Fault location method for t-type non-transposed line of distribution network based on line voltage measurement

Abstract

This invention relates to the field of line detection, and specifically to a fault location method for T-type non-transposed lines in distribution networks based on line voltage measurement. The invention first establishes a set of location equations based on three-phase voltage and current, according to the relationship between self-inductance and mutual inductance. Then, the equations are processed by difference and variable substitution, replacing the unmeasurable phase voltages with line voltages to form new sets of location equations. Subsequently, three sets of equations assuming the fault occurs in different sections are solved separately, and the correct location result is selected according to given selection criteria. Simulation results show that this location method is unaffected by fault type or transition resistance, and has high location accuracy.

Description

Technical Field

[0001] This invention relates to the field of line detection, and in particular to a method for locating faults in T-type non-transposed lines of distribution networks based on line voltage measurement. Background Technology

[0002] In my country's distribution network, voltage transformers typically use V / V connections, which can only measure two line voltages and cannot obtain complete three-phase voltages. Furthermore, due to the relatively underdeveloped planning and construction of distribution networks and the lack of unified equipment selection standards, the quality of equipment used in distribution networks varies greatly, with significant differences in performance and parameters. Line impedance parameters are inaccurate or even unknown. Without phase voltages and accurate line parameters, existing impedance distance measurement algorithms cannot be directly applied to distribution networks. In addition, distribution networks often have short line lengths and experience non-transferring operations, leading to asymmetry in line parameters. Combined with the unique line voltage measurement conditions of distribution networks, existing fault location methods are ineffective for fault location.

[0003] Traditional symmetrical component methods can only decouple three-phase symmetrical lines and are not applicable to lines without transposition. Existing literature mainly presents two methods for handling lines without transposition. The first method is based on phase-mode transformation to achieve high-precision decoupling of three-phase lines without transposition, converting mutually coupled phase components into mutually independent mode components before fault location. The key to this method is solving the phase-mode transformation matrix. However, these methods require accurate line parameters and introduce significant errors during decoupling or parameter calculation, thus they are rarely used in practical engineering. The second method fully considers the phase-to-phase coupling of lines without transposition, deriving the voltage equations of the three-phase network and performing fault location. The advantage of this method is that it eliminates the need for decoupling line parameters, avoiding the errors introduced by the decoupling process in lines without transposition. Furthermore, considering the self-inductance and mutual inductance of the lines, the fault location equations are derived, making their physical meaning more intuitive. This type of method requires accurate line parameters and topology knowledge, which is often difficult to achieve in distribution networks.

[0004] Due to the differences between distribution networks and transmission networks, the above methods cannot be directly applied to fault location in distribution networks. There are three main reasons for this. First, voltage transformers in transmission networks mostly use a Y / Y connection, which can measure the complete three-phase voltage, making the fault location method easy to calculate the voltage sequence component. Second, the neutral point of distribution networks at 35kV and below typically uses a low-current grounding method, resulting in a lack of actual electrical connection between the distribution network and the ground. This renders the ground potential meaningless, so voltage transformers generally use an incomplete star connection, also known as a "V / V" connection. Figure 1 As shown, according to the power distribution network operation regulations, the measuring devices in actual engineering can only obtain two line voltages and cannot obtain three-phase voltages, which makes it difficult to apply the existing impedance distance measurement method.

[0005] Secondly, the management of transmission network line parameters is relatively strict, and the line parameters are relatively accurate; however, the planning and construction of distribution networks are relatively lagging behind, lacking unified equipment selection standards. Therefore, the equipment used in distribution networks varies significantly in terms of performance and parameters. In many cases, line impedance parameters are inaccurate or even unknown, which is also an important reason affecting the accuracy of impedance-based fault location.

[0006] Third, in transmission lines, to reduce current and voltage asymmetry during normal power system operation caused by unequal spacing between the three-phase conductors, engineers often transpose the three-phase conductors at regular intervals, ensuring each phase conductor is evenly positioned in three different locations. However, in distribution networks, due to shorter line distances and economic considerations, three-phase lines often operate without transposition. This lack of transposition leads to parameter asymmetry, resulting in asymmetry in both three-phase current and voltage, rendering the symmetrical component decoupling method ineffective. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention provides a fault location method for T-type non-transposed lines in distribution networks based on line voltage measurement. Since the parameters of non-transposed lines cannot be completely decoupled, and directly using the symmetrical component method would introduce significant errors, this invention, after fully considering the phase-to-phase mutual inductance of the non-transposed line, directly establishes fault location equations based on the self-inductance and mutual inductance relationships in the three-phase network. Because the three-phase self-inductance and mutual inductance relationships always exist, the established fault location equations are applicable to various fault types. In the three-phase network, the location equations are established based on the principle that the voltage at the tap point is equal along different paths and the voltage at the fault point is equal along different paths. Then, through differential processing and variable substitution of the equation system, the measurable line voltage replaces the unmeasurable phase voltage. Finally, the differences between the fault location, tap point location, and line impedance parameters are numerically solved together. The method of this invention is unaffected by fault type or transition resistance, and has good location accuracy.

[0008] The technical solution of this invention is: a method for fault location of T-type non-transposed lines in distribution networks based on line voltage measurement, the specific steps of which are:

[0009] Step 1. Input the total length L of the MN line. mn The total length of the PT section is L. pt Real-time measurement of voltage and current data of three terminals, namely, obtaining sampled values ​​of line voltage and phase current of terminals M, N, and P through μMPMU;

[0010] Step 2. Determine the occurrence of the fault. The voltage and current values ​​collected before the fault occurred are the line voltage and phase current values ​​before the fault occurred; the voltage and current values ​​collected after the fault occurred are the line voltage and phase current values ​​after the fault occurred.

[0011] Step 3. Assuming the faults occur in the MT, NT, and PT segments respectively, establish a fault location equation set based on the principle that the voltage at the tap point is equal along different paths and the voltage at the fault point is equal along different paths.

[0012] Step 4. Perform differential processing and variable substitution on the three sets of equations respectively, and replace the unmeasurable phase voltage with the line voltage;

[0013] Step 5. Determine whether the solutions of the distance measurement equations for the MT, NT, and PT segments meet the screening criteria, and take the solutions of the distance measurement equations that meet the screening criteria as the distance measurement results.

[0014] The technical solution of the present invention is as follows: The beneficial effects of the present invention are: it does not require complete three-phase voltage measurement, does not require precise line parameters, and has very small error when various types of short-circuit faults occur, and the fault location has high accuracy. Attached Figure Description

[0015] Figure 1 Two single-phase voltage transformers are connected in V / V configuration.

[0016] Figure 2 Schematic diagram of a T-type non-transferable line fault in a power distribution network.

[0017] Figure 3 Flowchart of the T-type non-transposition line fault location method.

[0018] Figure 4 Distance measurement error after an ag fault occurs in the MT segment.

[0019] Figure 5 Distance measurement error after an ab fault occurs in the MT segment.

[0020] Figure 6 Distance measurement error after the ABG fault occurs in the MT segment.

[0021] Figure 7 Distance measurement error after fault abc occurs in MT segment.

[0022] Figure 8 Distance measurement error after an ag fault occurs in the NT segment.

[0023] Figure 9 Distance measurement error after an ab fault occurs in the NT segment.

[0024] Figure 10 Distance measurement error after an abg fault occurs in the NT segment.

[0025] Figure 11 Distance measurement error after an abc fault occurs in the NT segment.

[0026] Figure 12Distance measurement error after an ag fault occurs in the PT segment.

[0027] Figure 13 Distance measurement error after an ab fault occurs in the PT segment.

[0028] Figure 14 Distance measurement error after the PT segment experiences an abg fault.

[0029] Figure 15 Distance measurement error after fault abc occurs in PT segment. Detailed Implementation

[0030] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0031] Since the lines are not transposed and the line parameters are asymmetrical, the symmetrical component method cannot be used for decoupling. Therefore, the fault location equation is directly established based on the self-inductance and mutual inductance relationship of the three-phase network.

[0032] Step 1. Collect basic data, input the total length L of the MN line. mn The total length of the PT section is L. pt Real-time measurement of voltage and current data of three terminals, namely, measuring the line voltage and phase current values ​​of terminals M, N, and P through μMPMU;

[0033] T-type non-transposition circuit, such as Figure 2 As shown, the neutral point is grounded via a small resistor. The three terminals are denoted as M, N, and P, and the tap point is T. Lines MN and PT represent the main line and tap line, respectively. The fault occurs in section MT, and the lengths of lines MN and PT are known. Since the tap point location may be inaccurate, the distance from terminal M to tap point T and the fault location are considered as unknown variables in the fault location equation. Typically, the impedance parameters of lines MT and NT are the same, but different from those of line PT. The impedance parameters of lines MN and PT also need to be solved in the fault location equation. Each terminal is powered and equipped with a micro-multifunctional phasor measurement unit (μMPMU) to provide synchronous measurements, i.e., the μMPMU meets the configuration requirements for fault observability. Fault observability refers to the ability to acquire fully observable electrical measurements (voltage, current) through the μMPMU under fault conditions, enabling fault diagnosis and fault location determination. Due to the short length of the distribution network lines, parallel capacitors are ignored in the fault location equation.

[0034] Step 2. Determine the occurrence of the fault. The voltage and current values ​​collected before the fault occurred are the line voltage and phase current values ​​before the fault occurred; the voltage and current values ​​collected after the fault occurred are the line voltage and phase current values ​​after the fault occurred.

[0035] The μMPMU and the master station jointly undertake the tasks of fault detection, fault timing determination, and fault location initiation. Each terminal's μMPMU uploads synchronous phasors of voltage and current to the master station every power frequency cycle, while simultaneously recording waveforms. The master station calculates the changes in voltage and current phasor amplitudes relative to the previous power frequency cycle in real time. If the increment exceeds a threshold of 5%, the master station initiates the fault detection function. Each terminal's μMPMU sends synchronous waveform data from 0.2 seconds before and 0.4 seconds after the abrupt change to the master station. The master station analyzes fault characteristics such as zero-sequence component increments and negative-sequence component increments to determine if a fault has occurred. Once a fault is detected, the master station determines the fault timing by comparing the instantaneous value increments of the sampled μMPMU data at 0.02-second (power frequency cycle) intervals. If the instantaneous value change exceeds the threshold of 2% three consecutive times, the fault timing can be determined. Executing this detection procedure allows for highly accurate calculation of the fault occurrence time, ensuring the correctness of signals before and after the fault during fault location.

[0036] Some variables are defined as follows (subscripts M, N, and P correspond to each terminal, subscript po indicates after the fault, and subscript pre indicates before the fault):

[0037]

[0038]

[0039] Meanwhile, the impedance matrices per unit length of lines MN and PT are set as follows:

[0040]

[0041] in,

[0042]

[0043] Because the model uses a non-transposed circuit, the distances between the conductors are different, resulting in unequal mutual impedances between phases, i.e., z ab1 ≠z ac1 ≠z bc1 , z ab2 ≠z ac2 ≠z bc2 .

[0044] Step 3. Assume that the fault occurs in the MT segment, NT segment and PT segment respectively. Based on the principle that the voltage at the tap point is equal along different paths and the voltage at the fault point is equal along different paths, establish a set of fault location equations.

[0045] Assuming the fault occurs in the MT segment, after the fault, the three-phase voltage and current at the N and P terminals are used to calculate the three-phase voltage at the tap point T along different paths. The calculated three-phase voltages at the tap point are then equal for each phase. The current reference direction is as follows: Figure 2 As shown.

[0046] After considering the mutual inductance between the three phases, the three-phase voltage at tap point T is calculated from the N terminal as follows:

[0047]

[0048] The three-phase voltages at tap point T, calculated from terminal P, are as follows:

[0049]

[0050] The three-phase voltages at the same location T are all equal, and based on this, the following equation can be constructed:

[0051]

[0052] Then, considering the three-phase self-inductance and mutual inductance, the three-phase voltage at fault point K is calculated from terminal M as follows:

[0053]

[0054] The three-phase voltage at fault point K, calculated from tap point T, is as follows:

[0055]

[0056] The calculated three-phase voltages at point K are all equal, and based on this, the following equation can be constructed:

[0057]

[0058] Since only line voltage can be measured under the existing measurement conditions, the lack of measurement of phase voltage makes equations (4) and (7) impossible to solve directly. It is necessary to perform differential processing on the equations and replace the unmeasurable phase voltage with the measurable line voltage. Therefore, differential processing is performed on the equations, and equation (8) can be obtained:

[0059]

[0060] Similarly, before the fault occurs, the three-phase voltage at the same point is uniquely determined. The voltages at the tap point T and the fault point K, calculated separately from different terminals, are each equal. Therefore, the same equation still holds before the fault occurs, and the ranging equation set can be established as follows:

[0061]

[0062]

[0063]

[0064] Substituting the calculation formulas (2) and (3) for the three-phase voltage at tap point T and the calculation formulas (5) and (6) for the three-phase voltage at fault point K into the ranging equation set (8) and (9), the complete ranging equation for the MT segment can be obtained, as shown in equation (10):

[0065]

[0066]

[0067] Similarly, assuming the faults occur in the NT segment and the PT segment respectively, the corresponding ranging equations (11) and (12) can also be established.

[0068] Assuming the fault occurs in segment NT, the complete ranging equation is:

[0069]

[0070]

[0071] Assuming the fault occurs in the PT segment, the complete ranging equation is:

[0072]

[0073]

[0074] Step 4. Perform difference processing and variable substitution on the three equations respectively, and replace the unmeasurable phase voltage with the line voltage.

[0075] For each fault location segment assumption, a set of nonlinear equations can be established, namely (10), (11), and (12). Variable substitution is performed on the equations, treating the difference in impedance parameters as a complete variable. The known quantities in any fault location equation are the line voltage and phase current before and after the fault. The unknowns are the fault location (d1, d2, or d3), where d1 is the distance between the fault point and terminal M when the fault occurs in segment MT, d2 is the distance between the fault point and terminal N when the fault occurs in segment NT, and d3 is the distance between the fault point and terminal P when the fault occurs in segment PT. The tap position (L...) mt The difference in impedance per unit length of the line (z) s1 -z ab1 ,z ac1 -z bc1 ,z ab1 -z ac1 ;z s2 -z ab2 ,z ac2 -z bc2 ,z ab2 -z ac2 ).because

[0076] z s1 -z bc1 =(z s1 -z ab1 )+(z ac1 -z bc1 )-(z ab1 -z ac1 (13)

[0077] z s2 -z bc2 =(z s2 -z ab2 )+(z ac2 -z bc2 )-(z ab2 -z ac2 (14)

[0078] Therefore (z) s1 -z bc1 ) and (z s2 -z bc2 Although it appears in the equation, it is not considered an independent unknown.

[0079] In summary, there are a total of 8 unknowns and 8 equations. Since the number of unknowns is the same as the number of equations, the nonlinear equation system can be solved using the trust region method. However, since the impedance parameters appear in the equations as differences, only the differences between the impedance parameters can be obtained, and each impedance parameter cannot be solved independently.

[0080] Step 5: Make a judgment based on the selection criteria of the distance measurement results.

[0081] Regardless of which section the fault occurs in, a ranging equation can be established based on the three-terminal synchronous measurement data. Then, the trust region algorithm can be used to solve the three sets of ranging equations corresponding to the three fault assumptions. Only when the assumed fault section is consistent with the actual fault point section is the solution of the equation a correct ranging result. Usually, the self-impedance of the line is much larger than the mutual impedance, which can also be used as a screening criterion for ranging results. Therefore, the complete screening criteria are shown in (15):

[0082]

[0083] Here, Re is the operation for extracting the real part of a complex number, and Im is the operation for extracting the imaginary part of a complex number.

[0084] The flowchart of the fault location method for T-type non-transposed lines proposed in this invention is as follows: Figure 3 As shown.

[0085] Simulation verification

[0086] To verify the effectiveness of the proposed fault location method, simulations were performed in PSCAD, and the method was run in MATLAB. (T-type lines are shown below.) Figure 2 As shown in Table 1, the system's neutral point is grounded through a small resistor for the following reasons: In the early years, my country's power distribution network development level was relatively low, and two grounding methods were commonly used: ungrounded neutral point and neutral point grounded through an arc suppression coil. With the expansion of the power distribution network, the capacitive current at the grounding point is far greater than 30A, making the ungrounded neutral point method no longer suitable. The rapid increase in the capacitive current of the power distribution network makes it difficult for the neutral point grounded through an arc suppression coil to compensate for the capacitive current, failing to achieve automatic arc extinguishing and easily expanding the scope of the accident. When a single-phase ground fault occurs, it cannot accurately select the fault line, causing safety hazards and no longer meeting the needs of power distribution network development. At this time, the neutral point grounded through a small resistor method is favored due to its accurate fault line selection capability. Neutral point grounded through a small resistor is a high-current grounding method; when a single-phase ground fault occurs, the fault current is large, facilitating rapid fault clearing. Therefore, in recent years, the proportion of neutral point grounded through a small resistor method in urban power distribution networks has gradually increased. In the Pudong area of ​​Shanghai, some 10kV power distribution networks have already been transformed to use the neutral point grounded through a small resistor method.

[0087] The phasors of line voltage and phase current before and after the fault are calculated using the DFT (Discrete Fourier Transform) algorithm and substituted into the fault location equation.

[0088] Table 1 Simulation Model Parameters for T-Type Non-Transposition Circuit

[0089]

[0090]

[0091] The impedance matrices per unit length for lines MN and PT are shown below:

[0092]

[0093]

[0094] The ranging results were considered under four main fault types (single-phase ground fault ag, two-phase short circuit ab, two-phase ground fault abg, and three-phase short circuit abc), and then the effects of fault location, fault type, and transition resistance on the ranging method were evaluated.

[0095] In the simulation results, the fault location error is calculated by equation (18).

[0096]

[0097] Fault location traversal results

[0098] A fault point was set at a position every 20% of the line length in each section. The simulation results are as follows: Figures 4-15 As shown, the relative error of fault location is less than 0.1%, and the absolute error is less than 10m. The fault section is accurately identified, demonstrating high location accuracy. Regardless of whether it is a single-phase ground fault, a two-phase ground fault, a two-phase short-circuit fault, or a three-phase short-circuit fault, the fault location equation based on the self-inductance and mutual inductance relationship in a three-phase network always holds true, utilizing the principle that the voltage at the same point calculated along different paths must be equal. Therefore, by constructing location equations by calculating the voltage at the tap point and the fault point along different paths, the proposed location method is, in principle, unaffected by the fault type. Figures 4-15 The results show that the error is small when various types of faults occur, and the fault location has high accuracy.

[0099] To investigate the impact of transition resistance on fault location methods, transition resistances for various fault types were set to 1, 10, and 100 Ω at different fault points. Since the fault location equations in this chapter do not include transition resistance, its impact on fault location is minimal. Figures 4-15 The results show that the fault location error corresponding to different transition resistances is within 10m, indicating that the location accuracy of the proposed method is not affected by the transition resistance.

Claims

1. A method for fault location in a distribution network's T-type non-transposed line based on line voltage measurement, the specific steps of which are: Step 1. Input the total length L of the MN line. mn The total length of the PT section is L. pt Real-time measurement of voltage and current data of three terminals, namely, obtaining sampled values ​​of line voltage and phase current of terminals M, N, and P through μMPMU; Step 2. Determine if a fault has occurred. The voltage and current values ​​collected before the fault occurred are the line voltage and phase current values ​​before the fault. The voltage and current values ​​collected after the fault occurred are the line voltage and phase current values ​​after the fault. Step 3. Assuming the faults occur in the MT, NT, and PT segments respectively, establish a fault location equation set based on the principle that the voltage at tap point T is equal along different paths and the voltage at fault point K is equal along different paths. The distance measurement equation for the MT segment is Formula 10: (10) Line voltage between ab and bc on the M-terminal bus after the fault Line voltage between ab and bc of the N-terminal bus after the fault Line voltage between ab and bc on the P-terminal bus after the fault After the fault, the three-phase currents (a, b, c) of the line at terminal M The three-phase currents (a, b, c) of the N-terminal line after the fault After the fault, the three-phase currents (a, b, c) of the P-terminal line... Line voltage between ab and bc of the M-terminal bus before the fault Line voltage between ab and bc of the N-terminal bus before the fault Before the fault, the line voltage between ab and bc of the P-terminal bus was... The three-phase currents (a, b, c) of the line at terminal M before the fault The three-phase currents (a, b, c) of the N-terminal line before the fault The three-phase currents (a, b, c) of the P-terminal line before the fault Line MN unit length self impedance The mutual impedance per unit length between ab, ac, and bc of line MN Self-impedance per unit length of the line PT The mutual impedance per unit length between ab, ac, and bc of the line PT Lengths of lines MN and PT Line length from terminal M to tap point T When the fault occurs in section MT, the distance from the fault point K to the M end is... Step 4. Perform finite difference processing and variable substitution on the three sets of equations respectively, replacing the unmeasurable phase voltages with line voltages; In step 4, the system of equations is subjected to difference processing: (8) After the fault, calculate the three-phase voltages (a, b, c) at tap point T from the N terminal. After the fault, calculate the three-phase voltages (a, b, c) at tap point T from terminal P. After the fault, calculate the three-phase voltages (a, b, c) at fault point K from terminal M. After the fault, the three-phase voltages (a, b, and c) at the fault point K are calculated from the tap contact T. (9) Before the fault, calculate the three-phase voltages (a, b, c) at tap point T from the N terminal. Before the fault, calculate the three-phase voltages (a, b, c) at tap point T from terminal P. Before the fault, calculate the three-phase voltages (a, b, c) at fault point K from terminal M. Before the fault, the three-phase voltages (a, b, c) at fault point K were calculated from tap point T. The variable substitution formula is: (13) Line MN unit length self impedance The mutual impedance per unit length between ab, ac, and bc of line MN (14) Self-impedance per unit length of the line PT The mutual impedance per unit length between ab, ac, and bc of the line PT The trust region algorithm was used to solve equations (10), (11), and (12) to obtain the fault locations, tap point T locations, and impedance parameter differences when the fault occurred in the MT, NT, and PT segments, respectively. The independent unknowns in the formulas include the differences z of six impedance parameters. s1 -z ab1 , z ac1 -z bc1 , z ab1 -z ac1 ; z s2 -z ab2 , z ac2 -z bc2 , z ab2 -z ac2 Add the location of the fault point (d1, d2, or d3) and the location of the tap point (L). mt ), a total of 8; Line MN unit length self impedance The mutual impedance per unit length between ab, ac, and bc of line MN Self-impedance per unit length of the line PT The mutual impedance per unit length between ab, ac, and bc of the line PT When the fault occurs in section MT, the distance from the fault point K to the M end is... When the fault occurs in segment NT, the distance from fault point K to end N is... When the fault occurs in the PT segment, the distance from the fault point K to the P end is... Line length from terminal M to tap point T Step 5. Determine whether the solutions to the ranging equations for the MT, NT, and PT segments meet the screening criteria. The solutions of the ranging equations that meet the screening criteria are taken as the ranging results. The self-impedance of the line is much larger than the mutual impedance, which is used as the screening criterion for the ranging results. Solve the fault ranging equations for the MT segment, the NT segment, and the PT segment in sequence. If the solutions of the corresponding segment ranging equations are satisfied, they are taken as the ranging results.

2. The method for fault location of a T-type non-transposed line in a distribution network based on line voltage measurement according to claim 1, characterized in that: In step 3, the distance measurement equation for the NT segment is Equation 11: (11) Line voltage between ab and bc on the M-terminal bus after the fault Line voltage between ab and bc of the N-terminal bus after the fault Line voltage between ab and bc on the P-terminal bus after the fault After the fault, the three-phase currents (a, b, c) of the line at terminal M The three-phase currents (a, b, c) of the N-terminal line after the fault After the fault, the three-phase currents (a, b, c) of the P-terminal line... Line voltage between ab and bc of the M-terminal bus before the fault Line voltage between ab and bc of the N-terminal bus before the fault Before the fault, the line voltage between ab and bc of the P-terminal bus was... The three-phase currents (a, b, c) of the line at terminal M before the fault The three-phase currents (a, b, c) of the N-terminal line before the fault The three-phase currents (a, b, c) of the P-terminal line before the fault Line MN unit length self impedance The mutual impedance per unit length between ab, ac, and bc of line MN Self-impedance per unit length of the line PT The mutual impedance per unit length between ab, ac, and bc of the line PT Lengths of lines MN and PT Line length from terminal M to tap point T When the fault occurs in segment NT, the distance from fault point K to end N is... The distance measurement equation for the PT segment is Formula 12: (12) Line voltage between ab and bc on the M-terminal bus after the fault Line voltage between ab and bc of the N-terminal bus after the fault Line voltage between ab and bc on the P-terminal bus after the fault After the fault, the three-phase currents (a, b, c) of the line at terminal M The three-phase currents (a, b, c) of the N-terminal line after the fault After the fault, the three-phase currents (a, b, c) of the P-terminal line... Line voltage between ab and bc of the M-terminal bus before the fault Line voltage between ab and bc of the N-terminal bus before the fault Before the fault, the line voltage between ab and bc of the P-terminal bus was... The three-phase currents (a, b, c) of the line at terminal M before the fault The three-phase currents (a, b, c) of the N-terminal line before the fault The three-phase currents (a, b, c) of the P-terminal line before the fault Line MN unit length self impedance The mutual impedance per unit length between ab, ac, and bc of line MN Self-impedance per unit length of the line PT The mutual impedance per unit length between ab, ac, and bc of the line PT Lengths of lines MN and PT Line length from terminal M to tap point T When the fault occurs in the PT segment, the distance from the fault point K to the P end.

3. The method for fault location of a T-type non-transposed line in a distribution network based on line voltage measurement according to claim 1, characterized in that: The selection criteria in step 5 are as follows: (15) When the fault occurs in section MT, the distance from the fault point K to the M end is... When the fault occurs in segment NT, the distance from fault point K to end N is... When the fault occurs in the PT segment, the distance from the fault point K to the P end is... Lengths of lines MN and PT Line length from terminal M to tap point T Line length from N terminal to tap point T Line MN unit length self impedance The mutual impedance per unit length between ab, ac, and bc of line MN Self-impedance per unit length of the line PT The mutual impedance per unit length between ab, ac, and bc of the line PT.

4. The method for fault location of a T-type non-transposed line in a distribution network based on line voltage measurement according to any one of claims 1 to 3, characterized in that: Step 5 is as follows: Solve the fault location equations for the MT segment, and determine whether the solution of the MT segment fault location equations meets the screening criteria. If it does, the solution of the MT segment fault location equations is used as the location result; otherwise, solve the fault location equations for the NT segment, and determine whether the solution of the NT segment fault location equations meets the screening criteria. If it does, the solution of the NT segment fault location equations is used as the location result; otherwise, solve the fault location equations for the PT segment, and use the solution of the equations as the location result.

5. The method for fault location of a T-type non-transposed line in a distribution network based on line voltage measurement according to any one of claims 1 to 3, characterized in that: The process of determining the occurrence of a fault in step 2 is as follows: The master station calculates the changes in voltage and current phasor amplitudes relative to the previous power frequency cycle in real time; if the increment is greater than the threshold of 5%, the master station starts the fault detection function; the μMPMU on each terminal sends the synchronous waveform data before and after the abrupt change to the master station; the master station analyzes and judges whether a fault has occurred based on the fault characteristics of the zero-sequence component increment and the negative-sequence component increment; once a fault is detected, the master station determines the fault time by comparing the instantaneous value increment of the sampled data from the sampled μMPMU.

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