A method for solving the protection distance between medium and short wave radio stations and ultra-high voltage transmission lines

Abstract

The present invention provides a method for solving the protection distance between medium and short wave radio stations and ultra-high voltage transmission lines, including the following steps: establishing a mathematical model of passive interference of five iron towers with rough soil ground; solving the induced current on the transmission line by the moment method, so as to find out the interference level of the ultra-high voltage transmission circuit to the medium and short wave radio station; using a vertically polarized plane wave for excitation, first determining the incident wave angle when the passive interference maximum value appears in the whole frequency band, and then constructing a curve of the passive interference extreme value with the protection distance through the values ​​obtained by multiple cycles, so as to obtain the protection distance under the specified limit. The present invention is no longer based on a good conductor ground, but adopts a rough ground model that fits the actual situation. By determining the incident wave angle and the resonant frequency when the passive interference extreme value appears, a fitting function is constructed and solved, so that the obtained protection distance value is more accurate.

Description

Technical Field

[0001] The invention belongs to the field of electromagnetic compatibility of ultra-high voltage power transmission and transformation projects, and specifically is a method for solving the protection distance between a medium-wave and short-wave radio station and an ultra-high voltage power transmission line after taking rough ground into account. Background Art

[0002] In recent years, China's UHV transmission technology has been leading the world. The development of UHV transmission lines has reduced the transportation cost of electric energy, reduced line corridors, and solved the problems of reverse distribution of energy resources and energy demand and regional network interconnection in my country. However, while building UHV power grids, the electromagnetic compatibility problem between UHV transmission lines and nearby radio stations along the lines has become increasingly apparent. Compared with high-voltage and ultra-high-voltage transmission lines, the newly built UHV transmission lines currently use double circuits or even multiple circuits on the same tower, which increases the height of the tower. There must be a certain difference between the passive interference of the UHV transmission lines and the high-voltage and ultra-high-voltage lines, and there is no national standard for the protection distance between UHV transmission lines and nearby radio stations. On the other hand, existing studies have regarded the earth as a pure conductor and ignored the resistivity of the soil. Obviously, this simplified processing method will have a certain impact on the calculation of passive interference of transmission lines. Therefore, after considering the rough ground, it is of certain significance to study the solution method of the protection distance between UHV transmission lines and nearby radio stations.

[0003] At present, there is limited research on the passive interference problem of UHV transmission lines in China. In previous studies, there were some problems in the solution methods for UHV transmission lines and nearby radio stations. For example, the earth was treated as an ideal conductor in the calculation model; the angle selection of the incident plane wave and the determination of the resonant frequency point were not rigorous enough, and there was no comprehensive analysis and research on the incident wave angle and resonant frequency when the passive interference extreme value appeared.

[0004] The present invention models the transmission line and the rough ground, and based on the established five-tower solution model, by determining the incident wave angle and the resonant frequency when the passive interference extreme value appears, constructs and solves the fitting function, and develops a solution method for the protection distance between medium and short wave radio stations and ultra-high voltage transmission lines. Summary of the invention

[0005] The purpose of the present invention is to take into account the rough ground environment in which the actual transmission line is erected, and by determining the incident wave angle and the resonant frequency when the passive interference extreme value appears, construct and solve the fitting function, thereby providing a method for solving the protection distance between medium and short wave radio stations and ultra-high voltage transmission lines.

[0006] In order to achieve the above-mentioned object of the invention, the present invention is implemented by the following technical solutions:

[0007] A method for solving the protection distance between a medium-wave and short-wave radio station and an ultra-high voltage transmission line, the method comprising the following steps:

[0008] Step 1: In combination with the topographical features of the UHV transmission lines in my country, several typical rough ground surfaces are constructed based on the four-component model proposed by Schmugge and Wang. The present invention selects sandy loam ground as the research object, substitutes the roughness parameters of the rough surface into the exponential spectral power density function, and generates a geometric model of the sandy loam ground using a linear filtering method;

[0009] Step 2: Based on the actual spatial truss structure of the tower in the UHV transmission line, a tower line model with actual tower size was established. Vertically polarized plane waves were used to simulate the electromagnetic wave signals emitted by medium and short wave stations, thereby establishing a five-tower solution model for solving the protection distance between medium and short wave radio stations and UHV transmission lines;

[0010] Step 3: Simulate the five-tower solution model established in step 2 to obtain the electric field integral equation of the transmission line, and solve it using the moment method to obtain the induced current on the transmission line, and then calculate the passive interference level of the UHV transmission line to the nearby radio stations;

[0011] Step 4: Based on the passive interference level of the transmission line to the radio station obtained in step 3, the protection distance is solved. First, a protection distance is assumed, and the plane wave incident angle when the passive interference extreme value appears in the full frequency band is determined. If the passive interference extreme value exceeds the specified limit at this plane wave incident angle, the protection distance is increased. After multiple cycles and binary divisions, the appropriate protection distance interval is obtained. Finally, a curve of the passive interference extreme value changing with the protection distance is constructed through the function fitting method, and the curve is solved to obtain the protection distance value.

[0012] By comparing with the traditional method for solving the protection distance between the transmission line and the radio station, the protection distance value calculated by the method adopted in the present invention is larger, which can effectively solve the problem of abnormal operation of the radio station caused by passive interference from the transmission line due to mistakenly establishing the radio station within the error range of the protection distance solved by the traditional algorithm. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 The invention discloses a geometric model of sandy loam ground based on a method for solving a protection distance between a medium- and short-wave radio station and an ultra-high voltage transmission line.

[0014] Figure 2 The invention discloses a solution model for passive interference of five iron towers based on a solution method for the protection distance between medium and short wave radio stations and ultra-high voltage transmission lines.

[0015] Figure 3 The present invention discloses a solution process of a method for solving a protective spacing between a medium-wave and short-wave radio station and an ultra-high voltage transmission line.

[0016] Figure 4 The invention discloses a method for solving the protection distance between medium and short wave radio stations and ultra-high voltage transmission lines, which is based on the passive interference level under omnidirectional excitation of a plane wave at a frequency of 1.2 MHz.

[0017] Figure 5 The invention discloses a method for solving the protection distance between medium and short wave radio stations and ultra-high voltage transmission lines, and provides a full-band passive interference level at each protection distance. DETAILED DESCRIPTION

[0018] The present invention will be further described below by describing a preferred specific embodiment in detail in conjunction with the accompanying drawings.

[0019] Step 1: Modeling of rough ground. This step includes the following steps:

[0020] Step 1.1, combined with the topographical features of the transmission lines in my country, based on the four-component soil model proposed by Schmugge and Wang, a variety of typical rough ground are constructed. In this embodiment, the sandy loam ground type is selected. This rough ground type has a fixed soil moisture w v =0.2g / m 3 and soil temperature T = 28 °C, the parameters are: sand content (S) 51.5%, clay content (C) 13.5%, RMS height 1.1 cm, correlation length 6.3 cm and relative dielectric constant 9.6674-j0.6010.

[0021] Step 1.2, substitute the sandy loam surface roughness parameters in step 1.1 into the power spectral density function of the exponential distribution, and use the linear filtering method to generate the geometric model of the sandy loam surface, as shown in Figure 1 shown.

[0022] Step 2: Construct a solution model for the five-tower system, such as Figure 2 This step includes the following steps:

[0023] Step 2.1, select the tower type. In this embodiment, a typical "steel"-shaped tower is selected with a tower height of 86.5 m.

[0024] Step 2.2: In this embodiment, the excitation adopts a vertically polarized plane wave, so the conductors and ground wires in the transmission line are ignored, and the electric field strength of the excitation electromagnetic wave is 1V / m. Five iron towers are selected, the tower spacing is 500m, the ground is the sandy loam rough ground in step 1, the transmission line is distributed on the x-axis, and the observation point P(0,D a ,2) Moving along the positive half of the y-axis, the angle between the plane wave and the positive direction of the x-axis is the incident angle

[0025] Step 3: Solve the passive interference level of the transmission line. This step includes the following steps:

[0026] Step 3.1, according to the dyadic Green's function and the vector wave equation, we can get Figure 2 The integral equation of the electric field line at the midfield point P in the five-base iron tower model shown is:

[0027]

[0028] In the formula, E i (P) is the field intensity of the incident electromagnetic wave; l is the unit vector in the direction of the central axis of each equivalent thin-wire structure of the iron tower; g(P,P'(l')) is the Green's function; I(l) is the line current density in the direction of the central axis of each equivalent thin-wire structure of the iron tower, I(l) = 2πaJ(l), J(l) is the induced current density on the transmission line, and a is the radius of the equivalent thin wire.

[0029] Step 3.2, use the moment method to solve the electric field integral equation in step 3.1, where the basis function selects the pulse basis function and the test function selects the Diracδ test function, which can solve the induced current in the transmission line and then obtain the scattered field of the transmission line.

[0030] Step 3.3, after obtaining the scattered field of the transmission line in step 3.2, the passive interference problem of the transmission line to the radio station can be solved. The passive interference level to the transmitting and receiving antennas is expressed in decibels:

[0031]

[0032] In the formula, E 有输电线路 It represents the superimposed electric field strength at the observation point when the transmission line exists; E 无输电线路 Represents the electric field strength at the observation point when there is no transmission line.

[0033] Step 4, solving the protection distance, the overall solution process is as follows Figure 3 This step includes the following steps:

[0034] Step 4.1, the solution model of the protection distance is based on Figure 2The five-tower model shown in FIG. 1 is a five-tower model. In this embodiment, the initial protection distance D is selected. a The initial observation point is P(0,3800,2) if the altitude is 3800m. The range of the incident angle of the vertically polarized plane wave is 245°-295°, and the calculation frequency band is selected as the frequency band of medium and short wave radio stations, 0.3MHz-30MHz, with a step size of 0.1MHz, for a total of 298 points.

[0035] Step 4.2, first find the plane wave incident angle corresponding to the maximum value of passive interference at each protection distance If the interference extreme value exceeds 0.4dBV / m selected in this embodiment, the protection distance is increased in steps of 100m. When the protection distance is increased to 4000m, the extreme value of passive interference is less than 0.4dBV / m, and the frequency corresponding to this extreme value is 1.2MHz. The plane wave incident angle It is 293°.

[0036] Step 4.3: To ensure that the plane wave incident angle is the maximum at the extreme frequency, perform a plane wave omnidirectional Stimulus test, the results are as follows Figure 4 As shown, it is found that the passive interference extreme value still appears in the direction

[0037] In step 4.4, use the binary search method to shorten the protection distance interval obtained in step 4.2. When the length of the protection distance interval is less than 15m, stop the binary search. At this time, the protection distance interval is [3987.5,4000]. Figure 5 is the full-band passive interference level at each protection distance.

[0038] Step 4.5, select the five sets of protection distance values ​​and passive interference extreme values ​​D obtained in the solution process of steps 4.2 and 4.4 x1 =3900 and S x1 =0.4178, D x2 =3950 and S x2 =0.410003, D x3 =3975 and S x3 =0.405168, D x4 =3987.5 and S x4 =0.402522, D x5 =4000 and S x5 =0.398725. Through the above five sets of data, a quadratic fitting curve is fitted using the curve fitting method:

[0039] f(D x )=-10.42332+0.00567D x -7.41828×10-7 ·D x 2 (3)

[0040] Let f(D x )=0.4, and we get D x The protection distance without interference is 3997m. Table 1 shows the relevant data in the protection distance solution process of the method of the present invention.

[0041] Table 1 Data list of the optimization algorithm during the calculation process (allowable interference: 0.4dBV / m)

[0042]

[0043] Step 4.6, using the traditional protection distance algorithm to solve the protection distance of this embodiment, the protection distance is 3712.5m. Table 2 shows the relevant data in the process of solving the protection distance by the traditional method.

[0044] Table 2 Data list of the traditional algorithm during the calculation process (allowable interference: 0.4dBV / m)

[0045]

[0046] It can be seen that compared with the protection distance obtained by the traditional method, the protection distance obtained by the method adopted in the present invention has a larger range. Combined with the actual engineering significance, it avoids the abnormal operation caused by the passive interference of the transmission line due to the radio station being mistakenly established within the error range of the protection distance solved by the traditional algorithm.

[0047] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. After reading the above content, various modifications and substitutions of the present invention will be obvious to those skilled in the art. Therefore, the protection scope of the present invention shall be defined by the attached claims.

Claims

1. A method for solving the protection distance between medium and short wave radio stations and ultra-high voltage transmission lines, characterized in that: The method comprises the following steps: Step 1: select a rough ground type based on the topographical features of the UHV transmission lines in my country; Step 2: According to the actual spatial truss structure of the tower in the UHV transmission line, a tower line model that matches the actual tower size is established, and a model for solving the protection distance between the medium and short wave radio stations and the UHV transmission line is constructed, and vertically polarized plane waves are used for excitation; Step 3, performing simulation calculation on the solution model established in step 2, and solving it by using the moment method, wherein the basis function selects the pulse basis function, and the test function selects the Dirac δ test function, thereby obtaining the passive interference level of the passive interference to the radio station; Step 4, based on the solution model in step 2 and the simulation results in step 3, solve the protection distance; first determine the plane wave incident angle when the passive interference extreme value appears in the full frequency band. If the passive interference extreme value exceeds the specified limit at this plane wave incident angle, increase the protection distance, and obtain a suitable protection distance interval after multiple cycles and binary divisions; finally, through the function fitting method, construct a curve of the passive interference extreme value changing with the protection distance, solve the curve, and obtain the protection distance value.

2. The method for solving the protection distance between medium and short wave radio stations and ultra-high voltage transmission lines according to claim 1 is characterized in that: In the step 1, the roughness parameter of the selected rough ground is substituted into the exponential spectral power density, and a geometric model of the corresponding rough ground is generated by using a linear filtering method.

3. The method for solving the protection distance between medium and short wave radio stations and ultra-high voltage transmission lines according to claim 1 is characterized in that: In the step 2, in the simulation calculation model, a vertically polarized plane wave is used for excitation.

4. The method for solving the protection distance between medium and short wave radio stations and ultra-high voltage transmission lines according to claim 1 is characterized in that: In the step 3, the method of moments is used to solve the simulation, the basis function selects the impulse basis function, and the test function selects the Dirac δ test function.

5. The method for solving the protection distance between medium and short wave radio stations and ultra-high voltage transmission lines according to claim 1 is characterized in that: In step 4, the incident angle range of the vertically polarized plane wave is given and the incident angle of the plane wave when the passive interference extreme value appears in the full frequency band is determined, five groups of protection spacing values ​​and passive interference extreme values ​​are selected in the solution process, and a quadratic fitting curve is fitted, and the curve function is made equal to the passive interference limit value, thereby obtaining the protection spacing value.

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