[0032] Such as figure 1 Shown is a flow chart of the method for monitoring the thickness of ice on a transmission line provided by the present invention.
[0033] The method for monitoring the thickness of ice on a transmission line provided by the present invention includes the following steps:
[0034] (1) Obtain historical meteorological data, historical icing conditions data, and geographic environment data along the transmission line, and store them in the database; historical meteorological data include temperature, wind speed, relative humidity, and precipitation; historical icing conditions include ice coating Thickness, icing type, icing weight, as well as the appearance characteristics and density of each icing type. The icing type refers to the different ice blocks attached to the transmission line, including rime, mixed song, soft rime and hoarfrost. Different types of icing are produced under meteorological conditions and geographical environment; geographical environment data mainly refers to the altitude along the transmission line; a one-to-one correspondence relationship is established between historical meteorological data, historical icing situation data, and geographical environment data, that is, at a certain altitude Transmission line, under certain conditions of temperature, wind speed, relative humidity, and precipitation, the icing conditions, such as the thickness, type, and weight of icing; for example, in mountains above 500 meters, the temperature is -4-0℃, When the wind speed is 3-15m/s, rime is produced. According to historical data, the thickness and weight of the rime on the transmission line can also be determined.
[0035] (2) Set the start date and end date of icing monitoring, obtain the current date, and compare it with the start date and end date of icing monitoring. Before the icing end date, start the transmission line icing thickness monitoring and go to step (4), otherwise go to step (3);
[0036] (3) Obtain current meteorological data and geographic environmental data, including temperature, wind speed, relative humidity, precipitation, geographic environmental data including altitude; combine current meteorological data and geographic environmental data with historical meteorological data and geographic environmental data stored in the database By comparison, determine whether there is a possibility of icing on the transmission line under current weather and geographic environmental conditions, that is, whether there is a record of icing in the historical data under current meteorological and geographic environmental conditions; if there is a record of icing, proceed to step (4); otherwise, stop monitoring; by comparing the current meteorological and geographic environment conditions with the data in the database, it can avoid the improper setting of the start date and the end date of the icing monitoring, which may lead to missing monitoring.
[0037] (4) The imaging module installed on the tower is driven by the digital model processor DSP to obtain the image of the transmission line. The imaging module is a CCD sensor; the obtained image is converted into a digital signal through the codec module, and transmitted to the digital signal through the communication module The processor DSP, the digital signal processor performs grayscale processing on the image that has been converted into digital signals, uses the median filter algorithm to enhance the image, and then performs two-dimensional segmentation of the image according to the Snake model algorithm based on the level set method to extract The shape characteristics of the image;
[0038] (5) Use the shape matching algorithm to compare the shape feature of the extracted image with the shape feature of each icing type acquired in advance and stored in the database to determine the icing type of the current icing on the transmission line; If the shape feature of the extracted image cannot match the shape feature of each ice coating type obtained in advance, then the current transmission line has no ice coating, and return to step (4); usually, use the current meteorological data and geographic environment data obtained, The type of icing can be roughly judged. In lowlands below 500 meters above sea level, when the temperature is -2-0℃, or in mountains above 500 meters above sea level, when the temperature is -4-0℃ and wind speed is 3-15m/s. , It is easier to produce rime; in the lowlands below 500 meters, the temperature is -5-0℃, or the mountains above 500 meters above the sea level, the temperature is -10-3℃, and the wind speed is 3-15m/s. In mountains above 500 altitudes, the temperature is -13-8℃, and soft rime is easy to form under moderate wind speed; while the temperature is lower than -10℃, the wind speed is low or there is no wind, it is easy to produce hoarfrost. The error of determining the type of icing based on meteorological data and geographic environment data is relatively large. For example, mixed songs are generally produced when rime is formed and the weather is cloudy and sunny.
[0039] (6) Obtain the current icing density on the transmission line according to the icing type. If the icing type is rime, the density is 0.8-0.9g/cm 3 , The icing type is mixed song, the density is 0.6-0.8g/cm 3 , The icing type is rime, the density is 0.3-0.6g/cm 3 , The icing type is hoarfrost, the density is 0.1-0.3g/cm 3;
[0040] (7) Use the wind speed sensor to obtain the current wind speed, use the temperature sensor to obtain the current ice surface temperature and ambient temperature, and obtain the current precipitation rate; the icing density is taken into the icing thickness calculation formula to calculate the icing thickness:
[0041] t i+1 The formula for calculating the ice thickness at the moment is as follows:
[0042] b i + 1 = b i + R i 2 + Δ m i / ( ρ i π ) - R i ,
[0043] Then calculate the icing thickness from the beginning of the icing to the current time T. At this time, the length of the time period is T, and it is calculated once every time length L, and then a total of T/L times are measured. The ice density is not a fixed value, then the ice thickness is related to the variable ice density ρ i The formula is:
[0044] B 1 = X i = 0 T / L ( b 0 + R i 2 + Δ m i / ( ρ i π ) - R i ) ,
[0045] From this, the icing density can be obtained:
[0046] B = ∫ z 1 z 2 [ X i = 0 T / L ( b 0 + R i 2 + Δ m i / ( ρ i π ) - R i ) ] z 2 - z 1
[0047] Where: b 0 The initial value of is 0, z 1 i 2 , Δm i From t i To t i+1 The increase in icing during the period of time; R i Is t i Ice thickness at any moment, R i = B i +R 0 , R 0 Is the original radius of the transmission line;
[0048] Δm i = 2R i α 1 α 2 α 3 w i v i Δt i ,
[0049] Where: α 1 Is the collision coefficient, α 2 Is the capture factor, α 3 Is the freezing factor; v i Is t i Wind speed at the moment, w i Is t i The relationship between the liquid water content and the precipitation rate at the moment, P i Is t i The precipitation rate at any moment, namely t i The precipitation rate of a certain time segment at the time;
[0050] α 1 The calculation formula is as follows:
[0051]
[0052]
[0053] Among them, K=ρ ω a 2 v/9μD, Re=ρ a av/μ; μ is the air viscosity coefficient, ρ w Is the water drop density, ρ a Is the air density, a is the median volume diameter of the droplet, and v is the wind speed;
[0054] α 2 The calculation formula is as follows:
[0055] α 2 =1/(1+1.64μ/va), where μ is the air viscosity coefficient, v is the wind speed, and a is the median volume diameter of the water drop;
[0056] α 3 = [ 2 Rwv α 1 α 2 L f + R h f r c v 2 / C a + R α 1 α 2 w v 3 - 2 πR ( h f + h n ) ( T s - T a ) - 2 π R x e ( T s ) + 2 π R x e ( T a ) - 2 πRϵσ ( T s 4 - T a 4 ) - 2 R α 1 wv c w T F ( T F - T a ) - 2 R α 1 wv c w ( T s - T a ) ] / [ 2 Rwv α 1 α 2 c i ( T F - T s ) ( T F - T s ) / 2 + 2 R α 1 wv c w ( T s - T a ) ] ,
[0057] Among them: w is the liquid water content, v is the wind speed, e(T) is the saturated water vapor pressure on the icing surface at the temperature T, R x Is the evaporation coefficient, R is the resistivity per unit length of the wire, L f =3.34×10 5 J/kg, r c =0.79, c a =1014J/(kg·k), c i Is the specific heat capacity of ice at the film temperature, in J/(kg·k), T s , T a Respectively ice surface temperature and ambient temperature, unit ℃, T F Is the solid temperature of the water droplet, c w = 4220J/(kg·k), ε=0.95, σ=5.67×10 -8 W/(m 2 ·K 4 ), h a , H f Is the heat transfer coefficient of natural convection and forced convection, in J(m 2 ·K).
[0058] Through the analysis of the actual power grid, when the wire diameter is 11.0mm, calculate the rime change within one hour, select the interval L as 10 minutes, and then calculate a total of 6 times. The calculation results are as follows:
[0059]
[0060]
[0061] It can be seen from the table that due to changes in wind speed, air density, temperature, etc., the collision coefficient α 1 , Capture coefficient α 2 , Freezing coefficient α 3 All changes within an hour, but not much. The thickness of icing has also increased, but there is not much change. This is due to the fact that within an hour, the meteorological conditions have not changed much, and the factors leading to the increase of icing have not changed much.
