Control method and structure for shortening closing time of steam extraction check valve
By adding an independent trip output circuit to the ETS system and connecting it in series with the original extraction steam non-return valve control circuit via a normally closed contact, the control logic was optimized, which solved the problem of the turbine extraction steam non-return valve closing time exceeding the standard, thus improving safety and economy and avoiding the risk of turbine overspeed caused by the non-return valve closing delay.
Patent Information
- Application Number
- CN202610134239.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-01-30
- Publication Date
- 2026-03-10
AI Technical Summary
In 300MW units of thermal power plants, the closing time of the turbine extraction check valves generally exceeds the standard, failing to meet the requirement of "total closing time of extraction check valve < 1s". This results in design or commissioning shortcomings in the unit's rapid cut-off and protection, affecting the system's safety and reliability.
By adding an independent trip output circuit to the turbine emergency trip system (ETS) and connecting it in series with the original extraction non-return valve control circuit via a normally closed contact, a control architecture with direct control and dual-mode switching is formed. This directly acts on the extraction non-return valve closing circuit, optimizing the control logic to shorten the closing time.
Without altering the valve's mechanical structure, the control loop delay is significantly reduced, with the total closing time controlled within 950ms. This solves the problems of mechanical and control delays, improves system safety and economy, and avoids the risk of turbine overspeed caused by the non-return valve's closing delay.
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Figure CN121630541A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the technical field of steam turbine control of thermal power plant, in particular to a control method and structure for shortening the closing time of extraction check valve. BACKGROUND
[0002] In the current operation practice of 300MW unit in thermal power plant, the closing time of extraction check valve of steam turbine is generally over-standard, which is difficult to meet the key recommended value of "total closing time of extraction check valve <1s". This situation directly reflects the obvious short board in the design or debugging of the unit in terms of rapid cut-off and protection, which has become a prominent hidden danger affecting the safety and reliability of the system.
[0003] Specifically, the long closing time is mainly caused by the delay accumulation in the closing process, including the control loop delay and the mechanical action delay. The delay of the control loop is reflected in the signal transmission and processing lag between the issuance of the turbine trip command and the actual action of the relay of each extraction check valve control station, and the delay caused by the output of the trip signal via the control station card is particularly significant. In the mechanical aspect, the delay is mainly caused by the factors such as the large mechanical resistance in the valve closing process, the insufficient spring stiffness or pre-tightening force of the cylinder, and the unreasonable setting of the limit switch, which causes the time delay between the relay action and the disappearance of the "opened" signal of the valve.
[0004] These delays not only make the valve unable to achieve rapid and tight closing, but also easily cause the steam in the extraction pipe to flow backward under the conditions of unit load rejection or emergency shutdown, which may cause serious accidents such as turbine overspeed and rotor damage, and also poses a continuous threat to the coordinated control and operation stability of the unit. Therefore, systematically analyzing and solving the closing delay problem of extraction check valve has become an urgent technical demand to improve the performance of the unit regulation and protection system and to ensure the safe and economic operation of the power plant. SUMMARY
[0005] The present application aims to provide a control method and structure for shortening the closing time of extraction check valve, which solves the problem of closing delay of existing extraction check valve and cannot achieve rapid and tight closing.
[0006] To achieve the above purpose, the present application adopts the following technical scheme: a control method for shortening the closing time of extraction check valve, comprising the following steps: S1, performing mechanical performance pre-test on the extraction check valve to obtain its own closing time; S2, performing performance test on the emergency trip system (ETS) of the steam turbine to obtain its scanning period, wherein the scanning period of the ETS system is ≤50ms; S3, adding an independent trip output loop in the ETS system and configuring pulse output logic, wherein the pulse output logic is a 10s pulse signal; S4, connect the signal interface of the trip output circuit in series with the original extraction steam non-return valve control circuit; S5: The monitoring device collects key signals in real time during the test to verify whether the total closing time of the extraction steam non-return valve meets the standard. If it does not meet the standard, return to S1 to re-perform the mechanical performance test, or return to S3 to optimize the logic configuration of the trip output circuit.
[0007] Meanwhile, this solution also provides a control structure for shortening the closing time of the extraction non-return valve, applied to the aforementioned control method for shortening the closing time of the extraction non-return valve, including: The turbine emergency trip system (ETS) control station is equipped with an independent trip output circuit; A digital output (DO) channel is electrically connected to the trip output circuit, and the signal interface of the DO channel adopts a normally closed contact design. The original extraction steam non-return valve control circuit includes a DCS control channel, and the normally closed contact is connected in series with the DCS control channel to form a dual-mode control path. The monitoring device is connected to the position signal output terminal of the extraction non-return valve and is used to collect the open and closed signals.
[0008] The principles and advantages of this scheme are: This solution breaks through the signal transmission bottleneck of traditional control loops by constructing an innovative architecture of "direct control + dual-mode switching". Its core lies in directly applying the ETS system's trip command to the extraction steam non-return valve closing circuit through a newly added independent DO channel, forming a series structure with the original DCS control channel. When the ETS is triggered, the normally closed contact instantaneously conducts, skipping the signal relay link between the original control stations, compressing the valve closing command response time to less than 50ms. The 10s pulse logic design cleverly achieves seamless switching between emergency control and normal operation, ensuring rapid action during tripping while avoiding prolonged occupation of normal DCS control authority.
[0009] Compared with existing technologies, traditional solutions rely on the step-by-step transmission of signals between control stations, resulting in control loop delays generally exceeding 300ms. Furthermore, the combined mechanical and control delays make it difficult to meet the 1s standard. In contrast, this solution, through the serial design of hardware interfaces and optimization of timing logic, controls the total closing time to 950ms without altering the valve's mechanical structure. This reduces the control loop delay by 83%, creatively resolving the technical contradiction between "uncontrollable mechanical delay" and "the need to eliminate control delay."
[0010] Unexpectedly, this "minimum modification" approach not only avoided the high costs of on-site pipeline modifications, but also achieved signal interference elimination and 10ms-level time monitoring accuracy through the collaboration of the filtering unit and the time recording unit. This enabled the problem that originally required complex mechanical adjustments to be solved through control logic optimization, providing a standardized modification path that is both safe and economical for similar units, and completely eliminating the risk of turbine overspeed caused by the delay in closing the non-return valve. Attached Figure Description
[0011] Figure 1 This is a flowchart illustrating a control method for shortening the closing time of the extraction non-return valve according to the present invention. Figure 2 This is a schematic diagram of the extraction steam non-return valve closing control loop in the control structure for shortening the closing time of the extraction steam non-return valve according to the present invention; Figure 3 This is a schematic diagram of the trip output circuit in the control structure for shortening the closing time of the extraction non-return valve according to the present invention; Figure 4 This is a schematic diagram of the existing extraction non-return valve closing control circuit. Detailed Implementation
[0012] The following detailed description illustrates the specific implementation method: This embodiment presents a control method and structure for shortening the closing time of a non-return valve during steam extraction. Through hardware interface serialization and logic optimization, the total closing time is controlled to 950ms without altering the valve's mechanical structure, reducing control loop delay by 83%. This creatively resolves the contradiction between "uncontrollable mechanical delay" and "the need to eliminate control delay."
[0013] Option 1 A control method for shortening the closing time of the extraction non-return valve is provided, as shown in the attached figure. Figure 1 As shown, it includes the following steps: S1, perform a mechanical performance pre-test on the extraction non-return valve to obtain its own closing time.
[0014] In this embodiment, the self-closing time is the time interval between the loss of the open position signal and the issuance of the closed position signal from the extraction steam non-return valve. During testing, a high-precision time recorder (resolution ≤1ms) is connected to the extraction steam non-return valve position sensor. The valve is triggered to close by simulating a power failure. The test is repeated three times and the average value is taken to ensure that the mechanical closing time from the loss of the "open position signal" to the issuance of the "close position signal" is ≤900ms, i.e., the self-closing time is ≤900ms. Additionally, before testing, it is necessary to clean the moving parts of the valve and apply special lubricant to eliminate any jamming or interference.
[0015] S2, Perform performance testing on the turbine emergency trip system (ETS) and obtain its scan cycle; the scan cycle of the ETS system is ≤50ms to ensure a rapid response to the trip command.
[0016] In this embodiment, the system diagnostic interface is accessed through the ETS engineer station to monitor the controller scan cycle (≤50ms) and DO module response time (≤20ms). A signal generator is used to simulate a trip command, and an oscilloscope is used to measure the delay time from the command issuance to the DO channel output. The maximum value is taken after 10 consecutive tests.
[0017] S3. Add an independent trip output circuit to the ETS system and configure pulse output logic, which is a 10s pulse signal.
[0018] Combined with appendix Figure 2 As shown, an independent trip output circuit is added to the ETS control station programming environment, using ladder logic to implement a 10s pulse output function (the rising edge of the pulse triggers valve closure, and the falling edge automatically resets). In this embodiment, the trip output circuit outputs signals through the digital output channel of the ETS system. The signal interface of the digital output channel uses normally closed contacts, which are connected in series with the DCS control channel in the original extraction steam non-return valve control circuit.
[0019] When the ETS system activates, the normally closed contact triggers the extraction non-return valve to close; after the 10s pulse signal ends, the normally closed contact resets, and the original DCS control channel regains normal operating authority over the extraction non-return valve.
[0020] In this embodiment, the specific configuration includes the following sub-steps: S3.1, Create intermediate variables for the ETS trip signal.
[0021] In this embodiment, if a new BOOL-type intermediate variable “ETS_Trip_Signal” is added to the variable table of the ETS control station programming environment, it is associated with the main trigger signal of the turbine emergency trip system (such as the “OR” operation result of protection logic such as speed over-limit and large axial displacement). The variable address allocation follows the IEC 61131-3 standard format (such as %M0.0), and the variable description is marked as “used for independent trip control of extraction steam non-return valve”.
[0022] S3.2, add TON timer (default value 10000ms).
[0023] In this embodiment, a standard timer instruction (TON) such as Siemens S7-300 series is inserted into the logic programming interface. The timer number is assigned as T100, the preset value (PT) is set to 10000ms (i.e. 10s), the timer start signal (IN) is associated with the "ETS_Trip_Signal" variable created in S3.1, the timer output (Q) is defined as "Trip_Pulse_Output", and the real-time monitoring function of the current timer value (ET) is enabled.
[0024] S3.3, Configure the DO channel output logic (output normally closed contact conduction signal during pulse period).
[0025] In this embodiment, an AND logic network is constructed in the ladder diagram, and the timer output "Trip_Pulse_Output" is connected in series with the DO channel enable signal (%Q0.0). When "Trip_Pulse_Output" is 1, the normally closed contact (terminals 3-4) of the DO channel is triggered to conduct momentarily, and a 24VDC control signal is output to the extraction steam non-return valve closing coil. At the same time, a pulse end reset instruction is added to the logic ("ETS_Trip_Signal" is automatically reset when ET≥PT) to ensure that the contact returns to the normally closed state after 10s and releases the DCS control authority.
[0026] S4, connect the signal interface of the trip output circuit in series with the original extraction steam non-return valve control circuit.
[0027] In this embodiment, the normally closed contact (terminal number 3-4) of the newly added DO channel is connected via a 2.5mm... 2 The shielded cable is connected in series to the K1 relay coil circuit of the original DCS control circuit. The cable shield is grounded at one end (grounding resistance ≤ 4Ω) and kept at a distance of ≥ 30cm from the power cable to avoid electromagnetic interference.
[0028] S5: The monitoring device collects key signals in real time during the test to verify whether the total closing time of the extraction steam non-return valve meets the standard. If it does not meet the standard, return to S1 to re-perform the mechanical performance test, or return to S3 to optimize the logic configuration of the trip output circuit.
[0029] In this embodiment, the monitoring device is a filtering device, and its key signals include the manual ETS trigger signal, the extraction non-return valve open-to-position signal, and the closed-to-position signal. The total closing time is the time interval from the issuance of the manual ETS trigger signal to the issuance of the closed-to-position signal, and the total closing time is ≤1s.
[0030] In this embodiment, a filter device is installed in the control cabinet to receive three signals: 1) manual ETS trigger signal (24VDC); 2) valve open signal (NPN proximity switch); 3) valve closed signal (NPN proximity switch). The time recording unit uses an NI cDAQ-9174 acquisition module with a sampling rate set to 1kHz. The time interval between the trigger signal and the closed signal is calculated in real time using LabVIEW software.
[0031] Its joint debugging and testing process includes: 1) Static test: Simulate ETS operation to verify the output pulse width (10±0.5s) of the DO channel and the on / off status of the contacts.
[0032] 2) Dynamic test: Perform three manual ETS trigger tests under no-load conditions and record the total shutdown time (required ≤1s).
[0033] 3) Disturbance test: Apply 50Hz electromagnetic interference during valve operation to verify the filtering unit's ability to suppress signal jitter (signal fluctuation amplitude required ≤50mV).
[0034] If the test fails, prioritize checking: ① DO channel wiring polarity (ensure normally closed contacts are correctly connected in series); ② ETS logic scan cycle (improve response speed by increasing priority); ③ Mechanical resistance (reduce invalid stroke by adjusting valve limit switch position). After each optimization, three verification tests must be performed to ensure consistent results.
[0035] In this embodiment, a trip circuit output is added in the ETS control station. After the ETS is activated, a 10-second pulse is sent to the newly added DO channel normally closed contact. This normally closed contact and the corresponding extraction steam non-return valve are connected in series in the DCS to control the DO channel to close. When the ETS is activated, the valve closes immediately. After the pulse time, the DCS can operate normally. According to actual measurements, the time from the ETS command to the DO channel activation is about 50ms.
[0036] Option 2 In this embodiment, a control structure for shortening the closing time of the extraction non-return valve is also provided. Applied to the aforementioned control method for shortening the closing time of the extraction non-return valve, it requires no modification to the on-site piping and achieves the goal solely through control logic optimization. Its structure is shown in the attached figure. Figure 2 As shown, it includes: The turbine emergency trip system (ETS) control station is equipped with an independent trip output circuit. In this embodiment, the ETS control station can be configured with an IM460-1 interface module to achieve high-speed data interaction with the DO channel.
[0037] The independent trip output circuit is directly connected to the CPU module via the backplane bus, with signal transmission delay controlled within 20ms. (See attached image) Figure 3 As shown, the trip output circuit includes a pulse logic module. In this embodiment, the pulse logic module is configured to output a pulse signal with a duration of 10s. The DO channel remains in the conducting state during the pulse signal output and returns to the normally closed state after the pulse signal ends.
[0038] The digital output (DO) channel is electrically connected to the trip output circuit. The signal interface of the DO channel adopts a normally closed contact design. In this embodiment, the DO channel can be selected from digital output modules such as the Siemens SM 322-1BH01, whose normally closed contacts adopt a gold-plated contact design, with a contact resistance ≤50mΩ and a mechanical life ≥1 million cycles, ensuring long-term stable operation.
[0039] The original extraction steam non-return valve control circuit includes a DCS control channel. The normally closed contact is connected in series with the DCS control channel to form a dual-mode control path. In this embodiment, the DCS control channel in the original extraction steam non-return valve control circuit can communicate with the ETS system using the MODBUS RTU protocol. The communication baud rate is set to 19200bps, and the data frame format is 8 data bits, 1 stop bit, and even parity. The physical layer connection is achieved through a twisted-pair shielded cable, with both ends of the cable shield grounded to suppress common-mode interference.
[0040] And a monitoring device, which is connected to the position signal output terminal of the extraction steam non-return valve, to collect the open and closed signals.
[0041] In this embodiment, the monitoring device includes a filtering unit and a time recording unit. The filtering unit incorporates an RC low-pass filter circuit (cutoff frequency 1kHz) and a TVS transient suppression diode (response time <1ns), effectively filtering out electromagnetic interference (30V / m@10kHz-1GHz) in the industrial environment. The filtering unit is connected to the position sensor of the extraction steam non-return valve to eliminate signal interference. The time recording unit is configured to calculate the time interval from the ETS trigger signal to the reception of the closed position signal, with a measurement accuracy of ≤10ms. In this embodiment, the time recording unit is paired with an NI 9213 analog input module, with a sampling resolution of 16 bits and a sampling rate of 1kHz. It uses LabVIEW real-time acquisition software to synchronously record the trigger signal, open position signal, and closed position signal, achieving a timestamp accuracy of 1ms, meeting the metrological requirements of the testing system. The entire device is installed in an IP54-rated control cabinet, internally mounted on 35mm DIN rails. Each module is powered by a redundant 24VDC power supply to ensure continued monitoring functionality even in the event of a single power supply failure.
[0042] As attached Figure 4As shown, existing control technologies generally employ a series structure of "step-by-step transmission between control stations." ETS trip commands must pass through multiple stages, including the DCS control station, I / O modules, and relays. Control loop delays typically exceed 300ms, and with the mechanical delay added, the total shutdown time often exceeds 1.5s, making it difficult to meet standard requirements. Furthermore, existing technologies often rely on mechanical structure modifications (such as replacing springs with high-stiffness ones or optimizing cylinder stroke), which are not only costly (modification costs for a single unit exceed 200,000 yuan) but also prone to secondary problems such as pipeline vibration.
[0043] This solution, through a parallel architecture of "independent DO channel + dual-mode switching", directly introduces ETS commands into the valve closing loop, forming a redundant control path with the original DCS control channel. The optimization method is simple, directly activating the on-site extraction steam non-return valve closing loop, eliminating the transmission time between control stations, and compressing the control loop delay from 300ms to less than 50ms, a reduction of 83%, fundamentally solving the "signal relay bottleneck" problem.
[0044] Furthermore, this solution adopts a "minimally invasive" design, requiring no modification to the on-site control gas pipelines. Functional upgrades are achieved through logic configuration and hardware interface interconnection, without requiring any modifications to the on-site extraction steam non-return valve. This saves on construction workload, shortens the modification cycle to 1 / 5 of the traditional solution, and keeps the modification cost per unit below 30,000 yuan. At the same time, it avoids the safety risks that may be caused by mechanical modifications, effectively improves the safety performance of the steam turbine, avoids the safety hazards caused by the extraction steam non-return valve not closing in time during steam turbine tripping, and solves the long-standing problem in various power plants where the extraction steam non-return valve closing time exceeds 1 second.
[0045] The above descriptions are merely embodiments of the present invention, and common knowledge such as specific technical solutions and / or characteristics are not described in detail here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the technical solutions of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.
Claims
1. A control method for shortening the closing time of a steam extraction check valve, characterized by, The method comprises the following steps: S1, mechanical performance pre-test is performed on the extraction steam check valve to obtain its own closing time; S2, performance test is performed on the emergency trip system (ETS) of the steam turbine to obtain its scanning period; the scanning period of the ETS system is less than or equal to 50 ms; S3, an independent trip output loop is added in the ETS system, and pulse output logic is configured, wherein the pulse output logic is a 10 s pulse signal; S4, the signal interface of the trip output loop is connected in series with the original extraction steam check valve control loop; S5, key signals in the test process are collected in real time by a monitoring device to verify whether the total closing time of the extraction steam check valve meets the standard; if not, the mechanical performance test is performed again or the logic configuration of the trip output loop is optimized.
2. The control method of claim 1, wherein the control method is characterized by: In S1, the own closing time is the time interval from the loss of the opening to position signal to the issuance of the closing to position signal of the extraction steam check valve, and the own closing time is less than or equal to 900 ms.
3. The control method of claim 1, wherein the control method is characterized by: In S3, the trip output loop realizes signal output through the digital output channel of the ETS system.
4. The control method of claim 3, wherein the control method is characterized by: The signal interface of the digital output channel adopts a normally closed contact point, and the normally closed contact point is connected in series with the DCS control channel in the original extraction steam check valve control loop.
5. The control method of claim 1, wherein the control method is characterized by: In S5, the monitoring device is a filtering device, and the key signals include a manual ETS trigger signal, an extraction steam check valve opening to position signal and a closing to position signal.
6. The control method of claim 5, wherein the control method is characterized by: The total closing time is the time interval from the issuance of the manual ETS trigger signal to the issuance of the closing to position signal, and the total closing time is less than or equal to 1 s.
7. The control method of claim 4, wherein the control method is characterized by: When the ETS system acts, the normally closed contact point triggers the closing of the extraction steam check valve; after the 10 s pulse signal ends, the normally closed contact point resets, and the original DCS control channel restores the normal operation right of the extraction steam check valve.
8. A control structure for shortening the closing time of a steam extraction check valve, characterized by The control method is applied to the extraction steam check valve closing time shortening method in any one of claims 1-7, comprising: an emergency trip system (ETS) control station of a steam turbine, wherein the ETS control station is provided with an independent trip output loop; a digital output (DO) channel, wherein the DO channel is electrically connected with the trip output loop, and the signal interface of the DO channel adopts a normally closed contact point design; an original extraction steam check valve control loop, wherein the original extraction steam check valve control loop comprises a DCS control channel, and the normally closed contact point and the DCS control channel are connected in series to form a dual-mode control path; and a monitoring device, wherein the monitoring device is connected with the position signal output end of the extraction steam check valve, and is used to collect an opening to position signal and a closing to position signal.
9. The control structure for shortening the closing time of the extraction check valve according to claim 8, characterized in that: The trip output loop comprises a pulse logic module, the pulse logic module is configured to output a pulse signal with a duration of 10 s, the DO channel remains in a conduction state during the pulse signal output, and returns to a normally closed state after the pulse signal ends.
10. The control structure for shortening the closing time of the extraction check valve according to claim 8, characterized in that: The monitoring device comprises a filtering unit and a time recording unit, the filtering unit is connected with a position sensor of the extraction steam check valve, and is used to eliminate signal interference; the time recording unit is configured to calculate a time interval from the issuance of an ETS trigger signal to the reception of a closing to position signal, and the measurement accuracy of the time interval is less than or equal to 10 ms.