CN111428942B - Line icing thickness prediction method for extracting micro-terrain factors based on variable grid technology - Google Patents
Line icing thickness prediction method for extracting micro-terrain factors based on variable grid technology Download PDFInfo
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Abstract
The invention discloses a line icing thickness prediction method for extracting micro-terrain factors based on a variable grid technology, which comprises the following steps: step 1, acquiring a digital elevation model of a research area, and correcting image coordinates by using geographic information system software; step 2, collecting ice region distribution map vector files, power grid space data, ice coating monitoring terminal data and ice coating thickness, and preprocessing the data; step 3, extracting micro-terrain factor data of each monitoring terminal position by adopting a variable grid technology; step 4, calculating the average value of the maximum ice coating thickness of each ice coating monitoring terminal in the latest 5 ice periods in the step 2; step 5, carrying out normalization processing on the data in the step 3; and 6, establishing a prediction model between the micro-terrain factor and the line icing thickness by taking the data in the step 5 as independent variables and the data in the step 4 as dependent variables and adopting a neural network method, so that the problems that the extraction of the micro-terrain factor is time-consuming and the prediction of the icing thickness of the power transmission line is inaccurate are solved.
Description
Technical Field
The invention belongs to the field of risk assessment of icing disasters of power transmission lines; in particular to a line icing thickness prediction method for extracting micro-terrain factors based on a variable grid technology.
Background
The mountainous area terrain is complex and changeable, and due to the influence of micro-terrain factors on local weather, the icing grades of power transmission lines at different parts of the same mountain are different, and the icing of the power transmission lines in the mountainous area seriously jeopardizes the safe operation of a power system. Although a power grid company monitors the ice condition of a line by a series of means, such as an ice coating monitoring system, a manual handheld ice observation device and the like, the ice coating thickness calculation method is single, so that the ice coating condition of all micro-terrain areas cannot be represented, and the ice coating condition of the line cannot be accurately mastered because of the fact that the manual work cannot directly reach the ice coating site of the line due to special terrain. The GIS technology can accurately identify the micro-terrain factors in the adjacent area of the line, and has great significance in establishing a line icing thickness prediction model considering the micro-terrain factors. The literature, namely micro-terrain factor identification and extraction based on GIS, introduces identification of various micro-terrain factors, and micro-terrain factors are extracted by using grids with the same size, so that the method is long in time consumption; the patent: a power line icing thickness prediction method (CN103020740A) based on microclimate data inputs predicted meteorological data into an artificial neural network model to calculate corresponding icing thickness, and the method comprises the following steps: a method (CN106682771A) for predicting icing thickness of a power transmission line based on microclimate information trains a regression model with icing thickness as a dependent variable and microclimate temperature as an independent variable by using historical icing thickness data of the power transmission line and microclimate historical temperature data corresponding to the historical icing thickness, and predicts the icing thickness by using the trained model and a meteorological station to predict the meteorological temperature. The method obtains icing thickness prediction by training different models by using microclimate data, seriously depends on meteorological prediction data provided by a professional meteorological station, and has inaccurate icing thickness prediction result due to the fact that meteorological conditions change greatly and errors exist between the prediction data and actual monitoring data.
Disclosure of Invention
The technical problems to be solved by the invention are as follows: the method for predicting the icing thickness of the line based on the variable grid technology extraction micro-terrain factor is provided, so that the problems that the micro-terrain factor extraction is time-consuming and the prediction of the icing thickness of the power transmission line is inaccurate are solved.
The technical scheme of the invention is as follows:
a line icing thickness prediction method for extracting micro-terrain factors based on a variable grid technology comprises the following steps:
step 1, acquiring a prediction area digital elevation model, and correcting the image coordinates of the prediction area digital elevation model by using geographic information system software;
step 2, acquiring vector files of ice region distribution maps in a prediction region, historical cold tide development paths, power grid space data, ice coating monitoring terminal data and ice coating thickness, preprocessing the data, and taking the corrected digital elevation model as a coordinate system to obtain the vector files of the ice region distribution maps, the power grid space data and coordinates of the ice coating monitoring terminal on the corrected digital elevation model;
step 3, extracting micro-terrain factor data of the positions of the ice-coating monitoring terminals by adopting a variable grid technology, wherein the micro-terrain factors comprise elevation, gradient, slope direction, terrain roughness and terrain relief degree, and quantizing the slope direction;
Step 4, calculating the average value of the maximum ice coating thickness monitored by each ice coating monitoring terminal in the last 5 ice periods in the step 3; step 5, carrying out normalization processing on the micro terrain factor data processed in the step 3;
and 6, establishing a prediction model between the micro-terrain factor and the line icing thickness by adopting a neural network method by taking the micro-terrain factor processed in the step 5 as an input layer and the maximum icing thickness average value processed in the step 4 as an output layer.
The power grid space data acquired in the step 2 comprise 35kV and line names, pole tower longitude and latitude and line icing fault historical data, the icing monitoring terminal data comprise administrative divisions, voltage classes and longitude and latitude, the icing thickness data comprise historical data of the latest 5 icing periods, and the data preprocessing method comprises the following steps:
step 2.1, carrying out standard processing of naming and removing weight on the ice-coating monitoring terminal data;
and 2.2, checking the position information of the icing terminal by utilizing the power grid space data and field investigation.
Step 3, the grid-changing technology comprises the following steps:
step 3.1, extracting area surface files of each icing magnitude according to the vector file of the ice area distribution map of the prediction area;
step 3.2, dividing the icing magnitude of 30mm-40mm, 40mm-50mm and above into historical icing severe regions, and dividing the rest icing magnitude regions into historical icing lighter regions;
And 3.3, carrying out grid division on the digital elevation model of the prediction area by adopting a variable grid technology, dividing the historical ice-coated severe area into more than two fine grids, and dividing the historical ice-coated lighter area into more than two coarse grids.
And 3, the method for extracting the elevation, the gradient, the slope direction, the terrain roughness and the terrain relief degree comprises the following steps:
the elevation is directly obtained by a digital elevation model;
the gradient extraction adopts a three-order inverse distance square weight difference method, namely a 3 multiplied by 3 window consisting of 9 small grids, and a calculation formula of the gradient and the gradient direction of a central point e is as follows:
Aspect＝Slopen/Slopec
in the formula, Slope is the gradient, Aspect is the Slope direction, SlopecSlope in the x-axis direction, SlopenThe grid gradient is the gradient of the y axis direction, Cellsize is the grid size of a digital elevation model, e5 is the grid gradient of the central point e in the northwest direction adjacent to the central point e, e1 is the grid gradient of the central point e in the positive west direction adjacent to the central point e, e8 is the grid gradient of the central point e in the southwest direction adjacent to the central point e, e7 is the grid gradient of the central point e in the southeast direction adjacent to the central point e, e3 is the grid gradient of the central point e in the positive east direction adjacent to the central point e, and e6 is the grid gradient of the central point e in the northeast direction adjacent to the central point e;
the surface roughness calculation method comprises the following steps:
m＝s/st
where m is the surface roughness, s is the surface area of each grid cell, s tProjecting an area for each grid cell;
the surface relief degree calculation method includes:
and respectively calculating the maximum elevation value DMAX and the minimum elevation value DMIN of the digital elevation model in each fine grid and each coarse grid according to the division result of the digital elevation model variable grid technology of the research area by using a Focal function, and then calculating the difference value.
The method for quantizing the slope direction comprises the following steps:
extracting results of the slope directions into 8 directions of east, south, west, north, southeast, northeast, southwest and northwest, respectively quantitatively scoring the influence degrees of the 8 slope directions of the tower positions where the icing monitoring terminals are located on the line icing by adopting an expert percentile scoring method and combining an ice region distribution diagram, a historical cold tide development path and line icing fault historical data, and finally taking the average value of the evaluation values.
The formula for normalizing the microtopography factor data processed in the step 3 in the step 5 comprises:
in the formula, xijIn order to be a value after the processing,
as an initial value of index, xmaxj、xminjThe j index maximum value and the j index minimum value are respectively.
Step 6, the method for establishing the relation model between the micro-terrain factor and the line icing thickness by adopting the neural network method comprises the following steps: adopting three layers of BP neural network mathematical models, namely an input layer, a hidden layer and an output layer, wherein the input layer is the data of each micro-terrain factor in the step 5, and the output layer is the icing thickness value corresponding to the jth micro-terrain factor;
The hidden layer calculation expression is:
in the formula yjIs the output value, x, of the jth node of the hidden layeriInputting data for the micro-terrain factor of the ith node,
ajthreshold, ω, for the ith node of the hidden layerjiThe weighted value from the ith node of the hidden layer to the jth node of the output layer is shown, N is the number of the nodes of the hidden layer, and f (x) is an S-shaped excitation function;
the output value calculation expression of the jth node of the output layer is as follows:
in the formula ZjIs the output value of the jth node of the output layer, bjIs the jth node threshold of the output layer, yiFor the output value of the ith node of the hidden layer, ωjiFor the weight from the ith node of the hidden layer to the jth node of the output layerThe weight value M is the number of output layer nodes, namely the ice coating thickness, and f (x) is an S-shaped excitation function;
the error function expression of the calculation result of the established three-layer BP neural network mathematical model is as follows:
wherein e is the model calculation error, the error critical value is set to be 0.001, when the model calculation error is less than the critical value, the training is stopped, and Z isjOutput layer calculation for BP model, zjAn observed value of the icing monitoring terminal is obtained;
weight function omegajiThe calculation expression is:
ωji(yp+1)＝ωji(yp)+Δωji
wherein ω isji(yp) Is the weight, ω, of the p-th sample node i to node jji(yp+1) is the weight from node i to node j for the p +1 th sample, Δ ω jiIs the weight value change quantity;
weight value change Δ ωjiThe calculation expression is:
in the formula, eta is learning efficiency, values are distributed between 0 and 1, e is model calculation error, omegajiIs a weight function.
The invention has the beneficial effects that:
in order to overcome the defect of time consumption for extracting the micro-topographic factors by using grids with the same size, the invention utilizes a Digital Elevation Model (DEM) and adopts a variable grid technology to identify the micro-topographic factors, namely, an ice-covered serious area adopts fine grid division, an ice-covered non-serious area adopts coarse grid division, the extraction efficiency of the micro-topographic factors of a large area is improved, and a prediction model between the micro-topographic factors and line ice is established by combining ice-covered data and power grid space data of an ice-covered monitoring terminal and adopting a neural network algorithm.
Drawings
FIG. 1 is a schematic flow diagram of the present invention;
FIG. 2 is a schematic view of a 3 × 3 grid window;
the specific implementation mode is as follows:
the method for selecting the digital elevation model for predicting the regional area in the invention is a 12.5m resolution digital elevation model in Guizhou province, and the specific implementation mode is shown in FIG. 1, and the method comprises the following steps:
step 1, acquiring a prediction area digital elevation model, and correcting the image coordinates of the prediction area digital elevation model by using geographic information system software;
Step 2, acquiring vector files of ice region distribution maps in a prediction region, historical cold tide development paths, power grid space data, ice coating monitoring terminal data and ice coating thickness, preprocessing the data, and taking the corrected digital elevation model as a coordinate system to obtain the vector files of the ice region distribution maps, the power grid space data and coordinates of the ice coating monitoring terminal on the corrected digital elevation model;
step 3, extracting micro-terrain factor data of the positions of the ice-coating monitoring terminals by adopting a variable grid technology, wherein the micro-terrain factors comprise elevation, gradient, slope direction, terrain roughness and terrain waviness, and quantizing the slope direction;
step 4, calculating the average value of the maximum ice coating thickness monitored by each ice coating monitoring terminal in the last 5 ice periods in the step 3;
step 5, carrying out normalization processing on the micro terrain factor data processed in the step 3;
and 6, establishing a prediction model between the micro-terrain factor and the line icing thickness by adopting a neural network method by taking the micro-terrain factor processed in the step 5 as an input layer and the maximum icing thickness average value processed in the step 4 as an output layer.
The power grid space data acquired in the step 2 comprise 35kV and line names, pole tower longitude and latitude and line icing fault historical data, the icing monitoring terminal data comprise administrative divisions, voltage classes and longitude and latitude, the icing thickness data comprise historical data of the latest 5 icing periods, and the data preprocessing method comprises the following steps:
Step 2.1, carrying out standard processing of naming and removing weight on the ice-coating monitoring terminal data;
and 2.2, checking the position information of the icing terminal by utilizing the power grid space data and field investigation.
Step 3, the grid changing technology comprises the following steps:
step 3.1, extracting area surface files of each icing magnitude according to the vector file of the ice area distribution map of the prediction area;
step 3.2, dividing the icing magnitude of 30mm-40mm, 40mm-50mm and above into historical icing severe regions, and dividing the rest icing magnitude regions into historical icing lighter regions;
and 3.3, carrying out grid division on the digital elevation model of the prediction area by adopting a variable grid technology, dividing the historical ice-coated severe area into more than two fine grids, and dividing the historical ice-coated lighter area into more than two coarse grids.
The ice region distribution diagram of the Guizhou power grid 2018 version is selected in the embodiment;
the digital elevation model is a 12.5m resolution digital elevation model selected in Guizhou province;
the specification of the fine grid of the digital elevation model is as follows: 5 m.times.5 m;
the digital elevation model coarse grid specification: 500m × 500 m;
and 3, the method for extracting the gradient, the slope direction, the terrain roughness and the terrain relief degree comprises the following steps:
the elevation is directly obtained by a digital elevation model;
The gradient extraction adopts a three-order inverse distance square weight difference method, namely a 3 multiplied by 3 window consisting of 9 small grids, and a calculation formula of the gradient and the gradient direction of a central point e:
Aspect＝Slopen/Slopec
in the formula, Slope is the gradient, Aspect is the Slope direction, SlopecSlope in the x-axis direction, SlopenThe grid gradient is the gradient of the y axis direction, Cellsize is the grid size of a digital elevation model, e5 is the grid gradient of the central point e in the northwest direction adjacent to the central point e, e1 is the grid gradient of the central point e in the positive west direction adjacent to the central point e, e8 is the grid gradient of the central point e in the southwest direction adjacent to the central point e, e7 is the grid gradient of the central point e in the southeast direction adjacent to the central point e, e3 is the grid gradient of the central point e in the positive east direction adjacent to the central point e, and e6 is the grid gradient of the central point e in the northeast direction adjacent to the central point e;
the surface roughness calculation method comprises the following steps:
m＝s/st
where m is the surface roughness, s is the surface area of each grid cell, stProjecting an area for each grid cell;
the surface relief degree calculation method includes:
and respectively calculating the maximum elevation value DMAX and the minimum elevation value DMIN of the digital elevation model in each fine grid and each coarse grid according to the division result of the digital elevation model variable grid technology of the research area by using a Focal function, and then calculating the difference value.
The method for quantizing the slope direction comprises the following steps:
The method mainly comprises the steps of dividing the extraction result of the slope direction into 8 directions of east, south, west, north, southeast, northeast, southwest and northwest, quantitatively scoring the influence degree of the 8 slope directions of the tower positions where the icing monitoring terminals are located on the icing of the line respectively by adopting an expert percentile scoring method and combining an ice region distribution diagram, a historical cold tide development path and historical line icing fault data, and finally taking the average value of the evaluation results.
The formula for normalizing the result factors in the step 3 in the step 5 comprises:
in the formula (I), the compound is shown in the specification,
as an initial value of index, xmaxj、xminjThe j index maximum value and the j index minimum value are respectively.
Step 6, the concrete implementation method for establishing the relation model between the micro-terrain factor and the line icing thickness by adopting the neural network method comprises the following steps: adopting three layers of BP neural network mathematical models, namely an input layer, a hidden layer and an output layer, wherein the input layer is the data of each micro-terrain factor in the step 5, and the output layer is the icing thickness value corresponding to the jth micro-terrain factor;
the hidden layer calculation expression is:
in the formula yjIs the output value, x, of the jth node of the hidden layeriFor the i-th node microtopography factor input data, ajThreshold, ω, for the ith node of the hidden layerjiThe weighted value from the ith node of the hidden layer to the jth node of the output layer is shown, N is the number of the nodes of the hidden layer, and f (x) is an S-shaped excitation function;
The output value calculation expression of the jth node of the output layer is as follows:
in the formula ZjIs the output value of the jth node of the output layer, bjIs the jth node threshold of the output layer, yiFor the output value of the ith node of the hidden layer, ωjiThe weight value from the ith node of the hidden layer to the jth node of the output layer, M is the number of the nodes of the output layer, namely the thickness of the ice coating, and f (x) is an S-shaped excitation function;
Wherein e is the model calculation error, the error critical value is set to be 0.001, when the model calculation error is less than the critical value, the training is stopped, and Z isjOutput layer calculation for BP model, zjAn observed value of the icing monitoring terminal is obtained;
weight function omegajiThe calculation expression is:
ωji(yp+1)＝ωji(yp)+Δωji
wherein ω isji(yp) Is the weight, ω, of the p-th sample node i to node jji(yp+1) is the weight from node i to node j for the p +1 th sample, Δ ωjiIs the weight value change quantity;
weight value change Δ ωjiThe calculation expression is:
in the formula, eta is learning efficiency, values are distributed between 0 and 1, e is model calculation error, omegajiIs a weight function;
the time required by BP model training is shorter when the eta value is larger, but the model is not easy to converge, so the eta value in the invention is 0.2.
The invention discloses a line icing thickness prediction method for extracting a micro-terrain factor based on a variable grid technology, which mainly extracts the micro-terrain factor based on the variable grid technology and is used for solving the line icing thickness prediction problem. The above examples are merely illustrative of the technical solutions of the present invention and are not intended to be limiting, and with reference to the above examples, several additions and modifications may be made without departing from the scope of the present invention.
Claims (7)
1. A line icing thickness prediction method for extracting micro-terrain factors based on a variable grid technology comprises the following steps:
step 1, acquiring a predicted area digital elevation model, and correcting image coordinates of the predicted area digital elevation model by using geographic information system software;
step 2, acquiring vector files of ice region distribution maps in a prediction region, historical cold tide development paths, power grid space data, ice coating monitoring terminal data and ice coating thickness, preprocessing the data, and taking the corrected digital elevation model as a coordinate system to obtain the vector files of the ice region distribution maps, the power grid space data and coordinates of the ice coating monitoring terminal on the corrected digital elevation model;
step 3, extracting micro-terrain factor data of the positions of the ice-coating monitoring terminals by adopting a variable grid technology, wherein the micro-terrain factors comprise elevation, gradient, slope direction, terrain roughness and terrain waviness, and quantizing the slope direction;
Step 3, the grid changing technology comprises the following steps:
step 3.1, extracting area files of each icing magnitude according to the vector file of the ice area distribution map of the prediction area;
step 3.2, dividing icing magnitude of 30mm-40mm, 40mm-50mm and 50mm or more into historical icing serious regions, and dividing the rest icing magnitude regions into historical icing light regions;
step 3.3, grid division is carried out on the digital elevation model of the prediction area by adopting a variable grid technology, the historical ice-coated severe area is divided into more than two fine grids, and the historical ice-coated lighter area is divided into more than two coarse grids;
step 4, calculating the average value of the maximum ice coating thickness monitored by each ice coating monitoring terminal in the last 5 ice periods in the step 3;
step 5, carrying out normalization processing on the micro terrain factor data processed in the step 3;
and 6, establishing a prediction model between the micro-terrain factor and the line icing thickness by adopting a neural network method by taking the micro-terrain factor processed in the step 5 as an input layer and the maximum icing thickness average value processed in the step 4 as an output layer.
2. The line icing thickness prediction method for extracting the micro-terrain factor based on the variable mesh technology as claimed in claim 1, wherein: the power grid space data acquired in the step 2 comprise 35kV and line names, pole tower longitude and latitude and line icing fault historical data, the icing monitoring terminal data comprise administrative divisions, voltage classes and longitude and latitude, the icing thickness data comprise historical data of the latest 5 icing periods, and the data preprocessing method comprises the following steps:
Step 2.1, carrying out naming and de-duplication standardization processing on the ice coating monitoring terminal data;
and 2.2, checking the position information of the icing terminal by utilizing the power grid space data and field investigation.
3. The method for predicting the ice coating thickness of the line based on the extraction of the micro-terrain factor by the variable mesh technology as claimed in claim 1, wherein: and 3, the method for extracting the elevation, the gradient, the slope direction, the terrain roughness and the terrain relief degree comprises the following steps:
the elevation is directly obtained by a digital elevation model;
the gradient extraction adopts a three-order inverse distance square weight difference method, namely a 3 multiplied by 3 window consisting of 9 small grids, and a calculation formula of the gradient and the gradient direction of a central point e is as follows:
Aspect＝Slopen/Slopec
in the formula, Slope is the gradient, Aspect is the Slope direction, SlopecSlope in the x-axis direction, SlopenIs the gradient of the y-axis direction, Cellsize is the grid size of the digital elevation model, e5 is the gradient of the grid near the northwest direction of the center point e, e1 is the gradient of the grid near the positive west direction of the center point e, e8 is the gradient of the grid near the southwest direction of the center point e, e7 is the gradient of the grid near the southeast direction of the center point e, e3 is the gradient of the grid near the positive east direction of the center point e, e6 is the gradient of the grid near the positive east direction of the center point ee grid slope in the northeast direction;
The surface roughness calculation method comprises the following steps:
m＝s/st
where m is the surface roughness, s is the surface area of each grid cell, stProjecting an area for each grid cell;
the surface relief degree calculation method includes:
and respectively calculating the maximum elevation value DMAX and the minimum elevation value DMIN of the digital elevation model in each fine grid and each coarse grid according to the division result of the digital elevation model variable grid technology of the research area by using a Focal function, and then calculating the difference value.
4. The line icing thickness prediction method for extracting the micro-terrain factor based on the variable mesh technology as claimed in claim 1, wherein: the method for quantizing the slope direction comprises the following steps:
extracting results of the slope directions into 8 directions of east, south, west, north, southeast, northeast, southwest and northwest, respectively quantitatively scoring the influence degrees of the 8 slope directions of the tower positions where the icing monitoring terminals are located on the line icing by adopting an expert percentile scoring method and combining an ice region distribution diagram, a historical cold tide development path and line icing fault historical data, and finally taking the average value of the evaluation values.
5. The line icing thickness prediction method for extracting the micro-terrain factor based on the variable mesh technology as claimed in claim 1, wherein: the formula for normalizing the microtopography factor data processed in the step 3 in the step 5 comprises:
In the formula, xijIn order to be a value after the processing,
is an initial value of the index, xmaxj、xminjThe j index maximum value and the j index minimum value are respectively.
6. The line icing thickness prediction method for extracting the micro-terrain factor based on the variable mesh technology as claimed in claim 1, wherein: step 6, the method for establishing the relation model between the micro-terrain factor and the line icing thickness by adopting the neural network method comprises the following steps: adopting three layers of BP neural network mathematical models, namely an input layer, a hidden layer and an output layer, wherein the input layer is the data of each micro-terrain factor in the step 5, and the output layer is the icing thickness value corresponding to the jth micro-terrain factor;
the hidden layer calculation expression is:
in the formula yjIs the output value, x, of the jth node of the hidden layeriFor the i-th node microtopography factor input data, ajThreshold, ω, for the ith node of the hidden layerjiThe weighted value from the ith node of the hidden layer to the jth node of the output layer is shown, N is the number of the nodes of the hidden layer, and f (x) is an S-shaped excitation function;
the output value calculation expression of the jth node of the output layer is as follows:
in the formula ZjIs the output value of the jth node of the output layer, bjIs the jth node threshold of the output layer, yiFor the output value of the ith node of the hidden layer, ωjiThe weight value from the ith node of the hidden layer to the jth node of the output layer, M is the number of the nodes of the output layer, namely the thickness of the ice coating, and f (x) is an S-shaped excitation function.
7. The line icing thickness prediction method for extracting the micro-terrain factor based on the variable mesh technology as claimed in claim 6, wherein the method comprises the following steps: the error function expression of the calculation result of the established three-layer BP neural network mathematical model is as follows:
wherein e is the model calculation error, the error critical value is set to be 0.001, when the model calculation error is less than the critical value, the training is stopped, and Z isjOutput layer calculation for BP model, zjAn observed value of the icing monitoring terminal is obtained; weight function omegajiThe calculation expression is:
ωji(yp+1)＝ωji(yp)+Δωji
wherein ω isji(yp) Is the weight, ω, of the p-th sample node i to node jji(yp+1) is the weight from node i to node j for the p +1 th sample, Δ ωjiIs the weight value change quantity;
weight value change Δ ωjiThe calculation expression is:
in the formula, eta is learning efficiency, values are distributed between 0 and 1, e is model calculation error, omegajiIs a weight function.
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