A Harmonic Source Tracing Method Based on Fault Recording

Abstract

The present invention discloses a harmonic tracing method based on fault recording. The technical solution adopted by the present invention is as follows: synchronously obtain the fault recording data of each measurement node in the regional power grid; perform fundamental wave power flow calculation to obtain the fundamental wave voltage phase of each measurement node; perform Fourier analysis on the fault recording data to obtain the harmonic voltage amplitude, voltage phase angle deviation, harmonic current amplitude and current phase angle deviation of each measurement node; determine the harmonic voltage phase angle and harmonic current phase angle of each measurement node; generate a power grid admittance matrix according to the accurate parameters of the line and transformer; calculate the open-circuit voltage and short-circuit current on the power grid side of the port to be traced; form a Norton model on the power grid side at the port to be traced; calculate the equivalent harmonic current and impedance of the port to be traced. According to the existing fault recording system, the present invention can perform harmonic tracing on the regional power grid without adding new power quality monitoring equipment, and quantitatively analyze the characteristics of harmonic sources, which is convenient for timely carrying out harmonic control.

Description

Technical Field

[0001] The present invention belongs to the technical field of power grid power quality, and specifically relates to a harmonic tracing method based on fault recording. Background Art

[0002] In recent years, power grid power quality problems have become increasingly serious. In particular, the waveform distortion problem caused by harmonics is prominent, and in severe cases, electrical equipment is damaged. The grid harmonic exceeding the standard is usually the 5th and 7th harmonics, and the harmonic sources are complex. In order to ensure the power grid power quality, it is necessary to carry out harmonic tracing among multiple substations and multiple loads to determine the pollution sources affecting the grid harmonics.

[0003] Traditional power grid harmonic tracing is obtained by installing a large number of power quality monitoring devices and comprehensively analyzing the power quality measurement data of each node. In the actual power grid, the coverage rate of power quality monitoring points is very low. Taking the Zhejiang power grid as an example, power quality monitoring devices are only installed at some special loads and new energy sites, and the monitoring coverage rate is about 20%. The power quality monitoring coverage rate of the Zhejiang power grid ranks among the top in the country, but it is still not enough to cover the main nodes of the power grid. The monitoring ratio on the load side is even lower, and the harmonic analysis on the load side requires on-site tests by staff. The number of power quality monitoring devices configured in the power grid is temporarily insufficient to carry out large-scale harmonic tracing.

[0004] Therefore, when there is a power quality problem in a local area, a large number of devices and human resources are often assembled to conduct temporary monitoring on each node in the area, and it is difficult to cover comprehensively, and the simultaneity of measurement data cannot be guaranteed. Compared with power quality monitoring devices, the fault recording configuration in substations is very comprehensive and can basically cover all intervals of 110 kV and above. However, the fault recording system is a power grid transient data monitoring and acquisition system, which mainly monitors power grid faults and has no harmonic monitoring function.

[0005] In summary, providing a method for carrying out large-scale power quality online monitoring by using the existing power grid transient data acquisition system and automatically analyzing the dominant harmonic source is an urgent problem for those skilled in the art at present. Summary of the Invention

[0006] In view of this, the technical problem to be solved by the present invention is to overcome the defects of the above-mentioned existing technologies, and provide a harmonic tracing method based on fault recording, which is realized by the existing fault recording system and identifies the amplitude and direction of each harmonic current of the harmonic source according to the harmonic power flow.

[0007] To achieve the above object, the present invention adopts the following technical solutions: A harmonic tracing method based on fault recording, which includes:

[0008] Step 1), synchronously obtain the fault recording data of each measurement node in the regional power grid;

[0009] Step 2), perform fundamental wave power flow calculation to obtain the fundamental wave voltage phase θ of each measurement node;

[0010] Step 3), perform Fourier analysis on the fault recording data to obtain the harmonic voltage amplitude U h of each measurement node, the voltage phase angle deviation Δθ h , the harmonic current amplitude I h and the current phase angle deviation ΔФ h ; According to the fundamental wave voltage phase θ, the voltage phase angle deviation Δθ h and the current phase angle deviation ΔФ h , determine the harmonic voltage phase angle θ h and the harmonic current phase angle Ф h of each measurement node;

[0011] Step 4), generate the network admittance matrix Y according to the accurate parameters of the line and transformer; use the measured current outside the port to be traced as the injection quantity of the admittance matrix Y, and calculate the open-circuit voltage and short-circuit current on the grid side of the port to be traced; form the Norton model of the grid side at the port to be traced;

[0012] Step 5), calculate the equivalent harmonic current and impedance of the port to be traced according to the harmonic current and voltage measurement results at the tracing port and the Norton model of the grid side.

[0013] Furthermore, in Step 1), the timing-triggered recording technology is adopted to synchronously obtain the fault recording data of each measurement node in the regional power grid.

[0014] Furthermore, in Step 1), the timing-triggered recording technology is as follows: remotely synchronously trigger the recording through the recording master station; when conditions are met, trigger the recording through setting or substation time pulses.

[0015] Furthermore, in Step 1), automatically identify, eliminate, and correct incorrect data through the network topology model and SCADA data.

[0016] Furthermore, in Step 1), synchronize each recording data according to the recording time through the interpolation resampling technology.

[0017] Furthermore, in Step 2), the calculation of the fundamental wave power flow is as follows: the fault recorder measures the fundamental wave active power P and fundamental wave reactive power Q of each branch of the power grid, and calculates the fundamental wave voltage amplitude V and phase angle θ of each measurement node in the power grid through formula (1):

[0018]

[0019] Wherein, for a given power grid with n nodes, the node numbers of the power grid are i ∈ {1, 2... n}, which is a set of integers from 1 to n, and the slack node is set as the nth node; the fundamental injection active power and fundamental injection reactive power of the ith node are P i and Q i respectively; the fundamental voltage amplitude and phase angle of the ith node are V i and θ i respectively;

[0020] According to the power grid topology, P i and Q i are expressed as functions of V1, V2... V n and θ1, θ2... θ n ; P i and Q i are input quantities, V1, V2... V n and θ1, θ2... θ n are quantities to be solved, and V1, V2... V n and θ1, θ2... θ n are calculated by means of numerical iteration; k is the number of iteration calculations, and ΔP i (k) , ΔV i (k) , are respectively the active power error, reactive power error, voltage amplitude error and voltage phase angle error of the ith node in the kth iteration calculation.

[0021] Furthermore, in step 3), the Fourier analysis is as follows: The waveform f(t) is recorded by the fault recorder, and the amplitude A h and phase angle

[0022] of the waveform f(t) at the hth harmonic frequency are obtained by Fourier analysis through formula (2). When analyzing the voltage of the fault recorder, let U h = A h , When analyzing the current of the fault recorder, let I h = A h ,

[0023]

[0024] Wherein, F h represents the Fourier analysis function of the waveform f(t), T represents the time period of Fourier analysis, and ω represents the angular frequency of the power grid power frequency voltage.

[0025] The harmonic voltage phase angle θ h and harmonic current phase angle φ of each measurement node are determined through formula (3).h :

[0026] θ h = θ + Δθ h , φ h = θ + Δφ h (3).

[0027] Furthermore, in step 4), the diagonal elements of matrix Y are the self-admittances of the nodes, and the self-admittance of a node is the sum of the admittances of the branches electrically connected to the node; the off-diagonal elements of matrix Y are the mutual admittances of the nodes, and the mutual admittance between nodes is the negative value of the sum of the admittances of the branches connecting the two nodes;

[0028]

[0029] In the formula, y n1,h , y 1n,h , y nn,h respectively represent the element in the first column of the nth row, the element in the nth column of the first row, and the element in the nth column of the nth row of matrix Y under the hth harmonic condition.

[0030] Even further, the harmonic voltage vector U and the harmonic current vector I are respectively defined by formulas (5) and (6). The values of U and I are the measured harmonic voltage and current of the branch monitored by the fault recorder, and there is a mathematical relationship of formula (7) between U and I:

[0031] U = [U 1,h U 2,h …U N,h T (5)

[0032] I = [I 1,h I 2,h …I N,h T (6)

[0033] I = YU (7)

[0034] In the formula, U n,h , I n,h respectively represent the measured values of the hth harmonic voltage and current of branch n monitored by the fault recorder.

[0035] Furthermore, in step 5), for an electrical network with N nodes, when analyzing the Norton equivalent model of the external circuit of the kth node, first, the external circuit of node k is virtually opened, that is, the kth row of the harmonic current vector I is set to zero, and the harmonic voltage vector U' is calculated using formula (7). The kth row element of U' is the open-circuit voltage U OFF ; secondly, the external circuit of node k is virtually short-circuited, the kth row of the harmonic voltage vector U is set to zero, and the harmonic current vector I' is calculated using formula (7). The kth row element of I' is the short-circuit current I​​SH , I SH is the equivalent harmonic current of the harmonic Norton equivalent model, and the equivalent impedance Z of the harmonic Norton model nor see Equation (8):

[0036] Z nor = U OFF / I SH (8).

[0037] The beneficial effects of the present invention are as follows: Based on the existing fault recording system, the present invention can trace the harmonics of the regional power grid without adding new power quality monitoring equipment, and quantitatively analyze the characteristics of harmonic sources, that is, identify the amplitude and direction of each harmonic current of the harmonic source, which is convenient for timely harmonic control. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained according to the provided drawings without creative efforts.

[0039] Figure 1 is a schematic flow chart of the harmonic tracing method of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0040] The present invention will be described in detail below with reference to the drawings of the specification and the specific embodiments.

[0041] This embodiment provides a harmonic tracing method based on fault recording, as Figure 1 shown, and the steps are as follows:[[]]

[0042] Step 1), synchronously obtain the fault recording data of each measurement node in the regional power grid;

[0043] Step 2), perform fundamental wave power flow calculation to obtain the fundamental wave voltage phase θ of each measurement node;

[0044] Step 3), perform Fourier analysis on the fault recording data to obtain the harmonic voltage amplitude U h , voltage phase angle deviation Δθ h , harmonic current amplitude I h and current phase angle deviation ΔФ h ; according to the fundamental wave voltage phase θ, voltage phase angle deviation Δθ h and current phase angle deviation ΔФ h , determine the harmonic voltage phase angle θ h and harmonic current phase angle Ф h of each measurement node;

[0045] Step 4), according to the accurate parameters of the line and transformer, generate the network admittance matrix Y; taking the measured current outside the port to be traced as the injection quantity of the admittance matrix Y, calculate the open-circuit voltage and short-circuit current on the grid side of the port to be traced; form the Norton model of the grid side at the port to be traced.

[0046] Step 5), according to the harmonic current and voltage measurement results at the tracing port and the Norton model of the grid side, calculate the equivalent harmonic current and impedance of the port to be traced.

[0047] Specifically, in step 1), the timing-triggered waveform recording technology is adopted to synchronously obtain the fault waveform recording data of each measurement node in the regional power grid. The timing-triggered waveform recording technology is as follows: remotely synchronously trigger the waveform recording through the waveform recording master station; when conditions are met, trigger the waveform recording by setting or substation time pulses.

[0048] Specifically, in step 1), through the network topology model and SCADA data, automatically identify, eliminate, and correct incorrect data. Synchronize each waveform recording data according to the waveform recording time through the interpolation resampling technology.

[0049] Specifically, in step 2), the fundamental power flow is calculated as follows: the fault recorder measures the fundamental active power P and fundamental reactive power Q of each branch of the power grid, and calculates the fundamental voltage amplitude V and phase angle θ of each measurement node in the power grid through formula (1):

[0050]

[0051] In the formula, for a given n-node power grid, the node numbers i of each node in the power grid belong to the set {1, 2... n}, which is the set of integers from 1 to n, and the balanced node is set as the nth node; the fundamental injected active power and fundamental injected reactive power of the ith node are P i , Q i respectively; the fundamental voltage amplitude and phase angle of the ith node are V i , θ i respectively;

[0052] According to the power grid topology, P i , Q i are expressed as functions of V1, V2... V n and θ1, θ2... θ n ; P i , Q i are input quantities, V1, V2... V n and θ1, θ2... θ n are quantities to be solved, and calculate V1, V2... V n and θ1, θ2... θ n through numerical iteration; k is the number of iterative calculations, ΔPi (k) and ΔV i (k) and are the active power error, reactive power error, voltage magnitude error, and voltage phase angle error calculated for the i-th node at the k-th iteration, respectively.

[0053] Specifically, in step 3), the Fourier analysis is as follows: The waveform f(t) is recorded by the fault recorder, and the amplitude A of the waveform f(t) at the h-th harmonic frequency is obtained through Fourier analysis using formula (2). h and phase angle

[0054] When analyzing the voltage of the fault recorder, denote U h = A h , When analyzing the current of the fault recorder, denote I h = A h ,

[0055]

[0056] where F h represents the Fourier analysis function of the waveform f(t), T represents the time period of the Fourier analysis, and ω represents the angular frequency of the power grid's power frequency voltage.

[0057] The harmonic voltage phase angle θ h and harmonic current phase angle φ h are determined through formula (3):

[0058] θ h = θ + Δθ h , φ h = θ + Δφ h (3).

[0059] Specifically, in step 4), the diagonal elements of the matrix Y are the node self-admittances, and the node self-admittance is the sum of the admittances of the branches electrically connected to the node; the non-diagonal elements of the matrix Y are the node mutual admittances, and the node mutual admittance between two nodes is the negative of the sum of the admittances of the branches connecting the two nodes.

[0060]

[0061] where y n1,h , y 1n,h , y nn,h represent the element in the n-th row and 1st column, the element in the 1st row and n-th column, and the element in the n-th row and n-th column of the matrix Y in the case of the h-th harmonic, respectively.

[0062] The harmonic voltage vector U and the harmonic current vector I are respectively defined by formulas (5) and (6). The values of U and I are the measured harmonic voltage and current values of the monitored branch of the fault recorder. There is a mathematical relationship of formula (7) between U and I:

[0063] U = [U 1,h U 2,h …U N,h T (5)

[0064] I = [I 1,h I 2,h …I N,h T (6)

[0065] I = YU (7)

[0066] In the formula, U n,h and I n,h respectively represent the measured values of the h-th harmonic voltage and current of the monitored branch n of the fault recorder.

[0067] In step 5), for the electrical network with N nodes, when analyzing the Norton equivalent model of the external circuit of the k-th node, first, the external circuit of the k-th node is virtually opened, that is, the k-th row of the harmonic current vector I is set to zero, and the harmonic voltage vector U' is calculated using formula (7). The k-th row element of U' is the open-circuit voltage U OFF ; secondly, the external circuit of the k-th node is virtually short-circuited, the k-th row of the harmonic voltage vector U is set to zero, and the harmonic current vector I' is calculated using formula (7). The k-th row element of I' is the short-circuit current I SH , I SH is the equivalent harmonic current of the harmonic Norton equivalent model, and the equivalent impedance Z nor of the harmonic Norton model is shown in formula (8):

[0068] Z nor = U OFF / I SH (8).

[0069] The above has introduced in detail the harmonic tracing method based on fault recording provided by the present invention. Specific examples are used in this article to elaborate on the principle and implementation manner of the present invention. The description of the above embodiments is only used to help understand the method and its core idea of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.​​

Claims

1. A harmonic tracing method based on fault recording, characterized in that, Including: Step 1), synchronously acquiring the fault recording data of each measurement node in the regional power grid; Step 2), performing fundamental power flow calculation to obtain the fundamental voltage phase θ of each measurement node; Step 3), perform Fourier analysis on the fault recording data to obtain the harmonic voltage amplitude U of each measurement node h , the voltage phase angle deviation Δθ h , the harmonic current amplitude I h and the current phase angle deviation ΔФ h ; According to the fundamental wave voltage phase θ, the voltage phase angle deviation Δθ h and the current phase angle deviation ΔФ h , determine the harmonic voltage phase angle θ h and the harmonic current phase angle Ф h of each measurement node; Step 4), generating the network admittance matrix Y according to the accurate parameters of lines and transformers; Taking the measured current outside the port to be traced as the injection quantity of the admittance matrix Y, calculating the open-circuit voltage and short-circuit current on the grid side of the port to be traced; forming the Norton model of the grid side at the port to be traced; Step 5), calculating the equivalent harmonic current and impedance of the port to be traced according to the measurement results of harmonic current and voltage at the tracing port and the Norton model of the grid side; In Step 2), the calculation of the fundamental power flow is as follows: The fault recorder measures the fundamental active power P and fundamental reactive power Q of each branch of the power grid, and calculates the fundamental voltage amplitude V and phase angle θ of each measurement node in the power grid through formula (1): In the formula, for a given n - node power grid, the node numbers of the power grid are \(i\in\{1,2,\cdots,n\}\), which is the set of integers from 1 to n, and the slack node is set as the n - th node; the fundamental - wave injected active power and fundamental - wave injected reactive power of the \(i\) - th node are \(P\) i and \(Q\) i respectively; the fundamental - wave voltage amplitude and phase angle of the \(i\) - th node are \(V\) i and \(\theta\) i respectively; According to the power grid topology, P i and Q i are represented by functions of V1, V2…V n and θ1, θ2…θ n ; P i and Q i are input quantities, V1, V2…V n and θ1, θ2…θ n are the quantities to be solved, and V1, V2…V n and θ1, θ2…θ n are calculated by means of numerical iteration; k is the number of iterative calculations, and ΔP i (k) , ΔQ i (k) , ΔV i (k) , and Δθ i (k) are respectively the active power error, reactive power error, voltage amplitude error, and voltage phase angle error of the i-th node in the k-th iterative calculation.

2. The harmonic tracing method based on fault recording according to claim 1, wherein In Step 1), the timing trigger recording technology is adopted to synchronously acquire the fault recording data of each measurement node in the regional power grid.

3. A harmonic tracing method based on fault recording according to claim 2, characterized in that, In Step 1), the timing trigger recording technology is: remotely synchronously triggering the recording through the recording master station; when conditions are met, triggering the recording by setting or substation time pulses.

4. A harmonic tracing method based on fault recording according to claim 1, characterized in that, In Step 1), through the network topology model and SCADA data, automatically identify, eliminate and correct incorrect data.

5. A harmonic tracing method based on fault recording according to claim 1, characterized in that, In Step 1), synchronize each recording data according to the recording time through the interpolation resampling technology.

6. The harmonic tracing method based on fault recording according to claim 1, wherein In step 3), the Fourier analysis is as follows: The waveform f(t) is recorded by the fault recorder, and the amplitude A of the waveform f(t) at the hth harmonic frequency is obtained through Fourier analysis by formula (2) h , phase angle When analyzing the voltage of the fault recorder, record U h = A h , When analyzing the current of the fault recorder, record I h = A h , where F h represents the Fourier analysis function of the waveform f(t), T represents the time period of the Fourier analysis, and ω represents the angular frequency of the power grid power frequency voltage; Determine the harmonic voltage phase angle θ of each measurement node through formula (3) h and the harmonic current phase angle φ h : θ h = θ + Δθ h , φ h = θ + Δφ h (3).

7. A harmonic tracing method based on fault recording according to claim 1, characterized in that, In Step 4), the diagonal elements of the matrix Y are the node self-admittances, and the node self-admittance is the sum of the admittances of the branches electrically connected to the node; the non-diagonal elements of the matrix Y are the node mutual admittances, and the mutual admittance between nodes is the negative value of the sum of the admittances of the branches connecting the two nodes; where y n1,h , y 1n,h , y nn,h respectively represent the element in the first column of the n-th row, the element in the n-th column of the first row, and the element in the n-th column of the n-th row of matrix Y in the case of the h-th harmonic.

8. A harmonic tracing method based on fault recording according to claim 7, characterized in that, The harmonic voltage vector U and harmonic current vector I are respectively defined by formula (5) and formula (6), the values of U and I are the measured values of harmonic voltage and current of the branches monitored by the fault recorder, and there is a mathematical relationship of formula (7) between U and I: U = [U 1,h U 2,h …U n,h T (5)​ I = [I 1,h I 2,h …I n,h T (6)​ I = YU (7) Where U n,h and I n,h respectively represent the measured values of the h-th harmonic voltage and current of the monitoring branch n of the fault recorder.

9. A harmonic tracing method based on fault recording according to claim 8, characterized in that, In step 5), for the electrical network with N nodes, when analyzing the Norton equivalent model of the external circuit of the k-th node, first, virtually open the external circuit of the k-th node, that is, set the k-th row of the harmonic current vector I to zero, and calculate the harmonic voltage vector U′ using formula (7). The k-th row element of U′ is the open-circuit voltage U of the port. OFF Secondly, virtually short-circuit the external circuit of the k-th node, set the k-th row of the harmonic voltage vector U to zero, and calculate the harmonic voltage vector I′ using formula (7). The k-th row element of I′ is the short-circuit current I of the port. SH , I SH is the equivalent harmonic current of the harmonic Norton equivalent model, and the equivalent impedance Z of the harmonic Norton model nor is shown in formula (8): Z nor = U OFF / I SH (8).

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