Single-phase grounding fault diagnosis method for distributed power supply resonant grounding system

Abstract

The present invention relates to the technical field of power system fault analysis, and in particular to a single-phase grounding fault diagnosis method for a distributed power supply resonant grounding system. The fault diagnosis method of the present invention sets a feeder terminal FTU on each line of the distribution network as a detection device for detecting harmonic content in the line, and determines whether a single-phase grounding fault occurs through three-phase voltage and current information. When a single-phase grounding fault occurs, the fault type is first determined by analyzing the fault phase voltage, and then the conduction angle of the arc suppression coil is adjusted so that the zero-sequence current of the arc suppression coil is filtered and flows into the line. The harmonic content in the line is detected by the feeder terminal FTU to perform section positioning, thereby quickly and accurately locating the fault position.

Description

Technical Field

[0001] The invention relates to the technical field of power system fault analysis, and in particular to a single-phase grounding fault diagnosis method for a distributed power supply resonant grounding system. Background Art

[0002] With the increasing expansion of the scale of my country's medium-voltage distribution network, a large number of distributed power sources have been connected to the network, which has had a great impact on the judgment of single-phase grounding fault current. At the same time, in order to prevent arcing when a grounding fault occurs, especially intermittent arcing, the grounding method of the medium-voltage distribution network has gradually evolved from ungrounded neutral point to grounding through arc suppression coils, that is, the neutral point of the transformer or generator is grounded through an arc suppression coil to reduce the grounding current; when a single-phase grounding fault occurs, the fault signal characteristics are usually not obvious, and it is difficult to quickly locate and eliminate the fault, which poses a hidden danger to the power supply unit and users. The rapid location of single-phase grounding faults with neutral point grounded through arc suppression coils is of great significance to shortening the scope and duration of power outages and improving the safety and reliability of distribution networks.

[0003] Most of the existing single-phase grounding fault diagnosis methods use the ratio of similar entropy, the time-frequency characteristics of the transient characteristic modulus or the similarity of VMD and zero-sequence current transient quantity to locate the fault section. The essence is to determine the fault location by detecting the change of current or voltage in the line. For the resonant grounding system, when a single-phase grounding fault occurs, the inductive current generated by the arc suppression coil will effectively offset the line-to-ground capacitive current, thereby reducing the grounding current. The zero-sequence current flowing through the faulty line is equal to the sum of the line-to-ground capacitive current and the residual current at the grounding point. Its direction is the same as the zero-sequence current of the non-fault line, which is still from the busbar to the line, and the phase is consistent. Therefore, it is impossible to use the difference in direction to distinguish between the faulty line and the non-faulty line. In addition, since the overcompensation degree of the arc suppression coil is not large, it is also difficult to use the difference in zero-sequence current to find the faulty line as in the neutral point ungrounded system. Summary of the invention

[0004] The technical problem to be solved by the present invention is that the existing single-phase grounding fault diagnosis method cannot quickly and accurately find the fault line and fault position of the resonant grounding system.

[0005] In order to solve the above problem, the present invention provides a fault diagnosis method capable of quickly and accurately finding the fault line and fault location of a resonant grounding system, and the specific scheme thereof is:

[0006] A single-phase grounding fault diagnosis method for a distributed power supply resonant grounding system comprises the following steps:

[0007] Step 1: Ground the neutral point of the transformer through an arc suppression coil, and set up multiple feeder terminals FTU on each line of the distribution network;

[0008] Step 2: Obtain three-phase voltage and current information, and determine whether a single-phase grounding fault occurs based on the three-phase voltage and current information;

[0009] Step 3: Calculate the fault phase voltage of the bus in the distributed generation distribution network;

[0010] Step 4: When a single-phase grounding fault occurs, the conduction angle of the arc suppression coil is adjusted by the power electronic switch so that the harmonics generated by the arc suppression coil traverse each line;

[0011] Step 5: The harmonic content flowing through the line position is detected by the feeder terminal FTU. When the harmonic content detected by a feeder terminal FTU does not exceed the set parameter, the line between the feeder terminal FTU and the previous feeder terminal FTU is judged to be a fault section.

[0012] Step 6: Calculate the voltage at the fault point by combining the fault phase voltage of the busbar with the fault section judgment result to determine the type of single-phase grounding fault.

[0013] Compared with the prior art, the present invention using the above technical solution has the following beneficial effects:

[0014] The fault diagnosis method of the present invention sets a feeder terminal FTU on each line of the distribution network as a detection device for detecting the harmonic content in the line, and determines whether a single-phase grounding fault occurs through three-phase voltage and current information. When a single-phase grounding fault occurs, the fault type is first determined by fault phase voltage analysis, and then the conduction angle of the arc suppression coil is adjusted so that the zero-sequence current of the arc suppression coil is filtered and flows into the line. The harmonic content in the line is detected by the feeder terminal FTU to perform section positioning, thereby quickly and accurately locating the fault position.

[0015] Preferably, a further technical solution of the present invention is:

[0016] The calculation of the fault phase voltage of the bus in the distributed power distribution network is specifically as follows: assuming that a ground fault occurs in phase A at the distributed power access location, the three-phase voltages at the fault point are respectively:

[0017]

[0018] in, is the phase voltage of the grounding point before the fault; the positive sequence component, negative sequence component and zero sequence component are calculated according to the symmetrical component method:

[0019]

[0020]

[0021] in, is the positive sequence component, is the zero sequence component, is the negative sequence component; then the positive sequence voltage, negative sequence voltage and zero sequence voltage at the bus position are:

[0022]

[0023] in, is the positive sequence voltage, is the zero sequence voltage, is the negative sequence voltage, then the bus phase A voltage is:

[0024] The method of adjusting the conduction angle of the arc suppression coil in the circuit by the power electronic switch is specifically as follows: the inductance of the arc suppression coil is connected to the neutral point of the transformer through an anti-parallel thyristor, and the conduction angle of the thyristor is controlled by the power electronic switch, thereby adjusting the inductance current of the arc suppression coil.

[0025] The detection and judgment process of step 4 and step 5 is specifically as follows: the three-phase voltage and current information is detected by the power management unit PMU, and whether a single-phase grounding fault occurs is determined based on the three-phase voltage and current information; if a single-phase grounding fault occurs, the power electronic switch is controlled to adjust the conduction angle of the arc suppression coil, and the zero-sequence current harmonics of the arc suppression coil flow into the fault line, and the harmonic content of each position is detected by the feeder terminal FTU on the fault line. When the harmonic content detected by a feeder terminal FTU does not exceed the set parameters, it is determined that the line between the feeder terminal FTU and the previous feeder terminal FTU is a fault section.

[0026] The judgment step of step 5 is specifically as follows: the third harmonic flowing through the position when a single-phase grounding fault occurs is detected by the feeder terminal FTU. The calculation formula of the third harmonic is:

[0027]

[0028] Among them, D i is the parameter of the high-order harmonic content of measuring device i; i3 represents the third harmonic amplitude of measuring device i; I ref3 They represent the third harmonics that the arc suppression coil can generate under the control of the thyristor; U0 represents the zero-sequence voltage during the actual ground fault, U ref Indicates the zero-sequence voltage of metallic grounding;

[0029] Setting parameter C ons As the judgment standard, when D i ≥C ons When D i <C ons When , it is judged that the harmonic content detected by the feeder terminal FTU does not exceed the set parameters. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a schematic diagram of the connection of the adjustable arc suppression coil of the present invention;

[0031] Figure 2 It is a steady-state schematic diagram of a single-phase grounding fault of a line containing an arc suppression coil according to the present invention;

[0032] Figure 3 It is a schematic diagram of the harmonic circuit of the arc suppression coil grounding distribution network of the present invention;

[0033] Figure 4 It is a detection and judgment flow chart of step 4 and step 5 of the present invention;

[0034] Figure 5 It is a single-phase grounding fault section positioning model diagram of the present invention;

[0035] Figure 6 It is a simulation model diagram of the single-phase grounding fault section location of the present invention;

[0036] Figure 7 It is a single-phase ground fault current waveform diagram of the present invention;

[0037] Figure 8 This is a simulation model diagram of a distributed power supply connected to a single-phase grounding fault of the present invention;

[0038] Fig. 9 This is a current waveform diagram of a distributed power supply connected to a single-phase grounding fault of the present invention;

[0039] Fig.10 This is a simulation model diagram of the adjustable arc suppression coil of the present invention connected to a single-phase grounding fault;

[0040] Fig.11 This is the output current waveform diagram of the adjustable arc suppression coil of the present invention;

[0041] Fig.12 It is a schematic diagram of the modulus value result of the zero-sequence current fast Fourier transform when there is a low-resistance grounding fault in the present invention;

[0042] Fig.13 It is a schematic diagram of the modulus value result of the zero-sequence current fast Fourier transform when a high-resistance grounding fault occurs in the present invention;

[0043] Fig.14 It is the bus voltage waveform diagram of the present invention;

[0044] Fig.15 is a fault point voltage waveform diagram of the present invention; DETAILED DESCRIPTION

[0045] The present invention will be further described below in conjunction with embodiments, the purpose of which is only to provide a better understanding of the content of the present invention. Therefore, the examples given do not limit the protection scope of the present invention.

[0046] When the neutral point of a centralized power supply is not grounded, ignoring the impedance on the line, the grounding current expression after a single-phase grounding fault occurs is:

[0047]

[0048] Among them, R represents the transition resistance of the grounding point, C ∑ Indicates the capacitance of all lines in the system to ground. It indicates the phase voltage of the grounding point before the fault. When a large-capacity three-phase symmetrical distributed power source is connected to the end of the line, the voltage at the access point will increase significantly. When a single-phase grounding fault occurs in the line close to the photovoltaic injection point, according to formula (1), the single-phase grounding current will increase significantly. my country's "Technical Guidelines for Distribution Networks" (Q / GDW 10370-2016 Edition) clearly stipulates that "for 10kV distribution networks, the neutral point should be ungrounded when the single-phase grounding fault current is 10A or less, and the neutral point should be grounded through an arc suppression coil when it exceeds 10A and is less than 100A-150A". Therefore, if a large number of distributed power sources are connected, it is possible that the original distribution network with a single-phase grounding fault current of less than 10A will become more than 10A. At this time, the neutral point grounding method needs to be changed, and the existing single-phase grounding fault diagnosis method cannot accurately judge the single-phase grounding fault judgment of the neutral point grounding through an arc suppression coil.

[0049] When the neutral point is grounded through an arc suppression coil, ignoring the impedance on the line, the grounding current expression after a single-phase grounding fault occurs is:

[0050]

[0051] Where L represents the inductance of the arc suppression coil. From formula (2), it can be seen that although the access of distributed power sources leads to an increase in the capacitive current in the line, it also increases the inductive current compensated by the arc suppression coil, which basically does not affect the compensation effect.

[0052] See attached Figure 1-15 The embodiment of the present invention discloses a single-phase grounding fault diagnosis method for a distributed power supply resonant grounding system, comprising the following steps:

[0053] Step 1: Ground the neutral point of the transformer through an arc suppression coil, and set up multiple feeder terminals FTU on each line of the distribution network. Each feeder terminal FTU is connected to a corresponding wireless terminal DTU. The wireless terminal DTU is used to transmit the signal detected by the feeder terminal FTU to the control station for subsequent information integration and calculation;

[0054] Step 2: Obtain three-phase voltage and current information, and determine whether a single-phase grounding fault occurs through the three-phase voltage and current information; specifically, obtain the voltage signal and current signal of the line through the feeding terminal FTU, and transmit them to the control station through the wireless terminal DTU. The characteristics of a single-phase grounding fault are that the voltage of the faulty phase decreases to close to 0, and the voltage of the non-faulty phase increases to close to the original value at the same time. And the fault phase grounding current is large.

[0055] Step 3: Calculate the fault phase voltage of the busbar in the distributed generation distribution network. Assume that a ground fault occurs in phase A at the distributed generation access location. The three-phase voltages of A, B, and C at the fault point are:

[0056]

[0057] in, is the phase voltage of the grounding point before the fault; the positive sequence component, negative sequence component and zero sequence component are calculated according to the symmetrical component method:

[0058]

[0059] in, is the positive sequence component, is the zero sequence component, is the negative sequence component; then the positive sequence voltage, negative sequence voltage and zero sequence voltage at the bus position are:

[0060]

[0061] in, is the positive sequence voltage, is the zero sequence voltage, is the negative sequence voltage, represents the current flowing from the distributed power source to the bus, z represents the positive sequence impedance between the distributed power source and the bus, then the A phase voltage of the bus is:

[0062]

[0063] From formula (4), it can be seen that the voltage of phase A where the ground fault occurs at the busbar is not zero. This may lead to the judgment that a single-phase grounding occurs through the transition resistance, resulting in a diagnostic error. From formula (3) and formula (4), it can be seen that if the three-phase voltage of the busbar is measured, and The sequence voltages of the bus voltage can be calculated based on this and The three-phase voltages at the fault point are:

[0064]

[0065] Step 4: When a single-phase grounding fault occurs, the conduction angle of the arc suppression coil is adjusted by the power electronic switch so that the harmonics generated by the arc suppression coil traverse each line;

[0066] Step 5: The harmonic content flowing through the line position is detected by the feeder terminal FTU. When the harmonic content detected by a feeder terminal FTU does not exceed the set parameter, the line between the feeder terminal FTU and the previous feeder terminal FTU is judged to be a fault section.

[0067] Step 6: Fault three-phase voltage through the bus and Combined with the fault section judgment result, the voltage at the fault point is calculated to determine the type of single-phase grounding fault. The specific method is as follows: using the measured bus voltage and distributed power supply current, combined with formula (3) to formula (5), the calculated voltage value at the fault point is obtained to determine the magnitude of the fault phase voltage modulus. If the calculated fault phase voltage is less than 10V, it is determined to be a metallic grounding fault. Otherwise, it is considered to be a resistor grounding fault.

[0068] In this embodiment, the arc extinguishing coil adopts an adjustable arc extinguishing coil. The inductance of the adjustable arc extinguishing coil is connected to the neutral point of the transformer through an anti-parallel thyristor. Under normal circumstances, the adjustable arc extinguishing coil is adjusted to a state away from the resonance point, and no damping resistor is required to be connected in series. After a single-phase grounding fault occurs, the conduction angle of the thyristor of the adjustable arc extinguishing coil is controlled by a power electronic switch, thereby adjusting the inductance current of the arc extinguishing coil, and then controlling the fundamental effective value of the grounding current.

[0069] The impedance angle θ of the adjustable arc suppression coil is:

[0070]

[0071] Among them, R is the resistance value of the arc suppression coil, L p is the inductance of the arc suppression coil, and ω is the angular frequency of the three-phase current.

[0072] When a single-phase grounding fault occurs in the distribution network, the neutral point voltage is U N , when ωt=α, the thyristor VT1 is given a turn-on signal, and the initial state of the thyristor is 0. At this time, the load current satisfies the relationship:

[0073]

[0074] Among them, U Nm is the instantaneous maximum value of the neutral point voltage; i L is the current value flowing through the arc suppression coil.

[0075] Solving the differential equation of formula (7) yields:

[0076]

[0077] The voltage of the arc extinguishing coil can be expressed by formula (9):

[0078]

[0079] In the formula,

[0080] It can be seen from formulas (7), (8) and (9) that since the current function is symmetrical, the generated harmonics do not contain DC components and even-order harmonic components.

[0081]

[0082] Formula (10) is the harmonic expression, formula (11) is the calculation formula of the fundamental component constant a1, formula (11) is the calculation formula of the fundamental component constant b1, and formula (13) is the calculation formula of the remaining harmonic components; where n is 3, 5, 7... for the odd harmonic components except the fundamental.

[0083] The effective value of the fundamental wave and each harmonic can be expressed as:

[0084]

[0085] From the above analysis, it can be seen that the adjustable arc suppression coil realizes current conversion through reverse parallel thyristors, which will contain odd harmonic components with large amplitude in addition to the fundamental wave. In order to suppress the harmonic current, a filtering device needs to be installed. To avoid harmonics affecting normal power supply, the present invention utilizes the characteristic of thyristors generating harmonics, and judges the fault section through harmonics, thereby realizing rapid and accurate positioning of the fault section.

[0086] In this embodiment, the detection and judgment process of step 4 and step 5 is specifically as follows: the three-phase voltage and current information is detected by the power management unit PMU, the detection line is defined as k in the control station, and the line between the two feeder terminals FTU is defined as section i, and whether a single-phase grounding fault occurs is determined according to the three-phase voltage and current information. If a single-phase grounding fault occurs, the power electronic switch is controlled to adjust the conduction angle of the arc suppression coil, and the zero-sequence current harmonics of the arc suppression coil flow into the kth fault line. The harmonic content of each position is detected by the feeder terminal FTU on the fault line, and it is first determined whether the fault falls into the kth line. If not, k=k+1 is executed, and the previous fault route determination step is performed again; if yes, it is determined whether the harmonic content detected by each feeder terminal FTU exceeds the set parameter. If not, it is determined that the section line between the feeder terminal FTU and the previous feeder terminal FTU is a fault section.

[0087] In this embodiment, when a single-phase grounding fault occurs, the power electronic switch is used to adjust the conduction angle for a short time to generate larger harmonics, and the filter device is locked so that the zero-sequence current filter can enter the fault line for a short time. Due to the access of large-capacity distributed power sources, a fifth harmonic component with a large amplitude may be generated, but no third harmonic will be generated. Therefore, the feeder terminal FTU and wireless terminal DTU devices installed in each section of the line detect the third harmonic component, so as to obtain the flow of the third harmonic of the zero-sequence current in each section. The third harmonic flowing through the position when a single-phase grounding fault occurs is detected by the feeder terminal FTU. The calculation formula of the third harmonic is:

[0088]

[0089] Among them, D i is the parameter of the high-order harmonic content of measuring device i; i3 represents the third harmonic amplitude of measuring device i; I ref3 They represent the third harmonics that the arc suppression coil can generate under the control of the thyristor; U0 represents the zero-sequence voltage during the actual ground fault, U ref Indicates the zero-sequence voltage of metallic grounding;

[0090] Setting parameter C ons As the judgment standard, when D i ≥C ons When D i <C ons When the harmonic content detected by the feeder terminal FTU does not exceed the set parameters, it is considered that a small amount of harmonics flows through the feeder terminal FTU. Preferably, C ons Set to 80% of the harmonic content.

[0091] like Figure 3 When a single-phase grounding fault occurs in the feeder terminal FTU2 to feeder terminal FTU3 section of the line shown, the third harmonic content of the zero-sequence current is detected from the busbar outlet to the end of the line. The harmonic detection results obtained by the control station should be that feeder terminals FTU1 and FTU2 can detect larger third harmonics, and feeder terminals FTU3 and FTU4 detect very small third harmonic content. Therefore, after traversing the detection results of the entire line, it can be obtained that the fault section is the section between feeder terminals FTU2 and FTU3. After the section positioning is completed, the arc suppression coil is quickly adjusted to the resonant state and the filter device is re-entered.

[0092] The fault diagnosis method of the present invention sets a feeder terminal FTU on each line of the distribution network as a detection device for detecting the harmonic content in the line, and determines whether a single-phase grounding fault occurs through three-phase voltage and current information. When a single-phase grounding fault occurs, the fault type is first determined by fault phase voltage analysis, and then the conduction angle of the arc suppression coil is adjusted so that the zero-sequence current of the arc suppression coil is filtered and flows into the line. The harmonic content in the line is detected by the FTU to perform section positioning, thereby quickly and accurately locating the fault position.

[0093] Simulation experiment

[0094] A medium voltage distribution network is used as an experimental object to verify the accuracy of the above algorithm, and the EMTP / ATP software is used to model and simulate the system network. Figure 5 As shown, the line voltage level is 10kV.

[0095] The positive and negative sequence parameters of the simulated line per unit length are:

[0096] R 1,2 =1.23×10 -4 Ω / m;

[0097] L 1,2 =2.292×10 -7 H / m;

[0098] C 1,2 =2.84×10 -10 F / m;

[0099] The zero sequence parameters are:

[0100] R0=1.23×10 -4 Ω / m;

[0101] L0=9.167×10 -7 H / m;

[0102] C0=2.58333×10 -10 F / m;

[0103] 1. Impact of distributed power supply on ground current

[0104] Assume that the neutral point is not grounded, such as Figure 6 As shown, after metallic grounding occurs, the fault current waveform is as follows Figure 7 As shown, the single-phase ground current is 8.2A.

[0105] Assume that the end of line 4 is connected to a distributed power supply, and its output current is 150A. Figure 8 shown.

[0106] After metallic grounding occurs, the fault current waveform is as follows: Fig. 9 As shown, the single-phase ground current is 12.2A.

[0107] The simulation shows that the access of distributed power sources can increase the single-phase grounding fault current, and the original neutral point ungrounded method should be changed to the neutral point grounded method through the arc suppression coil.

[0108] 2. Section positioning technology based on harmonic injection method

[0109] On the basis of the above simulation model, an adjustable arc suppression coil is added, such as Fig.10 As shown;

[0110] Assuming the conduction angle of the arc-extinguishing coil thyristor is 45°, the current of the arc-extinguishing coil under the condition of metallic grounding is as follows: Fig.11 As shown, I can be calculated ref3 =1.5634A.

[0111] (1) Low resistance ground fault

[0112] Assume that the grounding resistance is 10Ω and the fault phase is phase A. Taking the single-phase grounding fault in section 1-2 as an example, the zero-sequence current harmonic components detected by each feeder terminal FTU are analyzed by fast Fourier transform FFT, such as Fig.12 As shown; Fig.12 In the figure, black represents the zero-sequence current result of the non-fault line, blue represents the feeder terminal FTU1, green represents the feeder terminal FTU2, and red represents the feeder terminal FTU3. Since the grounding resistance is very small, U0≈U in formula (15) ref , calculated by formula (15) the result is as follows:

[0113]

[0114] From the above results, we can analyze that the fault occurred in section 1-2, and the section location is completed.

[0115] (2) High resistance ground fault

[0116] Assume that the grounding resistance is 5000Ω and the fault phase is phase A. Taking the single-phase grounding fault in section 1-2 as an example, the zero-sequence current harmonic components detected by each feeder terminal FTU are analyzed by fast Fourier transform FFT, such as Fig.13 As shown:

[0117] Since the grounding resistance is large, U0≠U in equation (13) ref . Set U0 = 524.9V, U ref =5773V is substituted into formula (13) and the result is as follows:

[0118]

[0119] From the above results, we can analyze that the fault occurred in section 1-2, and the section location is completed;

[0120] (3) Comprehensive calculation results

[0121] In order to verify the effectiveness of the algorithm under different grounding conditions, different grounding resistances are used for simulation and the solution is obtained according to the above ideas. The results are shown in Table 1:

[0122] Table 1 Fault interval location results

[0123]

[0124] It can be seen from the above table that under the conditions of different fault distances and grounding resistances, the section location method proposed in this paper has high accuracy, indicating that the method proposed in this paper has strong practicality.

[0125] 3. Fault identification method

[0126] After single-phase metallic grounding occurs, the bus voltage is as follows: Fig.14 As shown in the figure, it can be seen that the voltage of the fault phase after the fault is not zero, and it will be identified as grounded through high resistance. Using the fault section location result and formula (5), it can be estimated that the fault phase voltage at the fault point is 20.5V, indicating that the actual fault is a low resistance grounding fault in the transition resistance fault. The fault point simulation voltage is as follows Fig.15 shown.

[0127] The above description is only a preferred feasible embodiment of the present invention, and does not limit the scope of rights of the present invention. All equivalent changes made using the contents of the present specification and its drawings are included in the scope of rights of the present invention.

Claims

1. A single-phase grounding fault diagnosis method for a distributed power supply resonant grounding system, characterized in that: The following steps are involved: Step 1: Ground the neutral point of the transformer through an arc suppression coil, and set up multiple feeder terminals FTU on each line of the distribution network; Step 2: Obtain three-phase voltage and current information, and determine whether a single-phase grounding fault occurs based on the three-phase voltage and current information; Step 3: Calculate the fault phase voltage of the bus in the distributed generation distribution network; Step 4: When a single-phase grounding fault occurs, the conduction angle of the arc suppression coil is adjusted by the power electronic switch so that the harmonics generated by the arc suppression coil traverse each line; Step 5: The harmonic content flowing through the line position is detected by the feeder terminal FTU. When the harmonic content detected by a feeder terminal FTU does not exceed the set parameter, the line between the feeder terminal FTU and the previous feeder terminal FTU is judged to be a fault section. Step 6: Calculate the voltage at the fault point by combining the fault phase voltage of the busbar with the fault section judgment result to determine the type of single-phase grounding fault.

2. The single-phase grounding fault diagnosis method of a distributed power supply resonant grounding system according to claim 1 is characterized in that: The calculation of the fault phase voltage of the bus in the distributed power distribution network is specifically as follows: assuming that a ground fault occurs in phase A at the distributed power access location, the three-phase voltages at the fault point are respectively: in, is the phase voltage of the grounding point before the fault; the positive sequence component, negative sequence component and zero sequence component are calculated according to the symmetrical component method: in, is the positive sequence component, is the zero sequence component, is the negative sequence component; then the positive sequence voltage, negative sequence voltage and zero sequence voltage at the bus position are: in, is the positive sequence voltage, is the zero sequence voltage, is the negative sequence voltage, then the bus phase A voltage is:

3. The single-phase grounding fault diagnosis method of a distributed power supply resonant grounding system according to claim 1 is characterized in that: The method of adjusting the conduction angle of the arc suppression coil in the circuit by the power electronic switch is specifically as follows: the inductance of the arc suppression coil is connected to the neutral point of the transformer through an anti-parallel thyristor, and the conduction angle of the thyristor is controlled by the power electronic switch, thereby adjusting the inductance current of the arc suppression coil.

4. The single-phase grounding fault diagnosis method of a distributed power supply resonant grounding system according to claim 1 is characterized in that: The detection and judgment process of step 4 and step 5 is specifically as follows: the three-phase voltage and current information is detected by the power management unit PMU, and whether a single-phase grounding fault occurs is determined based on the three-phase voltage and current information; if a single-phase grounding fault occurs, the power electronic switch is controlled to adjust the conduction angle of the arc suppression coil, and the zero-sequence current harmonics of the arc suppression coil flow into the fault line, and the harmonic content of each position is detected by the feeder terminal FTU on the fault line. When the harmonic content detected by a feeder terminal FTU does not exceed the set parameters, it is determined that the line between the feeder terminal FTU and the previous feeder terminal FTU is a fault section.

5. The single-phase grounding fault diagnosis method of a distributed power supply resonant grounding system according to claim 1 is characterized in that: The judgment step of step 5 is specifically as follows: the third harmonic flowing through the position when a single-phase grounding fault occurs is detected by the feeder terminal FTU. The calculation formula of the third harmonic is: Among them, D i is the parameter of the high-order harmonic content of measuring device i; i3 represents the third harmonic amplitude of measuring device i; I ref3 They represent the third harmonics that the arc suppression coil can generate under the control of the thyristor; U0 represents the zero-sequence voltage during the actual ground fault, U ref Indicates the zero-sequence voltage of metallic grounding; Setting parameter C ons As the judgment standard, when D i ≥C ons When D i <C ons When , it is judged that the harmonic content detected by the feeder terminal FTU does not exceed the set parameters.

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