CN110514890B - Optimal design method suitable for ion current measuring devices with different voltage levels - Google Patents
Optimal design method suitable for ion current measuring devices with different voltage levels Download PDFInfo
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- CN110514890B CN110514890B CN201910804500.3A CN201910804500A CN110514890B CN 110514890 B CN110514890 B CN 110514890B CN 201910804500 A CN201910804500 A CN 201910804500A CN 110514890 B CN110514890 B CN 110514890B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R15/00—Details of measuring arrangements of the types provided for in groups G01R17/00 - G01R29/00, G01R33/00 - G01R33/26 or G01R35/00
- G01R15/002—Switches for altering the measuring range or for multitesters
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R19/00—Arrangements for measuring currents or voltages or for indicating presence or sign thereof
- G01R19/0092—Arrangements for measuring currents or voltages or for indicating presence or sign thereof measuring current only
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R19/00—Arrangements for measuring currents or voltages or for indicating presence or sign thereof
- G01R19/08—Measuring current density
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Abstract
The invention discloses an optimal design method of an ion current measuring device suitable for different voltage grades, which comprises the following steps: 1) calculating an ion flow field around a lead in the direct current transmission line, and extracting the ion current density near the ground as a boundary condition of an ion current density measurement error analysis model; 2) establishing an ion current density measurement error analysis model based on a field coupling method; 3) selecting a sampling resistor of a Wilson board in a measuring platform; 4) the method includes the steps that ion current densities around wires in the direct current transmission line are simulated by Wilson boards of different sizes, the influence of the length, the width and the thickness of the Wilson boards on measurement errors of the ion current densities is analyzed, the length, the width and the thickness of the corresponding Wilson boards with the minimum errors are utilized to construct an ion current measuring device of the current voltage level, and the ion current measuring device designed by the method can effectively improve the accuracy of ion current measurement of the high-voltage direct current transmission line.
Description
Technical Field
The invention relates to an optimal design method of an ion current measuring device, in particular to an optimal design method of an ion current measuring device suitable for different voltage grades.
Background
High voltage direct current transmission has great advantages in long distance transmission. However, when the electric field around the wire reaches a certain intensity, corona discharge will occur around the wire, and when the transmission line is operating normally, a certain corona discharge is also allowed around the wire. The space charge generated by the corona is transferred to form an ion flow field. At present, the ion current density near the ground of a +/-800 kV direct current transmission line specified in China cannot exceed 100nA/m2Therefore, it is important to accurately measure the ion current density.
The Wilson board is widely applied to measurement of ionic current of a high-voltage direct-current transmission line at present, but the research on the measurement device is few at present, experts and scholars mainly concern numerical calculation methods of an ionic flow field of the high-voltage direct-current transmission line, tests generally verify the accuracy of numerical calculation results or research the distribution condition of the ionic flow field, and the premise that the accuracy of measurement data is verified by simulation accuracy is often ignored.
Wilson plate measurement principle: as shown in FIG. 1, which is a measurement principle of a Wilson plate, when charges generated by a wire corona fall to an ion collecting area, the Wilson plate collects ions and passes the ions through a sampling resistor RZFlowing underground, the voltage across the sampling resistor can be measured by a voltmeter and the average ion current density is calculated as:
Jav＝I/S
wherein, I is the current on the sampling resistor.
The wilson plate is placed above ground and the potential of the ion collection area of the wilson plate can be considered to be 0V because the magnitude of the sampling resistance is quite small compared to the magnitude of the ion current. Therefore, we believe that the wilson plates do not affect the ion flux field distribution during the measurement process.
The Wilson board currently adopted in engineering is generally 1m multiplied by 1m, the size refers to the power industry standard (direct current converter station and line combined field intensity and ion current density measurement method) of the people's republic of China, and no specific specification is provided for the thickness. Due to the difference of voltage grades, the line model selection, the line laying mode, the distribution of the ion current density and the like are different when the power transmission line is laid, and the Wilson board with the same size is obviously not suitable for ion flow fields with different voltage grades, so that an optimal design method suitable for the ion current measuring devices with different voltage grades is required to be designed for improving the ion current measuring accuracy of the high-voltage direct-current power transmission line and reducing the measuring error of equipment.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provides an optimal design method of an ionic current measuring device suitable for different voltage grades, and the ionic current measuring device designed by the method can effectively improve the ionic current measuring accuracy of a high-voltage direct-current transmission line.
In order to achieve the above object, the method for optimally designing an ion current measuring device suitable for different voltage levels according to the present invention comprises the following steps:
1) calculating an ion flow field around a lead in the direct current transmission line, and extracting the ion current density near the ground as a boundary condition of an ion current density measurement error analysis model;
2) establishing an ion current density measurement error analysis model based on a field coupling method;
3) selecting a sampling resistor of a Wilson board in a measuring platform;
4) simulating ion current density measurement around a lead in a direct current transmission line by using Wilson boards with different sizes, analyzing the influence of the length, width and thickness of the Wilson boards on ion current density measurement errors based on an ion current density measurement error analysis model, determining the length, width and thickness of the Wilson boards corresponding to the minimum measurement errors, and constructing the ion current measurement device of the current voltage grade by using the length, width and thickness of the Wilson boards corresponding to the minimum errors.
When the Wilson board is used for an 800kV direct current transmission line, the length, the width and the thickness of the corresponding Wilson board with the minimum error are respectively 0.8m, 1m and 0.05m.
When ion current densities around the wires in the direct current transmission line are aligned by using Wilson boards of different sizes, the width direction of the Wilson boards is aligned with the vertical direction of the wires, and the length direction of the Wilson boards is aligned with the direction of the guide.
The ion current density measurement error analysis model constructed in the step 2) is as follows:
Error＝|U/Rz-∫Jds|/∫Jds (6)
wherein Error is the measurement Error of the ion current density.
The invention has the following beneficial effects:
according to the optimization design method of the ion current measuring device suitable for different voltage grades, during specific operation, an ion current density measurement error analysis model is firstly constructed, the ion current density measurement error analysis model is used for analyzing the influence of the length, the width and the thickness of a Wilson board on the ion current density measurement error, and then the ion current measuring device of the current voltage grade is constructed by using the length, the width and the thickness of the Wilson board corresponding to the minimum error, so that the accuracy of the ion current measurement of the high-voltage direct-current transmission line is improved.
Drawings
FIG. 1 is a schematic diagram of a Wilson board measurement;
FIG. 2 is a model diagram of an 800kV DC transmission line;
FIG. 3 is a graph showing a charge density distribution around a conductive line;
FIG. 4 is a graph of ion current density distribution near ground;
FIG. 5 is a graph of ion current measurement points near ground;
FIG. 6 is a diagram of a field coupling model for ion current density measurement;
FIG. 7 is a graph of the effect of different Wilson plate thicknesses on ion current measurement density;
FIG. 8 is a graph of the effect of different Wilson plate widths on measured density of ion current;
FIG. 9 is a graph of the effect of different Wilson plate widths on measured density of ion current;
FIG. 10 is a graph of the effect of shape on ion current measurement density measurement error;
figure 11 is a diagram of the placement of a wilson plate under laboratory conditions.
Detailed Description
The invention is described in further detail below with reference to the accompanying drawings:
at present, the high-voltage direct-current transmission line mainly adopts a positive and negative 800kV direct-current transmission line, the invention takes the transmission line with the voltage grade as an example, and the specific operation process is as follows:
1) calculating an ion flow field around a lead in the positive and negative 800kV direct current transmission line, and extracting the ion current density near the ground as a boundary condition of an ion current error analysis model;
and establishing a high-voltage direct-current power transmission line model by adopting a numerical calculation method, such as a finite element iteration method and an upstream finite element method, calculating the ion current field distribution around the power transmission line, and extracting the ion current density near the ground.
The governing equation of the ion flow field is:
where ρ is the density of space charge; ε is the gas dielectric constant, the current density J is:
wherein k is the mobility of charge movement, E is the electric field strength, the simulation is a static process, the divergence of the current density is constant 0, then the current continuity equation is:
wherein D is a diffusion coefficient, and the expression of D is as follows:
D＝kBTk/e0 (4)
wherein k isBIs the Boltzmann constant, T is the absolute temperature, e0Is an electronic charge.
Fig. 2 is a model of an 800kV dc transmission line with a wilson board placed under the wire for measurement.
FIG. 3 shows the charge density distribution around a conductive line, where the charge density is larger closer to the periphery of the conductive line, and the maximum value of the charge density is 280nC/m3；
Fig. 4 shows the ion current density distribution near the ground, the farther away from the position of the wire, the smaller the ion current density, and since the curve is symmetrical about the wire, 6 positions on the right side of the wire were selected for study, with 6 points on the curve as starting points and the width of the wilson plate as the length of the curve extraction. These extracted curves are then used as dirichlet boundary conditions for an ion current density measurement error analysis model.
And (5) fitting the curve in the figure 4 by using a formula, wherein the fitting result is shown in a formula (5).
Wherein, a0＝5.935，a1＝-5.345，b1＝-8.574，a2＝-3.001，b2＝6.117，a3＝4.094,b3＝-0.4139，a4＝-1.439，b4＝-1.859，a5＝-0.4251，b5＝1.155，a6＝0.6145，b6＝-0.1257，a7＝-0.2261，b7＝-0.2411，a8＝-0.03581，b8＝0.1388，w＝0.04155。
FIG. 5 shows ion current measurement points near the ground, corresponding to the 6 measurement points in FIG. 4, with a 10m distance between each plate.
2) Ion current density measurement error analysis model established based on field path coupling method
Fig. 6 is a field-path coupling model of wilson board measurement, a dashed box represents a path structure of the wilson board, a current source in fig. 6 is the ion current density extraction curve, and RZ and a voltmeter form a path model.
The error in the ion current density measurement is:
Error＝|U/Rz-∫Jds|/∫Jds (6)
3) selection of sampling resistor
The sampling resistance in the measurement platform of the Wilson board is a very important parameter, and the selection principle of the sampling resistance RZ is summarized as follows;
a) the sampling resistance cannot be larger than or close to the resistance of the Wilson board, otherwise, the Wilson board shunts the current on the RZ, and the measurement accuracy is influenced;
b) because the ion current density in the air is very small, the ion current density is generally nA/m2Number order, so the sampling resistance cannot be too small, otherwise, RZThe measured voltage will be less than the range of the measuring device.
4) Selection of Wilson board size parameter
The initial dimensions of the wilson plates are 1m x 0.03m, and fig. 7 shows the effect of different wilson plate thicknesses on the measured density of the ion current, and the measurement error of the wilson plates will increase with increasing thickness. When the thickness is 5cm, the position with the smallest measurement error is at the first Wilson plate, which is 4.7%. When the thickness is 3cm, the measurement error at the same position is 7.7%, which is increased by 3% compared to a Wilson board with a thickness of 5 cm. The wilson plates of different thicknesses all showed minimal values for the measurement error curve at the fifth wilson plate. This is because the measurement principle of the wilson plate is to take the average value of the ion currents as the value of the center of the wilson plate. When the ion current curve on the active Wilson plate is a 45 ° straight line, the measurement error is 0. The greater the asymmetry of the curve acting on the wilson plate, the greater the measurement error, and for economic reasons the thickness of the wilson plate is chosen to be 5cm without increasing it any more.
The length of the Wilson plates in the direction perpendicular to the wires is defined as the width, where the initial dimension of the Wilson plates is 1m 0.05m, as shown in FIG. 8, which illustrates the effect of different Wilson plate widths on the measured density of the ion current. As the wilson plate width increases, the measurement error increases. When the width of the Wilson board is 0.8m, the measurement error is the lowest among all the width-induced measurement errors, and the measurement errors of the Wilson boards at the 1 st and 6 th blocks in the curve are the minimum and the maximum, respectively, and have values of 4% and 4.7%, respectively. When the width of the Wilson board is 1.2m, the measurement error is highest among all the width-caused measurement errors, and the measurement errors of the Wilson boards at the 1 st and 6 th blocks in the curve are respectively the minimum and the maximum, and the values are respectively 6.25% and 7.2%. The errors in the measurement of the wilson plates of the two widths differed by 2.5%. The reasons for this phenomenon are: the narrower the wilson plate, the closer the ion current density on the wilson plate to a 45 ° line.
The length of the Wilson plates along the wire direction is defined as the length, where the initial dimension of the Wilson plates is 1m 0.05m, FIG. 9 illustrates the effect of different Wilson plate widths on the measured density of the ion current. The measurement error is proportional to the length. When the length of the wilson board is 0.8m, the measurement error of the wilson board at this time is the smallest in all the lengths. The measurement errors of the wilson boards at block 1 and 6 in the curve are minimum and maximum, respectively, with values of 3.7% and 4.5%, respectively. When the length of the wilson board is 1.2m, the measurement error is highest among the measurement errors caused by all the widths, and the measurement errors of the wilson board 1 and the wilson board 6 in the curve are respectively the minimum and the maximum, and the values are respectively 6.25% and 7.1%. The Wilson plate error for the two lengths differed by 2.6%. These errors are mainly caused by two factors, firstly the asymmetry of the ion current density curve acting on the plate and secondly the different edge effects caused by the different lengths. The error caused by changing the length is mainly affected by edge effects.
FIG. 10 shows the influence of the shape on the measurement error of the ion current density, where the square size is 1 m.times.1 m.times.0.05 m and the circle area is 1m2The thickness was 0.05m, the dimensions of the rectangle 1 were 0.8 m.times.1 m.times.0.05 m, and the dimensions of the rectangle 2 were 1 m.times.0.8 m.times.0.05 m. As can be seen, the square error is greatest, the circle is next, square 2 is third, and square 1 is fourth. When using square 1 for measurement, the measurement error of the six wilson boards will be less than 5%, so the wilson board design should be referenced to the shape of square 1.
From the above studies we can conclude that: in order to improve the measurement accuracy of Wilson, an ion flow field of an 800kV direct current transmission line is suggested to be 0.8m multiplied by 1m multiplied by 0.05m.
And (3) verification: the ion flow field is measured by Wilson plates of different shapes to verify the correctness of the model, the height of a hall is 2.8m, and the sectional area of a lead is 0.5mm2The voltage levels applied to the wires were 40kV and 50 kV. Since wire size, voltage class, and laboratory space in the laboratory are all smaller than in real engineering, wilson boards need to employ a scaled model. Fig. 11 shows the placement of the wilson boards, with two wilson boards below the wire, board 1 having an area of 0.5m x 0.5m and board 2 having an area of 0.3m x 0.3m, both boards being placed directly below the wire.
Table 1 shows the measurement Error of the wilson board, Error1 represents the actual measurement Error, and Error2 represents the measurement Error of the model calculation. As can be seen from table 1, the actual measurement error of the plate 2 and the measurement error calculated by the model are both smaller than those of the plate 1 at different voltage levels. Meanwhile, when the voltage grade is 50kV, the measurement error and the measurement error calculated by the model are both smaller than the voltage grade of 40 kV. Therefore, it can be considered that the ion current measuring device with different voltage levels needs to optimally design the wilson board, and meanwhile, the length and the width of the wilson board are reduced by a proper amount, so that the measurement accuracy of the wilson board is favorably controlled, and the result of the error analysis model is verified.
TABLE 1
Claims (3)
1. An optimal design method of an ion current measuring device suitable for different voltage levels is characterized by comprising the following steps:
1) calculating an ion flow field around a lead in the direct current transmission line, and extracting the ion current density near the ground as a boundary condition of an ion current density measurement error analysis model;
2) establishing an ion current density measurement error analysis model based on a field coupling method;
3) selecting a sampling resistor of a Wilson board in a measuring platform;
4) simulating the measurement of the ion current density around the wire in the direct current transmission line by using Wilson boards with different sizes, analyzing the influence of the length, width and thickness of the Wilson boards on the measurement error of the ion current density based on an ion current density measurement error analysis model, determining the length, width and thickness of the Wilson board corresponding to the minimum measurement error, and constructing an ion current measurement device of the current voltage grade by using the length, width and thickness of the Wilson board corresponding to the minimum error;
the ion current density measurement error analysis model constructed in the step 2) is as follows:
wherein Error is the measurement Error of the ion current density,Jis the ion current density, and is,Uin order to sample the voltage across the resistor,R Z is a sampling resistor.
2. The method of claim 1, wherein when ion current density around the wire in the dc transmission line is measured by using different sizes of wilson boards, the width direction of the wilson boards is aligned with the vertical direction of the wire, and the length direction of the wilson boards is aligned with the direction of the wire.
3. The method of claim 1, wherein when the method is applied to an 800kV DC transmission line, the length, width and thickness of the Wilson board with the minimum error are 0.8m, 1m and 0.05m, respectively.
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