JPS6242124B2 - - 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. It 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, the internal phase difference angle δ of the generator is shown on the horizontal axis, and the output is shown on the vertical axis.
Taking Pe, during normal synchronous operation, the motor is operated at a point X (δ _p , T _n ) where the electric power, δ _O on the phase angle diagram, and mechanical torque T _n are balanced. 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 0, so X ₁ (δ _p ,
0), and when the fault point is cleared at (δ _c , 0), it is overspeeded on the A ₂ curve determined by the system impedance of the remaining one line. During this time, the response of the governor is slow and ignored, mechanically the torque T _n is constant, S _a is the energy used for acceleration, and S _r is the energy used for deceleration. In order for it to return, it is necessary for it to become S _a S _r . That is,
As is clear from the figure, when EVA is applied, S _r can be increased by reducing the mechanical torque, resulting in stability; when EVA is not applied, S _a > S _r on the power phase plane. As a result, the deceleration energy is insufficient, leading to a 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, the conventional method uses a logic circuit (power load imbalance) that detects system failures or imbalances in electrical output and mechanical output, as shown in Figure 3a and b, to control the steam control valve. The hydraulic pressure of ICV 2 or ICV 5 is temporarily removed to fully close it, and the 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 inlet 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 starts, ICV5 completely closes because the control hydraulic pressure of ICV5 is removed regardless of the speed governor signal, but when the system failure point is isolated and the imbalance between generator output and mechanical output is cleared again. , operate ICV5 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 it is effective in preventing step-out because the sudden valve opening and closing operation mentioned above causes the load to suddenly decrease and temporarily lower the mechanical output. .

[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 blunt system in the figure, it only affects the reheating steam pressure 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 fluctuate greatly.) 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 faulty part of the power system and returning to the single circuit, the steam turbine output remains unchanged.
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 synchronized 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 is controlled to a predetermined valve opening degree at a relatively gentle schedule set in advance. The steam control valve is controlled to close until the end of the valve opening, and after the closing control, the steam control valve is controlled based on a set load value corresponding to the valve opening predetermined by a load limiter.

[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, numeral 9 denotes an ICV adjustment rate circuit which inputs the deviation between the set speed 10 and the actual speed 11, 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 will be zero, and if a deviation occurs on the acceleration side, the opening correction value signal 12 will be zero.
Generates a signal in the direction of closing ICV5. 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 opening of the ICV 5 is controlled by controlling the servo valve 16, and the opening 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 of the ICV 5. are doing. Furthermore, 18 responds to the EVA operation signal from the logic circuit shown in Figure 3b.
This is an EVA start command contact, and its ON operation causes the servo valve 16 to be fully closed at high speed, and its OFF operation causes it to be fully opened at high speed.

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 value signal 2
A steam control valve opening command value signal 22 is obtained from the deviation between 0 and the load setting value 21, and this is further passed through a load limiter 23 to control a servo valve 25 based on the deviation from the steam control valve actual opening signal 24. Steam control valve 2
and feeds back the opening degree of the steam regulating valve 2 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. are doing. Furthermore, 27 is an EVA start command contact, 28 is a steam control valve opening setting device, 29 is a steam control valve closing speed setting device,
30 is a steam regulating valve closing schedule signal generator, which generates the opening set by the steam regulating valve opening setting device 28 at the speed change rate set by the steam regulating valve closing speed setting device 29 when the contact 27 is turned on. It is configured to generate an opening control schedule signal for the servo valve 25 to control the closing of the steam control valve 2 up to α. Further, 31 is a steam regulating valve opening degree deviation detector that detects the deviation between the steam regulating valve opening command value from the load limiter 23 and the steam regulating valve actual opening degree 24. Here, the EVA start command contact 27 is
It is turned on by the EVA operation signal applied from the logic circuit, and turned off when the output deviation of the steam control valve opening degree deviation detector 31 is approximately zero. The servo valve 25 is normally controlled by the steam regulator opening command value 22 (governor command) input via the load limiter 23, but when the contact 27 is turned on due to the start of EVA, the steam regulator valve closing control schedule signal generator The servo valve 25 is controlled with priority given to the signal from 30, and the steam control valve 2 is controlled according to the schedule.

On the other hand, 32 is an automatic load setting device that separately sets the load in consideration of stabilization after EVA operation, and 33 is EVA
This is a switching device that accepts and outputs a signal from the automatic load setter 32 after generation, and the set value is processed in a loop with an integrator 35 according to the deviation from the actual load (generator output) 34, and then sent to the load limiter 23. is input. The load limiter 23 receives the signal from the integrator 35 and the steam control valve opening command value signal 22, and generates a valve opening control signal based on the smaller of the two inputs. In this case, since the set value of the automatic load setter 32 that suppresses the power is always smaller than the load setting 20 before the EVA operation, it is controlled exclusively by the automatic load setter 32.

Note that the steam regulating valve opening degree setting device 28 and the steam regulating 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 is fully closed at high speed, and when turned off, it is controlled at high speed until fully open. Further, when the EVA operation signal is generated, the EVA start command contact 27 is turned on, and the steam valve opening setting device 28 is operated at the set opening α by relatively gentle control set by the steam regulating valve closing speed setting device 29. The steam control valve 2 is controlled until. 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 EVA occurs, and finally it is run back to the value A set by the automatic load setting device 32, and as a result, the EVA operation becomes automatic load control (ALR). This controls the load. Therefore, the load shown in A is controlled without being affected by the system frequency.

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 ICV as described above, (a) ICV5 performs high-speed fully closed and fully opened 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 to suppress 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) The automatic load setting device 32 allows the load setting after EVA, so the load after EVA is suppressed to a predetermined setting value to suppress power consumption and maintain stable power even after grid failure is restored. Load operation can be performed (ensuring dynamic stability). Also,
After EVA, it is possible to shift to load control using ALR, so it is not affected by grid frequency fluctuations after EVA operation.

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 ensure stable operation of a steam turbine plant while ensuring improved stability of the power system.

[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,
23...Load limiter, 24...Steam control valve actual opening degree, 18, 27...EVA start 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 degree deviation detector,
32... Automatic load setting device, 33... Switching device, 34
...Actual load, 35...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 steam control valve is closed based on a set load value corresponding to the valve opening predetermined by a load limiter. A high-speed valve control method characterized by controlling.