Method for ice shedding bounce analysis under conditions of overhead ground wire icing prediction and ice melting

Abstract

The invention discloses an overhead ground wire icing prediction and deicing bounce analysis method under an ice melting condition, which comprises the following steps: monitoring the icing thickness of an overhead ground wire through a monitoring device, analyzing the ice melting process under different icing thicknesses, establishing a critical icing shedding condition equivalent model, and establishing an icing shedding judgment criterion. And analyzing the deicing jump of the overhead base line at the deicing moment. According to the method, reference is provided for solving and analyzing natural melting and deicing of the overhead ground wire and researching the deicing jump of the overhead ground wire under natural melting.

Description

Technical Field

[0001] The invention relates to an overhead ground wire ice coverage prediction and ice shedding bounce analysis method under ice melting conditions, belonging to the technical field of power transmission line status monitoring and diagnosis. Background Art

[0002] Overhead ground wires are installed in areas with complex terrain, harsh environment and natural climate, and are susceptible to extreme weather such as strong winds and icing, resulting in overhead line jumps in different regions. Deicing is a natural phenomenon that is highly dangerous to overhead transmission lines and overhead ground wires. Severe icing disasters on overhead transmission lines can cause widespread and serious damage, such as conductor galloping, insulator flashover, structural failure, and even grid collapse, causing huge economic losses to many other countries. Since overhead ground wires are mostly melted by natural melting, when critical deicing conditions are reached, the ground wire de-ices and jumps, which can easily cause ground wire breakage and phase flashover of the conductor and ground wire. In severe cases, it can cause conductor breakage and tower collapse, leading to large-scale power outages and endangering the stable and continuous operation of the power grid.

[0003] There are many factors that affect the ice shedding and bouncing of overhead ground lines, and each factor is related to each other. Therefore, relevant data are monitored by detection devices, and an equivalent model of critical ice shedding conditions is established for the natural deicing of ice-covered ground lines. In-depth research is carried out on the problem of ice shedding and bouncing of overhead ground lines, and its influencing mechanism is explored. This is of great significance for guiding the rational design of transmission line structures and further improving their ability to resist dancing damage. Summary of the invention

[0004] The purpose of the present invention is to provide a method for predicting ice coating of overhead ground wires and analyzing ice shedding bounce under ice melting conditions. By simulating and predicting the ice coating thickness of the conductors under different ice coating environments, the ice melting process under different ice coating thicknesses is analyzed, and then the ice shedding jump of the overhead ground wire at the ice shedding moment is analyzed.

[0005] The technical solution adopted by the present invention is a method for predicting ice coverage of overhead ground wires and analyzing ice shedding bounce under ice melting conditions, comprising the following steps:

[0006] Step 1: Use the monitoring device to collect the ice thickness and meteorological conditions of the on-site ground wire, and transmit the collected large amount of on-site data, images / videos to the background monitoring center through the wireless communication network to pre-process and analyze the data, so as to identify various fault conditions and output corresponding results and alarm information;

[0007] Step 2: Based on the preprocessed and analyzed data, an equivalent model of critical ice shedding conditions is established based on the melting process, and the ice shedding judgment criteria are established;

[0008] Step 3: According to the ice shedding judgment criteria, perform ice shedding jump analysis on the overhead ground wire.

[0009] Step 2 is implemented as follows:

[0010] Step 2.1: Establish an equivalent model of critical ice shedding conditions. The ice melting process is divided into the warming stage, ice melting stage and shedding stage.

[0011] Step 2.2: According to the energy conservation equation, the heat balance equation process of the overhead ground wire ice melting stage can be expressed as follows:

[0012] Q n -Q cq -Q e =0 (1)

[0013] Where Q n is the heat flux caused by solar radiation, which can be expressed as

[0014] Q n =(1-α)I (2)

[0015] Where I is the incident solar radiation (W / m 2 ), α is the reflectivity, that is, the proportion of the ice layer reflecting the incident solar radiation energy. It can be 0.4 to 0.8 depending on the form of ice and snow.

[0016] Q cq The heat flux caused by ice convective heat transfer can be expressed as

[0017] Q cq =h(T is -T air ) (3)

[0018] Where h is the convective heat transfer coefficient of the substance, T is is the surface temperature of the ice layer, T air is the air temperature.

[0019]

[0020] Where N u is the Nourse number N u =hl / λ air , h is the convective heat transfer coefficient, a is the radius of the raindrop, λ is the thermal conductivity of the air, Re is the Reynolds number, Re=lv / υ, v is the wind speed, υ is the air motion viscosity, and Pr is the Prandtl constant.

[0021] Where Q e is the latent heat of ice vaporization, which can be expressed as

[0022]

[0023] Where ε is the molecular weight ratio of water vapor, LV is the latent heat of vaporization, Cp is the specific heat of air, P is the atmospheric pressure, e is and e air are the saturated vapor pressure corresponding to the ice layer surface temperature and air temperature respectively. e Approximately the heat flux Q caused by ice convective heat transfer cq 0.2 to 0.3 times of.

[0024] Step 2.3: Determine the ice shedding conditions. Since the ice melting caused by solar radiation is relatively slow, the displacement of the ground line during the melting process is ignored. The ice shedding jump is only determined by the gravity G of the ice on the ground line and the adhesion F between the ice and the ground line. adhesion Constraint: When the ice on the ground line satisfies the condition that the gravity of the ice is greater than or equal to the adhesion between the ice and the ground line, it is judged as ice shedding, that is:

[0025] G≥F adhesion (7)

[0026] Step 3 is specifically implemented as follows:

[0027] Step 3.1: According to the finite element method, define the key points between the ground wires to represent various positions on the ground wires, including the starting point and the end point of the span; use units to connect the defined key points to form a line representing the ground wire; assign material properties to the ground wires and mesh them to generate nodes and units to facilitate the subsequent finite element analysis of the ground wires;

[0028] Step 3.2: Comprehensively consider the effects of the deadweight and tension of the ground wire on its shape, determine the initial displacement shape of the ground wire when it reaches a balanced state under the action of its deadweight, and use the direct iteration method of the nonlinear finite element method to calculate the initial configuration of the ground wire;

[0029] Step 3.3: Apply appropriate constraints to both ends of the ground wire to simulate the hanging state of the ground wire within the gear span;

[0030] Step 3.4: Select the transient dynamic solution method to simulate the dynamic response of the overhead ground wire during the ice shedding process;

[0031] Step 3.5: When the ice shedding judgment criteria are met, the shape of the ground wire ice is equivalent to annular ice. The method is as follows:

[0032]

[0033] Where: b is the equivalent ice thickness, D is the maximum transverse dimension of the ground wire after ice coating, B is the maximum longitudinal dimension of the ground wire after ice coating, and r is the radius of the ground wire;

[0034] According to the ground line icing model, the force at each point of the ground line before critical detachment is calculated using equally spaced concentrated forces:

[0035]

[0036] It can be seen that the density of ice is 900kg / m 3 , the thickness of the wire is b, the outer diameter of the wire is D, the length of the wire is L, and g is the acceleration of gravity; the wire is divided into n units for calculation, the length of each unit is L / n, and the mass of ice on the unit is m, kg / m;

[0037] Calculate the resultant force on the ground wire under the action of ice and other external forces, and apply it to the transmission line using the load application method;

[0038] Step 3.6: The amount of deicing and the deicing method are reflected by the amount of ice load removed. The solution time step is set to 0.01s to ensure that the dynamic process of deicing jump can be captured. The total solution time is set to 100s as needed to simulate the deicing process of the overhead ground wire under complex conditions and analyze its deicing dynamic response characteristics.

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] 1. The present invention monitors ice samples of different appearances through an ice monitoring device, and establishes an equivalent model of critical ice shedding conditions to determine the shedding criteria for the natural melting of ice on overhead ground wires.

[0041] 2. The present invention can perform deicing bounce analysis based on the equivalent model of critical icing shedding conditions to reduce the occurrence of accidents. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 It is a flow chart of an overhead ground wire icing prediction and de-icing bounce analysis method under ice melting conditions according to the present invention;

[0043] Figure 2 Transmission line channel visualization block diagram;

[0044] Figure 3 It is the natural melting process of ice covering the overhead ground wire;

[0045] Figure 4 It is a schematic diagram of the equivalent model of critical ice shedding conditions; DETAILED DESCRIPTION

[0046] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0047] like Figure 2As shown in the figure, the visual ice monitoring device includes a front-end video / image detection unit, a back-end monitoring center, a 4G signal tower, etc. The front-end video / image detection unit includes a pan / tilt camera, a drone, a transmission line meteorological monitoring sensor, a conductor temperature and tilt monitoring device, a pole tower video monitoring device, and a small meteorological station, etc. The back-end monitoring center includes a video server, intelligent software, etc.

[0048] like Figure 1 As shown, this embodiment discloses a method for predicting ice coverage of overhead ground wires and analyzing ice shedding bounce under ice melting conditions, including the following steps:

[0049] Step 1: Use pan-tilt cameras, drones and transmission line meteorological monitoring sensors to collect on-site conductor ice thickness and meteorological conditions such as wind speed, temperature, humidity, etc., and transmit a large number of collected on-site images / videos to the background monitoring center through a wireless communication network. Pre-process and analyze the data to identify various fault conditions and output corresponding results and alarm information; at the same time, according to the cooperation of conductor temperature and inclination monitoring devices, tower video monitoring devices and small meteorological stations, real-time comprehensive monitoring of line ice can be achieved.

[0050] Step 2: Based on the preprocessed and analyzed data, an equivalent model of critical ice shedding conditions is established based on the ice melting process, and the judgment criteria for ice shedding are established;

[0051] Step 2.1: Based on the data preprocessing in step 1, an equivalent model of critical ice shedding conditions is established. The ice melting process is divided into the warming stage, ice melting stage and shedding stage, such as Figure 3 As shown;

[0052] Step 2.2: The heat balance equation process of the overhead ground wire ice melting stage can be expressed by the following formula:

[0053] Q n -Q cq -Q e =0 (1)

[0054] Where Q n is the heat flux caused by solar radiation, which can be expressed as

[0055] Q n =(1-α)I (2)

[0056] Where I is the incident solar radiation (W / m2), and α is the reflectivity, that is, the proportion of the incident solar radiation energy reflected by the ice layer. It can be 0.4 to 0.8 depending on the form of ice and snow.

[0057] Q cq The heat flux caused by ice convective heat transfer can be expressed as

[0058] Qcq =h(T is -T air ) (3)

[0059] Where h is the convective heat transfer coefficient of the substance, T is is the surface temperature of the ice layer, T air is the air temperature.

[0060]

[0061] Where N u is the Nourse number N u =hl / λ air , h is the convective heat transfer coefficient, a is the radius of the raindrop, λ is the thermal conductivity of the air, Re is the Reynolds number, Re=lv / υ, v is the wind speed, υ is the air motion viscosity, and Pr is the Prandtl constant.

[0062] Where Q e is the latent heat of ice vaporization, which can be expressed as

[0063]

[0064] Where ε is the molecular weight ratio of water vapor, L V is the latent heat of vaporization, Cp is the specific heat of air, P is the atmospheric pressure, e is and e air are the saturated vapor pressure corresponding to the ice layer surface temperature and air temperature respectively. e Approximately the heat flux Q caused by ice convective heat transfer cq 0.2 to 0.3 times of.

[0065] Step 2.3: Determine the ice shedding conditions. Since the ice melting caused by solar radiation is relatively slow, the displacement of the ground line during the melting process is ignored. The ice shedding jump is only determined by the gravity G of the ice on the ground line and the adhesion F between the ice and the ground line. adhesion Constraint: When the ice on the ground line satisfies the condition that the gravity of the ice is greater than or equal to the adhesion between the ice and the ground line, it is judged as ice shedding, that is:

[0066] G≥F adhesi (7) Step 3: Perform ice shedding jump analysis on overhead ground wires according to ice shedding judgment criteria

[0067] Step 3.1: According to the finite element method, define the key points between the ground wires to represent various positions on the ground wires, including the starting point and the end point of the span; use units to connect the defined key points to form a line representing the ground wire; assign material properties to the ground wires and mesh them to generate nodes and units to facilitate the subsequent finite element analysis of the ground wires;

[0068] Step 3.2: Comprehensively consider the effects of the deadweight and tension of the ground wire on its shape, determine the initial displacement shape of the ground wire when it reaches a balanced state under the action of its deadweight, and use the direct iteration method of the nonlinear finite element method to calculate the initial configuration of the ground wire;

[0069] Step 3.3: Apply appropriate constraints to both ends of the ground wire to simulate the hanging state of the ground wire within the gear span;

[0070] Step 3.4: Select the transient dynamic solution method to simulate the dynamic response of the overhead ground wire during the ice shedding process;

[0071] Step 3.5: When the ice shedding judgment criteria are met, the shape of the ground wire ice is equivalent to annular ice. The method is as follows:

[0072]

[0073] Where: b is the equivalent ice thickness, D is the maximum transverse dimension of the ground wire after ice coating, B is the maximum longitudinal dimension of the ground wire after ice coating, and r is the radius of the ground wire;

[0074] According to the ground line icing model, the force at each point of the ground line before critical detachment is calculated using equally spaced concentrated forces:

[0075]

[0076] It can be seen that the density of ice is 900kg / m 3 , the thickness of the wire is b, the outer diameter of the wire is D, the length of the wire is L, and g is the acceleration of gravity; the wire is divided into n units for calculation, the length of each unit is L / n, and the mass of ice on the unit is m, kg / m;

[0077] Calculate the resultant force on the ground wire under the action of ice and other external forces, and apply it to the transmission line using the load application method;

[0078] Step 3.6: The amount of deicing and the deicing method are reflected by the amount of ice load removed. The solution time step is set to 0.01s to ensure that the dynamic process of deicing jump can be captured. The total solution time is set to 100s as needed to simulate the deicing process of the overhead ground wire under complex conditions and analyze its deicing dynamic response characteristics.

[0079] The above is only a specific implementation of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other implementations obtained by ordinary technicians in this field without creative work belong to the scope of protection of the present invention. Any changes or substitutions that can be easily thought of by any technician familiar with the field within the technical scope disclosed in the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for predicting ice coverage of overhead ground wires and analyzing ice shedding bounce under ice melting conditions, characterized in that: Follow the steps below to implement it: Step 1: Use the monitoring device to collect the ice thickness and meteorological conditions of the on-site ground wire, and transmit the collected large amount of on-site data, images / videos to the background monitoring center through the wireless communication network to pre-process and analyze the data, so as to identify various fault conditions and output corresponding results and alarm information; Step 2: Based on the preprocessed and analyzed data, an equivalent model of critical ice shedding conditions is established based on the ice melting process, and the judgment criteria for ice shedding are established; Step 3: According to the ice shedding judgment criteria, perform ice shedding jump analysis on the overhead ground wire.

2. The method for predicting ice coverage and analyzing ice shedding bounce under ice melting conditions of a transmission line according to claim 1 is characterized in that: The step 2 is specifically implemented according to the following steps: Step 2.1: Establish an equivalent model of critical ice shedding conditions. The ice melting process is divided into three stages: warming stage, ice melting stage and shedding stage. Step 2.2: The heat balance equation of the overhead ground wire ice melting stage is expressed by the following formula: Q n -Q cq -Q e =0 (1) Where Q n is the heat flux caused by solar radiation, expressed as Q n =(1-a)I (2) Where I is the incident solar radiation (W / m 2 ), α is the reflectivity, that is, the proportion of the ice layer reflecting the incident solar radiation energy, which is 0.4 to 0.8 according to the different forms of ice and snow; Q cq The heat flux caused by ice convective heat transfer is expressed as Q cq =h(T is -T air ) (3) Where h is the convective heat transfer coefficient of the substance, T is is the surface temperature of the ice layer, T air is the air temperature, Where N u is the Nourse number N u =hl / λ air , h is the convective heat transfer coefficient, a is the radius of the raindrop, λ is the thermal conductivity of the air, Re is the Reynolds number, Re = lv / υ, v is the wind speed, υ is the air motion viscosity, and Pr is the Prandtl constant; Where Q e is the latent heat of ice vaporization, expressed as Where ε is the molecular weight ratio of water vapor, L V is the latent heat of vaporization, Cp is the specific heat of air, P is the atmospheric pressure, e is and e air are the saturated vapor pressure corresponding to the ice layer surface temperature and air temperature, and the ice layer vaporization latent heat Q e is the heat flux Q caused by ice convective heat transfer cq 0.2 to 0.3 times; Step 2.3: Determine the ice shedding conditions. The ice shedding jump is determined only by the ice gravity G on the ground line and the adhesion force F between the ice and the ground line. adhesion Constraint: When the ice on the ground line satisfies the condition that the gravity of the ice is greater than or equal to the adhesion between the ice and the ground line, it is judged as ice shedding, that is: G≥F adhesion (7) 3. The method for predicting ice coverage of overhead ground wires and analyzing ice shedding bounce under ice melting conditions according to claim 1 is characterized in that: The step 3 is specifically implemented according to the following steps: Step 3.1: According to the finite element method, define the key points between the ground wires to represent various positions on the ground wires, including the starting point and the end point of the span; use units to connect the defined key points to form a line representing the ground wire; assign material properties to the ground wires and mesh them to generate nodes and units to facilitate the subsequent finite element analysis of the ground wires; Step 3.2: Comprehensively consider the effects of the deadweight and tension of the ground wire on its shape, determine the initial displacement shape of the ground wire when it reaches a balanced state under the action of its deadweight, and use the direct iteration method of the nonlinear finite element method to calculate the initial configuration of the ground wire; Step 3.3: Apply appropriate constraints to both ends of the ground wire to simulate the hanging state of the ground wire within the gear span; Step 3.4: Select the transient dynamic solution method to simulate the dynamic response of the overhead ground wire during the ice shedding process; Step 3.5: When the ice shedding judgment criteria are met, the shape of the ground wire ice is equivalent to annular ice. The method is as follows: Where: b is the equivalent ice thickness, D is the maximum transverse dimension of the ground wire after ice coating, B is the maximum longitudinal dimension of the ground wire after ice coating, and r is the radius of the ground wire; According to the ground line icing model, the force at each point of the ground line before critical detachment is calculated using equally spaced concentrated forces: It can be seen that the density of ice is 900kg / m 3 , the thickness of the wire is b, the outer diameter of the wire is D, the length of the wire is L, and g is the acceleration of gravity; the wire is divided into n units for calculation, the length of each unit is L / n, and the mass of ice on the unit is m, kg / m; Calculate the resultant force on the ground wire under the action of ice and other external forces, and apply it to the transmission line using the load application method; Step 3.6: The amount of deicing and the deicing method are reflected by the amount of ice load removed. The solution time step is set to 0.01s to ensure that the dynamic process of deicing jump can be captured. The total solution time is set to 100s as needed to simulate the deicing process of the overhead ground wire under complex conditions and analyze its deicing dynamic response characteristics.

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