JPS6242125B2 - - Google Patents

Description

Detailed Description of the Invention [Technical Field of the Invention] The present invention provides system control by high-speed control of a steam control valve and an intercept valve (hereinafter referred to as ICV) of a turbine speed control system when the load of a turbine generator changes. This invention relates to a high-speed valve control (hereinafter referred to as EVA) method for stabilizing the

[Technical background of the invention]

If an accident such as a ground fault occurs in the power system and the electrical output decreases while the turbine generators are operating synchronously in the power system, the turbine generators will be accelerated and the internal phase difference angle will increase. This leads to loss of synchronicity. Therefore, in order to prevent this and stabilize the power system, the so-called EVA method has been adopted, which rapidly reduces the mechanical torque of the turbine to rapidly reduce the excess acceleration energy applied to the generator in the event of a system failure.

Below, we will explain in detail the case where this EVA method is adopted in a thermal power plant. FIG. 1 shows the system configuration of a steam turbine plant. In the figure, steam from a boiler 1 is guided to a high-pressure turbine 3 through a steam control valve 2, and after doing work in the high-pressure turbine 3, the steam is heated to a high temperature in a reheater 4, and then passes through an ICV 5 to an intermediate-pressure turbine 6 and By guiding the pressure to the low-pressure turbine 7, the generator 8 is driven by the turbines 3, 6, and 7 at each pressure.

In such a system, the steam control valve 2 and the ICV
5 is controlled by a turbine governor, and when the steam turbine is accelerated due to a system accident or the like, the steam control valve 2 and ICV 5 are controlled to close, respectively, to prevent this from happening. However, in this case, this operation is slow with the original governor, so in addition to the governor movement, due to a system failure or unbalance of mechanical output or electrical output, the EVA directly closes or opens the steam control valve 2 and ICV 5 quickly. is being carried out.

On the other hand, FIGS. 2a and 2b show the principle of improving stability by such an EVA method. In the figure, if the internal phase difference angle δ of the generator is plotted on the horizontal axis and the output P _e is plotted on the vertical axis, during normal synchronous operation, this power, δ _p on the phase angle diagram, and the mechanical torque T _n are balanced. It is operating at point X (δ _p , T _n ). Note that the curve _A1 is determined based on the system impedance and other factors.

Now, if an accident occurs in a power system, for example, in one transmission line, the electrical output will be O, so X ₁ (δ _p ,
O), and when the fault point is cleared at (δ _c , O), it is accelerated on the A ₂ curve determined by the system impedance of the remaining line. During this time, if the governor's response is slow and ignored, the mechanical torque T _n is constant, S _a is the energy used for acceleration, and S _r is the energy used for deceleration.
In order not to step out, in other words, in order to return the phase, S
It is necessary that _a S _r . In other words, as is clear from the figure, when EVA is applied, S _r can be increased by reducing the mechanical torque, making it stable, and when EVA is not applied, S _a > on the power phase plane. S _r , and the deceleration energy is insufficient, resulting in step-out.

By the way, although FIG. 2 is a very general explanation, the steam control valve 2 and ICV 5 of a steam turbine are targeted as means of this EVA. That is, the first
In the figure, the steam control valve 2 and the ICV 5 are controlled by the original steam turbine speed control, and opening and closing of the valves prevents the steam turbine from accelerating. However, when applying EVA to this, conventional methods use a logic circuit (power load unbalance) that detects system failures or unbalances in electrical output and mechanical output to control steam control, as shown in Figure 3 a and b. The hydraulic pressure of valve 2 or ICV 5 is temporarily removed to fully close it, and steam control valve 2 or ICV 5 is restarted when the system accident is restored or the imbalance in electrical output and mechanical output is resolved.

Figures 3a and 3b show the behavior when EVA is applied to the ICV 5, and the states and circuits for starting EVA and restarting the valve, respectively. In the figure, the mechanical output normally takes the post-reheat pressure (ICV input pressure) and starts EVA (assuming that it is a factor that makes the internal phase difference angle unstable, including system failures). In other words, when EVA started, ICV5 was fully closed to remove ICV5's control oil pressure regardless of the speed governor signal, but the system failure point was isolated and the imbalance between generator output and mechanical output was cleared again. At this time, ICV5 is operated to fully open (return control oil pressure). In Figure 3a, the load (mechanical output) is
It is shown along the time axis during EVA operation, and it can be seen that the sudden valve opening and closing operations described above are effective in preventing step-out because the load suddenly decreases and the mechanical output is temporarily lowered. .

[Problems with background technology]

Figure 3 above shows the case where EVA is applied only to ICV5. Normally, EVA is applied to (a) ICV only (EVA signal is applied only to ICV) (b) ICV and steam control valve. There are two possible cases: applying the EVA signal to both the ICV and the steam control valve.

First, in case (a), sudden high-speed valve operation is the first
Considering the plant system in the figure, it only affects the reheat steam output from the high-pressure turbine 3 outlet to the intermediate-pressure turbine 6 inlet, and generally there is little disturbance to the boiler 1 (EVA is not applied to the steam control valve 2, so (This is because the steam control valve 2 does not swell significantly). For this reason, case (a) is mainly used for plant operation, but on the other hand, as can be seen from the characteristics in Figure 3a,
The movement of ICV5 by EVA is a simple sequence of fully closing and fully opening, so even after disconnecting the power system fault and returning to the single circuit, the steam turbine output remains
The power returns to the level before EVA operation. Typically,
After the power system recovers from an accident, the generated power must be appropriately suppressed; otherwise, even if transient stability can be achieved, subsequent synchronous operation, that is, dynamic stability, will be hindered. In other words, even if EVA is successful, if the generated power is not suppressed, the internal phase difference angle will not converge and will diverge, meaning there is no load control function.

On the other hand, in case (b), if EVA is applied to both steam control valve 2 and ICV 5 in the system shown in Figure 1,
The reason for ICV5 is the same as above. Regarding the steam control valve 2, its opening and closing causes a sudden pressure rise in the boiler 1 (due to a sudden increase in main steam pressure), which causes combustion instability in the boiler 1, and generally helps maintain the stability of the power system. Even if it were possible to do so, it would be impossible to sustainably operate a thermal power plant, and in this case it would be extremely difficult to apply it as it is.

[Purpose of the invention]

The present invention has been made in view of the above circumstances, and its purpose is to provide a high-speed valve control method that allows stable operation of a steam turbine plant while ensuring improved stability of the power system. It's about doing.

[Summary of the Invention] In order to achieve the above object, the high-speed valve control method of the present invention controls the intercept valve to be fully closed and fully opened at high speed, and the steam control valve to a preset relatively gentle schedule. The steam regulating valve is controlled to close to a predetermined valve opening degree, and after the closing control, the set load value is changed to a value corresponding to the valve opening degree, and the steam control valve is controlled based on this. .

[Embodiments of the invention]

An embodiment of the present invention shown in the drawings will be described below. Figures 4a and b are according to the invention.
This figure shows an example of a block configuration for realizing the EVA method. Figure a shows EVA for ICV5,
Figure b shows the configuration of the EVA for the steam control valve 2, respectively.

In FIG. 4a, 9 is an ICV adjustment rate circuit that inputs the deviation between the set speed 10 and the actual speed, and generates an opening correction value signal 12 for the ICV 5 in accordance with the deviation. In other words, if there is no deviation, the opening correction value signal 12
is zero, and if a deviation occurs on the acceleration side, ICV5
Generates a signal in the direction of closing. Further, the ICV opening command value signal 14 is obtained from the deviation between the opening correction value signal 12 and the ICV opening setting value 13, and furthermore, based on the deviation between the opening command value signal 14 and the ICV actual opening signal 15, The servo valve 16 is controlled to control the opening degree of the ICV 5, and the opening degree of the ICV 5 is fed back as the ICV actual opening signal 15 by a demodulator 17 such as a differential transformer, thereby forming an opening control loop for the ICV 5. ing. Furthermore, 18 is an EVA start command contact that responds to the EVA operation signal from the logic circuit shown in FIG. ing.

In addition, the setting speed 10 above is the frequency setting of 50Hz or 60Hz, and the ICV opening setting value 13 is
It is set to 100% opening.

Next, in FIG. 4b, 19 is the above-mentioned set speed 1
This is a steam control valve adjustment rate circuit that receives as input the deviation between 0 and the actual speed 11, and generates an opening correction value signal 20 for the steam control valve 2 in accordance with the deviation. That is, if there is no deviation, the opening correction value signal 20 is zero, and if a deviation occurs on the acceleration side, a signal in the direction of closing the steam control valve 2 is generated. In addition, this opening correction signal 20
The steam regulating valve opening command value signal 22 is obtained from the deviation between the load setting value 21 and the steam regulating valve actual opening signal 24, and the servo valve 25 is controlled based on the deviation from the steam regulating valve actual opening signal 24 to open the steam regulating valve 2. The opening degree of the steam regulating valve 2 is fed back as the steam regulating valve actual opening signal 24 by a demodulator 26 such as a differential transformer, thereby forming an opening control loop for the steam regulating valve 2. There is. Furthermore, 27 is an EVA start command contact,
28 is a steam regulator valve opening degree setter, 29 is a steam regulator valve closing speed setter, and 30 is a steam regulator valve closing schedule signal generator, which is set by the steam regulator valve closing speed setter 29 when the contact 27 is turned on. The system is configured to generate an opening control schedule signal for the servo valve 25 to control the closing of the steam regulating valve 2 to the opening α set by the steam regulating valve opening setting device 28 at the speed change rate. . Further, 31 is a steam regulating valve opening degree deviation detector that detects the deviation between the steam regulating valve opening command value 22 and the steam regulating valve actual opening degree 24. Here, the EVA opening command contact 27 is turned on by the EVA operation signal applied from the logic circuit shown in FIG. 3b, and turned off when the output deviation of the steam regulating valve opening deviation detector 31 is approximately zero. be. Furthermore, the servo valve 25 is controlled by the steam regulating valve opening command value 22 (governor command), but when the contact 27 is turned on due to the start of EVA, the signal from the steam regulating valve closing control schedule signal generator 30 is prioritized and the servo valve is valve 2
5, and the steam control valve 2 is controlled according to the schedule.

On the other hand, 32 is a set value of automatic load control (ALR), 33 is an automatic load setter loaded in consideration of power suppression, and 34 is a switch that receives the above set value 32 and the output value of the automatic load setter 33 as input. Before EVR occurs, the set value is 32, and after EVR occurs, the output value is 33.
is switched and output, and the output is the actual load (generator output) 3
5 is processed in a loop having an integrator 36, and outputted as the load set value signal 21.

Note that the steam adjustment valve opening setting device 28 and the steam adjustment valve closing speed setting device 29 described above can be variably set, and are set in consideration of the allowable value of steam flow rate fluctuation of the steam turbine plant.

In this example, due to the occurrence of a system accident,
When the EVA operation signal is generated, as shown in Figure 5,
When the EVA start command contact 18 turns on, the ICV
5, it opens fully at high speed, and when it is off, it is controlled at high speed until it fully opens. Furthermore, when the EVA operation signal is generated, the EVA opening command contact 27 is turned on, and the steam valve opening setting device 28 is controlled to a relatively gentle control set by the steam regulating valve closing speed setting device 29. The steam control valve 2 is controlled up to α. on the other hand,
The load on the generated power is rapidly reduced by the operation of the ICV 5 at the same time as the EVA occurs, and finally it is run back to the value A set by the automatic load setting device 33, and as a result, the EVA operation is controlled by normal automatic load control (ALR). ), and the load is thereby controlled.

As mentioned above, by using this EVA method, the following effects can be obtained.

In other words, instead of the simple operation of fully closing and fully opening the EVA (steam control valve) and LCV as described above, (a) ICV5 performs high-speed fully closed and fully open control, so it is possible to control torque changes. In other words, the effect of EVA can be demonstrated. In other words, the medium-pressure and low-pressure turbines 6 and 7 torque accounts for 70% of the total, which disturbs only the so-called reheated steam and has almost no effect on the boiler fuel system, making it possible to fully close and fully open the boiler at high speeds. be.

(b) Since the steam control valve 2 is closed on a certain schedule within an allowable range while suppressing disturbances to the plant, the operation of the boiler and thus the plant can be stabilized without directly affecting the boiler fuel system. can be done.

(c) Since the automatic load setting device 33 enables load setting after EVA, the load after EVA is suppressed to a predetermined setting value to suppress power;
It is possible to perform stable load operation even after the system fault is restored.

These measures are taken, and the steam turbine plant can be operated stably while maintaining the stability of the system.

It should be noted that the present invention is not limited to the above embodiments, and can be implemented with various modifications without changing the gist thereof.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to provide an extremely reliable high-speed valve control method that can improve the stability of an electric power system and ensure stable operation of a turbine plant.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the system configuration of a steam turbine plant, Fig. 2 a and b are principle diagrams for explaining stability improvement, and Fig. 3 a and b are conventional EVA operations,
FIGS. 4a and 4b are diagrams showing logic circuits of the present invention.
FIG. 5 is a block diagram showing an embodiment for implementing the EVA method, and is a diagram for explaining the operation of the embodiment. 1... Boiler, 2... Steam control valve, 3... High pressure turbine, 4... Reheater, 5... ICV, 6... Intermediate pressure turbine, 7... Low pressure turbine, 8... Generator, 9 ...ICV adjustment rate circuit, 10...Setting speed,
11...Actual speed, 12...ICV opening correction value, 13
...ICV opening setting value, 14...ICV opening command value,
15...ICV actual opening degree, 16,25...Servo valve,
17, 26...Demodulator, 19...Steam control valve adjustment rate circuit, 20...Steam control valve opening correction value, 21...
...Load setting value, 22...Steam control valve opening command value,
24... Steam control valve actual opening degree, 18, 27...
EVA opening command contact, 28...Steam control valve opening setting device, 29...Steam control valve closing speed setting device, 30...
...Steam control valve closing schedule signal generator, 31...
... Steam valve opening deviation detector, 32 ... ALR setting value, 33 ... Automatic load setting device, 34 ... Switching device,
35...Actual load, 36...Integrator.

Claims (1)

[Claims] 1 In an electric power system where a steam turbine generator exists,
In a high-speed valve control method for stabilizing a power system by controlling a steam control valve and an intercept valve of a steam turbine speed control system in the event of a system failure, the intercept valve is fully closed and fully open controlled at high speed, and the steam control valve is Closing control is performed to a predetermined valve opening according to a relatively gentle schedule set in advance, and after the closing control, the set load value is changed to a value corresponding to the valve opening, and the steam control valve is closed based on this. A high-speed valve control method characterized by controlling.