JPH0553921B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a speed governing mode switching device for a steam turbine device.

[Conventional technology]

The most typical speed governing methods for steam turbines are the throttle regulating method, in which multiple steam regulating valves (flow control valves) are opened simultaneously, and the nozzle closing regulating method, in which multiple steam regulating valves are opened sequentially. known as the method. In the throttle control system, each steam control valve is opened at the same opening degree according to the load, as shown by curve 22 in FIG. 5, so that steam is evenly distributed throughout the steam turbine. Therefore, no temperature differences occur within the turbine and no thermal stress occurs. However, since the valve opening degree is gradually increased, there is a loss in flow rate while the valve is being throttled, and there is a drawback that efficiency deteriorates under partial load. On the other hand, in the nozzle closing speed regulating system, as shown in Fig. 5, the first valve is first
When a predetermined load is reached, the second valve is opened as shown in line 24a, and each valve is sequentially fully opened one by one. Since each of them immediately becomes fully open, there is no loss of flow rate due to the restriction. However, there is a drawback that thermal stress is generated due to the large temperature difference between the portion of the valve that is not yet opened and the portion of the valve that is fully open. Therefore, which speed regulating method to adopt is determined based on the operating characteristics of the turbine. In other words, in a turbine with peak load characteristics, in which operation is stopped late at night and started early in the morning to cope with the daytime peak load, a throttling speed control method that does not generate thermal stress is adopted. In addition, for base-load turbines that are started or stopped only about once a year, a nozzle shut-off speed regulating system is used that has high thermal efficiency over a wide load range.

Conventional speed governing systems generally use one of the two speed governing systems described above in a fixed manner. However, for example, in a turbine that uses a nozzle shutoff system, in addition to the problem of large thermal stress, steam may flow only through some valves at partial load, so erosion of that valve may affect other valves. A problem has arisen in that the valve is large compared to the valve. This erosion is mainly caused by flying objects such as scale from the side of the steam generator such as a boiler. However, flying objects such as scale are extremely large when restarting after a shutdown, and almost disappear after that. Some systems use the throttling control method only when restarting, and then switch to the nozzle closing speed control method when there are no more flying objects such as scale.

For example, there is a device that switches the speed regulating method as shown in Japanese Patent No. 1034856, but here, the opening degree of multiple steam control valves is changed by
Control is performed so that the difference in opening before and after switching changes at the same ratio.

In other words, assuming that there are first and second valves as steam control valves, first the fifth valve is used during throttling speed control.
The first and second valve opening degrees are changed at the same opening degree along the curve 22 in the figure, and after reaching the predetermined valve opening degree, the mode is switched to the nozzle speed control method, and the first valve is changed to the curve 22.
3b, and the second valve opens along curve 24b.
The opening degree is changed at the same ratio so that the opening is closed along the .

[Problem that the invention seeks to solve]

However, according to the above-mentioned speed control type switching device, although the opening degree of each valve changes at a constant ratio, if there is a non-linear characteristic in the relationship between the valve opening degree and the flow rate, the first valve As shown in Figure 6, the steam flow rate passing through the second valve and the second valve no longer change in a fixed ratio relationship, and as a result, the total steam flow rate flowing into the turbine fluctuates during the switching of the regulating method, causing load fluctuations. There was a problem that this occurred.

SUMMARY OF THE INVENTION An object of the present invention is to provide a speed governing system switching device that can switch the speed governing system without causing load fluctuations.

[Means for solving problems]

The present invention is provided with means for converting the opening degree command for each valve so that the flow rate of steam passing through each steam control valve changes at the same ratio before and after switching the regulating method.

[Effect]

The opening degree command for each valve is converted into an opening degree command such that the steam flow rate passing through each valve changes at the same ratio based on the opening degree and flow rate characteristics of each valve, and is given to each valve. Therefore, even if there is a non-linear relationship between the opening degree and flow rate characteristics of each valve, the sum of the changes in the steam flow rate passing through each valve will always be zero, that is, the sum of the steam flow rates flowing into the turbine will always be It becomes constant and load fluctuations are prevented.

〔Example〕

FIG. 1 is a block diagram showing one embodiment of the present invention, which is applied to a speed control system switching device for a turbine having two steam control valves α and β. Therefore, two opening control systems, a system with a subscript α and a system with a subscript β, are provided as systems for controlling the opening degree of each valve.

In FIG. 1, 1 is the speed deviation determined by the deviation between the actual rotational speed N _A of the turbine detected by the speed detection means 20 and the rated speed N _S (N _S - N _A ) and the regulation rate δ _N
Basic control means that calculates the load command value L _R by adding the set value set by the load setting device 21 to L _N. 2α and 2β throttle the load command value L _R output from the basic control means 1. load/opening conversion means for converting into a request signal for the opening of the steam control valve during speed control;
3α and 3β are load/opening conversion means for converting the required steam amount into an opening request signal at the time of nozzle closing speed regulation (nozzle speed regulation), and 4α ₁ and 4β ₂ are the above-mentioned conversion means 2.
Opening degree/flow rate conversion means 5α ₁ to 5β ₂ convert each opening request signal outputted from α, 2β, 3α, and 3β into a required steam flow rate signal based on the characteristic relationship between the valve opening degree and the steam flow rate. Speed control method switching ratio signal 13,1
4 is a multiplier for manipulating the required steam flow rate signal outputted from the conversion means 4α ₁ to 4β ₂ , 6α is an adder for adding the output signals of multipliers 5α ₁ and 5α ₂ , and 6β is
is an adder that adds the output signals of multipliers 5β ₁ and 5β ₂ , and 7α and 7β are flow rate/flow rates that convert the required steam flow rate signal output from the adders 6α and 6β into a corresponding request signal for the valve opening degree. Opening degree conversion means, 8α, 8
β is a valve position control means that controls the actual valve opening according to the valve opening request signal outputted from the conversion means 7α and 7β, and 9 and 10 are each valve determined from the two regulating methods when switching the regulating method. A switching ratio signal generator 11 generates switching ratio signals 13 and 14 for internally dividing the required steam flow rate at each time;
A switching drive circuit 12 is a speed-governing type switching command circuit that gives an operation command to the switching drive circuit 11.

Next, in the configuration shown in Figure 1, load command value L _R
The process of finding the valve opening request signal corresponding to the following will be explained with reference to the flowchart shown in FIG.

First, the valve opening command values αP ₁ and αP ₂ during throttle control and nozzle speed control are determined based on the load command value L _R .

αP ₁ = f ₂ (L _R ) …(1) αP ₂ = f ₃ (L _R ) …(2) However, f ₂ is the throttle regulating cam characteristic of the conversion means 2α and 2β, and f ₃ is the conversion means These are the nozzle speed regulating cam characteristics of 3α and 3β.

Next, flow rate command values αF ₁ and αF ₂ are determined.

αF ₁ = f ₄ (αP ₁ ) ...(3) αF ₂ = f ₄ (αP ₂ ) ...(4) However, f ₄ represents the flow rate of passing steam with respect to the valve opening degree of the conversion means 4α ₁ to 4β ₂ It is a conversion property.

Next, switching ratio signals K ₁ and K ₂ for switching between the two speed governing systems are generated. In other words, K ₂ = 1 - K ₁ ...(5), K ₁ = 1 ... (6) during nozzle speed control, K ₁ = 0 ... (7), and from nozzle speed control to aperture control. When switching to speed, K ₁ = K ₁ + ΔK ... (8) When switching from throttle speed control to nozzle speed control, K ₁ = K ₁ - ∆K ... (9), and use equation (8) or (9) The formula is repeatedly calculated to generate switching ratio signals K ₁ and K ₂ that change over time with a change width of ΔK.

Next, the steam flow rate command F _L 〓 for the load command value L _R
Find F _L 〓 = αF ₁ ×K ₁ + αF ₂ ×K ₂ ... (10) Here, as can be seen from the above-mentioned equations (5) to (9), the switching ratio signals K ₁ , K ₂ moves between "1" and "0" at a constant speed over time, so the amount of change in the flow rate command F _L α at the time of switching the governor mode becomes a constant value. If the time for K ₁ to move from "1" to "0" or from "0" to "1" is T, then the amount of change in F _L 〓 is dF _L 〓/dt=αF ₁ −αF ₂ /T...( 11) becomes.

Since this calculation is performed for each valve, for the valves in the system indicated by the subscript β, dF _L 〓/dt=βF ₁ −βF ₂ /T (12). In addition, since the total flow rate before and after switching is constant, the relationship αF ₁ + βF ₁ = αF ₂ + βF ₂ ...(13) is established, and from equations (11) to (13), during switching of the governing system, dF _L 〓/dt＋dF _L 〓/dt=0...(14) Therefore, no fluctuation in the flow rate command occurs.

In actual control, the steam flow rate is controlled by adjusting the valve opening, so
The flow rate command F _L 〓 obtained by the formula is used as the opening command using the following formula.
Convert back to Pα.

Pα＝f ₄ ^-1 (F _L 〓) ...(15) The above is the valve opening command value Pα for the load command value L _R
This is the flow until it is found.

Next, how the valve opening degree changes will be explained with reference to FIG. First, it is assumed that the system is currently in throttle control mode, operating at operating point P, and will now switch to the nozzle speed control mode.

The opening degrees of each valve before switching are the opening degrees αP ₁ and βP ₁ at the intersection of the operating point P and the curve 27, so the steam flow rates at this time are αF ₁ and βF _1, respectively.

At this time, the basic control means 1 is outputting the load command value L _R corresponding to the operating point P, and the conversion means 2α,
2β outputs signals corresponding to the opening degrees αP ₁ and βP ₁ . Further, the converting means 3α and 3β output signals corresponding to the opening degrees αP ₂ and βP ₂ necessary to obtain the current steam flow rate (αF ₁ +βF ₁ ) when the nozzle speed is controlled.

These signals are converted by converting means 4α ₁ to 4β ₂ according to the relationship between the opening degree and the flow rate. Therefore, the conversion means 4α ₁ and 4β ₁ output signals corresponding to αF ₁ and βF ₁ as required steam flow rate signals for throttle speed control, and the conversion means 4α ₂ and 4β ₂ output signals corresponding to the steam flow rate signals for nozzle speed control. Signals corresponding to αF ₂ and βF ₂ are output as flow signals.

Since the operating state is throttle controlled, the switching ratio signal 13 (=K ₁ ) is "1" and the switching ratio signal 14 (=K ₂ ) is "0". Therefore, the outputs of multipliers 5α ₂ and 5β ₂ are “0”,
Only the required steam flow rate signal for throttling control is sent to the multiplier 5.
It will be output from α ₁ and 5β ₁ , and adder 6
The output signals of α and 6β are signals corresponding to the flow rates αF ₁ and βF ₁ . This signal is converted into converting means 7α, 7β
is converted into a valve opening degree command by αP ₁ and βP ₁ and inputted to valve position control circuits 8α and 8β. As a result, the valve opening degrees are controlled to αP ₁ and βP ₁ .

When switching to nozzle speed control in this state, the outputs of the switching ratio signal generators 9 and 10 are gradually moved to the nozzle speed control side by the switching drive circuit 11. Therefore, the switching ratio signal 13 (=K ₁ ) changes from "1" to "0" and the switching ratio signal 14 (=K ₂ ) changes from "0" to "1" at the same speed.
At this time, if the operating point is P, the conversion means 4α ₁ to 4
Since β ₂ outputs signals corresponding to the flow rates αF ₁ , βF ₁ , αF ₂ , βF ₂ , these signals are sent to the multipliers 5α ₁ to
The signals 13 and 14 are multiplied by 5β ₂ to be distributed proportionally. As a result, the adders 6α and 6β output signals obtained by internally dividing the required steam flow rate signals in the two regulating systems.

That is, as shown in FIG. 3, signals that linearly change from αF ₁ to αF ₂ and from βF ₁ to βF ₂ are input to the conversion means 7α and 7β as time passes from the start of switching. Ru.

Upon receiving such a signal, the converting means 7α and 7β output an opening degree command that changes as shown in FIG. As a result, when the actual valve opening corresponds to the opening command, the flow rate of steam passing through each valve changes from αF ₁ to αF ₂ and from βF ₁ to βF ₂ .

Note that the switching is completed by the switching ratio signal generator 9,
10 is when the nozzle has completely moved to the speed regulating side,
This completes switching of each valve.

Here, since the sum total of the steam passing flow rate of each valve during the switching becomes constant as shown by αF ₂ in FIG. 4, it is possible to prevent load fluctuations due to switching of the regulating method.

In addition, in the embodiment, a case has been described in which there are two steam control valves, but the present invention can be similarly applied to a case having even more steam control valves.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, the speed governing method can be switched without causing load fluctuations, and stability can be improved.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention;
FIG. 2 is a flowchart for explaining the operation of FIG. 1, FIGS. 3 and 4 are explanatory diagrams for explaining the relationship between the valve opening and the steam flow rate when switching the regulating method, and FIG. FIG. 6 and FIG. 6 are explanatory diagrams for explaining the relationship between the valve opening degree and the steam flow rate when switching the regulating method in the conventional device. 1...Basic control means, 2α, 3α, 2β, 3β...
Load/opening conversion means, 4α ₁ , 4α ₂ , 4β ₁ , 4β ₂ ...
Opening degree/flow rate conversion means, 5α ₁ , 5α ₂ , 5β ₁ , 5β ₂ ...
Multiplier, 7α, 7β...Flow rate/opening conversion means, 9,
10...Switching ratio signal generator.

Claims (1)

[Scope of Claims] 1. A plurality of steam regulating valves that adjust the output of the steam turbine, an opening control means that variably controls the opening degrees of these steam regulating valves, and a speed governing system that switches the speed governing method using the steam regulating valves. In a steam turbine apparatus having a switching means, when switching the speed governing method, an opening is issued from the opening control means so that the difference in steam flow rate passing through each steam control valve before and after switching changes at the same ratio. What is claimed is: 1. A speed control system switching device characterized by comprising means for converting a speed command. 2. The speed governing method switching device according to claim 1, wherein the ratio is changed at a constant speed.