Method for testing stress of bucket of impulse turbine

Abstract

The invention discloses a method for testing the stress of a bucket of an impulse turbine, which belongs to the technical field of water turbine testing, and designs a bucket strain sensor installation protection device and a signal cable channel by locally transforming the impulse turbine, so that a strain gauge can successfully collect stable and reliable strain signals of a working surface of the bucket; the problem that a strain gauge falls off or a signal cable is damaged in a test is avoided, long-term stable operation of test equipment is guaranteed, long-term stress test and full-head stress test and analysis of the water turbine can be achieved by installing and debugging a strain sensor and a wireless strain gauge, the stress states of the water turbine under different working conditions can be comprehensively evaluated, and the test efficiency is improved. And powerful support is provided for optimization design, safe operation and fault prediction of the unit.

Description

Technical Field

[0001] The invention belongs to the technical field of water turbine stress testing, and in particular relates to a method for testing the bucket stress of an impulse water turbine. Background Art

[0002] The invention belongs to the technical field of stress testing of impulse turbines, and in particular relates to a bucket stress testing method of an impulse turbine.

[0003] The impeller of a Pelton turbine is the core component of the unit, and its safety and stability are of vital importance. Due to the high head characteristics of the implton turbine, the runner bucket is subjected to a large jet impact pressure during operation, and the bucket has sufficient strength and toughness. Understanding the stress conditions of the prototype implton turbine bucket under different working conditions is conducive to optimizing the operation mode, analyzing and predicting the occurrence of bucket fatigue cracks, and avoiding the risk of bucket breakage. At the same time, stress testing of the prototype bucket is conducive to reviewing the structural design of the turbine and accumulating experience for subsequent turbine research and development. However, there are several difficulties in completing the stress test of the implton bucket: (1) The bucket has an irregular curved surface, and the strain gauge is difficult to install and fix, and is easily washed away; (2) The runner is an underwater rotating component, and the data cable is difficult to install; (3) At high speeds, the stability of the strain gauge and the difficulty in external data transmission are difficult.

[0004] CN 112763236 A method for testing the dynamic stress of a runner is invented. This method is aimed at the runner of a Francis turbine. By directly pasting the strain gauge on the measuring point of the runner blade, it is not suitable for long-term measurement, and the strain gauge is easily washed away by water; at the same time, the wiring of the strain gauge requires welding a cable protection sleeve on the runner and the drain cone, which has an impact on the operation of the turbine and needs to be removed after the test, and the process is complicated. This test method is only suitable for short-term stress measurement and cannot achieve long-term real-time measurement.

[0005] CN118346488 A invented a wheel and method for real-time stress measurement. In this method, a plurality of cable holes are set in the wheel body, and a stress measuring device is installed in the high stress area on the back of the bucket, and the cable is led out from the center of the main shaft to the central control room. This method requires opening holes in the wheel body, which has the risk of affecting the structural strength of the wheel. At the same time, the stress measuring device is installed in the high stress area on the back, and the installation method is not described. It can only measure the stress on the back of the bucket. Since the wheel is a rotating component, the patent does not introduce the cable lead-out connection method.

[0006] CN200910063348 invented a wireless stress tester for hydropower units, introduced the composition and functions of the measuring instrument, and realized wireless stress testing. However, it did not specifically introduce the installation method of the runner blade strain sensor, did not consider the specific connection method between the strain gauge and the strain meter, and did not consider the specific installation location of the strain meter and other equipment, so the implementation was not very practical. At the same time, the stress tester is only for the test environment, and did not consider the equipment installation and power supply methods under long-term online monitoring conditions.

[0007] CN 111120181 A A test system and method for measuring dynamic stress on the surface of impulse turbine is invented. The invention tests the dynamic stress on the surface of impulse turbine by test simulation method and measures the stress value of the model runner under transient jet flow. It cannot be applied to the stress test of prototype bucket.

[0008] Therefore, the existing technology cannot realize long-term stress testing of the prototype impact wheel bucket, which is not conducive to optimizing the operation mode of the unit and ensuring its safe and stable operation. Summary of the invention

[0009] The invention provides a method for testing the stress of an impulse turbine bucket, which solves the problem that the prior art cannot realize long-term stress testing of a prototype impulse turbine bucket.

[0010] To achieve the above object, the present invention provides the following technical solutions: A method for testing bucket stress of an impulse turbine, comprising: Through fluid-structure coupling simulation calculation of impulse turbine, the location of high stress area in bucket is obtained; Design and install the strain sensor protection device structure according to the location of the high stress area of ​​the bucket; Design and install cable casing structure for impulse turbine; Install and commission strain sensors and wireless strain gauges on Pelton turbines; Conduct full head stress testing and analysis on the installed impulse turbine.

[0011] Preferably, the step of obtaining the location of the bucket high stress area by fluid-solid coupling simulation calculation of the impulse turbine is specifically as follows: according to the structural dimensions of the prototype turbine, different nozzle combinations and nozzle openings are selected, a three-dimensional model of the flow channel of the water distribution ring pipe and the direct current nozzle is established, and a three-dimensional structure model of the runner is established at the same time, and meshing is performed; Based on the three-dimensional flow channel model of the water distribution ring pipe and DC nozzle and the three-dimensional structural model of the runner, the boundary parameters of the turbine operating condition are input to carry out flow channel CFD and fluid-solid coupling simulation calculations, and the position of the high stress area of ​​the bucket is obtained according to the calculation results.

[0012] Preferably, the position of the high stress area is 80% of the maximum stress position - the maximum stress position.

[0013] Preferably, a structural analysis is performed based on the location of the high stress area to determine the number of measurement points and the center positions of the measurement points. According to the determined center positions of the measurement points, a protective structure design for the stress measurement device is performed. The stress measurement device structure is a two-layer structure. The bottom layer is a base plate with a rectangular or trapezoidal cross-section, and the upper layer is a "convex" shaped cover plate. After installation, the base plate is a rectangle when viewed from above, and has installation positions for multiple stress sensors inside. The base plate is welded to the inner wall of the water bucket on all sides and polished for a smooth transition. After the sensor is installed, the "convex" shaped cover plate is embedded in the base plate, and the two ends of the cover plate are welded to the base plate as a whole.

[0014] Preferably, the cable casing structure of the impulse turbine is designed and installed in the following steps: the cable casing is divided into a bucket section, a runner flange section, a main shaft ring section and a main shaft vertical section. First, the cable casing structure of the bucket section is designed and installed. The cable casing of the bucket section is installed at the water outlet of the bucket by welding. The casing diameter selection must meet the threading requirements and be smaller than the thickness of the water outlet. The casing shape is bent along the water outlet of the bucket to the root of the bucket. The cable casing of the runner flange section is welded to the flange, and both ends of the casing are connected to the bucket section and the main shaft ring section through elbows. The main shaft ring section divides the cables of each flange branch section into two equal strands, which are respectively inserted into two vertical main shaft vertical casings to ensure that all casings are symmetrically arranged. The main shaft vertical casing is welded to the inner wall of the main shaft in sections.

[0015] Preferably, the steps of installing and debugging the strain sensor on the impulse turbine are specifically as follows; First, the strain sensor installation base plate is installed. According to the calculated section with the largest stress of the bucket, a long strip installation base is first installed on the "W" section of the bucket. The side and end of the installation base are welded to the inner surface of the bucket. A rectangular groove is reserved at the bottom of the installation base, which is used to install the strain gauge. A cover plate slot is set on the side of the installation base for matching with the cover plate. The cover plate has a "convex" cross section and forms a closed shell after being combined with the installation base to protect the strain gauge installed inside from being directly impacted by the water flow. Then install the strain sensor, polish the inner surface of the water bucket with a rectangular groove reserved on the installation base plate, and clean the installation area with alcohol or acetone. After the surface is dry, use the special glue for strain gauges to stick the strain sensor on the blade at the installation hole position, and then lead the lead wire of the strain sensor to the threading pipe opening at the water outlet of the water bucket according to the direction of the cable trough. After the resistance strain gauge and the lead wire are installed, fill the upper surface with glue, and the filling height is level with the side groove. After the glue is dry, polish and grind the surface; Finally, the cover plate is installed, and the cover plate is connected to the installation base plate through the slot, so that the installation base plate, strain sensor, glue and cover plate form a closed entity. At the same time, the cover plate and the installation base plate are welded in sections to avoid the position of the strain sensor.

[0016] Preferably, the strain sensor is installed on a symmetrical bucket of the impulse turbine.

[0017] Preferably, the steps of installing and debugging the wireless strain gauge are specifically as follows: A platform for installing a strain gauge is pre-arranged on the upper end surface of the generator shaft, and a fixing bracket for fixing the strain gauge and the battery is installed on the platform. The fixing bracket is fixed to the platform by foundation bolts or welding, and a baffle or top screw bolt for fixing the strain gauge and the battery is provided on the fixing bracket; Then proceed with the signal cable conduit threading, wireless strain gauge and battery installation, signal cable wiring and debugging host computer installation.

[0018] Preferably, the specific operation of passing the signal cable through the pipe is: The multi-core signal cable from the strain sensor to the strain gauge starts from the upper large shaft flange and passes through the main shaft vertical section, main shaft ring pipe section, runner flange section and bucket section downwards, and is finally connected to the lead-out wire of the strain sensor by soldering. After connection, it is wrapped with insulating tape. The single signal cable is grouped at the position of the vertical casing outlet hole. The grouped signal cables pass through the runner flange section branch pipe and the bucket section branch pipe to reach the strain sensor installation position. The transition area where the signal cable passes through different casings is wrapped with a cable insulating sheath and sealed with glue. The specific operations for installing the wireless strain gauge and battery are as follows: A mounting bracket for the battery of the wireless strain gauge is evenly installed above the upper shaft flange. The wireless strain gauge and the battery are installed on the bracket. The lithium battery is connected in parallel. At the same time, a power point is set on the generator cover. The lithium battery provides a DC power supply, which is connected to the wireless strain gauge through a power terminal line.

[0019] The specific operations for signal cable wiring are as follows: After the signal cable is connected to the strain sensor, record the cable number of 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 that it is consistent with the sensor resistance parameter. Then connect one end of the signal cable to the terminal block of the wireless strain gauge. A single strain sensor is connected by 3 signal lines, one of which is connected to the strain sensor and then connected to the power terminal EXC of the strain gauge to provide an excitation voltage to the sensor. The other two signal lines are combined and connected to the strain sensor and then connected to the analog input terminal AI and the common terminal RC of the strain gauge. The AI ​​terminal is used to measure the bridge voltage value, and the RC terminal is used to form a 1 / 4 bridge circuit. The specific steps for installing and debugging the host computer are: The host computer is installed within 200m of the unit and placed in a cabinet or chassis. 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 the strain gauge, set the basic parameters of data acquisition, and complete the debugging of the equipment.

[0020] Preferably, the steps of performing full head stress testing and analysis on the installed impulse turbine are specifically as follows: Set the turbine under dry conditions, start the strain gauge to set parameters and zero each strain sensor measurement point, and record a section of raw data; According to the unit parameters, set the stress test water head and test plan, set different nozzle combinations and lifting load measurement intervals and stabilization times. The test time after a load is stable is greater than 2 minutes, and the measurement points are greater than 10; Carry out the start-up and shutdown and load lifting test under the water head. First, record the stress change waveform during the start-up process, then carry out the load lifting test according to the test plan. After the load point is measured to be stable, record the test time. After reaching the maximum load, carry out the load reduction test in the same way. Through the test, obtain the stress value and its change trend of the transition process and stable load point of the bucket measuring point under the water head. Carry out stress test under unit load shedding condition, and record stress change data of bucket measuring point under load shedding condition in combination with unit load shedding test.

[0021] Compared with the prior art, the present invention has the following beneficial effects: the present invention proposes a method for testing bucket stress of an impulse turbine, and through partial modification of the impulse turbine, a bucket strain sensor installation protection device and a signal cable channel are designed, so that the strain gauge can successfully collect stable and reliable strain signals from the bucket working surface, avoiding the problem of strain gauge falling off or signal cable damage during the test, and ensuring the long-term stable operation of the test equipment. Then, through the installation and debugging of strain sensors and wireless strain gauges, the turbine can achieve long-term stress testing, full-head stress testing and analysis, and can comprehensively evaluate the stress state of the turbine under different working conditions, providing strong support for the optimized design, safe operation and fault prediction of the unit. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Flow chart of the Pelton turbine bucket stress test method.

[0023] Figure 2 Schematic diagram of the installation layout of the bucket stress test system.

[0024] Figure 3 Sectional view of the stress sensor installation section AA.

[0025] Figure 4 Schematic diagram of the stress sensor and its installation basis.

[0026] Figure 5 Schematic diagram of the stress sensor protective cover.

[0027] Figure 6 Schematic diagram of the stress sensor after installation.

[0028] Figure 7 This is a schematic diagram of the plan layout of the wire sleeve.

[0029] 1- bucket, 2- protective cover, 3- installation base plate, 4- strain sensor, 5- glue, 6- bucket section casing, 7- runner flange section casing, 8- runner flange section annular casing, 9- spindle vertical section casing, 10- lithium battery, 11- wireless strain gauge, 12- upper end shaft, 13- upper end shaft flange platform, 14- weld, 15- signal cable, 16- host computer. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0031] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. 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.

[0032] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0033] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings.

[0034] like Figure 1 As shown, an embodiment of the present invention provides a method for testing bucket stress of an impulse turbine, comprising: S1 simulates the fluid-structure coupling of the impulse turbine and obtains the location of the high stress area of ​​the bucket; S2 designs and installs the structure of the strain sensor protection device according to the location of the high stress area of ​​the bucket; S3 designs and installs the cable casing structure of the impulse turbine; S4 Install and debug strain sensors and wireless strain gauges on impulse turbines; S5 performs full head stress testing and analysis on installed impulse turbines.

[0035] The sub-steps of step S1 are as follows: Step S1.1, according to the structural dimensions of the prototype turbine, select different nozzle combinations and nozzle openings, establish the three-dimensional flow channel model of the water distribution ring pipe and the direct current nozzle, and simultaneously establish the three-dimensional structure model of the runner and perform meshing.

[0036] Step S1.2, input the boundary parameters of the turbine operating condition to perform flow channel CFD and fluid-solid coupling simulation calculations, and obtain the high stress area position of the bucket based on the technical results, the maximum 80%-maximum.

[0037] The sub-steps of step S2 are as follows: Step S2.1, perform structural analysis in the high stress area obtained by simulation calculation, determine the number of measurement points and the center position of the measurement points, and generally select a relatively flat area around the measurement points.

[0038] Step S2.2, design the protection structure of the stress measurement device according to the determined measuring point center. Generally, the protection structure is a two-layer structure, the bottom layer is a "base plate" with a rectangular or trapezoidal cross-section, and the upper layer is a "convex" cover plate. After the base plate is installed, it is a rectangle when viewed from above, and multiple stress sensors can be installed in the internal position.

[0039] Step S2.3 The base plate is welded to the inner wall of the water bucket around the periphery and polished to make a smooth transition. After the sensor is installed, the "convex" cover plate is embedded in the base plate, and the two ends of the cover plate are welded to the base plate as a whole.

[0040] The sub-steps of step S3 are as follows: Step S3.1 The cable casing is divided into the bucket section, the runner flange section, the main shaft ring section, and the main shaft vertical section. First, the bucket section cable casing structure is designed and installed. The bucket section cable casing is installed at the bucket outlet by welding. The casing diameter selection must meet the threading requirements and is generally smaller than the thickness of the outlet. The casing shape is bent along the bucket outlet to the root of the bucket.

[0041] Step S3.2 The cable sleeve of the runner flange section is welded to the flange, and both ends of the sleeve are connected to the bucket section and the main shaft ring pipe section through elbows.

[0042] Step S3.3 Spindle ring pipe section Divide the cables of each flange branch pipe section into two equal strands and insert them into two vertical spindle vertical sleeves respectively to ensure that all sleeves are arranged symmetrically and do not affect the dynamic balance of the unit. The spindle vertical sleeves are welded to the inner wall of the spindle in sections.

[0043] The sub-steps of step S4 are as follows: Step S4.1, installation of the strain sensor mounting base plate. According to the calculated section with the largest stress of the bucket, first install a long strip mounting base on the "W"-shaped section of the bucket, and weld the side and end of the mounting base to the inner surface of the bucket. A rectangular groove is reserved at the bottom of the mounting base, which is used to install the strain gauge; a cover plate slot is set on the side of the mounting base for matching with the cover plate; the cover plate section is "convex" shaped, and after being combined with the mounting base, a closed shell is formed to protect the strain gauge installed inside from being directly impacted by the water flow.

[0044] Step S4.2, strain sensor installation. Polish the inner surface of the water bucket with a rectangular groove reserved on the installation base plate, and clean the installation area with alcohol or acetone; after the surface is dry, use the special glue for strain gauges to stick the strain sensor on the blade at the installation hole position; then lead the lead wire of the strain sensor to the threading pipe opening at the water outlet of the water bucket according to the direction of the cable trough. After the resistance strain gauge and lead wire are installed, fill the upper surface with high-strength AB glue, and the filling height is level with the side groove; after the glue is dry, polish and grind the surface.

[0045] Step S4.3, cover plate installation. Connect the cover plate and the installation base plate through the card slot, so that the installation base plate, strain sensor, AB glue, and cover plate form a closed entity. At the same time, the cover plate and the installation base plate are section welded at the position avoiding the strain sensor, so that it can withstand a large water flow impact.

[0046] Step S4.4: Preferably, in order to reduce the influence of the strain sensor on the dynamic balance of the runner, the sensor should be arranged on a symmetrical water bucket.

[0047] Step S4.4: Installation and debugging of wireless strain gauge.

[0048] Step S4.4.1. Pre-set a platform for installing the strain gauge on the upper end face of the generator shaft, and install a fixing bracket for fixing the strain gauge and the battery on the platform; the fixing bracket is fixed to the platform by foundation bolts or welding, and the fixing bracket has a baffle or top screw bolts for fixing the strain gauge and the battery to ensure the stability of the equipment when the unit rotates.

[0049] Step S4.4.2: Pipe the signal cable: The multi-core signal cable from the strain sensor to the strain gauge starts from the upper large shaft flange and passes through the main shaft vertical section, main shaft ring pipe section, runner flange section, and bucket section. It is finally connected to the lead-out wire of the strain sensor by soldering and wrapped with insulating tape after connection. The single signal cable is grouped at the position of the vertical casing outlet hole. The grouped signal cables pass through the runner flange section branch pipe and the bucket section branch pipe to reach the strain sensor installation position. The transition area where the signal cable passes through different casings is wrapped with a cable insulation sheath and sealed with AB glue. Step S4.4.3: Install the wireless strain gauge and battery: The mounting brackets of the batteries of the wireless strain gauges are evenly installed above the upper shaft flange, and the wireless strain gauges and batteries are installed on the brackets; the installation position of the wireless strain gauges should have an open space and channel for wireless transmission to facilitate the sending and transmission of signals; large-capacity lithium batteries are connected in parallel to ensure long-term power supply for the strain gauges; at the same time, a 220V power supply point is set on the generator cover, and the battery can be charged when the unit is shut down or overhauled, ensuring that the blade stress can be monitored for a longer time; the lithium battery can provide a 9-30V DC power supply, which is connected to the wireless strain gauge through the power terminal line.

[0050] Step S4.4.4: Connect the signal cables: After the signal cable is connected to the strain sensor, record the cable number of 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 that it is consistent with the sensor resistance parameters, and then connect one end of the signal cable to the terminal block of the wireless strain gauge; A single strain sensor is connected by 3 signal lines, one of which is connected to the strain sensor and then connected to the power terminal EXC of the strain gauge to provide an excitation voltage to the sensor; one end of the other two signal lines are merged 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 offset the resistance of the line itself.

[0051] Step S4.4.5, install and debug the host computer: The host computer is installed within 200m of the unit and placed in a cabinet or chassis. The receiving antenna of the host computer needs to be led out to an open position to facilitate the sending and receiving of signals. After the sensor, strain gauge and host computer are installed, power on the strain gauge and the host computer, start the host computer software and connect the strain gauge, set the basic parameters of data acquisition, and complete the debugging of the equipment.

[0052] Preferably, the sub-steps of step S5 are: Step S5.1, zeroing: after the strain sensor is installed and the turbine is in a waterless condition, start the strain gauge to set parameters and zero each strain sensor measuring point, and record a section of raw data; Step S5.2, conduct full head dynamic stress test and analysis: 1) According to the unit parameters, set the stress test water head and test plan, set different nozzle combinations and load lifting measurement intervals and stabilization time. The test should be longer than 2 minutes after a load is stable, and there should be no less than 10 measurement points; 2) Carry out start-up and shutdown and load lifting tests under various water heads: First, record the stress change waveform during the start-up process; then carry out the load lifting test according to the test plan, and record the test time after the measured load point stabilizes; after reaching the maximum load, carry out the load reduction test in the same way; through the test, obtain the stress value and its change trend of the transition process and stable load point of the bucket measuring point under the water head; 3) Carry out stress test under unit load rejection condition: Combined with the unit load rejection test, record the stress change data of the unit's buoy measuring point under load rejection condition.

[0053] Another embodiment of the present invention provides a method for testing the stress of a water bucket of an impulse turbine, comprising; The stress of the bucket of the impulse turbine of a large hydropower station was tested. The unit capacity of the unit is 300MW, the rated head is 600m, the diameter of the turbine runner is 5000mm, the height is 1000mm, there are 20 buckets and 6 nozzles. It is planned to install strain sensors on the inner surface of the lower part of 4 buckets at even intervals. 2 sets of dual-axis 90° and 2 sets of triaxial 45° strain sensors are installed on each bucket, which can measure 10 stress data. The main installation direction of the strain sensor is along the water flow direction. A total of 16 sets (40 measuring points) of strain sensors are installed.

[0054] Step S1, fluid-solid coupling simulation calculation of impulse turbine, obtain the location of high stress area of ​​bucket. Firstly, three-dimensional modeling and fluid-solid coupling simulation calculation are performed on the turbine, and three working conditions with the highest water head and large nozzle opening are selected for simulation to obtain the stress distribution diagram of bucket. The location with the largest stress is selected to determine the installation section of strain sensor. According to the calculation, the maximum stress is about 1 / 3 of the bucket diameter direction, such as Figure 2 AA section position shown.

[0055] Step S2, structural design and installation of stress sensor protection device (2, 3). According to the size of stress sensor 4, design sensor installation base 3 and protective cover plate 2, such as Figure 4-5As shown. The installation base 3 is a "base plate" with a rectangular cross section, and the protective cover plate 2 is a "convex" cover plate. The base plate is rectangular when viewed from above after installation, and 4 stress sensors are installed inside. First, the installation base 3 is welded to the inner wall of the bucket on all sides, and the weld 14 is polished to make a smooth transition. After the sensor 4 is installed, the "convex" cover plate 2 is embedded in the installation base 3, and the two ends of the cover plate 2 are welded to the installation base as a whole.

[0056] Step S3: Design and install the cable casing structure. Figure 2 , Figure 7 As shown, the cable sleeve is divided into four sections: the bucket section 6, the runner flange section 7, the main shaft ring section 8, and the main shaft vertical section 9. First, the structure design and installation of the cable sleeve 6 of the bucket section are carried out. The cable sleeve 6 of the bucket section is installed at the water outlet of the bucket 1 by welding. The sleeve diameter selection needs to meet the threading requirements. At the same time, it is generally smaller than the thickness of the water outlet of the bucket 1. The sleeve shape is bent along the water outlet of the bucket until the root of the bucket. The cable sleeve 7 of the runner flange section is welded to the flange, and the two ends of the sleeve are connected to the bucket section 6 and the main shaft ring section 8 through elbows. The main shaft ring section 8 collects the cables of each flange branch section 7 and divides them into two strands, which are respectively inserted into two vertical main shaft vertical sleeves 9 to ensure that all sleeves are arranged symmetrically and do not affect the dynamic balance of the unit. The main shaft vertical sleeve 9 is welded on the inner wall of the main shaft 12 in sections.

[0057] Step S4: installation and debugging of strain sensors and wireless strain gauges.

[0058] S4.1. Design a water bucket stress test system. The system includes: a resistance strain sensor 4, a signal cable 14 from the sensor to the strain gauge, a wireless strain gauge 11, a strain gauge power supply system 10, a host computer 15, and analysis equipment. The system can realize real-time monitoring of water bucket stress data and data storage. (1) The resistance strain sensor uses a waterproof uniaxial strain gauge with a strain gauge resistance of 120Ω, a sensitivity coefficient greater than 2.1, a grid length of 5mm, a substrate size of 10mm×5mm, a linear expansion coefficient less than 11×10-6 / °C, and a temperature coefficient less than 0.01% / °C.

[0059] (2) The signal cable from the sensor to the strain gauge should be a multi-core waterproof signal cable with a single core area of ​​0.2 mm2, 32 cores, a total of 6 cables, and a single cable length of 35 m.

[0060] (3) Each channel of the wireless strain gauge 8 is equipped with 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 of which provides a constant excitation power supply voltage, a single-channel sampling rate of 0-10kHz, a 24-bit resolution, an excitation voltage of 2.0V, an operating voltage of 9-30V, and a 1 / 4 bridge. The wireless strain gauge is internally installed with a controller, an acquisition module, a filter, a memory, and a wireless signal transmitter. The strain gauge 8 terminal transmits data with the router and the host computer 16 via WIFI, sends information to the host computer 16, and receives instructions from the host computer. The strain gauge 11 is powered by a large-capacity lithium battery pack 10, which can be charged when the unit is shut down or overhauled.

[0061] (4) The host computer 16 has data acquisition, storage and analysis functions, and can realize human-computer interaction. The host computer 16 is connected to a wireless signal transmitter, and can be connected to the wireless strain gauge via WIFI to receive the strain signal collected by it. The host computer 16 is installed with an operating system and a strain measurement and analysis device. The analysis device can realize real-time display and storage of the strain at the measuring point, has an embedded Hooke's law, can convert stress values ​​in real time, and has time domain, spectrum analysis and list display functions. The analysis device automatically searches for the measurement module, automatically identifies the configuration, and completes the real-time acquisition and storage of the signal. The host computer 16 can also control the signal acquisition or sleep of the strain gauge. When the unit is shut down, the strain gauge can be suspended to save storage space and battery power.

[0062] Step S4.2, installation of strain sensor mounting base plate 3. According to the calculated section with the largest stress of the bucket, first install the long strip mounting base 3 on the "W"-shaped section of the bucket, and weld the side and end of the mounting base 3 to the inner surface of the bucket. A rectangular groove is reserved at the bottom of the mounting base 3, which is used to install the strain sensor 4; a cover plate slot is provided on the side of the mounting base for matching with the cover plate 2; the cover plate section is "convex" shaped, and after being combined with the mounting base, a closed shell is formed to protect the strain gauge installed inside from being directly impacted by the water flow. Due to the large turning radius of the bucket section, the mounting base plate 3 can be installed in two sections.

[0063] Step S4.3, installation of strain sensor 4. Polish the inner surface of the water bucket with a rectangular groove reserved on the installation base plate 3, and clean the installation area with alcohol or acetone; after the surface is dry, use special glue for strain gauges to stick the strain sensor 4 on the inner wall of the water bucket at the installation hole position; then lead the lead wire of the strain sensor 4 to the inlet of the threading sleeve 6 at the water outlet of the water bucket according to the direction of the cable trough. After the resistance strain gauge and the lead wire are installed, fill the upper surface with high-strength AB glue 5, and the filling height is level with the side groove; after the glue is dry, polish and grind the surface.

[0064] Step S4.3, cover plate installation. Connect the cover plate 2 and the installation base plate 3 through the card slot, so that the installation base plate 3, the strain sensor 4, the AB glue 5, and the cover plate 2 form a closed entity. At the same time, the cover plate 2 and the installation base plate 3 are welded in sections at the position avoiding the strain sensor, and polished to make it smooth so that it can withstand a large water flow impact and reduce the impact on the flow state. Use the same method to install sensors on the other three symmetrical water buckets.

[0065] Step S4.4: Installation and debugging of wireless strain gauge.

[0066] Step S4.4.1, pre-set a platform 13 for installing the strain gauge on the upper end surface of the generator shaft 12, and install a fixing bracket for fixing the strain gauge and the battery on the platform; the fixing bracket is fixed to the platform by foundation bolts or welding, and the fixing bracket has a baffle or top screw bolts for fixing the strain gauge 11 and the battery 10 to ensure the stability of the equipment when the unit rotates.

[0067] Step S4.4.2: Pipe the signal cable: The multi-core signal cable 15 from the strain sensor to the strain gauge starts from the upper large shaft platform 13 and passes downward through the main shaft vertical section, main shaft ring pipe section, runner flange section and bucket section, and is finally connected to the lead wire of the strain sensor 4 by soldering. After connection, it is wrapped with insulating tape; the single signal cable is grouped at the vertical casing outlet hole position, and the grouped signal cables pass through the runner flange section branch pipe 7 and the bucket section branch pipe 6 to reach the strain sensor installation position; the transition area where the signal cable passes through different casings is wrapped with a cable insulating sheath and sealed with AB glue.

[0068] Step S4.4.3, installing the wireless strain gauge 11 and the battery 10: The mounting brackets of the batteries 10 of the wireless strain gauge are evenly installed above the upper shaft flange, and the wireless strain gauge 11 and the battery are installed on the bracket; the installation position of the wireless strain gauge 11 should have an open space and channel for wireless transmission to facilitate the sending and transmission of signals; the large-capacity lithium battery 10 is connected in parallel to ensure long-term power supply to the strain gauge; at the same time, a 220V power supply point is set on the generator cover, and the battery can be charged when the unit is shut down or overhauled, ensuring that the blade stress can be monitored for a longer time; the lithium battery can provide a 9-30V DC power supply, which is connected to the wireless strain gauge through the power terminal line.

[0069] Step S4.4.4: Connect the signal cables: After the signal cable 15 is connected to the strain sensor 4, the cable number of each measuring point is recorded. Before connecting the signal cable to the strain gauge, the resistance value of the strain sensor is measured with a multimeter to ensure that it is consistent with the sensor resistance parameters, and then one end of the signal cable is connected to the terminal block of the wireless strain gauge; a single strain sensor is connected by 3 signal lines, one of which is connected to the strain sensor and then connected to the power terminal EXC of the strain gauge to provide an excitation voltage to the sensor; one end of the other two signal lines are merged 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, where 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 offset the resistance of the line itself.

[0070] Step S4.4.5, install and debug the host computer: The host computer 16 is installed within 200m of the unit and placed in a cabinet or chassis. The receiving antenna of the host computer needs to be led out to an open position to facilitate the sending and receiving of signals. After the sensor, strain gauge and host computer are installed, the strain gauge 11 and the host computer 16 are powered on, the host computer software is started and the strain gauge is connected, the basic parameters of data acquisition are set, and the equipment debugging is completed.

[0071] Step S5: Conduct full water head stress test and analysis.

[0072] Step S5.1, zeroing: after the strain sensor is installed and the turbine is in a waterless condition, start the strain gauge to set parameters and zero each strain sensor measuring point, and record a section of raw data; Step S5.2, conduct full head dynamic stress test and analysis: 1) According to the unit parameters, three test water heads are set for stress testing, namely the maximum head, rated head and minimum head. The nozzle combinations are set to be single nozzle, double nozzle, 3 nozzles, 4 nozzles and 6 nozzles. The load lifting measurement interval is 40MW. After a load is stable, the test is more than 2 minutes, and there are no less than 10 measurement points. 2) Carry out start-up and shutdown and load lifting tests under various water heads. First, record the stress change waveform during the start-up process; then carry out the load lifting test according to the test plan, and record the test time after the measured load point stabilizes; after reaching the maximum load, carry out the load reduction test in the same way; through the test, obtain the stress value and its change trend of the transition process and stable load point of the bucket measuring point under the water head; 3) Carry out stress test under unit load rejection condition: Combined with the unit load rejection test, record the stress change data of the unit's buoy measuring point under load rejection condition.

[0073] Although the embodiments of the present invention are described above in conjunction with the accompanying drawings, the present invention is not limited to the above-mentioned specific embodiments and application fields, and the above-mentioned specific embodiments are only illustrative and instructive, rather than restrictive. Under the guidance of the specification, a person skilled in the art can also make many forms without departing from the scope of protection of the claims of the present invention, all of which belong to the scope of protection of the present invention.

Claims

1. A method for testing bucket stress of an impulse turbine, characterized in that: include: Through fluid-structure coupling simulation calculation of impulse turbine, the location of high stress area in bucket is obtained; Design and install the strain sensor protection device structure according to the location of the high stress area of ​​the bucket; Design and install cable casing structure for impulse turbine; Install and commission strain sensors and wireless strain gauges on Pelton turbines; Conduct full head stress testing and analysis on the installed impulse turbine.

2. A method for testing bucket stress of an impulse turbine according to claim 1, characterized in that: The steps for obtaining the location of the high stress area of ​​the bucket by fluid-solid coupling simulation calculation of the impulse turbine are as follows: according to the structural dimensions of the prototype turbine, different nozzle combinations and nozzle openings are selected, and the flow channel three-dimensional models of the water distribution ring pipe and the DC nozzle are established. At the same time, the three-dimensional structure model of the runner is established and meshed; Based on the three-dimensional flow channel model of the water distribution ring pipe and DC nozzle and the three-dimensional structural model of the runner, the boundary parameters of the turbine operating condition are input to carry out flow channel CFD and fluid-solid coupling simulation calculations, and the position of the high stress area of ​​the bucket is obtained according to the calculation results.

3. A method for testing bucket stress of an impulse turbine according to claim 2, characterized in that: The location of the high stress area is 80% of the maximum stress position - the maximum stress position.

4. A method for testing bucket stress of an impulse turbine according to claim 1, characterized in that: Based on the location of the high stress area, a structural analysis is performed to determine the number of measurement points and the center positions of the measurement points. According to the determined center positions of the measurement points, the protection structure of the stress measurement device is designed. The stress measurement device structure is a two-layer structure. The bottom layer is a base plate with a rectangular or trapezoidal cross-section, and the upper layer is a "convex" cover plate. After installation, the base plate is a rectangle when viewed from above, and there are installation positions for multiple stress sensors inside. The base plate is welded to the inner wall of the water bucket on all sides and polished for a smooth transition. After the sensor is installed, the "convex" cover plate is embedded in the base plate, and the two ends of the cover plate are welded to the base plate as a whole.

5. The method for testing bucket stress of an impulse turbine according to claim 1, characterized in that: The specific steps for designing and installing the cable casing structure of the impulse turbine are as follows: the cable casing is divided into a bucket section, a runner flange section, a main shaft ring section and a main shaft vertical section. First, the cable casing structure of the bucket section is designed and installed. The cable casing of the bucket section is installed at the water outlet of the bucket by welding. The casing diameter selection must meet the threading requirements and be smaller than the thickness of the water outlet. The casing shape is bent along the water outlet of the bucket to the root of the bucket. The cable casing of the runner flange section is welded to the flange, and both ends of the casing are connected to the bucket section and the main shaft ring section through elbows. The main shaft ring section divides the cables of each flange branch section into two strands, which are respectively inserted into two vertical main shaft vertical casings to ensure that all casings are arranged symmetrically. The main shaft vertical casing is welded to the inner wall of the main shaft in sections.

6. The method for testing bucket stress of an impulse turbine according to claim 1, characterized in that: The specific steps for installing and debugging strain sensors on impulse turbines are: First, install the strain sensor installation base plate. According to the calculated section with the largest stress of the bucket, first install a long strip installation base on the "W" section of the bucket. The side and end of the installation base are welded to the inner surface of the bucket. A rectangular groove is reserved at the bottom of the installation base, which is used to install the strain gauge. A cover plate slot is set on the side of the installation base for matching with the cover plate. The cover plate has a "convex" cross section and forms a closed shell after being combined with the installation base to protect the strain gauge installed inside from being directly impacted by the water flow. Then install the strain sensor, polish the inner surface of the water bucket with a rectangular groove reserved on the installation base plate, and clean the installation area with alcohol or acetone. After the surface is dry, use the special glue for strain gauges to stick the strain sensor on the blade at the installation hole position, and then lead the lead wire of the strain sensor to the threading pipe opening at the water outlet of the water bucket according to the direction of the cable trough. After the resistance strain gauge and the lead wire are installed, fill the upper surface with glue, and the filling height is level with the side groove. After the glue is dry, polish and grind the surface; Finally, the cover plate is installed, and the cover plate is connected to the installation base plate through the slot, so that the installation base plate, strain sensor, glue and cover plate form a closed entity. At the same time, the cover plate and the installation base plate are welded in sections to avoid the position of the strain sensor.

7. A method for testing bucket stress of an impulse turbine according to claim 6, characterized in that: The strain sensors are installed on the symmetrical buckets of the impulse turbine.

8. The method for testing bucket stress of an impulse turbine according to claim 1, characterized in that: The specific steps for installation and debugging of wireless strain gauges are as follows: A platform for installing a strain gauge is pre-arranged on the upper end surface of the generator shaft, and a fixing bracket for fixing the strain gauge and the battery is installed on the platform. The fixing bracket is fixed to the platform by foundation bolts or welding, and a baffle or top screw bolt for fixing the strain gauge and the battery is provided on the fixing bracket; Then proceed with the signal cable conduit threading, wireless strain gauge and battery installation, signal cable wiring and debugging host computer installation.

9. A method for testing bucket stress of an impulse turbine according to claim 8, characterized in that: The specific operations for signal cable conduit insertion are as follows: The multi-core signal cable from the strain sensor to the strain gauge starts from the upper large shaft flange and passes through the main shaft vertical section, main shaft ring pipe section, runner flange section and bucket section downwards, and is finally connected to the lead-out wire of the strain sensor by soldering. After connection, it is wrapped with insulating tape. The single signal cable is grouped at the position of the vertical casing outlet hole. The grouped signal cables pass through the runner flange section branch pipe and the bucket section branch pipe to reach the strain sensor installation position. The transition area where the signal cable passes through different casings is wrapped with a cable insulating sheath and sealed with glue. The specific operations for installing the wireless strain gauge and battery are as follows: The mounting bracket of the battery of the wireless strain gauge is evenly installed above the upper end shaft flange. The wireless strain gauge and the battery are installed on the bracket. The lithium battery is connected in parallel. At the same time, a power point is set on the generator cover. The lithium battery provides a DC power supply, which is connected to the wireless strain gauge through the power terminal line. The specific operations for signal cable wiring are as follows: After the signal cable is connected to the strain sensor, record the cable number of 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 that it is consistent with the sensor resistance parameter. Then connect one end of the signal cable to the terminal block of the wireless strain gauge. A single strain sensor is connected by 3 signal lines, one of which is connected to the strain sensor and then connected to the power terminal EXC of the strain gauge to provide an excitation voltage to the sensor. The other two signal lines are combined and connected to the strain sensor and then connected to the analog input terminal AI and the common terminal RC of the strain gauge. The AI ​​terminal is used to measure the bridge voltage value, and the RC terminal is used to form a 1 / 4 bridge circuit. The specific steps for installing and debugging the host computer are: The host computer is installed within 200m of the unit and placed in a cabinet or chassis. 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 the strain gauge, set the basic parameters of data acquisition, and complete the debugging of the equipment.

10. The method for testing bucket stress of an impulse turbine according to claim 1, characterized in that: The specific steps for full head stress testing and analysis of installed impulse turbines are as follows: Set the turbine under dry conditions, start the strain gauge to set parameters and zero each strain sensor measurement point, and record a section of raw data; According to the unit parameters, set the stress test water head and test plan, set different nozzle combinations and lifting load measurement intervals and stabilization times. The test time after a load is stable is greater than 2 minutes, and the measurement points are greater than 10; Carry out the start-up and shutdown and load lifting test under the water head. First, record the stress change waveform during the start-up process, then carry out the load lifting test according to the test plan. After the load point is measured to be stable, record the test time. After reaching the maximum load, carry out the load reduction test in the same way. Through the test, obtain the stress value and its change trend of the transition process and stable load point of the bucket measuring point under the water head. Carry out stress test under unit load shedding condition, and record stress change data of bucket measuring point under load shedding condition in combination with unit load shedding test.

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