Wire temperature distribution calculation method based on daily heat radiation quantity of power transmission line

Abstract

The invention discloses a wire temperature distribution calculation method based on the daily heat radiation quantity of a power transmission line, and the method comprises the steps: 1, building a heat exchange balance formula according to the heat effect and heat loss of the surface of a wire; step 2, calculating radiant heat of a microtopography area line; step 3, constructing a micro-topography power transmission line temperature distribution calculation model based on the thermal radiation prediction function; step 4, taking airflow disturbance as a heat source into the temperature distribution calculation model, and obtaining temperature distribution of the icing line under different terrains; according to the method, the airflow disturbance and the solar radiation amount are taken as heat sources to be considered into the temperature distribution model, the temperature distribution rule of the iced line under different terrains is obtained, important theoretical support is provided for the ice-resistant design of the power transmission line, and reasonable site selection and wind-resistant and ice-resistant design of the power transmission line are guided.

Description

Technical Field

[0001] The invention belongs to the technical field of transmission line icing monitoring, and in particular relates to a method for calculating conductor temperature distribution based on daily heat radiation of a transmission line. Background Art

[0002] The safe operation of transmission lines is seriously affected by atmospheric icing, especially in mountainous areas. The complex micro-topography causes changes in local meteorological factors, and the resulting microclimate areas can lead to significant changes in line icing. It is crucial to calculate the temperature distribution of iced transmission lines in micro-topography and microclimate areas, make reasonable arrangements for ice melting of transmission lines, improve the current power grid's ability to prevent ice and reduce disasters, and guide the planning of transmission lines in mountainous areas.

[0003] In the current method for calculating the temperature distribution of transmission line conductors in micro-terrain areas, solar radiation is usually considered to be 0, and the consideration of the ice melting process in the existing ice prediction model generally ignores the influence of solar radiation heat. It is reasonable not to consider solar radiation when the transmission line is iced. After severe weather, solar radiation will become an important heat source for ice melting on the transmission line, affecting the thermal balance process of ice melting. The current method for calculating the temperature distribution of conductors cannot fully meet the needs of ice monitoring in terms of reliability.

[0004] Current research on micro-topography airflow disturbances mainly focuses on simple terrain and complex terrain. Simple terrain research fails to include all three typical micro-topography types: overlapping double-mountain passes, high mountain watersheds, and terrain uplift. Complex terrain research focuses more on airflow field analysis in mesoscale areas, and does not pay enough attention to the micro-topography areas that appear in the region, which cannot meet the monitoring needs of icing on power transmission lines in micro-topography areas. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a method for calculating the conductor temperature distribution based on the daily thermal radiation of the transmission line, so as to solve the problem that the existing conductor temperature calculation method lacks consideration of factors such as air flow disturbance in the micro-topography area and differences in solar radiation, and cannot meet the technical problems such as the need for monitoring icing on the transmission line.

[0006] The technical solution of the present invention is:

[0007] A method for calculating conductor temperature distribution based on daily heat radiation of a transmission line, the method comprising:

[0008] Step 1: Establish a heat exchange balance equation based on the thermal effect and heat loss on the conductor surface;

[0009] Step 2, calculate the radiant heat of the line in the micro-topography area;

[0010] Step 3: construct a temperature distribution calculation model for micro-topography power transmission lines based on thermal radiation prediction function;

[0011] Step 4: Consider the air flow disturbance as a heat source into the temperature distribution calculation model to obtain the temperature distribution of the ice-covered line under different terrains.

[0012] The heat exchange balance equation is:

[0013] Q I +Q Sun =Q c +Q w +Q r +Q k +Q v

[0014] Q I is the Joule heat of the electric current; Q Sun is the solar shortwave radiation, which is considered to be absorbed by the surface of the ice-covered conductor; Q c is forced convection heat transfer; Q w To guide the heat loss when the supercooled water droplets are heated to the freezing temperature; Q r is the heat loss taken away by the water droplet when it finally leaves the wire; Q k The kinetic energy of water droplets is converted into heat energy; Q v The friction between the airflow flowing on the surface of the wire and the surface of the wire converts part of the kinetic energy of the air into heat energy.

[0015] Calculation of radiant heat for micro-topography area lines includes:

[0016] The transmission line is considered as a straight line. The surface solar radiation is related to the slope and aspect of each point. The position of the sun is defined by the azimuth and zenith angle. The direct component is decomposed into two components, the direction from the zenith angle of 0° and the direction of the azimuth angle. For any direction of the conductor, the coefficient f is used. Angle Correct the actual amount of radiation received:

[0017]

[0018] In the formula, angle is the angle between the transmission line and the horizontal direction, and aspect is the direction of the transmission line;

[0019] For a point at a certain height from the ground, the direct radiation flux is calculated based on the sun's position, atmospheric attenuation, and terrain shielding. The radiation for the entire day is calculated and summed up at each moment:

[0020] Q SunDir =f Hide Q SunConst β m(ζ) Δt,

[0021] Q const is the solar intensity outside the Earth's atmosphere, β is the transmittance of the shortest path of sunlight through the atmosphere, and f hide is the shielding coefficient, which is 0 when the location is shielded by the terrain and 1 when there is no terrain shielding at the location; m(ζ) is the relative light path length.

[0022] The construction of a micro-terrain transmission line temperature distribution calculation model based on thermal radiation prediction function includes:

[0023] The absorption coefficient η of the ice-covered conductor surface is used to describe the absorption capacity of the ice-covered conductor to solar radiation. According to the surface area and absorption coefficient of the ice-covered conductor, the energy density of solar radiation received by the conductor surface is calculated, that is,

[0024] q=ηAQ S un

[0025] A is the surface area of ​​the wire; q is the energy density.

[0026] When calculating the heat dissipation by thermal convection, the difference in wind speed at different locations is taken into account, and different heat transfer coefficients are used accordingly, and finally the temperature distribution of the ice-covered line is obtained considering the airflow disturbance factor.

[0027] Beneficial effects of the present invention:

[0028] The present invention is based on the radiation heat prediction function of the transmission line, takes into account the influence of micro-topography on the distribution characteristics of the airflow field, and realizes the temperature distribution of ice-covered transmission lines under different micro-topography. This method comprehensively considers the influence of micro-topography on the temperature distribution of the conductor and fully considers the solar radiation factor, and adapts to the requirements of actual engineering for the temperature distribution data of the transmission line.

[0029] Based on the radiation heat prediction function of the transmission line, the present invention establishes the surface heat balance equation of the ice-covered transmission line, proposes a temperature distribution calculation model, explores the distribution law of airflow disturbance caused by different terrains in the micro-topography area, takes airflow disturbance and solar radiation as heat sources into consideration in the temperature distribution model, and obtains the temperature distribution law of ice-covered lines under different terrains, which provides important theoretical support for the anti-icing design of transmission lines and guides the reasonable site selection and wind and ice resistance design of transmission lines. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a flow chart of the present invention;

[0031] Figure 2 A flow chart of the method for calculating temperature distribution of power transmission lines in micro-topography areas is constructed for the present invention. DETAILED DESCRIPTION

[0032] The present invention is further described in detail below in conjunction with the accompanying drawings.

[0033] The present invention provides a method for calculating the conductor temperature distribution based on the daily heat radiation of a transmission line, comprising the following steps:

[0034] S1. Consider the thermal effects and heat losses that have a greater impact based on the heat exchange on the conductor surface.

[0035] There are many heat exchange processes on the surface of the conductor in an ice-covered environment. The heat mainly comes from Joule heat of the current in the live conductor, air friction heating, heating of water droplets colliding with the conductor, short-wave radiation heating from sunlight, latent heat released when water droplets freeze, heat released when they are cooled to the steady-state temperature of the ice surface after freezing, thermal effect of corona current, natural or forced convection heat transfer loss, latent heat loss of evaporation of water droplets on the conductor surface, heat loss when supercooled water droplets are heated to the freezing temperature, long-wave radiation heat loss on the conductor surface, heat conduction loss, and heat loss taken away when the water droplets finally leave the conductor.

[0036] The heat exchange on the surface of the wire is complex, and the smaller values ​​can be ignored. Taking into account the influence of various orders of magnitude and mathematical model derivation in the heat exchange process, the present invention only considers the Joule heating of current, heating of water droplets colliding with the wire, short-wave radiation heating, heat loss when supercooled water droplets are heated to the freezing temperature, natural or forced convection heat transfer loss, and heat loss taken away when the water droplets finally leave the wire.

[0037] Thermal effects and heat losses on the surface of the wire: Joule heating of electric current, heating by water droplets colliding with the wire, short-wave radiation heating, heat loss when supercooled water droplets are heated to freezing temperature, natural or forced convection heat loss, and heat loss taken away when the water droplets finally leave the wire. The heat exchange balance equation is as follows.

[0038] Q I +Q Sun =Q c +Q w +Q r +Q k +Q v

[0039] QI is the Joule heat of the current; QSun is the solar shortwave radiation, which is considered to be absorbed by the surface of the ice-covered wire; Qc is the forced convection heat transfer; Qw is the heat loss when the supercooled water droplets are heated to the freezing temperature; Qr is the heat loss taken away when the water droplets finally leave the wire; Qk is the kinetic energy of the water droplets converted into heat energy; Qv is the friction between the airflow flowing on the surface of the wire and the surface of the wire, that is, part of the kinetic energy of the air is converted into heat energy

[0040] S2. Calculation of radiation heat of lines in micro-topography areas.

[0041] Solar radiation is affected by terrain and other surface features and is decomposed into direct, diffuse and reflected radiation. Direct radiation is the largest component of total radiation, while diffuse radiation is the second largest component, and reflection is usually negligible. The intensity of diffuse radiation at any moment is determined by the direct intensity at that moment. After the direct intensity of the sun is calculated according to time, this amount is used as the basis for the calculation of diffuse radiation. Considering the shielding effect of terrain, the radiation amount of each solar sector is finally summed to obtain the diffuse radiation amount at that moment.

[0042] Solar radiation energy plays a decisive role in the temperature distribution of the conductors of transmission lines. As an important regulating factor for solar radiation energy to reach the ground, the topography’s shielding and reflection effects on solar radiation energy cannot be ignored.

[0043] The transmission line is considered as a straight line, and the surface solar radiation is related to the slope and aspect of each point. The position of the sun is defined by the azimuth and zenith angles, and the direct component is decomposed into two components, from the zenith angle of 0° and the azimuth direction. For conductors of any orientation, the coefficient f is used. Angle Correct for the actual amount of radiation received.

[0044]

[0045] Where angle is the angle between the transmission line and the horizontal direction, and aspect is the direction of the transmission line.

[0046] For a point at a certain height from the ground, the direct radiation flux is calculated based on the position of the sun, atmospheric attenuation, and terrain shielding. The radiation for the entire day can be obtained by summing the radiation calculations at each moment.

[0047] Q SunDir =f Hide Q SunConst β m(ζ) Δt,

[0048] Q const is the solar intensity outside the Earth's atmosphere, which can be considered a constant. β is the transmittance of the shortest path of sunlight through the atmosphere, which is 0.5 in clear weather. hide is the shielding coefficient, which is 0 when the location is shielded by terrain, and 1 when there is no terrain shielding. m(ζ) is the relative light path length. When sunlight is not incident from the zenith direction, the path through the atmosphere will become longer, which is determined by the zenith angle ζ and the altitude z.

[0049] S3. Construct a temperature distribution calculation model for micro-terrain transmission lines based on thermal radiation prediction function;

[0050] The method for constructing the temperature distribution calculation model of micro-topography transmission lines is as follows: based on the temperature distribution calculation model of ice-covered transmission lines, based on the calculation method of solar radiation shielding by terrain in the micro-topography area, the thermal radiation received by the transmission line every day that changes with the direction of the ground terrain is obtained, and based on the phase change heat absorption model of ice, its equivalent Joule heat is obtained, and finally the distribution law of the conductor temperature in the micro-topography area is obtained.

[0051] The surface of the ice-covered conductor will be affected by solar radiation, and the absorption capacity of the conductor surface depends on the type, thickness and shape of the ice. The absorption of solar radiation by the ice layer mainly occurs on the top and sides of the conductor. The absorption coefficient η of the surface of the ice-covered conductor is usually used to describe the absorption capacity of the ice-covered conductor to solar radiation. According to the surface area and absorption coefficient of the ice-covered conductor, the energy density of solar radiation received by the conductor surface can be calculated. That is,

[0052] q=ηAQ S un

[0053] A is the surface area of ​​the wire; q is the energy density.

[0054] The surface of the ice-covered conductor will be affected by solar radiation, and the absorption capacity of the conductor surface depends on the type, thickness and shape of the ice. The Joule heat of the current is an important heat source in the heat exchange process. In order to unify the influence of the Joule heat of the current on the heat exchange process under various micro-topography, the critical ice melting current is calculated using the following formula.

[0055]

[0056] Ilin is the critical ice melting current; heq is the heat transfer coefficient; teq is the time required for freezing.

[0057] S4. Consider the air flow disturbance as a heat source into the temperature distribution model to obtain the temperature distribution of ice-covered lines under different terrains.

[0058] In the micro-topography of Shuangshan Pass, a significant acceleration effect will occur when the airflow passes through the narrow pass. This effect increases first and then decreases with the increase of the depth of the pass. The degree of disturbance of the airflow by the terrain is different at different observation positions. The degree of airflow disturbance on the windward and leeward sides of the alpine watershed is different. The foot of the windward side is a negative acceleration zone, which gradually becomes a positive acceleration zone upward along the foot of the mountain, and reaches the maximum acceleration ratio at the top of the mountain. There is no leeward side in the terrain of the uplift, and behind the top of the mountain is a flat land of the same height as the top of the mountain, which is different from the alpine watershed.

[0059] For ice-covered conductors in micro-topography areas, changes in terrain will cause airflow disturbances, resulting in inconsistent wind speeds at different locations on the surface of the ice-covered conductors. When calculating the heat dissipation by convection, it is necessary to consider the difference in wind speeds at different locations and use different heat transfer coefficients accordingly, so as to finally obtain the temperature distribution of the ice-covered line considering the airflow disturbance factor.

[0060] The existence of micro-topography significantly changes the distribution characteristics of airflow, including the acceleration and deceleration of airflow velocity. Taking airflow disturbance into consideration, the temperature distribution of ice-covered lines under different terrains is obtained.

Claims

1. A method for calculating conductor temperature distribution based on daily heat radiation of a transmission line, characterized in that: The method comprises: Step 1: Establish a heat exchange balance equation based on the thermal effect and heat loss on the conductor surface; Step 2, calculate the radiant heat of the line in the micro-topography area; Step 3: construct a temperature distribution calculation model for micro-topography power transmission lines based on thermal radiation prediction function; Step 4: Consider the air flow disturbance as a heat source into the temperature distribution calculation model to obtain the temperature distribution of the ice-covered line under different terrains.

2. The method for calculating the conductor temperature distribution based on the daily heat radiation of a transmission line according to claim 1, characterized in that: The heat exchange balance equation is: Q I +QS un =Q c +Q w +Q r +Q k +Q v Q I is the Joule heat of the electric current; Q Sun is the solar shortwave radiation, which is considered to be absorbed by the surface of the ice-covered conductor; Q c is forced convection heat transfer; Q w To guide the heat loss when the supercooled water droplets are heated to the freezing temperature; Q r is the heat loss taken away by the water droplet when it finally leaves the wire; Q k The kinetic energy of water droplets is converted into heat energy; Q v The friction between the airflow flowing on the surface of the wire and the surface of the wire converts part of the kinetic energy of the air into heat energy.

3. The method for calculating the conductor temperature distribution based on the daily heat radiation of a transmission line according to claim 1, characterized in that: Calculation of radiant heat for micro-topography area lines includes: The transmission line is considered as a straight line. The surface solar radiation is related to the slope and aspect of each point. The position of the sun is defined by the azimuth and zenith angle. The direct component is decomposed into two components, the direction from the zenith angle of 0° and the direction of the azimuth angle. For any direction of the conductor, the coefficient f is used. Angle Correct the actual amount of radiation received: In the formula, angle is the angle between the transmission line and the horizontal direction, and aspect is the direction of the transmission line; For a point at a certain height from the ground, the direct radiation flux is calculated based on the sun's position, atmospheric attenuation, and terrain shielding. The radiation for the entire day is calculated and summed up at each moment: Q SunDir =f Hide Q SunConst β m(ζ) Δt, Q const is the solar intensity outside the Earth's atmosphere, β is the transmittance of the shortest path of sunlight through the atmosphere, and f hide is the shielding coefficient, which is 0 when the location is shielded by the terrain and 1 when there is no terrain shielding at the location; m(ζ) is the relative light path length.

4. The method for calculating the conductor temperature distribution based on the daily heat radiation of a transmission line according to claim 1, characterized in that: The construction of a micro-terrain transmission line temperature distribution calculation model based on thermal radiation prediction function includes: The absorption coefficient η of the ice-covered conductor surface is used to describe the absorption capacity of the ice-covered conductor to solar radiation. According to the surface area and absorption coefficient of the ice-covered conductor, the energy density of solar radiation received by the conductor surface is calculated, that is, q=ηAQ S and A is the surface area of ​​the wire; q is the energy density.

5. The method for calculating the conductor temperature distribution based on the daily heat radiation of a transmission line according to claim 1, characterized in that: When calculating the heat dissipation by thermal convection, the difference in wind speed at different locations is taken into account, and different heat transfer coefficients are used accordingly, and finally the temperature distribution of the ice-covered line is obtained considering the airflow disturbance factor.

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