Hydroelectric generating set runner blade crack on-line monitoring method based on stress test system

Abstract

A kind of water turbine generator runner blade crack online monitoring method based on stress test system, steps are as follows: step S1, carry out Francis turbine structure modification;Step S2, arrange Francis turbine runner blade wireless stress test system;Step S3, carry out installation and debugging of strain sensor and wireless strain gauge;Step S4, carry out full water head stress test and analysis;Step S5, carry out unit full water head vibration area optimization;Step S6, carry out runner blade crack real-time monitoring.Through the local modification of existing large Francis turbine structure, permanent stress sensor is installed on runner blade, and signal cable channel and stress tester installation position are designed, to realize the stable acquisition of stress data;And using wireless communication technology, long-term real-time acquisition of runner stress data and online monitoring analysis of crack are realized, to optimize unit operation mode, so as to discover runner blade crack defect in time, and provide technical support for unit condition-based maintenance.

Description

Technical Field

[0001] This invention belongs to the field of hydropower turbine blade crack monitoring technology, and specifically relates to an online monitoring method for hydropower turbine blade cracks based on a stress testing system. Background Technology

[0002] The turbine runner is a core component of a hydroelectric generating unit, and its safety and stability are crucial. Because the stable operation of a mixed-flow turbine is significantly affected by hydraulic factors, it operates in a vibration or low-efficiency zone under partial load. In this zone, the blades are subjected to substantial alternating stress, which can lead to fatigue cracks over long-term. According to relevant literature, cracks in mixed-flow turbine runner blades often occur at the radius (R) of the weld between the blade's outlet edge and the upper crown, and at the radius (R) of the weld between the blade's outlet edge and the lower ring. Currently, the operating range of mixed-flow units is primarily determined by conducting full-head vibration zone tests to obtain unit vibration, sway, and flow channel pressure pulsation values, rather than directly assessing the stress on the blades, which has limitations. According to fatigue theory, the occurrence of cracks in components is directly related to the stress they experience. The detection of runner cracks requires draining the flow channel during maintenance and then performing non-destructive testing, significantly increasing the maintenance workload and safety risks of the power plant. Therefore, understanding the stress conditions of mixed-flow turbine runner blades under different operating conditions is beneficial for analyzing and predicting blade crack occurrence. It also helps to verify the operating range of the mixed-flow unit, rationally adjust the unit's operating mode, avoid prolonged operation under high-stress conditions, and reduce the probability of blade cracking. Furthermore, it can reduce the frequency of runner maintenance, thereby lowering maintenance costs and safety risks.

[0003] Dynamic stress testing began both domestically and internationally as early as the 1960s, but progress was slow due to limitations in software and hardware technology at the time. This was mainly because the turbine runner operated in water, making it difficult to install strain gauges on the blades and prone to being washed away; the turbine runner being a rotating component made data transmission difficult; and there were difficulties in the installation location of the strain gauges and external wireless transmission. Currently, obtaining the dynamic stress of the turbine runner blades mainly involves obtaining short-term stress values ​​of some blades through on-site testing. This requires installing temporary metal sleeves on the turbine runner blades and temporarily drilling holes in the turbine's main shaft air supply device. Furthermore, the test data is generally stored in the strain gauge, making it impossible to observe the data acquisition process. This results in a low success rate, and the added cable sleeves significantly impact the stable operation of the turbine, requiring removal during the next maintenance period, which in turn affects the turbine runner to some extent.

[0004] CN 112763236 discloses a method for testing the dynamic stress of a turbine runner. In this method, strain gauges are directly attached to the measuring points on the runner blades, making it unsuitable for long-term measurements. The strain gauges are easily washed away by water. Furthermore, the strain gauge wiring requires welding protective sleeves to the runner and the spillway cone, which affects turbine operation and needs to be removed after the test, making the process complex. This testing method is only suitable for short-term stress measurements and cannot achieve online monitoring of blade cracks.

[0005] CN200910063348 invented a wireless stress tester for hydropower units, introducing the instrument's structure and functions to achieve wireless stress testing. However, it does not specifically describe the installation method of the strain sensor for the turbine blades, nor does it consider the specific connection method between the strain gauge and the strain meter, or the specific installation location of the strain meter and other equipment, making its operability weak. Furthermore, this stress tester is only designed for experimental testing environments and does not consider the installation and power supply methods under long-term online monitoring conditions.

[0006] Therefore, existing technologies cannot achieve online stress monitoring of turbine runner blades and obtain stress data for the entire head, and cannot detect the occurrence and development of cracks in a timely manner, which is not conducive to optimizing the unit's operation mode and ensuring its safe and stable operation. Summary of the Invention

[0007] In view of the technical problems existing in the background technology, the present invention provides an online monitoring method for cracks in turbine runner blades of hydropower units based on a stress testing system. This method involves partially modifying the existing large mixed-flow turbine structure, installing permanent stress sensors on the runner blades, and designing signal cable channels and stress testing instrument installation positions to achieve stable acquisition of stress data. Furthermore, it utilizes wireless communication technology to achieve long-term real-time acquisition of runner stress data and online monitoring and analysis of cracks, thereby optimizing the unit's operation mode and enabling timely detection of crack defects in the runner blades. Simultaneously, it provides technical support for condition-based maintenance of the unit.

[0008] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0009] A method for online monitoring of cracks in the turbine blades of a hydroelectric generator based on a stress testing system, comprising the following steps:

[0010] Step S1: Modify the structure of the mixed-flow turbine;

[0011] Step S2: Deploy the wireless stress testing system for the runner blades of the mixed-flow turbine;

[0012] Step S3: Install and debug the strain sensor and wireless strain gauge;

[0013] Step S4: Conduct full head stress testing and analysis;

[0014] Step S5: Optimize the vibration zone of the unit at full head.

[0015] Step S6: Perform real-time monitoring of turbine blade cracks.

[0016] Preferably, the sub-steps of step S1 are as follows:

[0017] Step S1.1: Modify the turbine shaft center air supply valve (including float and air supply pipe): The modification includes setting up a signal cable channel connecting the strain sensor and the strain gauge and a sealing structure for the signal cable, so as to realize the strain signal of the runner blade to reach the strain gauge installed on the top of the unit through wired transmission, improve the accuracy of the collected data and the anti-interference ability, and not affect the normal operation of the shaft center air supply valve.

[0018] Step S1.2: Modify the runner's drain cone: Drill a wire hole on the runner's drain cone and weld a short wire pipe. The orientation of the wire hole corresponds to the blade, and the elevation is the outlet elevation of the main shaft air supply pipe. One end of the short wire pipe is led to the end of the crown R angle on the blade's water outlet side, and the other end is led to the opening of the drain cone. The diameter of the short wire pipe is determined by the signal line required for installing a strain sensor on a single blade.

[0019] Step S1.3: Modify the runner blades: The modification of the runner blades includes installing a quadrilateral base plate of equal size on both sides of the blade near the R-angle of the blade outlet edge (including the upper crown and lower ring) for mounting strain sensors and their leads, and installing a blade threading sleeve from the upper crown to the lower ring on the runner blade outlet edge. The thickness of the quadrilateral base plate is 1-2 mm greater than the thickness of the strain sensor, and the diameter of the blade threading sleeve is smaller than the thickness of the outlet edge. There are wire outlet holes near the upper crown and lower crown at positions corresponding to the lead grooves of the base plate. The quadrilateral base plate and the blade threading sleeve are fixed to the blade by welding. The routing of the blade threading sleeve is consistent with the blade shape at the outlet edge of the blade to avoid its influence on the turbine flow.

[0020] Preferably, the sub-step of step S1.1 is as follows:

[0021] Step S1.1.1: Design 2 to 4 symmetrical variable diameter wire holes on the mounting flange of the air supply valve at the center of the turbine shaft, and design 2 to 4 symmetrical wire holes on the float flange. Design a wire sealing structure at the outlet of the wire hole at the top to prevent water leakage during unit operation. The wire sealing structure includes variable diameter wire holes, segmented sealing material, sealing pressure plate and connecting bolts, etc.

[0022] Step S1.1.2: Symmetrically arrange and weld vertical metal sleeves for threading between the air supply valve flange and the float support, as well as on the inner wall of the main shaft air supply pipe. The position of the metal sleeve corresponds vertically to the position of the flange hole. The diameter of the hole and the threading pipe is determined according to the size of the signal line required by the strain sensor. A horizontal branch pipe is set at the outlet of the vertical sleeve. The horizontal branch pipe is welded to the bottom flange of the air supply pipe and leads to each impeller blade.

[0023] Step S1.1.3: Install a fixing bracket on the upper flange of the main shaft air supply valve for fixing the strain gauge and battery; the fixing bracket is fixed to the air supply valve flange by foundation bolts or welding. The fixing bracket has baffles or set screws for fixing the strain gauge and battery to ensure the stability of the equipment when the unit rotates.

[0024] Preferably, in step S2, the wireless stress testing system includes a resistance strain sensor, a signal cable from the sensor to the strain gauge, a wireless strain gauge, a strain gauge power supply system, a host computer, and analysis equipment; the wireless stress testing system is used to realize the acquisition and analysis of stress data of the runner blade, as well as the real-time monitoring and early warning of cracks.

[0025] (1) The resistance strain sensor uses a waterproof uniaxial strain gauge with a resistance value of 120Ω or 350Ω, a sensitivity coefficient greater than 2.1, a grid length of about 5mm, a base size of about 10mm×5mm, a linear expansion coefficient of less than 11×10-6 / °C, and a temperature coefficient of less than 0.01% / °C.

[0026] (2) The signal cable from the sensor to the strain gauge shall be a multi-core signal cable with a single core area of ​​0.15–0.2 mm². 2 The number of cables, cores, and length are determined based on the number of measuring points and unit parameters.

[0027] (3) Each channel of the wireless strain gauge has an independent high-precision bridge, an independent high-stability signal amplification and conditioning circuit, and a high-performance AD ​​converter. The number of channels of the wireless strain gauge is determined according to the number of rotor blades and the number of strain sensors installed, generally greater than 32 channels. Each channel provides a constant excitation power supply voltage, with a single-channel sampling rate of 0-10kHz, 24-bit resolution, excitation voltage of 2.0V, operating voltage of 9-30V, and a 1 / 4 bridge. The wireless strain gauge internally houses a controller, acquisition module, filter, memory, and wireless signal transmitter. The wireless strain gauge terminal transmits data with a router and computer via WIFI, sending information to the host computer and receiving instructions from the host computer. The wireless strain gauge is powered by a high-capacity lithium battery, which can be charged when the unit is shut down or under maintenance.

[0028] (4) The host computer has data acquisition, storage, and analysis functions, and can realize human-computer interaction. The host computer is connected to a wireless signal transmitter, which can connect to the wireless strain gauge via WIFI to receive the strain signals acquired by it. The host computer is equipped with an operating system and strain measurement and analysis software. The software can realize real-time display and storage of strain at the measuring point, embeds Hooke's law, can calculate stress values ​​in real time, and has time domain, spectrum analysis, and list display functions. The software automatically searches for measurement modules, automatically identifies configurations, and completes real-time acquisition and saving of signals. The host computer can also control the signal acquisition or sleep mode of the strain gauge. When the unit is shut down, the strain gauge can be paused to save storage space and battery power.

[0029] Preferably, the sub-step of step S3 is as follows:

[0030] Step S3.1: Install the strain sensor.

[0031] 1) Determine the installation position of the strain sensor based on the historical data of crack occurrence and the blade manufacturing drawings. After determining the position, process the rectangular holes for strain gauge installation and the cable groove on the mounting base plate, and weld the mounting base plate to the blade around the perimeter. Grind the welded parts to reduce the impact on the blade profile.

[0032] 2) Polish the blade surface at the bottom of the mounting rectangular hole and clean the mounting area with alcohol or acetone; after the surface dries, use strain gauge adhesive to attach the strain sensor to the blade at the mounting hole position; then lead the strain sensor lead wire to the conduit according to the cable tray route, and fix the signal wire in the cable tray with adhesive; after the resistance strain gauge and lead wire are installed, cover the upper surface with high-strength AB adhesive, making it flush with the mounting base plate; after the adhesive dries, polish and grind the surface to ensure a smooth transition in the measurement area;

[0033] Step S3.2: Run the signal cable through the conduit.

[0034] The multi-core signal cable from the strain sensor to the strain gauge starts from the flange hole of the main shaft air supply valve at the top and passes down sequentially through the float flange hole, the vertical sleeve of the main shaft air supply pipe, the horizontal branch pipe at the bottom of the main shaft air supply pipe, the cable threading hole of the drain cone, the short pipe of the drain cone, and the sleeve at the water outlet of the blade. Finally, it is soldered to the lead wire of the strain sensor and then wrapped with insulating tape. The single signal cable is grouped at the cable outlet of the vertical sleeve. The grouped signal cables pass through the horizontal branch pipe, the cable threading hole of the drain cone, the short pipe of the drain cone, and the sleeve at the water outlet of the blade before reaching the installation position of the strain sensor. The transition area where the signal cable passes through different sleeves is wrapped with cable insulation sheath and sealed with AB glue.

[0035] Step S3.3: Install the wireless strain gauge and battery.

[0036] A mounting bracket for the batteries of the wireless strain gauges is evenly installed above the flange of the main shaft air supply valve. The wireless strain gauges and batteries are mounted on the brackets. The installation location of the wireless strain gauges should have an open space and channel for wireless transmission to facilitate signal transmission. High-capacity lithium batteries are connected in parallel to ensure long-term power supply to the strain gauges. At the same time, a 220V power point is provided on the generator cover to charge the batteries when the unit is shut down or under maintenance, ensuring longer monitoring of blade stress. The lithium batteries can provide 9-30V DC power, which is connected to the wireless strain gauges through the power terminal wires.

[0037] Step S3.4: Connect the signal cables:

[0038] After connecting the signal cable to the strain sensor, record the cable number at each measuring point. Before connecting the signal cable to the strain gauge, use a multimeter to measure the resistance value of the strain sensor to ensure it matches the sensor's resistance parameters. Then, connect one end of the signal cable to the wireless strain gauge terminal block. A single strain sensor is connected by three signal lines. One signal line, after being connected to the strain sensor, is connected to the strain gauge's power supply terminal EXC to provide excitation voltage to the sensor. The other two signal lines are combined at one end and connected to the strain sensor, then connected to the strain gauge's analog input terminal AI and common terminal RC, respectively. The AI ​​terminal is used to measure the bridge voltage value, and the RC terminal is used to form a 1 / 4 bridge circuit. This wiring method can cancel out the resistance of the line itself.

[0039] Step S3.5: Install and debug the host computer:

[0040] The host computer is installed within 200m of the unit and placed in a panel or chassis. The receiving antenna of the host computer needs to be led out to an open position to facilitate signal transmission and reception. After the sensor, strain gauge, and host computer are installed, power on the strain gauge and host computer, start the host computer software and connect to the strain gauge, set the basic parameters for data acquisition, and complete the equipment debugging.

[0041] Preferably, the sub-step of step S4 is as follows:

[0042] Step S4.1, Zeroing: After the strain sensors are installed and the turbine is dry, start the strain gauge to set and zero the parameters of each strain sensor measuring point, and record a piece of raw data;

[0043] Step S4.2: Conduct full head dynamic stress test:

[0044] 1) Based on the unit parameters, set the stress test head and test plan, set the load increase and decrease measurement interval and stabilization time, and test for more than 2 minutes after a load stabilizes, with no less than 10 measurement points;

[0045] 2) Conduct start-up, shutdown, and load increase / decrease tests at various water heads: First, with the turbine filled with water and not started, record the stress data at each measuring point in the shutdown state at a certain water head; second, automatically start the unit and record the stress change waveform during the start-up process; then, conduct a load increase test according to the test plan, and record the test time after the measured load point stabilizes; after reaching the maximum load, conduct a load decrease test in the same way; through the test, obtain the transient process of the runner blades at that water head and the stress value and its changing trend at the stable load point;

[0046] 3) Conduct stress tests under load rejection conditions: Combine the unit load rejection test with the data of stress change of the turbine blades under load rejection conditions;

[0047] Step S4.3: Perform statistical analysis on the test data and propose a stress safety threshold:

[0048] 1) Based on the static stress values ​​of each measuring point before and after start-up and shutdown, propose the static stress safety threshold for each measuring point in the shutdown state.

[0049] 2) Based on the trend chart of static stress, dynamic stress and total stress under stable load: propose the static stress safety threshold and dynamic stress safety threshold for each measuring point under stable working conditions; the safety threshold can be set according to "high, medium and low" head, and the safety threshold is set as the maximum stress value collected, and 1.5 times and 2.0 times the maximum dynamic stress value and static stress value of the stable operating load section are respectively taken as the first-level alarm value and the second-level alarm value.

[0050] 3) Based on the proposed stress threshold, draw the safety threshold diagram for each measuring point.

[0051] Preferably, in step S5, based on the full head stress and vibration zone test data, the trend diagrams of unit vibration amplitude, swing amplitude, pressure pulsation amplitude and dynamic stress amplitude as a function of load can be obtained. The dynamic stress of the runner blade as a function of load is introduced to verify and optimize the vibration zone, and the optimized stable operating range of the unit is proposed.

[0052] Preferably, in step S6, the runner blade stress testing system is used to collect and analyze data in real time, which can obtain the range of dynamic and static stresses at each monitoring point of the runner blade, and based on this, a stress safety threshold is proposed, and an alarm value is set in the host computer software.

[0053] A crack alarm signal will be triggered under the following circumstances:

[0054] 1) When the unit is in a shutdown state, the measured static stress is greater than its safety threshold, and it is mainly manifested as tensile stress;

[0055] 2) When the unit is running under stable conditions, the stress measurement value changes abruptly. The static stress value is greater than the set static stress safety threshold, and the dynamic stress amplitude also increases and is greater than the dynamic stress safety threshold. After shutdown, the static stress value at the measuring point cannot return to near the initial value.

[0056] 3) During the operation of the unit, the dynamic and static stress at the measuring point shows an increasing trend, eventually leading to the disappearance of the measurement signal.

[0057] The present invention can achieve the following beneficial effects:

[0058] (1) This invention makes partial modifications to the main shaft air supply valve and runner blades of the mixed-flow turbine, and designs a strain sensor mounting base and signal cable channel, so that the strain gauge can collect a stable and reliable strain signal, avoid the problem of strain gauge falling off or signal cable being damaged during the test, and ensure the long-term stable operation of the test equipment.

[0059] (2) The present invention introduces a wireless transmission strain measurement system, which transmits the strain signal collected by the strain gauge to the host computer via WIFI, thereby realizing the real-time monitoring function of the stress and timely grasping the stress change trend of the rotor blade.

[0060] (3) The present invention optimizes the division of the vibration zone of the unit. Based on the traditional method of dividing the vibration zone by measuring the unit's swing, vibration and pressure pulsation, the stress factor of the runner blade is introduced. The optimized vibration zone is more conducive to the safe and stable operation of the unit.

[0061] (4) This invention utilizes the full head database obtained from the runner stress test to propose a safe operating threshold for runner blade stress. It uses the stress data characteristics and stress threshold obtained from real-time monitoring to determine the standard for runner blade cracks, thereby achieving the purpose of indirect online monitoring of runner blade cracks and solving the problem of difficult runner blade crack monitoring.

[0062] (5) After adopting online monitoring of turbine blade stress and cracks, turbine cracks can be detected in time to avoid the expansion of defects; at the same time, maintenance items can be optimized based on the stress data of turbine operation, reducing the investment of manpower and financial resources in maintenance and providing technical support for condition-based maintenance of the unit. Attached Figure Description

[0063] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0064] Figure 1 This is a flowchart illustrating the online monitoring and optimized operation process for cracks in a mixed-flow turbine according to the present invention.

[0065] Figure 2 This is a schematic diagram of the layout of the mixed-flow turbine strain testing system of the present invention;

[0066] Figure 3 This is an enlarged view of the installation position of the resistance strain gauge of the present invention;

[0067] Figure 4 This is a side view of the strain gauge mounting position of the present invention;

[0068] Figure 5 This is a schematic diagram of the conduit layout of the present invention;

[0069] Figure 6 This is a schematic diagram of the main signal cable threading and sealing structure of the present invention;

[0070] Figure 7 This is a schematic diagram of stress measurement data acquisition at the measuring point in this invention;

[0071] Figure 8 This is a schematic diagram illustrating the vibration and dynamic stress trend analysis of the unit in this invention;

[0072] Figure 9 This is a schematic diagram showing the change in strain data when a suspected crack appears at the measuring point of this invention.

[0073] In the diagram: 1-Upper crown of the impeller, 2-Impeller blade, 3-Lower ring of the impeller, 4-Impeller drain cone, 5-Main shaft center air supply pipe, 6-Float, 7-Main shaft air supply valve, 8-Strain gauge, 9-Lithium battery pack, 10-Main signal cable, 11-Cable sealing structure, 12-Cable vertical sleeve, 13-Cable horizontal branch pipe, 14-Drain cone wire hole, 15-Drain cone wire short pipe, 16-Blade wire sleeve, 17-Upper crown strain sensor, 18-Upper crown quadrilateral base plate, 19-Lower ring strain sensor, 20-Lower ring quadrilateral base plate, 21-Host computer, 22-Mounting bracket;

[0074] 2-1-Blade weld, 6-1-Upper support for pontoon, 6-2-Lower support for pontoon, 7-1-Flange flange for central air supply valve of main shaft. Detailed Implementation

[0075] Example 1:

[0076] Preferred solutions include Figures 1 to 2 As shown, an online monitoring method for turbine runner blade cracks based on a stress testing system is used to monitor the stress and cracks of turbine runner blades in a large hydropower station. The unit is a mixed-flow turbine with a single unit capacity of 650MW, a rated head of 200m, a turbine runner diameter of 6700mm, a height of 2900mm, a total of 16 blades, and a blade thickness of approximately 20mm at the water outlet edge. The turbine is equipped with a main shaft air supply valve and a float device.

[0077] The plan is to install strain sensors at the upper crown and lower ring R-angle of 8 blades at intervals. Two strain sensors will be installed on each blade in the crack-prone areas near the upper crown and lower ring on both sides. The strain sensors will be installed perpendicular to the water flow direction, for a total of 64 strain sensors.

[0078] Step S1: Modification of the mixed-flow turbine structure. For example... Figures 2-6 As shown.

[0079] (1) Modification of the central air supply valve (including float and air supply pipe) of the turbine shaft.

[0080] First, two symmetrical through holes are designed on the flange (7-1) of the air supply valve at the center of the turbine shaft. The upper inner diameter of the through hole is 45mm and the lower diameter is 30mm. At the same time, two symmetrical through holes are designed on the upper support 6-1 and lower support 6-2 of the float 6. The diameter of the through holes is 30mm. The through holes of the two flanges correspond to each other. A through hole sealing structure 11 is designed at the outlet of the through hole at the top. The through hole sealing structure consists of a variable diameter through hole, a split sealing material (11-2), a sealing pressure plate (11-1), and connecting bolts (11-3).

[0081] Secondly, two vertical metal sleeves 12 are symmetrically arranged and welded between the air supply valve flange (7-1) and the float support (6-1), as well as on the inner wall of the main shaft air supply pipe 5. The position of the metal sleeves 12 corresponds vertically to the position of the flange hole. A horizontal branch pipe 13 is provided at the outlet of the vertical sleeve 12. The horizontal branch pipe 13 is welded to the bottom flange of the air supply pipe and leads to each blade.

[0082] Next, a mounting bracket 22 for fixing the strain gauge and battery is installed on the upper flange of the main shaft air supply valve. The mounting bracket is fixed to the air supply valve flange (7-1) by base bolts or welding. The mounting bracket 22 has baffles or set screws for fixing the strain gauge and battery to ensure the stability of the equipment when the unit rotates.

[0083] (2) Modification of the runner's drain cone. Drill a wire hole 14 on the runner's drain cone 4 and weld a short wire pipe 15. The position of the wire hole 14 corresponds to the blade, and its elevation is the outlet elevation of the main shaft air supply pipe 5. One end of the short wire pipe 15 is led to the end of the crown R angle on the water outlet side of the blade, and the other end is led to the opening 14 of the drain cone. The diameter of the short wire pipe 15 is selected as 16mm.

[0084] (3) Modification of the runner blade. The modification of the runner blade 2 includes installing a quadrilateral mounting base plate of the same size on the positive and negative blades near the R-angle of the blade outlet edge (including the upper crown and the lower ring) for strain sensors and their leads. The base plate includes an upper crown quadrilateral base plate 18 and a lower ring quadrilateral base plate 20, and a blade threading sleeve 16 installed from the upper crown to the lower ring at the runner blade outlet edge. The quadrilateral mounting base plate is 5mm thick, approximately 2mm thick for the strain sensor. The diameter of the blade threading sleeve 16 is 16mm. There are wire outlet holes near the upper crown and the lower crown corresponding to the lead grooves of the mounting base plate. The quadrilateral mounting base plate and the blade threading sleeve 16 are fixed to the blade by welding. The routing of the blade threading sleeve is consistent with the blade shape at the blade outlet edge.

[0085] Step S2: Design a wireless stress testing system for the runner blades of a mixed-flow turbine. This system includes: a resistance strain sensor, a signal cable 10 from the sensor to the strain gauge, a wireless strain gauge 8, a strain gauge power supply system 9, a host computer 21, and analysis equipment. This system can realize real-time monitoring and early warning of stress data and cracks in the runner blades, as well as data storage. The resistance strain sensor includes an upper crown strain sensor 17 and a lower ring strain sensor 19.

[0086] (1) A waterproof uniaxial strain gauge is selected as the resistance strain sensor. The strain gauge resistance value is 120Ω, the sensitivity coefficient is greater than 2.1, the grid length is 5mm, the substrate size is 10mm×5mm, and the coefficient of linear expansion is less than 11×10. -6 / °C, temperature coefficient less than 0.01% / °C.

[0087] (2) The signal cable from the sensor to the strain gauge shall be a multi-core waterproof signal cable with a single core area of ​​0.2 mm². 2 It has 32 cores, a total of 6 cables, with 3 cables per group, and each cable is 35m long.

[0088] (3) Each channel of the wireless strain gauge 8 has an independent high-precision bridge, an independent high-stability signal amplification and conditioning circuit, and a high-performance AD ​​converter. The strain gauge has 64 channels, each providing a constant excitation power supply voltage. The single-channel sampling rate is 0-10kHz, with 24-bit resolution, an excitation voltage of 2.0V, an operating voltage of 9-30V, and a 1 / 4 bridge. The wireless strain gauge internally houses a controller, acquisition module, filter, memory, and wireless signal transmitter. The strain gauge 8 terminal transmits data with the router and host computer 21 via WIFI, sending information to the host computer 21 and receiving instructions from the host computer 21. The strain gauge 8 is powered by a large-capacity lithium battery pack 9, which can be charged when the unit is shut down or under maintenance.

[0089] (4) The host computer 21 has data acquisition, storage, and analysis functions, and can realize human-computer interaction. The host computer 21 is connected to a wireless signal transmitter, which can connect to the wireless strain gauge via WIFI to receive the strain signals acquired by it. The host computer 21 is equipped with an operating system and strain measurement and analysis equipment. The analysis equipment can realize real-time display and storage of strain at the measuring point, embeds Hooke's law, can convert stress values ​​in real time, and has time domain, spectrum analysis, and list display functions. The analysis equipment automatically searches for measurement modules, automatically identifies configurations, and completes real-time acquisition and saving of signals. The host computer 21 can also control the signal acquisition or sleep mode of the strain gauge. When the unit is shut down, the strain gauge can be paused to save storage space and battery power.

[0090] Step S3: Installation and commissioning of strain sensors and wireless strain gauges.

[0091] (1) Installation of strain sensor.

[0092] like Figure 3 As shown, firstly, based on historical data of crack occurrence and blade manufacturing drawings, the installation positions of the strain sensors were determined. Point A, 50mm from the center line of the upper crown weld and 50mm from the water outlet edge, and point B, 100mm from the center line of the upper crown weld and 80mm from the water outlet edge, were selected as the installation positions for the measuring points near the upper crown. Point C, 50mm from the center line of the lower ring weld and 50mm from the water outlet edge, and point D, 100mm from the center line of the lower ring weld and 80mm from the water outlet edge, were selected as the installation positions for the measuring points near the lower ring. The sensors were installed symmetrically on opposite sides of the blade. Figure 3 and Figure 4 As shown. After determining the position, rectangular holes for strain gauge installation and cable grooves are machined on the quadrilateral mounting base plate, and the mounting base plate is welded to the blade. The welded parts are then ground.

[0093] Next, grind the blade surface at the bottom of the mounting rectangular hole and clean the mounting area with alcohol or acetone. After drying, use strain gauge adhesive to attach the strain sensor to the blade at the mounting hole position. Then, lead the strain sensor lead wire to the opening on the blade conduit 16 according to the cable groove, and fix the signal wire with adhesive. After the resistance strain gauge and lead wire are installed, cover the upper surface with high-strength AB adhesive, making it flush with the mounting base plate. After the adhesive dries, polish and grind the surface to ensure a smooth transition in the measurement area.

[0094] (2) Run the signal cable 10 through the conduit. The multi-core signal cable 10 from the strain sensor to the strain gauge 8 starts from the flange hole of the upper shaft air supply valve 7 and passes down sequentially through the flange hole of the float 6, the vertical sleeve 12 of the shaft air supply pipe, the horizontal branch pipe 13 at the bottom of the shaft air supply pipe, the cable hole 14 of the drain cone, the short pipe 15 of the drain cone, and the blade outlet sleeve 16. Finally, it is soldered to the lead wire of the strain sensor and wrapped with insulating tape after connection. The single signal cable is grouped after the cable outlet hole of the vertical sleeve 12. The grouped signal cables pass through the horizontal branch pipe 13, the cable hole 14 of the drain cone, the short pipe 15 of the drain cone, and the blade outlet sleeve 16 to reach the installation position of the strain sensor. The transition area where the signal cable 10 passes through different sleeves is wrapped with cable insulation sheath and sealed with AB glue.

[0095] (3) Installation of strain gauge 8 and battery 9. Mounting brackets 22 for the wireless strain gauge 8 and battery 9 are evenly installed above the flange of the main shaft air supply valve 7. The wireless strain gauge 8 and battery 9 are mounted on the brackets 22. The installation location of the wireless strain gauge 8 should have an open space and channel for wireless transmission to facilitate signal transmission. High-capacity lithium batteries 9 are connected in parallel to ensure long-term power supply to the strain gauge. A 220V power point is also provided on the generator cover, allowing for battery charging during unit shutdown or maintenance, ensuring longer-term monitoring of blade stress. The lithium battery provides 9-30V DC power, which is connected to the wireless strain gauge via a power terminal line.

[0096] (4) Wiring of signal cable 10. After connecting signal cable 10 to the strain sensor, record the cable number of each measuring point. Before connecting signal cable 10 to the strain gauge, use a multimeter to measure the resistance value of the strain sensor to ensure that it is consistent with the sensor resistance parameter. Then, pass signal cable 10 through the sealing plate 11-1 of the wire sealing structure 11 and fill the upper hole with segmented sealing material 11-2. Then, use connecting bolts 11-3 to fix the sealing plate 11-1 to the flange 7-1 of the main shaft air supply valve to achieve its sealing function. Then, connect the multi-core signal line at one end of signal cable 10 to the terminal block of the wireless strain gauge 8 according to the measuring point number. A single strain sensor is connected by three signal lines. One signal line is connected to the strain sensor and then to the power supply terminal EXC of the strain gauge to provide excitation voltage to the sensor. The other two signal lines are combined at one end and connected to the strain sensor, and then connected to the analog input terminal AI and the common terminal RC of the strain gauge, respectively. The AI ​​terminal is used to measure the bridge voltage value, and the RC terminal is used to form a 1 / 4 bridge circuit. This wiring method can cancel out the resistance of the line itself.

[0097] (5) Install and debug the host computer 21. The host computer 21 is installed within 200m of the unit and placed in a panel or chassis. The receiving antenna of the host computer 21 needs to be led out to an open position to facilitate signal transmission and reception. After the sensor, strain gauge, and host computer are installed, power on the strain gauge 8 and the host computer 21, start the host computer 21 to analyze the equipment and connect it to the strain gauge, set the basic parameters for data acquisition, and complete the debugging of the test equipment.

[0098] Step S4: Conduct dynamic stress testing and analysis of the full head.

[0099] (1) Zeroing. After the strain sensor is installed and the turbine is without water, start the strain gauge 8 to set the parameters and zero the measuring points of each stress sensor, and record a piece of raw data.

[0100] (2) Conduct dynamic stress tests at full head.

[0101] 1) Based on the unit parameters, set the stress test head and test plan, set the load increase / decrease measurement interval and stabilization time, measure one point every 30MW, and test for 2 minutes after the load stabilizes.

[0102] 2) Conduct start-up, shutdown, and load increase / decrease tests at various water heads. First, with the turbine filled with water and not started, record the stress data at each measuring point in the shutdown state at a certain water head; second, automatically start the unit and record the stress change waveforms during the start-up process, such as... Figure 7 Then, according to the test plan, a load increase test was conducted. After the load point stabilized, the test time was recorded. After reaching the maximum load, a load decrease test was conducted in the same way. Through the test, the transient process of the runner blades under that head and the stress value and its variation trend at the stable load point can be obtained.

[0103] 3) Conduct stress tests under load rejection conditions. Combined with the load rejection tests, record data on the stress changes in the turbine blades under load rejection conditions.

[0104] (3) Perform statistical analysis on the test data and propose stress safety thresholds.

[0105] 1) Based on the static stress values ​​of each measuring point before and after start-up and shutdown, propose a safe threshold for the static stress value of each measuring point in the shutdown state.

[0106] 2) Based on the trend diagrams of static stress, dynamic stress, and total stress under stable load, propose the static stress values ​​and dynamic stress safety thresholds for each measuring point under stable operating conditions. The safety thresholds can be set according to the head levels of "high (210-215m), medium (180-210m), and low (165-180m)," with the safety threshold set as the maximum stress value collected. Furthermore, 1.5 times and 2.0 times the maximum dynamic stress value and static stress value in the stable operating load section are taken as the first-level alarm value and the second-level alarm value, respectively.

[0107] 3) Based on the proposed stress threshold, draw the safety threshold diagram for each measuring point.

[0108] Step S5: Optimization of the full head vibration zone of the unit.

[0109] Based on the dynamic stress and vibration zone test data of the full head, trend graphs of unit vibration amplitude, swing amplitude, pressure pulsation amplitude, and stress amplitude as a function of load can be obtained. The dynamic and static stress of the turbine runner blades as a function of load is introduced to verify and optimize the vibration zone, and an optimized stable operating range for the unit is proposed. For example... Figure 8 The figure shows the trend of unit stability parameters as a function of load at a water head of 190m. Figure 8 It is known that before the introduction of dynamic stress data, the unit exhibited an increased swing range within the 280-420MW range, generally considered a vibration zone, while other regions were considered stable operating zones. After introducing dynamic stress data, it was found that the dynamic stress amplitude of the unit exceeded 40MPa in the 0-100MW and 550MW-650MW ranges, which could easily accelerate fatigue cracking if operated for a long period. Therefore, long-term operation in these two regions should be avoided when selecting an operating strategy. The same method was used to optimize the stable operating regions for other heads.

[0110] Step S6: Real-time monitoring of runner blade cracks. Real-time data acquisition and analysis are performed using a runner blade stress testing system to obtain the range of dynamic and static stresses at each monitoring point on the runner blade. Based on this, a stress safety threshold is proposed, and alarm values ​​are set in the host computer analysis equipment.

[0111] A crack alarm signal will be triggered under the following circumstances:

[0112] (1) When the unit is in a shutdown state, the measured static stress is greater than its safety threshold and is mainly manifested as tensile stress.

[0113] (2) When the unit is running under stable conditions, the stress measurement value changes abruptly. Its static stress value is greater than the set static stress safety threshold, and the dynamic stress amplitude also increases and is greater than the dynamic stress safety threshold. After the unit is shut down, the static stress value of the measuring point cannot return to the vicinity of the initial value.

[0114] (3) When the unit is in operation, the dynamic and static stress at the measuring point tends to increase, and eventually the measurement signal disappears.

[0115] like Figure 9 As shown, at a certain measuring point, during stable operation of the unit, the static stress value and the peak value of the stress suddenly changed at 10.85s. The static stress value suddenly increased from 20MPa to 120MPa, exceeding the first-level alarm value of 80MPa. The peak value of the dynamic stress increased by about 30MPa. At this time, the online monitoring system will issue an alarm signal, indicating that there is a high probability of cracks in the area of ​​the measuring point. During operation, the monitoring of this measuring point should be strengthened. If the data continues to increase, the turbine runner should be inspected at an opportune time.

[0116] The above embodiments are merely preferred technical solutions of the present invention and should not be considered as limitations on the present invention. The scope of protection of the present invention should be defined as the technical solutions described in the claims, including equivalent substitutions of the technical features described in the claims. That is, equivalent substitutions and improvements within this scope are also within the scope of protection of the present invention.

Claims

1. A method for on-line monitoring of cracks in runner blades of a hydroelectric unit based on a stress testing system, characterized by The method comprises the following steps: Step S1, structural modification of the Francis turbine is performed; Step S2, a wireless stress testing system for the runner blade of the Francis turbine is arranged; Step S3, installation and debugging of the strain sensor and the wireless strain gauge are performed; Step S4, full-head stress testing and analysis are performed; Step S5, full-head vibration zone optimization of the unit is performed; Step S6, real-time monitoring of the runner blade cracks is performed; The sub-step of step S3 is: Step S3.1, installation of the strain sensor is performed: 1) The installation position of the strain sensor is determined according to historical data of cracks and blade manufacturing drawings; after the position is determined, the strain gauge installation rectangular hole and the cable groove are processed on the installation base plate, and the installation base plate is welded to the blade around; the welding part is polished to reduce the influence on the blade profile; 2) the surface of the blade at the bottom of the installation rectangular hole is polished, and the installation area is cleaned with alcohol or acetone; after the surface is dried, the strain sensor is pasted on the blade at the installation hole position with special strain gauge glue; then the lead wire of the strain sensor is led to the wire pipe according to the cable groove, and the signal wire in the wire groove is fixed with glue; after the installation of the resistance strain gauge and the lead wire is completed, high-strength AB glue is covered on the upper surface, and the installation base plate is flat after covering; after the glue is dry, the surface is polished and polished to ensure smooth transition of the measurement area; Step S3.2, signal cable threading is performed: The multi-core signal cable from the strain sensor to the strain gauge is sequentially threaded from the upper large shaft air supply valve flange hole, the float flange hole, the large shaft air supply pipe vertical sleeve, the large shaft air supply pipe bottom horizontal branch pipe, the drain cone threading hole, the drain cone short pipe and the blade water outlet edge sleeve, and finally connected with the lead wire of the strain sensor by tin soldering, and then wrapped with insulating tape; the single signal cable is grouped at the vertical sleeve outlet hole position, and after grouping, the signal cable is threaded through the horizontal branch pipe, the drain cone threading hole, the drain cone short pipe and the blade water outlet edge sleeve to reach the strain sensor installation position; the signal cable is wrapped with cable insulation sheath at the transition area of the different sleeves, and is sealed with AB glue; Step S3.3, wireless strain gauge and battery installation is performed: The battery installation bracket of the wireless strain gauge is uniformly installed above the large shaft air supply valve flange, and the wireless strain gauge and the battery are installed on the bracket; the wireless strain gauge installation position should have an open space and channel for wireless transmission to facilitate signal transmission; the large-capacity lithium battery is connected in parallel to ensure long-term power supply for the strain gauge; at the same time, a 220V power supply point is arranged on the generator cover, which can charge the battery when the unit is stopped or overhauled, and ensure longer monitoring of the blade stress; the lithium battery can provide 9-30V DC power, which is connected to the wireless strain gauge through the power terminal line; Step S3.4, signal cable wiring is performed: After the signal cable is connected with the strain sensor, the cable number of each measuring point is recorded, and before the signal cable is connected with the strain meter, the resistance value of the strain sensor is measured by using a multimeter to ensure that it is consistent with the resistance parameter of the sensor, and then one end of the signal cable is connected with the terminal row of the wireless strain meter; Step S3.5, install and debug the upper computer: The upper computer is installed within a range of 200 m near the unit, placed in a disc cabinet or a case, and the receiving antenna of the upper computer needs to be led out to an open position to facilitate signal transmission and reception; after the sensor, strain meter and upper computer are installed, the strain meter and upper computer are powered on, the upper computer software is started and connected with the strain meter, the basic parameters of data acquisition are set, and the debugging of the equipment is completed.

2. The method for on-line monitoring of cracks in runner blades of a hydroelectric generating unit based on a stress testing system according to claim 1, characterized in that: The sub-steps of step S1 are as follows: Step S1.1, the center air supply valve of the water turbine shaft is modified: the modification includes setting a signal cable channel connecting the strain sensor and the strain meter and a sealing structure of the signal cable, so that the strain signal of the runner blade is transmitted to the strain meter installed on the top of the unit through a wired transmission, the accuracy and anti-interference ability of the collected data are improved, and the normal work of the center air supply valve of the water turbine shaft is not affected; Step S1.2, the runner water discharge cone is modified: a through hole and a through line short pipe are drilled and welded on the runner water discharge cone, the through hole is corresponding to the blade, and the elevation is the outlet elevation of the shaft air supply pipe; one end of the through line short pipe is led to the end of the R angle of the blade water outlet edge, and the other end is led to the opening of the water discharge cone; the diameter of the through line short pipe is determined by the signal line required by the strain sensor to be installed on a single blade; Step S1.3, the runner blade is modified: the modification of the runner blade includes installing a quadrilateral base plate for installing the strain sensor and its lead line on the front and back surfaces of the blade near the R angle of the blade water outlet edge (including the upper crown and the lower ring), and installing a blade through line sleeve on the runner blade from the upper crown to the lower ring, the thickness of the quadrilateral base plate is 1-2 mm greater than the thickness of the strain sensor, the diameter of the blade through line sleeve is smaller than the thickness of the water outlet edge, there are through holes corresponding to the lead line grooves of the base plate near the upper crown and the lower crown, and the quadrilateral base plate and the blade through line sleeve are fixed on the blade by welding, the wire line of the blade through line sleeve is consistent with the blade water outlet edge profile to avoid affecting the flow pattern of the water turbine.

3. The method for on-line monitoring of cracks in runner blades of a hydroelectric generating unit based on a stress testing system according to claim 2, characterized in that: The sub-steps of step S1.1 are as follows: Step S1.1.1: 2-4 symmetrical variable-diameter through holes are designed on the flange of the center air supply valve of the water turbine shaft, 2-4 symmetrical through holes are designed on the float flange, and a through line sealing structure is designed at the outlet of the through hole on the top to prevent water leakage during the operation of the unit; Step S1.1.2: vertical metal sleeves are symmetrically arranged and welded between the air supply valve flange and the float bracket, and on the inner wall of the shaft air supply pipe, the positions of the metal sleeves correspond to the positions of the flange holes, the diameters of the drilled holes and the through line pipes are determined according to the size of the signal line required by the strain sensor, and a horizontal branch pipe is arranged at the outlet of the vertical sleeve and welded on the bottom flange of the air supply pipe and led to each runner blade. Step S1.1.3: Install a fixing bracket for fixing the strain gauge and battery on the upper flange of the large shaft air supply valve; the fixing bracket is fixed on the air supply valve flange by means of base bolts or welding, and the fixing bracket has a baffle or a top screw bolt for fixing the strain gauge and the battery, so as to ensure the stability of the equipment during rotation of the unit.

4. The method for on-line monitoring of cracks in runner blades of a hydroelectric generating unit based on a stress testing system according to claim 1, characterized in that: In step S2, the wireless stress testing system comprises a resistance strain sensor, a signal cable from the sensor to the strain gauge, a wireless strain gauge, a strain gauge power supply system, an upper computer and an analysis device; the wireless stress testing system is used to realize stress data acquisition and analysis of the runner blade, and real-time monitoring and early warning of cracks.

5. The method for on-line monitoring of cracks in runner blades of hydroelectric generating units based on a stress testing system according to claim 1, characterized in that: The sub-steps of step S4 are as follows: Step S4.1, zero setting: after the installation of the strain sensor is completed and the water turbine is in a water-free condition, the strain gauge is started to set parameters and zero of each strain sensor measuring point, and a section of original data is recorded; Step S4.2, dynamic stress testing under full water head: 1) according to the unit parameters, the stress testing water head and the test scheme are set, the lifting load measurement interval and the stable time are set, and after a load is stable for more than 2 minutes, the measurement points are not less than 10; 2) open and stop machine test under each water head: firstly, the stress data of each measuring point in the stop machine state at a certain water head are recorded under the condition that the water turbine is filled with water and not started; secondly, the unit is automatically started, and the stress change waveform of the starting process is recorded; then, the lifting load test is carried out according to the test scheme, and after the measured load point is stable, the test time is recorded; after reaching the maximum load, the load reduction test is carried out according to the same method; through the test, the stress values and their change trends of the runner blade at the transition process and the stable load point under the water head are obtained; 3) stress test under unit load rejection condition: combined with the unit load rejection test, the stress change data of the runner blade under the unit load rejection condition are recorded; Step S4.3, statistical analysis of test data and proposal of stress safety threshold: 1) according to the static stress values of each measuring point before and after the start and stop of the machine, the static stress safety threshold of each measuring point in the stop machine state is proposed; 2) according to the change trend diagram of the static stress, dynamic stress and total stress under the stable load, the static stress safety threshold and the dynamic stress safety threshold of each measuring point under the stable working condition are proposed; 3) according to the proposed stress value threshold, the safety threshold diagram of each measuring point is drawn. In step S5, according to the stress and vibration zone test data under full water head, the load change trend diagram of the unit vibration amplitude, swing amplitude, pressure fluctuation amplitude and dynamic stress amplitude can be obtained, the vibration zone is reviewed and optimized by introducing the dynamic stress of the runner blade varying with the load, and the optimized stable operation range interval of the unit is proposed. In step S6, real-time data acquisition and analysis are carried out by using the runner blade stress testing system, the range interval of the dynamic and static stress received by each monitoring point of the runner blade is obtained, the stress safety threshold is proposed accordingly, and the alarm value is set in the upper computer software; 6. The method for on-line monitoring of cracks in runner blades of hydroelectric generating units based on a stress testing system according to claim 1, characterized in that: The crack alarm signal is generated when the following conditions occur:

7. The method for on-line monitoring of cracks in runner blades of hydroelectric generating units based on a stress testing system according to claim 1, characterized in that: 1) when the unit is in the stop machine state, the measured static stress is greater than the safety threshold, and the main performance is tensile stress; ​ ​ 2) When the unit is running in stable condition, the stress measurement value changes suddenly, the static stress value is greater than the set static stress safety threshold value, the dynamic stress amplitude also increases and is greater than the dynamic stress safety threshold value, and the static stress value of the measuring point cannot return to the vicinity of the initial value after shutdown; 3) When the unit is running, the dynamic and static stresses of the measuring point show an increasing trend, and finally the measurement signal disappears.

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