CN112924758A - Impulse grounding resistance measurement method based on pilot frequency impedance - Google Patents

Impulse grounding resistance measurement method based on pilot frequency impedance Download PDF

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CN112924758A
CN112924758A CN202110100271.4A CN202110100271A CN112924758A CN 112924758 A CN112924758 A CN 112924758A CN 202110100271 A CN202110100271 A CN 202110100271A CN 112924758 A CN112924758 A CN 112924758A
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张占龙
李一釥
旦乙画
叶华睿
邓军
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Chongqing University
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Abstract

The invention relates to an impulse grounding resistance measuring method based on pilot frequency impedance, belonging to the technical field of operation and management of power transmission and transformation equipment, comprising the following steps: s1: selecting lightning current waveforms with different waveform parameters, researching the frequency spectrum characteristics and the energy characteristics of the lightning current subjected to period extension to obtain a frequency spectrum graph and an energy spectrum graph of the lightning current, and determining a concentrated frequency range and a measuring frequency point of the amplitude and the energy of the lightning current; s2: researching the impedance response of the grounding electrode in the frequency range to obtain the numerical value of the end potential of the grounding electrode under different frequencies; s3: and providing a time domain response expression of the end part electric potential of the grounding electrode containing unknown characteristic parameters, carrying out forward Fourier transform on the time domain response expression to obtain an impedance response expression containing the unknown parameters, and determining the characteristic parameters in the expression according to an undetermined coefficient method. The method can more accurately measure the impulse grounding resistance value, reduces the calculated amount, and effectively realizes the accurate and efficient measurement of the tower impulse grounding resistance.

Description

Impulse grounding resistance measurement method based on pilot frequency impedance
Technical Field
The invention belongs to the technical field of operation and management of power transmission and transformation equipment, and relates to an impulse grounding resistance measuring method based on pilot frequency impedance.
Background
The accurate measurement of the impulse grounding resistance of the grounding device has important engineering significance for effective lightning protection of the transmission line tower. When lightning impulse current flows through the tower grounding device, a complex electromagnetic transient process is generated with the surrounding soil environment, and the grounding performance is difficult to evaluate by adopting a general expression. Therefore, accurate measurement of impulse grounding resistance has always been an important issue in the field of grounding.
At present, a great deal of research is carried out at home and abroad on the electromagnetic transient process with complex surrounding space when impact current flows through a grounding electrode. Gupta provides an empirical formula and a method for calculating the inductance of a center grounding network and an angle grounding network of a square grounding network, and the effectiveness of an analysis method is verified through a model test. Velazquez the impact properties of the earth electrode were evaluated from a numerical analysis perspective by programming the relevant computer program. The M.I.Lorentzou establishes an electromagnetic transient program considering the mutual coupling effect between the conductors of the grounding system, and researches the influence of the mutual coupling effect of the conductors on the system response. Visacro proposes a method for measuring the change of the resistivity and the dielectric constant of the soil in a typical lightning current frequency component range, and corrects the values of the resistivity and the dielectric constant of the soil. Ramamoort adopts the concept of complex resistivity, and researches the influence of ground capacitance on the high-frequency transient performance of a grounding grid through a moment method numerical calculation method. Hablanic carries out simulation modeling on a simple grounding system and a complex grounding system buried in uniform or non-uniform soil, and provides a simulation model based on a finite element method aiming at the ionization phenomenon of the soil around the grounding system. And the transient process of the earth electrode under the action of the impact current can be accurately described by the calculation method of the finite difference time domain numerical value, which is provided by adopting a Maxwell equation set and a space-time variable resistivity function by the G.Ala. A, C, Liew establishes a dynamic model for describing the characteristics of a plurality of concentrated grounding nonlinear surge currents, can accurately describe the fluctuation behavior of soil under the action of high-frequency impact currents, and provides a theoretical basis for the proposal of a surge suppression factor in the test process. A Jinliang team considers dynamic and nonlinear effects of soil ionization around the grounding electrode, builds a transient characteristic analysis model of the grounding electrode under the action of lightning impulse, and provides a calculation formula of the effective impact length of the grounding electrode. The Cao bin studies a Fourier form of a lightning current waveform expression, and proposes a thought of converting transient lightning impulse response into steady-state response by taking decomposed sine waves as excitation to be loaded on a grounding device.
The research mainly focuses on the electromagnetic transient process of soil around a grounding electrode under the action of lightning impulse and the forward Fourier change process of lightning current, and does not solve the problems of frequency range selection and time-frequency response conversion of a grounding device after lightning current decomposition. The existing impulse grounding resistance measuring method mainly comprises an impulse coefficient method and a field measuring method, wherein the impulse coefficient method cannot accurately reflect the impulse characteristics of a tower grounding electrode under the action of lightning stroke, and easily causes the problems of inaccurate calculation result and the like; the field measurement rule requires a worker to carry an impulse current source, and the overlarge power supply equipment and the complicated terrain environment increase the difficulty and the labor cost for accurately measuring the tower impulse grounding resistance.
Therefore, it is an urgent problem to provide a method for measuring impulse grounding resistance with small calculation amount, high measurement accuracy and high environmental adaptability.
Disclosure of Invention
In view of the above, the present invention aims to obtain a narrow frequency range and a small number of measurement frequency points representing the amplitude and energy characteristics of a lightning current by performing forward fourier transform and energy analysis after extending the waveform period of the lightning current, measure the impedance response of a grounding electrode in the narrow frequency range, determine characteristic parameters in an expression by using an undetermined coefficient method in combination with a time domain expression of the end potential of the grounding electrode containing unknown parameters, and provide a method for measuring impulse grounding resistance based on pilot frequency impedance, so as to obtain a more accurate impulse grounding resistance value.
In order to achieve the purpose, the invention provides the following technical scheme:
a method for measuring impulse grounding resistance based on pilot frequency impedance comprises the following steps:
s1: selecting lightning current waveforms with different waveform parameters, researching the frequency spectrum characteristics and the energy characteristics of the lightning current subjected to period extension to obtain a frequency spectrum graph and an energy spectrum graph of the lightning current, and determining a concentrated frequency range and a measuring frequency point of the amplitude and the energy of the lightning current;
s2: researching the impedance response of the grounding electrode in the frequency range to obtain the numerical value of the end potential of the grounding electrode under different frequencies;
s3: and providing a time domain response expression of the end part electric potential of the grounding electrode containing unknown characteristic parameters, carrying out forward Fourier transform on the time domain response expression to obtain an impedance response expression containing the unknown parameters, and determining the characteristic parameters in the expression according to an undetermined coefficient method.
Further, the resistivity of the soil is 150 Ω · m, the length of the grounding electrode is 10m, the buried depth is 0.8m, and the radius of the grounding electrode is 0.006 m.
Further, the step S1 specifically includes the following steps:
s11: selecting lightning current with waveform parameters of 2.6/50 mus and amplitude of 10kA to obtain a double-exponential function representing the waveform parameters and carrying out periodic continuation to obtain a calculation model;
s12: obtaining a lightning current function period and fundamental wave frequency according to the calculation model; carrying out forward Fourier transform on the periodically extended double-exponential function to obtain a discrete spectrogram of a lightning current function;
s13: according to the Pasval power conservation theorem, the lightning energy under different frequency points is obtained and the energy proportion distribution of different frequency ranges is solved; and determining a concentrated frequency range and a small number of measuring frequency points of the lightning current amplitude and the energy according to the lightning current spectrogram and the energy proportion map.
Further, in step S11, the double exponential function of the waveform parameter is:
I(t)＝10474×(e-14790t-e-1877833t) (1)。
further, in step S12, performing forward fourier transform on the periodically extended dual-exponential function to obtain expressions of a continuous periodic dual-exponential function dc component and an nth harmonic component:
Figure BDA0002905665620000031
Figure BDA0002905665620000032
wherein Im＝1×104Substituting the formula (2) and (3) with α -147900 and β -1877833 to obtain a discrete spectrogram of the lightning current; with harmonic frequency kf0The amplitude spectrum decays and eventually approaches zero, increasing, i.e. the higher the frequency, the more the current amplitude approaches zero.
Further, in step S13, the total energy of the lightning current is:
Figure BDA0002905665620000033
the total energy of the lightning current is obtained by bringing the values of alpha, beta and M into formula (4): w is 3.62 × 103And substituting different frequency values to obtain the energy sizes of different frequencies, thereby obtaining the energy proportion distribution of different frequency ranges.
Further, in the lightning current spectrogram and the energy proportion map obtained in step S1, the amplitude of the lightning current is mainly concentrated in the low frequency part; 2.6/50 mu s of lightning current energy is mainly concentrated in 0-10 kHz, wherein the energy of the lightning current in the frequency range of 0 kHz-10 kHz is the most, and accounts for 90% of the total energy of the lightning current;
according to fundamental frequency
Figure BDA0002905665620000034
Measuring only the frequency point f in the low frequency range of 0-10 kHz0～f3The frequency response of the grounding electrode is realized, so that the purpose of accurately obtaining a time domain response expression of the end part of the grounding electrode is achieved.
Further, step S2 specifically includes the following steps:
and measuring the impedance response of the grounding electrode at different measuring frequency points by using a tripolar method according to the obtained measuring frequency range and measuring frequency points to obtain the numerical value of the potential of the end part of the grounding electrode at the measuring frequency points.
Further, in step S2, the grounding electrode length L is 10m, and the linear distance L between the potential measuring electrode P and the tower foundation is set to be shorter than the linear distance L between the potential measuring electrode P and the tower foundationPG2.5L-25 m, the linear distance L of the current pole C from the tower baseCG＝4L＝40m；
With infinity as a reference point, the potential of the ground should be:
Figure BDA0002905665620000041
the potential difference generated by the grounding body current I between the grounding electrode G and the voltage electrode P is:
Figure BDA0002905665620000042
similarly, the potential difference generated between the grounding body G and the voltage pole P by the current I flowing through the recycling current pole C is:
Figure BDA0002905665620000043
the voltage between the GPs obtained by the superposition theorem is:
Figure BDA0002905665620000044
further, step S3 specifically includes the following steps:
providing an earth electrode end potential time domain response expression U (t) a.e containing unknown parametersb·t+c·ed·tAnd carrying out forward Fourier transform on U (t) to obtain an impedance response expression containing unknown parameters, wherein the frequency domain response of the potential at the end part of the grounding electrode meets the formula U-Z.I, the amplitude of the injection current is set to be 1A, and the following equation is obtained:
Figure BDA0002905665620000045
the equations are solved simultaneously to obtain the numerical values of a, b, c and d, so that the impulse grounding resistance is as follows:
Figure BDA0002905665620000046
the invention has the beneficial effects that: compared with an impact coefficient method, the method can more accurately measure the impact grounding resistance value, select a low-frequency range and a small number of measuring frequency points, and greatly reduce the calculated amount. In addition, the field measurement method has the problems of overlarge equipment, poor environmental adaptability and the like, and the accurate and efficient measurement of the tower impulse grounding resistance can be effectively realized.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by the means of the instrumentalities and combinations particularly pointed out hereinafter.
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For the purposes of promoting a better understanding of the objects, aspects and advantages of the invention, reference will now be made to the following detailed description taken in conjunction with the accompanying drawings in which:
FIG. 1 is a time domain calculation model diagram of a lightning current after a period extension;
FIG. 2 is a 2.6/50 μ s lightning current discrete spectrum diagram;
FIG. 3 is a 2.6/50 μ s lightning current energy ratio graph;
FIG. 4 is a general flow diagram of the method of the present invention.
Detailed Description
The embodiments of the present invention are described below with reference to specific embodiments, and other advantages and effects of the present invention will be easily understood by those skilled in the art from the disclosure of the present specification. The invention is capable of other and different embodiments and of being practiced or of being carried out in various ways, and its several details are capable of modification in various respects, all without departing from the spirit and scope of the present invention. It should be noted that the drawings provided in the following embodiments are only for illustrating the basic idea of the present invention in a schematic way, and the features in the following embodiments and examples may be combined with each other without conflict.
Wherein the showings are for the purpose of illustrating the invention only and not for the purpose of limiting the same, and in which there is shown by way of illustration only and not in the drawings in which there is no intention to limit the invention thereto; to better illustrate the embodiments of the present invention, some parts of the drawings may be omitted, enlarged or reduced, and do not represent the size of an actual product; it will be understood by those skilled in the art that certain well-known structures in the drawings and descriptions thereof may be omitted.
The same or similar reference numerals in the drawings of the embodiments of the present invention correspond to the same or similar components; in the description of the present invention, it should be understood that if there is an orientation or positional relationship indicated by terms such as "upper", "lower", "left", "right", "front", "rear", etc., based on the orientation or positional relationship shown in the drawings, it is only for convenience of description and simplification of description, but it is not an indication or suggestion that the referred device or element must have a specific orientation, be constructed in a specific orientation, and be operated, and therefore, the terms describing the positional relationship in the drawings are only used for illustrative purposes, and are not to be construed as limiting the present invention, and the specific meaning of the terms may be understood by those skilled in the art according to specific situations.
As shown in FIG. 4, the invention provides an impulse grounding resistance measurement method based on different-frequency impedance, which is characterized in that according to the design requirements of DL/T5092-1999 technical code for designing 110-500 kV overhead power transmission lines, the method selects the soil resistivity of 150 Ω · m, the grounding electrode length of 10m, the buried depth of 0.8m and the grounding electrode radius of 0.006m for analysis, and comprises the following steps:
step 1: the method comprises the steps of selecting lightning current waveforms with different waveform parameters, researching the frequency spectrum characteristics and the energy characteristics of the lightning current after period extension to obtain a frequency spectrum graph and an energy spectrum graph of the lightning current, and determining the concentrated frequency range and the measuring frequency point of the amplitude and the energy of the lightning current.
Step 1, selecting a double-exponential function to represent the waveform characteristics of lightning current, selecting the lightning current with the waveform parameter of 2.6/50 mus and the amplitude of 10kA, and obtaining the double-exponential function representing the waveform parameter as follows:
I(t)＝10474×(e-14790t-e-1877833t) (1)
the double-exponential function representing the lightning current characteristic is a non-periodic function, and in order to obtain the current amplitude of the lightning current at different frequency points, the formula (1) is subjected to periodic continuation. Considering that the time value of the current amplitude is zero is one period, T equals 400 μ s, as shown in fig. 1. And (3) carrying out forward Fourier transform on the double-exponential function subjected to periodic continuation to obtain expressions of a continuous periodic double-exponential function direct-current component and an nth harmonic component:
Figure BDA0002905665620000061
Figure BDA0002905665620000062
wherein Im＝1×104The discrete spectrum of the lightning current obtained by substituting the formula (2) (3) with α -147900 and β -1877833 is shown in fig. 2. With harmonic frequency kf0The amplitude spectrum decays and eventually approaches zero as it increases. I.e. the higher the frequency, the more the current amplitude goes to zero. According to a Fourier series expression of forward decomposition and a Pasval power conservation theorem, namely, energy contained in the lightning current is constantly equal to the sum of energy of each component in a complete orthogonal function set, the total energy of the lightning current in a time domain is equal to the total energy in a frequency domain, and the total energy of the lightning current is obtained as follows:
Figure BDA0002905665620000063
the total energy of the lightning current can be obtained by bringing the values of α, β and M into formula (4): w is 3.62 × 103Bringing different frequency values into the available valuesThe energy of different frequencies is obtained, and further the energy proportion distribution of different frequency ranges is obtained.
TABLE 12.6/50 μ s lightning current frequency component amplitude values
Figure BDA0002905665620000064
Figure BDA0002905665620000071
And obtaining the energy distribution of the lightning current according to a Fourier series expression of forward decomposition and the Pasval power conservation theorem.
TABLE 22.6/50 μ s lightning current energy distribution
Frequency range/kHz Angular frequency range/(rad/s) (Energy)
0～0.1 0 98.6
0.1～1 15708 834
1～10 31415.9 2180
10～100 47123.9 477
100～1000 62831.8 0.155
As can be seen from fig. 3, table 1 and table 2, the harmonic frequency kf is associated with0The amplitude spectrum decays and eventually approaches zero as it increases. I.e. the higher the frequency, the more the current amplitude goes to zero. The 2.6/50 mu s lightning current energy is mainly concentrated in 0-10 kHz, wherein the energy of the lightning current in the frequency range of 0 kHz-10 kHz is the most, and accounts for 96.7% of the total energy of the lightning current.
In summary, by studying the amplitude characteristic and the energy characteristic of the lightning current at 2.6/50 μ s, it can be known that the amplitude and the energy of the lightning current are mainly concentrated in the low frequency part. When analyzing the frequency domain response of the grounding electrode, according to the frequency of the fundamental wave
Figure BDA0002905665620000072
Measuring only the frequency point f in the low frequency range of 0-10 kHz0～f3The frequency response of the grounding electrode can achieve the purpose of accurately obtaining the time domain response expression of the end part of the grounding electrode.
Step 2: and (4) researching the impedance response of the grounding electrode in the frequency range to obtain the numerical value of the end potential of the grounding electrode under different frequencies.
The end part electric potential of the grounding electrode at different frequency points can be measured by a tripolar method, and if the length of the grounding electrode is L-10 m, the linear distance L between the potential measuring electrode P and the tower foundation of the tower is measuredPG2.5L-25 m, the linear distance L of the current pole C from the tower baseCG＝4L＝40m。
With infinity as a reference point, the potential of the ground should be:
Figure BDA0002905665620000073
the potential difference generated by the grounding body current I between the grounding electrode G and the voltage electrode P is:
Figure BDA0002905665620000074
similarly, the potential difference generated between the grounding body G and the voltage pole P by the current I flowing through the recycling current pole C is:
Figure BDA0002905665620000081
the voltage between the GPs obtained by the superposition theorem is:
Figure BDA0002905665620000082
the end potential of the earth electrode at different frequency points can be measured by a tripolar method. Current injected into the earth electrode 1A at frequency f0～f3Calculating U by combining equations (5) to (8)0～U3。
And step 3: and providing a time domain response expression of the end part electric potential of the grounding electrode containing unknown characteristic parameters, carrying out forward Fourier transform on the time domain response expression to obtain an impedance response expression containing the unknown parameters, and determining the characteristic parameters in the expression according to an undetermined coefficient method.
The impulse grounding resistance is the ratio of the maximum value of the grounding electrode potential and the peak value of the lightning current when the lightning current flows through the grounding electrode. Under the action of complete lightning current impact, the change of the end potential conforms to the characteristics of a double-exponential function, and the time-domain response expression of the end potential is U (t) a.eb·t+c·ed·t. And (4) carrying out forward Fourier transform on the U (t) to obtain an impedance response expression containing unknown parameters. The frequency domain response of the end potential of the grounding electrode meets the formula U-Z.I, the amplitude of the injection current is set to be 1A, and the following equation is obtained:
Figure BDA0002905665620000083
the numerical values of a, b, c and d can be obtained by simultaneously solving the equations. a is 2.24 × 105，b＝-1.54×104，c＝-2.25×105，d＝-2.53×106. The time domain response of the earth terminal potential is expressed as
Figure BDA0002905665620000084
Therefore, the impulse grounding resistance is:
Figure BDA0002905665620000085
finally, the above embodiments are only intended to illustrate the technical solutions of the present invention and not to limit the present invention, and although the present invention has been described in detail with reference to the preferred embodiments, it will be understood by those skilled in the art that modifications or equivalent substitutions may be made on the technical solutions of the present invention without departing from the spirit and scope of the technical solutions, and all of them should be covered by the claims of the present invention.

Claims (10)

1. A method for measuring impulse grounding resistance based on pilot frequency impedance is characterized in that: the method comprises the following steps:
s1: selecting lightning current waveforms with different waveform parameters, researching the frequency spectrum characteristics and the energy characteristics of the lightning current subjected to period extension to obtain a frequency spectrum graph and an energy spectrum graph of the lightning current, and determining a concentrated frequency range and a measuring frequency point of the amplitude and the energy of the lightning current;
s2: researching the impedance response of the grounding electrode in the frequency range to obtain the numerical value of the end potential of the grounding electrode under different frequencies;
s3: and providing a time domain response expression of the end part electric potential of the grounding electrode containing unknown characteristic parameters, carrying out forward Fourier transform on the time domain response expression to obtain an impedance response expression containing the unknown parameters, and determining the characteristic parameters in the expression according to an undetermined coefficient method.
2. The impulse grounding resistance measurement method based on pilot frequency impedance according to claim 1, characterized in that: the resistivity of the soil is 150 omega m, the length of the grounding electrode is 10m, the buried depth is 0.8m, and the radius of the grounding electrode is 0.006 m.
3. The impulse grounding resistance measurement method based on pilot frequency impedance according to claim 2, characterized in that: the step S1 specifically includes the following steps:
s11: selecting lightning current with waveform parameters of 2.6/50 mus and amplitude of 10kA to obtain a double-exponential function representing the waveform parameters and carrying out periodic continuation to obtain a calculation model;
s12: obtaining a lightning current function period and fundamental wave frequency according to the calculation model; carrying out forward Fourier transform on the periodically extended double-exponential function to obtain a discrete spectrogram of a lightning current function;
s13: according to the Pasval power conservation theorem, the lightning energy under different frequency points is obtained and the energy proportion distribution of different frequency ranges is solved; and determining a concentrated frequency range and a small number of measuring frequency points of the lightning current amplitude and the energy according to the lightning current spectrogram and the energy proportion map.
4. The impulse grounding resistance measurement method based on pilot frequency impedance according to claim 3, characterized in that: the double exponential function of the waveform parameter in step S11 is:
I(t)＝10474×(e-14790t-e-1877833t) (1)。
5. the impulse grounding resistance measurement method based on pilot frequency impedance according to claim 4, characterized in that: in step S12, forward fourier transform is performed on the cyclic extended double-exponential function to obtain expressions of the continuous cyclic double-exponential function dc component and the nth harmonic component:
Figure FDA0002905665610000011
Figure FDA0002905665610000012
wherein Im＝1×104Substituting the formula (2) and (3) with α -147900 and β -1877833 to obtain a discrete spectrogram of the lightning current; with harmonic frequency kf0The amplitude spectrum decays and eventually approaches zero, increasing, i.e. the higher the frequency, the more the current amplitude approaches zero.
6. The impulse grounding resistance measurement method based on pilot frequency impedance according to claim 5, characterized in that: in step S13, the total energy of the lightning current is:
Figure FDA0002905665610000021
the total energy of the lightning current is obtained by bringing the values of alpha, beta and M into formula (4): w is 3.62 × 103And substituting different frequency values to obtain the energy sizes of different frequencies, thereby obtaining the energy proportion distribution of different frequency ranges.
7. The impulse grounding resistance measurement method based on pilot frequency impedance according to claim 6, characterized in that: in the lightning current spectrogram and the energy proportion map obtained in the step S1, the amplitude of the lightning current is mainly concentrated in the low frequency part; 2.6/50 mu s of lightning current energy is mainly concentrated in 0-10 kHz, wherein the energy of the lightning current in the frequency range of 0 kHz-10 kHz is the most, and accounts for 90% of the total energy of the lightning current;
according to fundamental frequency
Figure FDA0002905665610000022
Measuring only the frequency point f in the low frequency range of 0-10 kHz0～f3The frequency response of the grounding electrode is obtained, so that the time domain response expression of the end part of the grounding electrode is accurately obtainedThe purpose is.
8. The impulse grounding resistance measurement method based on pilot frequency impedance according to claim 2, characterized in that: step S2 specifically includes the following steps:
and measuring the impedance response of the grounding electrode at different measuring frequency points by using a tripolar method according to the obtained measuring frequency range and measuring frequency points to obtain the numerical value of the potential of the end part of the grounding electrode at the measuring frequency points.
9. The impulse grounding resistance measurement method based on pilot frequency impedance according to claim 8, characterized in that: in step S2, the grounding electrode length is 10m, and the linear distance L between the potential measuring electrode P and the tower footing is 10mPG2.5L-25 m, the linear distance L of the current pole C from the tower baseCG＝4L＝40m；
With infinity as a reference point, the potential of the ground should be:
Figure FDA0002905665610000023
the potential difference generated by the grounding body current I between the grounding electrode G and the voltage electrode P is:
Figure FDA0002905665610000024
similarly, the potential difference generated between the grounding body G and the voltage pole P by the current I flowing through the recycling current pole C is:
Figure FDA0002905665610000031
the voltage between the GPs obtained by the superposition theorem is:
Figure FDA0002905665610000032
10. the impulse grounding resistance measurement method based on pilot frequency impedance according to claim 2, characterized in that: step S3 specifically includes the following steps:
providing an earth electrode end potential time domain response expression U (t) a.e containing unknown parametersb·t+c·ed·tAnd carrying out forward Fourier transform on U (t) to obtain an impedance response expression containing unknown parameters, wherein the frequency domain response of the potential at the end part of the grounding electrode meets the formula U-Z.I, the amplitude of the injection current is set to be 1A, and the following equation is obtained:
Figure FDA0002905665610000033
the equations are solved simultaneously to obtain the numerical values of a, b, c and d, so that the impulse grounding resistance is as follows:
Figure FDA0002905665610000034
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