrinth packing: Gap area of labyrinth packing (m2) r
s: Low surface radius (m) PH2:
Pressure after the second stage of the high pressure turbine (ata) However, in Figure 11, the pressure ratio after the first stage and after the second stage (P2/P
Since I) can be considered to be approximately constant even if the operating state of the turbine, ie, the speed, acceleration rate, and load change, it is actually calculated as a constant.

Next, the rotor temperature distribution calculation 109 will be explained using FIG. 12.

Since the heat movement inside the rotor can be regarded as a one-dimensional flow consisting only of the radial direction, the rotor is divided into m virtual cylinders as shown in Fig. 12, and the temperature distribution is calculated by focusing on the heat balance between each cylinder. demand.

If the time step size of heat balance calculation is τ1, Qf,S is τ1
Qs,t is the amount of heat transferred from the steam to the rotor surface during that time, and Qs,t is the amount of heat transferred from the rotor surface to the outermost cylinder center,
QJtj+t is the amount of heat transferred from the 'th cylinder to the j+1th cylinder.

However, since the bore is in an adiabatic state, Qm is always
m+t=O.

Now, assuming that the current time is t, the amount of heat transfer that occurs between each cylinder during the time t - τ1 to t is expressed as follows.

Qf,s(t)−2πrsK(t)(THI(t)−T
s(f-τ1))τ1 (7)・・・・・・・・・・・・
・(8) Here, λ is the thermal conductivity of the rotor material.

From the relationship Qf,S(t)=Qs,1(t), Ts(t-
T) is expressed by the following formula.

Here, r'=4r2+3Δr W(t)=ΔrK(t)/λM The amount of heat ΔQj(t) accumulated in the J-th cylinder is Δ(J(
t)=Qj-t,j(t) Qj,j+t(t)
Since it is expressed as (13), the temperature Tj of the j-th cylinder is expressed by the following equation.

Tj(t)=T(t-r1)+ΔQj(t)/VjρM
CM...(14) Here, V1: Volume per unit length of the j-th cylinder ρM: Density of the rotor material CM: Specific heat of the rotor material Also, the rotor bore temperature Tb(t) is the temperature distribution By approximating with the following equation, it is expressed by the following equation.

FIG. 13 shows the detailed procedure of this processing function described above.

Next, rotor thermal stress calculation 110 will be explained.

The rotor thermal stress, that is, the rotor surface thermal stress σST and the rotor bore thermal stress σBT, is expressed by the following equation based on the temperature distribution obtained by the rotor temperature distribution calculation 109 described above.

Here, E: Young's modulus of rotor material α: Linear expansion coefficient of rotor material ν: Poisson's ratio of rotor material Ts: Rotor surface temperature Tb: rotor bore temperature TM: Rotor volume average temperature Note that the rotor volume average temperature TM is expressed by the following equation.

Next, rotor stress calculation 111 that also takes centrifugal stress into consideration will be explained.

Since centrifugal stress is proportional to the square of the turbine speed N, if the rated speed is No and the bore centrifugal stress at the rated speed is σBOR, then the centrifugal stress σBc acting on the bore at speed N is expressed by the following equation. The bore stress σB is σB:σBT+σBe (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
8 becomes σS:σnail (21).

This completes the explanation regarding the current stress estimation 161.

The next current stress level check 162 is as follows: σ8, σ
8 is a function for determining whether or not the stress limit value set in the stress limit value determination 102 described above is exceeded.

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.

That is, when it is specified that the predictive calculation is to be performed once every n times, the processing function 19 has the function of bypassing the best speed increase rate search 170 for n-1 times out of n times.

Next, the maximum acceleration rate search 170 will be explained.

This processing function uses the current time as a reference to determine the predicted time.
The stress generated on the rotor surface and rotor bore after the prediction time t determined in step 03 is predicted in time step width (τ1), and each time it is compared with the stress limit value, and the stress during this period exceeds the limit value. This function searches for the maximum acceleration rate that cannot be exceeded.

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 the stress prediction 172 first predicts the stress on the rotor surface and bore after τ1 from the current time, and compares it with the stress limit value in the predicted stress level check 173.

As a result of this comparison, if both stresses are less than the limit value, the process returns to the stress prediction 172 and further predicts the stress after τ1.

In this way, the stress is predicted at intervals of τ1 until after tP for a given acceleration rate assumption Nx, and compared with the limit value, but if either the rotor surface stress or the bore stress exceeds the limit value. In this case, the process is returned to the acceleration rate assumption 171, the assumed acceleration rate value is changed, and the stress is similarly predicted.

In this case, the assumption of the acceleration rate is made in ascending order, and in the prediction time arrival judgment 174, if the stress predicted value for the assumed acceleration rate value does not exceed the limit value over the entire prediction period ip, the assumption of the acceleration rate at this time is The speed rate is determined as the maximum speed increase 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 of zero is set as the thickest 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 the steam condition to the amount of load change is used as explained in FIG. 9 and equation (6).

That is, the time rate of change of the main steam temperature with respect to the assumed value Nx of the speed increase rate is expressed by the following equation.

The critical speed determination 164 is a function of determining whether the current turbine speed is in the critical speed region, and the result of this determination has an important meaning in the next optimal speed increase rate determination 165.

Note that this optimum acceleration rate determination 165 has already been described.

As explained above, the optimum acceleration rate is set for the governor 10 every τ1, but the current value of the stress is set for the period τ1.
If the limit value is exceeded, the speed is maintained, so turbine speed increase control is performed safely even in the face of fluctuations in the turbine inlet steam conditions due to disturbances that were not taken into account at the time of prediction.

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

In the load control system 140, the processing methods of current stress estimation 141, current stress level check 142, calculation mode judgment 143, and maximum load change rate search 150 are basically performed by the respective processing functions 161, 162, 163 of the speed control system 160.
, 170.

However, the only difference is that in the speed control system 140, the speed increase rate is the target of the maximum value search, whereas in the load control system 160, the load change rate is the target of the maximum value search.

Load change rate assumption 15 in maximum load change rate search 150
1 assumes that if the load request LR is a load increase request for the current load, it is assumed in order from the largest load change rate among multiple load change rates prepared in advance; Assumptions are made in descending order of the ratio.

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 found in the maximum load change rate search 150 at a cycle of τ1 to ALR7 and correct it. If the current stress exceeds the stress limit value during nτ1, Another function is to directly hold the load, and the other is the load limiting function, which sets an upper limit on the load depending on the main steam conditions. This function is to prevent erosion of the final stage blade.

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 load limitation based on the main steam temperature, and if the main steam temperature does not exceed the lower limit value TMSL2 matching the main steam pressure PMS, the load is maintained.

Further, FIG. 15 shows load limitation based on the reheat steam temperature, and if the reheat steam temperature does not exceed the lower limit value TRHL that matches the load L, the load is maintained.

Next, the search room signal generation 145 will be explained.

As a method for predicting the rate of change in steam conditions, Figure 9 and (6)
The method used is to learn the rate of change in steam conditions using the method shown in the formula and predict future values based on this.

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 rate greater than that under normal conditions.

In such a case, the stress will be predicted to be higher than the actual one, and even though the actual stress is sufficiently small compared to the limit value, a long-term load retention phenomenon will occur, making it impossible to increase the load. There is a fear.

The search signal generation 145 is a function to prevent this phenomenon.

This specific method uses the search signal ΔLE as shown in FIG.
By superimposing X on the load, the change in steam conditions at that time is expressed as (6
) in the same way as the formula.

In this case, the rate of change (ΔT
Ma/ΔL EX), the rate of change that has already been learned (
ΔTMS/ΔL).

The correction method uses a weighting coefficient β as shown in the following equation.

Next, this search signal ΔLEX is generated at the same period as the maximum load change rate search period nτ1, and its change rate is determined as follows and set in ALR7.

Now, among the values obtained by normalizing the current stress on the rotor surface and bore of the high/intermediate pressure turbine by the limit value, the value having the maximum absolute value is defined as σMN.

That is, it is expressed by the following equation.

Here, σLs: Rotor surface stress limit value σLB: Rotor bore stress limit value σHS: High pressure turbine rotor surface stress σ1s: Medium pressure turbine rotor surface stress σHB: High pressure turbine rotor bore stress σ1B: Medium pressure turbine rotor bore stress This σMN Accordingly, the rate of change LBXR of the search signal as shown in FIG. 17 is determined.

The steam condition change rate learning 104 has a learning value correction function using a search signal as described above, but it also has a so-called forgetting characteristic in which the learning 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.

According to equations (26) and (27), if the learning results are corrected with a period of τ1, a forgetting characteristic with a time constant of τ1 will be obtained.
The response of turbine inlet steam conditions to a load increase, especially the temperature increase characteristics of reheat steam temperature, changes significantly from the time of combustion at turbine startup until the low load range.

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 adjust the operation cycle, that is, the optimum load change rate A
It is necessary to make corrections in response to changes in the time constant of the period set to LR.

In order to realize this, the calculation mode determination 143 of the load control system 140 is provided with the function shown in FIG.

In other words, in the low load region, the maximum load change rate search period is 0τ1
After learning the response of steam conditions with a large time constant by increasing the maximum load change rate search 1.
50.

FIG. 19 shows another embodiment of the present invention.

This embodiment differs from FIG. 2 in the prediction time determination 103' and the annexation permission determination 190', but the other partial processing contents are exactly the same as those shown in FIG.

In this example, when making a decision to permit annexation, the prediction time for stress prediction is not determined in advance, and the stress prediction and predicted stress level check are performed every τ1 cycle, and the predicted stress actually reaches an extremely large value. This process is repeated until Kokichi is confirmed, and an order to permit annexation is issued.

First, when the speed N reaches around the rated speed NO during speed-up of the turbine, a sufficiently large prediction time is set in prediction time determination 103'.

(In reality, this predicted time is considered invalid).

In the annexation permission determination 190l, it is first assumed in the initial load annexation assumption 191 that the initial load annexation has been carried out at the present time, and then the future value of stress after the annexation is predicted in the stress prediction 192.

Next, a predicted stress level check 193 determines whether the predicted stress exceeds the stress limit value, and if the predicted stress exceeds the stress limit value, the annexation permission determination process is interrupted and the next process cycle is waited.

If the predicted stress does not exceed the maximum value, it is determined whether the predicted stress has reached the maximum value in the stress maximum value reaching judgment 196, and if the predicted stress has not reached the maximum value, the process returns to the stress prediction 192 described above and the stress is predicted in τ1 increments. and repeat the process of checking the predicted stress level.

The stress maximum value reaching determination 196 makes the following determination.

Now, assuming that the time of addition is t, the predicted value TRH (t■-n[tau]1) of the reheated steam temperature after n[tau]1 after the addition is given by the following equation.

TRH(t■+nrl)=TRH(tI)+(TMsI
TRH (tI)) (I-e-/nτl/tC)...
・(28) Therefore, n at which the stress after joining is at its peak
p is the minimum value of n that satisfies the following equation.

However, σIS: Intermediate-pressure turbine rotor surface stress σIB: Intermediate-pressure turbine rotor bore stress σLS: Rotor surface stress limit value σLB: Rotor bore stress limit value Therefore, in the judgment 196 to reach the extreme stress value, it is determined whether the equation (29) is satisfied or not. to decide.

If the predicted stress reaches the maximum stress value without exceeding the stress limit value, the annex permission command 15 is issued by the annex permission 195, and the breaker 16 is closed.

After the initial load is added, the prediction time determination 103' gradually shortens the prediction time in the same manner as in FIG. 2 103.

As can be seen from the above explanation, the present invention predicts the stress up to the maximum value when applying the initial load and does not make unnecessary predictions after that, so the amount of calculation required for prediction can be minimized. The load on the computer can be reduced, and the load can be added quickly by effectively using the turbine life consumption, making it possible to start up the turbine quickly.

[Brief explanation of drawings]

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 Plan L, FIG. 2 shows the processing procedure in the control system of the present invention, and FIG. The figure shows the cross section of the rotor and casing after the first stage of the turbine and its temperature state. Figure 4 shows the method for determining the initial temperature distribution of the rotor. Figure 5 shows the stress limit value 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 load addition, Figure 7 shows the predicted time before load addition, and Figure 8
The figure shows the predicted time after joining, Figure 9 shows the learning method of the steam condition change rate, Figure 10 shows the estimation method of the steam condition after the first stage, and Figure 11 shows the heat transfer of the labyrinth packing part. Fig. 12 shows the concept of heat balance between the virtual divided cylinders of the rotor. Fig. 13 shows the specific calculation procedure for the rotor temperature distribution. Fig. 14 shows the method for calculating the rotor temperature distribution. Figure 15 shows the lower limit of main steam temperature. Figure 15 shows the lower limit of reheat steam temperature for load limiting. Figure 16 shows the search signal. Figure 17 shows the method for determining the rate of change of the search signal. FIG. 18 is a flowchart showing a method of determining the operation cycle, and FIG. 19 is a flowchart showing another embodiment of the present invention. 100...Thermal stress prediction turbine control system,
200... High pressure turbine, 300...
Medium pressure turbine, 400...Low pressure turbine, 50
0-... Generator, 1...- High pressure first stage rear labyrinth packing section, 2-... Medium pressure first stage rear labyrinth packing section, 3... Bore (center hole), 4
---Optimal acceleration rate, 6--Optimal load change rate, 7--ALR, 8--Instantaneous target speed, 9--Instantaneous target Load, 10...Governor, 11...Adjustment valve, 12...Actuator, 13...Valve position command, 14...
... Synchronous annexation function, 15... annexation permission command, 1
6... Breaker, 17... Breaker ON/
OFF state, 18... Load request value, 19...
...Speed, 20...5.Main steam, 2,1...
Reheat steam, 22... Control valve position, 23...
・・Main steam pressure, 24・・・・Main steam temperature, 25・
... Reheat steam temperature, 26 ... High pressure first stage rear casing outer wall temperature, 27 ... High pressure first stage after casing inner wall temperature, 28 ... High pressure Steam pressure after 1st stage, 29... Medium pressure steam chamber outer wall temperature, 30.
...Intermediate pressure steam indoor wall temperature, 40...Casing, 41...Lower temperature, 140...
Load control system, 160...Speed control system, 150.
... Maximum load change rate search, 1701... Maximum acceleration rate search, 101... Initial temperature distribution determination,
102... Stress limit value determination, 103, 103'
...Determination of predicted time, 104...Steam condition change rate learning, 105...Operation mode judgment, 1
06...Steam condition prediction, 107...1st 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...Ustem stop judgment, 141...Current stress estimation, 142...
...Current stress level check, 143...Calculation mode judgment, 144...Optimum load change rate determination,
145... Search signal generation, 151...
Load change rate assumption, 152... Stress prediction, 153
...Predicted stress level check, 154...
... 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... Optimal acceleration rate determination, 17
1...Acceleration rate assumption, 172...Stress prediction, 173...Predicted stress level check, 174...
... Judgment of reaching predicted time, 180... Judgment of reaching rated speed, 190, 191'-... Judgment of permission to join, 191... Initial load assumption, 192 ...
... Stress prediction, 193 ... Predicted stress level check, 194 ... Judgment of arrival of predicted time, 195
... Permission to annex, 196 ... Judgment that the stress has reached the maximum value.

Claims (1)

[Claims] 1. A power generation system consisting of a working fluid generation source for driving a turbine, a valve that controls the flow rate of the working fluid generated from the source, a turbine operated by the fluid, and a generator mechanically connected to the turbine. In a control system for power generation equipment, which is applied to equipment and calculates the stress generated in the turbine due to changes in the state of the working fluid, and operates the turbine according to the calculated stress, when the turbine speed reaches the rated speed, the turbine is means for predicting the stress generated in the rotor; and means for issuing permission to add load to the generator when the predicted stress is within a limit value; A method for adding load to a turbine power plant, characterized in that the time when the subsequent generated stress reaches an extremely large value is calculated, and this time is used as the predicted time for the stress prediction. 2 Applicable to power generation equipment consisting of a working fluid generation source for driving a turbine, a valve that controls the flow rate of the working fluid generated from the source, a turbine operated by the fluid, and a generator mechanically connected to the turbine. In a control system for power generation equipment that calculates the stress generated in the turbine due to changes in the state of the fluid and operates the turbine according to the calculated stress, the turbine is operated at a predetermined time interval after the turbine speed reaches the rated speed and after the load is applied. It has a means for sequentially predicting future values of rotor stress, and when the predicted value of the stress reaches an extremely large value and the extremely large value is within a limit value, the load addition to the generator is permitted. How to add load to a turbine generator.