Distribution network single-phase earth fault distance measurement method and system based on zero and negative sequence components

Abstract

The invention discloses a distribution network single-phase earth fault distance measurement method and system based on zero and negative sequence components, and belongs to the technical field of power systems, the distribution network single-phase earth fault distance measurement method based on zero and negative sequence components comprises the following steps: carrying out line section division on a distribution network line, and obtaining line parameter information; when the system operates normally, the detection device monitors three-phase voltage and current and carries out data processing; judging whether a single-phase earth fault occurs or not according to the data change; based on a fault judgment result, a fault section is obtained from the distribution automation system, and equivalent zero-sequence and negative-sequence networks of the system are established; measuring three-phase voltage and current time domain signals after the fault by using a detection device at the bus, and carrying out data processing again; and establishing a distance measurement function of the fault section, solving the function, and calculating the distance from the fault point to the head end of the fault section. According to the method, high precision is kept under various distribution network structures such as a mixed line and a multi-branch line, and the distance measurement precision is not affected by grounding resistance.

Description

Technical Field

[0001] The present invention belongs to the technical field of power systems, and more specifically, relates to a distribution network single-phase grounding fault distance measurement method and system based on zero negative sequence components. Background Art

[0002] China's medium-voltage distribution network mainly adopts three grounding methods: ungrounded neutral point, grounded through arc suppression coils, and grounded through small resistors. According to statistics, single-phase grounding faults account for more than 80% of distribution network faults. Therefore, accurately determining the fault location is of great significance to improving the power supply reliability of the distribution network. The application of fault distance measurement technology in the transmission network has been relatively mature. In the distribution network, many fault distance measurement methods have been proposed, but the distribution network structure is complex and the line investment cost is high. At present, in engineering applications, the fault location of the distribution network is still at the stage of section location.

[0003] The two commonly used methods for fault distance measurement technology are the traveling wave method and the impedance method. The traveling wave method calculates the fault distance by measuring the propagation time of the traveling wave between the fault point and the measuring end. The distribution network is mostly a mixed line mode of overhead lines and cables. The change of wave impedance makes it difficult to determine the wave speed; and the traveling wave signal usually uses a transient high-frequency signal. Factors such as noise, grounding resistance, and fault phase angle will affect the acquisition of the wave head. At the same time, the distribution network has a complex topology, short lines, and many branches. It is necessary to install high-sampling-rate traveling wave ranging devices at multiple nodes, which is costly. Therefore, the traveling wave method has not been widely used in the distribution network. The impedance method is to determine the relevant information of the fault loop impedance and the fault location based on the relationship between the voltage and current when the fault occurs, and then obtain the fault distance. According to the different measurement locations of the required electrical quantities, the impedance method is divided into the single-end method and the double-end method. The double-end impedance method has good anti-interference and high positioning accuracy, but the double-end impedance method requires the installation of a synchronous timing device, which is costly, and the distribution network has many branches. If the double-end impedance method is used, a large number of terminal devices need to be installed. The single-ended impedance method only requires electrical quantities on one side, has low hardware requirements, and is easy to implement without communication. The key point of the single-ended impedance method is to reduce the influence of grounding resistance and power supply at the measuring end and improve the ranging accuracy. The research on the single-ended impedance method is currently mainly concentrated in the transmission network, and less research is done in the distribution network.

[0004] In summary, there is an urgent need to propose a single-ended impedance distribution network fault location technology that is applicable to a variety of distribution network structures, has strong applicability and low cost. Summary of the invention

[0005] In order to solve the deficiencies in the prior art, the present invention provides a distribution network single-phase grounding fault ranging method and system based on zero negative sequence component, and obtains steady-state zero-sequence and negative-sequence signals after a single-phase grounding fault occurs in the line through a detection device at the busbar. A distribution network single-phase grounding fault ranging technology based on zero negative sequence component is proposed, which is suitable for radial distribution networks with ungrounded neutral points, grounded through arc suppression coils, and grounded through small resistances.

[0006] The present invention adopts the following technical solution.

[0007] The first aspect of the present invention proposes a distribution network single-phase grounding fault distance measurement method based on zero negative sequence component, comprising the following steps:

[0008] Divide the distribution network lines into sections and obtain the distribution network line parameter information;

[0009] Based on the obtained distribution network lines, when the system is operating normally, the detection device at the busbar monitors the three-phase voltage and current at low frequency, and synthesizes the zero-sequence and negative-sequence voltage and current; based on the line voltage, i.e., symmetry, the change of zero-sequence voltage, and the change of zero-sequence and negative-sequence current on the line, it is determined whether a single-phase grounding fault occurs;

[0010] Based on the obtained fault judgment results, the fault section is obtained from the distribution automation system, and the system equivalent zero-sequence and negative-sequence networks are established; the three-phase voltage and current time domain signals are measured using the detection device at the bus, and the steady-state zero-sequence and negative-sequence voltage and current power frequency components at the bus are obtained through the symmetrical component method and fast Fourier transform;

[0011] According to the obtained distribution network line parameters, the obtained system equivalent zero-sequence and negative-sequence networks, and the power frequency components of the steady-state zero-sequence and negative-sequence voltages and currents at the busbar, a distance measurement function of the fault section is established, the function is solved, and the distance from the fault point to the head end of the fault section is calculated.

[0012] The neutral point grounding method of the distribution network is that the neutral point is not grounded, is grounded through an arc suppression coil, or is grounded through a small resistor; the distribution network topology is a radial distribution network; the line types include a single cable line, a single overhead line, and a cable-overhead line mixed line.

[0013] Dividing the line sections includes: dividing the line sections into trunk line sections and branch line sections;

[0014] The trunk line section includes: the section from the beginning of the trunk line to the beginning of the branch line, the section from the beginning of the branch line to the fault point, and the section from the end of the trunk line to the beginning of the branch line;

[0015] The branch line section includes: the section from the beginning of the branch line to the end of the branch line.

[0016] Obtaining the distribution network line parameter information includes: online identification or obtaining the set distribution line zero-sequence parameter information, negative-sequence parameter information, distribution network topology, detection device information, and line section length.

[0017] In the embodiment, the distribution network line parameter information can be considered as the set line parameter information. Some PMU and FTU devices can also identify the zero and negative sequence parameters of the line online. Both methods are acceptable. The information of the detection device mainly includes the installation position of the detection device in the distribution network and the sampling frequency of the detection device.

[0018] Determining whether a single-phase grounding fault occurs includes:

[0019] Set the zero-sequence voltage starting value;

[0020] The detection device is used to measure the three-phase voltage at low frequency and calculate the synthetic line voltage and zero-sequence voltage, measure the three-phase current and calculate the synthetic zero-sequence and negative-sequence current;

[0021] Based on the set zero-sequence voltage starting value and the line voltage, zero-sequence voltage, zero-sequence current and negative-sequence current under normal operation, when the line phase voltage changes, if the amplitude and phase difference of the three line voltages remain unchanged, the line zero-sequence voltage value exceeds the zero-sequence voltage starting value, and there are zero-sequence and negative-sequence currents, it is determined that a single-phase grounding fault has occurred;

[0022] Based on the fault judgment result, the single-phase grounding fault location is started, and the three-phase voltage and current are collected at high frequency by the detection device, and the steady-state zero-sequence and negative-sequence voltage and current at the bus are calculated and synthesized;

[0023] Based on the time domain signals of the steady-state three-phase voltage and current within the delayed sampling period at the time of fault occurrence, the high-order harmonic components are filtered out and the power frequency components of the steady-state zero-sequence and negative-sequence voltage and current are synthesized.

[0024] In the equivalent zero-sequence and negative-sequence networks after a single-phase grounding fault, each section adopts a concentrated parameter π-type equivalent circuit.

[0025] Calculating the distance from the fault point to the beginning of the fault section includes:

[0026] Based on the obtained system equivalent zero-sequence network, the power frequency components of the steady-state zero-sequence voltage and current at the bus, and the line parameters, for the fault section, the power frequency components of the zero-sequence voltage and zero-sequence current at the bus are used, based on the system equivalent zero-sequence network after the fault, combined with the line parameters, to obtain the expression of the zero-sequence voltage at the fault point and the zero-sequence current flowing from the fault point to the bus side with respect to the fault distance;

[0027] Based on the obtained zero-sequence voltage at the fault point and the expression of the zero-sequence current flowing from the fault point to the bus side with respect to the fault distance and the line parameters, the zero-sequence voltage at the fault point, the equivalent zero-sequence network of the system after the fault, and the line parameters are used to obtain the expression of the zero-sequence current flowing from the fault point to the end of the line with respect to the fault distance, and the zero-sequence current expression at the fault point is obtained by adding it to the expression of the zero-sequence current flowing from the fault point to the bus side with respect to the fault distance;

[0028] Based on the obtained system equivalent negative sequence network, the power frequency components of the steady-state negative sequence voltage and current at the bus, and the line parameters, the power frequency components of the negative sequence voltage and negative sequence current at the bus are used, based on the system equivalent negative sequence network after the fault, combined with the line parameters, to obtain the expression of the negative sequence voltage at the fault point and the negative sequence current flowing from the fault point to the bus side with respect to the fault distance;

[0029] Based on the obtained zero-sequence current expression at the fault point and the obtained negative-sequence current expression at the fault point, the negative-sequence voltage at the fault point, the equivalent negative-sequence network of the system after the fault, and the line parameters, the expression of the negative-sequence current flowing from the fault point to the end of the line with respect to the fault distance is obtained, and the expression of the negative-sequence current flowing from the fault point to the bus side with respect to the fault distance is added to obtain the negative-sequence current expression at the fault point;

[0030] The second aspect of the present invention proposes a distribution network single-phase grounding fault distance measurement system based on zero negative sequence component, comprising: a signal collection module, a data preprocessing module, a signal processing module, and a fault location module;

[0031] Signal collection module, used to obtain three-phase voltage and current information, and record the corresponding waveforms; obtain distribution line parameter information;

[0032] A data preprocessing module is connected to the signal collection module, and synthesizes the line voltage, zero-negative sequence voltage and current through data preprocessing based on the three-phase voltage and current collected by the signal collection module;

[0033] The fault judgment module is connected to the data preprocessing module, and based on the line voltage, zero-negative sequence voltage and current data obtained by the data preprocessing module, the data change is analyzed to determine whether a single-phase grounding fault occurs;

[0034] The signal processing module is connected to the data preprocessing module and the fault judgment module, and is used to perform fast Fourier transform on the three-phase voltage and current time domain signals collected by the detection device at the bus after determining that a single-phase grounding fault has occurred, calculate the line voltage, and obtain the zero-sequence and negative-sequence voltage and current power frequency components at the bus by the symmetrical component method;

[0035] The fault location module is connected to the signal collection module, the signal processing module and the fault judgment module. After determining that a fault has occurred according to the judgment result of the fault judgment unit, it is used to determine the fault location according to the fault distance measurement method in combination with the signal processing information.

[0036] The signal collection module includes a detection device;

[0037] The detection device includes a low-frequency acquisition unit and a high-speed acquisition unit;

[0038] The low-frequency acquisition unit is used to collect three-phase voltage and current at low frequency during normal operation;

[0039] The high-speed acquisition unit is used to collect three-phase voltage and current at high frequency after a single-phase grounding fault occurs.

[0040] The fault location module includes: a first unit, a second unit, and a third unit;

[0041] The first unit is connected to the signal collection module and the signal processing module, and based on the distribution line parameter information obtained by the signal collection module and the power frequency component of the zero-sequence voltage and current obtained by the signal processing module and the equivalent zero-sequence network, it calculates the expression of the zero-sequence current flowing from the fault point to the bus side with respect to the fault distance and the zero-sequence current expression at the fault point, and adds them to obtain the zero-sequence current expression at the fault point;

[0042] The second unit is connected to the signal collection module and the signal processing module, and based on the distribution line parameter information obtained by the signal collection module and the power frequency component of the negative sequence voltage and current obtained by the signal processing module and the equivalent negative sequence network, it calculates the expression of the negative sequence current flowing from the fault point to the bus side with respect to the fault distance and the negative sequence current expression at the fault point, and adds them to obtain the negative sequence current expression at the fault point;

[0043] The third unit is connected to the first unit and the second unit. Based on the zero-sequence current expression at the fault point obtained by the first unit and the negative-sequence current expression at the fault point obtained by the second unit, and through the boundary condition that the zero-sequence and negative-sequence currents at the fault point are equal, the objective function is set to the modulus of the difference between the zero-sequence current and the negative-sequence current. The search method is used to search within the length of the fault section to obtain the fault distance, that is, the distance that minimizes the objective function.

[0044] The beneficial effect of the present invention is that, compared with the prior art, the present invention can maintain high accuracy in various distribution network structures such as hybrid lines and multi-branch lines, and the ranging accuracy is not affected by the grounding resistance. Fault ranging can be achieved according to the detection device at the busbar, reducing the dependence of the positioning method on communication. The technical principle is simple, the engineering feasibility is strong, and it has great academic value and practicality. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1The present invention proposes a flow chart of a single-phase ground fault distance measurement method for a distribution network based on zero negative sequence components;

[0046] Figure 2 This is a fault schematic diagram when a single-phase grounding fault occurs in the AD section of the multi-branch hybrid line of the distribution network in Example 1 of the present invention;

[0047] Figure 3 In Example 1 of the present invention Figure 2 The corresponding equivalent zero-sequence network diagram after the fault;

[0048] Figure 4 In Example 1 of the present invention Figure 2 The corresponding equivalent negative sequence network diagram after the fault;

[0049] Figure 5 It is the ranging function curve in Example 1 of the present invention. DETAILED DESCRIPTION

[0050] In order to make the purpose, technical scheme and advantages of the present invention clearer, the technical scheme of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. The embodiments described in this application are only embodiments of a part of the present invention, rather than all embodiments. Based on the spirit of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work belong to the protection scope of the present invention.

[0051] Embodiment 1 of the present invention proposes a single-phase grounding fault distance measurement method for distribution network based on zero-negative sequence components, using the zero-sequence, negative-sequence voltage and current at the bus of the radial distribution network, combined with the zero-sequence and negative-sequence parameters of the line to calculate the zero-sequence, negative-sequence voltage at the fault point and the zero-sequence, negative-sequence current flowing from the fault point to the bus side about the fault distance expression, and then from the zero-sequence, negative-sequence voltage at the fault point, the zero-sequence, negative-sequence current flowing from the fault point to the end about the fault distance expression is calculated, and the current flowing from the fault point to both sides is added to obtain the zero-sequence, negative-sequence current at the fault point. Finally, the boundary condition that the zero-sequence and negative-sequence currents at the fault point are equal during a single-phase grounding fault is used to establish a fault distance measurement objective function and determine the fault distance.

[0052] The single-phase ground fault location method of distribution network based on zero negative sequence component, such as Figure 1 As shown, the following steps are included:

[0053] Step 1: divide the distribution network lines into sections and obtain the distribution network line parameter information;

[0054] Dividing the line sections includes: dividing the line sections into trunk line sections and branch line sections;

[0055] The trunk line section includes: the section from the beginning of the trunk line to the beginning of the branch line, the section from the beginning of the branch line to the fault point, and the section from the end of the trunk line to the beginning of the branch line;

[0056] The branch line section includes: the section from the beginning of the branch line to the end of the branch line;

[0057] Obtaining distribution line parameter information includes: online identification or obtaining set distribution line zero-sequence parameter information, negative-sequence parameter information, distribution network topology, detection device information, and line section length.

[0058] The detection device information includes the installation location of the detection device in the distribution network and the sampling frequency of the detection device.

[0059] The distribution network topology is a radial distribution network; the line type is a single cable line, a single overhead line or a cable-overhead line mixed line.

[0060] It is worth noting that the distribution line parameters obtained when locating a single-phase grounding fault in the distribution network in Example 1 of the present application include but are not limited to: the line length of each section, the topology of the distribution network, and the zero-sequence parameters and negative-sequence parameters of each section line.

[0061] For a single-phase ground fault in a radial distribution network, Figure 2 A fault schematic diagram is shown when a single-phase grounding fault occurs in the line AD section of the distribution network in Embodiment 1 of the present invention.

[0062] Figure 2 The middle line section includes: cable line section MA, cable line section AD, cable line section DN, overhead line section AB, overhead line section DE. The arrows in the figure indicate the direction of current.

[0063] In Example 1, the line lengths of the trunk line MA section, AD section, and DN section, and the branch line AB section and DE section are L respectively. MA , L AD , L DN , L AB , L DE , the fault point is point K, a single-phase grounding fault occurs, the fault phase is phase A, and the distance between the fault point K and the head end point A of the fault section is l AK The zero-sequence capacitance reactance values ​​on both sides of the MA section are Z CM0 , Z CA0.L , the zero-sequence capacitance reactance values ​​on both sides of the AD section are Z CA0.R , Z CD0.L , the zero-sequence capacitance reactance values ​​on both sides of the DN section are Z CD0.R , Z CN0 The zero-sequence capacitance reactance values ​​on both sides of the AB section are Z CA0.U , ZCB0 , the zero-sequence capacitance reactance values ​​on both sides of the DE section are Z CD0.D , Z CE0 R0, L0, C0 are the zero-sequence resistance, inductance and capacitance of the cable line per unit length, R2, L2, C2 are the negative-sequence resistance, inductance and capacitance of the cable line per unit length, R0′, L0′, C0′ are the zero-sequence resistance, inductance and capacitance of the overhead line per unit length, and R2′, L2′, C2′ are the negative-sequence resistance, inductance and capacitance of the overhead line per unit length.

[0064] Step 2, based on the distribution line obtained in step 1, when the system operates normally, the detection device monitors the three-phase voltage and current, and synthesizes the zero-sequence and negative-sequence voltage and current; determines whether a single-phase grounding fault occurs based on the line voltage, i.e., symmetry, changes in the zero-sequence voltage, and changes in the zero-negative sequence current on the line.

[0065] In Example 1, the three-phase voltage and current are monitored by a detection device installed at the busbar at the head end of the line, and the zero-sequence and negative-sequence voltages and currents are synthesized; whether a single-phase grounding fault occurs is determined based on the symmetry of the line voltage, the change in the zero-sequence voltage, and the change in the zero-sequence and negative-sequence currents on the line.

[0066] Specifically, step 2 includes:

[0067] Step 2.1, set the zero-sequence voltage starting value;

[0068] Step 2.2, based on the detection device obtained in step 1, low-frequency sampling measures the three-phase voltage and calculates the synthetic line voltage and zero-sequence voltage, measures the three-phase current and calculates the synthetic zero-sequence and negative-sequence current;

[0069] In Example 1, the low-frequency sampling in step 2.2 has a sampling frequency of 6400 Hz;

[0070] Step 2.3, based on the zero-sequence voltage starting value set in step 2.1 and the line voltage, zero-sequence voltage, zero-sequence current, and negative-sequence current obtained in normal operation in step 2.2, when the line phase voltage changes, if the amplitudes and phase differences of the three line voltages remain unchanged at this time, the line zero-sequence voltage value exceeds the zero-sequence voltage starting value, and there are zero-sequence and negative-sequence currents, it is determined that a single-phase grounding fault occurs;

[0071] Step 3, based on the result of the fault judgment in step 2, the system equivalent zero-sequence and negative-sequence networks are established from the fault section obtained from the distribution automation system; the three-phase voltage and current time domain signals after the fault are measured by the detection device at the bus, and the steady-state zero-sequence and negative-sequence voltage and current power frequency components at the bus are obtained by the symmetrical component method and fast Fourier transform;

[0072] Step 3.1, based on the judgment result obtained in step 2, start the single-phase grounding fault location, use the detection device to collect the three-phase voltage and current at high frequency, and calculate and synthesize the steady-state zero-sequence and negative-sequence voltage and current at the bus;

[0073] In Example 1, the high frequency acquisition in step 3.1 has a sampling frequency of 12800 Hz or above;

[0074] Step 3.2: Use fast Fourier transform to filter out high-order harmonic components from the time domain signals of the steady-state three-phase voltage and current within 4 sampling periods after the fault occurs with a delay of 0.5s, and synthesize the steady-state zero-sequence and negative-sequence voltage and current power frequency components through the symmetrical component method.

[0075] Specifically, in step 3, in the equivalent zero-sequence and negative-sequence networks after a single-phase grounding fault, each fault section adopts a concentrated parameter π-type equivalent circuit.

[0076] In Example 1, Figure 3 and Figure 4 They respectively represent the post-fault equivalent zero-sequence and negative-sequence networks corresponding to a single-phase grounding fault in the AD section of the distribution network.

[0077] Step 4: Based on the distribution network line parameters obtained in step 1, the system equivalent zero-sequence and negative-sequence networks obtained in step 3, and the power frequency components of the steady-state zero-sequence and negative-sequence voltages and currents at the bus, establish a distance measurement function for the fault section, solve the function using the search method, and calculate the distance from the fault point to the head end of the fault section.

[0078] In Example 1, the zero-sequence and negative-sequence components of the voltage and current at the bus are synthesized based on the three-phase voltage and current sampling information after the fault at the bus, and the zero-sequence and negative-sequence voltages at the fault point and the zero-sequence and negative-sequence currents flowing from the fault point to the bus side are combined to calculate the expression of the fault distance; then, the zero-sequence and negative-sequence voltages at the fault point are used to calculate the expression of the zero-sequence and negative-sequence currents flowing from the fault point to the end about the fault distance. Finally, the boundary condition that the zero-sequence and negative-sequence currents at the fault point are equal during a single-phase grounding fault is used, and the modulus of the difference between the zero-sequence current and the negative-sequence current phasor is used as the fault distance measurement objective function. A search is performed within the length of the fault section so that the distance with the minimum objective function is the fault distance.

[0079] Specifically, in step 4, calculating the fault distance of the fault section includes:

[0080] Step 4.1, based on the system equivalent zero-sequence network obtained in step 3, the power frequency components of the steady-state zero-sequence voltage and current at the bus, and the line parameters obtained in step 1, for the fault section, using the power frequency components of the zero-sequence voltage and zero-sequence current at the bus, based on the system equivalent zero-sequence network after the fault, combined with the line parameters, obtain the expression of the zero-sequence voltage at the fault point and the zero-sequence current flowing from the fault point to the bus side with respect to the fault distance;

[0081] In Example 1, according to the bus zero-sequence voltage and current The zero-sequence voltage at point A can be calculated

[0082]

[0083] In the formula,

[0084] Z0 is the zero-sequence impedance of the cable line per unit length.

[0085] Step 4.2, based on the zero-sequence voltage at the fault point obtained in step 4.1 and the expression of the zero-sequence current flowing from the fault point to the bus side with respect to the fault distance and the line parameters obtained in step 1, the zero-sequence voltage at the fault point, the equivalent zero-sequence network of the system after the fault, and the line parameters are used to obtain the expression of the zero-sequence current flowing from the fault point to the end of the line with respect to the fault distance, and the expression of the zero-sequence current flowing from the fault point to the bus side with respect to the fault distance is added to obtain the expression of the zero-sequence current at the fault point;

[0086] In Example 1, according to the zero-sequence voltage at the fault point A From this, the current flowing from point A to the fault point can be obtained

[0087]

[0088] In the formula,

[0089] Z0′ is the zero-sequence impedance of the overhead line per unit length;

[0090] Y AB0 is the admittance of the AB section of the branch line.

[0091] According to the zero-sequence voltage at point A and current The zero-sequence voltage at the fault point can be obtained and zero sequence current flowing to the left

[0092]

[0093] In the formula,

[0094] Z CA0.R , Z CK0.LIt is the capacitive reactance value of the zero-sequence capacitor on the left and right sides of the line AK section.

[0095] According to the zero-sequence voltage at the fault point and line parameters, the zero-sequence current flowing to the right at the fault point for:

[0096]

[0097] In the formula,

[0098] Y DN0 It is the admittance of the AB section of the trunk line;

[0099] Y DE0 is the admittance of the branch line DE section.

[0100] Let the fault point flow to both sides of the zero sequence current After adding and expanding, the zero-sequence current at the fault point can be obtained About the fault distance l AK expression.

[0101] Step 4.3, based on the system equivalent negative sequence network obtained in step 3, the power frequency components of the steady-state negative sequence voltage and current at the bus, and the line parameters obtained in step 1, the power frequency components of the negative sequence voltage and negative sequence current at the bus, based on the system equivalent negative sequence network after the fault, combined with the line parameters, obtain the expression of the negative sequence voltage at the fault point and the negative sequence current flowing from the fault point to the bus side with respect to the fault distance;

[0102] Step 4.4, based on the negative sequence voltage at the fault point obtained in step 4.3 and the expression of the negative sequence current flowing from the fault point to the bus side with respect to the fault distance and the line parameters obtained in step 1, the negative sequence voltage at the fault point, the equivalent negative sequence network of the system after the fault, and the line parameters are used to obtain the expression of the negative sequence current flowing from the fault point to the end of the line with respect to the fault distance, and the expression of the negative sequence current flowing from the fault point to the bus side with respect to the fault distance is added to obtain the expression of the negative sequence current at the fault point;

[0103] In Example 1, according to the same method, the negative sequence current at point K can be calculated as

[0104] Step 4.5, based on the zero-sequence current expression at the fault point obtained in step 4.2 and the negative-sequence current expression at the fault point obtained in step 4.4, using the boundary condition that the zero-sequence and negative-sequence currents at the fault point are equal when a single-phase grounding fault occurs in the line, set the objective function as the modulus of the difference between the zero-sequence current and the negative-sequence current, subtract the zero-sequence current expression at the fault point from the negative-sequence current expression at the fault point, and use the search method to search within the length of the fault section to obtain the fault distance, that is, the distance with the minimum objective function.

[0105] Specifically, in step 4.5, the fault distance objective function F(l) is the modulus of the difference between the zero-sequence current and the negative-sequence current. The search is performed within the length of the fault section, i.e., the real number interval (0, L). The l with the smallest objective function is the fault distance. The search step length is determined according to the actual fault distance measurement and line conditions. It can be set to 1m in engineering applications:

[0106] In Example 1, the fault location objective function F(l) is the zero-sequence current at the fault point With negative sequence current The modulus of the difference.

[0107]

[0108] In the formula,

[0109] is the zero-sequence current at the fault point,

[0110] is the negative sequence current at the fault point,

[0111] l is the fault distance, which is the distance from the fault point to the beginning of the fault section.

[0112] According to formula (5), in the real number interval (0,L AD ) to search for the l with the smallest F(l) * That is the fault distance. The search step size is determined according to the actual fault distance measurement and line conditions and can be set to 1m.

[0113] According to the same method, the zero-sequence and negative-sequence currents at the fault point when the fault occurs in the trunk line MA and DN sections and the branch line AB and DE sections can be calculated respectively, and the fault distance function can be established by making them equal, and the fault distance can be solved by the search method. In summary, the zero-sequence and negative-sequence voltage and current at the busbar can be used to realize the fault distance measurement of each section of the radial distribution network according to the single-end electrical information.

[0114] In order to verify the correctness of the proposed single-phase grounding fault location strategy, the simulation model was built using the EMTP / ATP simulation software. Among them, the line voltage level is 10kV, the neutral point is grounded through a small resistor, the total length of the distribution line MN is 10km, the MN section of the trunk line is a 10km long cable line, and the trunk line has two branch lines AB and DE at 4km and 7km away from point M. The AB branch line is a 5km long overhead line, and the DE branch line is a 6km long overhead line.

[0115] The zero-sequence parameter of the cable line per unit length is: R0 = 1.23 × 10 -3 Ω / m, L0=9.167×10 -7 H / m,C0=2.58333×10 -10 F / m;

[0116] Negative sequence parameter: R2 = 1.23 × 10 -3 Ω / m, L2=2.292×10 -7 H / m,

[0117] C2=2.84×10 -10 F / m.

[0118] The zero-sequence parameter of overhead line per unit length is: R0′=2.1×10 -4 Ω / m, L0′=7×10 -6 H / m,

[0119] C0′=4.66×10 -12 F / m;

[0120] Negative sequence parameter: R2′=2.1×10 -4 Ω / m, L2′=1.273×10 -6 H / m, C2′=9.07×10 -12 F / m.

[0121] The fault point is set in the AD section, 2 km away from the head end point A, and the grounding resistance is set to 100Ω.

[0122] The fault section is read as the AD section from the distribution automation system. Using the AD section distance measurement formula, the zero-sequence and negative-sequence voltage and current at the bus are synchronously sampled and Fourier transformed. The zero-sequence and negative-sequence voltage and current phasor values ​​are obtained as follows: Substituting into equation (3) and equation (4), we get the expression of zero-sequence and negative-sequence current at the fault point with respect to the fault distance l. Subtract the two and take the modulus value, which is the corresponding distance measurement function F(l). Search in the AD section (0,3000). At this time, the distance measurement function F(l) curve is as follows: Figure 5 shown.

[0123] When l = 1984m, F(l) is the smallest, that is, the ideal l value with the smallest F(l) is obtained, and the fault distance l * =1984m. In order to compare the distance measurement results and errors at different fault points, the fault points are set at different positions of the line. The results are shown in the following table.

[0124]

[0125]

[0126] It can be seen from the above table that the single-ended zero negative sequence component method has a maximum absolute error of 71m, a maximum relative error of 3.55%, and an average relative error of 1.98% in the trunk line cable section; in the branch support empty line section, the maximum absolute error is 78m, the maximum relative error is 6.30%, and the average relative error is 2.79%. The ranging accuracy can meet the engineering needs and is not affected by the grounding resistance. The simulation results prove that the fault ranging method proposed in the present invention is correct and effective.

[0127] For the two operating modes of neutral point ungrounded and arc suppression coil, the method proposed in the present invention can maintain high accuracy by setting the fault points in different sections and setting the grounding resistance to 10Ω, 100Ω, 1000Ω, and 2000Ω respectively.

[0128] The present invention can maintain high accuracy under various distribution network structures such as hybrid lines, multi-branch lines, etc., and the ranging accuracy is not affected by the grounding resistance.

[0129] Embodiment 2 of the present invention proposes a distribution network single-phase grounding fault distance measurement system based on zero negative sequence component, including: a signal collection module, a data preprocessing module, a fault judgment module, a signal processing module and a fault location module;

[0130] Signal collection module, used to obtain three-phase voltage and current information, and record the corresponding waveforms; obtain distribution line parameter information;

[0131] The distribution line parameter information includes: distribution line zero-sequence parameter information, negative-sequence parameter information, distribution network topology, detection device information, and line section length.

[0132] Wherein, the signal collection module includes a detection device;

[0133] The detection device includes a low-frequency acquisition unit and a high-speed acquisition unit;

[0134] The low-frequency acquisition unit is used to collect three-phase voltage and current at low frequency during normal operation;

[0135] The high-speed acquisition unit is used to collect three-phase voltage and current at high frequency after a single-phase grounding fault;

[0136] A data preprocessing module is connected to the signal collection module, and synthesizes the line voltage, zero-negative sequence voltage and current through data preprocessing based on the three-phase voltage and current collected by the signal collection module;

[0137] The fault judgment module is connected to the data preprocessing module, and based on the line voltage, zero-negative sequence voltage and current data obtained by the data preprocessing module, the data change is analyzed to determine whether a single-phase grounding fault occurs;

[0138] The signal processing unit is connected to the data preprocessing module and the fault judgment module, and is used to obtain the fault section from the distribution automation system and establish the system equivalent zero-sequence and negative-sequence network after determining that a single-phase grounding fault occurs; perform fast Fourier transform on the three-phase voltage and current time domain signals collected by the detection device at the bus, calculate the line voltage, and obtain the zero-sequence and negative-sequence voltage and current power frequency components at the bus by the symmetrical component method;

[0139] The fault location module is connected with the signal collection module, the signal processing module and the fault judgment module. After determining that a fault has occurred according to the judgment result of the fault judgment module, it is used to determine the fault location according to the fault distance measurement method in combination with the signal processing information.

[0140] The fault location module includes: a first unit, a second unit, and a third unit;

[0141] The first unit is connected to the signal collection module and the signal processing module, and based on the distribution line parameter information obtained by the signal collection module and the power frequency component of the zero-sequence voltage and current obtained by the signal processing module and the equivalent zero-sequence network, it calculates the expression of the zero-sequence current flowing from the fault point to the bus side with respect to the fault distance and the zero-sequence current expression at the fault point, and adds them to obtain the zero-sequence current expression at the fault point;

[0142] The second unit is connected to the signal collection module and the signal processing module, and based on the distribution line parameter information obtained by the signal collection module and the power frequency component of the negative sequence voltage and current obtained by the signal processing module and the equivalent negative sequence network, it calculates the expression of the negative sequence current flowing from the fault point to the bus side with respect to the fault distance and the negative sequence current expression at the fault point, and adds them to obtain the negative sequence current expression at the fault point;

[0143] The third unit is connected to the first unit and the second unit. Based on the zero-sequence current expression at the fault point obtained by the first unit and the negative-sequence current expression at the fault point obtained by the second unit, and through the boundary condition that the zero-sequence and negative-sequence currents at the fault point are equal, the objective function is set to the modulus of the difference between the zero-sequence current and the negative-sequence current. The search method is used to search within the length of the fault section to obtain the fault distance, that is, the distance that minimizes the objective function.

[0144] The system is suitable for a distribution network with an ungrounded neutral point, grounded via an arc suppression coil or grounded via a small resistor; the distribution network topology is a radial distribution network; the line type is a single cable line, a single overhead line or a cable-overhead line mixed line.

[0145] The beneficial effect of the present invention is that, compared with the prior art, the present invention can maintain high accuracy in various distribution network structures such as hybrid lines and multi-branch lines, and the ranging accuracy is not affected by the grounding resistance. Fault ranging can be achieved according to the detection device at the busbar, reducing the dependence of the positioning method on communication. The technical principle is simple, the engineering feasibility is strong, and it has great academic value and practicality.

[0146] The distribution network single-phase grounding fault distance measurement system based on zero negative sequence component provided in the embodiment of the present invention has the same technical features as the distribution network single-phase grounding fault distance measurement method based on zero negative sequence component provided in the above embodiment, so it can also solve the same technical problems and achieve the same technical effects.

[0147] Those skilled in the art can clearly understand that, for the convenience and brevity of description, the specific working process of the system and device described above can refer to the corresponding process in the aforementioned method embodiment, and will not be repeated here.

[0148] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents, and any modifications or equivalent replacements that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A single-phase ground fault distance measurement method for distribution network based on zero negative sequence component, characterized in that: The following steps are involved: Divide the distribution network lines into sections and obtain the distribution network line parameter information; Based on the obtained distribution network lines, when the system is operating normally, the three-phase voltage and current are monitored through the detection device, and the zero-sequence and negative-sequence voltage and current are synthesized; according to the line voltage, i.e. symmetry, the change of zero-sequence voltage, and the change of zero-sequence and negative-sequence current on the line, it is determined whether a single-phase grounding fault occurs; Based on the obtained fault judgment results, the fault section is obtained from the distribution automation system, and the system equivalent zero-sequence and negative-sequence networks are established; the three-phase voltage and current time domain signals after the fault are measured using the detection device at the busbar, and the steady-state zero-sequence and negative-sequence voltage and current power frequency components at the busbar are converted; According to the obtained distribution network line parameters, the obtained system equivalent zero-sequence and negative-sequence networks, and the power frequency components of the steady-state zero-sequence and negative-sequence voltages and currents at the busbar, a distance measurement function of the fault section is established, the function is solved, and the distance from the fault point to the head end of the fault section is calculated.

2. The method for measuring single-phase ground fault distance in a distribution network based on zero negative sequence component according to claim 1 is characterized in that: The neutral point grounding mode of the distribution network is that the neutral point is not grounded, grounded through an arc suppression coil, or grounded through a small resistor; the topological structure of the distribution network is a radial distribution network; Line types include single cable line, single overhead line, and cable-overhead line hybrid line.

3. The method for measuring single-phase ground fault distance in distribution network based on zero negative sequence component according to claim 2 is characterized in that: Dividing the line sections includes: dividing the line sections into trunk line sections and branch line sections; The trunk line section includes: the section from the beginning of the trunk line to the beginning of the branch line, the section from the beginning of the branch line to the fault point, and the section from the end of the trunk line to the beginning of the branch line; The branch line section includes: the section from the beginning of the branch line to the end of the branch line.

4. The method for measuring single-phase ground fault distance in distribution network based on zero negative sequence component according to claim 3 is characterized in that: Obtaining the distribution network line parameter information includes: online identification or obtaining the set distribution line zero-sequence parameter information, negative-sequence parameter information, distribution network topology, detection device information, and line section length.

5. The method for measuring single-phase ground fault distance in distribution network based on zero negative sequence component according to claim 4 is characterized in that: Determining whether a single-phase grounding fault occurs includes: Set the zero-sequence voltage starting value; The detection device is used to measure the three-phase voltage at low frequency and calculate the synthetic line voltage and zero-sequence voltage, measure the three-phase current and calculate the synthetic zero-sequence and negative-sequence current; Based on the set zero-sequence voltage starting value and the line voltage, zero-sequence voltage, zero-sequence current, and negative-sequence current under normal operating conditions, when the line phase voltage changes, if the amplitudes and phase differences of the three line voltages remain unchanged, the line zero-sequence voltage value exceeds the zero-sequence voltage starting value, and there are zero-sequence and negative-sequence currents, it is determined that a single-phase grounding fault has occurred.

6. The method for measuring single-phase ground fault distance in distribution network based on zero negative sequence component according to claim 5, characterized in that: Based on the fault judgment result, the single-phase grounding fault location is started, and the three-phase voltage and current are collected at high frequency by the detection device, and the steady-state zero-sequence and negative-sequence voltage and current at the bus are calculated and synthesized; Based on the obtained fault occurrence time, the time domain signals of the steady-state three-phase voltage and current within the delayed sampling period are set, the high-order harmonic components are filtered out, and the steady-state zero-sequence and negative-sequence voltage and current power frequency components are synthesized.

7. The method for measuring single-phase ground fault distance in distribution network based on zero negative sequence component according to claim 6, characterized in that: In the equivalent zero-sequence and negative-sequence networks after a single-phase grounding fault, each section adopts a concentrated parameter π-type equivalent circuit.

8. The method for measuring single-phase ground fault distance in distribution network based on zero negative sequence component according to claim 7, characterized in that: Calculating the distance from the fault point to the beginning of the fault section includes: Based on the obtained system equivalent zero-sequence network, the power frequency components of the steady-state zero-sequence voltage and current at the bus, and the line parameters, for the fault section, the power frequency components of the zero-sequence voltage and zero-sequence current at the bus are used, based on the system equivalent zero-sequence network after the fault, combined with the line parameters, to obtain the expression of the zero-sequence voltage at the fault point and the zero-sequence current flowing from the fault point to the bus side with respect to the fault distance; Based on the obtained zero-sequence voltage at the fault point and the expression of the zero-sequence current flowing from the fault point to the bus side with respect to the fault distance and the line parameters, the zero-sequence voltage at the fault point, the equivalent zero-sequence network of the system after the fault, and the line parameters are used to obtain the expression of the zero-sequence current flowing from the fault point to the end of the line with respect to the fault distance, and the zero-sequence current expression at the fault point is obtained by adding it to the expression of the zero-sequence current flowing from the fault point to the bus side with respect to the fault distance; Based on the obtained system equivalent negative sequence network, the power frequency components of the steady-state negative sequence voltage and current at the bus, and the line parameters, the power frequency components of the negative sequence voltage and negative sequence current at the bus are used, based on the system equivalent negative sequence network after the fault, combined with the line parameters, to obtain the expression of the negative sequence voltage at the fault point and the negative sequence current flowing from the fault point to the bus side with respect to the fault distance; Based on the obtained negative sequence voltage at the fault point and the expression of the negative sequence current flowing from the fault point to the bus side with respect to the fault distance and the line parameters, the negative sequence voltage at the fault point, the equivalent negative sequence network of the system after the fault, and the line parameters are used to obtain the expression of the negative sequence current flowing from the fault point to the end of the line with respect to the fault distance, and the expression of the negative sequence current flowing from the fault point to the bus side with respect to the fault distance is added to obtain the expression of the negative sequence current at the fault point; Based on the obtained zero-sequence current expression at the fault point and the obtained negative-sequence current expression at the fault point, using the boundary condition that the zero-sequence and negative-sequence currents at the fault point are equal when a single-phase grounding fault occurs in the line, the objective function is set as the modulus of the difference between the zero-sequence current and the negative-sequence current, and the zero-sequence current expression at the fault point is subtracted from the negative-sequence current expression at the fault point. The search method is used to search within the length of the fault section to obtain the fault distance, that is, the distance that minimizes the objective function.

9. A distribution network single-phase grounding fault distance measurement system based on zero negative sequence component, running the distribution network single-phase grounding fault distance measurement method based on zero negative sequence component according to any one of claims 1 to 8, comprising: The signal collection module, the data preprocessing module, the fault judgment module, the signal processing module and the fault location module are characterized by: Signal collection module, used to obtain three-phase voltage and current information, and record the corresponding waveforms; obtain distribution line parameter information; The data preprocessing module is connected to the signal collection module, and synthesizes the line voltage, zero-negative sequence voltage and current through data preprocessing based on the three-phase voltage and current collected by the signal collection module; The fault judgment module is connected to the data preprocessing module, and based on the line voltage, zero-negative sequence voltage and current data obtained by the data preprocessing module, the data change is analyzed to determine whether a single-phase grounding fault occurs; The signal processing module is connected to the data preprocessing module and the fault judgment module, and is used to perform fast Fourier transform on the three-phase voltage and current time domain signals collected by the detection device at the bus after determining that a single-phase grounding fault has occurred, calculate the line voltage, and obtain the zero-sequence and negative-sequence voltage and current power frequency components at the bus by the symmetrical component method; The fault location module is connected to the signal collection module, the signal processing module and the fault judgment module. After determining that a fault has occurred according to the judgment result of the fault judgment unit, it is used to determine the fault location according to the fault distance measurement method in combination with the signal processing information.

10. The distribution network single-phase grounding fault distance measurement system based on zero negative sequence component according to claim 9, characterized in that: The signal collection module includes a detection device; The detection device includes a low-frequency acquisition unit and a high-speed acquisition unit; The low-frequency acquisition unit is used to collect three-phase voltage and current at low frequency during normal operation; The high-speed acquisition unit is used to collect three-phase voltage and current at high frequency after a single-phase grounding fault occurs.

11. The distribution network single-phase grounding fault distance measurement system based on zero negative sequence component according to claim 9, characterized in that: The fault location module includes: a first unit, a second unit, and a third unit; The first unit is connected to the signal collection module and the signal processing module, and based on the distribution line parameter information obtained by the signal collection module and the power frequency component of the zero-sequence voltage and current obtained by the signal processing module and the equivalent zero-sequence network, it calculates the expression of the zero-sequence current flowing from the fault point to the bus side with respect to the fault distance and the zero-sequence current expression at the fault point, and adds them to obtain the zero-sequence current expression at the fault point; The second unit is connected to the signal collection module and the signal processing module, and based on the distribution line parameter information obtained by the signal collection module and the power frequency component of the negative sequence voltage and current obtained by the signal processing module and the equivalent negative sequence network, it calculates the expression of the negative sequence current flowing from the fault point to the bus side with respect to the fault distance and the negative sequence current expression at the fault point, and adds them to obtain the negative sequence current expression at the fault point; The third unit is connected to the first unit and the second unit. Based on the zero-sequence current expression at the fault point obtained by the first unit and the negative-sequence current expression at the fault point obtained by the second unit, and through the boundary condition that the zero-sequence and negative-sequence currents at the fault point are equal, the objective function is set to the modulus of the difference between the zero-sequence current and the negative-sequence current. The search method is used to search within the length of the fault section to obtain the fault distance, that is, the distance that minimizes the objective function.

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