JPH0751884B2 - Steam turbine controller - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a speed control system switching device for a steam turbine, and in particular, it is required to minimize load fluctuation during switching and switch the speed control system in a short time. The present invention relates to a speed control system switching device suitable for use in a steam turbine.

[Background of the Invention]

Conventionally, the following two methods have been widely adopted as the speed control of the steam turbine. That is, a throttle control system that simultaneously opens a plurality of steam control valves (flow control valves),
This is a nozzle shutoff speed control method in which a plurality of steam control valves are sequentially opened. Similarly, each speed control method has inevitable advantages and disadvantages obtained from each valve opening characteristic. That is, in the throttle control method, each valve is opened at the same opening all at once depending on the load, so that steam is uniformly given to the whole, so that no temperature difference occurs in the turbine and thermal stress does not occur, but gradually. Since the valve is opened, it is unavoidable that there is a loss of flow rate while the throttle is being throttled, and the efficiency at partial load is low. On the other hand, in the nozzle shutoff speed control method, since each valve is fully opened in sequence, one valve is immediately fully opened, and there is no loss due to throttling, which is efficient. However, the temperature difference between the valve and the portion of the valve that has not been opened is large, and the problem of thermal stress occurs.

It is mainly the operation required for the turbine that is the basis for selecting which one of them is applied to the actual equipment, that is, which one of such speed control methods is adopted in, for example, a large steam turbine for power generation. It is a characteristic. Generally, peak load (intermediate thermal power. For example, stop driving at midnight,
In a turbine that is operated for severe start-up and start such that it starts early in the morning and peaks in the daytime, a thermal stress advantageous throttling method is adopted to withstand frequent rapid start. It Also, base load (basic firepower.
It operates with almost no change, for example, it stops and starts once a year. It can be said that the nozzle shut-off speed control method, which has high thermal efficiency over a wide load range, is more suitable for use in (1).

Most of the speed control methods in the prior art have any one type according to the demand. However, in the turbine that adopts the nozzle dead-end speed control method, in addition to the problem that the thermal stress is large, the erosion of that nozzle can be compared with others by causing steam to flow only to some nozzles under partial load. There was a problem of being extremely large. This nozzle erosion is mainly due to flying objects such as scales from the steam generator side of the boiler or the like, and these flying objects are remarkably large at the time of restarting after the stop and hardly exist thereafter. Therefore, it has been required to improve the thermal efficiency by adjusting the throttle speed only when restarting after stopping and switching to the nozzle shutoff speed control method regardless of the operating load at that time when there are no flying objects such as scales. .

As a publicly known example that enables this request, Japanese Patent No. 103485
There is No. 6. According to this patent, it is possible to switch the speed control method to reduce the thermal stress.

In the present invention, the cam characteristics are prepared for a plurality of valves for each speed control system, and when the speed control system is switched, the openings of the plurality of valves are the same as shown in FIG. 2 with respect to the opening difference before and after the switching. The ratio is changed. According to the present invention, even if there is non-linearity between the opening of the valve and the flow rate of steam passing therethrough, if the cam characteristic is made to have this non-linearity, it will pass through multiple valves before and after switching the speed control system. However, it is possible to start and end the switching at the same time as the cam characteristics of all the valves by making the total steam flow rate flowing into the turbine the same.

However, in the present invention, when the speed control system is switched,
Although the opening of each valve changes at a constant rate, the flow rate through each valve does not change linearly due to non-linearity, and as a result the total steam flow into the turbine changes during switching, so keep the load constant. There was a problem that I could not do it.

[Object of the Invention]

An object of the present invention is to minimize the load fluctuation in all regions from the start of switching to the completion of switching by making the sum of fluctuations in the amount of steam passing through each valve at the time of speed control system switching almost zero. Another object is to provide a speed control method switching device.

[Outline of Invention]

In order to prevent large load fluctuations from occurring during switching in the conventional speed control system switching device, the present invention considers the nonlinear characteristics of each valve, and changes in the steam flow rate passing through each valve during switching. The sum of the minutes is set to almost zero, and switching of multiple valves is started and ended at the same time, and switching of the speed-regulating method at the time of load fluctuation is interrupted and speed-controlled switching is performed when the load fluctuation disappears. Is.

Example of Invention

FIG. 1 shows an embodiment of the present invention. Although this embodiment is for a turbine having two steam control valves α and β, it can be similarly implemented even if the number of valves is further increased.

This device is a basic control that finds the load command value L _R by the speed load command L _N and the load setting device 21 which is determined by the deviation between the actual speed N _A detected by the speed detection function 20 and the rated speed N _S and the constant rate S _N. function
1, Throttle control cam characteristics (2α, 2β) that convert the load command L _R from the basic control function to each steam control valve opening demand signal during throttle control, the required steam flow rate during nozzle deadline control Nozzle shutoff speed control cam characteristic (3
α, 3β) and the cam characteristic (2α, 2β, 3α, 3β), the steam flow rate converted to the required steam flow rate for each valve by using the characteristic curve of the valve-specific opening and the passing steam amount Conversion function (4α, 4β), multiplier 5 and adder 6 for operating the required steam flow rate by the speed control system switching control signal,
Further, the opening inverse conversion function (7α, 7) for converting the opening to obtain the required steam flow rate for each valve output from the adder 6
β), a valve position control circuit (8α, 8) for controlling each actual valve opening in accordance with the opening command output from each opening inverse conversion function.
β), switching ratio signal generators 9 and 10 that generate a signal for internally dividing the required steam flow rate for each valve obtained from the two speed control systems when switching the speed control system, switching for driving the switching ratio signal Drive circuit 11, speed control method switching command circuit 12 for operating the switching drive circuit, function for detecting load 30, function for detecting load immediately before switching 31, subtractor 32, load before and during switching It is composed of a comparator 33 that detects a change.

Next, the function and operation will be described with reference to FIGS.

The actual operation of the portion for obtaining the opening degree of each valve from the load command value L _{R in} the functional diagram of FIG. 1 will be described with reference to the flowchart of FIG.

From the load command value L _R obtained by the basic control function 1, the valve opening command values αP ₁ and αP ₂ at the time of throttle speed control and nozzle speed control are respectively calculated by the following equations.

αP ₁ = f ₂ (L _R ) (1) αP ₂ = f ₃ (L _R ) (2) where f ₂ is the throttle speed control cam characteristic and f ₃ is the nozzle speed control cam characteristic. The flow rate command values αF ₁ and αF ₂ at the time of throttle speed control to the valve and nozzle speed control according to the command value L _R are (1) and (2)
It is expressed by the following equation using αP ₁ and αP ₂ in the equation.

αF ₁ = f ₄ (αP ₁ ) (3) αF ₂ = f ₄ (αP ₂ ) (4) where f ₄ is the passing steam flow rate characteristic with respect to the valve opening. Signals for switching K ₁ , K
_The following relationships should be established between the _two .

K ₂ = 1-K ₁ (5) where K ₁ is the throttle speed K ₁ = 1 (6) Nozzle speed K ₁ = 0 (7) When switching K ₁ = K ₁ + ΔK (8) When switching to throttle adjustment nozzle speed control K ₁ = K ₁ −ΔK (9) By returning equation (8) or equation (9) and calculating Try to change K ₁ over time.

Next, the passing steam flow rate command to the valve when the load command value is L _R
F _{L α} is _calculated by the following formula.

F _{L α} = αF ₁ × K ₁ + αF ₂ × K ₂ (10) Here, K ₁ and K ₂ are constant with time according to the formula (6) and the speed control system switching formulas (8) and (9). the amount of change in F _{L alpha} during governor system switch to move between 1 and 0 at a rate is constant amount. The time for K ₁ to move from 1 to 0 or 0 to 1 is T
Then, the amount of change is expressed by equation (11).

In this description, only one valve is taken up, but the same calculation is performed for other valves. Therefore, when this is represented by the subscript β, It is represented by. In addition, since the total flow rate before and after switching is constant, the relationship αF ₁ + βF ₁ = αF ₂ + βF ₂ (13) holds, and from the equations (11), (12), (13) At The flow rate command does not fluctuate.

In actual control, by adjusting the valve opening,
In order to control the steam flow rate, the opening degree Pα for actually obtaining the steam flow rate obtained by the equation (10) is obtained by the following equation.

Pα = f ₄ ^-1 (F _{L α} ) (15) Next, in FIG. 5, it is assumed that the nozzle speed control mode is switched during operation by adjusting the aperture at the operating point P.

The opening of each steam control valve before switching is α _P1 , β _P1 , respectively,
The steam flow rates passing through each valve at that time are α _F1 and β _F1 , respectively. The operation of this apparatus at this time is as follows. In FIG. 1, the basic control function 1 outputs a signal of the operating point P. In response to this signal, the throttle control cam characteristics (2α, 2
beta) is outputting each alpha _P1, beta _P1 corresponding signal. Further, the nozzle speed control method characteristics (3α, 3β) are α _P2 and β _P2 , respectively.
It outputs a considerable signal.

The output signals of these opening degree conversion functions output the signals corresponding to α _F1 and β _F1 as the required steam flow rate signals for throttle speed control to the steam control valves α and β by the steam flow rate conversion functions 4α and 4β. is doing. Further, a signal corresponding to α _F2 and β _F2 is output as the required steam flow rate signal for controlling the nozzle speed.

The switching control signal 13 is 0 because the operation is currently performed at the throttle control.
And the switching control signal 14 is 1. Therefore, the multiplier 5 outputs only the required steam flow rate signal for each valve for throttle control, and the output of the adder 6 is a signal corresponding to α _F1 and β _F1 for each valve. This signal becomes the valve opening command signals α _P1 and β _P1 by the opening inverse conversion function (7α, 7β) and is input to the valve position control circuit (8α, 8β), and the actual adjustable valve opening is set to α _F1 , Control to β _F1 .

Next, the operation of switching the speed control method from the throttle speed control to the nozzle speed control will be described.

In FIG. 1, the switching ratio signal generators 9 and 10 are switching drive circuits.
It gradually moves to the nozzle control side by 11. As a result, the switching control signal 13 gradually changes from 0 to 1, and the switching control signal 14 changes from 1 to 0 at the same rate. At this time, basic control function 1
If the output of is constant at point P, the steam flow rate conversion function (4
α, 4β) outputs α _F1 , β _F1 , α _F2 , β _F2 for throttle speed control and nozzle speed control, respectively, and therefore is proportionally distributed by the switching control signals 13 and 14, At the output of the adder 6, a value obtained by internally dividing the required steam flow rate command by the speed control method is output for each valve.

That is, as shown in FIG. 5, the opening inverse conversion functions 7α and 7β are linearly changed from α _F1 to α _F2 and from β _F1 to β _F2 with the passage of time from the start of switching. The changed signal is input.

As a result, the opening degree inverse conversion functions 7α and 7β output the opening degree command of the steam control valve as shown in FIG. When the actual valve position is controlled to this opening command value by the valve position control circuits 8α and 8β, as a result, the amount of steam passing through each valve changes from α _F1 to α _F2 and β _{F1 as} shown in FIG. Changes to β _F2 .

The switching is completed when the switching ratio signal generators 9 and 10 are completely moved to the nozzle speed control side, and the switching is completed simultaneously for each valve.

Here, the sum of the steam flow rates passing through each valve during switching is constant as α _F1 + β _F1 = α _F2 + β _F2 as shown in FIG. 6, so the load fluctuation due to the switching of the speed control system is always minimized. Can be kept.

Although the load fluctuation during switching can be kept to a minimum by the method described above, the load fluctuation during switching may occur for some reason, for example, a change in the valve flow rate characteristic.

A method of reducing the load fluctuation when the load fluctuation occurs during the switching will be described below.

As a method of detecting the load, the load can be detected by the actual load or the first stage rear pressure. In the following description, the function 30 for detecting the load is the first stage rear pressure detector.

The output of the first stage rear pressure detector 30 immediately before switching is set as the output P _{2 during} switching of P ₁ . The output of the load holding circuit 31 is P ₁ and does not change during switching.

Now, when the absolute value of the output ε = P ₁ -P ₂ of the subtractor 32 exceeds the specified value, the comparator 33 operates and the output of the comparator 33 locks the signal of the speed control switching circuit 12. In addition, the lock can be automatically excluded (manual exclusion is also possible) when it falls within the specified value. In FIG. 5, the switching is interrupted at time t, and the flow rates of the steam control valves α and β are changed.
The position is held by α _F1 and β _F1 .

Now, for example, if ε> 0, it means that the load is reduced before and during the switching.

In order to correct this load, it is necessary to increase the amount of steam flowing into the regulator valve. That is, it is necessary to increase the load command from P to P'as shown in FIG. The method of increasing the load command is as follows: 1) The operation of the comparator 33 is detected (alarm), and the operator operates the load predictor in the increasing direction.

2) Add the output of the subtractor 32 to the load command value L _R.

There is.

In the present invention, the output of the subtracter 32 as shown in FIG. 1 is added to the load command value L _R , the load command is increased from P to P ′, and the flow rate α _Ft −β _Ft is set to α ′ _Ft , β ′. _It is increased to _Ft to prevent the load from decreasing.

When ε <0, it is possible to prevent the load from increasing by decreasing the load command P.

It is also possible to correct the load by adding the output of the subtractor 32 to only an arbitrary regulator valve, for example, only the regulator valve α.

As described above, the present invention can prevent load fluctuation during switching.

〔The invention's effect〕

According to the present invention, it is possible to always minimize the fluctuation of the turbine output at the time of speed control mode switching, and it is possible to improve the stability of the system at the time of speed control mode switching during turbine operation.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is an explanatory diagram showing a valve behavior at the time of switching according to a conventional technique, and FIG.
FIG. 4 is a diagram showing valve behavior and total flow rate change at the time of switching according to the prior art, FIG. 4 is an operation flowchart of the present invention, FIG. 5 is a functional diagram of the present invention, and FIG. 6 is according to the present invention. FIG. 6 is a diagram showing a change in valve behavior and steam flow rate during switching. 1 ... Basic control function, 4α, 4β …… Steam flow rate conversion function,
7α, 7β ... Reverse opening conversion function, 8α, 8β ... Valve position control circuit, 9, 10 ... Switching ratio signal generator, 11 ... Switching drive circuit, 12 ... Speed control system switching command circuit.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshiki Ishikawa 5-2-1 Omika-cho, Hitachi City, Ibaraki Prefecture Hitachi Ltd. Omika Plant, Ltd. (72) Inventor Kei Ikeda 3-chome, Saiwaicho, Hitachi City, Ibaraki Prefecture No. 1 No. 1 Stock Company Hitachi Ltd. Hitachi factory

Claims (1)

[Claims] 1. A basic control function for setting an output of a steam turbine to output a load command signal, a plurality of steam control valves for adjusting a flow rate of steam supplied to the steam turbine, and an output from the basic control function. Based on the load command signal
A valve position control circuit that controls the opening degree of the steam control valve corresponding to each valve of the plurality of steam control valves; and a speed control method switching unit that switches a speed control method by the steam control valve, the speed control method. Method and for each steam control valve, the relationship characteristic between the load command signal and the opening degree of the steam control valve is determined, and the required opening degree of the steam control valve is obtained from the relationship characteristic and the load command signal to determine the steam control degree. In a steam turbine control device configured to control the opening degree of a valve, a request for each of the steam control valves based on the relationship between the required opening degree and the flow rate of steam passing through the steam control valve and the required opening degree. A steam flow rate conversion function for obtaining a steam flow rate and an actual opening degree of the steam control valve based on the required steam flow rate corresponding to the switching signal of the speed control method switching means, and an opening degree signal corresponding to the actual opening degree To the valve position control circuit Steam turbine control device characterized by providing an opening opposite conversion function that.