Method for preventing galloping of steam turbine in starting process

Abstract

The invention relates to the technical field of steam turbines, and discloses a method for preventing galloping of a steam turbine in the starting process, a control broken line table with the rotating speed as the horizontal axis and the valve opening as the vertical axis is introduced on the basis of an existing PID control module, and the mode of combining feedforward control and feedback control is adopted for controlling the speed increasing process of the steam turbine. Compared with an original control mode, feedforward control is added on the basis of keeping original functions, a safety range is set, and the situation that the rotating speed of the steam turbine is out of control due to the fact that the opening degree of a regulating valve is too large and the instantaneous steam admission flow is suddenly increased in the speed increasing process is prevented by limiting the maximum steam admission flow in different rotating speed intervals of the steam turbine. The risks of time delay and untimely equipment response existing in single feedback control can be effectively avoided, the advantages of feedforward control and feedback control are integrated, and malignant galloping accidents of the steam turbine are effectively avoided.

Description

Technical Field

[0001] The invention relates to the technical field of steam turbines, and in particular to a method for preventing a steam turbine from running out of control during its startup. Background Art

[0002] A steam turbine is a rotary power machine that converts steam energy into mechanical energy. It is widely used in the fields of electricity, industry, and ships. Steam turbine runaway is an abnormal state during use. Steam turbine runaway refers to the loss of control of the steam turbine speed. The actual speed greatly and quickly exceeds the safety range, which in turn causes the unit to vibrate more, emit abnormal noises, and increase the bearing temperature. It may even cause bearing damage, friction between moving and stationary blades, loose turbine impellers, blade breakage, broken shafts, damage to turbine generator sets, oil leakage and fire in the lubricating oil system, and casualties. When a steam turbine runaway occurs, it is very easy to cause the destruction of the machine and the death of people, and ultimately cause major economic losses. In addition, steam turbine runaway has the characteristics of a short time of occurrence, no time for personnel to respond, and very serious consequences of the accident. Therefore, steam turbine runaway is a serious and vicious accident that must be resolutely avoided in the thermal power generation industry.

[0003] Existing measures to prevent turbine overspeed include mechanical overspeed prevention and speed detection overspeed prevention. Among them, the main method of mechanical overspeed prevention is to set a speed limiter on the turbine rotor. When the turbine speed reaches the limit, the fly ring set on the rotor exceeds the specified centrifugal force, and the fly ring flies out to trigger the turbine safety system to operate, close the automatic main steam valve and regulating valve, and cut off the driving steam source. This method is a set of overspeed prevention system on the turbine body, but because the mechanical overspeed prevention measures are set on the turbine body, they are generally only tested during major and medium repairs, and are basically no longer adjusted after being put into use. In addition, mechanical parts are prone to limit value migration, and there are many uncontrollable factors, and the reliability of preventing overspeeding is not guaranteed.

[0004] The speed detection and overspeed prevention measures are to control the steam turbine in real time by continuously detecting and tracking the steam turbine speed. When the steam turbine speed is detected to exceed the limit value, the automatic main steam valve and the regulating valve are closed to cut off the driving steam source. However, if the speed detector is not installed correctly and the speed sensor is prone to fail to detect the signal in the low speed area, the actual speed value will be seriously low or even undetectable. At this time, due to the large deviation between the detected speed and the set speed value, the control program will gradually increase the opening of the steam inlet regulating valve after judgment. For example: when the steam turbine is speeding up, the speed is set to 500rpm, but due to the speed sensor, the speed is not detected for a long time or the detected speed is lower than the actual speed. At this time, the control program will increase the opening of the steam inlet valve to increase the turbine speed. At this time, there may be a problem of excessive valve opening, which will cause the actual speed of the steam turbine to soar, and eventually lead to a runaway accident.

[0005] SUMMARY OF THE INVENTION

[0006] The technical problem solved by the present invention is: how to prevent a runaway accident from occurring during the start-up and speed-up process of a steam turbine.

[0007] The purpose of the present invention can be achieved through the following technical solutions:

[0008] A method for preventing a steam turbine from running away during startup, comprising the following steps:

[0009] Step 1: First, obtain the target steam turbine characteristic curve diagram and its regulating valve characteristic curve diagram;

[0010] Step 2: Divide the speed-up curve of the steam turbine into multiple speed-up stages to form multiple speed nodes, and output corresponding speed node values ​​A1, A2...Ax as speed setting values ​​for different speed-up stages;

[0011] Step 3: Based on the turbine characteristic curve and regulating valve characteristic curve obtained in step 1, the flow rate at the specified steam temperature and pressure is used as the intermediate quantity, and the valve opening values ​​B1, B2...Bx corresponding to each speed node value A1, A2...Ax of the turbine are obtained as the valve opening setting upper limit value in the corresponding speed increase stage, and a speed-valve opening control line chart is prepared;

[0012] Step 4: After the equipment is started, the real-time speed At of the steam turbine is obtained through the speed sensor, and the real-time speed At is compared with the speed node value Ax through the PID control module;

[0013] Step 41: During the first speed-up stage control process, the speed node value is A1, and the corresponding valve opening upper limit value is set to B1, including a speed-up process and a maintenance process;

[0014] Step 411: During the speed increase process, when the real-time speed At is less than the set speed A1, the PID control module determines that the valve opening is increased, and outputs the increased valve opening value as Bt. When Bt is less than B1, the actual opening of the control valve is controlled to increase to Bt; when Bt is greater than B1, the actual opening of the control valve is controlled to be B1;

[0015] Step 412: When the real-time speed At is equal to the set speed A1, the speed increase process ends and enters the maintenance process;

[0016] Step 413: During the maintenance process, when the real-time speed At is less than the set speed A1, the PID control module determines that the valve opening increases, and outputs the increased valve opening value as Bt. When Bt is less than B1, the actual opening of the regulating valve is controlled to increase to Bt; when Bt is greater than B1, the actual opening of the regulating valve is controlled to be B1; when the real-time speed At is greater than the set speed A1, the PID control module determines that the valve opening decreases, and issues an alarm message;

[0017] Step 414: The maintenance process is terminated after the specified time is maintained and a confirmation signal is obtained, and the next speed increase phase is entered, while the speed node value and the corresponding valve opening value are changed;

[0018] Step 42: During the second speed-up stage control process, the speed node value is A2, and the corresponding valve opening upper limit value is set to B2, including the speed-up process and the maintenance process; repeat steps 411 to 414 until entering the next speed-up stage;

[0019] Step 43: Repeat step 42 until entering the xth speed-up stage control process, in which the speed node value is Ax, and the corresponding valve opening setting upper limit value is Bx, including the speed-up process and the maintenance process; the entire control process ensures that the actual valve opening value does not exceed the valve opening setting upper limit value Bx;

[0020] Step 44: When the actual rotation speed At reaches the preset grid-connected speed, the steam turbine equipment is transformed into a grid-connected state, and the upper limit value of the actual valve opening after grid connection is increased to the valve fully open.

[0021] In one solution of the present invention: the number of rotation speed nodes is set to at least three.

[0022] In one solution of the present invention: the valve opening value corresponding to each speed node is increased by a specified margin c as the valve opening setting upper limit value during the corresponding speed-up phase of the steam turbine.

[0023] In one solution of the present invention: the specified margin c=2%.

[0024] In one embodiment of the present invention, the equipment information of the target flywheel machine, the set speed data, the valve opening data, the designated margin data and the actual speed increase curve are stored in a database.

[0025] In one embodiment of the present invention, the speed-up process of the target flywheel is timed, and when the actual speed-up time exceeds twice the preset speed-up time, an alarm message is issued.

[0026] In one scheme of the present invention: when the speed A1 is set to 500rpm, the corresponding upper limit of the valve opening B1 is 12%; when the speed A2 is set to 1200rpm, the corresponding upper limit of the valve opening B2 is 25%; when the speed A3 is set to 2500rpm, the corresponding upper limit of the valve opening B3 is 32%; when the speed A4 is set to 3000rpm, the corresponding upper limit of the valve opening B4 is 41%.

[0027] In one solution of the present invention: when the actual rotation speed reaches the preset grid-connected speed, a grid-connected application signal is sent out, and the grid-connected action is performed after confirmation.

[0028] In one embodiment of the present invention, the rotation speed-valve opening control line chart has the rotation speed as the horizontal axis and the valve opening as the vertical axis.

[0029] Beneficial effects of the present invention:

[0030] Based on the existing PID control module, this application introduces a control line chart with speed as the horizontal axis and valve opening as the vertical axis, and adopts a combination of feedforward control and feedback control to control the turbine speed-up process. Compared with the original control method, feedforward control is added on the basis of maintaining the original function, and a safety range is set. By limiting the maximum steam inlet flow rate in different speed ranges of the steam turbine, the turbine is prevented from losing speed control during the speed-up process due to excessive opening of the regulating valve and sudden increase in instantaneous steam inlet flow rate. It can effectively avoid the time lag and the risk of untimely equipment response in single feedback control, and combines the advantages of feedforward control and feedback control to effectively avoid vicious runaway accidents of steam turbines.

[0031] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The above and / or additional aspects and advantages of the present invention will become apparent and easy to understand from the description of the embodiments in conjunction with the following drawings. Obviously, the drawings in the following description are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative work. Among them:

[0033] Figure 1 It is the control flow chart of the existing PID control module;

[0034] Figure 2 It is a schematic diagram of the control process of the present invention;

[0035] Figure 3 It is a speed-opening control line graph of an embodiment of the present invention. DETAILED DESCRIPTION

[0036] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0037] In the description of the present invention, it should be understood that descriptions involving orientations, such as up, down, front, back, left, right, etc., and orientations or positional relationships indicated are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0038] In the description of the present invention, "several" means one or more, "more" means more than two, "greater than", "less than", "exceed" etc. are understood as not including the number itself, and "above", "below", "within" etc. are understood as including the number itself. If there is a description of "first" or "second", it is only used for the purpose of distinguishing the technical features, and cannot be understood as indicating or implying the relative importance or implicitly indicating the number of the indicated technical features or implicitly indicating the order of the indicated technical features.

[0039] When the steam turbine is in the grid-connected state, due to the power grid, the speed of the steam turbine changes synchronously with the frequency of the power grid. When the power factor is constant, the change of the driving steam source will only bring about the change of the generator power. Therefore, generally speaking, the steam turbine will only have a vicious runaway accident when it is not in the grid-connected state. There are two reasons for the runaway of the steam turbine in the non-grid-connected state. One is that the steam turbine is disconnected from the grid due to a fault in the grid-connected state. The emergency measure taken in this state is to directly cut off the steam source; the other is that during the startup and speed-up process of the steam turbine, the speed of the steam turbine soars due to speed detection failure or receiving a wrong signal, which eventually leads to a runaway accident.

[0040] The main reasons for turbine runaway during startup are: (1) The speed sensor is not installed accurately or the sensor cannot detect a signal at low speed, resulting in the detected speed being lower than the actual speed value. At this time, due to the large deviation between the detected speed and the set speed value, the control program will increase the steam inlet valve opening to increase the turbine speed. At this time, there may be a problem of valve opening being too large, which will cause the actual turbine speed to soar, and eventually lead to a runaway accident. (2) The generator grid connection signal is delivered incorrectly, causing the control system to misjudge the grid connection and directly increase the set speed to the grid connection speed. Since the set speed and valve opening after grid connection are both large, the wrong grid connection will cause the turbine to speed up too quickly and cause loss of control. (3) The turbine steam inlet regulating valve is out of control, causing a sudden increase in the steam inlet volume, which in turn causes the actual turbine speed to soar, and eventually leads to a runaway accident.

[0041] Regardless of the reason for the turbine overspeed, it is because the control of the driving steam source deviates from the desired control value. The existing speed control process is: first detect the abnormal increase in the turbine speed, and then limit the driving gas source. Figure 1 The basic control process of the existing PID control module is: detect the turbine speed -> compare with the speed given value and make a judgment -> control the opening of the regulating valve. Specifically, the turbine speed is detected by the speed sensor during use, and then compared with the given value. If it is less than the given value, the valve opening is increased. When abnormal speed increase is detected, the regulating valve is closed. However, due to various reasons (such as sensor failure, inaccurate sensor installation, difficulty in obtaining speed signals in low-speed areas, detection signal delay, etc.), it may not detect the speed or the detected speed is too low, which will cause the valve opening to be too large, which is easy to cause a runaway accident. Even if it can detect the abnormal speed increase, it is difficult to prevent the occurrence of a runaway accident due to its hysteresis.

[0042] Moreover, the control process of the existing PID control module belongs to the feedback control mode. Feedback control is based on accurate, reliable and rapid signal detection, accurate program judgment, and reliable and rapid field equipment. Inevitably, there are risks of accuracy, lag and equipment reliability in each link. Especially in the low-speed area, the speed loss is prone to occur. And because of the suddenness of the turbine runaway, once an accident occurs, any one-second delay will cause irreversible loss of the unit. However, the reliability risks and lags in the existing feedback control mode are difficult to fully meet the needs of preventing runaway accidents. In order to solve the aforementioned problems, the present application provides a method for preventing runaway during the turbine startup process during the turbine startup and speed increase process.

[0043] See also Figure 2-3 The embodiment of the present invention provides a method for preventing a turbine from running away during startup, comprising the following steps:

[0044] First, the characteristic curve of the target steam turbine and the characteristic curve of its regulating valve are obtained; the characteristic curve of the steam turbine includes the steam flow at the specified temperature and pressure corresponding to the steam turbine at different speeds and loads. The characteristic curve of the steam turbine regulating valve includes the steam flow at the specified temperature and pressure corresponding to the different openings of the regulating valve.

[0045] Then, the speed increase curve of the steam turbine is divided into multiple speed increase stages to form multiple speed nodes, and the corresponding speed node values ​​A1, A2...Ax are output as the speed setting values ​​of different speed increase stages; that is, the speed gear that the steam turbine needs to stay in during the speed increase process. Among them, x is a positive integer, which can be 1, 2, 3, 4... The number of speed nodes is at least three or more. Based on the obtained steam turbine characteristic curve diagram and regulating valve characteristic curve diagram, the flow rate at the specified steam temperature and pressure is used as the intermediate quantity, and the valve opening values ​​B1, B2...Bx corresponding to each speed node value A1, A2...Ax of the steam turbine are obtained as the valve opening setting upper limit value of the corresponding speed increase stage, and a speed-valve opening control line table is made, and the speed-valve opening control line table uses the speed as the horizontal axis and the valve opening as the vertical axis. In each speed-up stage, the corresponding valve opening setting upper limit value is used as the upper limit of the actual valve opening. Even if the detection speed is low or lost, the valve opening will not increase suddenly, but will be maintained within a safe valve opening range, effectively avoiding runaway accidents.

[0046] In actual use, after the equipment is started, the speed sensor is used to obtain the real-time speed At of the steam turbine, and the real-time speed At is compared with the speed node value Ax through the PID control module; the entire speed-up stage of the steam turbine is divided into x speed-up stages for control, and the valve opening setting upper limit value Bx is set for each speed-up stage, and the actual valve opening is ensured not to exceed the upper limit value Bx of the speed-up stage. The specific control process is as follows:

[0047] In the first speed-up stage control process, the speed node value is A1, and the corresponding valve opening setting upper limit value is B1, including the speed-up process and the maintenance process; in the speed-up process, when the real-time speed At is less than the set speed A1, the PID control module determines that the valve opening increases, and outputs the increased valve opening value as Bt. When Bt is less than B1, the actual opening of the control valve is controlled to increase to Bt; when Bt is greater than B1, the actual opening of the control valve is controlled to be B1; when the real-time speed At is equal to the set speed A1, the speed-up process ends and enters the maintenance process; in the maintenance process, when the real-time speed At is equal to the set speed A1, the speed-up process ends and enters the maintenance process. When the speed At is less than the set speed A1, the PID control module determines that the valve opening increases, and outputs the increased valve opening value as Bt. When Bt is less than B1, the actual opening of the control valve is controlled to increase to Bt; when Bt is greater than B1, the actual opening of the control valve is controlled to be B1; when the real-time speed At is greater than the set speed A1, the PID control module determines that the valve opening decreases, and issues an alarm message; the maintenance process ends after the specified time is maintained and a confirmation signal is obtained, and the next speed increase stage is entered, while the speed node value and its corresponding valve opening value are changed.

[0048] Each other speed-up stage is the same as the first speed-up stage, except that the speed node value and its corresponding upper limit of valve opening value are different. This is repeated until the x-th speed-up stage control process is entered. In the x-th speed-up stage control process, the speed node value is Ax, and the corresponding valve opening setting upper limit value is Bx. This process includes the speed-up process and the maintenance process. During the speed-up process, when the real-time speed At is less than the set speed Ax, the PID control module determines that the valve opening increases, and outputs the increased valve opening value as Bt. When Bt is less than Bx, the actual opening of the control valve is controlled to increase to Bt; when Bt is greater than Bx, the actual opening of the control valve is controlled to be Bx. When the real-time speed At is equal to the set speed Ax, the speed increase process ends and enters the maintenance process; during the maintenance process, when the real-time speed At is less than the set speed Ax, the PID control module determines that the valve opening increases, and outputs the increased valve opening value as Bt. When Bt is less than Bx, the actual opening of the control valve is controlled to increase to Bt; when Bt is greater than Bx, the actual opening of the control valve is controlled to be Bx; when the real-time speed At is greater than the set speed Ax, the PID control module determines that the valve opening decreases. At this time, there may be an abnormal speed increase, and an alarm message needs to be issued to notify relevant personnel for confirmation so that the problem can be promptly handled and eliminated. The maintenance process ends after the specified time and the confirmation signal is obtained, and the next speed increase stage is entered, and the speed node value and its corresponding valve opening value are changed at the same time.

[0049] When the actual speed At reaches the preset grid-connected speed, the steam turbine equipment is transformed into the grid-connected state, and the upper limit value of the actual valve opening after the grid connection is increased to the valve fully open. Further, when the actual speed reaches the preset grid-connected speed, a grid-connected application signal is issued, and the grid-connected action is performed after confirmation. Because the grid-connected signal does not participate in the speed setting during the startup process of the steam turbine, this application adds a grid-connected manual judgment input button, and a grid-connected application is issued when the grid-connected speed is reached. After confirmation, the button is activated to receive the generator grid-connected signal and perform the grid-connected action. This can solve the occurrence of runaway accidents caused by the erroneous delivery of the grid-connected signal. Among them, the preset grid-connected speed can correspond to the speed node value in the control process of the last speed-up stage.

[0050] See also Figure 2-3 In one embodiment of the present invention, when the control line table is generated after obtaining the valve opening value Bx corresponding to each speed node Ax, the valve opening value corresponding to each speed node can be increased by a specified margin c (as an example, the specified margin c=2%) as the upper limit of the valve opening at different stages during the turbine speed increase process. At this time, the control line table is the control line graph (such as Figure 3 ). The margin can be set according to the actual situation, and the margin is set to ensure that the valve opening can meet the power demand for the turbine speed increase drive. When in use, the equipment information of the target flyturbine, the set speed data, the valve opening data, the specified margin data and the actual speed increase curve can be stored in the database. So as to continuously correct and improve the division of the rated temperature, pressure, speed node, valve opening and the rationality of the specified margin setting through historical data. At the same time, when in use, the speed increase process of the target flyturbine can be timed to obtain the actual speed increase time T, and the time information required for the expected speed increase curve can be obtained. When the actual speed increase time exceeds the preset speed increase time y times (such as 1.5 times, 2 times), at this time, there may be a situation where the sensor detection speed is low or even cannot effectively monitor the speed. At this time, an alarm message is issued to the relevant personnel for manual confirmation and troubleshooting to prevent runaway accidents.

[0051] Working principle of the present invention:

[0052] As an example, under the conditions of rated pressure and temperature, if the steam flow rate required for the turbine speed to reach 500rpm is 20t / h, then the opening corresponding to the flow rate of 20t / h is obtained in the valve flow curve, assuming it is 10%. On this basis, a certain margin is appropriately added (assuming it is 2%), and we can obtain that the maximum valve opening at the turbine speed of 500rpm is 12%. In this way, the speed-valve opening line table of each key point of the turbine is gradually formed (such as Figure 3As shown in the figure, 1200rpm corresponds to a maximum opening limit of 25%, 2500rpm corresponds to 32%, and 3000rpm corresponds to 41%. After grid connection, the maximum opening limit is increased to full opening. That is, when the speed is set to A1 = 500rpm, the corresponding valve opening upper limit B1 = 12%; when the speed is set to A2 = 1200rpm, the corresponding valve opening upper limit B2 = 25%; when the speed is set to A3 = 2500rpm, the corresponding valve opening upper limit B3 = 32%; when the speed is set to A4 = 3000rpm, the corresponding valve opening upper limit B4 = 41%.

[0053] The speed increase control process of the steam turbine is as follows:

[0054] After the equipment is started, the turbine speed increases from zero and enters the first speed-up stage. The actual speed of the turbine is detected by the sensor, and then compared with the set speed. If the actual speed detected is less than the set speed A1, the operating range of the control valve is 0-12%, that is, the actual speed is less than 500rpm. At this time, the PID control module will determine that the valve opening is increased in order to speed up. At this time, the increased valve opening Bt is output. When Bt is less than B1=12%, assuming Bt=8%, the actual opening of the control valve is controlled to increase to 8%; when Bt is greater than B1, assuming Bt=14%, the actual opening of the control valve is controlled to be B12%; when the real-time speed detected reaches 500rpm, the speed-up process of the first speed-up stage ends, and the maintenance process is entered to warm up the equipment. In this process, when the real-time speed is less than 500, the valve opening is controlled to increase, and the control process is the same as the speed-up process. When the real-time speed is greater than 500, the valve opening is controlled to decrease and an alarm is issued to avoid abnormal speed increase. After the maintenance process lasts for a certain period of time (such as half an hour) and is confirmed, the maintenance process can be ended and the second speed increase stage can be entered. At this time, the set speed is changed to A2 = 1200rpm, and the corresponding valve opening upper limit is also changed to B2 = 25%. At this time, the actual speed obtained by detection is compared with the set speed A2 = 1200rpm, and the control process is the same as the first speed increase process. This process is repeated until the grid-connected speed is reached and the grid is connected.

[0055] In summary, the present application introduces a control line table based on the existing PID control module to control the opening of the gas source regulating valve as the power source, so that the steam inlet regulating valve of the steam turbine cannot exceed the maximum valve opening corresponding to the set speed. By adopting a feedforward control method, even if the detected speed of the steam turbine obtained by detection is lower than the actual speed, or the speed cannot be detected, due to the existence of the upper limit of the regulating valve opening, the regulating valve opening will not continue to increase, ensuring that the steam source of the steam turbine is always limited within a safe range, thereby effectively reducing the incidence of runaway accidents. Even if an abnormal speed increase occurs, the reaction time can be increased and the accident loss can be reduced. The present application can be implemented using the existing steam turbine regulating valve, or a regulating valve can be added in front of the steam turbine steam inlet regulating valve to implement this function, so as to prevent the steam inlet regulating valve from losing control and causing a sudden increase in the steam intake.

[0056] The above is a detailed description of an embodiment of the present invention, but the content is only a preferred embodiment of the present invention and cannot be considered to limit the scope of implementation of the present invention. All equivalent changes and improvements made according to the scope of application of the present invention should still fall within the scope of the claims of the present invention.

Claims

1. A method for preventing a steam turbine from running out of control during startup, characterized in that: The steps include: Step 1: First, obtain the target steam turbine characteristic curve diagram and its regulating valve characteristic curve diagram; Step 2: Divide the speed increase curve of the steam turbine into multiple speed increase stages to form multiple speed nodes, and output corresponding speed node values ​​A1, A2...Ax as speed setting values ​​for different speed increase stages; Step 3: Based on the turbine characteristic curve and regulating valve characteristic curve obtained in step 1, the flow rate at the specified steam temperature and pressure is used as the intermediate quantity, and the valve opening values ​​B1, B2...Bx corresponding to each speed node value A1, A2...Ax of the turbine are obtained as the valve opening setting upper limit value in the corresponding speed increase stage, and a speed-valve opening control line chart is prepared; Step 4: After the equipment is started, the real-time speed At of the steam turbine is obtained through the speed sensor, and the real-time speed At is compared with the speed node value Ax through the PID control module; Step 41: During the first speed-up stage control process, the speed node value is A1, and the corresponding valve opening setting upper limit value is B1, including the speed-up process and the maintenance process; Step 411: During the speed increase process, when the real-time speed At is less than the set speed A1, the PID control module determines that the valve opening is increased, and outputs the increased valve opening value as Bt. When Bt is less than B1, the actual opening of the control valve is controlled to increase to Bt; when Bt is greater than B1, the actual opening of the control valve is controlled to be B1; Step 412: When the real-time speed At is equal to the set speed A1, the speed increase process ends and enters the maintenance process; Step 413: During the maintenance process, when the real-time speed At is less than the set speed A1, the PID control module determines that the valve opening increases, and outputs the increased valve opening value as Bt. When Bt is less than B1, the actual opening of the regulating valve is controlled to increase to Bt; when Bt is greater than B1, the actual opening of the regulating valve is controlled to be B1; when the real-time speed At is greater than the set speed A1, the PID control module determines that the valve opening decreases, and issues an alarm message; Step 414: the maintenance process is terminated after a specified time is maintained and a confirmation signal is obtained, and the next speed increase phase is entered, while the speed node value and the corresponding valve opening value are changed; Step 42: During the second speed-up stage control process, the speed node value is A2, and the corresponding valve opening upper limit value is set to B2, including the speed-up process and the maintenance process; repeat steps 411 to 414, and ensure that the actual valve opening in this process does not exceed B2 until entering the next speed-up stage; Step 43: Repeat step 42 until entering the xth speed increase stage control process, in which the speed node value is Ax, and the corresponding valve opening setting upper limit value is Bx, including the speed increase process and the maintenance process; The entire control process ensures that the actual valve opening value does not exceed the valve opening setting upper limit value Bx until the control process ends; Step 44: When the real-time rotation speed At reaches the preset grid-connected speed, the steam turbine equipment is transformed into the grid-connected state, and the upper limit value of the actual valve opening after the grid connection is increased to the valve fully open.

2. A method for preventing runaway during the startup of a steam turbine according to claim 1, characterized in that: Set the number of speed nodes to at least three.

3. A method for preventing a turbine from running out of control during startup according to claim 1, characterized in that: The valve opening value corresponding to each speed node is increased by a specified margin c as the upper limit of the valve opening at different stages during the turbine speed increase process.

4. A method for preventing a turbine from running out of control during startup according to claim 3, characterized in that: The specified margin c=2%.

5. A method for preventing runaway during the startup of a steam turbine according to claim 3, characterized in that: The equipment information of the target flywheel machine, the set speed data, the valve opening data, the designated margin data and the actual speed increase curve are stored in the database.

6. A method for preventing runaway during the startup of a steam turbine according to claim 1, characterized in that: The speed-up process of the target flyturbine is timed, and when the actual speed-up time exceeds twice the preset speed-up time, an alarm message is issued.

7. A method for preventing runaway during the startup of a steam turbine according to claim 1, characterized in that: When the speed is set to A1=500rpm, the corresponding upper limit of valve opening is B1=12%; when the speed is set to A2=1200rpm, the corresponding upper limit of valve opening is B2=25%; when the speed is set to A3=2500rpm, the corresponding upper limit of valve opening is B3=32%; when the speed is set to A4=3000rpm, the corresponding upper limit of valve opening is B4=41%.

8. A method for preventing runaway during the startup of a steam turbine according to claim 1, characterized in that: When the actual speed reaches the preset grid-connected speed, a grid-connected application signal is sent out, and the grid-connected action is performed after confirmation.

9. A method for preventing runaway during the startup of a steam turbine according to claim 1, characterized in that: The speed-valve opening control line chart has the speed as the horizontal axis and the valve opening as the vertical axis.

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