Power cable non-intrusive load and partial discharge synchronous monitoring method

Abstract

The invention provides a non-intrusive load and partial discharge synchronous monitoring method for a power cable, and belongs to the technical field of power monitoring. According to the method, an anti-Stokes signal temperature rapid characterization model is established, the constraint relation between hardware parameters of a distributed optical fiber sensing system is defined, and on the basis of the constraint relation, novel optical fiber high-speed demodulation equipment is developed, and transient temperature changes of a power cable can be responded in time. Meanwhile, a power cable finite element multi-physical field simulation model considering multiple specifications / multiple environment variables is established, the dynamic range and precision of F-P cavity vibration response are defined, and then the power cable partial discharge on-line monitoring system based on the F-P optical fiber sensing technology is developed. And the pilot application of the power cable load and partial discharge integrated monitoring system is realized. According to the invention, the cable state can be monitored in real time and the risk can be accurately predicted, so that cable accidents are effectively prevented, the power supply stability is improved and the power failure loss is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of power monitoring, and in particular relates to a method for synchronously monitoring a power cable non-intrusive load and partial discharge. Background Art

[0002] Power cables, especially underground cables, are affected by many factors such as ambient temperature, humidity, soil pH, underground organisms, etc., and their insulation level will be greatly affected. Once the cable transmits a large load, the cable insulation degradation will be accelerated, and then discharge will occur. In severe cases, it will directly cause major power accidents. Therefore, two important requirements are put forward for the current cable monitoring technology: 1) the ability to quickly and accurately obtain cable loads; 2) the ability to quickly detect cable discharge phenomena.

[0003] At present, the main way to obtain cable load is still based on current transformers. As a primary power device, current transformers are an intrusive monitoring technology with problems such as large size, inconvenient installation and maintenance, and are not suitable for underground cable applications. The emerging distributed fiber optic sensing technology uses optical fiber to monitor the surface temperature of power cables in real time, and uses the temperature load inversion algorithm to calculate the load state of the cable. However, there are two technical constraints in the latter. One is that the time response speed of the distributed fiber optic sensing system is very slow, reaching the order of minutes, but the short-circuit fault current will cause the cable temperature to rise rapidly in a short time, so there is a certain gap in time response; second, most of the existing load inversion models use temperature-load comparison tables. For different cable body structures and operating environments, the calculation results have large errors, which is not conducive to obtaining accurate cable loads.

[0004] On the other hand, the conventional method of power cable temperature monitoring is to place discrete temperature sensing devices such as thermocouples at places where the cable is prone to failure for temperature monitoring; or to use infrared thermal imaging sensors to detect power cables one by one. Obviously, the traditional method is not only time-consuming and labor-intensive, but also has the common problems of poor anti-electromagnetic interference ability and low insulation performance of electrical sensors; and the partial discharge monitoring of power cables generally adopts ultrasonic detection method, pulse current detection method, differential method, etc. In actual working conditions, this method has many limiting factors such as large noise interference and difficulty in obtaining power on site. Summary of the invention

[0005] The technical problem to be solved by the present invention is that conventional monitoring methods have defects to varying degrees in monitoring effects and implementation methods.

[0006] In order to achieve the above technical objectives, the present invention adopts the following technical solutions:

[0007] The non-intrusive load and partial discharge synchronous monitoring method of power cables includes:

[0008] 1) Construct a model based on the anti-Stokes fast characterization algorithm and establish a high-speed demodulation algorithm for distributed optical fiber temperature signals;

[0009] 2) Establish a finite element multi-physics field simulation physical model, determine the electrical and thermal parameters, and verify the power cable heat-load inversion calculation model;

[0010] 3) The dynamic range and accuracy of the FP cavity vibration response are calculated, and partial discharge monitoring of power cables is performed based on the FP optical fiber sensor.

[0011] Preferably, the method further comprises the following step 4): establishing a power cable load and partial discharge monitoring system, and verifying the power cable load and partial discharge monitoring system.

[0012] Preferably, step 1) includes: using the relationship between anti-Stokes light intensity and ambient temperature to expand and construct a characterization model to achieve optical fiber temperature measurement; calibrating the optical fiber temperature measurement under the new algorithm by using a high and low temperature chamber, and verifying the effectiveness of the model.

[0013] Preferably, step 2) comprises: constructing physical structure models of various types of XLPE cables through COMSOL multi-physics field simulation software; including conductor loss parameters, insulation loss parameters, and metal sheath loss parameters in the physical structure model; calculating the heating characteristics of the cable using the parameters; and constructing mathematical models of temperature field and fluid field under steady-state and transient conditions.

[0014] Preferably, in step 3), in the process of calculating the dynamic range and accuracy of the FP cavity vibration response, factors including cavity parameters, vibration frequency and amplitude, light source characteristics, and environmental conditions are introduced, and the interference peak movement caused by the vibration is estimated by calculating the relationship between the optical path difference and the vibration response. Then, the dynamic range and accuracy are calculated based on factors including the signal-to-noise ratio, light source stability, and environmental noise.

[0015] Preferably, in step 3), the partial discharge monitoring of the power cable based on the FP optical fiber sensor includes: configuring the FP optical fiber sensing system, establishing a correlation model between partial discharge and sensing signals, collecting and analyzing data in real time, designing a real-time alarm system, conducting field verification tests to verify performance, and integrating the sensing system into the power cable network to achieve remote monitoring.

[0016] Preferably, in step 4), the power cable load and partial discharge monitoring system includes a cable temperature subsystem, a load subsystem and a partial discharge monitoring subsystem, and its communication mode is 485 bus or Ethernet, and the communication protocol of the data link is 101 protocol, 104 protocol or IEC61850 protocol.

[0017] Preferably, in step 4), the verification of the power cable load and partial discharge monitoring system includes: configuring an FP optical fiber sensing system to monitor the cable temperature and partial discharge signal in real time; then, using a high-speed demodulation system to convert the temperature data of the optical fiber sensor into a real-time temperature distribution diagram; establishing a partial discharge online monitoring system to detect the discharge activity inside the cable; and drawing a cable status image.

[0018] Preferably, in step 1):

[0019] When the distance from the scattered light position to the incident end of the optical fiber is L:

[0020]

[0021] In the above formula, c is the speed of light in vacuum, which is 3×10 8 m / s; n is the effective refractive index of the optical fiber, △t is the time required for the light signal to return from the incident end of the optical fiber to the scattered signal at L, and Vg is the group velocity of the transmitted light; the total light intensity at the optical fiber L is:

[0022] P t (L) = P i exp(-αL)2

[0023] Where Pi is the incident light intensity, α is the total transmission loss, which consists of scattering loss αs and absorption loss αa; the scattered light intensity at this time is:

[0024] P ts (L) = α i P t (L)V g w 3

[0025] In the above formula, w is the pulse width of the incident light; the intensity of the backscattered light is:

[0026]

[0027] Where NA is the numerical aperture of the fiber, which is calculated as:

[0028]

[0029] n1 and n2 are the refractive indices of the core and cladding, respectively;

[0030] The temperature on the optical fiber is calculated using the Raman ratio; the Raman ratio is the ratio of the intensity of the anti-Stokes light Ias to the intensity of the Stokes light Is; the light intensities of the two are expressed by equations 6 and 7:

[0031]

[0032]

[0033] In the above formula, h is Planck's constant, which is 6.63×10 -34 J·s; k is the Boltzmann constant, which is 1.38×10 -23 J / K; △v is the Raman frequency shift; Ks and Kas are the position-dependent scattering loss factors of Stokes light and anti-Stokes light, respectively; the scattering loss factor is the superposition of losses caused by non-temperature factors including optical fiber transmission loss and bending loss;

[0034] Furthermore, the Raman ratio is:

[0035]

[0036] The temperature at any position along the measuring fiber is:

[0037]

[0038] In the above formula, T0 is the reference temperature measured by the reference optical fiber.

[0039] Preferably, in step 3):

[0040] The sensor cavity length is λ 1 , 2 is the wavelength of the adjacent peaks in the spectrum, n is the refractive index of the medium, and the reflected light intensity Ir and the projected light intensity It in the reflection spectrum are:

[0041]

[0042]

[0043] In the above formula, the optical path difference λ is the wavelength of light in vacuum; n is the refractive index of the medium of the FP cavity; d is the length of the FP cavity; F is the finesse,

[0044] The deformation formula of the elastic diaphragm of the optical fiber FP sensor is:

[0045]

[0046] In the above formula, ω(l) is the deflection of the diaphragm; P is the pressure on the diaphragm; μ is the Poisson's ratio; E is the Young's modulus; h is the thickness of the diaphragm; r is the effective radius of the film; l is the radius of any part of the silicon membrane;

[0047] At the center point of the diaphragm, i.e., l=0, the expression of pressure sensitivity Y is obtained as follows:

[0048]

[0049] The change in pressure is calculated based on the change in the FP cavity length and the pressure sensitivity Y, and the pressure value at the current moment is further calculated.

[0050] The present invention provides a method for synchronously monitoring the load and partial discharge of power cables in a non-intrusive manner. The method establishes a rapid characterization model of anti-Stokes signal temperature, clarifies the constraint relationship between the hardware parameters of the distributed optical fiber sensing system, and develops a new type of optical fiber high-speed demodulation equipment based on this, which can respond to transient temperature changes of power cables in a timely manner. At the same time, the present invention establishes a finite element multi-physics field simulation model of power cables that considers multiple specifications / multi-environmental variables, clarifies the dynamic range and accuracy of the FP cavity vibration response, and then develops an online monitoring system for partial discharge of power cables based on FP optical fiber sensing technology, realizing the pilot application of a comprehensive monitoring system for load and partial discharge of power cables. The application of the present invention can monitor the cable status in real time and accurately predict risks, thereby effectively preventing cable accidents, improving power supply stability and reducing power outage losses.

[0051] Compared with the prior art, the present invention has the following beneficial effects:

[0052] (1) Compared with conventional distributed optical fiber sensing systems, the present invention aims at the demand for monitoring rapid transient temperature changes of power cables and will develop a new type of high-speed optical fiber demodulation equipment based on the anti-Stokes signal temperature rapid characterization algorithm.

[0053] (2) The traditional correspondence between cable surface temperature and load has a large error problem. The present invention will comprehensively consider cable specifications and external environmental variables, and perform cable heat-load inversion calculation based on finite element multi-physics field simulation technology, which can effectively improve the accuracy of load calculation.

[0054] (3) By utilizing the sensitivity of FP resonance technology to sound waves, the present invention will develop a new type of passive power cable partial discharge monitoring system.

[0055] (4) Different from the traditional cable current carrying capacity analysis system, the power cable load and partial discharge comprehensive monitoring system developed by the present invention can simultaneously monitor the changes in cable partial discharge, temperature rise and load characteristics. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 It is a cable simulation model diagram in the present invention. DETAILED DESCRIPTION

[0057] The specific embodiments of the present invention will be described in detail below. In order to avoid too much unnecessary details, the well-known structures or functions will not be described in detail in the following examples. The approximate language used in the following examples can be used for quantitative expression, indicating that the quantity can be allowed to have a certain change without changing the basic function. Unless otherwise defined, the technical and scientific terms used in the following examples have the same meaning as those generally understood by those skilled in the art to which the present invention belongs.

[0058] 1. Distributed fiber high-speed demodulation technology based on anti-Stokes fast characterization model

[0059] (1) Anti-Stokes-based rapid characterization model and verification;

[0060] (2) High-speed demodulation algorithm for distributed optical fiber temperature signals;

[0061] The relationship between anti-Stokes light intensity and ambient temperature will be used to expand and construct a characterization model to achieve fiber temperature measurement. The fiber temperature measurement under the new algorithm will be calibrated by using a high and low temperature chamber, and the effectiveness of the model will be verified. This step is to ensure the accuracy and reliability of the temperature measurement system.

[0062] The mutual constraints between various characteristic parameters of the distributed optical fiber temperature sensing system will be analyzed from a theoretical perspective. After clarifying the target requirements that require high-speed response, these parameters will be readjusted and a new distributed optical fiber temperature signal high-speed demodulation algorithm will be established to respond to transient temperature changes of power cables in a timely manner.

[0063] Optical Time Domain Reflectometry (OTDR) measurement technology can obtain information such as the length, loss, and breakage of optical fibers by detecting scattered signals in optical fibers. It is widely used in the field of optical fiber communications. Assuming that the distance from the position of the scattered light to the incident end of the optical fiber is L, we have:

[0064]

[0065] In the formula, c is the speed of light in vacuum, which is 3×108m / s; n is the effective refractive index of the optical fiber, △t is the time required for the light signal to return to the incident end from the incident end of the optical fiber to the scattered signal at L, and Vg is the group velocity of the transmitted light. The total light intensity at the optical fiber L is:

[0066] P t (L) = P i exp(-αL)1-2

[0067] Among them, Pi is the incident light intensity, α is the total transmission loss, which is composed of scattering loss αs and absorption loss αa. The scattered light intensity at this time is:

[0068] P ts(L) = α i P t (L)V g w 1-3

[0069] Where w is the pulse width of the incident light. The intensity of the backscattered light is:

[0070]

[0071] Here, NA is the numerical aperture of the optical fiber, which is used to measure the ability of the optical fiber incident end to collect light, and its calculation method is:

[0072]

[0073] n1 and n2 are the refractive indices of the core and cladding, respectively.

[0074] The Raman type distributed optical fiber sensing system demodulates the intensity of the Raman scattering signal in the optical fiber based on the OTDR to obtain the temperature distribution information of the optical fiber. In the Raman type distributed optical fiber sensing system, the Raman ratio is used to calculate the temperature on the optical fiber. The Raman ratio is the ratio of the intensity of the anti-Stokes light (Ias) to the intensity of the Stokes light (Is). The light intensity of the two can be expressed by formulas 1-6 and 1-7:

[0075]

[0076]

[0077] In the formula, h is Planck's constant, which is 6.63×10-34J·s; k is Boltzmann's constant, which is 1.38×10-23J / K; △v is the Raman frequency shift; Ks and Kas are the position-dependent scattering loss factors of Stokes light and anti-Stokes light, respectively. The scattering loss factor is the superposition of the loss caused by non-temperature factors such as optical fiber transmission loss and bending loss.

[0078] Furthermore, the Raman ratio is:

[0079]

[0080] Then the temperature at any position along the measuring optical fiber is:

[0081]

[0082] In the formula, T0 is the reference temperature measured by the reference optical fiber. It can be seen that the Raman distributed optical fiber sensing system is only sensitive to temperature, and the strain of the optical fiber has no effect on the temperature measurement of the system. In the temperature characterization process, the calculation of the Raman ratio will consume a large amount of system resources of the demodulation equipment, which will reduce the overall temperature response speed of the system. If the optical fiber can better shield the external environmental stress, the anti-Stokes method can be directly used for rapid temperature characterization.

[0083] Distributed fiber high-speed demodulation technology based on the anti-Stokes fast characterization algorithm has excellent data processing and demodulation performance. Its uniqueness lies in the fast and efficient processing of large amounts of distributed fiber optic sensor data. One of the advantages of this technology is that it can demodulate fiber optic sensor signals with high precision, ensuring the accuracy and reliability of monitoring results. Its fast nature means that the system can analyze monitoring data on a real-time or quasi-real-time basis, thereby promptly detecting and responding to any changes in the system.

[0084] 2. Power cable heat-load inversion calculation model based on finite element multi-physics field simulation technology

[0085] (1) Establishment of finite element multi-physics field simulation physical model;

[0086] (2) Selection of electrical and thermal parameters for multiple models / complex environments;

[0087] (3) Practical verification of the power cable heat-load inversion calculation model.

[0088] By using COMSOL multi-physics simulation software, physical structure models of various types of XLPE cables were constructed. In these mathematical models, factors such as conductor loss, insulation loss, and metal sheath loss need to be considered to calculate the heating characteristics of the cable. At the same time, mathematical models of temperature field and fluid field under steady-state and transient conditions were further constructed to more comprehensively describe the performance of the cable.

[0089] According to the operating environment of underground cables and the structural characteristics of the cable body, appropriate simulation parameters were selected based on the results of the literature. This ensures the accuracy and reliability of the mathematical model, enabling it to truly reflect the heating and temperature distribution of the cable under different working conditions.

[0090] The algorithm was packaged into load analysis software and tested for effectiveness by a third party. This process aims to verify the performance and usability of the software, ensuring that it can meet the load analysis needs of the power engineering field and provide a powerful tool for the design and management of cable systems. This work helps improve the efficiency and reliability of power cable systems and ensure their safe and stable operation under various conditions.

[0091] Conductor temperature is an important parameter during cable operation and has a direct impact on the service life of insulation materials. Real-time monitoring of cable operation status can be achieved by monitoring cable conductor temperature. However, due to technical limitations and the high potential of cable conductors, cable temperature monitoring technology cannot accurately measure the real-time temperature of cable conductors. By learning to use the finite element method, effective application calculations can be performed on temperature fields based on power cables. The finite element method is used to calculate the cable temperature field in various environments, and the relationship between conductor temperature and surface temperature under different loads, environmental conditions and boundary conditions is obtained. The surface temperature is indirectly estimated to calculate the conductor temperature and reduce the problem of damage to the cable structure. The cable simulation model is shown in the figure below. Figure 1 shown.

[0092] Finite element multi-physics simulation technology is an advanced numerical analysis method that focuses on comprehensive simulation and solving the problem of mutual coupling between multiple different physical fields. It combines the finite element analysis method with the interaction of multiple physical fields, and can simultaneously consider multiple physical phenomena such as structural mechanics, heat conduction, electromagnetic fields, fluid dynamics, etc., so as to achieve a comprehensive simulation and analysis of the behavior of complex systems. This technology has the characteristics of multi-physics coupling, suitable for complex system modeling, multi-scale analysis and solving practical problems, and is widely used in engineering, electronics, materials science, energy and environment. Whether it is optimizing engineering structures, studying material properties, improving electronic equipment or supporting environmental protection, finite element multi-physics simulation technology provides powerful tools and methods for solving multi-physics problems, and promotes innovation and development in the field of science and technology.

[0093] According to the basic laws of thermodynamics, when there is a temperature difference in a system, a heat exchange process from high temperature to low temperature will occur inside the system. Heat exchange methods are divided into three types: heat conduction, heat convection, and heat radiation.

[0094] The heat exchange method of heat conduction is mostly heat transfer from a higher temperature to a lower temperature. The heat exchange law of heat conduction can be expressed by Fourier's law, as shown in formula 2-10.

[0095]

[0096] Where, qc is the conduction heat flux density; k is the thermal conductivity; is the temperature gradient per unit area.

[0097] During the operation of the cable, air flows over the cable surface and takes away some heat. This heat transfer method is called convection heat transfer. According to different causes, convection heat transfer can be divided into natural convection and forced convection. Natural convection is caused by different temperatures inside the fluid and has nothing to do with external forces. Forced convection is the flow of fluid caused by external forces such as fans. For a cable tunnel with a fan turned on, its convection heat transfer method is forced convection, and the heat flux density is shown in Formula 2-11.

[0098] q d =h(T 1 -T 2 )2-11

[0099] Where h is the convective heat transfer coefficient; T1 is the fluid temperature; T2 is the surface temperature of the object.

[0100] Thermal radiation refers to the heat transfer process in which an object has temperature and produces radiated electromagnetic waves, and the higher the temperature, the greater the thermal radiation.

[0101] The power cable heat-load inversion calculation model based on finite element multi-physics field simulation technology involves coupling analysis of multiple physical field parameters in the cable system, such as current load and heat conduction, through finite element analysis methods to establish an accurate calculation model. Its key features include complex coupling analysis of multiple physical fields, numerical simulation of finite element simulation, and inversion and prediction of cable thermal state and load information.

[0102] 3. Passive Fabry-Perot resonance technology for cable partial discharge monitoring

[0103] (1) Calculation of dynamic range and accuracy of FP cavity vibration response;

[0104] (2) A new method for online monitoring of partial discharge in power cables based on FP optical fiber sensing technology;

[0105] First, the dynamic range and accuracy of the vibration response of the FP (Fabry-Perot) cavity need to be calculated considering multiple factors, including cavity parameters, vibration frequency and amplitude, light source characteristics, environmental conditions, etc. By calculating the relationship between the optical path difference and the vibration response, the interference peak shift caused by the vibration can be estimated. Then, the dynamic range and accuracy are calculated based on factors such as signal-to-noise ratio, light source stability, and environmental noise to determine the performance of the FP cavity. This comprehensive calculation takes into account many factors and helps to evaluate the usability and accuracy of the FP cavity in vibration measurement.

[0106] The main methods include configuring an FP fiber optic sensing system suitable for power cables, establishing a correlation model between partial discharge and sensing signals, real-time data acquisition and analysis, designing a real-time alarm system, conducting field verification tests to verify the performance, integrating the sensing system into the power cable network, realizing remote monitoring, and continuously optimizing the method, aiming to provide an efficient online monitoring method for partial discharge in power cables to improve the availability and safety of the power system.

[0107] The goal of this series of work is to achieve accurate monitoring of partial discharge in a complex power system environment and combine it with vibration sensing technology to provide more comprehensive information on the health status of power equipment. This will help prevent potential power equipment failures and ensure the reliable operation of the power system.

[0108] The fiber Fabry-Perot interferometry method changes the optical path between different optical paths through external interference, forming phase difference and intensity difference in the coherent result. Fabry-Perot sensors are divided into two types: intrinsic Fabry-Perot sensors and extrinsic Fabry-Perot sensors. According to the characteristics of partial discharge signals, sensors based on extrinsic types are generally used.

[0109] The fiber optic sensor used for partial discharge monitoring adopts the FP (Fabry-Perot) interference principle. The light emitted by the broadband light source enters the sensor through optical fiber coupling, and is reflected on the silicon wafer and reflective layer surface of the sensor FP cavity to form double-beam interference. When the mechanical wave vibration generated by partial discharge acts on the surface of the silicon film to deform it, the air gap of the FP cavity changes, that is, the cavity length d changes, causing the spectrum of the interference signal to change. The cavity length d can be obtained through the fiber optic white light interferometric demodulation technology, thereby obtaining the partial discharge characteristics.

[0110] According to the white light interferometry technique, the sensor cavity length λ 1 , 2 is the wavelength of adjacent peaks in the spectrum (phase difference 2π), and n is the refractive index of the medium. The reflected light intensity Ir and the projected light intensity It in the reflection spectrum are:

[0111]

[0112]

[0113] In the formula, the optical path difference λ is the wavelength of light in vacuum (m); n is the refractive index of the medium of the FP cavity; d is the length of the FP cavity (nm) It is the fineness, which is related to the reflectivity R. The higher the reflectivity, the higher the fineness.

[0114] The deformation formula of the elastic diaphragm of the optical fiber FP sensor is:

[0115]

[0116] Where ω(l) is the deflection of the diaphragm; P is the pressure on the diaphragm (N); μ is the Poisson's ratio; E is the Young's modulus; h is the diaphragm thickness (nm); r is the effective radius of the film (nm); l is the radius of any part of the silicon membrane (nm).

[0117] At the center point of the diaphragm, i.e., l=0, the expression of pressure sensitivity Y can be obtained as

[0118]

[0119] The change in pressure can be calculated based on the change in the FP cavity length and the pressure sensitivity Y, and the pressure value at the current moment can be further calculated.

[0120] Partial discharge monitoring technology based on optical fiber sensing is an advanced and efficient method for monitoring power systems and high-voltage equipment. Its main feature is the high sensitivity of optical fiber sensors, which can detect tiny partial discharge events, and these sensors can be installed in cables or equipment in a distributed manner to achieve real-time monitoring of the entire system without interrupting equipment operation. The real-time monitoring capability of this technology helps to detect potential power system failures in a timely manner and take measures in advance to ensure the reliability of power supply. It has a wide range of applications, including power systems, power transmission and distribution networks, industrial equipment, and the oil and gas industry, providing strong support for preventing equipment failures, extending equipment life, improving production efficiency, and reducing maintenance costs.

[0121] 4. Development and verification of comprehensive monitoring system for power cable load and partial discharge

[0122] (1) Development of comprehensive monitoring system for power cable load and partial discharge;

[0123] (2) Verification of the comprehensive monitoring system for power cable load and partial discharge.

[0124] The previous results are effectively integrated to build a comprehensive monitoring system for power cable load and partial discharge. The monitoring layer of the system includes three subsystems: cable temperature, load and partial discharge monitoring. The communication method mainly adopts 485 bus and Ethernet, and the data link follows the standard communication protocol, such as 101 / 104 / IEC61850.

[0125] At the data level, data collection, analysis and database establishment were implemented. This step helps to effectively manage and process the monitored information. The application layer realizes the monitoring of partial discharge and load based on the above achievements. The system uses an intuitive navigation interface to guide users into the hierarchical management mode. At the same time, the interactive interface is written in C / C++ language to ensure the efficiency and reliability of the system.

[0126] In order to verify the feasibility of the synchronous monitoring system of power cable load change and partial discharge, the following scheme is proposed: First, configure the FP optical fiber sensing system suitable for power cable monitoring to monitor the cable temperature and partial discharge signal in real time. Then, use the high-speed demodulation system to convert the temperature data of the optical fiber sensor into a real-time temperature distribution map. At the same time, establish an online partial discharge monitoring system to detect the discharge activity inside the cable. Ensure data synchronization and integration to draw a comprehensive picture of the cable status. Through experimental verification and performance evaluation, determine the effectiveness of the system, and further improve the system to improve performance and feasibility, so as to achieve synchronous monitoring of power cable load changes and partial discharge, and improve the safety and reliability of the power system.

[0127] 5. Algorithms and Systems

[0128] (1) High-speed demodulation algorithm of distributed optical fiber temperature signal based on anti-Stokes signal

[0129] A rapid temperature characterization model for anti-Stokes signals is established, and the precise mathematical relationship between temperature and anti-Stokes signals is established by combining experimental data with theoretical models. This will help achieve accurate temperature measurement and provide more reliable data for the application of distributed optical fiber sensing systems.

[0130] Clarify the constraints between the various parameters of the distributed fiber optic sensing system, including fiber length, reflector characteristics, and light source power. By clarifying the mutual influence between these parameters, we can better understand the performance of the system and provide a basis for system optimization and stability.

[0131] Develop a high-speed demodulation algorithm that can process the data generated by the distributed fiber optic sensing system in real time and convert it into actual temperature information. This will provide a practical solution for fast and accurate temperature monitoring, and is expected to be applied in power cable monitoring, industrial automation and environmental monitoring, improving the efficiency of data collection and enhancing the real-time perception of temperature changes.

[0132] (2) Practical verification of the power cable heat-load inversion calculation model

[0133] In the cable heat-load inversion calculation, it is necessary to deal with the complex coupling problem of multiple physical fields, and it is also necessary to consider the diversity of different cable models, structures and application environments. In this process, the selection of parameters becomes a key factor in establishing an accurate model. Different types of cables may involve different physical phenomena, such as current conduction, heat conduction, thermal-electric coupling, etc., so the interaction of these physical fields needs to be considered when establishing the model.

[0134] In addition, the structural characteristics, insulation materials, conductor materials, etc. of the cable will also affect the model parameters. In different application environments, such as high temperature, humid or corrosive environments, the selection of model parameters must also be adjusted accordingly. Therefore, establishing an accurate cable heat-load inversion model requires a deep understanding of the characteristics of different cable types and application scenarios to determine the appropriate parameter settings, thereby ensuring that the model accurately inverts and predicts the thermal state and load conditions of the cable system.

[0135] (3) Design of partial discharge monitoring system based on Fabry-Perot resonant sensor

[0136] For partial discharge monitoring systems based on Fabry-Perot (FP) resonant sensors, the accuracy and reliability of the system are critical. The selection and configuration of sensors are top priorities, as different power equipment may require different types of sensors. Suitable sensors should be able to sense tiny partial discharge signals and operate stably in power equipment. In addition, the location and layout of the sensors also need to be carefully considered to ensure the best signal capture and monitoring effects.

[0137] The acquisition and processing of monitoring data is the core of the system. A high-precision signal acquisition system is essential to ensure the accuracy of the data. The system should be able to capture high-frequency partial discharge signals and convert them into digital data. Subsequently, the data needs to undergo complex processing and analysis to extract the characteristics of the partial discharge signal. This may include algorithms such as peak detection, spectrum analysis, and waveform analysis to help determine the type and severity of partial discharge activity.

[0138] A successful partial discharge monitoring system should also have a real-time alarm function. Once the system detects abnormal partial discharge activity, it should be able to trigger an alarm immediately to notify the operation and maintenance personnel to take necessary maintenance measures, thereby reducing potential equipment damage or accident risks. In addition, the performance of the system should be experimentally verified and regularly evaluated to ensure its feasibility and effectiveness in monitoring and maintaining different power equipment. By continuously improving hardware and software components, the stability and accuracy of the system can be improved, providing the power industry with more reliable monitoring tools, detecting potential faults in advance, and ensuring the reliable operation of power equipment.

[0139] (4) Development of comprehensive monitoring system for power cable load and partial discharge

[0140] The integrated monitoring system for power cable load and partial discharge is an important technological innovation in the power sector. It integrates a variety of advanced sensing technologies and data analysis methods, and has the following key features and application value: the system can not only monitor the load of the cable in real time, including parameters such as current and voltage, but also capture the partial discharge signal inside the cable with high precision. This comprehensive monitoring capability enables power companies to fully understand the operating status of the power system; by monitoring partial discharge phenomena, the system can detect potential fault signs of cables or equipment in advance, thereby reducing the risk of sudden failures and reducing maintenance costs, while ensuring the continuous power supply of the power system; the monitoring system usually has advanced data analysis and processing functions, which can perform real-time analysis and trend prediction of monitoring data, provide decision support for power companies, and help them better plan maintenance and load scheduling.

[0141] This monitoring system is applied on a specific power device or cable segment to verify its performance and effectiveness. Once proven effective, the system can be expanded to the wider power network to improve overall power system reliability.

[0142] The embodiments of the present invention are described in detail above, but the contents are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the scope of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for synchronously monitoring power cable load and partial discharge without intrusion, characterized in that: include: 1) Construct a model based on the anti-Stokes fast characterization algorithm and establish a high-speed demodulation algorithm for distributed optical fiber temperature signals; 2) Establish a finite element multi-physics field simulation physical model, determine the electrical and thermal parameters, and verify the power cable heat-load inversion calculation model; 3) The dynamic range and accuracy of the FP cavity vibration response are calculated, and partial discharge monitoring of power cables is performed based on the FP optical fiber sensor.

2. The method for synchronously monitoring non-intrusive load and partial discharge of power cables according to claim 1, characterized in that: The method also includes the following steps 4): establishing a power cable load and partial discharge monitoring system, and verifying the power cable load and partial discharge monitoring system.

3. The method for synchronously monitoring non-intrusive load and partial discharge of power cables according to claim 1, characterized in that: Step 1) includes: using the relationship between anti-Stokes light intensity and ambient temperature to expand and construct a characterization model to achieve optical fiber temperature measurement; calibrating the optical fiber temperature measurement under the new algorithm by using a high and low temperature chamber, and verifying the effectiveness of the model.

4. The method for synchronously monitoring non-intrusive load and partial discharge of power cables according to claim 1, characterized in that: Step 2) includes: constructing physical structure models of various types of XLPE cables through COMSOL multi-physics field simulation software; including conductor loss parameters, insulation loss parameters, and metal sheath loss parameters in the physical structure model; calculating the heating characteristics of the cable using the parameters; and constructing mathematical models of temperature field and fluid field under steady-state and transient conditions.

5. The method for synchronously monitoring non-intrusive load and partial discharge of power cables according to claim 1, characterized in that: In step 3), in the process of calculating the dynamic range and accuracy of the FP cavity vibration response, factors including cavity parameters, vibration frequency and amplitude, light source characteristics, and environmental conditions are introduced. By calculating the relationship between the optical path difference and the vibration response, the interference peak movement caused by the vibration is estimated. Then, the dynamic range and accuracy are calculated based on factors including the signal-to-noise ratio, light source stability, and environmental noise.

6. The method for synchronously monitoring non-intrusive load and partial discharge of power cables according to claim 1, characterized in that: In step 3), the partial discharge monitoring of the power cable based on the FP optical fiber sensor includes: configuring the FP optical fiber sensing system, establishing a correlation model between partial discharge and sensing signals, real-time data collection and analysis, designing a real-time alarm system, conducting field verification tests to verify performance, and integrating the sensing system into the power cable network to achieve remote monitoring.

7. The method for synchronously monitoring non-intrusive load and partial discharge of power cables according to claim 2, characterized in that: In step 4), the power cable load and partial discharge monitoring system includes a cable temperature subsystem, a load subsystem and a partial discharge monitoring subsystem, and its communication mode is 485 bus or Ethernet, and the communication protocol of the data link is 101 protocol, 104 protocol or IEC61850 protocol.

8. The method for synchronously monitoring non-intrusive load and partial discharge of power cables according to claim 2, characterized in that: In step 4), the verification of the power cable load and partial discharge monitoring system includes: configuring the FP optical fiber sensing system to monitor the cable temperature and partial discharge signal in real time; then, using a high-speed demodulation system to convert the temperature data of the optical fiber sensor into a real-time temperature distribution map; establishing a partial discharge online monitoring system to detect the discharge activity inside the cable; and drawing a cable status image.

9. The method for synchronously monitoring non-intrusive load and partial discharge of power cables according to claim 1, characterized in that: In step 1): When the distance from the scattered light position to the incident end of the optical fiber is L: In the above formula, c is the speed of light in vacuum, which is 3×10 8 m / s; n is the effective refractive index of the optical fiber, △t is the time required for the light signal to return from the incident end of the optical fiber to the scattered signal at L, and Vg is the group velocity of the transmitted light; the total light intensity at the optical fiber L is: P t (L)=P i exp(-αL) 2 Where Pi is the incident light intensity, α is the total transmission loss, which consists of scattering loss αs and absorption loss αa; the scattered light intensity at this time is: P ts (L)=α i P t (L)V g w 3 In the above formula, w is the pulse width of the incident light; the intensity of the backscattered light is: Where NA is the numerical aperture of the fiber, which is calculated as: n1 and n2 are the refractive indices of the core and cladding, respectively; The temperature on the optical fiber is calculated using the Raman ratio; the Raman ratio is the ratio of the intensity of the anti-Stokes light Ias to the intensity of the Stokes light Is; the light intensities of the two are expressed by equations 6 and 7: In the above formula, h is Planck's constant, which is 6.63×10 -34 J·s; k is the Boltzmann constant, which is 1.38×10 -23 J / K; △v is the Raman frequency shift; Ks and Kas are the scattering loss factors of the position-dependent Stokes light and anti-Stokes light, respectively; the scattering loss factor is the superposition of the loss caused by non-temperature factors including optical fiber transmission loss and bending loss; Furthermore, the Raman ratio is: The temperature at any position along the measuring fiber is: In the above formula, T0 is the reference temperature measured by the reference optical fiber.

10. The method for synchronously monitoring non-intrusive load and partial discharge of power cables according to claim 1, characterized in that: In step 3): The sensor cavity length is λ1 and λ2 are the wavelengths of adjacent peaks in the spectrum, n is the refractive index of the medium, and the reflected light intensity Ir and the projected light intensity It in the reflection spectrum are: In the above formula, the optical path difference λ is the wavelength of light in vacuum; n is the refractive index of the medium of the FP cavity; d is the length of the FP cavity; F is the finesse, The deformation formula of the elastic diaphragm of the optical fiber FP sensor is: In the above formula, ω(l) is the deflection of the diaphragm; P is the pressure on the diaphragm; μ is the Poisson's ratio; E is the Young's modulus; h is the thickness of the diaphragm; r is the effective radius of the film; l is the radius of any part of the silicon membrane; At the center point of the diaphragm, i.e., l=0, the expression of pressure sensitivity Y is obtained as follows: The change in pressure is calculated based on the change in the FP cavity length and the pressure sensitivity Y, and the pressure value at the current moment is further calculated.

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