Weak fiber grating array temperature monitoring system and method for non-overhead high-voltage cable joint

Abstract

The invention relates to a weak fiber grating array temperature monitoring system and method for a non-overhead high-voltage cable joint. The system comprises an optical fiber sensing unit laid along a high-voltage cable, a weak fiber grating array demodulation unit and a control and identification unit. The optical fiber sensing unit is provided with three groups of high-density weak optical fiber grating arrays at each cable joint, and the three groups of high-density weak optical fiber grating arrays are respectively attached to the surfaces of three-phase conductor joints and are distinguished through spatial position coding, wavelength coding or intensity coding; the demodulation unit realizes real-time acquisition and demodulation of spectrum signals of the weak fiber grating array; and the control and identification unit is used for carrying out code identification, peak value extraction, wavelength drift calculation and temperature mapping on the spectral signal. Absolute positioning and high-precision temperature monitoring of the non-overhead high-voltage cable joint can be realized, and the system has the advantages of large capacity, fast response, strong anti-interference capability, high long-term stability and the like, and is suitable for the field of high-voltage cable operation and maintenance and safety monitoring.

Description

Technical Field

[0001] This application relates to the field of high-voltage cable condition monitoring technology, specifically to a temperature monitoring system and method for non-overhead high-voltage cable joints, particularly based on a weak fiber optic grating array to achieve absolute positioning and temperature sensing of the cable joint. Background Technology

[0002] Non-overhead high-voltage cables (such as underground cables or tunnel cables) are commonly used in urban underground power distribution networks, large industrial parks, and rail transit power supply systems. They operate with high current, high power density, and long laying lengths. In such long-distance power transmission systems, cables often employ a multi-segment connection structure, with a splicing point set at regular intervals to achieve long-distance transmission. Due to the characteristics of three-phase power transmission, a splicing point typically corresponds to three joints of the three-phase conductors. As a critical node in power transmission, the cable joint's conductivity, contact resistance, and thermal stability directly affect the system's safety and reliability. Overheating at the joint during long-term operation can lead to insulation aging, partial discharge, or even thermal breakdown, potentially causing power accidents. Therefore, real-time monitoring of the joint temperature is crucial for assessing the operational status of high-voltage cables and providing early fault warnings.

[0003] Existing temperature monitoring technologies are mainly divided into point temperature sensors (such as thermocouples and resistance temperature detectors) and distributed fiber optic sensing technologies (such as Raman scattering and Brillouin scattering). Point sensors are complex to install and have limited coverage, making it difficult to achieve high-density monitoring at multiple points. Although distributed fiber optic sensing technologies can monitor continuously, their spatial resolution is low (usually greater than 1 meter), making it impossible to accurately locate cable joints. They are also susceptible to environmental interference, resulting in insufficient measurement accuracy and reliability.

[0004] Existing temperature monitoring technologies mainly include thermocouple sensing, infrared thermometry, fiber optic Raman distributed temperature measurement (DTS), and traditional fiber optic grating (FBG) sensing. However, these technologies have the following shortcomings: thermocouple or infrared thermometry requires independent power supply or line-of-sight conditions, making it difficult to operate stably for a long time in enclosed tunnels or underground cable trenches; although fiber optic Raman distributed temperature measurement has a wide coverage area, its response time is slow (usually greater than 10 seconds) and its spatial resolution is limited (usually >1 meter), making it impossible to achieve high-precision temperature monitoring and location positioning of connectors; traditional fiber optic grating sensing systems use high-reflectivity gratings, and the number of sensors is limited by demodulation bandwidth, making it difficult to achieve low-cost, multi-point, high-density deployment over long lines.

[0005] Therefore, there is an urgent need for a technical solution that can achieve precise positioning of multiple joints and high-resolution temperature monitoring in non-overhead high-voltage cable systems, which can meet capacity requirements while maintaining demodulation accuracy and response speed. Summary of the Invention

[0006] The purpose of this invention is to overcome the problems of limited monitoring point capacity, insufficient spatial resolution, and complex installation in existing technologies, and to provide a low-density fiber optic grating array temperature monitoring system and method for non-overhead high-voltage cable joints. This system achieves high-precision temperature monitoring and absolute positioning of three-phase conductor joints by deploying multiple sets of high-density low-density fiber optic grating arrays at the cable joint, and has advantages such as large capacity, high signal-to-noise ratio, good real-time performance, and low cost.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A weak fiber optic grating array temperature monitoring system for non-overhead high-voltage cable joints includes a fiber optic sensing unit, a weak fiber optic grating array demodulation unit, and a control and identification unit.

[0009] The fiber optic sensing unit includes several sets of high-density weak fiber grating arrays distributed at the cable joints, used to realize the absolute positioning and temperature sensing of the cable joints.

[0010] The weak fiber grating array demodulation unit is used to demodulate the reflection spectrum signal of the weak fiber grating array in real time.

[0011] The control and identification unit is used to perform spectral decoding and temperature data calculation on the demodulation results, and output the absolute position and real-time temperature information of the cable connector.

[0012] Preferably, the fiber optic sensing unit has three sets of weak fiber grating arrays at each cable joint, which are respectively attached to the surface of the three-phase conductor joint; the three sets of weak fiber grating arrays are distinguished by spatial position coding; and each grating inside each set of weak fiber grating arrays is distinguished by a combination of one or more of spatial spacing coding, wavelength coding and intensity coding.

[0013] Preferably, the reflection intensity of the weak fiber Bragg grating array is between -30dB and -40dB, so as to balance the system signal-to-noise ratio and the number of sensing points.

[0014] Preferably, the spatial spacing of the fiber Bragg grating array is less than 5 cm to achieve high spatial resolution temperature distribution measurement.

[0015] Preferably, the weak fiber Bragg grating array demodulation unit is composed of a wavelength scanning laser source, an optical pulse modulator, an optical amplifier, an optical circulator, a photodetector, and a high-speed acquisition card, which can realize high-precision, large-capacity real-time spectral demodulation of weak fiber Bragg grating arrays.

[0016] Preferably, the control and identification unit includes a signal filtering module, a peak extraction module, a grating spectrum-connector position mapping module, and a wavelength drift-temperature conversion module.

[0017] A method for monitoring the temperature of a cable joint based on the above system includes the following steps:

[0018] Weak fiber grating array sensing fibers are laid along non-overhead high-voltage cables. Three sets of weak fiber grating arrays are prepared at each cable joint position, and ordinary single-mode fibers without weak fiber grating arrays are placed between the joints.

[0019] The reflectance spectrum signal of the array is acquired in real time through the weak fiber grating array demodulation unit;

[0020] The reflectance spectrum signal is subjected to spectral decoding analysis and peak extraction through a control and recognition unit.

[0021] The absolute location of the cable joint is located by spectral decoding analysis, and the temperature change is calculated by peak wavelength drift.

[0022] Preferably, a lookup table matching algorithm is used for spectral coding analysis and connector positioning; a multi-point calibration model is used for the conversion of peak wavelength drift and temperature change to improve temperature measurement accuracy and reliability.

[0023] Preferably, the data acquisition cycle is less than 1 second to achieve real-time monitoring of the cable joint temperature.

[0024] Preferably, by combining historical temperature curves with the absolute position of the joint, a precise health assessment of the cable joint can be achieved for long-term operation.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1. By deploying a high-density coding array of weak fiber optic gratings, absolute positioning of cable joints and high spatial resolution (less than 5 cm) temperature monitoring are achieved, overcoming the problems of difficult positioning and low temperature monitoring accuracy of distributed sensing.

[0027] 2. The weak fiber grating array sensing unit and the weak fiber grating array demodulation unit with a reflection intensity of -30dB to -40dB are adopted, which greatly increases the sensing point capacity while ensuring the signal-to-noise ratio, and is suitable for long-distance high-voltage cable monitoring.

[0028] 3. By using a hybrid coding method that combines the spatial location, center wavelength, and reflection intensity of the weak fiber optic grating, each cable connector is given a unique optical identification code, which improves the system's identification capability and anti-interference ability.

[0029] 4. The demodulation and control units employ high-performance hardware and algorithms to achieve real-time spectral demodulation and temperature calculation, with a data acquisition cycle of less than 1 second, meeting real-time monitoring requirements.

[0030] 5. By combining historical data, long-term health assessments can be conducted, potential faults can be predicted in advance, and the reliability of cable operation can be improved. Attached Figure Description

[0031] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments of this application will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0032] Figure 1 A schematic diagram of the overall system structure

[0033] Figure 2 Schematic diagram of the weak fiber optic grating array layout at the cable joint

[0034] Figure 3 Schematic diagram of the encoding principle of weak fiber Bragg grating array

[0035] Figure 4 Schematic diagram of the hardware composition of the weak fiber grating array demodulation unit

[0036] Figure 5 This is a functional block diagram of the control and identification unit. Detailed Implementation

[0037] The technical solutions of the embodiments of this application will now be described with reference to the accompanying drawings. It should be noted that similar reference numerals and letters in the following drawings indicate similar items; therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings.

[0038] The terms “comprising,” “including,” or any other variations thereof are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase “comprising one…” does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0039] The terms “first,” “second,” etc., are used only to distinguish one entity or operation from another, and should not be construed as indicating or implying relative importance, nor as requiring or implying any such actual relationship or order between these entities or operations.

[0040] refer to Figure 1The system comprises an optical fiber sensing unit 1, a low-density fiber Bragg grating array demodulation unit 2, and a control and identification unit 3. The optical fiber sensing unit 1 is laid along the high-voltage cable 4, with three sets of high-density low-density fiber Bragg grating arrays 6 attached to each cable joint 5, corresponding to the A-phase, B-phase, and C-phase conductor joints, respectively. Arrays are distinguished by spatial position coding; gratings within the same group are distinguished by differences in wavelength or reflection intensity. The low-density fiber Bragg grating array demodulation unit 2 is connected to the optical fiber sensing unit 1 via optical fiber, and the control and identification unit 3 is connected to the low-density fiber Bragg grating array demodulation unit 2 via a data transmission line or wirelessly.

[0041] refer to Figure 2 At each cable joint, three sets of weak fiber Bragg grating arrays are attached to the surface of the three-phase conductor joint (phase A, phase B, and phase C). Each array contains multiple weak fiber Bragg gratings21 (e.g., 10-20 gratings), with a spatial spacing of less than 5 cm between the gratings to ensure high spatial resolution. The reflection intensity of the weak fiber Bragg gratings is controlled between -30dB and -40dB. By reducing the reflection intensity, the sensing point capacity is increased, and the signal-to-noise ratio is optimized through a demodulation unit. The three arrays are distinguished by spatial position coding. Figure 2 The connecting optical fiber 22 between the intermediate connectors can realize optical pulse spatial position encoding.

[0042] The gratings within each array are distinguished by a combination encoding method, such as... Figure 3 As shown, for example:

[0043] Spacing coding: Different spacings between weakly reflective fiber gratings (such as 3cm, 4cm, 5cm, etc.) form a unique sequence.

[0044] Peak wavelength encoding: Each grating has a different Bragg peak wavelength (e.g., 1550nm, 1551nm, etc.), and they are distinguished by wavelength.

[0045] Reflection intensity coding: The reflection intensity of the grating varies slightly (e.g., -30dB, -32dB, etc.), but all are within the range of -30dB to -40dB.

[0046] The encoded information is pre-stored in the control and identification unit. Each connector corresponds to a set of encoded information, which is used for the absolute positioning of the sensor connector.

[0047] refer to Figure 4 The weak fiber grating array demodulation unit includes a wavelength scanning laser source, an optical pulse modulator, an optical amplifier, an optical circulator, a photodetector, and a high-speed acquisition card.

[0048] Wavelength scanning laser source: outputs tunable laser with a wavelength range covering the reflection band of weak fiber gratings (e.g., 1520-1570nm).

[0049] Optical pulse modulator: Modulates continuous laser light into pulses to distinguish reflected signals at different locations.

[0050] Optical amplifier: amplifies pulsed optical signals to compensate for the low reflection intensity of weak fiber optic gratings.

[0051] Optical circulator: It guides optical signals into the sensing fiber and receives reflected signals to the photodetector.

[0052] Photodetector: Converts light signals into electrical signals.

[0053] High-speed acquisition card: Acquires electrical signals, performs analog-to-digital conversion, and transmits them to the control and identification unit.

[0054] The low-frequency fiber grating array demodulation unit operates at a high frequency, enabling multiple scans per second and ensuring a data acquisition cycle of less than 1 second.

[0055] refer to Figure 5 The control and identification unit includes the following modules:

[0056] Signal filtering module: performs digital filtering (such as low-pass filtering) on ​​the acquired electrical signals to remove noise.

[0057] Spectral decoding module: Extracts spatial location spacing information, grating wavelength, and reflection intensity information of weak fiber grating array from the filtered spectral signal.

[0058] Peak extraction module: Extracts reflection peaks from the filtered spectral signal and identifies the center wavelength information of each grating.

[0059] Grating Spectrum-Connector Location Mapping Module: Based on pre-stored encoded information (lookup table), the extracted spectral features are mapped to specific cable connector locations to achieve absolute positioning. The lookup table matching algorithm employs correlation matching or pattern recognition methods.

[0060] Wavelength drift-temperature conversion module: Calculates temperature change based on peak wavelength drift, using a multi-point calibration model (e.g., obtaining wavelength-temperature relationship curves through experimental calibration to improve accuracy).

[0061] The control and identification unit also includes a data storage and communication module for recording historical temperature data and outputting real-time temperature information and health assessment results.

[0062] A weak fiber optic grating array temperature monitoring system and method for non-overhead high-voltage cable joints, the method for monitoring the temperature of cable joints includes the following steps:

[0063] Deploying the sensing fiber: Single-mode fiber is laid along the non-overhead high-voltage cable. At each cable joint, three weak fiber grating arrays are fabricated using ultraviolet laser grating technology. The fiber segments between joints are ordinary single-mode fiber without gratings. The encoding information of the grating arrays is pre-configured and stored in the control unit.

[0064] Real-time acquisition of spectral signals: The weak fiber Bragg grating array demodulation unit periodically emits pulsed light (acquisition period less than 1 second) and acquires the reflection spectral signal of the weak fiber Bragg grating array. After amplification and conversion, the reflected signal is transmitted to the control and recognition unit.

[0065] Spectral decoding and peak extraction: The control and recognition unit filters, decodes, and extracts peak wavelength data from the spectral signal to obtain the reflected wavelength and intensity of each grating, as well as the spatial spacing distribution of the gratings in the grating array. Using a lookup table matching algorithm, the spectral features are matched with pre-stored codes to determine the cable connector location corresponding to the spectrum (absolute positioning). For example, identifying the A-phase connector corresponding to a specific wavelength sequence.

[0066] Positioning of the cable connector and calculation of temperature changes: Based on the matching results, the absolute position information of the cable connector is output. The temperature value is calculated based on the peak wavelength drift using the wavelength drift-temperature conversion module. A multi-point calibration model considers fiber optic materials and nonlinear effects, using polynomial fitting of the calibration curve to improve the accuracy of temperature calculations.

[0067] Long-term health assessment: The control and identification unit continuously records temperature data and generates historical temperature curves. Combined with the absolute position of the joints, it analyzes temperature trends and abnormal fluctuations to achieve long-term health assessment. For example, when the temperature of a joint continues to rise or exceeds a threshold, an early warning signal is issued.

[0068] Example

[0069] Taking a 10-kilometer-long underground high-voltage cable as an example, the cable contains 20 splice points, each with 3 cable joints, for a total of 60 cable joints to be tested. At each splice point, three sets of weak-reflection fiber grating arrays are deployed. Each weak-reflection fiber grating array contains 15 gratings with a grating spacing of 4 cm. The reflection intensity of the weak-reflection fiber gratings is -35 dB. The center wavelength of each weak-reflection fiber grating array is selected within the range of 1530 nm to 1560 nm. Different wavelength selections and arrangements can create a unique optical identification code for each joint. The demodulation unit uses a wavelength scanning laser (scanning rate 100 Hz), and the control unit uses an industrial computer running customized software. Actual measurements show that the system's temperature measurement accuracy reaches ±0.5°C, with a spatial resolution of 3 cm. It can monitor the temperature distribution of each joint in real time and identify an overheating risk one week in advance.

[0070] The above description is merely an embodiment of this application and is not intended to limit the scope of protection of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A weak fiber optic grating array temperature monitoring system for non-overhead high-voltage cable joints, characterized in that, include: The fiber optic sensing unit, the weak fiber optic grating array demodulation unit, and the control and identification unit are laid along the high-voltage cable. The fiber optic sensing unit includes several groups of weak fiber grating arrays distributed at the cable joints, used to achieve absolute positioning and temperature sensing of the cable joints. The weak fiber grating array demodulation unit is used to demodulate the reflection spectrum signal of the weak fiber grating array in real time. The control and identification unit is used to perform spectral decoding and temperature data calculation on the demodulation results of the weak fiber grating array demodulation unit, and output the absolute position and real-time temperature information of the cable connector.

2. The weak fiber optic grating array temperature monitoring system for non-overhead high-voltage cable joints according to claim 1, characterized in that, The fiber optic sensing unit has three sets of weak fiber grating arrays at each cable joint, which are respectively attached to the surface of the three-phase conductor joint; the three sets of weak fiber grating arrays are distinguished by spatial position coding; each grating inside each set of weak fiber grating array is distinguished by a combination of one or more of the following methods: spatial spacing coding, wavelength coding, and intensity coding.

3. The weak fiber optic grating array temperature monitoring system for non-overhead high-voltage cable joints according to claim 1, characterized in that, The reflection intensity of the weak fiber grating array is between -30dB and -40dB to balance the system signal-to-noise ratio and the number of sensing points.

4. A weak fiber optic grating array temperature monitoring system for non-overhead high-voltage cable joints according to claim 1 or 2, characterized in that, The spatial spacing of the fiber grating array is less than 5 cm to achieve high spatial resolution temperature distribution measurement.

5. A weak fiber optic grating array temperature monitoring system for non-overhead high-voltage cable joints according to claim 1, characterized in that, The weak fiber Bragg grating array demodulation unit includes a wavelength scanning laser source, an optical pulse modulator, an optical amplifier, an optical circulator, a photodetector, and a high-speed acquisition card, enabling real-time spectral demodulation of the weak fiber Bragg grating array with high precision and large capacity.

6. A weak fiber optic grating array temperature monitoring system for non-overhead high-voltage cable joints according to claim 1, characterized in that, The control and identification unit includes a signal filtering module, a peak extraction module, a grating spectrum-connector position mapping module, and a wavelength drift-temperature conversion module.

7. A method for monitoring the temperature of a cable joint based on the system of claim 1, characterized in that, Includes the following steps: Weak fiber grating array sensing fibers are laid along non-overhead high-voltage cables. Three sets of weak fiber grating arrays are prepared at each cable joint position, and ordinary single-mode fibers without weak fiber grating arrays are placed between the joints. The reflectance spectrum signal of the array is acquired in real time through the weak fiber grating array demodulation unit; The reflectance spectrum signal is subjected to spectral decoding analysis and peak extraction through a control and recognition unit. The absolute location of the cable joint is located by spectral decoding analysis, and the temperature change is calculated by peak wavelength drift.

8. The method according to claim 7, characterized in that, The spectral coding analysis and connector positioning adopt a lookup table matching algorithm; the conversion between peak wavelength drift and temperature change adopts a multi-point calibration model to improve the temperature measurement accuracy and reliability.

9. The method according to claim 7, characterized in that, The data acquisition cycle is less than 1 second to achieve real-time monitoring of cable joint temperature.

10. The method according to claim 7, characterized in that, By combining historical temperature curves with the absolute position of the joint, a precise health assessment of the cable joint can be achieved for long-term operation.

Images