Power distribution network fault positioning method based on negative sequence parameter distribution characteristics

Abstract

The invention provides a power distribution network fault positioning method based on negative sequence parameter distribution characteristics. The method specifically comprises the following steps of identifying whether a power distribution line fault occurs or not; if a fault occurs, collecting fault voltage and current information, and extracting voltage and current fundamental frequency components; and voltage and current negative-sequence components are obtained through conversion. And identifying the feeder line with the maximum negative sequence current at the outlet as a fault line. And defining the space between the first two terminals with opposite phases of the fault line as a fault interval. And upstream and downstream negative sequence voltage distribution functions are established, and simultaneous equation set solving is carried out. And outputting a ranging result. According to the technical scheme, the problem that fault distance measurement and accurate fault positioning cannot be further realized on the basis of accurate fault line selection and accurate section positioning in the prior art is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of distribution network fault location, and in particular to a distribution network fault location method based on negative sequence parameter distribution characteristics. Background Art

[0002] Distribution network fault location technology helps to quickly repair and eliminate faults, prevent faults from expanding, and help to quickly restore power supply. It has gone through three development stages: fault line selection, fault section location, and fault distance measurement. It is of great significance to improving power supply reliability and improving operation and maintenance efficiency.

[0003] In recent years, with the in-depth development of distribution network fault location technology, the development of fault line selection and fault section location technology has gradually matured. At present, there are many methods for fault line selection and fault section location, such as steady-state methods such as amplitude comparison method and transient methods such as first half-wave method, but there are fewer fault distance measurement methods, and they are separated from fault line selection and fault section location methods, such as traveling wave method and impedance method, which are only effective for fault distance measurement, while fault line selection and section location need to rely on other methods to achieve, and there is no coordination. In addition, the current fault distance measurement methods have the problem of too high cost, such as the traveling wave method requires high-precision detection equipment, or there is a problem of unstable distance measurement effect, such as the impedance method is greatly affected by line parameters.

[0004] Therefore, a method is needed that can not only solve the coordination problem of fault line selection, section location method and fault distance measurement method, but also solve the practicality and stability problem of fault distance measurement method. Summary of the invention

[0005] The main purpose of the present invention is to provide a distribution network fault location method based on negative sequence parameter distribution characteristics, so as to solve the problem that the prior art cannot further realize fault distance measurement and accurate fault location on the basis of accurate fault line selection and accurate section location.

[0006] To achieve the above object, the present invention provides a distribution network fault location method based on negative sequence parameter distribution characteristics, which specifically includes the following steps:

[0007] S1, identify whether a distribution line fault occurs.

[0008] S2: If a fault has occurred, the fault voltage and current information are collected to extract the voltage and current fundamental frequency components.

[0009] S3, converts the voltage and current negative sequence components.

[0010] S4, identify the feeder with the largest negative sequence current at the outlet as the fault line.

[0011] S5, define the area between the first two terminals with opposite phases of the faulty line as the faulty section.

[0012] S6, establish the upstream and downstream negative sequence voltage distribution functions and solve the simultaneous equations.

[0013] S7, output the distance measurement result.

[0014] Furthermore, step S1 specifically includes the following steps:

[0015] S1.1. Distribution terminals with three-phase voltage and current detection capabilities shall be installed on each feeder under the same busbar of the distribution network. Terminals shall be configured at the outlet of each feeder and at the end of the line. The number of terminals for each feeder shall be no less than 3.

[0016] S1.2, when a fault occurs in the distribution line, each terminal detects a sudden change and collects the voltage and current of the three phases A, B and C.

[0017] Furthermore, step S3 specifically includes the following steps:

[0018] S3.1, filtering and base frequency extraction of the collected three-phase voltage and current.

[0019] S3.2, the fundamental frequency phasors of the three-phase voltage and current are transformed into negative sequence components of the voltage and current by phase mode transformation.

[0020] Furthermore, the baseband extraction calculation formula in step S3.1 is:

[0021]

[0022]

[0023]

[0024]

[0025] Among them, x(k) is the discrete value of the instantaneous current or voltage of a certain phase after analog-to-digital conversion, k is the sampling point number; N is the number of sampling points for the discrete value in one cycle, a1 is the real part of the fundamental frequency phasor, b1 is the real part of the fundamental frequency phasor, A is the amplitude of the fundamental frequency phasor, and θ is the phase angle of the fundamental frequency phasor.

[0026] Furthermore, in step S3.2, the fundamental frequency phasors of the three-phase voltage and current are decoupled into the positive, negative and zero-sequence components of the current and voltage through phase mode transformation as follows:

[0027]

[0028]

[0029] Where a = e j120° , a2=ej240° , and satisfies 1+a+a 2 =0,a 3 =1; They are the current phasors of phases A, B and C respectively: They are the voltage phasors of phases A, B and C respectively; They are the current phasors of three sequences: positive, negative and zero; They are the three-sequence voltage phasors: positive, negative and zero.

[0030] Furthermore, step S4 specifically includes: extracting the amplitude of the negative sequence component of the current at each feeder outlet and comparing them, and determining the feeder with the largest amplitude of the negative sequence component of the current at the feeder outlet as the fault line.

[0031] Furthermore, step S5 specifically includes the following steps:

[0032] S5.1, number the terminals on the faulty feeder as 1, 2, ..., n in order from the nearest to the feeder outlet.

[0033] S5.2, calculate the phase difference δ1, δ2, …, δ between the negative sequence voltage and the negative sequence current at each terminal n , where the phase difference δ n ≤±180°.

[0034] S5.3, starting from δ1, compare the difference between two adjacent phase differences one by one, i.e., δ1-δ2, δ2-δ3, …, δ n-1 -δ n .

[0035] S5.4, when |δ k -δ k+1 When |>90°, it is determined that the fault point is between terminal k and terminal k+1.

[0036] Furthermore, step S6 specifically includes the following steps:

[0037] S6.1, according to the fault interval determined in step S5, the terminals 1-k are grouped as upstream terminals of the fault point, and the terminals k+1-n are grouped as downstream terminals of the fault point.

[0038] S6.2, when k=1, the fault location is completed, otherwise it goes to step S6.3.

[0039] S6.3, when k ≥ 2, the negative sequence voltage distribution function of the upstream line of the fault point is obtained according to the upstream terminal and distance information of the fault point.

[0040] S6.4, obtain the negative sequence voltage distribution function of the line downstream of the fault point according to the downstream terminal and distance information of the fault point.

[0041] S6.5, solve the simultaneous equations.

[0042] Furthermore, step S6.3 specifically includes the following steps:

[0043] S6.3.1, assuming that the negative sequence voltage distribution function of the upstream line of the fault point is a linear function, the expression is shown in formula (4):

[0044] U2(x)=a1x+b1 (7).

[0045] S6.3.2, when k = 2, assuming that the distances from the two terminals to the feeder outlet and the negative sequence voltage amplitude are (x1, U2(x1)) and (x2, U2(x2)) respectively, substituting the two data into equation (7), we get the equation group shown in equation (8):

[0046]

[0047] Solving the equation group shown in formula (8) can obtain the values ​​of parameters a1 and b1. Otherwise, go to step S6.3.3.

[0048] S6.3.3, when k>2, let the distances from the k terminals to the feeder outlet and the negative sequence voltage amplitudes be (x1,U2(x1)),(x2,U2(x2)),…,(x k ,U2(x k )), then the least square method is used to solve the parameters a1 and b1. The formula for solving the parameters a1 and b1 by the least square method is shown in formula (9);

[0049]

[0050] Furthermore, step S6.4 specifically includes the following steps:

[0051] S6.4.1, assuming that the negative sequence voltage distribution function of the line downstream of the fault point is a linear function, the expression is shown in formula (10):

[0052] U2(x)=a2x+b2 (10).

[0053] S6.4.2, when the number of downstream terminals of the fault point n-(k+1)=1, assume that the distance from the terminal to the feeder outlet and the negative sequence voltage amplitude are (x1′, U2(x1′)), where n represents the total number of fault line terminals and n-(k+1) represents the total number of downstream terminals; at this time, use the terminal data (x1′, U2(x1′)) to fit equation (10) to a constant, that is, a2=0, b2=U2(x1′), and proceed to step S6.4.3.

[0054] S6.4.3, when the number of downstream terminals of the fault point [n-(k+1)]≥2, the solution method of parameters a2 and b2 in formula (10) is consistent with step S6.3.

[0055] Further, step S6.5 specifically includes the following steps: the simultaneous equations of equations (7) and (10) for which the parameters a1, b1 and the parameters a2, b2 have been obtained are as shown in equation (11):

[0056]

[0057] Solving the equations shown in formula (11), we can obtain That is, the distance from the fault point to the fault feeder outlet.

[0058] The present invention has the following beneficial effects:

[0059] 1. The method provided by the present invention integrates the distribution network fault line selection, fault section location, and fault distance measurement functions. It does not need to use other methods to achieve fault line selection and fault section location, realizes a complete distribution network fault location function, and has good distribution network field application performance.

[0060] 2. The method provided by the present invention only requires the steady-state negative-sequence current and steady-state negative-sequence voltage information when the distribution network fails to realize fault location. The required fault information is small and the principle is simple. Therefore, the fault location method has good stability and reliability.

[0061] 3. The method provided by the present invention finally realizes the distribution network fault distance measurement, which makes up for the current situation of insufficient distribution network fault distance measurement methods. In addition, the distance measurement method only requires the fault steady-state negative sequence voltage and the distance measurement principle is simple. Therefore, it can be implemented with the help of the existing distribution network automation system, with low cost and stable distance measurement effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] In order to more clearly illustrate the specific implementation of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the specific implementation or the prior art description. Obviously, the drawings described below are some implementations of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work. In the drawings:

[0063] Figure 1 A flow chart of a distribution network fault location method based on negative sequence parameter distribution characteristics of the present invention is shown;

[0064] Figure 2 The negative sequence voltage distribution diagram of the fault feeder is shown;

[0065] Figure 3A local line topology diagram of a 10kV distribution network in Example 1 is shown;

[0066] Figure 4 A local line topology diagram of a 10kV distribution network in Example 2 is shown;

[0067] Figure 5 A local line topology diagram of a 10kV distribution network in Example 3 is shown. DETAILED DESCRIPTION

[0068] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0069] like Figure 1 A distribution network fault location method based on negative sequence parameter distribution characteristics is shown, which specifically includes the following steps:

[0070] S1, identify whether a distribution line fault occurs.

[0071] S2: If a fault has occurred, the fault voltage and current information are collected to extract the voltage and current fundamental frequency components.

[0072] S3, converts the voltage and current negative sequence components.

[0073] S4, identify the feeder with the largest negative sequence current at the outlet as the fault line.

[0074] S5, define the area between the first two terminals with opposite phases of the faulty line as the faulty section.

[0075] S6, establish the upstream and downstream negative sequence voltage distribution functions and solve the simultaneous equations.

[0076] S7, output the distance measurement result.

[0077] Specifically, step S1 includes the following steps:

[0078] S1.1. Distribution terminals with three-phase voltage and current detection capabilities shall be installed on each feeder under the same busbar of the distribution network. Terminals shall be configured at the outlet of each feeder and at the end of the line. The number of terminals for each feeder shall be no less than 3.

[0079] S1.2, when a fault occurs in the distribution line, each terminal detects a sudden change and collects the voltage and current of the three phases A, B and C.

[0080] Specifically, step S3 includes the following steps:

[0081] S3.1, filtering and base frequency extraction of the collected three-phase voltage and current.

[0082] S3.2, the fundamental frequency phasors of the three-phase voltage and current are transformed into negative sequence components of the voltage and current by phase mode transformation.

[0083] Specifically, the base frequency extraction calculation formula in step S3.1 is:

[0084]

[0085]

[0086]

[0087]

[0088] Among them, x(k) is the discrete value of the instantaneous current or voltage of a certain phase after analog-to-digital conversion, k is the sampling point number; N is the number of sampling points for the discrete value in one cycle, a1 is the real part of the fundamental frequency phasor, b1 is the real part of the fundamental frequency phasor, A is the amplitude of the fundamental frequency phasor, and θ is the phase angle of the fundamental frequency phasor.

[0089] Specifically, in step S3.2, the fundamental frequency phasors of the three-phase voltage and current are decoupled into the positive, negative and zero sequence components of the current and voltage through phase mode transformation as follows:

[0090]

[0091]

[0092] Where a = e j120° , a2=e j240° , and satisfies 1+a+a 2 =0,a 3 =1; They are the current phasors of phases A, B and C respectively: They are the voltage phasors of phases A, B and C respectively; They are the current phasors of three sequences: positive, negative and zero; They are the three-sequence voltage phasors: positive, negative and zero.

[0093] Specifically, step S4 is as follows: extracting the amplitude of the negative sequence component of the current at each feeder outlet and comparing them, and determining the feeder with the largest amplitude of the negative sequence component of the current at the feeder outlet as the fault line.

[0094] Specifically, step S5 includes the following steps:

[0095] S5.1, number the terminals on the faulty feeder as 1, 2, ..., n in order from the nearest to the feeder outlet.

[0096] S5.2, calculate the phase difference δ1, δ2, …, δ between the negative sequence voltage and the negative sequence current at each terminal n , where the phase difference δ n ≤±180°.

[0097] S5.3, starting from δ1, compare the difference between two adjacent phase differences one by one, i.e., δ1-δ2, δ2-δ3, …, δ n-1 -δ n .

[0098] S5.4, when |δ k -δ k+1 When |>90°, it is determined that the fault point is between terminal k and terminal k+1.

[0099] Specifically, step S6 includes the following steps:

[0100] S6.1, according to the fault interval determined in step S5, the terminals 1-k are grouped as upstream terminals of the fault point, and the terminals k+1-n are grouped as downstream terminals of the fault point.

[0101] S6.2, when k=1, the fault location is completed, otherwise it goes to step S6.3.

[0102] S6.3, when k ≥ 2, the negative sequence voltage distribution function of the upstream line of the fault point is obtained according to the upstream terminal and distance information of the fault point.

[0103] S6.4, obtain the negative sequence voltage distribution function of the line downstream of the fault point according to the downstream terminal and distance information of the fault point.

[0104] S6.5, solve the simultaneous equations.

[0105] Specifically, step S6.3 includes the following steps:

[0106] S6.3.1, assuming that the negative sequence voltage distribution function of the upstream line of the fault point is a linear function, the expression is shown in formula (7):

[0107] U2(x)=a1x+b1 (7).

[0108] S6.3.2, when k = 2, assuming that the distances from the two terminals to the feeder outlet and the negative sequence voltage amplitude are (x1, U2(x1)) and (x2, U2(x2)) respectively, substituting the two data into equation (7), we get the equation group shown in equation (8):

[0109]

[0110] Solving the equation group shown in formula (8) can obtain the values ​​of parameters a1 and b1. Otherwise, go to step S6.3.3.

[0111] S6.3.3, when k>2, let the distances from the k terminals to the feeder outlet and the negative sequence voltage amplitudes be (x1,U2(x1)),(x2,U2(x2)),…,(x k ,U2(x k )), then the least square method is used to solve the parameters a1 and b1. The formula for solving the parameters a1 and b1 by the least square method is shown in formula (9);

[0112]

[0113] Specifically, step S6.4 includes the following steps:

[0114] S6.4.1, assuming that the negative sequence voltage distribution function of the line downstream of the fault point is a linear function, the expression is shown in formula (10):

[0115] U2(x)=a2x+b2 (10)

[0116] S6.4.2, when the number of downstream terminals of the fault point n-(k+1)=1, assume that the distance from the terminal to the feeder outlet and the negative sequence voltage amplitude are (x1′, U2(x1′)), where n represents the total number of fault line terminals and n-(k+1) represents the total number of downstream terminals; at this time, use the terminal data (x1′, U2(x1′)) to fit equation (7) to a constant, that is, a2=0, b2=U2(x1′), and proceed to step S6.4.3.

[0117] S6.4.3, when the number of downstream terminals of the fault point [n-(k+1)]≥2, the solution method of parameters a2 and b2 in formula (10) is consistent with step S6.3.

[0118] Specifically, step S6.5 includes the following steps:

[0119] The simultaneous equations of equations (7) and (10) with the obtained parameters a1, b1 and a2, b2 are as shown in equation (11):

[0120]

[0121] Solving the equations shown in formula (11), we can obtain That is, the distance from the fault point to the fault feeder outlet.

[0122] The principle of the present invention is described in detail below:

[0123] When a fault occurs in the distribution network, according to the negative sequence equivalent network, the negative sequence current generated by the virtual power supply at the fault point flows into the line from the fault point, and the fault path is the shortest path between the fault point and the power supply. In each circulation loop of the negative sequence network, the loop impedance formed by the fault path is the smallest, so the negative sequence current is the largest, and the loop impedance formed by other non-fault paths is large, so the negative sequence current is very small. Among them, the non-fault path includes the downstream line of the fault point, the non-fault feeder and each branch line. Based on this, it can be seen that when comparing the outlets of each feeder when the distribution network fails, the negative sequence current at the outlet of the feeder where the fault point is located is the largest. In the fault feeder, the negative sequence current flows from the fault point to both ends of the feeder. Therefore, when the positive direction is unified, the negative sequence current phases upstream and downstream of the fault point are opposite, but the negative sequence voltage phases upstream and downstream of the fault point are basically the same. By comparing the power frequency negative sequence current phase and the power frequency negative sequence voltage phase at each terminal of the fault feeder, it can be found that the phase difference of the upstream terminal of the fault point is in an opposite relationship to the phase difference of the downstream terminal of the fault point, that is, the phase difference is 180°. Therefore, the fault point is located between two adjacent terminals with opposite phase differences between the power frequency negative sequence voltage and the negative sequence current. In the fault feeder, the negative sequence current in the fault path between the fault point and the power source is large, and flows from the fault point to the feeder outlet. Due to the negative sequence impedance of the line, a large negative sequence voltage drop is formed between the fault point and the power source, and the negative sequence voltage gradually decreases from the fault point to the power source. When the line parameters are uniform, the negative sequence voltage from the fault point to the feeder outlet decreases linearly with the line length; the negative sequence current from the fault point to the end of the line is very small, and flows from the fault point to the end of the line. The flow relationship between the negative sequence voltage drop and the negative sequence current is consistent with that upstream of the fault point. The negative sequence voltage distribution characteristics in the fault feeder are as follows: Figure 2 shown.

[0124] Assume that the distance from any point on the fault feeder to the feeder outlet is x, the power frequency negative sequence voltage amplitude at any point is U2(x), and the power frequency negative sequence current amplitudes upstream and downstream of the fault point are I 2up ,I 2down , the negative sequence impedance per unit length of the fault feeder is Z2, and the length of the fault feeder is l, then the negative sequence voltage distribution law of the fault feeder can be expressed by formula (12).

[0125]

[0126] Where U2(0) is the negative sequence voltage amplitude at the fault feeder outlet, and U2(l) is the negative sequence voltage amplitude at the end of the fault feeder.

[0127] Assume the distance from the fault point to the fault feeder outlet is x f , the power frequency negative sequence voltage amplitude at the fault point is U2(x f ), then when x=x f Then, formula (13) holds.

[0128] U2(x f)=U2(0)+I 2up Z2x f =U2(l)+I 2d o wn Z2(lx f ) (13)

[0129] The above formula shows that the power frequency negative sequence voltage distribution curve upstream of the fault point and the power frequency negative sequence voltage distribution curve downstream of the fault point form an intersection at the fault point, and the negative sequence voltage distribution curve of the fault feeder is a continuous curve with the fault point as the inflection point.

[0130] Among them, since the negative sequence current in the downstream part of the fault point in the fault feeder is very small, the negative sequence voltage drop is very small. When considering approximately, it can be considered that the negative sequence voltage of each point downstream of the fault point is consistent. At this time, the power frequency negative sequence voltage amplitude of any point downstream of the fault point can be expressed as formula (14):

[0131] U2(x)=U2(x f )=U2(l) x≥x f (14).

[0132] Based on the above analysis and actual application scenarios on site, a distribution network fault location method based on negative-sequence parameter distribution characteristics is proposed. This method first determines the fault feeder according to the maximum negative-sequence current at the fault feeder outlet among the feeder outlets when the distribution network fails. Then, the section where the fault point is located is determined according to the opposite phases of the negative-sequence currents upstream and downstream of the fault point in the fault feeder. Considering that it is difficult to achieve accurate timing between the terminals on site, the power frequency negative-sequence current of each terminal is compared with the power frequency negative-sequence voltage to obtain the phase difference, and then the phase difference of each terminal is compared to determine the fault section. Finally, the fault feeder is divided into upstream and downstream parts according to the section where the fault point is located. The negative-sequence voltage amplitude of the upstream and downstream terminals and the distance to the feeder outlet are used to fit the negative-sequence voltage distribution function, and the two distribution function simultaneous equations are solved to determine the distance from the fault point to the feeder outlet.

[0133] In order to more clearly explain the purpose, technical solutions and advantages of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0134] Example 1

[0135] Two-phase short circuit fault

[0136] The local line topology of a 10kV distribution network is as follows Figure 3 shown.

[0137] The 10kV busbar of the local distribution network has a total of 4 feeders. Each feeder outlet and along the line are equipped with distribution terminals for real-time detection of voltage and current information. The length of each feeder is less than 15km, and the line end is connected to a typical load. A two-phase short circuit fault occurs on one of the feeders. Each distribution terminal obtains real-time fault recording data. Through data statistics, three groups of data are obtained, including the negative sequence current amplitude at each feeder outlet, the negative sequence voltage and current phase difference of each terminal of the faulty feeder, and the negative sequence voltage amplitude of each terminal of the faulty feeder, as shown in Table 1, Table 2, and Table 3.

[0138] Table 1 Negative sequence current amplitude at each feeder outlet

[0139]

[0140] Table 2 Negative sequence voltage and current phase difference at each terminal of the fault feeder

[0141]

[0142] Table 3 Negative sequence voltage amplitude at each terminal of the fault feeder

[0143]

[0144] Based on the above data, this method determines that the fault is located between terminals 3 and 4 in line 1, 8.03 km away from the feeder outlet.

[0145] The specific implementation process is as follows:

[0146] S1: Install distribution terminals with three-phase voltage and current detection capabilities on each feeder under the same busbar of the distribution network. Terminals should be configured at the outlet of each feeder and at the end of the line. The number of terminals for each feeder should be no less than 3;

[0147] S2: When a fault occurs in the distribution line, each terminal detects a sudden change and collects the voltage and current of the three phases A, B, and C;

[0148] S3: filtering and extracting the base frequency of the collected three-phase voltage and current;

[0149] S4: The fundamental frequency phasors of the three-phase voltage and current are transformed into negative sequence components of the voltage and current by phase model transformation;

[0150] S5: extracting the amplitude of the negative sequence component of the current at each feeder outlet and comparing them, as shown in Table 1, and determining line 1 with the largest amplitude of the negative sequence component of the current at the feeder outlet as the faulty feeder;

[0151] S6: performing a phase comparison between the negative sequence voltage and the negative sequence current component at each terminal of the faulty feeder line 1 to determine the fault section, specifically comprising the following steps:

[0152] S6.1 Number the terminals on the faulty feeder as 1, 2, 3, 4, 5 in order from the nearest to the feeder outlet;

[0153] S6.2 calculates the phase difference between the negative sequence voltage and the negative sequence current at each terminal, as shown in Table 2, and is set to δ1, δ2, δ3, δ4, δ5, where the phase difference δ ≤ ±180°;

[0154] S6.3 starting from δ1, the differences between two adjacent phase differences are compared one by one, i.e., δ1-δ2, δ2-δ3, δ3-δ4, δ4-δ5;

[0155] S6.4 Since |δ3-δ4|>90°, it is determined that the fault point is between terminal 3 and terminal 4;

[0156] S7: According to the fault section determined in step S6, terminals 1-3 are grouped as upstream terminals of the fault point, and terminals 4 and 5 are grouped as downstream terminals of the fault point;

[0157] S8: When k=1, the fault location is completed. At this time, the fault location accuracy can only reach the section location. Otherwise, it goes to step S9; because K=3, it goes to step S9;

[0158] S9: The number of upstream terminals of the fault point is k≥2. The negative sequence voltage distribution function of the upstream line of the fault point is obtained according to the upstream terminals and distance information of the fault point, which specifically includes the following steps:

[0159] S9.1 Assume that the negative sequence voltage distribution function of the upstream line of the fault point is a linear function, and the expression is shown in formula (1):

[0160] U2(x)=a1x+b1 (1)

[0161] S9.2 When k = 2, assume that the distances from the two terminals to the feeder outlet and the negative sequence voltage amplitude are (x1, U2(x1)) and (x2, U2(x2)) respectively. Substituting the two data into equation (1), we get the equation group shown in equation (2):

[0162]

[0163] Solving the equation group shown in formula (2) can obtain the values ​​of parameters a1 and b1. Otherwise, go to step S9.3. Since K=3, go to step S9.3.

[0164] S9.3 When k>2, let the distances from the k terminals to the feeder outlet and the negative sequence voltage amplitudes be (x1, U2(x1)), (x2, U2(x2)),…, (x k ,U2(x k)), the least square method is used to solve the parameters a1 and b1. The formula for solving the parameters a1 and b1 by the least square method is shown in formula (3).

[0165]

[0166] At this time, k = 3, the distances from the three terminals to the feeder outlet and the negative sequence voltage amplitudes are (0, 1050.73 V), (3 km, 2097.48 V), (6 km, 3144.24 V), respectively. Substituting the three data into formula (3), we can obtain a1 = 348.918, b1 = 1050.73.

[0167] S10: Obtaining the negative sequence voltage distribution function of the upstream line of the fault point according to the downstream terminal and distance information of the fault point, specifically including the following steps:

[0168] S10.1 Assume that the negative sequence voltage distribution function of the line downstream of the fault point is a linear function, and the expression is shown in formula (4):

[0169] U2(x)=a2x+b2 (4)

[0170] S10.2 When the number of downstream terminals of the fault point n-(k+1)=1, assume that the distance from the terminal to the feeder outlet and the negative sequence voltage amplitude are (x1′, U2(x1′)) respectively. At this time, the terminal data is used to fit equation (4) to a constant, that is, a2=0, b2=U2(x1′). Otherwise, proceed to step S10.3. At this time, n-(k+1)=2, so proceed to step S10.3.

[0171] S10.3 When the number of downstream terminals of the fault point [n-(k+1)]≥2, the solution method of parameters a2 and b2 in formula (4) is the same as step 9.

[0172] At this time, n-(k+1)=2, the distances from the two terminals to the feeder outlet and the negative sequence voltage amplitude are (10km, 3843.43V) and (12km, 3834.56V) respectively. Substituting the two data into equation (4), we get the equation group shown in equation (2), and we get a2=-4.435, b2=3887.78. S11: The equation group of equation (1) and equation (4) with the obtained parameters a1, b1 and a2, b2 is as shown in equation (5):

[0173]

[0174] Solving the equations shown in formula (5), we can obtain That is, the distance from the fault point to the fault feeder outlet.

[0175] At this time, a1=348.918, b1=1050.73, a2=-4.435, b2=3887.78, and substituting them into the equation group shown in formula (5), we get x=8.029, that is, the distance from the fault point to the fault feeder outlet is 8.029 km.

[0176] After later feedback, the actual fault point is located between terminals 3 and 4 of line 1, 8 km away from the feeder outlet. Therefore, the fault line selection and fault section positioning are accurate, and the fault distance measurement error is 0.029 km. The absolute distance measurement error is calculated according to the distance measurement error / line length, and the absolute error is 0.24%.

[0177] Example 2

[0178] Single-phase ground fault

[0179] Use MATLAB / simulink simulation software to build a 10kV single-ended radial, ungrounded system simulation model, such as Figure 4 There are three outgoing lines on the bus side, of which two healthy feeders are 8km and 10km long respectively, and the length of the faulty feeder is 12km. The line parameters and load parameters are all typical values.

[0180] A phase A single-phase grounding fault is set at a distance of 8 km from the fault feeder to the busbar, and the fault grounding resistance is 10Ω; 5 detection terminals are set at the fault feeder, and the distances to the busbar are 0km, 3km, 6km, 9km, and 11km, respectively, and are numbered 1, 2, 3, 4, and 5.

[0181] Three sets of data are obtained: the negative sequence current amplitude at each feeder outlet after the fault, the negative sequence voltage and current phase difference at each terminal of the fault feeder, and the negative sequence voltage amplitude at each terminal of the fault feeder, as shown in Table 4, Table 5, and Table 6.

[0182] Table 4 Negative sequence current amplitude at each feeder outlet

[0183]

[0184] Table 5 Negative sequence voltage and current phase difference at each terminal of the fault feeder

[0185]

[0186] Table 6 Negative sequence voltage amplitude at each terminal of the fault feeder

[0187]

[0188] Comparing the negative sequence current amplitudes at the outlets of each feeder in Table 4, line 1 is much larger than line 2 and line 3, so line 1 is judged to be the faulty feeder.

[0189] According to the negative sequence voltage and current phase difference of each terminal of the fault feeder in Table 5, starting from terminal 1, the comparison is made with the next terminal one by one. It is found that the negative sequence voltage and current phase difference of terminal 3 and the negative sequence voltage and current phase difference of terminal 4 are greater than 90°. Therefore, it is judged that the fault point is between terminal 3 and terminal 4.

[0190] According to the determined fault section, terminals 1-3 are grouped as upstream terminals of the fault point, and terminals 4 and 5 are grouped as downstream terminals of the fault point.

[0191] According to the distance from the terminal 1-3 to the feeder outlet and the negative sequence voltage amplitude in Table 6, the negative sequence voltage distribution function upstream of the fault point is fitted, as shown in formula (1).

[0192] U2(x)=4.7978x+14.365 (1)

[0193] According to the distance from terminals 4 and 5 to the feeder outlet and the negative sequence voltage amplitude in Table 6, the negative sequence voltage distribution function downstream of the fault point is fitted, as shown in formula (2).

[0194] U2(x)=-0.0605x+53.269 (2)

[0195] Solving the simultaneous equations of equation (1) and equation (2), we get the distance from the fault point to the fault feeder outlet is 8.0077 km, which is 0.0077 km different from the actual distance of the fault point, and the absolute error is 0.064%.

[0196] Example 3

[0197] Two-phase short circuit ground fault

[0198] Use MATLAB / simulink simulation software to build a 10kV single-ended radial, ungrounded system simulation model, such as Figure 5 There are three outgoing lines on the bus side, of which two healthy feeders are 8km and 10km long respectively, and the length of the faulty feeder is 12km. The line parameters and load parameters are all typical values.

[0199] A two-phase short-circuit grounding fault of phases A and B is set at a distance of 8 km from the faulty feeder to the busbar, and the fault grounding resistance is 10Ω; 5 detection terminals are set at the faulty feeder, and the distances to the busbar are 0km, 3km, 6km, 9km, and 11km, respectively, and are numbered 1, 2, 3, 4, and 5.

[0200] Three sets of data are obtained: the negative sequence current amplitude at each feeder outlet after the fault, the negative sequence voltage and current phase difference at each terminal of the fault feeder, and the negative sequence voltage amplitude at each terminal of the fault feeder, as shown in Table 7, Table 8, and Table 9.

[0201] Table 7 Negative sequence current amplitude at each feeder outlet

[0202]

[0203] Table 8 Negative sequence voltage and current phase difference at each terminal of the fault feeder

[0204]

[0205] Table 9 Negative sequence voltage amplitude at each terminal of the fault feeder

[0206]

[0207] Comparing the negative sequence current amplitudes at the outlets of each feeder in Table 7, line 1 is much larger than line 2 and line 3, so line 1 is judged to be the faulty feeder.

[0208] According to the negative sequence voltage and current phase difference of each terminal of the fault feeder in Table 8, starting from terminal 1, the comparison is made with the next terminal one by one. It is found that the negative sequence voltage and current phase difference of terminal 3 and the negative sequence voltage and current phase difference of terminal 4 are greater than 90°. Therefore, it is judged that the fault point is between terminal 3 and terminal 4.

[0209] According to the determined fault section, terminals 1-3 are grouped as upstream terminals of the fault point, and terminals 4 and 5 are grouped as downstream terminals of the fault point.

[0210] According to the distance from the terminal 1-3 to the feeder outlet and the negative sequence voltage amplitude in Table 9, the negative sequence voltage distribution function upstream of the fault point is fitted, as shown in formula (1).

[0211] U2(x)=351.19x+1049.9 (1)

[0212] According to the distance from terminals 4 and 5 to the feeder outlet and the negative sequence voltage amplitude in Table 9, the negative sequence voltage distribution function downstream of the fault point is fitted, as shown in formula (2).

[0213] U2(x)=-4.455x+3898.8 (2)

[0214] Solving the simultaneous equations of equation (1) and equation (2), we get the distance from the fault point to the fault feeder outlet is 8.0105 km, which is 0.0105 km different from the actual distance of the fault point, and the absolute error is 0.088%.

[0215] Compared with the prior art, the present invention integrates the distribution network fault line selection, fault section location, and fault distance measurement technologies into a technical whole through negative-sequence parameters, thereby realizing one method and three functions. Moreover, the method provided by the present invention can be realized with only negative-sequence parameters. On the one hand, the principle is simple and the performance is stable. On the other hand, the cost of field application is low and the practicality is good. At the same time, a new idea is provided in terms of fault distance measurement, which can provide technical support for reducing the scope of manual line patrol and improving the efficiency of fault inspection and repair on site.

[0216] The present invention can be widely used in the field of distribution network fault location of long distribution lines in various industries. It can provide specific fault point locations for on-site fault inspection and maintenance, greatly reducing manual line inspection time, thereby improving fault inspection and maintenance efficiency and power supply reliability. It is easy to implement with the help of existing equipment, has a simple principle, low cost, and has good application prospects.

[0217] The present invention is based on practical engineering applications and provides a combined method for distribution network fault line selection, section location and fault distance measurement based on the negative sequence parameter distribution characteristics. The method can achieve accurate progressive positioning of the line, section and specific location of the fault point, providing technical support for on-site fault location.

[0218] Of course, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or substitutions made by technicians in this technical field within the essential scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. A distribution network fault location method based on negative sequence parameter distribution characteristics, characterized in that: The specific steps include: S1, identifying whether a distribution line fault occurs; S2, if a fault has occurred, collect the fault voltage and current information and extract the voltage and current fundamental frequency components; S3, converting to obtain negative sequence components of voltage and current; S4, identifying the feeder with the largest negative sequence current at the outlet as the fault line; S5, the first two terminals with opposite phases of the faulty line are defined as the fault interval; S6, establish the upstream and downstream negative sequence voltage distribution functions and solve the simultaneous equations; S7, output the distance measurement result.

2. A distribution network fault location method based on negative sequence parameter distribution characteristics according to claim 1, characterized in that: Step S1 specifically includes the following steps: S1.

1. Distribution terminals with three-phase voltage and current detection capabilities shall be installed on each feeder under the same busbar of the distribution network. Terminals shall be configured at the outlet of each feeder and at the end of the line. The number of terminals for each feeder shall not be less than 3; S1.2, when a fault occurs in the distribution line, each terminal detects a sudden change and collects the voltage and current of the three phases A, B and C.

3. A distribution network fault location method based on negative sequence parameter distribution characteristics according to claim 1, characterized in that: Step S3 specifically includes the following steps: S3.1, filtering and fundamental frequency extraction of the collected three-phase voltage and current; S3.2, the fundamental frequency phasors of the three-phase voltage and current are transformed into negative sequence components of the voltage and current by phase mode transformation.

4. A distribution network fault location method based on negative sequence parameter distribution characteristics according to claim 3, characterized in that: The fundamental frequency extraction calculation formula in step S3.1 is: Among them, x(k) is the discrete value of the instantaneous current or voltage of a certain phase after analog-to-digital conversion, k is the sampling point number; N is the number of sampling points for the discrete value in one cycle, a1 is the real part of the fundamental frequency phasor, b1 is the real part of the fundamental frequency phasor, A is the amplitude of the fundamental frequency phasor, and θ is the phase angle of the fundamental frequency phasor.

5. A distribution network fault location method based on negative sequence parameter distribution characteristics according to claim 3, characterized in that: In step S3.2, the fundamental frequency phasors of the three-phase voltage and current are decoupled into the positive, negative and zero sequence components of the current and voltage through phase mode transformation: Where a = e j120° , a2=e j240° , and satisfies 1+a+a 2 =0,a 3 =1; They are the current phasors of phases A, B and C respectively: They are the voltage phasors of phases A, B and C respectively; They are the current phasors of three sequences: positive, negative and zero; They are the three-sequence voltage phasors: positive, negative and zero.

6. A distribution network fault location method based on negative sequence parameter distribution characteristics according to claim 1, characterized in that: Step S4 specifically includes: extracting the amplitude of the negative sequence component of the current at each feeder outlet and comparing them, and determining the feeder with the largest amplitude of the negative sequence component of the current at the feeder outlet as the fault line.

7. A distribution network fault location method based on negative sequence parameter distribution characteristics according to claim 1, characterized in that: Step S5 specifically includes the following steps: S5.1, number the terminals on the faulty feeder line in order from near to far from the feeder outlet as 1, 2, ..., n; S5.2, calculate the phase difference δ1, δ2, …, δ between the negative sequence voltage and the negative sequence current at each terminal n , where the phase difference δ n ≤±180°; S5.3, starting from δ1, compare the difference between two adjacent phase differences one by one, i.e., δ1-δ2, δ2-δ3, …, δ n-1 -δ n ; S5.4, when |δ k -δ k+1 When |>90°, it is determined that the fault point is between terminal k and terminal k+1.

8. A distribution network fault location method based on negative sequence parameter distribution characteristics according to claim 1, characterized in that: Step S6 specifically includes the following steps: S6.1, according to the fault interval determined in step S5, the terminals 1-k are grouped as upstream terminals of the fault point, and the terminals k+1-n are grouped as downstream terminals of the fault point; S6.2, when k=1, the fault location is completed, otherwise it goes to step S6.3; S6.3, when k ≥ 2, the negative sequence voltage distribution function of the upstream line of the fault point is obtained according to the upstream terminal and distance information of the fault point; S6.4, obtaining the negative sequence voltage distribution function of the line downstream of the fault point according to the downstream terminal and distance information of the fault point; S6.5, solve the simultaneous equations.

9. A distribution network fault location method based on negative sequence parameter distribution characteristics according to claim 8, characterized in that: Step S6.3 specifically includes the following steps: S6.3.1, assuming that the negative sequence voltage distribution function of the upstream line of the fault point is a linear function, the expression is shown in formula (7): U2(x)=a1x+b1; (7) S6.3.2, when k = 2, assuming that the distances from the two terminals to the feeder outlet and the negative sequence voltage amplitude are (x1, U2(x1)) and (x2, U2(x2)) respectively, substituting the two data into equation (7), we get the equation group shown in equation (8): Solving the equations shown in formula (8) can obtain the values ​​of parameters a1 and b1, otherwise go to step S6.3.3; S6.3.3, when k>2, let the distances from the k terminals to the feeder outlet and the negative sequence voltage amplitudes be (x1,U2(x1)),(x2,U2(x2)),…,(x k ,U2(x k )), then the least square method is used to solve the parameters a1 and b1. The formula for solving the parameters a1 and b1 by the least square method is shown in formula (9); 10. A distribution network fault location method based on negative sequence parameter distribution characteristics according to claim 8, characterized in that: Step S6.4 specifically includes the following steps: S6.4.1, assuming that the negative sequence voltage distribution function of the line downstream of the fault point is a linear function, the expression is shown in formula (10): U2(x)=a2x+b2 (10) S6.4.2, when the number of downstream terminals of the fault point n-(k+1)=1, assume that the distance from the terminal to the feeder outlet and the negative sequence voltage amplitude are (x1′, U2(x1′)), where n represents the total number of fault line terminals and n-(k+1) represents the total number of downstream terminals; at this time, use the terminal data (x1′, U2(x1′)) to fit equation (10) to a constant, that is, a2=0, b2=U2(x1′), and proceed to step S6.4.3; S6.4.3, when the number of downstream terminals of the fault point [n-(k+1)]≥2, the solution method of parameters a2 and b2 in formula (10) is consistent with step S6.

3.

11. A distribution network fault location method based on negative sequence parameter distribution characteristics according to claim 8, characterized in that: Step S6.5 specifically includes the following steps: The simultaneous equations of equations (7) and (10) with the obtained parameters a1, b1 and a2, b2 are as shown in equation (11): Solving the equations shown in formula (11), we can obtain That is, the distance from the fault point to the fault feeder outlet.

Images