A small current grounding system single-phase grounding fault line selection method

Abstract

The application provides a small-current grounding system single-phase grounding fault line selection method, and relates to the technical field of power distribution network fault detection.The method calculates the capacitive current of the system according to the measured zero sequence current data, counts and sums the capacitive current of each line to obtain the total capacitive current of the system, calculates the compensation degree of the arc suppression coil, extracts the fault characteristics, identifies the fault line after data processing and correction, compares the corrected zero sequence current signals of the fault line and the non-fault line, determines the fault line according to the difference between the corrected zero sequence current signals, and has high practicability and wide application prospect.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power distribution network fault detection, and particularly relates to a single-phase grounding fault line selection method for a small current grounding system. BACKGROUND

[0002] In a 10kV small current grounding system, single-phase grounding fault is the most common fault form. A small current grounding system refers to a power system in which the neutral point is grounded through a high impedance or not directly grounded. In such a system, the fault current during single-phase grounding fault is very small, usually only a few amperes or even smaller, far lower than the normal operating current of the system. Therefore, traditional current protection devices are difficult to effectively detect and locate the fault line.

[0003] In a small current grounding system, arc suppression coils (also known as neutral point reactors or neutral point reactors) are usually used to reduce the grounding fault current to protect equipment and improve the operational reliability of the system. The arc suppression coil compensates for the capacitive current of the system by adjusting its reactance value when connected to the system, thereby reducing the fault current. However, even with the compensation of the arc suppression coil, due to the small current and complex signals, existing fault detection and line selection methods still face many challenges.

[0004] The methods in the prior art mainly include:

[0005] 1. Zero sequence current method: This is one of the most commonly used methods, which is based on monitoring the zero sequence current of each line to determine the fault line. When a single-phase grounding fault occurs, the zero sequence current on the fault line is different from that of other lines. However, due to the small fault current, the zero sequence current method is difficult to accurately locate the fault in a small current grounding system.

[0006] 2. Zero sequence voltage method: This method detects the zero sequence voltage of the system to determine the fault location. The zero sequence voltage changes when a single-phase grounding fault occurs. Although this method can indicate the existence of a fault to some extent, the accuracy of fault location is not high due to the strong influence of the system's capacitive current on the zero sequence voltage.

[0007] 3. Harmonic analysis method: This method analyzes the harmonic components in the system during a fault to determine the fault line. Single-phase grounding fault generates specific frequency harmonics in the system, and harmonic analysis can be used to detect and locate faults. However, this method requires complex signal processing and high computing power, and its effectiveness is limited in practical applications.

[0008] 4. Transient analysis method: This method analyzes the transient signal characteristics at the moment of single-phase grounding fault occurrence to locate the fault. This method uses the high frequency components of the transient signal to accurately locate the fault. However, transient analysis requires high data acquisition and processing speed, and is easily disturbed by noise.

[0009] In general, the existing single-phase grounding fault line selection methods for small current grounding systems have the following main problems:

[0010] (1) Small fault current, difficult to detect: Due to the small single-phase grounding fault current, the signal detection and processing are difficult, and the traditional method is difficult to accurately identify the fault line in a complex electromagnetic environment.

[0011] (2) System capacitance current influence: The system capacitance current will significantly affect the accuracy of fault detection, especially in the case of incomplete or over-compensation of arc suppression coil.

[0012] (3) High complexity and cost of equipment: Some advanced fault detection methods (such as harmonic analysis method, transient analysis method) require complex equipment and high computing power, increasing the complexity and cost of the system.

[0013] Therefore, there is an urgent need for a new line selection method that can effectively deal with single-phase grounding faults in small current grounding systems. The method of the present application should be based on the characteristics of small current grounding systems, use the actual electrical parameters of the system, and through theoretical derivation and calculation, accurately identify the fault line, and is simple and low in cost. SUMMARY

[0014] Therefore, in order to overcome the problems of small fault current, difficult to detect, significant influence of system capacitance current, and high complexity and cost of equipment in the prior art, the purpose of the present application is to provide a single-phase grounding fault line selection method for small current grounding systems. Through accurate analysis and calculation of the system zero sequence current, through accurate analysis and calculation of the system capacitance current and the compensation degree of the arc suppression coil, the accuracy and reliability of fault location are improved, and many shortcomings of the prior art are overcome.

[0015] Based on the above purpose, in a first aspect, the present application provides a single-phase grounding fault line selection method for small current grounding systems, comprising the following steps:

[0016] Step one, system parameter measurement: when the system is running normally, use zero sequence current sensor and zero sequence voltage sensor to measure the zero sequence current and zero sequence voltage of each line, and record the zero sequence current and zero sequence voltage data of each line;

[0017] Step two, capacitance current calculation: according to the measured zero sequence current data, calculate the capacitance current of the system, and sum the capacitance current of each line to get the total capacitance current of the system;

[0018] Step three, arc suppression coil compensation degree calculation: according to the arc suppression coil reactance value configured by the system and the total capacitance current of the system, calculate the compensation degree of the arc suppression coil;

[0019] Step four, fault feature extraction: when single-phase grounding fault occurs, the zero sequence current and zero sequence voltage of each line during the fault are recorded in real time, and the fault feature signal is extracted;

[0020] Step five, data processing and correction: Fourier transform is performed on the zero sequence current signal collected during the fault to extract the harmonic component; the system capacitance current and the arc suppression coil compensation degree calculated during normal operation are used to correct the zero sequence current signal during the fault, and the influence of the system capacitance current and the arc suppression coil is eliminated;

[0021] Step six, fault line identification: the corrected zero sequence current signals of the fault line and the non-fault line are compared, and the fault line is determined according to the difference between the corrected zero sequence current signals.

[0022] As a further scheme of the present application, the single-phase grounding fault line selection method of the small current grounding system further comprises generating a fault report and alarm, after the fault line identification is completed, the system generates a fault report, records the time, position and parameters of the fault, starts an audible and visual alarm device, and transmits the fault information to the centralized control room through field bus or wireless communication technology.

[0023] As a further scheme of the present application, according to the arc suppression coil reactance value and the system total capacitance current of the system configuration, the neutral point grounding mode of the transformer of the arc suppression coil is divided into two modes of non-grounding ( ) and arc suppression coil grounding ( ) with 10% compensation, wherein the single-phase metallic grounding ( ) of the A phase is ignored ( ).

[0024] As a further scheme of the present application, when the compensation degree of the arc suppression coil is calculated, the calculation formula is:

[0025]

[0026] In the formula, is the total system capacitance current under the maximum operation mode of the system, is a compensation coefficient, is the rated voltage of the system.

[0027] As a further scheme of the present application, the fault feature signal comprises the zero sequence current waveform, high frequency component and harmonic feature at the fault instant.

[0028] As a further scheme of the present application, when the neutral point is not grounded, the capacitance current flowing from the bus to the line is generated on the non-fault line; the capacitance current flowing from the line to the bus is generated on the fault line, the zero sequence current direction is opposite, and the size is the sum of the zero sequence currents of the non-fault phases; when the arc suppression coil is grounded, the capacitance current flowing from the bus to the line is generated on the non-fault line.

[0029] As a further scheme of the application, in the fault analysis of the single-phase grounding fault line selection method of the small current grounding system, for single-phase grounding fault, three sets of sequence networks (positive sequence network, negative sequence network, zero sequence network) in normal operation state are constructed, and the Thevenin equivalent of each sequence network is calculated from the fault point. Among them, the positive sequence network in the three sets of sequence networks represents the symmetrical component of the power system in normal operation, representing the state of the system under balanced load condition; the negative sequence network represents the asymmetrical component in the system, reflecting the state of the system under unbalanced condition; the zero sequence network represents the zero sequence component in the system.

[0030] As a further scheme of the application, the fault boundary condition in the three sets of sequence networks is:

[0031] ;

[0032] ;

[0033] Symmetric decomposition is:

[0034] ;

[0035] ;

[0036] ;

[0037] After simplification, we get:

[0038] , indicating that the three sequence networks are in series.

[0039] As a further scheme of the application, in the fault analysis of the single-phase grounding fault line selection method of the small current grounding system, the series rule is:

[0040]

[0041] The sequence impedance of the three-phase magnetic circuit independent static element is equal, and the neutral point of the system is not directly grounded ( ∞):

[0042]

[0043] That is, the whole network appears .

[0044] As a further scheme of the application, in the fault analysis of the single-phase grounding fault line selection method of the small current grounding system, the positive and negative sequences are symmetrical, and the zero sequence network is analyzed:

[0045]

[0046]

[0047] In the formula, is the capacitive current generated by the bus to the line under , and is the inductive current injected by the arc suppression coil from the neutral point to the system under .

[0048] As a further scheme of the present application, , the left and right sides of the formula are multiplied by , and the following is obtained:

[0049] ;

[0050] ;

[0051] When single-phase ground fault occurs in any phase, the same amplitude of is generated, and under the action of which, the capacitive reactive power of the same over-compensation size is generated, and the amplitude comparison method comprises:

[0052] According to historical grounding data, the is estimated, and compared with the data, the fault line is found out; or

[0053] Enumerate each line , determine , meet , then is the target line.

[0054] Through the above steps, the present application realizes accurate positioning of single-phase ground fault of 10kV small current grounding system, overcomes the deficiencies in the prior art, and provides a strong guarantee for safe and stable operation of the power system.

[0055] Compared with the prior art, the small current grounding system single-phase ground fault line selection method provided by the present application has the following beneficial effects:

[0056] 1. Accurate positioning of the fault line: by real-time monitoring and analysis of the zero sequence current and zero sequence voltage signal, and combining the system capacitive current and the compensation degree correction of the arc suppression coil, the interference factors under normal operating state can be effectively eliminated, the fault line can be accurately identified, and misjudgment and missed judgment can be avoided.

[0057] 2. Improve the fault handling efficiency: the method of the present application can generate fault report and alarm information in time, and transmit to the centralized control room through field bus or wireless communication technology, so that the maintenance personnel can quickly locate the fault point, shorten the fault handling time, and improve the operation efficiency of the power system.

[0058] 3. Adaptability to multiple operating conditions: The method of the present application considers different situations of the system under non-grounded and arc suppression coil grounded modes when calculating the arc suppression coil compensation degree, which can adapt to different system configurations and improve the universality and adaptability of the method.

[0059] 4. Effective extraction of fault features: By Fourier transform, the harmonic components of the zero sequence current signal during the fault are extracted, and combined with the zero sequence current waveform and high frequency components at the fault instant, the fault feature signals can be comprehensively extracted, providing sufficient data support for subsequent fault identification.

[0060] 5. Elimination of system interference and improvement of system safety: Combined with the theoretical analysis of three sequence networks, the complex system circuit is simplified into an equivalent circuit, and the fault boundary conditions and series rules of each sequence network are clearly defined, providing a solid theoretical basis for fault analysis; During fault analysis, by constructing three groups of sequence networks under normal operating conditions, the effects of asymmetric components and zero sequence components in the system are eliminated, making the analysis results more accurate and reliable; By accurately positioning and quickly processing the fault, the power outage time and range of the power system are reduced, improving the safety and stability of the system operation, and providing more reliable power supply for power users.

[0061] In summary, the single-phase grounding fault line selection method for small current grounding systems proposed by the present application can realize accurate positioning of single-phase grounding faults through system parameter measurement, capacitance current calculation, arc suppression coil compensation degree calculation, fault feature extraction, data processing and fault line identification, and has strong practicability and wide application prospect.

[0062] These aspects or other aspects of the present application will be more apparent in the following description of the embodiments. It should be understood that the above general description and the following detailed description are only exemplary and explanatory, and cannot limit the present application. BRIEF DESCRIPTION OF DRAWINGS

[0063] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiment or prior art description. Obviously, the drawings in the following description are only some embodiments of the present application, and those skilled in the art can obtain other embodiments according to these drawings without creative labor.

[0064] In the drawings:

[0065] Figure 1 The flow chart of the single-phase grounding fault line selection method for small current grounding systems in the embodiments of the present application.

[0066] Figure 2Circuit diagram of single-phase grounding fault line selection circuit in the single-phase grounding fault line selection method of the small-current grounding system embodiment of the present application.

[0067] Figure 3 Circuit diagram of series regular circuit in the single-phase grounding fault line selection method of the small-current grounding system embodiment of the present application.

[0068] Figure 4 Circuit diagram of analyzing zero sequence network in the single-phase grounding fault line selection method of the small-current grounding system embodiment of the present application.

[0069] Figure 5 Data schematic diagram of line selection success in the single-phase grounding fault line selection method of the small-current grounding system embodiment of the present application. DETAILED DESCRIPTION

[0070] The application will be further described below in conjunction with the drawings and specific embodiments. It should be noted that the embodiments described below or the technical features thereof can be combined with each other to form new embodiments without conflict.

[0071] To make the objectives, technical solutions and advantages of the present application clearer, further detailed description will be made to the embodiments of the present application in conjunction with specific embodiments and by referring to the drawings. It should be understood that the specific embodiments described herein are only used to explain the present application and should not be used to limit the present application.

[0072] It should be noted that all the expressions of "first" and "second" in the embodiments of the present application are used to distinguish two non-identical entities or non-identical parameters with the same name. It can be seen that "first" and "second" are only used for the convenience of description and should not be understood as a limitation on the embodiments of the present application. In addition, the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusion, for example, the process, method, system, product or device inherently includes other steps or units.

[0073] The technical solutions in the embodiments of the present application will be described clearly and completely in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all the other embodiments obtained by those skilled in the art without creative labor are within the protection scope of the present application.

[0074] The flowchart shown in the drawings is only an example and does not necessarily include all the contents and operations / steps, nor does it necessarily be executed in the described order. For example, some operations / steps can be decomposed, combined or partially combined, so the actual execution order can be changed according to the actual situation.

[0075] Some embodiments of the present application will be described in detail with reference to the drawings below. The following examples and features in the examples can be combined with each other in the case of no conflict.

[0076] In order to overcome the problems of small fault current, difficult detection, significant influence of system capacitance current, and high complexity and cost of equipment in the prior art, the present application provides a single-phase grounding fault line selection method for a small current grounding system. Through accurate analysis and calculation of the system zero sequence current and the system capacitance current and arc suppression coil compensation degree, the accuracy and reliability of fault positioning are improved, and many shortcomings in the prior art are overcome.

[0077] Referring to Figure 1 The single-phase grounding fault line selection method for a small current grounding system provided by the embodiments of the present application includes the following steps:

[0078] Step S10, system parameter measurement: when the system is normally running, the zero sequence current and zero sequence voltage of each line are measured using a zero sequence current sensor and a zero sequence voltage sensor, and the zero sequence current and zero sequence voltage data of each line are recorded;

[0079] Step S20, capacitance current calculation: according to the measured zero sequence current data, the capacitance current of the system is calculated, the capacitance current of each line is counted and summed, and the total capacitance current of the system is obtained;

[0080] Step S30, arc suppression coil compensation degree calculation: according to the arc suppression coil reactance value configured by the system and the total capacitance current of the system, the compensation degree of the arc suppression coil is calculated;

[0081] Step S40, fault feature extraction: when a single-phase grounding fault occurs, the changes of the zero sequence current and zero sequence voltage of each line during the fault are recorded in real time, and a fault feature signal is extracted; wherein the fault feature signal includes the zero sequence current waveform, high-frequency component and harmonic feature at the moment of the fault;

[0082] Step S50, data processing and correction: the zero sequence current signal collected during the fault is subjected to Fourier transform to extract the harmonic component; the system capacitance current and the arc suppression coil compensation degree calculated during normal operation are used to correct the zero sequence current signal during the fault, and the influence of the system capacitance current and the arc suppression coil is eliminated;

[0083] Step S60, fault line identification: the corrected zero sequence current signals of the fault line and the non-fault line are compared, and the fault line is determined according to the difference between the corrected zero sequence current signals.

[0084] The single-phase grounding fault selection method for low-current grounding systems also includes generating fault reports and alarms. After the faulty line is identified, the system generates a fault report, records the time, location and parameters of the fault, activates the audible and visual alarm device, and transmits the fault information to the central control room via fieldbus or wireless communication technology.

[0085] In this embodiment, see Figure 2 As shown, based on the arc suppression coil reactance value and the total system capacitance current, the neutral point grounding method of the arc suppression coil transformer is either ungrounded or not. ) and arc suppression coil grounding ( Two methods are adopted (compensation of 10%), among which, phase A is single-phase metallic grounding ( The line-to-ground conductivity is negligible. ).

[0086] The formula for calculating the compensation degree of the arc suppression coil is as follows:

[0087]

[0088] In the formula, It is the sum of the system capacitor current under the system's maximum operating mode. It is the compensation coefficient. This is the system's rated voltage.

[0089] In the fault analysis of the single-phase grounding fault selection method for the low-current grounding system, for a single-phase grounding fault, three sets of sequence networks (positive sequence network, negative sequence network, and zero sequence network) are constructed under normal operating conditions. Thevenin equivalent of each sequence network is calculated from the perspective of the fault point. Among the three sets of sequence networks, the positive sequence network represents the symmetrical component of the power system under normal operating conditions, representing the state of the system under balanced load conditions; the negative sequence network represents the asymmetrical component of the system, reflecting the state of the system under unbalanced conditions; and the zero sequence network represents the zero sequence component of the system.

[0090] The fault boundary conditions in a three-order network are:

[0091] ;

[0092] ;

[0093] Symmetric decomposition into:

[0094] ;

[0095] ;

[0096] ;

[0097] After simplification, we get:

[0098] , indicating a three-order network connected in series.

[0099] Among them, see Figure 3 As shown, in the fault analysis of the single-phase grounding fault selection method for the low-current grounding system, the series connection rule is as follows:

[0100]

[0101] The sequence impedances of the independent static components in the three-phase magnetic circuit are equal, and the neutral point of the system is not directly grounded. ∞ ):

[0102]

[0103] That is: appearing across the entire network .

[0104] See Figure 4 As shown, in the fault analysis of the single-phase grounding fault selection method for the low-current grounding system, the positive and negative sequences are symmetrical, and the zero-sequence network is analyzed:

[0105]

[0106]

[0107] In the formula, For each phase The capacitive current generated below flows from the busbar to the line. For the arc suppression coil in The inductive current injected into the system from the neutral point.

[0108] When the neutral point is not grounded, a capacitive current is generated on the non-faulty lines, flowing from the busbar to the line; a capacitive current is generated on the faulty lines, flowing from the line to the busbar. The zero-sequence currents are in opposite directions and their magnitudes are the sum of the zero-sequence currents of the non-faulty phases; when grounded through an arc suppression coil, a capacitive current is generated on the non-faulty lines, flowing from the busbar to the line.

[0109] Furthermore, Multiply both sides of the formula by ,get:

[0110] ;

[0111] ;

[0112] A single-phase ground fault in any phase will produce the same amplitude. Under its action, it generates capacitive reactive power of the same overcompensation magnitude. The amplitude comparison method includes:

[0113] According to historical grounding data, estimate , compare with this data, find out the fault line; or

[0114] List each line , determine , meet , then That is the target line.

[0115] Exemplary, at present, there are 13 substations in the distribution network frame of Wan'an District, among which 11 substations have installed small current grounding line selection devices, respectively, Shanghai Keneng, Guodian Nanrui, Nanrui, Nanjing Houtai, the line selection principles of each party are different, and the line selection capabilities are uneven, at present, only Shanghai Keneng has a higher line selection success rate, and the line selection effect of the other three brands is poor. The other two substations do not install small current grounding line selection devices, and can only rely on trial pulling during grounding.

[0116] For single-phase grounding fault of neutral point ungrounded system, 25 grounding cases occurred in Wan'an District in 2024 are summarized, the change law of electrical parameters such as active power, reactive power, current and power factor, tangent of line before and after grounding is analyzed, and it is found that the reactive power and current of the fault line change more obviously before and after grounding, which can be used as an important reference quantity to assist line selection and line search.

[0117] When single-phase grounding occurs, the voltage of the fault phase drops to zero. The voltage of the non-fault phase rises to the line voltage. The current performance is: the grounding point current is the sum of the total network capacitance current, the non-fault line current is the line-to-ground capacitance current, flows to the grounding point, and flows out from the bus; the fault line current is the sum of the capacitance current of all other non-fault lines to the ground, flows from the grounding point, and flows to the bus.

[0118] The small current grounding system single-phase grounding fault line selection method of the application is applied, through analysis of 25 grounding data in 2023, the success rate of the first two grounding lines is 84%, and the results are shown in Table 1:

[0119]

[0120] Referring to Figure 5 , at 15:54 on January 19, after the grounding fault occurred in 10kV I bus of 110kV Jin Yuan transformer substation, the grounding auxiliary research and judgment strategy model was used for analysis, and the pull line priority of the four running lines on the fault bus was sorted, among which the current of 112 line increased and the reactive power decreased before and after grounding, and the change amplitude was the largest, so the grounding possibility was the largest, and the line search found that the internal fault of the special transformer caused the line selection to be successful.

[0121] Through the above steps, the application realizes accurate positioning of single-phase grounding fault of 10kV small current grounding system, overcomes the defects in the prior art, and provides a strong guarantee for safe and stable operation of the power system.

[0122] The above are exemplary embodiments disclosed by the application, but it should be noted that various changes and modifications can be made without departing from the scope of the embodiments disclosed by the application defined by the claims. The functions, steps and / or actions of the method claims described in the embodiments disclosed herein need not be performed in any particular order. In addition, although the elements of the embodiments disclosed by the application can be described or claimed in individual form, they can also be understood as plural unless explicitly limited as singular.

[0123] It should be understood that, as used herein, the singular forms "a", "an" and "the" are intended to include plural forms as well, unless the context clearly indicates otherwise. It should also be understood that "and / or" as used herein refers to any and all possible combinations of one or more of the associated listed items. The above embodiment numbers of the embodiments disclosed by the application are only for description and do not represent the advantages or disadvantages of the embodiments.

[0124] Those skilled in the art should understand that the above discussion of any of the embodiments is only exemplary and is not intended to imply that the scope of the embodiments disclosed by the application (including the claims) is limited to these examples; the technical features of the above embodiments or different embodiments can also be combined, and there are many other changes of the different aspects of the embodiments disclosed by the application as above. In order to be brief, they are not provided in details. Therefore, any omissions, modifications, equivalent replacements, improvements, etc. made in the spirit and principles of the embodiments disclosed by the application shall be included in the protection scope of the embodiments disclosed by the application.

Claims

1. A method for single-phase earth fault line selection in a small current grounding system, characterized in that, The method comprises the following steps: During normal operation of the system, the zero sequence current and the zero sequence voltage of each line are measured by using the zero sequence current sensor and the zero sequence voltage sensor, and the zero sequence current and the zero sequence voltage data of each line are recorded; According to the measured zero sequence current data, the capacitance current of the system is calculated, the capacitance current of each line is counted and summed up, and the total capacitance current of the system is obtained; According to the arc suppression coil reactance value of the system configuration and the system total capacitance current, the compensation degree of the arc suppression coil is calculated; wherein, when the arc suppression coil reactance value of the system configuration and the system total capacitance current are according to the system configuration, the transformer neutral point grounding mode of the arc suppression coil is divided into two modes of no grounding and arc suppression coil grounding, wherein, when no grounding, , when the arc suppression coil is grounded, , 10% compensation is taken; the single-phase metallic grounding of phase A is, that is, , the line-to-ground conductance is ignored, that is, ; wherein, when the compensation degree of the arc suppression coil is calculated, the calculation formula is: ; in the formula, is the total system capacitance current under the maximum operation mode of the system, is the compensation coefficient, is the system rated voltage; When a single-phase grounding fault occurs, the changes of the zero sequence current and the zero sequence voltage of each line during the fault are recorded in real time, and a fault characteristic signal is extracted; The zero sequence current signal collected during the fault is subjected to Fourier transform, and a harmonic component is extracted; the zero sequence current signal during the fault is corrected by using the system capacitance current and the arc suppression coil compensation degree calculated during normal operation, and the influence of the system capacitance current and the arc suppression coil is eliminated; The corrected zero sequence current signals of the fault line and the non-fault line are compared, and the fault line is determined according to the difference between the corrected zero sequence current signals; In the fault analysis of the single-phase grounding fault line selection method of the small current grounding system, for a single-phase grounding fault, three sets of sequence networks in the normal operation state are constructed, and the Thevenin equivalent of each sequence network is calculated from the fault point. The three sets of sequence networks include a positive sequence network, a negative sequence network and a zero sequence network. The positive sequence network in the three sets of sequence networks represents the symmetrical component of the power system in the normal operation state, and represents the state of the system under the condition of balanced load. The negative sequence network represents the asymmetrical component in the system, and reflects the state of the system under the condition of unbalanced load. The zero sequence network represents the zero sequence component in the system. Wherein, the fault boundary conditions of the three groups of sequence networks are: , indicating that the three sequence networks are in series; the positive and negative sequences are symmetrical, and the zero sequence network is analyzed: wherein is the capacitive current from the bus to the line for each phase is the capacitive current from the bus to the line for each phase is the inductive current injected from the arc suppression coil to the system for each phase is the inductive current injected from the arc suppression coil to the system for each phase wherein wherein both sides are multiplied by , we obtain: ； ； In case of single-phase ground fault of any phase, the same amplitude of ; When a single-phase grounding fault occurs, the voltage of the fault phase drops to zero; the voltage of the non-fault phase rises to the line voltage; the current at the grounding point is the sum of the capacitance currents of the whole network to the ground, the current of the non-fault line is the capacitance current of the line to the ground, and the current flowing from the grounding point to the bus is the sum of the capacitance currents of all the non-fault lines to the ground.

2. The single-phase-to-ground fault line selection method of a small current grounding system according to claim 1, characterized in that, The single-phase grounding fault line selection method of the small current grounding system further comprises generating a fault report and an alarm. After the fault line is identified, the system generates a fault report, records the time, position and parameters of the fault, starts an audible and visual alarm device, and transmits the fault information to the centralized control room through a field bus or wireless communication technology.

3. The single-phase-to-ground fault line selection method of a small current grounding system according to claim 2, characterized in that, The fault characteristic signal includes the zero sequence current waveform at the moment of the fault, a high-frequency component and a harmonic characteristic.

4. The single-phase-to-ground fault line selection method of a small current grounding system according to claim 3, characterized in that, When the neutral point is not grounded, the capacitance current from the bus to the line is generated on the non-fault line; the capacitance current from the line to the bus is generated on the fault line, the zero sequence current direction is opposite, and the size is the sum of the zero sequence currents of the non-fault phases; When the neutral point is grounded through an arc suppression coil, the capacitance current from the bus to the line is generated on the non-fault line.

5. The single-phase-to-ground fault line selection method of a small current grounding system according to claim 4, characterized in that, The fault boundary conditions in the three sets of sequence networks are: ； ； Symmetrical decomposition is: ； ； 。 6. The single-phase-to-ground fault line selection method of a small-current grounding system according to claim 5, characterized in that, In the fault analysis of the single-phase grounding fault line selection method of the small current grounding system, the series law is: The sequence impedances of the three-phase magnetic circuit independent static elements are equal, and the neutral point of the system is not directly grounded: All networks appear .

7. The single-phase-to-ground fault line selection method of a small current grounding system according to claim 6, characterized in that, In the fault analysis of the single-phase grounding fault line selection method of the small current grounding system, the capacitance reactive power of the same over-compensation size is generated under the action, and the amplitude comparison method comprises: Based on historical grounding data, estimate Compare this data to find the faulty line; or Enumerate routes , determine , meet , then That is, the target route.

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