A water turbine main shaft stress measurement device based on optical fiber sensing and a use method thereof

Abstract

A kind of water turbine main shaft stress measurement device based on optical fiber sensing and use method, including measurement system and host computer detection system;Measurement system includes fiber grating strain gauge and demodulator, multiple fiber grating strain gauges and multiple transmission optical fibers, demodulator are connected in turn, transmission optical fiber is fixed along hoop, hoop is assembled on main shaft, transmission optical fiber is connected with demodulator, demodulator and host computer detection system signal use wireless transmission mode to communicate, when application, the strain information of main shaft is acquired in real time by fiber grating strain gauge, wireless demodulator reads, analyzes, local storage and sends sensing information, host computer detection system completes the calculation, display, storage and data analysis of main shaft stress, fiber grating strain gauge is not interfered with by electromagnetic, so measurement precision is higher, demodulator is firmly fixed with main shaft by hoop, so signal transmission is reliable.Therefore, the present design is not interfered with by electromagnetic during measurement, measurement precision is higher, and signal transmission is reliable.

Description

Technical Field

[0001] This invention relates to a stress measuring device and its usage method, belonging to the field of turbine main shaft stress measurement, and particularly to a turbine main shaft stress measuring device based on fiber optic sensing. Background Technology

[0002] With the rapid development of the hydropower industry, in order to improve the economic benefits of hydropower units, the capacity and size of the units are gradually increasing. The key components of the units, such as the main shaft, are very important to ensure safe, stable and efficient operation. Therefore, it is necessary to monitor the main shaft to prevent it from malfunctioning. At present, resistive sensors are commonly used to measure the stress on the main shaft.

[0003] Chinese patent application number 200910063348.4, filed on July 28, 2009, discloses a wireless stress tester for hydropower units, including a lower-level distributed acquisition system, a wireless signal transmitter, and an upper-level main controller. The lower-level distributed acquisition system includes a resistance strain gauge sensor, a signal conditioner, and the lower-level main controller connected in sequence. The resistance strain gauge sensor is installed on the spindle to measure the stress of the spindle, and then transmits the measurement data to the signal conditioner and the lower-level main controller for processing. The lower-level main controller then transmits the data to the wireless signal transmitter, which in turn sends the data to the upper-level main controller for processing. Although this design achieves the measurement of spindle stress, it still has the following drawbacks:

[0004] In this design, a resistance strain gauge sensor is used to detect the stress on the spindle. However, resistance strain gauge sensors are susceptible to electromagnetic interference in high-voltage and strong magnetic field environments, and are prone to failure in humid and saline environments of hydroelectric generator sets. Furthermore, they have a large zero drift, resulting in low measurement accuracy in this design.

[0005] The information disclosed in this background section is intended only to enhance understanding of the overall background of this application and should not be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art. Summary of the Invention

[0006] The purpose of this invention is to overcome the defects and problems of existing technologies, such as susceptibility to electromagnetic interference and low measurement accuracy, and to provide a turbine main shaft stress measurement device and its usage method based on fiber optic sensing that is not subject to electromagnetic interference and has high measurement accuracy.

[0007] To achieve the above objectives, the technical solution of the present invention is:

[0008] A stress measurement device for the main shaft of a hydro turbine based on fiber optic sensing, comprising a measurement system, a demodulation system, and a host computer detection system; the measurement system includes multiple fiber Bragg grating strain gauges and a demodulator, each fiber Bragg grating strain gauge having a fiber Bragg grating, one side of which is connected to the outer surface of the main shaft, and leads of all fiber Bragg grating strain gauges connected to one end of a corresponding transmission fiber, all transmission fibers fixed along the outer surface of a clamp, and the other end of all transmission fibers connected to one end of the demodulator; the inner surface of the clamp is connected to the outer surface of the main shaft, and one end of the clamp is fixed to the outer surface of the demodulator; the demodulator includes a demodulation system comprising a demodulation module, a demodulation data processing module, and a wireless WIFI module, the demodulation module being signal-connected to the demodulation data processing module, the demodulation data processing module being signal-connected to the wireless WIFI module; the wireless WIFI module being signal-connected to the wireless receiving module of the host computer detection system, the wireless receiving module being signal-connected to the monitoring data processing module, and the monitoring data processing module being signal-connected to the monitoring display module.

[0009] The fiber Bragg grating strain gauge includes a first fiber Bragg grating strain gauge, a second fiber Bragg grating strain gauge, a third fiber Bragg grating strain gauge, and a fourth fiber Bragg grating strain gauge. The leads of the first, second, third, and fourth fiber Bragg grating strain gauges are respectively connected to one end of the corresponding transmission optical fiber. The first and second fiber Bragg grating strain gauges are symmetrically distributed along the main axis, and the first and fourth fiber Bragg grating strain gauges are symmetrically distributed along the perpendicular line of the main axis. The fourth and third fiber Bragg grating strain gauges are symmetrically distributed along the main axis.

[0010] The first fiber optic strain gauge has an angle of 45 degrees with the main axis, the second fiber optic strain gauge has an angle of 45 degrees with the main axis, the third fiber optic strain gauge has an angle of 135 degrees with the main axis, and the fourth fiber optic strain gauge has an angle of 135 degrees with the main axis.

[0011] The fiber Bragg grating strain gauge includes a fifth fiber Bragg grating strain gauge, a sixth fiber Bragg grating strain gauge, a seventh fiber Bragg grating strain gauge, and an eighth fiber Bragg grating strain gauge. The leads of the fifth, sixth, seventh, and eighth fiber Bragg grating strain gauges are each connected to one end of their respective transmission optical fibers. The fifth fiber Bragg grating strain gauge is symmetrically distributed with the first fiber Bragg grating strain gauge along the main axis. The sixth fiber Bragg grating strain gauge is symmetrically distributed with the second fiber Bragg grating strain gauge along the main axis. The seventh fiber Bragg grating strain gauge is symmetrically distributed with the third fiber Bragg grating strain gauge along the main axis. The eighth fiber Bragg grating strain gauge is symmetrically distributed with the fourth fiber Bragg grating strain gauge along the main axis.

[0012] The two ends of the fiber optic strain gauge are fixed to the two ends of the base, and the bottom surface of the base is connected to the outer surface of the main shaft.

[0013] The demodulation data processing module is signal-connected to the demodulation storage module, and the monitoring data processing module is signal-connected to the monitoring storage module.

[0014] The clamp includes multiple clamps that are arranged in a circular shape. One of the clamps is provided with a fixing bracket, and the fixing bracket has a fixing cavity in which a demodulator is inserted. The clamp is provided with a fixing hole at the part where it connects to the transmission optical fiber. A cable tie is inserted into the fixing hole, and multiple transmission optical fibers are fixed in the cable tie.

[0015] The clamp includes a top plate and a bottom plate arranged opposite to each other. A first support column, a second support column, and a third support column are provided between the top plate and the bottom plate. The first support column is located on one side of the top plate and the bottom plate, the second support column is located in the middle of the top plate and the bottom plate, and the third support column is located on the other side of the top plate and the bottom plate. A plurality of first support holes are evenly distributed on the first support column, and a third support hole is evenly distributed on the third support column. The first support hole of each clamp is opposite to the third support hole of the adjacent clamp, and a fixing bolt is inserted into the opposite first support hole and third support hole.

[0016] The top plate has multiple connecting holes evenly distributed at both ends, and the connecting holes correspond to the threaded holes on the connecting piece. Screws are inserted into the threaded holes and connecting holes. The connecting piece is located above the ends of two adjacent top plates.

[0017] An external power supply is installed in the fixed cavity below the demodulator. The external power supply is connected to one end of a power cord, and the other end of the power cord is connected to one end of the demodulator.

[0018] A counterweight is provided on one end of the clamp that is symmetrical to the demodulator along the main axis. The weight of the counterweight is the sum of the weight of the demodulator and the external power supply.

[0019] A method for using a fiber optic sensing-based stress measurement device for the main shaft of a hydro turbine, the method comprising the following steps:

[0020] Step 1: First, put the water turbine in a stopped state;

[0021] Step 2: First, fix multiple fiber optic strain gauges sequentially on one end of the outer surface of the spindle. Then, fix a clamp on the part of the spindle below the fiber optic strain gauges. Finally, fix a demodulator on one end of the clamp.

[0022] Step 3: First, connect the leads of multiple fiber optic strain gauges to one end of the corresponding transmission fiber in sequence. Then, fix all the transmission fibers to the clamps. Finally, connect the other end of all the transmission fibers to the demodulator in sequence.

[0023] Step 4: First, put the water turbine into working condition. At this time, the main shaft will be subjected to stress and deform. The deformation will then stretch the fiber optic strain gauge, which will then generate a wavelength change signal. The wavelength change signal will then be transmitted to the demodulation module by the transmission fiber.

[0024] Step 5: First, the demodulation module demodulates the wavelength change signal to obtain the wavelength change electrical signal. Then, the demodulation data processing module processes the wavelength change electrical signal to obtain the wavelength change digital signal. Finally, the wireless WIFI module transmits the wavelength change digital signal to the wireless receiving module wirelessly.

[0025] Step 6: First, the wireless receiving module receives the wavelength change digital signal, then the monitoring data processing module processes the wavelength change digital signal, calculates the spindle data based on the wavelength change digital signal, and then the monitoring display module displays the spindle data.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0027] 1. In the present invention, a stress measurement device and method for a turbine main shaft based on fiber optic sensing, the device includes a measurement system, a demodulation system, and a host computer detection system. The measurement system includes multiple fiber optic strain gauges fixed on the main shaft and a demodulator. The demodulator includes a demodulation system, which is signal-connected to the host computer detection system. In application, the stress on the main shaft causes wavelength change signals to be generated in the fiber optic strain gauges. The demodulation system then obtains a digital signal of wavelength change based on the wavelength change signal. Finally, the host computer detection system obtains data such as the stress of the main shaft based on the digital signal of wavelength change. The advantages of this invention also include:

[0028] Firstly, fiber optic strain gauges are used to measure the stress on the main shaft. Fiber optic strain gauges are not subject to electromagnetic interference during measurement and will not fail in humid or saline-alkali environments of hydroelectric generator sets. Therefore, they have high measurement accuracy and good stability, and are suitable for real-time monitoring of the turbine main shaft in complex electromagnetic environments.

[0029] Secondly, since the spindle is rotating during operation, it is not suitable for the wired data transmission method commonly used in existing technologies. The demodulation system and the host computer detection system are connected by a wireless signal to achieve the effect of transmitting digital signal data, which is adapted to the working state of the spindle rotation, so the signal transmission process is reliable.

[0030] Therefore, the present invention is not subject to electromagnetic interference during measurement, has high measurement accuracy, and reliable signal transmission.

[0031] 2. In the fiber optic sensing-based turbine main shaft stress measurement device and its usage method of the present invention, there are two sets of fiber optic strain gauges symmetrically distributed along the main shaft. Each set contains four fiber optic strain gauges, and the angle between each fiber optic strain gauge and the main shaft axis is 45 degrees or 135 degrees. In application, the stress of the main shaft is measured by the two sets of "X"-shaped fiber optic strain gauges, achieving a distributed measurement effect. Eight sets of data can be obtained simultaneously, and the data can be compared and verified to help determine the accuracy of the data. The stress is greatest in the "X" direction on the main shaft, hence the "X"-shaped distribution of the fiber optic strain gauges to measure the maximum stress of the main shaft. The torque and shaft power of the main shaft can also be measured, providing a basis for subsequent evaluation of the main shaft condition. Therefore, the present invention has the effect of distributed measurement.

[0032] 3. In the fiber optic sensing-based turbine main shaft stress measurement device and its usage method of the present invention, the fiber optic strain gauge is connected to the base, and the base is connected to the main shaft. During application, the base is first cleaned and polished, and then connected to the main shaft using a straightening rod. Because the main shaft cannot be welded, adhesive (AB glue or anchoring adhesive) is used to fix the base in place. The straightening rod ensures the installation effect of the base, laying a good foundation for the fixation of the fiber optic strain gauge and ensuring the measurement accuracy of the fiber optic strain gauge. Therefore, the present invention provides a good fixation effect for the fiber optic strain gauge.

[0033] 4. In the fiber optic sensing-based turbine main shaft stress measurement device and its usage method of the present invention, the demodulation system includes a demodulation storage module, a light source module, a photoelectric conversion module, and a signal processing module. The host computer detection system includes a monitoring storage module. In application, the light source module, photoelectric conversion module, and signal processing module are all low-power modules, which can work for a long time when paired with a large-capacity external power supply. The data obtained by the demodulator can be stored in the demodulation storage module, and the main shaft data obtained by the monitoring data processing module can be stored in the monitoring storage module. Therefore, data loss can be prevented, which is beneficial for later data retrieval for viewing and inspection. Therefore, the data storage effect of the present invention is good.

[0034] 5. In the present invention, a stress measurement device and method for a turbine main shaft based on fiber optic sensing, the clamp includes multiple clamps arranged in a circular ring. One clamp has a fixed support, and a demodulator is inserted into the fixed support. Adjacent clamps are connected by fixing bolts and connecting pieces. In application, the clamp fixes the demodulator so that it rotates with the main shaft, ensuring that the data collected by the fiber optic strain gauge can be stably transmitted to the demodulator for analysis. Simultaneously, finite element simulation technology was used to simulate the rotational state of this installation and fixing method, ensuring that the clamp will not break or fall off during operation. Field tests have also verified the safety and reliability of the aforementioned fixing method. Therefore, the present invention has good safety and reliability.

[0035] 6. In the present invention, a turbine main shaft stress measurement device and its usage method based on fiber optic sensing, an external power supply is fixed below the demodulator, and a counterweight is set on the clamp at a position symmetrical to the demodulator. During application, the demodulator is powered by the external power supply, which not only facilitates the periodic replacement of the external power supply but also effectively reduces the size and weight of the demodulator. The demodulator measures approximately 220×150×80mm and weighs approximately 1.5kg. The lightweight demodulator is less affected by centrifugal force, thus ensuring greater stability during rotation and preventing it from easily detaching from the clamp, guaranteeing the stability of high-speed signal transmission. Simultaneously, the counterweight ensures even weight distribution on the clamp, guaranteeing dynamic balance during main shaft rotation and reducing the impact of the clamp and other devices on the stability of the unit. Therefore, the present invention has a minimal impact on the stability of the unit. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the structure of the present invention.

[0037] Figure 2 yes Figure 1 A schematic diagram of the structure of the central clamp.

[0038] Figure 3 yes Figure 1 A schematic diagram of the structure of a fiber optic grating strain gauge.

[0039] Figure 4 yes Figure 1 A schematic diagram of the structure of the fifth fiber optic strain gauge.

[0040] Figure 5 yes Figure 2 A schematic diagram of the structure of the clamp.

[0041] Figure 6 yes Figure 5 A schematic diagram of the structure of the fixed bracket.

[0042] Figure 7 yes Figure 1 A schematic diagram of the demodulation system.

[0043] Figure 8 yes Figure 1 A schematic diagram of the structure of the upper-level computer monitoring system.

[0044] Figure 9 yes Figure 1 A schematic diagram of the structure of a fiber optic grating strain gauge.

[0045] Figure 10 This is a schematic diagram of the base structure in Example 3.

[0046] Figure 11 yes Figure 10 A schematic diagram of the upper and middle base.

[0047] Figure 12 yes Figure 10 A schematic diagram of the lower base.

[0048] Figure 13 This is a data comparison diagram of fiber optic strain gauges with a phase difference of 90 degrees within the first group of fiber optic strain gauges.

[0049] Figure 14 This is a data comparison diagram of fiber optic strain gauges with a phase difference of 90 degrees within the second group of fiber optic strain gauges.

[0050] Figure 15 This is a data comparison diagram of fiber optic strain gauges with a phase difference of 180 degrees within the first group of fiber optic strain gauges.

[0051] Figure 16 This is a data comparison diagram of fiber optic strain gauges in the second group that are 180 degrees out of phase.

[0052] Figure 17 This is a comparison chart of data from fiber grating strain gauges at corresponding positions within two sets of fiber grating strain gauges.

[0053] Figure 18 This is a schematic diagram of the simulation results of the clamp in Example 5.

[0054] In the diagram: Measurement System 1, Fiber Bragg Strain Gauge 11, Fiber Bragg Grating 111, Demodulator 12, Transmission Fiber 13, Clamp 14, Clip 141, Fixing Bracket 142, Fixing Cavity 143, Fixing Hole 144, Cable Tie 145, Base 15, Upper Base 151, Lower Base 152, External Power Supply 16, Counterweight 17, Demodulation System 2, Demodulation Module 21, Demodulation Data Processing Module 22, Wireless WIFI Module 23, Demodulation Storage Module 24, Host Computer Detection System 3, Wireless Receiving Module 31, Monitoring Data Processing Module 32, Monitoring Display Module 33, Monitoring Storage Storage module 34, main shaft 4, first fiber Bragg grating strain gauge 5, second fiber Bragg grating strain gauge 51, third fiber Bragg grating strain gauge 52, fourth fiber Bragg grating strain gauge 53, fifth fiber Bragg grating strain gauge 54, sixth fiber Bragg grating strain gauge 55, seventh fiber Bragg grating strain gauge 56, eighth fiber Bragg grating strain gauge 57, top plate 6, bottom plate 61, support column 62, first support column 621, second support column 622, third support column 623, first support hole 624, third support hole 625, fixing bolt 626, connecting piece 63, threaded hole 64, screw 65, connecting hole 66. Detailed Implementation

[0055] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0056] Please see Figure 1 — Figure 18A stress measurement device for the main shaft of a hydro turbine based on fiber optic sensing is disclosed. The device includes a measurement system 1, a demodulation system 2, and a host computer detection system 3. The measurement system 1 includes multiple fiber optic strain gauges 11 and a demodulator 12. Each fiber optic strain gauge 11 includes a fiber optic grating 111. One side of each fiber optic strain gauge 11 is connected to the outer surface of the main shaft 4. The leads of all fiber optic strain gauges 11 are connected to one end of a corresponding transmission fiber 13. All transmission fibers 13 are fixed along the outer surface of a clamp 14. The other end of each transmission fiber 13 is connected to one end of the demodulator 12. The inner surface of the clamp 14 is connected to the outer surface of the main shaft 4. The clamp 14 is fixed at one end to the outer surface of the demodulator 12. The demodulator 12 includes a demodulation system 2, which includes a demodulation module 21, a demodulation data processing module 22, and a wireless WIFI module 23. The demodulation module 21 is signal-connected to the demodulation data processing module 22, and the demodulation data processing module 22 is signal-connected to the wireless WIFI module 23. The wireless WIFI module 23 is signal-connected to the wireless receiving module 31 of the host computer detection system 3, the wireless receiving module 31 is signal-connected to the monitoring data processing module 32, and the monitoring data processing module 32 is signal-connected to the monitoring display module 33. The fiber optic strain gauge 11 includes a first fiber optic strain gauge 5, a second fiber optic strain gauge 51, a third fiber optic strain gauge 52, and a fourth fiber optic strain gauge 53. The leads of the first fiber optic strain gauge 5, the second fiber optic strain gauge 51, the third fiber optic strain gauge 52, and the fourth fiber optic strain gauge 53 are respectively connected to one end of the corresponding transmission fiber 13. The first fiber optic strain gauge 5 and the second fiber optic strain gauge 51 are symmetrically distributed along the main axis 4, the first fiber optic strain gauge 5 and the fourth fiber optic strain gauge 53 are symmetrically distributed along the perpendicular line of the main axis 4, and the fourth fiber optic strain gauge 53 and the third fiber optic strain gauge 52 are symmetrically distributed along the main axis 4. The first fiber optic strain gauge 5 has an angle of 45 degrees with the axis of the main shaft 4, the second fiber optic strain gauge 51 has an angle of 45 degrees with the axis of the main shaft 4, the third fiber optic strain gauge 52 has an angle of 135 degrees with the axis of the main shaft 4, and the fourth fiber optic strain gauge 53 has an angle of 135 degrees with the axis of the main shaft 4.The fiber Bragg grating strain gauge 11 includes a fifth fiber Bragg grating strain gauge 54, a sixth fiber Bragg grating strain gauge 55, a seventh fiber Bragg grating strain gauge 56, and an eighth fiber Bragg grating strain gauge 57. The leads of each of these strain gauges are connected to one end of their respective transmission optical fibers 13. The fifth fiber Bragg grating strain gauge 54 and the first fiber Bragg grating strain gauge 5 are symmetrically distributed along the main axis 4. The sixth fiber Bragg grating strain gauge 55 and the second fiber Bragg grating strain gauge 51 are symmetrically distributed along the main axis 4. The seventh fiber Bragg grating strain gauge 56 and the third fiber Bragg grating strain gauge 52 are symmetrically distributed along the main axis 4. The eighth fiber Bragg grating strain gauge 57 and the fourth fiber Bragg grating strain gauge 53 are symmetrically distributed along the main axis 4. Both ends of the fiber Bragg grating strain gauge 11 are fixed to both ends of a base 15, and the bottom surface of the base 15 is connected to the outer surface of the main axis 4. The demodulation data processing module 22 is signal-connected to the demodulation storage module 24, and the monitoring data processing module 32 is signal-connected to the monitoring storage module 34. The clamp 14 includes multiple clamps 141, which are arranged in a ring shape. One clamp 141 is provided with a fixing bracket 142, and the fixing bracket 142 has a fixing cavity 143, in which a demodulator 12 is inserted. The clamp 141 is provided with a fixing hole 144 at the connection point with the transmission optical fiber 13, and a cable tie 145 is inserted into the fixing hole 144, in which multiple transmission optical fibers 13 are fixed. The clamp 141 includes a top plate 6 and a bottom plate 61 disposed opposite to each other. A first support column 621, a second support column 622, and a third support column 623 are disposed between the top plate 6 and the bottom plate 61. The first support column 621 is located on one side of the top plate 6 and the bottom plate 61, the second support column 622 is located in the middle of the top plate 6 and the bottom plate 61, and the third support column 623 is located on the other side of the top plate 6 and the bottom plate 61. A plurality of first support holes 624 are evenly distributed on the first support column 621, and a third support hole 625 is evenly distributed on the third support column 623. The first support hole 624 of each clamp 141 is opposite to the third support hole 625 of its adjacent clamp 141, and a fixing bolt 626 is inserted into the opposite first support hole 624 and third support hole 625. Multiple connecting holes 66 are evenly distributed at both ends of the top plate 6. The connecting holes 66 correspond to the threaded holes 64 on the connecting piece 63. Screws 65 are inserted into the threaded holes 64 and the connecting holes 66. The connecting piece 63 is located above the ends of two adjacent top plates 6. An external power supply 16 is provided in the fixed cavity 143 below the demodulator 12. The external power supply 16 is connected to one end of a power cord, and the other end of the power cord is connected to one end of the demodulator 12.A counterweight 17 is provided on one end of the clamp 14 symmetrical to the demodulator 12 along the axis of the main shaft 4. The weight of the counterweight 17 is the sum of the weights of the demodulator 12 and the external power supply 16. A method for using a fiber optic sensing-based turbine main shaft stress measurement device includes the following steps: First, the turbine is put into a stopped state; Second, multiple fiber optic strain gauges 11 are sequentially fixed to one end of the outer surface of the main shaft 4, and a clamp 14 is fixed on the main shaft 4 below the fiber optic strain gauges 11, and then the demodulator 12 is fixed to one end of the clamp 14; Third, the leads of the multiple fiber optic strain gauges 11 are sequentially connected to one end of the corresponding transmission optical fibers 13, and all the transmission optical fibers 13 are fixed to the clamp 14, and then the other ends of all the transmission optical fibers 13 are sequentially connected to the demodulator 12; Fourth, the turbine is put into a working state. At this time, the main shaft 4 will be subjected to stress and deform, and the deformation will then cause… The fiber optic strain gauge 11 is stretched, and then the fiber optic strain gauge 11 generates a wavelength change signal, which is then transmitted to the demodulation module 21 via the transmission fiber 13. Fifth step: The demodulation module 21 first demodulates the wavelength change signal to obtain a wavelength change electrical signal, then the demodulation data processing module 22 processes the wavelength change electrical signal to obtain a wavelength change digital signal, and then the wireless WIFI module 23 wirelessly transmits the wavelength change digital signal to the wireless receiving module 31. Sixth step: The wireless receiving module 31 first receives the wavelength change digital signal, then the monitoring data processing module 32 processes the wavelength change digital signal, calculates the data of the main shaft 4 based on the wavelength change digital signal, and then the monitoring display module 33 displays the data of the main shaft 4.

[0057] The following are supplementary descriptions of the present invention:

[0058] The transmission optical fiber 13 described in this invention refers to an armored optical fiber, which is an optical fiber with an enhanced protective layer or a metal shell. It has strong durability and resistance to external damage, so it can stably connect the fiber optic strain gauge 11 and the demodulator 12 for a long time. Moreover, the transmission optical fiber 13 can be directly inserted into the optical fiber interface of the fiber optic strain gauge 11 and the demodulator 12, which is more convenient. In the prior art, the wire connection of electrical sensors requires hinge, crimping or welding, which is more inconvenient.

[0059] Example 1:

[0060] Please see Figure 1 — Figure 18A stress measurement device for the main shaft of a hydro turbine based on fiber optic sensing is disclosed. The device includes a measurement system 1, a demodulation system 2, and a host computer detection system 3. The measurement system 1 includes multiple fiber optic strain gauges 11 and a demodulator 12. Each fiber optic strain gauge 11 includes a fiber optic grating 111. One side of each fiber optic strain gauge 11 is connected to the outer surface of the main shaft 4. The leads of all fiber optic strain gauges 11 are connected to one end of a corresponding transmission fiber 13. All transmission fibers 13 are fixed along the outer surface of a clamp 14. The other end of each transmission fiber 13 is connected to one end of the demodulator 12. The inner surface of the clamp 14 is connected to the outer surface of the main shaft 4. The clamp 14 is fixed at one end to the outer surface of the demodulator 12. The demodulator 12 includes a demodulation system 2, which includes a demodulation module 21, a demodulation data processing module 22, and a wireless WIFI module 23. The demodulation module 21 is signal-connected to the demodulation data processing module 22, and the demodulation data processing module 22 is signal-connected to the wireless WIFI module 23. The wireless WIFI module 23 is signal-connected to the wireless receiving module 31 of the host computer detection system 3, the wireless receiving module 31 is signal-connected to the monitoring data processing module 32, and the monitoring data processing module 32 is signal-connected to the monitoring display module 33.

[0061] A method for using a fiber optic sensing-based stress measurement device for the main shaft of a hydro turbine, the method comprising the following steps:

[0062] Step 1: First, put the water turbine in a stopped state;

[0063] Step 2: First, fix multiple fiber optic strain gauges 11 sequentially on one end of the outer surface of the main shaft 4. Then, fix a clamp 14 on the part of the main shaft 4 located below the fiber optic strain gauges 11. Finally, fix a demodulator 12 on one end of the clamp 14.

[0064] Step 3: First, connect the leads of multiple fiber optic strain gauges 11 to one end of the corresponding transmission fiber 13 in sequence. Then, fix all the transmission fibers 13 to the clamp 14. Then, connect the other end of all the transmission fibers 13 to the demodulator 12 in sequence.

[0065] Step 4: First, put the water turbine into working condition. At this time, the main shaft 4 will be subjected to stress and deform. The deformation will then stretch the fiber optic strain gauge 11. Then the fiber optic strain gauge 11 will generate a wavelength change signal, which will be transmitted to the demodulation module 21 by the transmission fiber optic 13.

[0066] Step 5: First, the demodulation module 21 demodulates the wavelength change signal to obtain the wavelength change electrical signal. Then, the demodulation data processing module 22 processes the wavelength change electrical signal to obtain the wavelength change digital signal. Finally, the wireless WIFI module 23 transmits the wavelength change digital signal to the wireless receiving module 31 wirelessly.

[0067] Step 6: First, the wireless receiving module 31 receives the wavelength change digital signal, then the monitoring data processing module 32 processes the wavelength change digital signal, calculates the data of the main axis 4 based on the wavelength change digital signal, and then the monitoring display module 33 displays the data of the main axis 4.

[0068] Preferably, in the second step, a fiber Bragg grating strain gauge 11 is fixed at the location of the main shaft 4 between the water guide oil groove cover and the mechanical overspeed pendulum clamp. Preferably, the fiber Bragg grating strain gauge 11 includes two fiber Bragg gratings 111, one fiber Bragg grating 111 is used to measure the stress of the main shaft 4, and the other fiber Bragg grating 111 is used to measure the temperature for temperature compensation correction to avoid temperature interference with stress measurement.

[0069] Example 2:

[0070] The basic content is the same as in Example 1, except that:

[0071] Please see Figure 1 — Figure 17The fiber optic strain gauge 11 includes a first fiber optic strain gauge 5, a second fiber optic strain gauge 51, a third fiber optic strain gauge 52, and a fourth fiber optic strain gauge 53. The leads of the first fiber optic strain gauge 5, the second fiber optic strain gauge 51, the third fiber optic strain gauge 52, and the fourth fiber optic strain gauge 53 are respectively connected to one end of the corresponding transmission fiber 13. The first fiber optic strain gauge 5 and the second fiber optic strain gauge 51 are symmetrically distributed along the main axis 4, the first fiber optic strain gauge 5 and the fourth fiber optic strain gauge 53 are symmetrically distributed along the perpendicular line of the main axis 4, and the fourth fiber optic strain gauge 53 and the third fiber optic strain gauge 52 are symmetrically distributed along the main axis 4. The first fiber optic strain gauge 5 has an angle of 45 degrees with the axis of the main shaft 4, the second fiber optic strain gauge 51 has an angle of 45 degrees with the axis of the main shaft 4, the third fiber optic strain gauge 52 has an angle of 135 degrees with the axis of the main shaft 4, and the fourth fiber optic strain gauge 53 has an angle of 135 degrees with the axis of the main shaft 4. The fiber Bragg grating strain gauge 11 includes a fifth fiber Bragg grating strain gauge 54, a sixth fiber Bragg grating strain gauge 55, a seventh fiber Bragg grating strain gauge 56, and an eighth fiber Bragg grating strain gauge 57. The leads of the fifth fiber Bragg grating strain gauge 54, the sixth fiber Bragg grating strain gauge 55, the seventh fiber Bragg grating strain gauge 56, and the eighth fiber Bragg grating strain gauge 57 are all connected to one end of the corresponding transmission fiber 13. The fifth fiber Bragg grating strain gauge 54 and the first fiber Bragg grating strain gauge 5 are symmetrically distributed along the main axis 4. The sixth fiber Bragg grating strain gauge 55 and the second fiber Bragg grating strain gauge 51 are symmetrically distributed along the main axis 4. The seventh fiber Bragg grating strain gauge 56 and the third fiber Bragg grating strain gauge 52 are symmetrically distributed along the main axis 4. The eighth fiber Bragg grating strain gauge 57 and the fourth fiber Bragg grating strain gauge 53 are symmetrically distributed along the main axis 4. Preferably, the leads of the first fiber optic strain gauge 5, the second fiber optic strain gauge 51, the third fiber optic strain gauge 52, the fourth fiber optic strain gauge 53, the fifth fiber optic strain gauge 54, the sixth fiber optic strain gauge 55, the seventh fiber optic strain gauge 56, and the eighth fiber optic strain gauge 57 extend toward the clamp 14 in a vertically downward direction.

[0072] In application, all fiber optic strain gauges 11 can be divided into two groups. The first group of fiber optic strain gauges 11 consists of a first fiber optic strain gauge 5, a second fiber optic strain gauge 51, a third fiber optic strain gauge 52, and a fourth fiber optic strain gauge 53, symmetrically distributed along the main axis 4. The angle between these strain gauges and the main axis 4 is 45 degrees or 135 degrees, thus giving the fiber optic strain gauges 11 an "X" shape. This shape is in the same direction as the maximum stress within the main axis 4, allowing for measurement of the maximum stress. Furthermore, this shape can simultaneously measure the main stress. The torque of shaft 4 can be calculated to determine the shaft power of the main shaft 4, facilitating the assessment of the overall efficiency of the turbine. The second group of fiber optic strain gauges 11 consists of the fifth fiber optic strain gauge 54, the sixth fiber optic strain gauge 55, the seventh fiber optic strain gauge 56, and the eighth fiber optic strain gauge 57, symmetrically distributed along the main shaft 4 with the first group of fiber optic strain gauges 11. The leads of each group of fiber optic strain gauges 11 extend downwards into the clamp 14 and connect to the corresponding transmission fiber 13, significantly reducing the number of connecting lines on the main shaft 4. Please refer to [link to relevant documentation]. Figure 13 — Figure 17 In the figure, #1 is the first fiber Bragg grating strain gauge 5, #2 is the second fiber Bragg grating strain gauge 51, #3 is the third fiber Bragg grating strain gauge 52, #4 is the fourth fiber Bragg grating strain gauge 53, #5 is the fifth fiber Bragg grating strain gauge 54, #6 is the sixth fiber Bragg grating strain gauge 55, #7 is the seventh fiber Bragg grating strain gauge 56, and #8 is the eighth fiber Bragg grating strain gauge 57. Figure 13 This is a data comparison diagram of fiber optic strain gauges 11 within the first group of fiber optic strain gauges 11 that are 90 degrees out of phase. Figure 14 The image shows a comparison of data from fiber Bragg grating strain gauges 11 within the second group, which are 90 degrees apart. It can be seen that, except for the third fiber Bragg grating strain gauge 52 (whose data shows a slight difference due to installation issues), the data curves of the other fiber Bragg grating strain gauges 11 are basically identical, indicating good consistency among the fiber Bragg grating strain gauges 11. Figure 15 This is a data comparison chart of fiber optic strain gauges in the first group that are 180 degrees out of phase. Figure 16 The image shows a comparison of data from fiber optic strain gauges in the second group that are 180 degrees out of phase. It can be seen that the data curves of fiber optic strain gauge 11 are basically overlapping, indicating good consistency and regularity. Figure 17 The data comparison diagram of the fiber grating strain gauges 11 at corresponding positions in the two sets of fiber grating strain gauges shows that, except for the third fiber grating strain gauge 52, the data curves of the other fiber grating strain gauges 11 are basically overlapping, which indicates that the fiber grating strain gauges 11 have good consistency and the two sets of fiber grating strain gauges 11 have high symmetry. Therefore, it can be said that the performance of the fiber grating strain gauges 11 is relatively stable. Thus, the fiber grating strain gauges 11 have good consistency and are suitable for measuring the stress of the main shaft 4.

[0073] Example 3:

[0074] The basic content is the same as in Example 1, except that:

[0075] Please see Figure 1 — Figure 12 The fiber optic strain gauge 11 is fixed at both ends to the two ends of the base 15, and the bottom surface of the base 15 is connected to the outer surface of the main shaft 4. Preferably, the base 15 includes an upper base 151 and a lower base 152.

[0076] In application, the base 15 is first cleaned by high-temperature immersion in degreasing solution or ultrasonic cleaning. Then, the base 15 is polished to meet the installation requirements. Next, the two sets of bases 15 are placed on the main shaft 4 at the positions where the fiber optic strain gauges 11 are installed. Then, the two lower bases 152 are sequentially clipped onto the steps of the straightening rod. Then, the two upper bases 151 are connected to the straightening rod to fix the straightening rod. Then, the two lower bases 152 are sequentially fixed diagonally with adhesive. Then, the straightening rod is removed, and the fiber optic strain gauge 11 is installed and fixed between the upper base 151 and the lower base 152. The error between the two sets of bases 15 must be less than or equal to one millimeter to complete the installation of one fiber optic strain gauge 11. Repeat the above steps multiple times to complete the installation of all fiber optic strain gauges 11.

[0077] Example 4:

[0078] The basic content is the same as in Example 1, except that:

[0079] Please see Figure 1 — Figure 8 The demodulation data processing module 22 is signal-connected to the demodulation storage module 24, and the monitoring data processing module 32 is signal-connected to the monitoring storage module 34. Preferably, the demodulator 12 includes a power management module, a light source module, and an optical splitter; the demodulation module 21 includes a photoelectric conversion module; the demodulation data processing module includes a signal processing module; and the wireless WIFI module 23 includes a protocol conversion module.

[0080] In application, the incident light signal is first generated by the light source module, which employs a highly integrated tunable laser (TLS) and high-speed, high-precision tuning drive technology. High-speed wavelength tuning is achieved through a single device, reducing energy consumption and allowing the external power supply 16 to operate for a longer period. The incident light signal is then split into multiple incident light signals by an optical splitter and transmitted to multiple fiber Bragg grating strain gauges 11. The fiber Bragg grating strain gauges 11 then generate wavelength change signals. The photoelectric conversion module processes these wavelength-converted signals into wavelength-change electrical signals, which are then processed into wavelength-change digital signals by the signal processing module. The signal processing module uses a time synchronization algorithm to calculate characteristic wavelengths in real time, reducing redundant calculations and lowering processing power consumption, thus extending the operating time of the external power supply 16. Finally, the protocol conversion module packages the wavelength-change digital signals according to the detection layer protocol. The signal is then transmitted wirelessly to the wireless receiving module 31. During the aforementioned process, the wavelength change digital signal is sent to the demodulation storage module 24 for local storage, backing up the aforementioned signal to prevent its loss. The power management module supplies power to all modules within the demodulator, keeping the overall power consumption below 18W, and ensures stable operation in high-temperature environments through structural designs such as heat sinks. In application scenarios such as the main spindle 4 of the unit, which require strong shielding and are located in confined spaces, the demodulator 12 achieves wireless acquisition, stable transmission, and complete storage of dynamic strain signals at a high sampling rate of 2500Hz. The monitoring data processing module 32 calculates the stress, torque, and other data of the main spindle 4 based on the wavelength change digital signal, and then sends the stress, torque, and other data of the main spindle 4 to the monitoring storage module 34 for local storage, backing up the aforementioned data to prevent its loss.

[0081] Example 5:

[0082] The basic content is the same as in Example 1, except that:

[0083] Please see Figure 1 — Figure 18The clamp 14 includes multiple clamps 141, which are arranged in a ring shape. One of the clamps 141 is provided with a fixing bracket 142. The fixing bracket 142 has a fixing cavity 143, and a demodulator 12 is inserted into the fixing cavity 143. A fixing hole 144 is provided at the part of the clamp 141 that connects to the transmission optical fiber 13. A cable tie 145 is inserted into the fixing hole 144, and multiple transmission optical fibers 13 are fixed in the cable tie 145. The clamp 141 includes a top plate 6 and a bottom plate 61 disposed opposite to each other. A first support column 621, a second support column 622, and a third support column 623 are disposed between the top plate 6 and the bottom plate 61. The first support column 621 is located on one side of the top plate 6 and the bottom plate 61, the second support column 622 is located in the middle of the top plate 6 and the bottom plate 61, and the third support column 623 is located on the other side of the top plate 6 and the bottom plate 61. A plurality of first support holes 624 are evenly distributed on the first support column 621, and a third support hole 625 is evenly distributed on the third support column 623. The first support hole 624 of each clamp 141 is opposite to the third support hole 625 of its adjacent clamp 141, and a fixing bolt 626 is inserted into the opposite first support hole 624 and third support hole 625. The top plate 6 has multiple connecting holes 66 evenly distributed at both ends. The connecting holes 66 correspond to the threaded holes 64 on the connecting piece 63. Screws 65 are inserted into the threaded holes 64 and the connecting holes 66. The connecting piece 63 is located above the ends of two adjacent top plates 6.

[0084] In application, first determine the installation height of the clamp 14 on the spindle 4 according to the site environment, then place multiple clamps 141 sequentially at that height (for example, on a wooden stick at the same height). Next, align the first support hole 624 and the third support hole 625 of two adjacent clamps 141, leaving a small gap between them. Then, insert fixing bolts 626 into the first support hole 624 and the third support hole 625 to ensure a stable connection between the first support column 621 and the third support column 623 of the adjacent clamp 141. Securely connect two adjacent clamps 141, then position the connecting piece 63 above two adjacent top plates 6. Align the threaded holes 64 with the connecting holes 66 on the two adjacent top plates 6, and then screw the screws 65 into all the connecting holes 66 and threaded holes 64 in sequence to ensure that the two adjacent clamps 141 are at the same height. This completes the fixing of the two adjacent clamps 141. Repeat the aforementioned steps until all adjacent clamps 141 are fixed. The fixing bolts 626 are M10 bolts to ensure a stable connection between the clamps 141. Figure 18Simulation results confirmed that the clamp 14 would not break or fall off during the rotation of the spindle. Welding can be used to further fix the clamp 141. A bracket 142 is then fixed to one of the clamps 141 with screws. The demodulator 12 is then fixed in the fixing cavity 143. The antenna of the demodulator 12 is connected to the fixing bracket 142 with AB glue. After connecting the demodulator to the leads of multiple fiber optic strain gauges 11 using transmission optical fibers 13, cable ties 145 are inserted into the fixing holes 144. The cable ties 145 are then connected to multiple transmission optical fibers 13, and the multiple transmission optical fibers 13 are then tightly bound to one side of the top plate 6 using the cable ties 145. This completes the fixing of the transmission optical fibers 13 to the clamp 14, reducing the number of connecting lines distributed on the spindle 4. The transmission optical fibers 13 have high mechanical strength and are not easily broken, thus ensuring stable signal transmission.

[0085] Example 6:

[0086] The basic content is the same as in Example 1, except that:

[0087] Please see Figure 1 — Figure 6 An external power supply 16 is installed inside the fixed cavity 143, located below the demodulator 12. One end of the external power supply 16 is connected to a power cord, and the other end of the power cord is connected to one end of the demodulator 12. A counterweight 17 is installed on the end of the clamp 14 symmetrical to the demodulator 12 along the main shaft 4. The weight of the counterweight 17 is the sum of the weights of the demodulator 12 and the external power supply 16. Preferably, the housing of the external power supply 16 is made of aluminum.

[0088] In application, an external power supply 16 is first fixed at the bottom of the fixed cavity 143. Then, a power cord is used to connect the demodulator 12 and the external power supply 16. The external power supply 16 supplies power to all modules inside the demodulator 12 through a power management module. The external power supply 16 has a large capacity and can work for a long time when combined with a low-power light source module and a signal processing module. The distance between the demodulator 12 and the external power supply 16 is short, which can shorten the power cord line. The external power supply 16 has a charging interface to facilitate charging. The weight of the counterweight 17 is the sum of the weights of the demodulator 12 and the external power supply 16. The counterweight 17 and the demodulator 12 are symmetrically arranged along the main axis 4 to reduce the influence on the swing of the main axis 4.

[0089] Example 7:

[0090] The basic content is the same as in Example 1, except that:

[0091] Please see Figure 1 — Figure 6When the number of fiber optic strain gauges 11 is greater than the number of interfaces (eight) of the demodulator 12, the leads of the fiber optic strain gauges 11 can be connected to the optical splitter, and then the transmission fiber 13 can be led out from the optical splitter and then connected to the demodulator 12.

[0092] In application, when the number of fiber Bragg grating strain gauges 11 is greater than the number of interfaces (eight) of demodulator 12, an optical splitter can be introduced to connect multiple fiber Bragg grating strain gauges 11, so that one demodulator 12 can process more wavelength change signals of fiber Bragg grating strain gauges 11.

[0093] Example 8:

[0094] The basic content is the same as in Example 1, except that:

[0095] Please see Figure 1 — Figure 18 After the clamp 14 was designed based on the dimensions of the spindle 4, in order to ensure the stability of the clamp 14 in the working state, strain displacement simulation analysis was first performed on the clamp 14, and then fracture simulation analysis was performed on the clamp 14.

[0096] In application, the working state of clamp 14 was first simulated by remote displacement setting, i.e., clamp 14 had no displacement in the X or Y axis direction, only rotation in the Z axis, with the speed set to 100 rpm, much greater than the normal 62.5 rpm. During on-site installation, an actual preload is applied to the fixing bolt 626 to tighten it. The actual preload is about 70% to 80% of the ultimate preload. In the simulation, a preload of 8000 N is applied to the fixing bolt 626, which is much less than the actual preload. The actual fixing bolt is an M10 (8.8 grade strength) bolt, whose actual preload is much greater than the simulated preload. Then, standard gravity is applied to all clamps 141. Next, a detachment simulation analysis of clamp 14 is performed. At this time, the displacement of the upper end face of clamp 141 is analyzed to determine whether clamp 141 has displaced, thereby determining whether clamp 14 has detached. The analysis results are as follows. Figure 18 As shown, the deformation value is relatively small, so it can be assumed that the clamp 14 will not fall off. Next, the normal stress between the clamp 14 and the main shaft 4 is simulated to determine the tightness of the clamp 14. The software calculation shows that the total average stress of the clamp 14 is 5.8889 MPa. There are eight clamps 141, each with two contact surfaces with the main shaft 4, and the contact area of ​​a single clamp 141 with the main shaft 4 is 5038.8 mm². 2Based on the aforementioned data, the total normal stress is calculated to be 474767.8 N. With a friction coefficient set at 0.15, multiplying the total normal stress by the friction coefficient yields the critical friction force, which is 71215.2 N. This value is significantly greater than the weight of clamp 14, and the simulated preload of fixing bolt 626 is relatively small. If the tightening force is increased during installation, detachment is even less likely. Further fracture simulation analysis of clamp 14 is performed. Standard gravity, bolt preload, and rotational speed are applied to fixing bolt 626 to simulate normal working conditions. The analysis shows that the maximum equivalent stress of fixing bolt 626 ranges from 159.87 MPa to 165.36 MPa, all less than the yield strength of fixing bolt 626. Therefore, fixing bolt 626 will not fracture. Fixing bracket 14 2. The clamp 141 is connected to the bolt by a bolt. A preload of 5000N is applied to the bolt. Simulation analysis shows that the maximum equivalent stress of the bolt is between 240.94MPa and 696.62MPa, which is lower than the yield strength of the bolt (M10). Therefore, the bolt will not break, indicating that the connection between the fixed bracket 142 and the clamp 141 is stable. The stress of the clamp 141 itself is then simulated. The analysis shows that the maximum stress of the clamp 141 is 60.701MPa. The clamp 141 is made of Q235 steel with a yield strength of 235MPa and a safety factor of 3 or higher. Therefore, the clamp 141 itself will not break. In summary, the simulation analysis shows that the clamp 141 will not have any safety issues such as falling off or breaking. Therefore, the clamp 141 is safe and reliable.

[0097] The above description is only a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. Any equivalent modifications or changes made by those skilled in the art based on the content disclosed in the present invention should be included within the scope of protection set forth in the claims.

Claims

1. A device for measuring the stress of a turbine main shaft based on fiber optic sensing, characterized in that: The device includes a measurement system (1), a demodulation system (2), and a host computer detection system (3). The measurement system (1) includes multiple fiber optic strain gauges (11) and a demodulator (12). The fiber optic strain gauge (11) includes a fiber optic grating (111). One side of the fiber optic strain gauge (11) is connected to the outer surface of the main shaft (4). The leads of all fiber optic strain gauges (11) are connected to one end of the corresponding transmission fiber (13). All transmission fibers (13) are fixed along the outer surface of the clamp (14). The other end of all transmission fibers (13) is connected to one end of the demodulator (12). The inner surface of the clamp (14) is connected to the outer surface of the main shaft (4). One end of the clamp (14) is fixed to the outer surface of the demodulator (12). The demodulator (12) includes a demodulation system (2), which includes a demodulation module (21), a demodulation data processing module (22), and a wireless WIFI module (23). The demodulation module (21) is signal-connected to the demodulation data processing module (22), and the demodulation data processing module (22) is signal-connected to the wireless WIFI module (23). The wireless WIFI module (23) is connected to the wireless receiving module (31) of the host computer detection system (3) by signal, the wireless receiving module (31) is connected to the monitoring data processing module (32) by signal, and the monitoring data processing module (32) is connected to the monitoring display module (33) by signal. The clamp (14) underwent detachment simulation analysis and fracture simulation analysis; The detachment simulation analysis is as follows: First, the rotation speed of the working state of the clamp (14) is simulated, then the actual preload is applied to the fixing bolt (626), then the standard gravity is applied to the clamp (141), then the displacement of the clamp (141) is analyzed, then the normal stress between the clamp (14) and the main shaft (4) is simulated to obtain the tightness of the clamp (14), and the detachment simulation analysis result is obtained by combining the displacement of the clamp (141) and the tightness of the clamp (14). The fracture simulation analysis is as follows: First, standard gravity, bolt preload and rotation speed are applied to the fixing bolt (626) to simulate normal working conditions. Then, the maximum equivalent stress and yield strength of the fixing bolt (626) are compared to obtain the connection stability between the fixing bracket (142) and the clamp (141). Then, the stress of the clamp (141) itself is simulated to obtain the fracture simulation analysis results of the clamp (141).

2. The turbine main shaft stress measuring device based on fiber optic sensing according to claim 1, characterized in that: The fiber optic strain gauge (11) includes a first fiber optic strain gauge (5), a second fiber optic strain gauge (51), a third fiber optic strain gauge (52), and a fourth fiber optic strain gauge (53). The leads of the first fiber optic strain gauge (5), the second fiber optic strain gauge (51), the third fiber optic strain gauge (52), and the fourth fiber optic strain gauge (53) are respectively connected to one end of the corresponding transmission fiber (13). The first fiber optic strain gauge (5) and the second fiber optic strain gauge (51) are symmetrically distributed along the main axis (4). The first fiber optic strain gauge (5) and the fourth fiber optic strain gauge (53) are symmetrically distributed along the perpendicular line of the main axis (4). The fourth fiber optic strain gauge (53) and the third fiber optic strain gauge (52) are symmetrically distributed along the main axis (4).

3. The turbine main shaft stress measuring device based on fiber optic sensing according to claim 2, characterized in that: The angle between the first fiber optic strain gauge (5) and the axis of the main shaft (4) is 45 degrees, the angle between the second fiber optic strain gauge (51) and the axis of the main shaft (4) is 45 degrees, the angle between the third fiber optic strain gauge (52) and the axis of the main shaft (4) is 135 degrees, and the angle between the fourth fiber optic strain gauge (53) and the axis of the main shaft (4) is 135 degrees.

4. The turbine main shaft stress measuring device based on fiber optic sensing according to claim 3, characterized in that: The fiber Bragg grating strain gauge (11) includes a fifth fiber Bragg grating strain gauge (54), a sixth fiber Bragg grating strain gauge (55), a seventh fiber Bragg grating strain gauge (56), and an eighth fiber Bragg grating strain gauge (57). The leads of the fifth fiber Bragg grating strain gauge (54), the sixth fiber Bragg grating strain gauge (55), the seventh fiber Bragg grating strain gauge (56), and the eighth fiber Bragg grating strain gauge (57) are respectively connected to one end of the corresponding transmission fiber (13). The fifth fiber Bragg grating strain gauge (54) and the first fiber Bragg grating strain gauge (5) are symmetrically distributed along the main axis (4). The sixth fiber Bragg grating strain gauge (55) and the second fiber Bragg grating strain gauge (51) are symmetrically distributed along the main axis (4). The seventh fiber Bragg grating strain gauge (56) and the third fiber Bragg grating strain gauge (52) are symmetrically distributed along the main axis (4). The eighth fiber Bragg grating strain gauge (57) and the fourth fiber Bragg grating strain gauge (53) are symmetrically distributed along the main axis (4).

5. The turbine main shaft stress measuring device based on fiber optic sensing according to claim 1, characterized in that: The two ends of the fiber optic strain gauge (11) are fixed to the two ends of the base (15), and the bottom surface of the base (15) is connected to the outer surface of the main shaft (4).

6. The turbine main shaft stress measuring device based on fiber optic sensing according to claim 1, characterized in that: The demodulation data processing module (22) is signal-connected to the demodulation storage module (24), and the monitoring data processing module (32) is signal-connected to the monitoring storage module (34).

7. The turbine main shaft stress measuring device based on fiber optic sensing according to claim 1, characterized in that: The clamp (14) includes multiple clamps (141), which are arranged in a ring shape. A fixed bracket (142) is provided on one of the clamps (141), and a fixed cavity (143) is provided inside the fixed bracket (142). A demodulator (12) is inserted into the fixed cavity (143). A fixing hole (144) is provided at the part where the clamp (141) connects to the transmission optical fiber (13). A cable tie (145) is inserted into the fixing hole (144), and multiple transmission optical fibers (13) are fixed in the cable tie (145).

8. The turbine main shaft stress measuring device based on fiber optic sensing according to claim 7, characterized in that: The clamp (141) includes a top plate (6) and a bottom plate (61) arranged opposite to each other. A first support column (621), a second support column (622) and a third support column (623) are arranged between the top plate (6) and the bottom plate (61). The first support column (621) is located on one side of the top plate (6) and the bottom plate (61), the second support column (622) is located in the middle of the top plate (6) and the bottom plate (61), and the third support column is located on the other side of the top plate (6) and the bottom plate (61). The first support column (621) has a plurality of first support holes (624) evenly distributed on it, and the third support column (623) has a plurality of third support holes (625) evenly distributed on it; the first support hole (624) of each clamp (141) is opposite to the third support hole (625) of its adjacent clamp (141), and a fixing bolt (626) is inserted into the opposite first support hole (624) and third support hole (625).

9. The turbine main shaft stress measuring device based on fiber optic sensing according to claim 8, characterized in that: The top plate (6) has a plurality of connecting holes (66) evenly distributed at both ends. The connecting holes (66) correspond to the threaded holes (64) on the connecting piece (63). Screws (65) are inserted into the threaded holes (64) and the connecting holes (66). The connecting piece (63) is located above the ends of two adjacent top plates (6).

10. The turbine main shaft stress measuring device based on fiber optic sensing according to claim 9, characterized in that: An external power supply (16) is provided in the fixed cavity (143) below the demodulator (12). The external power supply (16) is connected to one end of a power cord, and the other end of the power cord is connected to one end of the demodulator (12).

11. The turbine main shaft stress measuring device based on fiber optic sensing according to claim 10, characterized in that: A counterweight (17) is provided on one end of the clamp (14) symmetrical to the demodulator (12) along the main shaft (4). The weight of the counterweight (17) is the sum of the weights of the demodulator (12) and the external power supply (16).

12. A method for measuring the main shaft stress of a hydro turbine based on fiber optic sensing as described in claim 1, characterized in that: The method includes the following steps: Step 1: First, put the water turbine in a stopped state; Step 2: First, fix multiple fiber optic strain gauges (11) sequentially on one end of the outer surface of the main shaft (4), then fix a clamp (14) on the part of the main shaft (4) below the fiber optic strain gauges (11), and then fix a demodulator (12) on one end of the clamp (14). Step 3: First, connect the leads of multiple fiber optic strain gauges (11) to one end of the corresponding transmission fiber (13) in sequence. Then, fix all the transmission fibers (13) to the clamp (14). Then, connect the other end of all the transmission fibers (13) to the demodulator (12) in sequence. Step 4: First, put the water turbine into working state. At this time, the main shaft (4) will be subjected to stress and deform. The deformation will then stretch the fiber optic strain gauge (11). Then the fiber optic strain gauge (11) will generate a wavelength change signal. The wavelength change signal will then be transmitted to the demodulation module (21) by the transmission fiber (13). Step 5: First, the demodulation module (21) demodulates the wavelength change signal to obtain the wavelength change electrical signal. Then, the demodulation data processing module (22) processes the wavelength change electrical signal to obtain the wavelength change digital signal. Finally, the wireless WIFI module (23) sends the wavelength change digital signal to the wireless receiving module (31) in a wireless transmission manner. Step 6: First, the wireless receiving module (31) receives the wavelength change digital signal, then the monitoring data processing module (32) processes the wavelength change digital signal, calculates the data of the main axis (4) based on the wavelength change digital signal, and then the monitoring display module (33) displays the data of the main axis (4).

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