CN110308332A - Method, system and medium for detecting grounding impedance of substation grounding grid - Google Patents

Abstract

The invention belongs to the field of measurement of grounding impedance of large-scale grounding grids. The invention discloses a grounding impedance detection method, system and medium of a substation grounding grid, including synchronously detecting a response voltage signal with an interference voltage signal superimposed on the grounding resistance, and the response voltage signal corresponds to The excitation current signal is generated by the modulation method that the power source transmits the sinusoidal current at interval intervals; the response voltage signal is obtained by differential demodulation of adjacent periods to obtain a voltage signal that eliminates interference, and then sinusoidal fitting is performed to obtain a sinusoidal voltage signal; according to the fitting The obtained sinusoidal voltage signal is used to calculate the grounding impedance of the substation grounding grid. The present invention only needs to apply a test current once and calculate through software to eliminate the influence of ground network interference on the test, accurately measure the ground impedance value, and carry out targeted real-time anti-interference processing according to the on-site measurement process, with real dynamic anti-interference Interference, and can achieve better interference rejection under the condition of small test current.

Description

Method, system and medium for detecting grounding impedance of substation grounding grid

technical field

The invention belongs to the field of engineering measurement, in particular to the field of measurement of grounding impedance of large-scale grounding grids, and in particular relates to a detection method, system and medium for grounding impedance of substation grounding grids.

Background technique

The grounding network area of the substation is large and the grounding resistance is small. It is very difficult to accurately measure the grounding resistance of large-scale grounding grids under strong external interference. At present, the precision of commonly used measurement methods is relatively low, and the accuracy and reliability of the measurement results are not high. It is necessary to study new measurement methods and measurement devices.

The traditional power frequency high current measurement method is still in use, and its characteristic is to increase the power frequency test current, improve the signal-to-noise ratio, and reduce the measurement error. However, it is difficult to inject a large test current into a large ground grid. The most important factor causing measurement error (sometimes up to several volts in a running substation) is external interference, which can be divided into two parts. One is the induced voltage generated by the external electromagnetic field on the voltage electrode measurement lead (such as the nearby The coupling of the transmission line or equipment), and the second is the voltage drop generated by the interference current in the ground (such as the unbalanced current of the system) on the grounding resistance of the ground grid. The grounding resistance of the substation grounding grid is generally less than 0.5 ohms, and the voltage drop on the grounding resistance of the test current of tens of amperes is not large. The traditional measure to eliminate external interference is the phase inversion method. Not only the measurement workload using the phase inversion method is heavy, but also the external interference before and after the phase inversion changes dynamically, so there are still errors in practical applications. In addition, in addition to the power frequency, there are low frequency, harmonic and high frequency components in the external interference. The reading of the ordinary voltmeter is not the reference value of the power frequency, which will also cause a certain error.

At present, digital measurement technology and instruments have been widely used in the field of power testing. Using them to measure voltage signals has high input impedance, and can be used to process various signals such as Fourier analysis and phase angle difference analysis, and advanced digital signal processing technology can be applied. Noise suppression can simplify the measurement process and improve measurement accuracy.

The dual vector analysis method is an existing grounding resistance measurement method, and the measurement of the grounding resistance by the dual vector analysis method requires the instrument to simultaneously measure current and voltage signals. The current signal is the test current, which is basically power frequency; the voltage signal contains power frequency, harmonics and high frequency components. The dual vector analysis method first performs Fourier decomposition on the signal to obtain the fundamental components of the current and voltage power frequency, so that harmonic and high frequency errors can be avoided. Let U be the fundamental wave voltage of the signal, U ₁ be the voltage drop of the test current I on the grounding resistance, U ₂ be the induced voltage (influence of mutual inductance) of the current in the current electrode measurement lead on the voltage electrode measurement lead, and U ₃ be The voltage drop of the interference current in the ground on the ground resistance, U ₄ is the induced voltage of the external electromagnetic field on the voltage electrode measurement lead. Obviously, there is a definite relationship between U ₁ and U ₂ and the test current, U ₃ and U ₄ have nothing to do with the test current, and their magnitudes and phases are unknown. The fundamental wave voltage of the signal is formula (1-1) and (1-2).

U＝U ₁ +U ₂ +U ₃ +U ₄ (1-1)

U＝IR+jkMI+U _ext (1-2)

In the formulas (1-1) and (1-2), U is the signal fundamental wave voltage, U is the signal fundamental wave voltage, U ₁ is the voltage drop of the test current I on the grounding resistance, and U ₂ is the voltage drop in the current electrode measurement lead. The induced voltage (influence of mutual inductance) of the current on the voltage electrode measurement lead, U ₃ is the voltage drop of the interference current in the ground on the ground resistance, U ₄ is the induced voltage of the external electromagnetic field on the voltage electrode measurement lead, and I is the test Current, R is the grounding resistance, M is the mutual inductance between the leads, U _ext is the external interference voltage (the joint action of U ₃ and U ₄ ), j is the imaginary unit, and k is the mutual inductance coefficient.

The actual external interference is very unstable, but the power frequency fundamental component can be considered relatively stable in a short period of time. Classical theory believes that the grounding resistance is purely resistive. As long as the magnitude of the current I and voltage U and their phase angle difference θ are measured and vector decomposition is carried out to study the resistive component in phase with the current, the mutual inductance between the leads can be eliminated. In this way, the two-phase transmission line can be used as the current line and the voltage line, which simplifies the arrangement of the measurement line.

At the same time, because the measured voltage U contains external disturbance U _tr , its magnitude and the phase relationship between it and the current I are unknown, so the vector decomposition result also contains the influence of external disturbance. Decompose the formula (1-2) into two components, horizontal and vertical, as shown in the following formulas (1-3) and (1-4):

U _cosθ ＝IR+U _it (1-3)

U _sinθ ＝IkM+U _jt (1-4)

In formulas (1-3) and (1-4), U _cosθ and U _sinθ are the two horizontal and vertical components of the signal fundamental voltage U, I is the test current, R is the grounding resistance, M is the mutual inductance between the leads, k is the mutual inductance coefficient, U _it and U _jt are the projections of the external disturbance U _tr on the horizontal direction and the vertical direction of the current respectively, the former does not contain the mutual inductance component, but only the resistive component and U _jt , and the latter contains the inductive component. Since the external interference is basically stable in a short period of time, if two different measurement currents are used under the same wiring condition, two groups of U ₁ , I ₁ , θ ₁ and U ₂ , I ₂ , θ ₂ can be measured. Measured values, corresponding to two sets of vectors, can be decomposed to obtain resistive components as shown in formulas (1-5) and (1-6):

U _1cosθ1 ＝I ₁ R+U _it (1-5)

U _2cosθ2 ＝I ₂ R+U _it (1-6)

In formulas (1-5) and (1-6), U _1cosθ1 and U _2cosθ2 are the horizontal components of the corresponding signal fundamental wave voltage U under two groups of measurement currents I ₁ and I ₂ respectively, and I ₁ and I ₂ are two groups Measure the current, R is the grounding resistance, U _it is the projection of external disturbance U _tr on the horizontal direction of the current. The grounding resistance value can be obtained as shown in formula (1-7):

R＝(U _2cosθ2 -U _1cosθ1 )/(I ₂ -I ₁ ) (1-7)

In formula (1-7), each parameter is the same as in formula (1-5) and (1-6), and formula (1-7) is the basic relational formula of double vector analysis method. However, the dual-vector analysis method only analyzes the fundamental component, and the actual measurement results will be affected by harmonics and high-frequency clutter, and some low-frequency interference in the measurement environment cannot be eliminated, and the anti-interference algorithm is single, and the application scene is single, which may cause measurement The error is large; in addition, assuming that the two-vector analysis method is used on the basis of the three-terminal method or the four-terminal method, the power frequency fundamental component can be considered relatively stable in a short period of time. It is ideal in environmental applications. When power frequency interference or low frequency interference changes, the measurement error caused by it is relatively large, and dynamic anti-interference cannot be realized. Therefore, this method has the deficiency and defect that the dynamic interference cannot be eliminated in principle. At the same time, in the case of large interference, the signal-to-noise ratio can only be improved by increasing the test current, and the anti-interference ability cannot be enhanced from the algorithm.

Contents of the invention

The technical problem to be solved by the present invention: Aiming at the above-mentioned problems of the prior art, a method, system and medium for detecting the grounding impedance of the substation grounding grid are provided. , on the basis of the idea of "phase inversion method" and "interference compensation method" for ground resistance measurement, combined with technologies such as phase-locked loop, program-controlled constant current source and signal processing, an adaptive anti-interference power frequency ground impedance test is proposed Method, by applying the incremental test current with the same frequency and phase as the zero-sequence current, time-sharing measurement of the interference voltage and the composite voltage, only one test current is applied and calculated by the software, the influence of the ground network interference on the test can be eliminated, and the accuracy Measure the ground resistance value. The invention proposes an effective method for ground network self-adaptive anti-jamming power frequency ground impedance testing in order to eliminate interference signals by adopting differential algorithms of different periods during the ground resistance measurement process. By sending the sinusoidal excitation current at intervals as the modulation signal, a response voltage signal is formed on the grounding impedance, which is superimposed with the interference voltage signal formed by the interference current on the grounding resistance. Through synchronous detection and collection of superimposed signals, and then through differential demodulation processing, interference signals are eliminated and response signals of real excitation signals are restored. Finally, the response signal is sinusoidally fitted to obtain its amplitude and phase information, and the grounding impedance is further obtained by using Ohm's law. This method performs targeted real-time anti-interference processing according to the on-site measurement process, has real dynamic anti-interference performance, and can achieve better interference rejection under the condition of a small test current.

In order to solve the problems of the technologies described above, the technical solution adopted in the present invention is:

A method for detecting grounding impedance of a substation grounding grid, the implementation steps comprising:

1) Synchronously detect the response voltage signal superimposed with the interference voltage signal on the grounding resistance, and the excitation current signal corresponding to the response voltage signal is an excitation signal generated by using a modulation method in which the power source sends an interval cycle output sinusoidal current;

2) Differentially demodulating the signals of adjacent periods of the response voltage signal to obtain the voltage signal after the interference is eliminated;

3) performing sinusoidal fitting on the voltage signal after differential demodulation to obtain a sinusoidal voltage signal;

4) Calculate the grounding impedance of the substation grounding grid according to the sinusoidal voltage signal obtained by fitting.

Optionally, step 2) differentially demodulates the signals of adjacent periods of the response voltage signal specifically refers to subtracting the odd number from the response voltage signal in an even period for the response voltage signal in two adjacent periods. The response voltage signal in the cycle is the excitation shunt signal after eliminating the interference voltage signal, wherein the even cycle is the cycle of outputting sinusoidal current, and the odd cycle is the cycle of not outputting sinusoidal current.

Optionally, step 2) further includes the step of subtracting the average value of adjacent odd-period signals from even-period signals to reduce the influence of phase differences when differentially demodulating signals of adjacent periods of the response voltage signal.

Optionally, Step 4) The detailed steps of calculating the grounding impedance of the substation grounding grid according to the fitted sinusoidal current signal include: firstly, obtain the fitted sinusoidal current signal to calculate the effective value U _m of the curve fitting voltage, curve fitting The phase Ф _U of the voltage, and then divide the effective value _{U m} of the curve fitting voltage by the effective value I _m of the applied current to obtain the effective value |Z| The phase Ф _I obtains the voltage and current phase angle difference θ, and then calculates the grounding impedance of the substation grounding network according to the effective value |Z| of the grounding impedance and the voltage and current phase angle difference θ.

A grounding impedance detection system for a substation grounding grid, comprising:

The signal acquisition program unit is used to synchronously detect the response voltage signal superimposed on the grounding resistance with an interference voltage signal, and the excitation current signal corresponding to the response voltage signal is an excitation signal generated by using a modulation method in which the power source sends an interval period to output a sinusoidal current;

The differential demodulation program unit is used to differentially demodulate the signals of adjacent periods of the response voltage signal to obtain the voltage signal after the interference is eliminated;

The sine fitting program unit is used to perform sine fitting on the differentially demodulated voltage signal to obtain a sine voltage signal;

The impedance calculation program unit is used to calculate the grounding impedance of the substation grounding grid according to the sinusoidal voltage signal obtained through fitting.

A grounding impedance detection system of a substation grounding grid includes computer equipment programmed or configured to execute the steps of the method for detecting grounding impedance of a substation grounding grid.

A grounding impedance detection system of a substation grounding grid includes computer equipment, and a computer program programmed or configured to execute the grounding impedance detection method of a substation grounding grid is stored on a storage medium of the computer equipment.

A substation ground grid ground impedance detection system, comprising interconnected signal acquisition equipment, signal processing equipment and signal display equipment, the signal processing equipment is programmed or configured to perform the steps of the substation ground grid ground impedance detection method; or A computer program programmed or configured to execute the method for detecting the grounding impedance of the substation grounding grid is stored on the storage medium of the signal processing device.

A computer-readable storage medium, on which a computer program programmed or configured to execute the grounding impedance detection method of a substation grounding grid is stored.

Compared with the prior art, the present invention has the following advantages:

1. The present invention analyzes the time-domain and frequency-domain characteristics of large-scale ground network interference signals in different environments, and combines the phase-locked loop, program-controlled constant Based on technologies such as current source and signal processing, an adaptive anti-interference power frequency grounding impedance test method is proposed. By applying an incremental test current with the same frequency and phase as the zero-sequence current, the interference voltage and the composite voltage are measured in time-sharing. Once the test current is calculated by software, the influence of ground grid interference on the test can be eliminated, and the grounding impedance value can be accurately measured.

2. The present invention proposes an effective method for ground grid self-adaptive anti-jamming power frequency ground impedance testing in order to eliminate interference signals by using differential algorithms of different periods during the ground resistance measurement process. By sending the sinusoidal excitation current at intervals as the modulation signal, a response voltage signal is formed on the grounding impedance, which is superimposed with the interference voltage signal formed by the interference current on the grounding resistance. Through synchronous detection and collection of superimposed signals, and then through differential demodulation processing, interference signals are eliminated and response signals of real excitation signals are restored. Finally, the response signal is sinusoidally fitted to obtain its amplitude and phase information, and the grounding impedance is further obtained by using Ohm's law. This method performs targeted real-time anti-interference processing according to the on-site measurement process, has real dynamic anti-interference performance, and can achieve better interference rejection under the condition of a small test current.

Description of drawings

Fig. 1 is a schematic flow diagram of the basic process of the method of the embodiment of the present invention.

Fig. 2 is a schematic diagram of a segment of an excitation current signal in a method according to an embodiment of the present invention.

Fig. 3 is a schematic diagram of the principle structure of the system of the embodiment of the present invention.

Detailed ways

As shown in Figure 1, the implementation steps of the method for detecting the grounding impedance of the substation grounding grid in this embodiment include:

1) Synchronously detect the response voltage signal with the interference voltage signal superimposed on the grounding resistance, and the excitation current signal corresponding to the response voltage signal is the excitation signal generated by the modulation method of outputting the sinusoidal current by the power source transmission interval period;

2) Differential demodulation of signals of adjacent periods of the response voltage signal to obtain a voltage signal that eliminates interference;

3) performing sinusoidal fitting on the voltage signal after differential demodulation to obtain a sinusoidal voltage signal;

4) Calculate the grounding impedance of the substation grounding grid according to the sinusoidal voltage signal obtained by fitting.

In this embodiment, a differential anti-interference method based on similar modulation and demodulation is used to test the grounding resistance, and the grounding resistance test needs to be carried out through the cooperation of the power source I and the voltmeter V. The power source I can be either a current source or a voltage source, and is responsible for sending the test current. The frequency of the test current can be 50 Hz of the power frequency, or a different frequency close to or different from the power frequency. The frequency range is not limited to 40-60 Hz . The series circuit model of grounding impedance consists of grounding resistance R and grounding inductance L connected in series. In order to eliminate the interference of the background noise current during the measurement process, especially the interference of the power frequency background noise, the present invention adopts a modulation method in which the power source I first sends an interval cycle output sinusoidal current to generate an excitation signal. Its waveform is shown in Figure 2. Both the sinusoidal current and the interval period are the power frequency period of 20ms, and the output can be regarded as the sequence output of 'with' and 'without' excitation current respectively. According to the characteristics of the modulated excitation current signal, it can be analyzed and judged that the circuit model of grounding impedance is resistance and inductance connected in series. The current sensor detects that since the excitation signal is a periodic "yes" and "no" signal, the detected current signal is a pure interference signal in the period without the excitation signal, and it is an interference signal and an interference signal in the period with the excitation signal. The superposition signal of the excitation signal. Through the synchronous detection technology, such different periodic signals can be effectively separated. And carry out effective differential demodulation through the following effective algorithm, which can greatly eliminate the influence of the same interference, retain the effective excitation current component, and greatly improve the signal-to-noise ratio in the case of a small measurement excitation current, and The method of sinusoidal fitting is further used to obtain accurate signal amplitude and phase information, which greatly improves the calculation accuracy of grounding impedance.

In this embodiment, step 2) demodulates the signal differential of adjacent periods of the response voltage signal specifically refers to subtracting the response voltage signal in the even-numbered period from the response voltage signal in two adjacent periods for the response voltage signal The response voltage signal in the odd-numbered period obtains the excitation shunt signal after eliminating the interference voltage signal, wherein the even-numbered period is a period in which sinusoidal current is output, and the odd-numbered period is a period in which no sinusoidal current is output.

In this embodiment, the model of the measurement signal is established as follows: Assume that the frequency of the power frequency interference signal is f _e +Δ, the frequency of the AM signal is f _e , the period of the AM signal is T _e , and the frequency of the AM and power frequency interference signal The difference is Δ, and the phase of the power frequency interference signal at the beginning of sampling is The amplitude of the AM signal is A _e , and the amplitude of the power frequency interference signal is A _n , then the power frequency interference signal is shown in formula (2-1):

In formula (2-1), X _n (t) is the power frequency interference signal, A _n is the amplitude of power frequency interference signal, f _e is the frequency of AM signal, Δ is the frequency difference between AM and power frequency interference signal, f _e +Δ is the frequency of power frequency interference signal, is the phase of the power frequency interference signal at the beginning of sampling. In this embodiment, the excitation current signal corresponding to the response voltage signal is an excitation signal generated by a modulation method in which the power source transmits a sinusoidal current at interval intervals, so the effective signal of the excitation signal is different in odd and even periods, and the expression is as in formula (2-2 ) as shown:

In formula (2-2), X _e (t) is the AM signal, A _e is the amplitude of the AM signal, f _e is the frequency of the AM signal, k is the number of cycles, T _e is the cycle of the AM signal, and t is time.

Therefore, the signal superimposed on odd and even periods is shown in formula (2-3):

For definitions of symbols in formula (2-3), refer to formula (2-2) and formula (2-1). It can be seen that in the signals superimposed with odd and even periods, the even periods contain interference and AM signals, while the odd periods only contain interference signals.

In order to eliminate the influence of interference, in this embodiment, adjacent even-numbered periods are used to subtract signals in odd-numbered periods, for example, signals in 2k+1 periods are subtracted from signals in 2k+2 periods, and the obtained results are as follows Formula (2-4) shows:

S(t)＝X((2k+1)T+t)-X(2kT+t) 0<t<T (2-4)

In formula (2-4), S(t) is the demodulated signal after adjacent difference, X is the superimposed signal, T is the cycle of the superimposed signal, k is the number of cycles, and t is time. The result of calculating S(t) using formula (2-4) is shown in formula (2-5):

For definitions of symbols in formula (2-5), refer to formula (2-4), formula (2-2) and formula (2-1). Obviously, if the frequency difference Δ=0 between AM and power frequency interference signal, the interference signal will be completely eliminated, on the contrary, if Δ is larger, the amplitude of the interference signal will be greater. It can be seen from formula (2-5) that the impact of interference is directly proportional to the error of the frequency of the power frequency signal and the amplitude of the power frequency signal.

The analysis found that the influence of the frequency leads to the difference of the initial phase of the interference signal in the even cycle and the odd cycle. During demodulation, it also includes the step of subtracting the average value of adjacent odd-period signals from even-period signals to reduce the influence of phase differences. For example, subtract the signal average value in 2k+1 and 2k+3 cycles from the signal in the 2k+2 cycle, as shown in formula (2-6):

S(t)＝X((2k+1)T+t)-(X(2kT+t)+X[(2k+2)T+t])/2 0<t<T (2-6)

For the definition of each symbol in formula (2-6), refer to formula (2-5).

Use the formula (2-6) to calculate the result of S(t) as the formula (2-7):

For the definition of each symbol in formula (2-7), refer to formula (2-5). From the formula (2-7), it can be seen that compared with the subtraction of odd and even periods, the amplitude of the residual signal changes from 2A _n sin(π(f _e +Δ)T) to 2A _n sin ² (π(f _e +Δ )T), that is, 2A _n sin(π(f _e +Δ)/f _e ) to 2A _n sin ² (π(f _e +Δ)/f _e ). If f _e =50, Δ=0.1, A _n =1, the margin of error changes from 2*0.0549 to 2*0.0549*0.0549=0.006 (44.44dB). By comparing with the former method, it can be found that the latter method can significantly suppress the interference under the condition of extremely low signal-to-noise ratio. Formula (2-7) is simplified to formula (2-8):

See formula (2-7) for the definition of symbols in formula (2-8). Where θ is the phase difference between the interference and the power frequency signal. When θ=±90, since the cosine function is used for fitting, the difference is exactly 90 degrees, so the corresponding fitting phases are 0 degrees and 180 degrees respectively. From the formula (2-8), it can be seen that it has nothing to do with the phase.

Sinusoidal fitting is performed on the data after differential demodulation, and then the amplitude and phase information of the response voltage signal that excites the shunt is obtained. In this embodiment, assuming that the response voltage signal of the excitation shunt extracted by differential demodulation satisfies the form of a trigonometric function, then the differential demodulation response voltage signal Xi of the _ith component is as in formula (2-9):

X _i ＝ Acos(θ+Δ _i )+ε _i +C (2-9)

In formula (2-9), A is the amplitude of the differential demodulation response voltage signal of the _i -th component, θ is the phase angle of the differential demodulation response voltage signal of the i-th component, and Δi is the The initial phase of the differential demodulation response voltage signal, ε _i is the error value of the differential demodulation response voltage signal of the i-th component, and C is the DC value of the differential demodulation response voltage signal of the i-th component. And Δ _i =i·2π/400, the sampling period point of the signal is 400.

The above formula (2-9) can be expanded into the following formula (2-10):

x _i =acosΔ _i +bsinΔ _i +c+ε _i (2-10)

In formula (2-10), x _i is the differential demodulation response voltage signal of the i-th component, a is the amplitude of the horizontal component, b is the amplitude of the vertical component, and Δ _i is the differential demodulation response of the i-th component The initial phase of the voltage signal, ε _i is the error value of the differential demodulated response voltage signal of the i-th component, and c is the DC component. Available formula (2-11):

In formula (2-11), A is the amplitude of the differential demodulation response voltage signal, a is the amplitude of the horizontal component of , b is the amplitude of the vertical component, and θ is the phase angle of the differential demodulation response voltage signal.

The fitting obtained by using the least squares method for formula (2-10) is as formula (2-12):

f(a,b,c)=∑ε _i ² ＝∑[ _xi -(acosΔ _i +bsinΔ _i +c)] ² ＝min (2-12)

In formula (2-12), f(a,b,c) is the fitting expression obtained by the least square method, ε _i is the error value of the differential demodulated response voltage signal of the i-th component, and x _i is the i-th The differential demodulation response voltage signal of the first component, a is the amplitude of the horizontal component, b is the amplitude of the vertical component, c is the direct current flow, Δi is the initial phase of the differential demodulation response voltage signal of the _i -th component, and min represents Minimum error value.

The partial derivatives are calculated for the parameters a, b, and c respectively, and the result is formula (2-13):

In formula (2-13), f is the fitting expression obtained by the least square method, x _i is the differential demodulation response voltage signal of the i-th component, and Δ _i is the differential demodulation response voltage signal of the i-th component In the initial phase, a is the amplitude of the horizontal component, b is the amplitude of the vertical component, and c is the DC component.

Formula (2-13) is sorted to get formula (2-14) and (2-15):

In formulas (2-14) and (2-15), matrix B and Y are shown in formulas (2-16) and (2-17), and the rest of the symbols are defined the same as in formula (2-13);

In formulas (2-16) and (2-17), x _i is the differential demodulation response voltage signal of the i-th component, and Δ _i is the initial phase of the differential demodulation response voltage signal of the i-th component. The following formula (2-18) can be obtained:

In formula (2-18), a is the amplitude of the horizontal component, b is the amplitude of the vertical component, and c is the DC component. The matrix B and Y are shown in formulas (2-16) and (2-17). Under the condition of the whole period, the matrices B and Y are:

In formulas (2-19) and (2-20), a is the amplitude of the horizontal component, b is the amplitude of the vertical component, c is the DC component, x _i is the differential demodulation response voltage signal of the i-th component, Δ _i is the initial phase of the differential demodulated response voltage signal of the ith component, and n is the number of components.

In this embodiment, step 4) The detailed steps of calculating the grounding impedance of the substation grounding grid according to the fitted sinusoidal voltage signal include: firstly, obtain the fitted sinusoidal voltage signal to calculate the effective value U _m of the curve fitting voltage, curve fitting Phase Ф _U of the combined voltage, and then divide the effective value U _m of the curve fitting voltage by the effective value I _m of the applied current to obtain the effective value |Z| of the grounding impedance, and subtract the applied current from the phase Ф _U of the curve fitting voltage The phase Ф _I of the voltage and current phase angle difference θ is obtained, and then the grounding impedance of the substation grounding grid is calculated according to the effective value |Z| of the grounding impedance and the voltage and current phase angle difference θ. The effective value of grounding impedance |Z| is shown in the functional expression (2-21); the functional expression of the voltage and current phase angle difference θ is shown in (2-22)

In the formula (2-21), U _m is the effective value of the curve fitting voltage, and I _m is the effective value of the applied current.

In formula (2-22), is the phase of the curve-fitting voltage, is the phase of the applied current.

Therefore, the functional expression (2-23) of the grounding impedance Z of the substation grounding grid is shown;

Z＝R+jX＝|Z|∠θ (2-23)

In formula (2-23), R is the resistance, X is the inductive reactance, θ is the phase angle difference of the voltage and current, the functional expression of the resistance R is shown in (2-24), and the functional expression of the inductive reactance X is (2-25 );

R＝|Z|cosθ (2-24)

In formula (2-24), |Z| is the effective value of the grounding impedance, θ is the phase angle difference of voltage and current.

X＝|Z|sinθ (2-25)

In formula (2-25), |Z| is the effective value of the grounding impedance, and θ is the phase angle difference of voltage and current.

In addition, this embodiment also provides a substation grounding grid grounding impedance detection system, including:

The signal acquisition program unit is used to synchronously detect the response voltage signal superimposed on the grounding resistance with an interference voltage signal, and the excitation current signal corresponding to the response voltage signal is an excitation signal generated by using a modulation method in which the power source sends an interval period to output a sinusoidal current;

The differential demodulation program unit is used to differentially demodulate signals of adjacent periods of the response voltage signal to obtain a voltage signal that eliminates interference;

The sine fitting program unit is used to perform sine fitting on the voltage signal after differential demodulation to obtain a sine voltage signal;

The impedance calculation program unit is used to calculate the grounding impedance of the substation grounding grid according to the sinusoidal voltage signal obtained through fitting.

In addition, this embodiment also provides a grounding impedance detection system for a substation grounding grid, including a computer device, which is programmed or configured to perform the steps of the aforementioned method for detecting the grounding impedance of a substation grounding grid in this embodiment.

In addition, this embodiment also provides a substation grounding grid grounding impedance detection system, including computer equipment, the storage medium of the computer equipment is stored with a computer program that is programmed or configured to perform the above-mentioned substation grounding grid grounding impedance detection method of this embodiment .

In addition, this embodiment also provides a substation grounding grid grounding impedance detection system, as shown in Figure 3, including interconnected signal acquisition equipment, signal processing equipment and signal display equipment, the signal processing equipment is programmed or configured to perform The steps of the aforementioned substation grounding grid grounding impedance detection method in this embodiment; or the storage medium of the signal processing device stores a computer program programmed or configured to execute the aforementioned substation grounding grid grounding impedance detection method in this embodiment.

In addition, this embodiment also provides a computer-readable storage medium, on which a computer program programmed or configured to execute the method for detecting the grounding impedance of a substation grounding grid described above in this embodiment is stored.

The above descriptions are only preferred implementations of the present invention, and the protection scope of the present invention is not limited to the above-mentioned embodiments, and all technical solutions under the idea of the present invention belong to the protection scope of the present invention. It should be pointed out that for those skilled in the art, some improvements and modifications without departing from the principles of the present invention should also be regarded as the protection scope of the present invention.

Claims (9)

1. A substation grounding grid grounding impedance detection method is characterized in that the implementation steps include: 1) Synchronously detect the response voltage signal superimposed with the interference voltage signal on the grounding resistance, and the excitation current signal corresponding to the response voltage signal is an excitation signal generated by using a modulation method in which the power source sends an interval cycle output sinusoidal current; 2) Differential demodulation of signals of adjacent periods of the response voltage signal to obtain a voltage signal that eliminates interference; 3) performing sinusoidal fitting on the voltage signal after differential demodulation to obtain a sinusoidal voltage signal; 4) Calculate the grounding impedance of the substation grounding grid according to the sinusoidal voltage signal obtained by fitting. 2. The substation grounding grid grounding impedance detection method according to claim 1, characterized in that, step 2) specifically refers to the response voltage signal, for two adjacent Response voltage signal in a cycle Subtract the response voltage signal in an even cycle from the response voltage signal in an odd cycle to obtain a voltage signal that eliminates interference, where the even cycle is the cycle that outputs sinusoidal current, and the odd cycle is the cycle that does not output sinusoidal current. 3. The substation grounding grid grounding impedance detection method according to claim 2, characterized in that, step 2) when demodulating the signal difference of the adjacent periods of the response voltage signal, it also includes subtracting the adjacent odd period from the signal of the even period A step that averages a periodic signal to reduce the effects of phase differences. 4. the substation grounding grid grounding impedance detection method according to claim 1, is characterized in that, step 4) according to the detailed step of the sinusoidal voltage signal that fitting obtains, calculates the grounding impedance of substation grounding grid comprising: first obtain the fitting obtained The sinusoidal voltage signal calculates the effective value U _m of the curve fitting voltage and the phase Ф _U of the curve fitting voltage, and then divides the effective value U _m of the curve fitting voltage by the effective value I _m of the applied current to obtain the effective value of the grounding impedance| _Z |, subtract the phase Ф _U of the applied current from the phase Ф U of the curve fitting voltage to obtain the phase angle difference θ of the voltage and current, and then calculate the substation grounding according to the effective value |Z| of the grounding impedance and the phase angle difference θ of the voltage and current The grounding impedance of the network. 5. A substation grounding grid grounding impedance detection system, characterized in that it comprises: The signal acquisition program unit is used to synchronously detect the response voltage signal superimposed on the grounding resistance with the interference voltage signal, and the excitation current signal corresponding to the response voltage signal is an excitation signal generated by using a modulation method in which the power source sends an interval period to output a sinusoidal current; The differential demodulation program unit is used to differentially demodulate signals of adjacent periods of the response voltage signal to obtain a voltage signal that eliminates interference; The sine fitting program unit is used to perform sine fitting on the voltage signal after differential demodulation to obtain a sine voltage signal; The impedance calculation program unit is used to calculate the grounding impedance of the substation grounding grid according to the sinusoidal voltage signal obtained through fitting. 6. A substation grounding grid grounding impedance detection system, comprising computer equipment, characterized in that the computer equipment is programmed or configured to perform the steps of the substation grounding grid grounding impedance detection method according to any one of claims 1-4. 7. A substation grounding grid grounding impedance detection system, including computer equipment, characterized in that, the computer equipment is stored on the storage medium programmed or configured to perform the substation grounding grid grounding described in any one of claims 1 to 4. A computer program for the impedance detection method. 8. A substation grounding grid grounding impedance detection system, comprising interconnected signal acquisition equipment, signal processing equipment and signal display equipment, characterized in that the signal processing equipment is programmed or configured to perform any of the following claims 1-4. A step of the substation grounding grid grounding impedance detection method; or the storage medium of the signal processing device is programmed or configured to perform the substation grounding grid grounding impedance detection method according to any one of claims 1 to 4 computer program. 9. A computer-readable storage medium, characterized in that the computer-readable storage medium is stored with a computer program that is programmed or configured to perform the grounding impedance detection method for substation grounding grids described in any one of claims 1 to 4 .