A method and system for real-time monitoring of sag in overhead transmission lines for dynamic capacity expansion verification

Abstract

A real-time monitoring method and system for sag in overhead transmission lines for dynamic capacity expansion verification is disclosed. The method includes: establishing a catenary equation related to conductor temperature and suspension point tilt angle, deriving the functional relationship between sag and temperature and tilt angle; collecting real-time tilt angle and temperature using a triaxial accelerometer, and transmitting the data to a sag intelligent calculation module via a wireless communication unit and hybrid network; calculating the real-time conductor length by substituting the real-time temperature into a thermal expansion formula, deriving catenary parameters, and calculating the real-time sag value based on the aforementioned functional relationship; and transmitting the sag value to a monitoring and early warning management module for display and over-limit warning via a hybrid network. This invention achieves high-precision real-time sag monitoring, overcoming the shortcomings of traditional methods such as strong environmental dependence and discontinuous monitoring. It has advantages such as all-weather stability, low cost, easy deployment, reliable data transmission, and intelligent early warning, providing technical support for the safety verification of dynamic capacity expansion of transmission lines.

Description

Technical Field

[0001] This invention relates to the field of overhead transmission line sag monitoring technology, specifically to a real-time sag monitoring method and system for dynamic capacity expansion verification of overhead transmission lines. Background Technology

[0002] With the rapid development of my country's economy and the rapid growth of social electricity demand, increasing the transmission capacity of overhead transmission lines has become an urgent task. However, the increased current-carrying capacity of the lines inevitably leads to higher conductor temperatures, resulting in increased line sag, which can easily cause grounding short circuits, line breaks, and other faults. Therefore, real-time and accurate monitoring of overhead transmission line sag is extremely important. However, existing methods for monitoring line sag (including indirect and direct monitoring methods) all have different limitations. For example:

[0003] Reference [1]: Mo Zhiyue, Qin Liwen, Ye Lei, et al. Research on sag calculation method using image recognition technology [J]. Science & Technology Vision, 2015(23): 18-19. This paper proposes an indirect monitoring method for extracting the sag of overhead lines by taking images of some conductor segments with a high-definition camera. However, this indirect monitoring method is costly and takes a long time to process image data, making it difficult to monitor the sag of the line in real time and at low cost.

[0004] Reference [2]: He Jinming, Liu Jianglong, Mao Ke, et al. A method for measuring the sag of overhead transmission conductors [J]. Power Survey and Design, 2023, 29 (7): 48-53. This reference proposes a direct monitoring method that uses a three-dimensional laser scanner to obtain conductor data, thereby calculating the sag at any position. However, this method establishes a static mathematical model, and the calculation error will increase when the conductor swings or gallops significantly, resulting in insufficient stability and making it difficult to achieve high-precision, long-term stable monitoring of line sag.

[0005] In summary, existing overhead line sag monitoring methods are insufficient for achieving real-time, low-cost, high-precision, and long-term stable monitoring of line sag. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a real-time monitoring method and system for dynamic capacity expansion verification of overhead transmission lines. This method enables high-precision real-time monitoring of line sag, eliminates safety hazards caused by increased line current carrying capacity, and provides reliable theoretical and technical support for power grid economic environment dispatching.

[0007] The technical solution adopted in this invention is as follows: A real-time sag monitoring system for dynamic capacity expansion verification of overhead transmission lines, the system comprising: A multi-parameter sensing module is installed on the power transmission line to collect real-time tilt angle data of the conductor suspension point and real-time temperature data of the conductor. The data communication module is used to transmit real-time tilt angle data and real-time conductor temperature data to the sag intelligent calculation module; The sag intelligent calculation module is used to calculate the real-time sag value of the transmission line based on the received real-time tilt angle data and real-time conductor temperature data, using a temperature-mechanical coupled catenary model. d ; The monitoring and early warning management module is used to receive and display real-time sag values ​​and issue early warnings when the real-time sag values ​​exceed a preset safety threshold.

[0008] The multi-parameter sensing module includes: A triaxial accelerometer is used to measure the real-time tilt angle of the conductor suspension point. θ The calculation formula is as follows: ; In the formula: a x , a z These are the acceleration components measured by the triaxial accelerometer in the tangential and normal directions of the conductor, respectively. Infrared temperature sensor for non-contact detection of real-time surface temperature of wires. T c ; Current transformers are used to obtain real-time line current. Environmental sensors are used to monitor environmental parameters such as temperature, humidity, wind speed, and light intensity. The microcontroller unit is used to preprocess the data collected by each sensor.

[0009] The sag intelligent calculation module calculates the real-time sag value according to the following formula. d : ; In the formula: These are the temperature-corrected catenary parameters; This refers to the real-time temperature of the conductor. This is the offset of the centerline of the inclined span after temperature correction; The height difference between the suspension points of the conductor; The horizontal span of the two towers; Temperature-corrected catenary parameters c ( T c The expression for ) is: ; In the formula: The coefficient of thermal expansion of the conductor. For reference temperature, Reference temperature The catenary parameter values ​​below.

[0010] The data communication module adopts a hybrid networking architecture of wireless communication unit and 4G / Wi-Fi. Data transmission between gateways is achieved through an adaptive data packet hopping algorithm, with a transmission coverage range of km. The gateway uses a quad-core processor as its computing core and is equipped with a waterproof and weather-resistant casing.

[0011] The multi-parameter sensing module draws power from the transmission line current through electromagnetic induction, achieving energy self-sufficiency.

[0012] The monitoring and early warning management module has a visual interface and supports historical sag data query, trend analysis, threshold setting and automatic alarm functions, and can be integrated with the power grid dispatching system.

[0013] A real-time monitoring method for sag of overhead transmission lines for dynamic capacity expansion verification includes the following steps: S1: Establish the equation of the span catenary related to conductor temperature and suspension point inclination angle, and derive the functional relationship between line sag and conductor temperature and suspension point inclination angle. S2: The real-time tilt angle and real-time temperature of the conductor suspension point are measured by using a triaxial accelerometer installed at each section of the line, and transmitted to the sag intelligent calculation module through a wireless communication unit and a hybrid network. S3: Substitute the real-time conductor temperature into the line length formula that takes thermal expansion into the real-time conductor length, derive the real-time catenary parameters based on the real-time conductor length, and calculate the real-time sag value of the line based on the functional relationship in S1. S4: Transmits the real-time sag value of the line to the monitoring and early warning management module through hybrid networking for data display and over-limit warning.

[0014] S1 includes: S1.1: Establish the equation for the catenary with span length without considering line temperature, and obtain the sag expression for horizontal span length: ; The expression for sag under inclined span: ; in: This is the ratio of horizontal tension to the weight per unit length of conductor at the reference temperature. The horizontal span of the two towers, The height difference between the suspension points of the conductor. This represents the centerline offset of the inclined span at the reference temperature. S1.2: Introducing temperature correction, we obtain the sag expression considering line temperature: ; in: Real-time temperature of the conductor. These are the temperature-corrected catenary parameters. This represents the offset of the centerline of the inclined span after temperature correction. This is the real-time sag value after taking temperature effects into account.

[0015] Temperature-corrected catenary parameters The expression is: ; in: The coefficient of thermal expansion of the conductor. For reference temperature, Reference temperature The catenary parameter values ​​below.

[0016] In step S2, the real-time tilt angle of the conductor suspension point is measured using a triaxial accelerometer. The expression is: ; In the formula: a x , a z These are the acceleration components measured by the triaxial accelerometer in the tangential and normal directions of the conductor, respectively. S3 includes: S3.1: Calculate the real-time conductor length based on the thermal expansion formula: ; in, This is the initial length of the target span at the initial line temperature. The coefficient of thermal expansion of the conductor. Real-time temperature of the conductor. For reference temperature; S3.2: Using known line parameters and real-time measured tilt angle The temperature-corrected catenary parameters were derived. Solve the simultaneous equations: ; ; S3.3: Will and Substituting into the sag formula, the real-time sag value of the line is calculated. : .

[0017] In step S4, the monitoring and early warning management module compares the real-time sag value of the line in real time. With a preset safety threshold, when the real-time sag value exceeds the threshold, an early warning message is automatically issued, and the sag data is integrated with the power grid dispatch system.

[0018] This invention provides a real-time monitoring method and system for sag of overhead transmission lines in the form of dynamic capacity expansion verification, with the following beneficial effects: 1) Achieve high-precision real-time dynamic monitoring of sag: The real-time tilt angle of the suspension point is directly measured by a triaxial accelerometer. Combined with the temperature-corrected catenary equation, an analytical relationship of "tilt angle-temperature-sag" is constructed, which overcomes the parameter dependence and environmental interference problems of traditional indirect monitoring methods and provides accurate real-time data for dynamic capacity expansion.

[0019] 2) Achieve all-weather, long-term stable monitoring: The multi-parameter sensing module uses electromagnetic induction to achieve energy self-sufficiency and is equipped with a waterproof and weather-resistant shell, making it suitable for harsh outdoor environments and breaking through the dependence of non-contact methods (such as lidar and image recognition) on environmental conditions.

[0020] 3) Achieve low-cost, easy-to-deploy large-scale monitoring: Integrate a triaxial accelerometer, infrared temperature sensor, current transformer, and environmental sensor into a single module, support two typical working conditions: horizontal and inclined. Derive a standardized sag analytical expression, enabling large-scale and rapid deployment and reducing monitoring and maintenance costs.

[0021] 4) Achieve long-distance, highly reliable data transmission: Adopt a hybrid network of wireless communication unit and 4G / Wi-Fi, combined with an adaptive data packet hopping algorithm, to achieve reliable transmission at the km level; The gateway adopts a quad-core processor, balancing computing power and environmental adaptability.

[0022] 5) Achieve visualized display and intelligent early warning of sag: The monitoring and early warning management module has a visual interface, supports historical data query, trend analysis, threshold setting and automatic alarm, and can be integrated with the power grid dispatching system to form a closed loop of "data acquisition-real-time calculation-early warning linkage" to eliminate safety hazards caused by increased line load. Attached Figure Description

[0023] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments: Figure 1 This is a flowchart illustrating the monitoring method of the present invention.

[0024] Figure 2 This is a schematic diagram of the catenary curve with the inclined span of the present invention.

[0025] Figure 3 This is a schematic diagram of the installation of the triaxial accelerometer of the present invention.

[0026] Figure 4 This is a flowchart illustrating how the system of the present invention works.

[0027] Figure 5 This is an architectural diagram of the sag monitoring function of the present invention. Detailed Implementation

[0028] Example 1: This embodiment provides a method and system for real-time monitoring of sag for dynamic capacity expansion verification of overhead transmission lines. For example... Figure 1 The diagram shows a flowchart of the monitoring method of the present invention, which specifically includes the following steps.

[0029] Step 1: Establish the equations for the catenary spans related to conductor temperature and suspension point inclination angle: like Figure 2 The diagram shown is a schematic of the catenary curve with an inclined span according to the present invention. First, a catenary model with the inclined span is established. When the line temperature is not considered, the horizontal tension... H Ratio to the weight per unit length of conductor Keeps constant, i.e., reference temperature. The value below. The geometry of the catenary is determined solely by its span. S Height difference h and mechanical parameters Decide.

[0030] When the span is horizontal, the catenary curves of the horizontal span are symmetrically distributed, taking the midpoint... x = S / 2, Establish a mathematical model for the sag of the horizontal span, and the equation of the catenary. y With sag value The expressions are as follows: ; ; When the span is a tilted span, the center offset at the reference temperature needs to be introduced. The length of the catenary with a horizontal span and the inclination angle of the conductor are derived. Let the distance from the line to the arc be... The sag value is maximum value .

[0031] , , , as well as The expressions are as follows: ; ; ; ; when right When the first derivative is 0 Reaching the maximum value, that is: ; After considering the line temperature, the calculation of the sag value needs to be combined with the temperature-corrected catenary equation and the line length formula for thermal expansion. and the angle of inclination of the conductor Corresponding real-time temperature The catenary parameters below are The temperature-corrected offset of the centerline of the inclined span is The length of the virtual horizontal conductor after temperature correction is The expressions are as follows: ; Temperature-corrected catenary parameters The expression is: ; in: The coefficient of thermal expansion of the conductor. For reference temperature, Reference temperature The catenary parameter values ​​below.

[0032] Temperature-corrected virtual horizontal conductor length for: ; Temperature-corrected tilt span centerline offset With real-time tilt angle The relationship is: ; Actual wire length after thermal expansion for: ; In the formula: The initial length of the target span at the initial line temperature.

[0033] Finally, we obtain the sag expression after taking temperature into account, which is the real-time sag value. : .

[0034] Step 2: Collect real-time tilt angle and conductor temperature, and transmit them via a hybrid network: like Figure 3The diagram shown is a schematic of the installation of the triaxial accelerometer of this invention. The real-time tilt angle of the conductor suspension point and the real-time temperature of the conductor are measured using triaxial accelerometers installed at various points on the line. The real-time tilt angle of the suspension point is calculated by measuring the acceleration components of the line using the triaxial accelerometer. The calculation formula is: ; In the formula: a x , a z These are the acceleration components measured by the triaxial accelerometer in the tangential and normal directions of the conductor, respectively. The collected tilt angle ,temperature Parameters such as current and environment are transmitted to the line gateway through the module's built-in wireless communication unit, and then transmitted to the sag intelligent computing module through the 4G / Wi-Fi hybrid network communication link.

[0035] Step 3: Calculate the real-time conductor length, derive the catenary parameters, and solve for the real-time sag value: First, calculate the real-time conductor length using the formula for line length based on thermal expansion. : ; Secondly, through known line parameters (span) Height difference ) and the tilt angle measured in real time The temperature-corrected catenary parameters were derived. Solve the following equations simultaneously: ; ; Finally, and Substituting the sag function relationship derived in step one, the real-time sag value of the line is calculated. : .

[0036] Step 4: Sag Data Transmission, Display, and Early Warning like Figure 4 The diagram shows a flowchart of the system operation of this invention. The real-time calculated value of the line sag is transmitted to the monitoring and early warning management module using the aforementioned hybrid network. The real-time sag monitoring system realizes the collection, transmission, calculation, display, and early warning of sag data.

[0037] like Figure 5The diagram shown illustrates the architecture of the sag monitoring function of this invention. The real-time sag monitoring system includes a multi-parameter sensing module, a data communication module, a sag intelligent calculation module, and a monitoring and early warning management module.

[0038] The deployment and configuration of the multi-parameter sensing module are as follows: The multi-parameter sensing module is suspended at the midpoint of the span of the target transmission line, or installed at key monitoring points within the span according to the line's operating conditions. This ensures the module is in close contact with the conductor without affecting the line's normal current carrying capacity and mechanical balance, making it suitable for inclined or horizontal spans of high-voltage and above voltage levels. Built-in components include: 1) A triaxial accelerometer is used to accurately collect the tangential and normal acceleration components of the conductor, and then calculate the real-time tilt angle; 2) Infrared temperature sensor, used for non-contact detection of real-time temperature of wire surface; 3) Environmental sensing unit, including temperature and humidity sensors and light sensors, used to collect outdoor environmental parameters; 4) Current transformer, with a transformation ratio adapted to the rated current of the line, is used to obtain real-time current data of the line; 5) The microcontroller unit is responsible for preprocessing the data collected by each component, including filtering, noise reduction, and format conversion, to ensure data validity. During installation, the triaxial accelerometer axis is strictly calibrated to ensure it is perfectly aligned with the wiring route, avoiding tilt angle measurement errors due to installation deviations. The module housing is made of high-strength engineering plastic, possessing waterproof, dustproof, and UV-resistant properties, capable of withstanding harsh environments such as extreme outdoor temperatures, strong winds, rain, and snow. The power supply design employs electromagnetic induction power extraction technology, extracting electrical energy from the transmission line current through a current transformer. After rectification, voltage regulation, and energy storage circuitry, this energy supplies the module's components, achieving energy self-sufficiency without the need for additional wiring or battery replacement, ensuring long-term stable operation.

[0039] The data communication module is constructed and transmitted as follows: A hybrid networking architecture combining wireless communication units and 4G / Wi-Fi is adopted. The multi-parameter sensing module has a built-in wireless communication unit responsible for short-range data transmission. Gateways are strategically deployed along the line, each integrating a 4G / Wi-Fi communication module to achieve interconnection between communication data and remote networks. An adaptive data packet skipping algorithm is used between gateways to dynamically adjust the data transmission path based on signal strength and transmission distance, ensuring reliable data transmission in complex electromagnetic environments in the field. For long transmission distances, the number of gateways can be flexibly increased or decreased according to line length, adapting to large-scale line monitoring needs. The gateway uses a quad-core processor as its computing core, possessing strong data processing capabilities, and can perform preliminary screening and caching of transmitted data. The gateway casing is waterproof and weather-resistant, adapting to uniform field operating conditions with the sensing module. The data transmitted includes pre-processed data from the multi-parameter sensing module, such as the suspension point tilt angle, conductor temperature, line current, ambient temperature and humidity, and illumination, which are transmitted in real-time to the sag intelligent calculation module to meet the timeliness requirements of real-time sag calculation.

[0040] The deployment and operation of the sag intelligent computing module are as follows: The sag intelligent computing module is deployed on a remote computing center server or a local computing unit on the gateway, possessing sufficient computing power to support real-time data processing and model calculations. It incorporates a temperature-mechanical coupled catenary calculation model, which pre-stores analytical expressions for sag under horizontal and inclined spans, as well as temperature-corrected catenary parameters. Derivation of the formula. The calculation process is as follows: After receiving the parameters transmitted by the data communication module, the real-time tilt angle of the suspension point is first calculated using the acceleration components collected by the triaxial accelerometer. Combined with the real-time temperature of the conductor The real-time catenary parameters are derived. ; Finally, substituting the functional relationship between sag, conductor temperature, and suspension point tilt angle: ; Fusion gear ratio Height difference Preset line parameters are used to accurately calculate and output the real-time sag value of the line. The entire calculation process takes a very short time.

[0041] The monitoring and early warning management module's functions and applications are as follows: It establishes a human-computer interactive visual interface, supporting web and mobile access. The interface displays real-time data such as sag values, conductor temperatures, environmental parameters, and line currents at each monitoring point, presented in numerical, curve, and map formats to intuitively reflect the line's operating status. An internal database stores historical sag data and related parameters, supporting data querying and export by time, monitoring point, and line segment. It features trend analysis capabilities, generating sag change trend charts through data statistics and fitting, providing data reference for power dispatching and line maintenance. Users can preset sag safety thresholds according to line design standards. The system compares the calculated sag value with the threshold in real time. When the sag value exceeds the threshold, it automatically issues early warning information via SMS, platform pop-ups, and audible and visual alarms to remind staff to handle the situation promptly. It also has an alarm record query function for easy fault tracing. An interface with the power grid dispatching system is reserved, supporting data exchange and command transmission. Sag monitoring data can be integrated into the power grid dispatching decision-making system, achieving closed-loop management of "monitoring-calculation-early warning-dispatch," and improving the safety and reliability of dynamic power grid capacity expansion.

[0042] Through the above calculations and system design, this invention achieves high-precision, real-time monitoring of overhead transmission line sag, accurately capturing sag fluctuations caused by temperature changes in conductors during dynamic capacity expansion. It provides reliable data support for the safety verification, line maintenance, and grid dispatching of high-voltage transmission lines during dynamic capacity expansion, effectively avoiding line faults caused by abnormal sag during dynamic capacity expansion, and ensuring the safe and stable operation of the line under dynamic capacity expansion conditions.

[0043] Example 2: This embodiment optimizes the deployment location of the multi-parameter sensing module based on Embodiment 1. For transmission lines with long spans or complex terrain, multiple sensing modules can be installed within the same span, at positions of 1 / 4, 1 / 2, and 3 / 4 of the span, respectively. Data fusion algorithms such as weighted averaging or Kalman filtering are used to improve the redundancy and accuracy of sag monitoring. Simultaneously, the data acquisition frequency of the sensing modules can be dynamically adjusted according to the real-time requirements of dynamic capacity expansion: when the line current is low, a lower acquisition frequency (e.g., once every 5 minutes) is used to reduce power consumption; when the line current approaches or exceeds the dynamic capacity expansion threshold, the acquisition frequency is automatically increased (e.g., once every 10 seconds) to achieve refined sag tracking.

[0044] Example 3: This embodiment focuses on the catenary parameters after temperature correction. This paper proposes a numerical iterative optimization method for solving the problem. Since the simultaneous equations in step three are transcendental equations, the Newton-Raphson iterative method can be used for rapid solution. Specifically, with As initial values, construct the residual function: ; First derivative of the residual function: ; The iterative formula is: ; When the residual is less than the preset accuracy, such as 10 6 Stop iteration when the time is right to obtain high-precision results. This method can further reduce calculation errors and improve the accuracy of sag monitoring.

[0045] Example 4: This embodiment features an enhanced communication link design. In remote mountainous areas with weak 4G signal coverage, relay nodes can be added between gateways, using LoRa spread spectrum communication technology as a backup link. When the 4G / Wi-Fi signal quality falls below a threshold, the system automatically switches to the LoRa link to transmit critical data, such as sag warning values ​​and abnormal temperature values, ensuring basic safety warning functions are still available even in extreme environments. The gateway's local cache capacity is at least 1 GB, capable of storing more than 7 days of historical data, which is automatically retransmitted after communication is restored.

[0046] Example 5: This embodiment optimizes the early warning logic of the monitoring and early warning management module. In addition to single threshold alarms, trend prediction alarms are also introduced: based on recent... Historical data on sag, Predicting the future using linear regression or exponential smoothing methods The trend of sag over a time period (e.g., 30 minutes), if the predicted value will be... If the value exceeds the safety threshold, an early warning will be issued to allow dispatchers time to take action. The module also supports multi-level threshold settings, such as a yellow warning threshold of 80% of the safety value and a red warning threshold of 100% of the safety value, enabling tiered alarms.

Claims

1. A real-time monitoring system for sag of overhead power transmission lines for dynamic capacity upgrade review, characterized in that The system includes: A multi-parameter sensing module is installed on the power transmission line to collect real-time tilt angle data of the conductor suspension point and real-time temperature data of the conductor. The data communication module is used to transmit real-time tilt angle data and real-time conductor temperature data to the sag intelligent calculation module; The sag intelligent calculation module is used for calculating the real-time sag value of the power transmission line through a temperature-mechanical coupling catenary model based on the received real-time inclination angle data and real-time temperature data of the conductor d ; The monitoring and early warning management module is used to receive and display real-time sag values ​​and issue early warnings when the real-time sag values ​​exceed a preset safety threshold.

2. The system for real-time monitoring of sag of overhead power transmission lines for dynamic ampacity review of claim 1, wherein: The multi-parameter sensing module includes: Tri-axial accelerometer for measuring real-time tilt angle of wire suspension point θ The calculation formula is: ； wherein: a x , a z are the acceleration components measured by the triaxial accelerometer in the tangential and normal directions to the wire, respectively. Infrared temperature sensor for non-contact detection of real-time surface temperature of wires. T c ; Current transformers are used to obtain real-time line current. Environmental sensors are used to monitor environmental parameters such as temperature, humidity, wind speed, and light intensity. The microcontroller unit is used to preprocess the data collected by each sensor.

3. The sag real-time monitoring system for dynamic capacity expansion verification of overhead transmission lines according to claim 2, characterized in that: The sag intelligent calculation module calculates the real-time sag value according to the following formula. d : ； In the formula: These are the temperature-corrected catenary parameters; This refers to the real-time temperature of the conductor. This is the offset of the centerline of the inclined span after temperature correction; The height difference between the suspension points of the conductor; The horizontal span of the two towers; Temperature-corrected catenary parameters c ( T c The expression for ) is: ； In the formula: is the coefficient of thermal expansion of the conductor. For reference temperature, Reference temperature The catenary parameter values ​​below.

4. The real-time sag monitoring system for dynamic capacity expansion verification of overhead transmission lines according to claim 3, characterized in that: The data communication module adopts a hybrid networking architecture of wireless communication unit and 4G / Wi-Fi, and data transmission between gateways is achieved through an adaptive data packet hopping algorithm; The gateway uses a quad-core processor as its computing core and is equipped with a waterproof and weather-resistant casing.

5. The real-time sag monitoring system for dynamic capacity expansion verification of overhead transmission lines according to claim 4, characterized in that: The monitoring and early warning management module has a visual interface and supports historical sag data query, trend analysis, threshold setting and automatic alarm functions, and can be integrated with the power grid dispatching system.

6. A method for real-time monitoring of sag for dynamic capacity expansion verification of overhead transmission lines, characterized in that... Includes the following steps: S1: Establish the equation of the span catenary related to conductor temperature and suspension point inclination angle, and derive the functional relationship between line sag and conductor temperature and suspension point inclination angle. S2: The real-time tilt angle and real-time temperature of the conductor suspension point are measured by using a triaxial accelerometer installed at each section of the line, and transmitted to the sag intelligent calculation module through a wireless communication unit and a hybrid network. S3: Substitute the real-time conductor temperature into the line length formula that takes thermal expansion into the real-time conductor length, derive the real-time catenary parameters based on the real-time conductor length, and calculate the real-time sag value of the line based on the functional relationship in S1. S4: Transmits the real-time sag value of the line to the monitoring and early warning management module through hybrid networking for data display and over-limit warning.

7. The real-time monitoring method for sag of overhead transmission lines for dynamic capacity expansion verification according to claim 6, characterized in that: S1 includes: S1.1: Establish the equation for the catenary with span length without considering line temperature, and obtain the sag expression for horizontal span length: ； The expression for sag under inclined span: ； in: This is the ratio of horizontal tension to the weight per unit length of conductor at the reference temperature. The horizontal span of the two towers, The height difference between the suspension points of the conductor. This represents the centerline offset of the inclined span at the reference temperature. S1.2: Introducing temperature correction, we obtain the sag expression considering line temperature: ； in: Real-time temperature of the conductor. These are the temperature-corrected catenary parameters. This represents the offset of the centerline of the inclined span after temperature correction. Real-time sag value after taking temperature effects into account; Temperature-corrected catenary parameters The expression is: ； in: is the coefficient of thermal expansion of the conductor. For reference temperature, Reference temperature The catenary parameter values ​​below.

8. The method for real-time monitoring of sag for dynamic capacity expansion verification of overhead transmission lines according to claim 7, characterized in that: In step S2, the real-time tilt angle of the conductor suspension point is measured using a triaxial accelerometer. The expression is: ； In the formula: a x , a z These are the acceleration components measured by the triaxial accelerometer in the tangential and normal directions of the conductor, respectively.

9. The real-time monitoring method for sag of overhead transmission lines for dynamic capacity expansion verification according to claim 8, characterized in that: S3 includes: S3.1: Calculate the real-time conductor length based on the thermal expansion formula: ； in, This is the initial length of the target span at the initial line temperature. is the coefficient of thermal expansion of the conductor. Real-time temperature of the conductor. For reference temperature; S3.2: Using known line parameters and real-time measured tilt angle The temperature-corrected catenary parameters were derived. Solve the simultaneous equations: ； ； S3.3: Will and Substituting into the sag formula, the real-time sag value of the line is calculated. : 。 10. The real-time monitoring method for sag of overhead transmission lines for dynamic capacity expansion verification according to claim 9, characterized in that: In step S4, the monitoring and early warning management module compares the real-time sag value of the line in real time. With a preset safety threshold, when the real-time sag value exceeds the threshold, an early warning message is automatically issued, and the sag data is integrated with the power grid dispatch system.

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