A method for locating ground faults in active distribution networks based on transient direction

Abstract

The present invention discloses a method for locating ground faults in an active distribution network based on transient direction: a ground fault monitoring device is installed in each feeder of the active distribution network. The ground fault monitoring device is responsible for synchronously sampling the phase voltage and phase current on the line, recording the voltage and current, and extracting three-phase transient characteristic signals from the waveform in real time through a filtering algorithm; when transient voltage and transient current signals are detected, the transient direction value is calculated to determine whether a ground fault occurs in the device, and each monitoring device uploads the ground fault judgment result to the main station, which completes the ground fault section positioning and fault isolation. This method overcomes the implementation difficulties of existing ground fault locating methods, high installation costs, inflexible on-site implementation, and the problem of misjudgment of ground faults in active distribution networks.

Description

Technical Field

[0001] The present invention relates to the technical field of power distribution automation, and in particular to a method for locating ground faults in an active power distribution network based on transient direction. Background Art

[0002] Most of the distribution networks in my country adopt the neutral point non-effective grounding method. For the distribution network without distributed power sources, many achievements have been made in the research on the steady-state and transient characteristics of single-phase grounding faults, and a series of grounding fault line selection and location methods have been proposed. With the implementation of the new national power system, a high proportion of distributed power sources will be connected to the distribution network, and the access of distributed power sources will affect the accuracy of the existing grounding fault line selection and location.

[0003] At present, the main technical solutions include a ground fault protection method based on phase current mutation. The Chinese invention patent application with publication number CN105914718A discloses a ground fault protection method based on phase current mutation, and its steps are: S1: online monitoring of the zero-sequence voltage of the distribution network, when the zero-sequence voltage exceeds the voltage limit value, collecting the transient phase current signal of each line; S2: extracting the transient phase current mutation of each line; S3: performing phase-to-phase correlation analysis on the phase current mutation of each line, obtaining the phase-to-phase correlation coefficient [ρABρBCρCA], and obtaining the minimum phase-to-phase correlation coefficient ρmin by comparison; S4: judging the fault line according to the size of the phase-to-phase correlation coefficient. A Chinese invention patent application with publication number CN106959403A discloses a method for detecting ground faults in a distribution network connected to a distributed power source, comprising the following steps: installing protection agents at each bus of a distribution network containing distributed power sources to centrally manage and control local protection devices; when the bus zero-sequence voltage exceeds the limit, recording the sampled data measured by the local protection device; calculating the relative distance between the sampled data and the historical fault data, and then determining the fault area; through a communication network, the protection agents coordinate and cooperate to finally determine the faulty line and send a tripping signal.

[0004] These two algorithms have the following problems:

[0005] 1) The ground fault protection method based on phase current mutation, its core algorithm is to perform phase-to-phase correlation analysis on the phase current mutation, obtain the phase-to-phase correlation coefficient array, and analyze it through the correlation coefficient. The waveform of the current mutation of the faulty phase of the faulty line is very different from that of the healthy phase, the minimum phase-to-phase correlation coefficient is very small or even negative, the waveform of the current mutation of each phase of the non-faulty line is similar, almost the same, and the phase-to-phase correlation system is large. This method is more accurate for ground faults in passive distribution networks, such as Figure 4 The main problem is that the algorithm is mainly used for grounding line selection, only determining the fault line and the non-fault line, but not the fault location. It has defects in grounding line selection and fault section location of active distribution network, such as Figure 3As shown in the waveform, the phase current mutation amount before the fault point of the fault line is not much different, which does not conform to the situation that the correlation coefficient is very small or even negative. The phase current mutation amount after the fault line is very different, which conforms to the situation that the correlation system is very small or even negative, which can easily lead to misjudgment.

[0006] 2) A method for detecting ground faults in the distribution network of distributed power sources, which uniformly manages and controls multiple protection devices installed in the power grid, collects zero-sequence voltage and zero-sequence current data, and analyzes the similarity between the real-time data collected by each protection device and the historical data, with high requirements for communication reliability and time synchronization. In addition, the line spacing of the overhead line of the 10kV distribution network is about 70 cm, and the zero-sequence current transformer needs to pass through the three-phase wires A, B, and C. It is difficult to install such a zero-sequence current transformer with a diameter of about 1 meter, and the project implementation is not flexible. Summary of the invention

[0007] The technical problem to be solved by the present invention is to provide a distribution network grounding fault location method which is applicable to a distributed active distribution network and does not require the installation of a zero-sequence current transformer.

[0008] In order to solve the above technical problems, the present invention provides a method for locating ground faults in an active distribution network based on transient direction, comprising the following steps:

[0009] Step S1, installing a ground fault monitoring device at each monitoring point of each feeder of the active distribution network, installing a ground fault locating module at the distribution network master station, and establishing a communication connection between the ground fault monitoring device at each monitoring point and the ground fault locating module at the distribution network master station.

[0010] Step S2, synchronously sampling the phase voltage and phase current on the line, and adopting one of the following two methods to perform the synchronous sampling of the phase voltage and phase current in step S2:

[0011] Method 1: Integrate a combined voltage and current transformer on the DTU or FTU product, and obtain three-phase voltage and current signals through synchronous sampling of the internal ADC chip;

[0012] Method 2: Install sensors on the A, B, and C phases of the feeder respectively, and each phase sensor completes synchronous sampling of the three-phase voltage and current signals through the internal ADC.

[0013] The sampling frequency for discrete sampling of three-phase voltage and current is 256 points per cycle; the storage period for recording and storing the sampled data is 12 cycles.

[0014] Record the voltage and current and filter the waveform:

[0015] A Butterworth bandpass filter is used, the filter order is 8th, the lower cutoff frequency is 628 rad / s, and the upper cutoff frequency is 20000 rad / s.

[0016] Real-time extraction of three-phase transient characteristic signals: continuous calculation of each phase transient phase voltage U with time Ts as the cycle x :

[0017]

[0018] Where, u is the voltage amplitude of any phase A, B, or C, ω is the voltage angular frequency, is the initial voltage phase angle.

[0019] Step S3, judging whether transient voltage and transient current signals are generated according to the extracted three-phase transient characteristic signals, the specific judging step is as follows: if a certain phase transient phase voltage U x If it is greater than the set threshold, it is determined that transient voltage and transient current signals are generated.

[0020] If transient voltage and transient current signals are generated, the transient direction value Q of this monitoring point is calculated. The calculation steps are as follows:

[0021] Step S31, record the start time t0 of the first half-wave of the transient current and voltage signals, the duration T of the first half-wave of the transient voltage, the duration T1 of the first half-wave of the transient current, and calculate the integral value S of the transient current waveform area of ​​the three phases A, B, and C in the T1 time period. IA , S IB , S IC :

[0022]

[0023]

[0024]

[0025] Step S32, select S IA , S IB , S IC The area integral value of the transient current waveform with the largest absolute value is recorded as S Imax ;

[0026] Step S33, calculate the integral value S of the transient voltage waveform area of ​​the three phases A, B, and C within the time period T UA , S UB , S UC :

[0027]

[0028]

[0029]

[0030] Step S34, select S Imax The integral value S of the transient voltage waveform area of ​​the corresponding phase U Perform difference calculation:

[0031] S UImax =|S U -S Imax |;

[0032] Step S35, calculate the transient direction value of the monitoring point: Q = |S UImax |-|S U |;

[0033] In steps S31 and S33, i A 、i B 、i C are the current amplitudes of phases A, B, and C respectively, u A 、u B 、u C are the voltage amplitudes of phases A, B, and C respectively, ω is the current or voltage angular frequency, is the initial phase angle of current or voltage.

[0034] Step S4, judging whether a ground fault occurs at the monitoring point according to the transient direction value of the monitoring point, the specific steps are:

[0035] When the transient direction value Q of the monitoring point is greater than 0, the fault current flows from the line to the busbar, which is judged as an internal fault, that is, the ground fault signal flows through the ground fault monitoring device;

[0036] When the transient direction value Q of the monitoring point is less than 0, the fault current flows from the busbar to the line, and it is judged as an out-of-bounds fault, that is, the ground fault signal does not flow through the ground fault monitoring device.

[0037] Then the ground fault judgment result is uploaded to the ground fault locating module of the distribution network master station.

[0038] Step S5: the ground fault location module of the distribution network master station locates the ground fault section according to the uploaded results received from the ground fault monitoring devices of each monitoring point. The specific steps are as follows:

[0039] Step S51, performing ground fault line selection judgment: if one or more ground fault monitoring devices on the feeder report a transient direction value Q>0 for the monitoring point, then a ground fault occurs on the feeder; if all ground fault monitoring devices on the feeder report a transient direction value Q<0 for the monitoring point, then no ground fault occurs on the feeder;

[0040] Step S52, locating the ground fault section: on the feeder where the ground fault occurs, if, among two adjacent ground fault monitoring devices, the transient direction value Q of the monitoring point reported by one ground fault monitoring device is greater than 0, and the transient direction value Q of the monitoring point reported by the other ground fault monitoring device is less than 0, then the ground fault occurs between the two ground fault monitoring devices;

[0041] Step S53, determining the ground fault phase: for the ground fault monitoring device reporting the transient direction value Q>0 of the monitoring point, the phase with the largest absolute value of the transient current waveform area integral value is the grounded phase.

[0042] Based on the fault location results, isolate the ground fault:

[0043] Step S54, the distribution network master station issues a tripping command to two adjacent ground fault monitoring devices at the point where the ground fault occurs according to the ground fault section positioning result, isolates the ground fault, and notifies the operating personnel to repair the ground fault;

[0044] Step S52: the distribution network master station maintains the distributed power supply to the non-fault area according to the distributed power supply operation strategy.

[0045] The beneficial effects of the present invention are:

[0046] The present application discloses a method for locating ground faults in an active distribution network based on transient direction, which is suitable for judging ground faults in a small current grounding system of a distribution network to which distributed power sources are connected. It can not only correctly identify the faulty line, but also accurately locate the faulty section.

[0047] The present application discloses an active distribution network ground fault location method based on transient direction, which is still suitable for passive distribution network ground fault line selection and location. Moreover, when the distributed power source is put into operation or withdrawn, there is no need to adjust the ground fault location method, that is, active and passive ground fault judgment are adaptively adjusted.

[0048] The present application discloses a method for locating ground faults in an active distribution network based on transient direction. The method performs calculations based on phase voltage and phase current only. Zero-sequence voltage and zero-sequence current are not required to participate in the calculation at each monitoring point. Therefore, a zero-sequence voltage transformer does not need to be installed. The method has low cost, is easy to implement on site, and is suitable for batch applications.

[0049] The present application discloses a method for locating ground faults in an active distribution network based on transient direction and an on-site fault judgment algorithm, which are independent of the analysis of a master station, reduce the communication and processing requirements of the master station, and clearly define the boundaries of responsibility between the master station and the equipment manufacturer, which is conducive to improving the efficiency of system operation and maintenance management, thereby improving the reliability of the scheme operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 It is a schematic diagram of the active power distribution network equipment circuit according to an embodiment of the present invention.

[0051] Figure 2 It is a flow chart of an embodiment of the present invention.

[0052] Figure 3 This is the simulation result of the active distribution network grounding fault location in the embodiment of the present invention.

[0053] Figure 4 This is the simulation result of the passive distribution network grounding fault location according to the embodiment of the present invention.

[0054] Figure 5 It is a flow chart of ground fault location and isolation of an active distribution network according to an embodiment of the present invention. Specific embodiments

[0055] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0056] It should be understood that when used in this specification and the appended claims, the terms "include" and "comprises" indicate the presence of described features, integers, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or combinations thereof.

[0057] It should be further understood that the term "and / or" used in the present description and the appended claims refers to any and all possible combinations of one or more of the associated listed items, and includes these combinations.

[0058] like Figure 1As shown, an active 10kV distribution network is composed of a grid power supply 1 and a distributed power supply 2. The distribution network has two feeders, namely feeder 1 and feeder 2, and each feeder is connected to a 0.4kV load. A ground fault monitoring device (hereinafter referred to as monitoring device) is installed on each feeder, and monitoring devices F11, F12, F13, and F14 are installed on feeder 1, and monitoring devices F21, F22, F23, and F24 are installed on feeder 2. Each monitoring device is equipped with a circuit breaker, which can switch on and off short circuits and ground faults. A distribution automation master station (hereinafter referred to as the master station) is arranged, and a ground fault locating module (not marked in the figure) is installed in the master station. The ground fault monitoring devices at each monitoring point establish a communication connection with the ground fault locating module of the distribution network master station (indicated by the dotted line in the figure), which is used for each monitoring device to upload a ground fault signal to the master station and for the master station to send a closing and opening command to each monitoring device. The communication connection can be a wired or wireless communication connection. Figure 1 In the figure, there is a ground fault between F21 and F22 (i.e., the lightning symbol of the line between F21 and F22 in the figure).

[0059] like Figure 2 , Figure 3 As shown, Figure 1 The specific steps of the ground fault location method of the active 10kV distribution network shown are as follows:

[0060] Step S201, a ground fault monitoring device is installed at each monitoring point of each feeder of the active distribution network, a ground fault locating module is installed at the distribution network master station, and each monitoring device establishes a communication connection with the master station ground fault locating module.

[0061] Step S202: synchronously sample the phase voltage and phase current on the line in one of the following two ways:

[0062] Method 1: Integrate a combined voltage and current transformer on the DTU or FTU product, and obtain three-phase voltage and current signals through synchronous sampling of the internal ADC chip;

[0063] Method 2: Install sensors on the A, B, and C phases of the feeder respectively, and each phase sensor completes synchronous sampling of the three-phase voltage and current signals through the internal ADC.

[0064] The sampling frequency of discrete sampling of three-phase voltage and current is 256 points per cycle; the storage period of sampled data for recording and storage is 12 cycles. The voltage and current are recorded, and a Butterworth bandpass filter is used. The filter order is 8, the lower cutoff frequency is 628rad / s, and the upper cutoff frequency is 20000rad / s to filter the signal.

[0065] The transient phase voltage U of each phase is calculated continuously with a period of time Ts = 10ms. x :

[0066]

[0067] Where, u is the voltage amplitude of any phase A, B, or C, ω is the voltage angular frequency, is the initial voltage phase angle.

[0068] Step S203, judging whether transient voltage and transient current signals are generated according to the extracted three-phase transient characteristic signals: if a transient phase voltage U x If it is greater than 30V, it is determined that transient voltage and transient current signals are generated. At this time, the transient direction value Q of this monitoring point is calculated. The calculation steps are as follows:

[0069] Record the starting time t0 of the first half wave of the transient current and voltage signals, the duration T of the first half wave of the transient voltage, and the duration T1 of the first half wave of the transient current. Calculate the integral value S of the transient current waveform area of ​​the three phases A, B, and C in the T1 time period. IA , S IB , S IC :

[0070]

[0071]

[0072]

[0073] Select S IA , S IB , S IC The area integral value of the transient current waveform with the largest absolute value is recorded as S Imax ;

[0074] Calculate the integral value S of the transient voltage waveform area of ​​phases A, B, and C within the T time period UA , S UB , S UC :

[0075]

[0076]

[0077]

[0078] Select S Imax The integral value S of the transient voltage waveform area of ​​the corresponding phase U Perform difference calculation:

[0079] S UImax =|S U -S Imax |;

[0080] Calculate the transient direction value of the monitoring point: Q = |S UImax |-|S U |;

[0081] Among them, i A 、i B 、i C are the current amplitudes of phases A, B, and C respectively, u A 、u B 、u C are the voltage amplitudes of phases A, B, and C respectively, ω is the current or voltage angular frequency, is the initial phase angle of current or voltage.

[0082] Figure 3 This is a simulation diagram of ground fault location in active distribution network. Figure 1 The simulation model of the active distribution network is established. The simulation model parameters are that the neutral point of the power grid 1 is ungrounded or arc-extinguishing coil, the total length of feeder 1 is 20 km, the total length of feeder 2 is 13 km, and the distributed power source is connected to feeder 2. The simulation diagrams from top to bottom are the transient voltage waveform, F21 transient current waveform, F22 transient current waveform, and F11 transient current waveform. It can be seen from the simulation waveform that: the A phase of the three-phase transient current waveform of F21 is the largest, and the direction is opposite to the transient voltage waveform; the A phase of the three-phase transient current waveform of F22 is the largest, and the direction is the same as the transient voltage waveform; the three-phase transient current waveform of F11 is basically the same, but the direction is the same as the transient voltage waveform.

[0083] In this embodiment, the ground fault occurs between the monitoring devices F21 and F22, and the grounded phase is phase A. The integral values ​​of the transient current waveform area of ​​the F21 monitoring device are calculated according to the above formula: S IA21 =55, S IB21 =26, S IC21 =24, S Imax For S IA21 =55, the integral values ​​of the transient voltage waveform area are: S UA =-65, S UB =-66, S UC =-64. The difference in area integral of transient voltage and current waveforms of F21 device is calculated as follows:

[0084] S UIA =|-65-55|=120,

[0085] Q 21 =|120|-|-65|=55,

[0086] Q 21 >0.

[0087] The integral values ​​of the transient current waveform area of ​​the F22 monitoring device are: SIA22 =-65, S IB22 =28, S IC22 =28, S Imax For S IA22 =-65, the integral values ​​of the transient voltage waveform area are: S UA =-64, S UB =-65, S UC =-64. The difference in area integral of transient voltage and current waveforms of F22 device is calculated as follows:

[0088] S UImax22 =|-64-(-65)|=1,

[0089] Q 22 =|1|-|-64|=-63,

[0090] Q 22 <0.

[0091] The integral values ​​of the transient current waveform area of ​​the F11 monitoring device are: S IA11 =-25, S IB11 =-25, S IC11 =-24, S Imax For S IA11 =-25, the integral values ​​of the transient voltage waveform area are: S UA =-64, S UB =-65, S UC =-64. The difference in area integral of transient voltage and current waveforms of F11 device is calculated as follows:

[0092] S UImax11 =|-25-(-65)|=40,

[0093] Q 11 =|40|-|-64|=-24,

[0094] Q 11 <0.

[0095] The integral value of each transient waveform area in the above calculation process is the calculated value after filtering the original ADC value and unifying the dimensions for easy analysis. The integral value is related to the line parameters and sampling design parameters, but does not affect the judgment of the result.

[0096] Step S204, judging whether a ground fault occurs at the monitoring point according to the transient direction value of the monitoring point, in this embodiment:

[0097] F21 Monitoring Device A Phase Q 21>0, F21 is judged as an internal fault, and the fault current flows from the grounding point to the busbar, that is, the grounding fault signal flows through this grounding fault monitoring device. Other monitoring devices calculate the transient direction value of phase A, Q 22 <0, Q 23 <0, Q 24 <0, F22, F23, F24 are judged as out-of-bounds faults, and the fault current flows from the bus to the line; Q 11 <0, Q 12 <0, Q 13 <0, Q 14 <0, F11, F12, F13, F14 are judged as out-of-bounds faults, and the fault current flows from the bus to the line.

[0098] Each monitoring device uploads the ground fault judgment result to the main station, and the main station grounding module completes the ground fault line selection, section positioning, and grounding phase identification.

[0099] Step S205: The ground fault location module of the master station locates the ground fault section according to the received results uploaded by the ground fault monitoring devices at each monitoring point, and isolates the ground fault:

[0100] Conduct ground fault line selection judgment: If the transient direction value Q>0 reported by one or more ground fault monitoring devices on the feeder, a ground fault occurs on the feeder; if the transient direction value Q<0 reported by all ground fault monitoring devices on the feeder, no ground fault occurs on the feeder;

[0101] Locate the ground fault section: On the feeder where the ground fault occurs, if the transient direction value Q of the monitoring point reported by one of the two adjacent ground fault monitoring devices is greater than 0, and the transient direction value Q of the monitoring point reported by the other ground fault monitoring device is less than 0, then the ground fault occurs between the two ground fault monitoring devices;

[0102] Determine the ground fault phase: For the ground fault monitoring device reporting the transient direction value Q>0 of the monitoring point, the phase with the largest absolute value of the transient current waveform area integral value is the grounded phase.

[0103] According to the ground fault section location results, the two adjacent ground fault monitoring devices at the point where the ground fault occurs are issued a trip command, the ground fault is isolated, and the operating personnel are notified to repair the ground fault. The master station maintains the distributed power supply to the non-fault area according to the distributed power supply operation strategy.

[0104] In this embodiment, the positioning result is: the ground fault occurs on feeder 2, and there is no ground fault on feeder 1. The grounding position occurs between F21 and F22, and phase A with the largest transient characteristic current is the grounded phase. The master station grounding module sends a trip command to F21 and F22 to isolate the ground fault and notify the operator to repair the ground fault. At the same time, according to the distributed power supply operation strategy, that is, island operation is allowed, and the generated power meets the load requirements, the distributed power supply can be maintained to supply power to the non-fault area of ​​feeder 2.

[0105] The embodiments of the present invention can be adjusted, merged and deleted in sequence according to actual needs.

[0106] The embodiments have been described in detail. Specific examples are used herein to illustrate the principles and implementation methods of the present invention. The above embodiments are only used to help understand the method of the present invention and its core idea. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A method for locating ground faults in an active distribution network based on transient direction, characterized in that: The following steps are involved: S1, installing a ground fault monitoring device at each monitoring point of each feeder of the active distribution network, installing a ground fault locating module at the distribution network master station, and establishing a communication connection between the ground fault monitoring device at each monitoring point and the ground fault locating module at the distribution network master station; S2, the ground fault monitoring device synchronously samples the phase voltage and phase current on the line, records the voltage and current, filters the waveforms and extracts three-phase transient characteristic signals in real time; S3, the ground fault monitoring device determines whether transient voltage and transient current signals are generated according to the extracted three-phase transient characteristic signals, and if so, calculates the transient direction value Q of the monitoring point; S4, the ground fault monitoring device determines whether a ground fault occurs at the monitoring point according to the transient direction value of the monitoring point, and uploads the ground fault judgment result to the ground fault locating module of the distribution network master station; S5, the ground fault locating module of the distribution network master station locates the ground fault section according to the uploaded results received from the ground fault monitoring devices of each monitoring point, and isolates the ground fault; The calculation steps of the transient direction value of the monitoring point in step S3 are: S31, record the start time t0 of the first half-wave of the transient current and voltage signals, the duration of the first half-wave of the transient voltage is T, the duration of the first half-wave of the transient current is T1, and calculate the integral value of the transient current waveform area of ​​the three phases A, B, and C in the T1 time period , , : ， ， ； S32, select , , The area integral value of the transient current waveform with the largest absolute value is recorded as ; S33, calculate the integral value of the transient voltage waveform area of ​​the three phases A, B, and C in the T time period , , : ， ， ； S34, select The integral value of the transient voltage waveform area of ​​the corresponding phase Perform difference calculation: = ； S35, calculate the transient direction value of the monitoring point: - ; In steps S31 and S33, , , are the current amplitudes of phases A, B and C respectively, , , are the voltage amplitudes of phases A, B, and C respectively, is the current or voltage angular frequency, is the initial phase angle of current or voltage.

2. According to claim 1, a method for locating ground faults in an active distribution network based on transient direction, characterized in that: The method for extracting the three-phase transient characteristic signal in real time in step S2 is to continuously calculate the transient phase voltage of each phase with a period of time Ts. : ， Where, u is the voltage amplitude of any phase A, B, or C. is the voltage angular frequency, is the initial voltage phase angle.

3. The method for locating ground faults in active distribution networks based on transient direction according to claim 1, characterized in that: The method for determining whether a ground fault occurs at the monitoring point in step S4 is: When the transient direction value Q of the monitoring point is greater than 0, the fault current flows from the line to the busbar, which is judged as an internal fault, that is, the ground fault signal flows through the ground fault monitoring device; When the transient direction value Q of the monitoring point is less than 0, the fault current flows from the busbar to the line, and it is judged as an out-of-bounds fault, that is, the ground fault signal does not flow through the ground fault monitoring device.

4. The method for locating ground faults in active distribution networks based on transient direction according to claim 1, characterized in that: The steps of locating the ground fault section in step S5 are: S51, performing ground fault line selection judgment: if the transient direction value Q of the monitoring point reported by one or more ground fault monitoring devices on the feeder is greater than 0, then a ground fault occurs on the feeder; if the transient direction value Q of the monitoring point reported by all ground fault monitoring devices on the feeder is less than 0, then no ground fault occurs on the feeder; S52, performing ground fault section location: on the feeder where the ground fault occurs, if, among two adjacent ground fault monitoring devices, the transient direction value Q of the monitoring point reported by one ground fault monitoring device is greater than 0, and the transient direction value Q of the monitoring point reported by the other ground fault monitoring device is less than 0, then the ground fault occurs between the two ground fault monitoring devices; S53, determining the ground fault phase: for the ground fault monitoring device reporting the transient direction value Q>0 of the monitoring point, the phase with the largest absolute value of the transient current waveform area integral value is the grounded phase.

5. The method for locating ground faults in active distribution networks based on transient direction according to claim 1, characterized in that: The steps of isolating the ground fault in step S5 are: S54, the distribution network master station issues a tripping command to two adjacent ground fault monitoring devices at the point where the ground fault occurs according to the ground fault section positioning result, isolates the ground fault, and notifies the operating personnel to repair the ground fault; S55, the distribution network master station maintains the distributed power supply to the non-fault area according to the distributed power supply operation strategy.

6. The method for locating ground faults in active distribution networks based on transient direction according to claim 1, characterized in that: The synchronous sampling of the phase voltage and the phase current in step S2 is performed in one of the following two ways: Method 1: Integrate a combined voltage and current transformer on the DTU or FTU product, and obtain three-phase voltage and current signals through synchronous sampling of the internal ADC chip; Method 2: Install sensors on the A, B, and C phases of the feeder respectively, and each phase sensor completes synchronous sampling of the three-phase voltage and current signals through the internal ADC.

7. The method for locating ground faults in active distribution networks based on transient direction according to claim 1, characterized in that: The method for sampling and recording the voltage and current in step S2 is: The sampling frequency for discrete sampling of three-phase voltage and current is 256 points per cycle; the storage period for recording and storing the sampled data is 12 cycles.

8. The method for locating ground faults in active distribution networks based on transient direction according to claim 1, characterized in that: The filtering method in step S2 is: A Butterworth bandpass filter is used with an order of 8, a lower cutoff frequency of 628 rad / s, and an upper cutoff frequency of 20000 rad / s.

9. The method for locating ground faults in active distribution networks based on transient direction according to claim 2, characterized in that: The steps of determining whether transient voltage and transient current signals are generated in step S3 are: If a phase transient voltage If it is greater than the set threshold, it is determined that transient voltage and transient current signals are generated.

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