A conductor fiber optic stranded power cable temperature strain real-time monitoring device and monitoring method

Abstract

The application discloses a kind of conductor fiber co-twisted power cable temperature strain real-time monitoring device and monitoring method, cable conductor and sensing fiber synchronous twist, and ultra-weak fiber grating demodulation module obtains temperature and strain mixed signal simultaneously by fiber grating array;Distributed Raman temperature measuring instrument provides the temperature distribution data of cable full length, by fusing the temperature measurement results of two kinds of sensing systems, combined with temperature-strain decoupling algorithm, accurately separate cable conductor real strain distribution and temperature field information.The monitoring architecture of the application organically combines point fiber grating sensing and distributed temperature measurement technology, simultaneously realizes local micro-strain high-precision monitoring and distributed measurement of full-line temperature field, significantly improves the reliability of high-voltage cable condition monitoring, increases the dimension of monitorable parameters, and provides advanced technical means for online diagnosis and fault warning of cable line.

Description

Technical Field

[0001] This invention relates to the field of power cable condition monitoring technology, and in particular to a real-time monitoring device and method for temperature and strain of power cables with stranded optical fibers. Background Technology

[0002] With the rapid development of high-voltage power transmission projects and urban power grid construction, the operational reliability of power cables, as the core carrier of power transmission, is crucial to ensuring the safety and stability of the power system. Conductor overheating and mechanical damage are the main factors causing cable failures. The former stems from Joule heat accumulation during long-term full-load or overload operation, heat dissipation attenuation due to insulation aging, and localized heat accumulation caused by poor ventilation in the laying environment. The latter is mostly caused by structural deformation due to improper tension and compression during installation, continuous mechanical stress from soil settlement or external construction during operation, and fatigue wear caused by long-term dynamic loads at the conductor stranding joints. Therefore, real-time monitoring of conductor temperature can capture thermal anomaly trends, providing data support for predicting insulation aging and avoiding thermal breakdown; continuous sensing of mechanical strain can accurately identify early characteristics of structural deformation and fatigue damage, preventing sudden mechanical failures. Collaborative monitoring of both is a necessary means to achieve full life-cycle management of cables and improve the reliability of the power system.

[0003] Currently, cable condition monitoring mainly employs Distributed Temperature Sensing (DTS) and Fiber Bragg Grating (FBG) sensing. DTS technology, based on the Raman scattering principle, can achieve temperature monitoring along the entire cable. However, this technology has a single measurement dimension, only sensing temperature parameters and failing to acquire crucial mechanical stress parameters during cable operation, thus making it difficult to meet the needs of multi-physics condition monitoring of cables. Traditional FBG sensor fiber optic deployment falls into two categories: external and internal. External deployment typically involves attaching the encapsulated FBG sensor to the outer sheath of the cable or fixing it to a bracket along the cable laying path. This method requires dense deployment to ensure monitoring coverage, increasing system complexity and deployment costs. Furthermore, the structural gap between the sensor and the cable body results in low strain transfer efficiency, making it difficult to accurately reflect the true mechanical state inside the conductor. Internal deployment attempts to embed FBG fibers between the cable insulation layer and the conductor shielding layer, but is limited by the high reflectivity and crosstalk risk of traditional FBG gratings, restricting fiber density. Additionally, the conductor stranding process can easily cause fiber compression damage, affecting sensing stability. Regardless of whether the deployment is external or internal, FBG technology faces the challenge of cross-sensitivity to temperature and strain. Summary of the Invention

[0004] Purpose of the invention: The present invention aims to provide a real-time temperature and strain monitoring device for power cables with conductors and optical fibers twisted together, which accurately obtains the true temperature and strain state inside the cable; another purpose of the present invention is to provide a real-time temperature and strain monitoring method for power cables with conductors and optical fibers twisted together.

[0005] Technical Solution: The real-time temperature and strain monitoring device for power cables with conductors and optical fibers twisted together as described in this invention includes a cable, a thermocouple, a distributed Raman thermometer, an ultra-weak fiber grating demodulation module, a column-type voltage regulator, and a host computer processing system. The cable includes a cable conductor and a sensing optical fiber twisted synchronously with the cable conductor. The distributed Raman thermometer is used to acquire temperature distribution data along the entire cable. The ultra-weak fiber grating demodulation module is used to acquire the temperature-strain mixed signal of the fiber grating array in the sensing optical fiber. The host computer processing system is used to receive signals, perform decoupling calculations, and visualize the monitoring results.

[0006] Furthermore, the sensing fiber includes a fiber optic protective sleeve, an ultra-weak fiber optic grating array fiber, and a multimode communication fiber. The ultra-weak fiber optic grating array fiber and the multimode communication fiber are arranged in parallel within the fiber optic protective sleeve to form a coupling structure. The lead-out end of the multimode communication fiber is connected to the signal input end of the distributed Raman thermometer through a fiber optic connector to form an optical signal transmission path. The lead-out end of the ultra-weak fiber optic grating array fiber is connected to the optical port of the ultra-weak fiber optic grating demodulation module through a fiber optic connector to form a grating signal detection path.

[0007] Furthermore, the cable also includes a conductor shielding layer, an insulation layer, an insulation shielding layer, a buffer layer, a metallic shielding layer, and an outer sheath layer.

[0008] Furthermore, the ultra-weak fiber grating array fiber and the multimode communication fiber are arranged in parallel within a stainless steel fiber optic protective sleeve encapsulated with epoxy resin.

[0009] The real-time temperature strain monitoring method for power cables with twisted optical fibers described in this invention is implemented using the aforementioned real-time temperature strain monitoring device for power cables with twisted optical fibers. The method includes the following steps:

[0010] (1) Perform coordinated temperature calibration on the distributed Raman thermometer and the ultra-weak fiber grating demodulation module to unify the temperature measurement benchmark;

[0011] (2) Measurement of the temperature-wavelength sensitivity coefficient of ultra-weak fiber grating array fiber With strain-wavelength sensitivity coefficient ;

[0012] (3) Connect the distributed Raman thermometer to the multimode communication fiber to collect the temperature distribution data of the entire cable. Connect the ultra-weak fiber grating array fiber to the ultra-weak fiber grating demodulation module to collect the mixed wavelength shift data of each grating point caused by the combined effect of temperature and strain, and transmit the data to the host computer system.

[0013] (4) Based on the sensitivity coefficient and decoupling model, the strain change is calculated, the temperature field and strain field distribution are constructed, and the cable condition monitoring and evaluation are carried out in combination with the allowable temperature and allowable strain threshold of the cable material.

[0014] Furthermore, step (1) is as follows:

[0015] The sensing components of the distributed Raman thermometer and the ultra-weak fiber grating demodulation module are placed in the same constant temperature chamber with a controllable temperature environment. Starting from the set initial temperature, the ambient temperature is gradually changed in fixed temperature steps.

[0016] After the temperature stabilizes, the temperature measurement values ​​of the distributed Raman thermometer and the temperature-related wavelength data fed back by the ultra-weak fiber optic demodulation module are recorded respectively. Through data comparison and calibration, the temperature measurement benchmark is unified.

[0017] Furthermore, step (2) is as follows:

[0018] (21) A temperature-strain testing system is set up. One end of the fiber of the ultra-weak fiber grating array is connected to the ultra-weak fiber grating demodulation module. The ultra-weak fiber grating demodulation module communicates with the host computer. One grating point of the ultra-weak fiber grating array fiber is placed on the heating platform. The grating point completely covers the heating area and the fiber is not squeezed or bent with the platform. The other end of the ultra-weak fiber grating array fiber is suspended by a pulley to form an axial strain loading path.

[0019] (22) With the strain fixed, the temperature was changed, and the center wavelength of the grating point was collected at different temperatures;

[0020] (23) Keep the temperature constant, change the stress, and collect the center wavelength of the grating point under different strains;

[0021] (24) Calculate the temperature-wavelength sensitivity coefficient based on the center wavelength of the grating point at different temperatures collected in step (22). Based on the center wavelength of the grating point under different strains acquired in step (23), calculate the strain-wavelength sensitivity coefficient. .

[0022] Furthermore, in step (2), the temperature-wavelength sensitivity coefficient for

[0023]

[0024] Strain-wavelength sensitivity coefficient for

[0025]

[0026] in, This is the center wavelength offset; This refers to the change in temperature. This represents the change in axial strain.

[0027] Furthermore, in step (4), the strain change is calculated based on the sensitivity coefficient and the decoupling model. for

[0028]

[0029]

[0030]

[0031] in, This is the measured wavelength offset. For temperature changes, The center wavelength of the ultra-weak fiber grating obtained from actual measurement. The reference center wavelength for the fiber of the ultra-weak fiber grating array. The measured temperature is obtained by a distributed Raman pyrometer. This is the reference temperature used during calibration.

[0032] Furthermore, the host computer processing system synchronously receives cable temperature distribution data from the distributed Raman thermometer and grating wavelength offset data collected by the ultra-weak fiber optic demodulation module through the communication interface; based on the temperature-strain decoupling model, it performs decoupling operations on the received mixed signals to separate the temperature component and strain component, eliminating the cross-sensitive interference between temperature and strain; and visualizes the processed temperature and strain data as curves.

[0033] Beneficial Effects: Compared with existing technologies, the significant advantages of this invention are: 1. This invention breaks through the limitations of traditional single-temperature monitoring. By leveraging the synergistic effect of ultra-weak fiber grating arrays and distributed temperature sensing technology, internal temperature and strain parameters can be simultaneously acquired during cable operation, achieving in-situ parameter measurement, which is closer to the actual operating state of the cable. The ultra-weak fiber grating array is based on the Bragg reflection principle, sensing temperature and strain through wavelength shift. The distributed temperature sensing is based on the Raman scattering principle, achieving long-distance continuous temperature measurement through changes in scattered light intensity. The two complement each other, taking into account both strain capture and large-scale temperature monitoring. 2. This invention synchronously couples the sensing fiber with the cable conductor layer, constructing an integrated structure of the conductor layer and the sensing fiber, completely eliminating the structural gaps of traditional external installations. This allows strain signals to bypass interface impedance and be directly and efficiently transmitted to the sensing element. Significantly improves the authenticity and reliability of strain parameter measurement; to further optimize transmission efficiency, an epoxy resin structural layer is added to the coupling interface. This structural layer, with its low modulus and high bonding strength, achieves tight bonding between the conductor layer and the sensing fiber, eliminating micro-gaps to form a continuous strain path; 3. This invention effectively eliminates the interference of cross-sensitivity on measurement results through multi-source data fusion and temperature-strain decoupling algorithms, while avoiding the system complexity caused by dense sensor deployment, improving the accuracy and stability of monitoring data, and providing a more reliable basis for cable condition assessment; 4. The integrated structural design does not require significant adjustments to the original cable laying process, reducing installation difficulty and deployment costs. It is also applicable to power cables of different voltage levels and laying environments, expanding the application scenarios of online monitoring technology and providing strong support for the safety management of cables throughout their entire life cycle. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the cable's cross-section;

[0035] Figure 2 This is a schematic diagram of the structure of the device of the present invention;

[0036] Figure 3 This is a schematic diagram of the temperature-strain testing system.

[0037] Figure 4 This is a schematic diagram of the universal testing machine.

[0038] Figure 5 This is a flowchart of the method of the present invention;

[0039] Figure 6 The graph shows the relationship between the temperature change and wavelength shift of an ultra-weak fiber grating.

[0040] Figure 7 The graph shows the relationship between the strain change of an ultra-weak fiber grating and the wavelength shift.

[0041] Figure 8 A graph showing the temperature distribution of a cable conductor monitored by a distributed Raman pyrometer;

[0042] Figure 9 A graph showing the temperature change of the cable conductor monitored by the three channels of the thermocouple;

[0043] Figure 10 The image shows the results of cable strain monitoring based on an ultra-weak fiber grating array.

[0044] Figure 11 The figure shows the results of cable strain monitoring based on an ultra-weak fiber optic grating array in the strain range of 0-1m. Detailed Implementation

[0045] The real-time temperature strain monitoring device for power cables with stranded conductor optical fibers described in this invention was tested on a 10kV single-core cross-linked polyethylene insulated power cable, specifically model YJY-8.7 / 10kV, with an actual cable length of 10.25m. The ultra-weak fiber grating array has a grating point spacing of 0.2m, center wavelengths of 1536nm and 1548nm, a reflectivity of less than 0.1%, and a constant room temperature of 32.5℃. The multimode communication fiber 1 and the ultra-weak fiber grating array fiber 2, twisted together in the cable conductor, can directly sense the temperature change and stress-strain of the conductor; the distributed Raman thermometer 13, based on the Raman scattering principle, collects temperature distribution data along the cable 11; the ultra-weak fiber grating demodulation module 15, using the Bragg reflection principle, captures the fiber wavelength shift to obtain temperature and strain correlation information; the first host computer 14 and the second host computer 16 fuse dual-source data and use a decoupled model to accurately calculate the temperature field and strain field; in addition, the thermocouple 12 is used to perform auxiliary temperature measurement of the cable conductor and the indoor temperature; the column-type voltage regulator 17 can adjust the voltage of the input cable and the current during loading, simulating the operating state of the cable under different load conditions, providing a test environment close to reality for the monitoring device, and ensuring that the monitoring results can effectively reflect the temperature and stress changes of the cable under various operating conditions.

[0046] Cable 11 includes a cable conductor 4 and sensing optical fibers twisted synchronously with the cable conductor. The sensing optical fibers include an optical fiber protective sleeve 3, an ultra-weak fiber grating array optical fiber 2, and a multimode communication optical fiber 1. The multimode communication optical fiber 1 and the ultra-weak fiber grating array optical fiber 2 are arranged within an epoxy resin-encapsulated stainless steel optical fiber protective sleeve 3 and are tightly twisted together with the copper conductor 4, allowing direct response to changes in the conductor's temperature field and mechanical strain. The multimode communication optical fiber 1 and the ultra-weak fiber grating array optical fiber 2 remain parallel and untangled, avoiding additional stress interference between the optical fibers. Cable 11 also includes a conductor shielding layer 5, an insulation layer 6, an insulation shielding layer 7, a buffer layer 8, a metal shielding layer 9, and an outer sheath layer 10. These layers work together to meet the basic requirements of power transmission and, through the co-twisting integration of the conductor and optical fibers, provide a structural basis for in-situ real-time monitoring of cable temperature and stress.

[0047] The real-time temperature strain monitoring method for power cables with twisted optical fibers described in this invention is implemented using the aforementioned real-time temperature strain monitoring device for power cables with twisted optical fibers. The method includes the following steps:

[0048] Step 1: Perform coordinated temperature calibration of the distributed Raman pyrometer and the ultra-weak fiber Bragg grating demodulation module. Place both in the same temperature-controlled constant temperature chamber, starting from the initial room temperature of 32.5℃, and gradually increase the temperature to 82.5℃ at 5℃ intervals. Record the temperature measurements of the distributed Raman pyrometer and the ultra-weak fiber Bragg grating demodulation module to ensure accurate temperature measurement.

[0049] Step 2: Test and obtain the temperature wavelength sensitivity coefficient of the ultra-weak fiber Bragg grating array fiber. and strain wavelength sensitivity coefficient Specifically, it includes:

[0050] Step 21: The system consists of a second host computer 16, an ultra-weak fiber optic demodulator 15, an ultra-weak fiber optic array fiber 2, a grating point 18 on the ultra-weak fiber optic array fiber 18, a heating platform 19, a pulley 20, and a weight 21. One end of the ultra-weak fiber optic array fiber 2 is connected to the ultra-weak fiber optic demodulation module 15, which in turn communicates with the second host computer 16. A grating point 18 on the array fiber 2 is placed on the heating platform 19, ensuring that the grating point 18 completely covers the heating area and that the fiber optic cable is not squeezed or bent against the platform. The other end of the fiber optic cable is suspended by a weight 21 via the pulley 20, forming an axial strain loading path.

[0051] Step 22: After setting up the test platform for the strain wavelength sensitivity coefficient and temperature wavelength sensitivity coefficient of the ultra-weak fiber grating array fiber, start the ultra-weak fiber grating demodulation module 15 and the second host computer 16, and configure the demodulation parameters in the host computer software; fix the strain setting, remove the weight 21 at the lower end of the pulley 20, so that the ultra-weak fiber grating array fiber 2 is in a state of no axial strain, and the initial strain is... Maintain this state until the test ends; start the heating stage 19, and control the ultra-weak fiber optic grating demodulation module 15 via the second host computer 16 to acquire the initial center wavelength of the grating point 18. The center wavelength value was recorded as the reference. The temperature of heating stage 19 was gradually adjusted from 33℃ to 83℃ in 5℃ increments (11 temperature points in total). After each temperature adjustment, the temperature was held stable for 10 minutes to ensure thermal equilibrium between the optical fiber and the heating stage. The center wavelength of grating point 18 at the corresponding temperature was then collected. The data is simultaneously recorded to the host computer.

[0052] Step 23: Set the temperature to a fixed value and do not start the heating stage 19. Allow the experiment to proceed at room temperature (32.5℃) to ensure no temperature interference during the test. Remove the weight 21 from the right pulley 20. After the optical fiber stabilizes, collect the initial center wavelength of the grating point 18. This value was recorded as the baseline value for the strain test. The mass of weight 21 was adjusted to achieve a value of 26.8... As the strain step size, 0~268 is applied to array fiber 2. Axial strain (A total of 11 strain points), strain Calculated by converting the weight of the weights to the cross-sectional area of ​​the optical fiber:

[0053]

[0054] in, In response to the situation; This refers to the tensile force acting on the optical fiber. For the mass of the weights; The elastic modulus of the optical fiber; The cross-sectional area of ​​the optical fiber; The acceleration is due to gravity. After each strain loading, the system is kept stable for 5 minutes, and the corresponding strain is collected. Center wavelength of lower grating point 4 The data is simultaneously recorded to the host computer.

[0055] Step 24: Process the data collected in Steps 22 and 23 to calculate the sensitivity coefficient, starting with the temperature-wavelength sensitivity coefficient. Organize the 11 sets of temperature and wavelength data obtained in step 2.2, and calculate the temperature change at each point. and wavelength offset ,based on The slope obtained from the fitting is... ,like Figure 6 As shown, the wavelength shift of the ultra-weak fiber grating exhibits a good linear relationship with the temperature change, and its linear fitting equation is: goodness of fit This indicates a very high linear correlation between the temperature change and the wavelength shift, validating the results obtained through this fitting. The effectiveness of the strain-wavelength sensitivity coefficient. Organize the 11 sets of strain and wavelength data from step 23, and calculate the strain change at each point. and wavelength offset ,based on The slope obtained from the fitting is... As shown in Figure 7, the wavelength shift of the ultra-weak fiber grating also exhibits an excellent linear relationship with the strain change, and the linear fitting equation is: goodness of fit This fully demonstrates the high linear correlation between strain change and wavelength shift, and the fitting obtained from this... It is reliable.

[0056] Step 3: During the cable conductor stranding process, a suitable space is pre-designed and reserved inside the conductor. A stainless steel fiber optic protective sleeve, manufactured using a seamless welding process, is installed at the central axis of the conductor. This sleeve possesses excellent mechanical strength and corrosion resistance. The inside of the sleeve is filled and encapsulated with epoxy resin, completely filling the gap between the sleeve and the fiber, forming a continuous, dense, rigid mechanical transmission medium. This design eliminates strain transmission attenuation caused by air gaps or looseness, ensuring efficient strain transmission from the sleeve to the fiber. Furthermore, it buffers the impact of torsional stress during conductor stranding and vibrations during operation on the fiber, protecting it and ensuring stable strain signal sensing under stress. After curing, the epoxy resin forms a dense encapsulation that effectively blocks moisture intrusion, preventing fretting wear at the fiber-sleeve interface caused by humidity penetration, thus maintaining the stability of strain transmission during long-term measurements. The epoxy resin material itself has extremely low interference with optical signals and will not affect the sensitivity and signal-to-noise ratio of the fiber optic sensor, ensuring the accuracy of strain sensing. Based on this structure, multimode communication optical fibers and sensing optical fibers carrying ultra-weak fiber grating arrays are arranged in parallel within a stainless steel sleeve, maintaining a parallel, non-intersecting, and non-entangled arrangement. This layout avoids localized stress concentration or signal crosstalk caused by mutual compression or entanglement of the optical fibers, ensuring that the strain generated by the conductor is uniformly and synchronously transmitted to the two optical fibers through the stainless steel sleeve-epoxy resin composite structure, ultimately achieving accurate, stable, and long-term reliable distributed monitoring of strain.

[0057] Step 4: Establish a real-time temperature and strain monitoring platform for power cables with twisted conductor optical fibers. A distributed Raman pyrometer and an ultra-weak fiber grating demodulation module will collect temperature and strain correlation data, specifically including:

[0058] Step 41: Multimode communication fiber 1 and ultra-weak fiber grating array fiber 2 are laid in parallel inside the conductor of cable 11 within a stainless steel protective sleeve 3. The sleeve is encapsulated with epoxy resin, and the two are twisted together with the conductor to form an integrated structure. The two ends of the fiber optic cables are led out from the cable terminals and connected to the corresponding data acquisition devices. The lead-out end of multimode communication fiber 1 is connected to the signal input end of distributed Raman thermometer 13 via a fiber optic connector, forming an optical signal transmission path. The Ethernet interface of distributed Raman thermometer 13 is connected to the first host computer 14 via a network cable to achieve real-time transmission of temperature data. The lead-out end of ultra-weak fiber grating array fiber 2 is connected to the optical port of ultra-weak fiber grating demodulation module 15 via a fiber optic connector, forming a grating signal detection path. The interface of ultra-weak fiber grating demodulation module 15 is connected to the second host computer 16 via a network port for transmitting wavelength offset data.

[0059] Step 42: Place the temperature measuring end of thermocouple 12 close to the conductor section of the first segment of cable 11 as the temperature calibration reference. The column-type voltage regulator 17 is connected to the conductor end of the cable 11 under test via a cable accessory, forming a power circuit. The output voltage is slowly adjusted by the column-type voltage regulator 17 to gradually increase the current in the conductor of cable 11 to the set value of 800A and maintain it stable, simulating the cable's load-bearing operation.

[0060] Step 43: As Figure 7 A universal testing machine 22 was introduced for strain monitoring. The length of the cable 11 containing five grating points of an ultra-weak fiber optic grating was fixed to the clamping devices 22 and 23 of the universal testing machine. The clamping position avoided the grating point area. During the experiment, only the 0-1m section of the cable was subjected to axial tension, while the 1-10m section was kept in a non-tensioned state to ensure that the displacement monitoring axis of the testing machine coincided with the line connecting the grating points in the 1m test section. An axial tensile load of 200με was applied. After each load level stabilized for 3 minutes, the total deformation of the 1m test section was measured by the high-precision displacement sensor of the testing machine 22, and the average actual strain value of each grating point interval was calculated.

[0061] Step 44: Start all devices. The host computer synchronously receives temperature distribution data along the cable from the distributed Raman thermometer 13, and grating point wavelength offset data collected by the ultra-weak fiber optic grating demodulation module 15. For example... Figure 8 The figure shows the temperature distribution curves of the cable conductor monitored three times by the distributed Raman thermometer 13 (temperature curve 1, temperature curve 2, and temperature curve 3 correspond to the three measurement results respectively). The three temperature curves show similar overall trends, with the temperature values ​​all stable at around 75℃, fluctuating slightly around 75℃, indicating that the temperature distribution of the cable conductor is relatively uniform and there is no obvious local overheating. Figure 9The display shows the temperature change curves of the cable conductor monitored by the three channels of the thermocouple. The thermocouples use a measurement time resolution of 10 seconds for data acquisition. The three curves corresponding to thermocouple channels 1, 2, and 3 all fluctuate within a small range around a temperature value of about 75°C, and the trend and numerical differences between the curves are extremely small.

[0062] Based on the pre-calibrated temperature wavelength sensitivity coefficient of ultra-weak fiber gratings and strain wavelength sensitivity coefficient Using a temperature-strain decoupling model The wavelength shift data is decomposed into wavelength changes caused by strain and wavelength changes caused by temperature. Combined with the corresponding temperature data acquired by the distributed Raman pyrometer 13, the strain value for each grating interval is calculated and compared with the reference strain value measured by the universal testing machine 22. Finally, the host computer visualizes the strain field in intervals with a grating spacing of 0.2m, independently monitoring and evaluating the operating status of each interval. Figure 10 The results of strain monitoring of a 10.25m long cable based on an ultra-weak fiber optic grating array are shown below. Figure 11 The enlarged view of the cable strain range of 0-1m shown has measurement points spaced 0.2m apart, presenting a comparison between the strain calculated from three measurements and the actual strain of 200με. Step 43 explicitly states that only the axial tensile load is applied to the 0-1m section of the cable, while the 1-10m section remains unstretched. Therefore, the monitoring results show strain response only in the 0-1m range. The strain calculated from the three measurements fluctuates moderately around 200με, which is within the reasonable error range of the ultra-weak fiber grating and shows good consistency with the actual strain, demonstrating the effectiveness and stability of this array in cable strain monitoring.

[0063] According to the statistical results of the cable conductor temperature monitoring by the Distributed Fiber Raman Thermometer (DTS) and thermocouples in Table 1, the average temperatures along the cable conductor measured by the three curves of the DTS were 75.05℃, 75.21℃, and 75.13℃, respectively, while the average temperature obtained by the single-point measurement of the three thermocouple channels was 75.10℃. The average temperatures obtained by both measurement methods remained stable around 75℃, indicating good consistency in the monitoring results. Regarding the dispersion of the measurement data, the standard deviations of the three DTS curves were 0.039℃, 0.044℃, and 0.044℃, respectively, while the standard deviations of each thermocouple channel were 0.049℃, 0.062℃, and 0.055℃, respectively. All standard deviation values ​​were at a low level, further verifying that the cable conductor temperature distribution was uniform and no local overheating occurred. This also reflects the consistency and reliability of both the DTS and thermocouple temperature measurement devices in monitoring the cable conductor temperature.

[0064] Table 1

[0065]

[0066] According to the statistical results of cable strain monitoring using ultra-weak fiber Bragg grating arrays in Table 2, the mean strain values ​​obtained from the three measurements were 199.74 με, 200.70 με, and 198.23 με, respectively. The deviations from the actual strain value of 200.00 με were small, with standard deviations of 4.85 με, 4.91 με, and 3.15 με, respectively. These results indicate that the fluctuation range of the three fitted strain values ​​is within a reasonable range, and the measured results show good consistency with the actual strain values. This verifies that ultra-weak fiber Bragg grating arrays possess high accuracy and stability when applied to cable strain monitoring.

[0067] Table 2

[0068]

[0069] This invention deeply integrates the local strain monitoring capability of ultra-weak fiber optic arrays with the full-line temperature sensing advantage of distributed Raman spectroscopy through innovative conductor fiber twisting and multi-sensor data fusion. On the one hand, by using a temperature-strain decoupling model and multi-source temperature data calibration, precise separation of cable strain and temperature is achieved, avoiding measurement deviations caused by cross-interference. On the other hand, with 0.2m grid point spacing for interval monitoring and visualization, local micro-strain can be captured simultaneously, and the overall operating status of the entire line can be controlled. This device and method not only solve the technical problem of synchronous and high-precision acquisition of temperature and strain in traditional cable monitoring, but also significantly improves the comprehensiveness, reliability, and real-time performance of high-voltage cable condition monitoring through integrated design adapted to actual cable operating scenarios. It provides key technical support for the long-term safe operation, online fault diagnosis, and preventive maintenance of cable lines, and has significant engineering application value and technological promotion significance.

Claims

1. A real-time temperature strain monitoring device for power cables with stranded optical fibers, characterized in that, Includes cable (11), thermocouple (12), distributed Raman thermometer (13), ultra-weak fiber optic demodulation module (15), column voltage regulator (17) and host computer processing system; cable (11) includes cable conductor and sensing optical fiber twisted synchronously with cable conductor; distributed Raman thermometer (13) is used to acquire temperature distribution data of the entire cable; The ultra-weak fiber grating demodulation module (15) is used to acquire the temperature-strain mixed signal of the fiber grating array in the sensing fiber; the host computer processing system is used to receive signals, perform decoupling operations and visualize monitoring results.

2. The real-time temperature strain monitoring device for power cables with stranded optical fibers according to claim 1, characterized in that, The sensing fiber includes a fiber optic protective sleeve (3), an ultra-weak fiber optic grating array fiber (2), and a multimode communication fiber (1). The ultra-weak fiber optic grating array fiber (2) and the multimode communication fiber (1) are arranged in parallel inside the fiber optic protective sleeve (3) to form a coupling structure. The lead-out end of the multimode communication fiber (1) is connected to the signal input end of the distributed Raman thermometer (13) through a fiber optic connector to form an optical signal transmission path. The lead-out end of the ultra-weak fiber grating array fiber (2) is connected to the optical port of the ultra-weak fiber grating demodulation module (15) through the fiber optic connector to form a grating signal detection path.

3. The real-time temperature strain monitoring device for power cables with stranded optical fibers according to claim 1, characterized in that, The cable (11) also includes a conductor shielding layer (5), an insulation layer (6), an insulation shielding layer (7), a buffer layer (8), a metal shielding layer (9), and an outer sheath layer (10).

4. The real-time temperature strain monitoring device for power cables with stranded optical fibers according to claim 1, characterized in that, The ultra-weak fiber grating array fiber (2) and the multimode communication fiber (1) are arranged in parallel inside a stainless steel fiber protective sleeve encapsulated with epoxy resin.

5. A method for real-time monitoring of temperature strain in a power cable with stranded optical fibers, characterized in that, This is achieved using the real-time temperature strain monitoring device for power cables with conductor optical fibers twisted together as described in any one of claims 1-4, the method comprising the following steps: (1) Perform coordinated temperature calibration on the distributed Raman thermometer and the ultra-weak fiber grating demodulation module to unify the temperature measurement benchmark; (2) Measurement of the temperature-wavelength sensitivity coefficient of ultra-weak fiber grating array fiber With strain-wavelength sensitivity coefficient ; (3) Connect the distributed Raman thermometer to the multimode communication fiber to collect the temperature distribution data of the entire cable. Connect the ultra-weak fiber grating array fiber to the ultra-weak fiber grating demodulation module to collect the mixed wavelength shift data of each grating point caused by the combined effect of temperature and strain, and transmit the data to the host computer system. (4) Based on the sensitivity coefficient and decoupling model, the strain change is calculated, the temperature field and strain field distribution are constructed, and the cable condition monitoring and evaluation are carried out in combination with the allowable temperature and allowable strain threshold of the cable material.

6. The method for real-time monitoring of temperature strain in power cables with stranded optical fibers according to claim 5, characterized in that, Step (1) is as follows: The sensing components of the distributed Raman thermometer and the ultra-weak fiber grating demodulation module are placed in the same constant temperature chamber with a controllable temperature environment. Starting from the set initial temperature, the ambient temperature is gradually changed in fixed temperature steps. After the temperature stabilizes, the temperature measurement values ​​of the distributed Raman thermometer and the temperature-related wavelength data fed back by the ultra-weak fiber optic demodulation module are recorded respectively. Through data comparison and calibration, the temperature measurement benchmark is unified.

7. The method for real-time monitoring of temperature strain in power cables with stranded optical fibers according to claim 5, characterized in that, Step (2) is as follows: (21) A temperature-strain testing system is set up. One end of the fiber of the ultra-weak fiber grating array is connected to the ultra-weak fiber grating demodulation module. The ultra-weak fiber grating demodulation module communicates with the host computer. One grating point of the ultra-weak fiber grating array fiber is placed on the heating platform. The grating point completely covers the heating area and the fiber is not squeezed or bent with the platform. The other end of the ultra-weak fiber grating array fiber is suspended by a pulley to form an axial strain loading path. (22) With the strain fixed, the temperature was changed, and the center wavelength of the grating point was collected at different temperatures; (23) Keep the temperature constant, change the stress, and collect the center wavelength of the grating point under different strains; (24) Calculate the temperature-wavelength sensitivity coefficient based on the center wavelength of the grating point at different temperatures collected in step (22). Based on the center wavelength of the grating point under different strains acquired in step (23), calculate the strain-wavelength sensitivity coefficient. .

8. The method for real-time monitoring of temperature strain in power cables with stranded optical fibers according to claim 7, characterized in that, In step (2), the temperature-wavelength sensitivity coefficient for Strain-wavelength sensitivity coefficient for in, This is the center wavelength offset; This refers to the change in temperature. This represents the change in axial strain.

9. The method for real-time monitoring of temperature strain in power cables with stranded optical fibers according to claim 8, characterized in that, In step (4), the strain change is calculated based on the sensitivity coefficient and the decoupling model. for in, This is the measured wavelength offset. For temperature changes, The center wavelength of the ultra-weak fiber grating obtained from actual measurement. The reference center wavelength for the fiber of the ultra-weak fiber grating array. The measured temperature is obtained by a distributed Raman pyrometer. This is the reference temperature used during calibration.

10. The method for real-time monitoring of temperature strain in a power cable with stranded optical fibers according to claim 8, characterized in that, The host computer processing system synchronously receives cable temperature distribution data from the distributed Raman thermometer and grating wavelength offset data collected by the ultra-weak fiber optic grating demodulation module through the communication interface; based on the temperature-strain decoupling model, it performs decoupling calculation on the received mixed signal to separate the temperature component and strain component, and eliminates the cross-sensitive interference of temperature and strain. The processed temperature and strain data are then visualized as curves to present the monitoring results.

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