Power distribution network fault accurate positioning method based on negative sequence component characteristics and two-end quantities

Abstract

The invention discloses a power distribution network fault accurate positioning method based on negative-sequence component characteristics and two-end quantities, and the method comprises the steps: collecting fault voltage and current information, and extracting voltage and current fundamental frequency components; performing phase-mode transformation on the fundamental frequency phasors of the three-phase voltage and the three-phase current to obtain negative-sequence components of the voltage and the current; the amplitudes of the current negative-sequence components at the outlets of all the lines are extracted and compared, and the line with the maximum current negative-sequence component amplitude at the outlet is judged as a fault line; establishing head-end quantity and tail-end quantity expressions of the negative-sequence voltage amplitude of the fault point; and solving and judging a fault point distance by using a simultaneous equation set of fault point negative sequence voltage amplitude expressions established by the head-end quantity and the tail-end quantity. According to the method, only the negative-sequence parameters at the two ends of the line and the negative-sequence impedance parameters of the fault line are needed, the cost is low, the practicability is good, a new thought is provided in the aspect of fault distance measurement, and technical support can be provided for reducing the manual line patrol range on site and improving the fault maintenance efficiency.

Description

Technical Field

[0001] This invention relates to the field of distribution network fault detection, specifically to a method for accurate fault location in distribution networks based on negative sequence component characteristics and end-point quantities. Background Technology

[0002] Fault location technology in power distribution networks can quickly determine the specific location of a fault through fault information, reducing the time spent on manual line inspections, thereby improving maintenance efficiency, quickly repairing faults and restoring power supply, which is of great significance for improving power supply reliability.

[0003] Fault location technology in distribution networks can be categorized into three development stages based on location accuracy: fault line selection, fault section location, and fault distance measurement. Currently, fault line selection and fault section location technologies are relatively mature and have been implemented in the field. However, fault distance measurement technology is still under development, with few reported applications in the field. In the field of fault distance measurement research, common methods include the traveling wave method, impedance method, and voltage distribution method. The traveling wave method requires high precision from the detection equipment, resulting in high equipment costs and hindering its widespread application in distribution networks. The impedance method has high requirements for line parameters and poor universality. The voltage distribution method is significantly affected by the accuracy of parameter measurement. In summary, existing fault distance measurement methods struggle to balance distance measurement cost, accuracy, and stability. Furthermore, these methods do not integrate well with fault line selection and fault section location technologies, requiring independent fault line selection and section location technologies for their combined application. Therefore, current fault distance measurement methods need to address both the balance between distance measurement accuracy, cost, and stability, and the integration with fault line selection and fault section location technologies.

[0004] Based on practical engineering applications, this invention provides a combined method for fault location and fault finding in distribution networks, which is based on the characteristics of negative sequence components and quantities at both ends of the line. This method can achieve two-stage precise positioning of the line and specific location of the fault point, providing technical support for on-site fault location. Summary of the Invention

[0005] To address the aforementioned problems in existing technologies, this invention provides a method for accurate fault location in distribution networks based on negative sequence component characteristics and end-point quantities. The method is rationally designed, overcomes the shortcomings of existing technologies, and has good results.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for fault location in distribution networks based on negative sequence component characteristics includes the following steps:

[0008] S1. Collect fault voltage and current information, and extract the fundamental frequency components of voltage and current;

[0009] S2. The fundamental frequency phasors of the three-phase voltage and current are transformed by phase mode to obtain the negative sequence components of the voltage and current.

[0010] S3. Extract the amplitude of the negative sequence component of the current at the outlet of each line and compare them. The line with the largest amplitude of the negative sequence component of the current at the outlet is identified as the faulty line.

[0011] S4. Establish the expressions for the first and last values ​​of the negative sequence voltage amplitude at the fault point;

[0012] S5. Solve the system of equations for the negative sequence voltage amplitude expression of the fault point established by the first and last quantities to determine the distance to the fault point.

[0013] Further, step S1 includes the following sub-steps:

[0014] S1.1 Install distribution terminals with three-phase voltage and current detection capabilities at the beginning and end of each line under the same busbar in the distribution network.

[0015] S1.2 When a fault occurs in the power distribution line, each terminal detects a sudden change in voltage. At this time, the A, B, and C phase voltages and currents at the beginning and end of each line are collected.

[0016] S1.3 Filter and extract the fundamental frequency of the collected three-phase voltage and current.

[0017] Furthermore, in S1.3, the real part of the fundamental frequency phasor is:

[0018]

[0019] The imaginary part of the fundamental phasor is:

[0020]

[0021] Where x(k) is the discrete value of the instantaneous current or voltage of a certain phase after analog-to-digital conversion;

[0022] k is the sampling point number;

[0023] N is the number of sampling points for discrete values ​​within one period;

[0024] Furthermore, the amplitude of the fundamental frequency phasor is:

[0025]

[0026] Furthermore, the phase angle of the fundamental phasor is:

[0027]

[0028] Furthermore, in S2, the formulas for decoupling the fundamental frequency phasors of the three-phase voltage and current into positive, negative, and zero-sequence components of the current and voltage through phase-mode transformation are as follows:

[0029]

[0030] Where a = e j120° a 2 =e j240° And satisfying 1+a+a 2 =0, a 3 =1;

[0031] The current phasors for phases A, B, and C are as follows:

[0032] These are the voltage phasors for phases A, B, and C, respectively.

[0033] These are the current phasors in positive, negative, and zero sequences, respectively;

[0034] These are voltage phasors in positive, negative, and zero sequences, respectively.

[0035] Further, step S4 includes the following sub-steps:

[0036] S4.1 Obtain the negative sequence impedance data per unit length of the faulty line, obtain the amplitude of the negative sequence voltage and the amplitude of the negative sequence current at the beginning and end of the faulty line, and obtain the length from the beginning to the end of the faulty line.

[0037] S4.2. Using the amplitude of the negative sequence voltage at the power frequency, the amplitude of the negative sequence current at the power frequency at the beginning of the faulty line, and the negative sequence impedance per unit length of the faulty line as known quantities, establish an expression for the magnitude of the negative sequence voltage at the beginning of the fault.

[0038] Furthermore, in S4.1, the expression for the negative sequence voltage amplitude at the fault point established from the first-end quantity is as follows:

[0039] U (2) (x f )=U (2) (0)+I (2) a Z2x f ;

[0040] In the formula, U (2) (x f The value of the negative sequence voltage at the power frequency at the fault point is unknown.

[0041] U (2) (0) represents the amplitude of the negative sequence voltage at the power frequency at the beginning of the faulty line;

[0042] I (2) a The amplitude of the negative sequence current at power frequency upstream of the fault point, measured at the beginning of the faulty line.

[0043] Z2 is the negative sequence impedance per unit length of the faulty line;

[0044] x f is the distance from the fault point to the beginning of the faulty line, and is the quantity to be determined.

[0045] Furthermore, in S4.2, the expression for the negative sequence voltage amplitude at the fault point established from the terminal quantity is as follows:

[0046] U (2) (x f )=U (2) (l)+I (2) b Z2(lx f );

[0047] In the formula, U (2) (x f The value represents the amplitude of the negative sequence voltage at the power frequency at the fault location.

[0048] U (2) (l) is the frequency negative sequence voltage amplitude at the end of the faulty line, which is an unknown quantity;

[0049] I (2) b The amplitude of the negative sequence current at power frequency upstream of the fault point, measured at the end of the faulty line.

[0050] Z2 is the negative sequence impedance per unit length of the faulty line;

[0051] l is the length from the beginning to the end of the faulty line;

[0052] x f is the distance from the fault point to the beginning of the faulty line, and is the quantity to be determined.

[0053] Furthermore, in S5, the simultaneous equations of the fault point power frequency negative sequence voltage amplitude expression established by the first-end quantity and the fault point power frequency negative sequence voltage amplitude expression established by the last-end quantity are as follows:

[0054]

[0055] Since the amplitude of the negative sequence voltage at the fault point is unique, the distance x from the fault point to the beginning of the faulty line can be obtained from the equations. f The expression is as follows:

[0056]

[0057] By substituting the relevant parameters, the distance x from the fault point to the beginning of the faulty line can be calculated. f Complete fault location.

[0058] The beneficial technical effects of this invention are as follows:

[0059] Compared with existing technologies, this invention integrates the fault location and fault finding technologies of distribution networks into a whole through the negative sequence component characteristics. The method of this invention only requires the negative sequence parameters at both ends of the line and the negative sequence impedance parameters of the faulty line, and can be implemented with the help of existing distribution network automation systems. 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, it provides a new approach to fault finding, which can provide technical support for reducing the scope of manual line inspection and improving the efficiency of fault repair in the field. Attached Figure Description

[0060] Figure 1 This is a schematic diagram of the negative sequence equivalent network for a distribution network fault.

[0061] Figure 2 This is a schematic diagram of the negative sequence voltage distribution of a faulty line during a distribution network fault.

[0062] Figure 3 This is a flowchart of the power distribution network fault location process in this invention;

[0063] Figure 4 This is a partial line topology diagram of the 10kV distribution network in Embodiment 1 of the present invention;

[0064] Figure 5 This is a partial line topology diagram of the 10kV distribution network in Embodiment 2 of the present invention; Detailed Implementation

[0065] The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this disclosure. Rather, they are merely examples of methods consistent with some aspects of this disclosure as detailed in the appended claims.

[0066] The terminology used in this disclosure is for descriptive purposes only and is not intended to be limiting. The singular forms “a,” “the,” and “the” used in this disclosure and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used herein refers to and includes any and all possible combinations of one or more of the associated listed items.

[0067] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings and specific examples:

[0068] When an asymmetrical fault occurs in the distribution network, a negative-sequence equivalent network is established based on the principle of sequence network diagram decomposition, such as... Figure 1 As shown;

[0069] According to the negative sequence equivalence network, the negative sequence current generated by the virtual power source at the fault point flows into the line from the fault point and flows to the upstream line, downstream line, healthy line and neutral point of the system respectively, forming a flow loop. The shortest path between the fault point and the power source (bus) is called the fault path.

[0070] In each flow loop, the fault path has the smallest loop impedance, therefore its negative sequence current is the largest. The loop impedances of other non-faulty paths are larger, therefore their negative sequence currents are very small, and the difference in current magnitude between the two is significant. Non-faulty paths include the downstream line of the fault point, non-faulty lines, and all branch lines. Therefore, by comparing the magnitude of the negative sequence current at the outlet of each line during a distribution network fault from the bus end, the negative sequence current at the outlet of the line where the fault point is located is the largest, which can be used to identify the faulty line.

[0071] In a faulty line, negative-sequence current flows from the fault point to both ends of the line. Due to the existence of negative-sequence impedance in the line, a negative-sequence voltage drop is generated along the direction of negative-sequence current flow. The negative-sequence voltage gradually decreases as the negative-sequence current flows, and because the line impedance is uniformly distributed, the negative-sequence voltage decreases uniformly. From this, we can obtain the basic characteristics of the negative-sequence voltage distribution in a faulty line during a distribution network fault: with the fault point as the boundary and the direction from the busbar to the end of the faulty line as positive, the magnitude of the negative-sequence voltage from the busbar to the fault point increases linearly with the line length, and the magnitude of the negative-sequence voltage from the fault point to the end of the line decreases linearly with the line length.

[0072] Furthermore, because the negative-sequence current in the fault path is larger than that in the non-fault path, the negative-sequence voltage gradient upstream of the fault point is large, while the negative-sequence voltage gradient downstream of the fault point is very small. When the downstream line is short, the negative-sequence voltage gradient can be approximately ignored. The negative-sequence voltage distribution characteristics in the faulted line are as follows: Figure 2 As shown.

[0073] Let x be the distance from any point on the faulty line to the line outlet, and let U be the amplitude of the negative sequence voltage at any point. (2) (x), the amplitudes of the negative sequence power frequency current upstream and downstream of the fault point are I... (2) a I (2) b If the negative sequence impedance per unit length of the faulted line is Z2 and the length of the faulted line is l, then the negative sequence voltage distribution law of the faulted line can be expressed by equation (1).

[0074]

[0075] In the formula, U (2) (0) represents the negative sequence voltage amplitude at the faulty line outlet;

[0076] U (2) (l) represents the negative sequence voltage amplitude at the end of the faulty line;

[0077] x f This is the distance from the fault point to the exit of the faulty line.

[0078] Let the amplitude of the power frequency negative sequence voltage at the fault point be U. (2) (x f ), then when x = x f When, equation (2) holds true.

[0079] U (2) (x f )=U (2) (0)+I (2) a Z2x f =U (2) (l)+I (2) b Z2(lx f (2)

[0080] 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 intersect at the fault point. The negative sequence voltage distribution curve of the faulted line is a continuous curve with the fault point as the inflection point.

[0081] In the power distribution lines on site, voltage and current detection devices are usually installed at both ends of the line to obtain voltage and current information at the beginning and end. Based on the information at both ends, the location of the fault point can be derived and calculated using the line impedance data. The equation set for calculating the distance from the fault point to the busbar is shown in equation (3).

[0082]

[0083] In equation (3), U (2) (0), U (2) (l), I (2) a I (2) b Z2 is a known quantity. According to equation (3), the distance x from the fault point to the busbar can be obtained. f The calculation formula is shown in equation (4).

[0084]

[0085] Based on the above analysis and combined with actual field application scenarios, a method for accurate fault location in distribution networks based on negative sequence component characteristics and quantities at both ends of the line is proposed. The implementation process of this method is as follows: Figure 3 As shown.

[0086] This method first identifies an asymmetrical fault in a distribution line by collecting the fundamental frequency components of voltage and current at the beginning and end of each line, and then obtains the negative sequence components of voltage and current through phase-mode transformation. Next, it compares the magnitude of the negative sequence current at the outlet of each line, identifying the line with the largest negative sequence current as the faulty line. Then, it extracts the negative sequence voltage and current data at the beginning and end of the faulty line, and calculates the magnitude of the negative sequence voltage at the fault point from both the beginning and end of the faulty line, based on the obtained negative sequence impedance. Finally, it solves a system of equations to determine the distance from the fault point to the busbar, thus achieving fault location. Specifically, it includes the following steps:

[0087] A method for accurate fault location in distribution networks based on negative sequence component characteristics and end-point quantities includes the following steps:

[0088] S1. Collect fault voltage and current information, and extract the fundamental frequency components of voltage and current;

[0089] S1 includes the following sub-steps:

[0090] S1.1 Install distribution terminals with three-phase voltage and current detection capabilities at the beginning and end of each line under the same busbar in the distribution network.

[0091] S1.2 When a fault occurs in the power distribution line, each terminal detects a sudden change in voltage. At this time, the A, B, and C phase voltages and currents at the beginning and end of each line are collected.

[0092] S1.3 Filter and extract the fundamental frequency of the collected three-phase voltage and current.

[0093] The fundamental frequency extraction formula is:

[0094]

[0095] Where x(k) is the discrete value of the instantaneous current or voltage of a certain phase after analog-to-digital conversion;

[0096] k is the sampling point number;

[0097] N is the number of sampling points for discrete values ​​within one period;

[0098] a1 is the real part of the fundamental frequency phasor;

[0099] b1 is the imaginary part of the fundamental frequency phasor;

[0100] A is the amplitude of the fundamental frequency phasor;

[0101] θ is the phase angle of the fundamental frequency phasor.

[0102] S2. The fundamental frequency phasors of the three-phase voltage and current are transformed by phase mode to obtain the negative sequence components of the voltage and current.

[0103] In S2, the formulas for decoupling the fundamental frequency phasors of the three-phase voltage and current into the positive, negative, and zero-sequence components of the current and voltage after phase mode transformation are as follows:

[0104]

[0105]

[0106] Where a = e j120° a 2 =e j240° And satisfying 1+a+a 2 =0, a 3 =1;

[0107] The current phasors for phases A, B, and C are as follows:

[0108] These are the voltage phasors for phases A, B, and C, respectively.

[0109] These are the current phasors in positive, negative, and zero sequences, respectively;

[0110] These are voltage phasors in positive, negative, and zero sequences, respectively.

[0111] S3. Extract the amplitude of the negative sequence component of the current at the outlet of each line and compare them. The line with the largest amplitude of the negative sequence component of the current at the outlet is identified as the faulty line.

[0112] S4. Establish the expressions for the first and last values ​​of the negative sequence voltage amplitude at the fault point;

[0113] S4 includes the following sub-steps:

[0114] S4.1 Obtain the negative sequence impedance data per unit length of the faulty line, obtain the amplitude of the negative sequence voltage and the amplitude of the negative sequence current at the beginning and end of the faulty line, and obtain the length from the beginning to the end of the faulty line.

[0115] In S4.1, the expression for the magnitude of the negative sequence voltage at the fault point, established from the first-end quantity, is as follows:

[0116] U (2) (x f )=U (2) (0)+I (2) a Z2x f ;

[0117] In the formula, U (2) (x f The value of the negative sequence voltage at the power frequency at the fault point is unknown.

[0118] U(2) (0) represents the amplitude of the negative sequence voltage at the power frequency at the beginning of the faulty line;

[0119] I (2) a The amplitude of the negative sequence current at power frequency upstream of the fault point, measured at the beginning of the faulty line.

[0120] Z2 is the negative sequence impedance per unit length of the faulty line;

[0121] x f is the distance from the fault point to the beginning of the faulty line, and is the quantity to be determined.

[0122] S4.2. Using the amplitude of the negative sequence voltage at the power frequency, the amplitude of the negative sequence current at the power frequency at the beginning of the faulty line, and the negative sequence impedance per unit length of the faulty line as known quantities, establish an expression for the magnitude of the negative sequence voltage at the beginning of the fault.

[0123] In S4.2, the expression for the magnitude of the negative sequence voltage at the fault point, established from the terminal quantity, is as follows:

[0124] U (2) (x f )=U (2) (l)+I (2) b Z2(lx f );

[0125] In the formula, U (2) ( xf The value represents the amplitude of the negative sequence voltage at the power frequency at the fault location.

[0126] U (2) (l) is the frequency negative sequence voltage amplitude at the end of the faulty line, which is an unknown quantity;

[0127] I (2) b The amplitude of the negative sequence current at power frequency upstream of the fault point, measured at the end of the faulty line.

[0128] Z2 is the negative sequence impedance per unit length of the faulty line;

[0129] l is the length from the beginning to the end of the faulty line;

[0130] x f is the distance from the fault point to the beginning of the faulty line, and is the quantity to be determined.

[0131] S5. Solve the system of equations for the negative sequence voltage amplitude expression of the fault point established by the first and last quantities to determine the distance to the fault point.

[0132] In S5, the simultaneous equations of the fault point power frequency negative sequence voltage amplitude expression established by the first-end quantity and the fault point power frequency negative sequence voltage amplitude expression established by the last-end quantity are as follows:

[0133]

[0134] Since the amplitude of the negative sequence voltage at the fault point is unique, the distance x from the fault point to the beginning of the faulty line can be obtained from the equations. f The expression is as follows:

[0135]

[0136] By substituting the relevant parameters, the distance x from the fault point to the beginning of the faulty line can be calculated. f Complete fault location.

[0137] Example 1: Two-phase short circuit fault

[0138] The local line topology of a certain 10kV distribution network is as follows: Figure 4 As shown.

[0139] This local distribution network has four 10kV busbars. Each line is equipped with a distribution terminal at its outlet and along its route to monitor voltage and current information in real time. Each line is less than 15km long and has a typical load connected at its end. A two-phase short-circuit fault occurred on one of the lines. Each distribution terminal acquired real-time fault waveform data. Through data statistics, two sets of data were obtained: the negative sequence current amplitude of each terminal and the negative sequence voltage amplitude at the beginning and end of the faulty line, as shown in Tables 1 and 2.

[0140] Table 1. Amplitude of negative sequence current at the beginning of each line

[0141]

[0142] Table 2. Negative sequence voltage amplitude at the beginning and end of the faulty line.

[0143]

[0144] Based on the above data, this method determines that the fault is located in line 1, 8.029 km from the line's exit.

[0145] The specific implementation process is as follows:

[0146] S1. Collect fault voltage and current information, and extract the fundamental frequency components of voltage and current;

[0147] S1 includes the following sub-steps:

[0148] S1.1: Install distribution terminals with three-phase voltage and current detection capabilities at the beginning and end of each line under the same busbar in the distribution network;

[0149] S1.2: When a fault occurs in the power distribution line, each terminal detects a sudden change in voltage. At this time, the A, B, and C phase voltages and currents at the beginning and end of each line are collected.

[0150] S1.3: Filter and extract the fundamental frequency of the collected three-phase voltage and current;

[0151] The formula for fundamental frequency extraction is as follows:

[0152]

[0153] Where x(k) is the discrete value of the instantaneous current or voltage of a certain phase after analog-to-digital conversion;

[0154] k is the sampling point number;

[0155] N is the number of sampling points for discrete values ​​within one period;

[0156] a1 is the real part of the fundamental frequency phasor;

[0157] b1 is the real part of the fundamental frequency phasor;

[0158] A is the amplitude of the fundamental frequency phasor;

[0159] θ is the phase angle of the fundamental frequency phasor.

[0160] S2: The fundamental frequency phasors of the three-phase voltage and current are transformed into negative sequence components of voltage and current through phase mode transformation;

[0161] The formulas for decoupling the fundamental frequency phasors of three-phase voltage and current into positive, negative, and zero-sequence components of current and voltage through phase-mode transformation are as follows:

[0162]

[0163] Where a = e j120° a 2 =e j240° And satisfying 1+a+a 2 =0, a 3 =1;

[0164] The current phasors for phases A, B, and C are as follows:

[0165] These are the voltage phasors for phases A, B, and C, respectively.

[0166] These are the current phasors in positive, negative, and zero sequences, respectively;

[0167] These are voltage phasors in positive, negative, and zero sequences, respectively.

[0168] S3: Extract the amplitude of the negative sequence component of the current at the outlet of each line and compare them. As shown in Table 1, the line 1 with the largest amplitude of the negative sequence component of the current at the outlet is identified as the faulty line.

[0169] S4: Obtain the negative sequence impedance data per unit length of the faulty line, obtain the power frequency negative sequence voltage amplitude and power frequency negative sequence current amplitude at the beginning and end of the faulty line, and obtain the length from the beginning to the end of the faulty line (not the actual line length, but the length between the two detection terminals at the beginning and end).

[0170] The expression for the negative sequence voltage amplitude at the fault point, established from the first-end quantity, is as follows:

[0171] U (2) (x f )=U (2) (0)+I (2) a Z2x f ;

[0172] In the formula, U (2) (x f The value represents the amplitude of the negative sequence voltage at the power frequency at the fault location.

[0173] U (2) (0) represents the frequency negative sequence voltage amplitude at the beginning of the faulty line.

[0174] ;I (2) a The amplitude of the negative sequence current at power frequency upstream of the fault point, measured at the beginning of the faulty line.

[0175] Z2 is the negative sequence impedance per unit length of the faulty line;

[0176] x f The distance from the fault point to the beginning of the faulty line is the quantity to be determined.

[0177] Where Z2 = 0.4081 / km, U (2) (0) = 1050.73V, I (2) a =854.99A.

[0178] The expression for the first-terminal quantity of the negative sequence voltage amplitude at the fault point is as follows:

[0179] U (2) (x f )=1050.73+854.99×0.4081×x f ;

[0180] Using the amplitude of the negative sequence voltage at the power frequency and the amplitude of the negative sequence current at the power frequency at the end of the faulted line, as well as the negative sequence impedance per unit length of the faulted line, as known quantities, an expression for the terminal quantity of the negative sequence voltage amplitude at the fault point is established.

[0181] The expression for the negative sequence voltage magnitude at the fault point, established from the terminal quantity, is as follows:

[0182] U (2) (x f )=U (2) (l)+I (2) b Z2(lx f );

[0183] In the formula, U (2) (x f The value represents the amplitude of the negative sequence voltage at the power frequency at the fault location.

[0184] U (2) (l) represents the frequency negative sequence voltage amplitude at the end of the faulty line;

[0185] I (2) b The amplitude of the negative sequence current at power frequency upstream of the fault point, measured at the end of the faulty line.

[0186] Z2 is the negative sequence impedance per unit length of the faulty line;

[0187] l is the length from the beginning to the end of the faulty line;

[0188] x f The distance from the fault point to the beginning of the faulty line is the quantity to be determined.

[0189] Where Z2 = 0.4081 / km, U (2) (l) = 3834.564V, I (2) b =10.88A.

[0190] The expression for the first-terminal quantity of the negative sequence voltage amplitude at the fault point is as follows:

[0191] U (2) (x f )=3834.56+10.88×0.4081×(12-x f );

[0192] S5: Solve the system of equations for the negative sequence voltage amplitude expression of the fault point established by the first and last quantities to determine the distance to the fault point;

[0193] The expression for the magnitude of the negative-sequence power frequency voltage at the fault point, established from the first-end quantity, and the expression for the magnitude of the negative-sequence power frequency voltage at the fault point, established from the last-end quantity, are combined into a system of equations, as follows:

[0194]

[0195] Since the amplitude of the negative sequence voltage at the fault point is unique, the distance x from the fault point to the beginning of the faulty line can be obtained from the equations. f The expression is as follows:

[0196]

[0197] By substituting the relevant parameters, the distance x from the fault point to the beginning of the faulty line can be calculated. f Complete fault location.

[0198] The distance x from the fault point to the beginning of the faulty line is obtained from step S5. f =8.029km.

[0199] According to subsequent feedback, the actual fault location was between terminals 3 and 4 of line 1, 8km away from the line exit. Therefore, the fault line selection and fault section location were accurate, and the fault ranging error was 0.029km. The absolute ranging error was calculated as 0.24% based on the ranging error / line length.

[0200] Example 2: Single-phase ground fault

[0201] A simulation model of a 10kV single-ended radial, ungrounded system was built using MATLAB / Simulink simulation software, such as... Figure 5 As shown. There are 3 outgoing lines on the busbar side, of which the two healthy lines are 8km and 10km long respectively, and the faulty line is 12km long. The line parameters and load parameters are all typical values.

[0202] A single-phase ground fault of phase A is set at a distance of 8km from the faulty line to the busbar, with a fault grounding resistance of 10Ω; detection terminals are set at the beginning and end of the faulty line, numbered 1 and 2 respectively.

[0203] Two sets of data were obtained after the fault: the negative sequence current amplitude of each terminal and the negative sequence voltage amplitude at the beginning and end of the faulty line, as shown in Tables 3 and 4.

[0204] Table 3. Negative sequence current amplitude at each terminal

[0205]

[0206] Table 4. Negative sequence voltage amplitude at the beginning and end of the faulty line.

[0207]

[0208] Comparing the negative sequence current amplitudes at terminals 1, A1, and B1 at the exit of each line in Table 3, line 1 is much larger than line 2 and line 3. Therefore, line 1 is determined to be the faulty line.

[0209] The impedance per unit length of the faulty line is Z2 = 0.401 Ω / km.

[0210] Based on the power frequency negative sequence voltage amplitude of terminal 1, the power frequency negative sequence current amplitude of terminal 1, and the impedance per unit length of the faulted line, the expression for the initial quantity of the negative sequence voltage amplitude at the fault point is obtained as follows:

[0211] U (2) (x f )=14.4+11.69×0.401×x f (1)

[0212] Based on the power frequency negative sequence voltage amplitude of terminal 2, the power frequency negative sequence current amplitude of terminal 2, the impedance per unit length of the faulted line, and the distance from terminal 2 to the line outlet, the final expression for the negative sequence voltage amplitude at the fault point is obtained as follows:

[0213] U (2) (x f )=52.73+0.0332×0.401×(12-x f (2)

[0214] Solving the system of equations (1) and (2) together, we find that the distance from the fault point to the fault line exit is 8.0077 km, which is 0.0077 km away from the actual fault point, with an absolute error of 0.064%.

[0215] Example 3: Two-phase short circuit fault

[0216] A simulation model of a 10kV single-ended radial, ungrounded system was built using MATLAB / Simulink simulation software, such as... Figure 5 As shown. There are 3 outgoing lines on the busbar side, of which the two healthy lines are 8km and 10km long respectively, and the faulty line is 12km long. The line parameters and load parameters are all typical values.

[0217] A two-phase short-circuit ground fault (A and B phases) is set at a distance of 8km from the faulty line to the busbar, with a fault grounding resistance of 10Ω; detection terminals are set at the beginning and end of the faulty line, numbered 1 and 2.

[0218] Two sets of data were obtained after the fault: the negative sequence current amplitude of each terminal and the negative sequence voltage amplitude at the beginning and end of the faulted line. These data are shown in Tables 5 and 6.

[0219] Table 5. Negative sequence current amplitude at each terminal

[0220]

[0221] Table 6. Negative sequence voltage amplitude at the beginning and end of the faulty line.

[0222]

[0223] Comparing the negative sequence current amplitudes at terminals 1, A1, and B1 at the exit of each line in Table 5, line 1 is much larger than line 2 and line 3. Therefore, line 1 is determined to be the faulty line.

[0224] The impedance per unit length of the faulty line is Z2 = 0.409 Ω / km.

[0225] Based on the power frequency negative sequence voltage amplitude of terminal 1, the power frequency negative sequence current amplitude of terminal 1, and the impedance per unit length of the faulted line, the expression for the initial quantity of the negative sequence voltage amplitude at the fault point is obtained as follows:

[0226] U (2) (x f )=1053.69+857.41×0.409×x f (1)

[0227] Based on the power frequency negative sequence voltage amplitude of terminal 2, the power frequency negative sequence current amplitude of terminal 2, the impedance per unit length of the faulted line, and the distance from terminal 2 to the line outlet, the final expression for the negative sequence voltage amplitude at the fault point is obtained as follows:

[0228] U (2) (x f )=3849.82+8.1425×0.409×(12-x f (2)

[0229] Solving the system of equations (1) and (2) together, we find that the distance from the fault point to the fault line exit is 8.0105km, which is 0.0105km different from the actual fault point distance, with an absolute error of 0.088%.

[0230] The preferred embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and the devices and structures not described in detail should be understood as being implemented in a conventional manner in the art. Any person skilled in the art can make many possible variations and modifications to the technical solutions of the present invention using the methods and techniques disclosed above, or modify them into equivalent embodiments with equivalent changes, without departing from the scope of the present invention. This does not affect the essential content of the present invention. Therefore, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the present invention's technical solutions still fall within the protection scope of the present invention.

Claims

1. A method for accurate fault location in distribution networks based on negative sequence component characteristics and end-point quantities, characterized in that, Includes the following steps: S1. Collect fault voltage and current information, and extract the fundamental frequency components of voltage and current; S2. The fundamental frequency phasors of the three-phase voltage and current are transformed by phase mode to obtain the negative sequence components of the voltage and current. S3. Extract the amplitude of the negative sequence component of the current at the outlet of each line and compare them. The line with the largest amplitude of the negative sequence component of the current at the outlet is identified as the faulty line. S4. Establish the expressions for the first and last values ​​of the negative sequence voltage amplitude at the fault point; S5. Solve the system of equations for the negative sequence voltage amplitude expression of the fault point established by the first and last quantities to determine the distance to the fault point.

2. The method for accurate fault location in a distribution network based on negative sequence component characteristics and end-point quantities according to claim 1, characterized in that, S1 includes the following sub-steps: S1.1 Install distribution terminals with three-phase voltage and current detection capabilities at the beginning and end of each line under the same busbar in the distribution network. S1.2 When a fault occurs in the power distribution line, each terminal detects a sudden change in voltage. At this time, the A, B, and C phase voltages and currents at the beginning and end of each line are collected. S1.3 Filter and extract the fundamental frequency of the collected three-phase voltage and current.

3. The method for accurate fault location in a distribution network based on negative sequence component characteristics and end-point quantities according to claim 2, characterized in that, In S1.3, the real part of the fundamental frequency phasor is: The imaginary part of the fundamental phasor is: Where 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 period, a1 is the real part of the fundamental frequency phasor, and b1 is the imaginary part of the fundamental frequency phasor.

4. The method for accurate fault location in a distribution network based on negative sequence component characteristics and end-point quantities according to claim 3, characterized in that, In S1.3, the amplitude of the fundamental frequency phasor is:

5. The method for accurate fault location in a distribution network based on negative sequence component characteristics and end-point quantities according to claim 4, characterized in that, In S1.3, the phase angle of the fundamental frequency phasor is:

6. The method for accurate fault location in a distribution network based on negative sequence component characteristics and end-point quantities according to claim 5, characterized in that, In S2, the formulas for decoupling the fundamental frequency phasors of the three-phase voltage and current into the positive, negative, and zero-sequence components of the current and voltage after phase-mode transformation are as follows: Where a = e j120° a 2 =e j240° And satisfying 1+a+a 2 =0, a 3 =1; The current phasors for phases A, B, and C are as follows: These are the voltage phasors for phases A, B, and C, respectively. These are the current phasors in positive, negative, and zero sequences, respectively; These are voltage phasors in positive, negative, and zero sequences, respectively.

7. The method for accurate fault location in a distribution network based on negative sequence component characteristics and end-point quantities according to claim 6, characterized in that, S4 includes the following sub-steps: S4.1 Obtain the negative sequence impedance data per unit length of the faulty line, obtain the amplitude of the negative sequence voltage and the amplitude of the negative sequence current at the beginning and end of the faulty line, and obtain the length from the beginning to the end of the faulty line. S4.

2. Using the amplitude of the negative sequence voltage at the power frequency, the amplitude of the negative sequence current at the power frequency, and the negative sequence impedance per unit length of the faulty line as known quantities, establish an expression for the amplitude of the negative sequence voltage at the fault point.

8. The method for accurate fault location in a distribution network based on negative sequence component characteristics and end-point quantities according to claim 7, characterized in that, In S4.1, the expression for the negative sequence voltage amplitude at the fault point established by the first-end quantity is as follows: U (2) (x f )=U (2) (0)+I (2) a Z2x f ; In the formula, U (2) (x f U is the amplitude of the negative sequence voltage at the power frequency at the fault point, which is an unknown quantity; (2) (0) represents the amplitude of the negative sequence voltage at the power frequency at the beginning of the faulty line; I (2) a Z1 is the amplitude of the negative sequence current at power frequency upstream of the fault point, measured at the beginning of the faulty line; Z2 is the negative sequence impedance per unit length of the faulty line; x f is the distance from the fault point to the beginning of the faulty line, and is the quantity to be determined.

9. The method for accurate fault location in a distribution network based on negative sequence component characteristics and end-point quantities according to claim 8, characterized in that, In S4.2, the expression for the negative sequence voltage amplitude at the fault point established by the terminal quantity is as follows: U (2) (x f )=U (2) (l)+I (2) b Z2(lx f ); In the formula, U (2) (xf) represents the amplitude of the negative sequence voltage at the power frequency at the fault point; U (2) (l) represents the amplitude of the negative-sequence voltage at the end of the faulty line, which is an unknown quantity; I (2) b Z1 is the amplitude of the negative sequence current at power frequency upstream of the fault point, measured at the end of the faulty line; Z2 is the negative sequence impedance per unit length of the faulty line. l is the length from the beginning to the end of the faulty line; x f is the distance from the fault point to the beginning of the faulty line, and is the quantity to be determined.

10. The method for accurate fault location in a distribution network based on negative sequence component characteristics and end-point quantities according to claim 9, characterized in that, In S5, the expression for the amplitude of the fault point power frequency negative sequence voltage established by the first-end quantity and the expression for the amplitude of the fault point power frequency negative sequence voltage established by the last-end quantity are combined into a system of equations, as follows: Since the amplitude of the negative sequence voltage at the fault point is unique, the distance x from the fault point to the beginning of the faulty line can be obtained from the equations. f The expression is as follows:

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