A method and system for analyzing and judging single-phase grounding fault of overhead distribution line

Abstract

The present invention provides a method for analyzing and judging a single-phase grounding fault of an overhead distribution line. Different sensors are used to collect power frequency, transient and high-frequency transient traveling wave voltage and current characteristic signals within different frequency bands. A variety of power frequency analysis methods, transient analysis methods and high-frequency transient traveling wave analysis methods are used for voltage and current characteristic signals within different frequency bands to respectively analyze and judge the single-phase grounding fault of the overhead distribution line. Finally, the analysis results given by different algorithms are integrated, and the most significant characteristic quantity is adaptively used to give the optimal solution, and finally a reliable single-phase grounding fault analysis result is given. The analysis result of this method can distinguish between instantaneous single-phase grounding faults, permanent single-phase grounding faults and power grid disturbances, effectively solving the problem that it is difficult to analyze and judge single-phase grounding faults of overhead distribution lines, reducing the occurrence of misjudgment, wrong judgment and missed judgment of single-phase grounding faults, and improving the power supply reliability of the overhead distribution network.

Description

Technical Field

[0001] The present application relates to the technical field of distribution line fault identification, and in particular to a method and system for analyzing and determining a single-phase grounding fault in an overhead distribution line. Background Art

[0002] Most of my country's 10kV power systems are small current grounding systems, with the neutral point not grounded or grounded through an arc suppression coil. When a single-phase grounding fault occurs somewhere in the overhead line, since the fault current has no grounding loop or is compensated by the arc suppression coil, the grounding fault power frequency current is very weak. Relying on the traditional fault power frequency current cannot reliably judge the single-phase grounding fault, resulting in the distribution network relay protection equipment often misjudgment, wrong judgment, missed judgment and other phenomena for the judgment of single-phase grounding fault, seriously affecting the power supply reliability.

[0003] The current single-phase grounding fault analysis method of the distribution network uses transient methods to analyze single-phase grounding faults, such as the fifth harmonic method, the first half-wave method, the characteristic frequency band method, etc. These transient methods are effective under certain conditions and are easily affected by line distributed parameters, grounding fault properties (such as high-resistance grounding, low-resistance grounding, arc grounding, intermittent grounding, etc.), grounding fault location and sensor acquisition accuracy. The accuracy of actual application analysis is not high. Summary of the invention

[0004] The present application provides a method and system for determining a single-phase grounding fault in an overhead distribution line, which solves the problem of low accuracy of a traditional method for determining a single-phase grounding fault in a distribution line.

[0005] The first aspect of the present application provides a method for analyzing and judging a single-phase grounding fault of an overhead distribution line, comprising the following steps:

[0006] S1, collects the power frequency current signal and power frequency zero sequence voltage signal of the distribution line;

[0007] S2, determine whether the power frequency current mutation value exceeds the power frequency current mutation threshold, if it exceeds, go to step S3, otherwise go to step S4;

[0008] S3, judging whether the power frequency zero-sequence voltage value exceeds the power frequency zero-sequence voltage threshold value, if so, it is judged as a permanent single-phase grounding fault, otherwise it is judged as a power grid disturbance;

[0009] S4, collecting the transient current signal of the distribution line, and determining whether the transient current mutation value exceeds the transient current mutation threshold value, if not, returning to step S2, otherwise proceeding to step S5;

[0010] S5, judging whether the power frequency zero sequence voltage value exceeds the power frequency zero sequence voltage threshold value, if not, judging it as a power grid disturbance, otherwise proceeding to step S6;

[0011] S6, simultaneously calling three transient analysis algorithms, namely, the fifth harmonic method, the first half-wave method and the characteristic frequency band method, to make a judgment. When any of the transient analysis algorithms judges that it is a ground fault, the process proceeds to step S7, otherwise it returns to step S2;

[0012] S7, collecting the high-frequency transient traveling wave current signal of the distribution line, and determining whether the high-frequency transient traveling wave current value exceeds the high-frequency transient traveling wave current threshold value, if not, returning to step S2, otherwise entering step S8;

[0013] S8, judging whether the power frequency zero-sequence voltage value exceeds the power frequency zero-sequence voltage threshold value, if so, it is judged as a permanent single-phase grounding fault, otherwise it is judged as a transient single-phase grounding fault.

[0014] In the technical solution provided by the present application, different sensors are used to collect power frequency, transient and high-frequency transient traveling wave voltage and current characteristic signals within different frequency bands. For the voltage and current characteristic signals within different frequency bands, a variety of power frequency analysis methods, transient analysis methods and high-frequency transient traveling wave analysis methods are used to respectively analyze the single-phase grounding fault of the overhead distribution line. Finally, the analysis results given by different algorithms are integrated, and the most significant characteristic quantity is adaptively used to give the optimal solution, and finally a reliable single-phase grounding fault analysis result is given. The analysis result of this method can distinguish between instantaneous single-phase grounding faults, permanent single-phase grounding faults and power grid disturbances, effectively solving the problem of difficulty in analyzing single-phase grounding faults in overhead distribution lines, reducing the occurrence of misjudgment, wrong judgment and missed judgment of single-phase grounding faults, and improving the power supply reliability of overhead distribution networks.

[0015] The second aspect of the present application provides a system for analyzing and judging a single-phase grounding fault of an overhead distribution line, comprising:

[0016] The power frequency zero-sequence voltage sensor is used to collect the power frequency zero-sequence voltage signal of the distribution line;

[0017] Three-phase power frequency current sensor, used to collect three-phase power frequency current signals of distribution lines;

[0018] Three-phase transient current sensor, used to collect three-phase transient current signals of distribution lines;

[0019] Three-phase high-frequency transient traveling wave current sensor, used to collect three-phase high-frequency transient traveling wave current signals of distribution lines;

[0020] The fault analysis device is electrically connected to the power frequency zero-sequence voltage sensor, the three-phase power frequency current sensor, the three-phase transient current sensor, and the three-phase high-frequency transient traveling wave current sensor, respectively, and is used to judge whether a single-phase grounding fault occurs in the distribution line and the type of the fault based on the collected power frequency zero-sequence voltage signal, the three-phase power frequency current signal, the three-phase transient current signal, and the three-phase high-frequency transient traveling wave current signal.

[0021] Specifically, the fault analysis and judgment device includes a data acquisition unit, a signal processing and storage unit, a central processing unit and a communication unit connected in sequence, and the central processing unit is also connected to a display unit and an operation unit;

[0022] The data acquisition unit is electrically connected to the power frequency zero-sequence voltage sensor, the three-phase power frequency current sensor, the three-phase transient current sensor, and the three-phase high-frequency transient traveling wave current sensor, respectively, and is used to convert the collected signals and transmit them to the signal processing and storage unit;

[0023] The signal processing and storage unit is used to preprocess and store the converted signal and transmit the preprocessed data to the central processing unit;

[0024] The central processing unit analyzes the pre-processed data to determine whether a single-phase grounding fault occurs in the distribution line and the type of the fault;

[0025] The display unit is used to display fault information of the power distribution line;

[0026] The operating unit is used for human-computer interaction with the central processing unit;

[0027] The communication unit is used to communicate with the remote master station system, transmit the fault information of the distribution line to the master station system, and receive various instructions sent by the master station system.

[0028] Further, the data acquisition unit includes an overvoltage protection module, a signal conditioning module and an analog-to-digital conversion module connected in sequence;

[0029] The overvoltage protection module is connected to a power frequency zero-sequence voltage sensor, a three-phase power frequency current sensor, a three-phase transient current sensor or a three-phase high-frequency transient traveling wave current sensor, and is used to perform overvoltage protection on the data acquisition unit;

[0030] The signal conditioning module is used to convert the voltage signal that has passed the overvoltage protection into a current signal;

[0031] The analog-to-digital conversion module is used to convert the current signal conditioned by the signal conditioning module into a digital signal and transmit it to the signal processing and storage unit.

[0032] Furthermore, the signal processing and storage unit includes an FPGA chip and a static memory and a clock management module connected to the FPGA chip, the FPGA chip is used to preprocess the converted signal, the static memory is used to store the preprocessed data, and the clock management module is used to add precise time stamps to the preprocessed data.

[0033] Furthermore, the operating unit includes a plurality of operating buttons, and the plurality of operating buttons are connected to the central processing unit via an optocoupler isolator.

[0034] Furthermore, the display unit includes a display screen and a plurality of indicator lights, and the display screen and the plurality of indicator lights are respectively connected to the central processing unit via an optocoupler isolator.

[0035] Furthermore, the communication unit includes a remote communication interface and a USB debugging interface, the remote communication interface is used for remote communication connection with the main station system; the USB debugging interface is used to connect to an external computer to set threshold parameters or update programs for the central processing unit.

[0036] The above description is only an overview of the technical solution of the present application. In order to more clearly understand the technical means of the present application, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The drawings in this application are used to illustrate preferred embodiments, so that those skilled in the art can clearly understand various other advantages and benefits, and should not be considered as limitations of this application. In addition, the same reference numerals are used throughout the drawings to represent the same or similar components.

[0038] Figure 1 A schematic diagram of a flow chart of a method for analyzing and determining a single-phase grounding fault of an overhead distribution line in one embodiment of the present application;

[0039] Figure 2 This is a structural diagram of a single-phase grounding fault analysis system for overhead distribution lines in one embodiment of the present application;

[0040] Figure 3 Schematic diagram of the internal functional modules of the fault analysis device in one embodiment of the present application. DETAILED DESCRIPTION

[0041] The technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0042] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0043] In the description of the embodiments of the present application, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "multiple" is more than two (including two), unless otherwise clearly and specifically defined.

[0044] In the description of the embodiments of the present application, the term "and / or" is only a description of the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0045] In the description of the embodiments of the present application, the technical terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, which are only for the convenience of describing the embodiments of the present application and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the embodiments of the present application.

[0046] In the description of the embodiments of the present application, unless otherwise clearly specified and limited, technical terms such as "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, and it can be the internal connection of two elements or the interaction relationship between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments of the present application can be understood according to the specific circumstances.

[0047] See also Figure 1 The first aspect of the embodiment of the present application provides a method for analyzing and determining a single-phase grounding fault of an overhead distribution line, comprising the following steps:

[0048] S1, collects the power frequency current signal and power frequency zero sequence voltage signal of the distribution line;

[0049] S2, determine whether the power frequency current mutation value exceeds the power frequency current mutation threshold (the power frequency current mutation threshold can be flexibly set according to actual conditions, such as 100A). If it exceeds, go to step S3, otherwise go to step S4;

[0050] S3, judging whether the power frequency zero-sequence voltage value exceeds the power frequency zero-sequence voltage threshold (the power frequency zero-sequence voltage threshold can be flexibly set according to the actual situation); if it exceeds, it is judged as a permanent single-phase grounding fault, otherwise it is judged as a power grid disturbance;

[0051] S4, collecting the transient current signal of the distribution line, and judging whether the transient current mutation value exceeds the transient current mutation threshold (the transient current mutation threshold can be flexibly set according to the actual situation, such as 80A), if not, returning to step S2, otherwise entering step S5;

[0052] S5, judging whether the power frequency zero-sequence voltage value exceeds the power frequency zero-sequence voltage threshold (the power frequency zero-sequence voltage threshold can be flexibly set according to actual conditions); if not, it is judged as a power grid disturbance, otherwise, proceeding to step S6;

[0053] S6, simultaneously call the three transient analysis algorithms of the fifth harmonic method, the first half-wave method and the characteristic frequency band method to make a judgment (judgment of whether the fifth harmonic exceeds the threshold, whether the polarity of the first half-wave is consistent, and whether the current change within the characteristic frequency band exceeds the threshold. These three transient analysis algorithms belong to the line grounding fault analysis methods commonly used in the field of power distribution systems, and are not described in detail in this application). When any of the transient analysis algorithms determines that it is a grounding fault, proceed to step S7, otherwise return to step S2;

[0054] S7, collecting the high-frequency transient traveling wave current signal of the distribution line, and judging whether the high-frequency transient traveling wave current value exceeds the high-frequency transient traveling wave current threshold (the high-frequency transient traveling wave current threshold can be flexibly set according to the actual situation, such as 50A), if not, returning to step S2, otherwise entering step S8;

[0055] S8, determine whether the power frequency zero-sequence voltage value exceeds the power frequency zero-sequence voltage threshold (the power frequency zero-sequence voltage threshold can be flexibly set according to actual conditions). If it exceeds, it is determined to be a permanent single-phase grounding fault, otherwise it is determined to be a transient single-phase grounding fault.

[0056] In the technical solution provided by the present application, different sensors are used to collect power frequency, transient and high-frequency transient traveling wave voltage and current characteristic signals within different frequency bands. For the voltage and current characteristic signals within different frequency bands, a variety of power frequency analysis methods, transient analysis methods and high-frequency transient traveling wave analysis methods are used to respectively analyze the single-phase grounding fault of the overhead distribution line. Finally, the analysis results given by different algorithms are integrated, and the most significant characteristic quantity is adaptively used to give the optimal solution, and finally a reliable single-phase grounding fault analysis result is given. The analysis result of this method can distinguish between instantaneous single-phase grounding faults, permanent single-phase grounding faults and power grid disturbances, effectively solving the problem of difficulty in analyzing single-phase grounding faults in overhead distribution lines, reducing the occurrence of misjudgment, wrong judgment and missed judgment of single-phase grounding faults, and improving the power supply reliability of overhead distribution networks.

[0057] See also Figure 2 , Figure 3 The second aspect of the present application provides a single-phase grounding fault analysis system for overhead distribution lines, comprising:

[0058] The power frequency zero-sequence voltage sensor is used to collect the power frequency zero-sequence voltage signal of the distribution line;

[0059] Three-phase power frequency current sensor, used to collect three-phase power frequency current signals of distribution lines;

[0060] Three-phase transient current sensor, used to collect three-phase transient current signals of distribution lines;

[0061] Three-phase high-frequency transient traveling wave current sensor, used to collect three-phase high-frequency transient traveling wave current signals of distribution lines;

[0062] The fault analysis device is electrically connected to the power frequency zero-sequence voltage sensor, the three-phase power frequency current sensor, the three-phase transient current sensor, and the three-phase high-frequency transient traveling wave current sensor, respectively, and is used to judge whether a single-phase grounding fault occurs in the distribution line and the type of the fault based on the collected power frequency zero-sequence voltage signal, the three-phase power frequency current signal, the three-phase transient current signal, and the three-phase high-frequency transient traveling wave current signal.

[0063] Specifically, in this embodiment, the overhead distribution line is an insulated conductor or a bare conductor, the insulated conductor model is JKL, the bare conductor model is JL / G1A-210 / 10 steel core aluminum stranded wire, the rated voltage is 10kV, and it includes three-phase lines A, B, and C, which transmit 10kV electric energy of the same frequency but different phases respectively, and have good heat resistance, voltage resistance and wear resistance.

[0064] Specifically, in this embodiment, the industrial frequency zero-sequence voltage sensor adopts the ceramic capacitor voltage division principle to convert the 10kV voltage signal into a 2.16V low-voltage signal. The transformation ratio is: (10kV / √3) / (6.5V / 3), accuracy level: 3P level, partial discharge: ≤20(1.2Um / √3)pC. Its main function is to collect the zero-sequence voltage of the 10kV overhead line.

[0065] Specifically, in this embodiment, the power frequency zero-sequence voltage sensor and the fault analysis device are connected via a power frequency zero-sequence voltage transmission cable, which is used to transmit the voltage signal collected by the power frequency zero-sequence voltage sensor to the fault analysis device.

[0066] Specifically, in this embodiment, the three-phase power frequency current sensor is based on the principle of Rogowski coil and has a snap-on structure design. Three sensors are installed on the overhead line respectively to collect the A, B, and C three-phase power frequency current signals of the overhead line in real time, and transmit the collected power frequency current signals to the fault analysis device through the power frequency current transmission cable (coaxial shielded twisted pair). The sampling bandwidth is 2hz~1khz, the signal input range is 0A~1000A (peak-to-peak value), and the signal output range is 3~5V. The accuracy is 1%.

[0067] Specifically, in this embodiment, the three-phase transient current sensor: based on the principle of Rogowski coil, snap-on structure design, three sensors are installed on the overhead line respectively, real-time acquisition of A, B, C three-phase transient current signals of the overhead line, through the transient current transmission cable (coaxial shielded twisted pair) to transmit the acquired transient current signal to the fault analysis device, sampling bandwidth: 1khz ~ 12khz, signal input range: 0A ~ 800A (peak-to-peak value), signal output range: 3 ~ 5V. The accuracy is 1%.

[0068] Specifically, in this embodiment, the three-phase high-frequency transient traveling wave current sensor: based on the principle of Rogowski coil, snap-on structure design, three sensors are installed on the overhead line respectively, real-time acquisition of the A, B, C three-phase high-frequency transient traveling wave current signals of the overhead line, and the collected high-frequency transient traveling wave current signals are transmitted to the single-phase grounding fault analysis device through the high-frequency transient traveling wave current transmission coaxial cable (coaxial shielded twisted pair), sampling bandwidth: 12khz ~ 25Mhz, signal input range: 0A ~ 600A (peak-to-peak value), signal output range: 3 ~ 5V. The accuracy is 1%.

[0069] Specifically, in this embodiment, the fault analysis device includes a main body shell (using a stainless steel shell, protection level IP34), and the front of the main body shell is provided with:

[0070] Liquid crystal display screen, used as human-computer interaction interface, LCD display, including equipment information display, fault information display, line operation information display, etc.;

[0071] Operation buttons, including "up, down, left, right, cancel, confirm" operation buttons;

[0072] Indicator lights, LED display, including status indicator light, power indicator light, communication indicator light, fault indicator light, operation indicator light, self-test indicator light, etc.

[0073] USB debugging interface, connected to an external computer, to update the program of the fault analysis device or set threshold parameters, etc.;

[0074] SIM card slot, used to place wireless 4G communication card;

[0075] The back of the main body shell is provided with a wiring terminal, which is used as a wiring terminal for connecting the power frequency current sensor, the transient current sensor, and the high-frequency transient traveling wave current sensor to the fault analysis device through a transmission coaxial cable.

[0076] Please continue reading Figure 3 Specifically, the fault analysis device includes a data acquisition unit, a signal processing and storage unit, a central processing unit and a communication unit connected in sequence, and the central processing unit is also connected to a display unit and an operation unit;

[0077] The data acquisition unit is electrically connected to the power frequency zero-sequence voltage sensor, the three-phase power frequency current sensor, the three-phase transient current sensor, and the three-phase high-frequency transient traveling wave current sensor, respectively, and is used to convert the collected signals and transmit them to the signal processing and storage unit;

[0078] The signal processing and storage unit is used to preprocess and store the converted signal and transmit the preprocessed data to the central processing unit;

[0079] The central processing unit analyzes the pre-processed data to determine whether a single-phase grounding fault occurs in the distribution line and the type of the fault;

[0080] The display unit is used to display fault information of the power distribution line;

[0081] The operating unit is used for human-computer interaction with the central processing unit;

[0082] The communication unit is used to communicate with the remote master station system, transmit the fault information of the distribution line to the master station system, and receive various instructions sent by the master station system.

[0083] Please continue reading Figure 3 , further, the data acquisition unit includes an overvoltage protection module, a signal conditioning module and an analog-to-digital conversion module connected in sequence;

[0084] The overvoltage protection module is connected to the power frequency zero-sequence voltage sensor, the three-phase power frequency current sensor, the three-phase transient current sensor or the three-phase high-frequency transient traveling wave current sensor, and is used to perform overvoltage protection on the data acquisition unit; the overvoltage protection module uses a 12V / 5A voltage regulator, and the voltage regulation range of the overvoltage protection module is 12V. The voltage regulation part is composed of a 7805 three-terminal voltage regulator and a current expansion transistor, and the potential of the adjustment end is raised by a voltage regulator diode and a light-emitting diode in series. The overvoltage protection uses a thyristor short-circuit power supply to force the fuse to blow quickly to protect the safety of the subsequent circuit, and the blowing time is 1 to 3 microseconds;

[0085] The signal conditioning module is used to convert the ±3-5V voltage signal that has been overvoltage protected into a ±2-3mA current signal;

[0086] The analog-to-digital conversion module is used to convert the current signal conditioned by the signal conditioning module into a digital signal and transmit it to the signal processing and storage unit. The analog-to-digital conversion module model used is AD9252, which has 8-channel high-speed A / D and 8-channel low-speed A / D, 14-bit, 50MSPS and 2k analog-to-digital converter (ADC). The module is powered by a single 1.8V power supply and has a built-in on-chip sampling and holding circuit. It has the advantages of low price, low power consumption, small size and ease of use. It uses a 64-pin LFCSP package that complies with the RoHS standard and is rated for an industrial temperature range of -40℃ to +85℃.

[0087] The A, B, C three-phase power frequency current sensor and power frequency zero sequence voltage sensor send the collected power frequency current and voltage signals to the low-speed analog-to-digital conversion A / D through the overvoltage protection module and the signal conditioning module. The low-speed analog-to-digital conversion A / D converts the power frequency current and voltage signals into digital signals and sends them to the signal processing and storage unit. The A, B, C three-phase transient current sensor sends the collected transient current signal to the high-speed analog-to-digital conversion A / D through the overvoltage protection module and the signal conditioning module. The high-speed analog-to-digital conversion A / D converts the transient current signal into a digital signal and sends it to the signal processing and storage unit. The A, B, C three-phase high-frequency transient traveling wave current sensor sends the collected high-frequency transient traveling wave current signal to the high-speed analog-to-digital conversion A / D through the overvoltage protection module and the signal conditioning module. The high-speed analog-to-digital conversion A / D converts the high-frequency transient traveling wave current into a digital signal and sends it to the signal processing and storage unit.

[0088] Please continue reading Figure 3 Furthermore, the signal processing and storage unit includes an FPGA chip and a static memory and a clock management module connected to the FPGA chip, the FPGA chip is used to preprocess the converted signal, the static memory is used to store the preprocessed data, and the clock management module is used to add an accurate time stamp to the preprocessed data.

[0089] The signal processing and storage unit mainly performs data preprocessing and pre-calculation. It has a 16-channel digital sampling interface inside. The FPGA chip performs data preprocessing and logic pre-calculation on the received digital signal. The FPGA chip model used is Xilinx's XC7Z020, which consists of 6 parts: programmable input and output unit, programmable logic unit, clock management, embedded block RAM, embedded bottom functional unit and embedded dedicated hardware module. The FPGA chip can be used repeatedly without a special programmer. It has the advantages of radiation resistance, high and low temperature resistance, low power consumption and high speed. It integrates commonly used RAM, clock management and DSP functions. Synchronous clock encoding inside the FPGA chip: The high-precision clock generates a time signal with an accuracy of ns level and sends it to the FPGA chip for accurate calibration of the trigger moment, and allows the recorded and stored waveforms to have accurate time stamps. The time signal input is 1PPS mode. The synchronous signal receiving circuit directly receives the 1PPS pulse from the GPS synchronous clock. SRAM1 to SRAM4 inside the FPGA chip are static random access memories, which cache the collected power frequency, transient and high-frequency traveling wave voltage and current signals of the overhead distribution lines.

[0090] Please continue reading Figure 3 Furthermore, the central processing unit is connected to the display unit, the operation unit and the communication unit at the same time. The MCU model used is the STM32f407VG DSC chip, which has many internal resources, large storage capacity and low price. At the same time, the ARM chip has a wireless communication interface and an Ethernet communication interface, and can also generate PWM waves, and can quickly process and output analog quantities, picture information, control signals, alarm signals, etc.

[0091] Please continue reading Figure 3 Furthermore, the operation unit includes a plurality of operation buttons, including "up, down, left, right, cancel, confirm" operation buttons. The plurality of operation buttons are connected to the central processing unit via an optocoupler isolator. The optocoupler isolator model used is TLP112, which ensures the stability and anti-interference of the input signal.

[0092] Please continue reading Figure 3 Furthermore, the display unit includes a display screen and a plurality of indicator lights, and the display screen and the plurality of indicator lights are respectively connected to the central processing unit through an optocoupler isolator. The liquid crystal display screen is a human-machine interactive interface, which displays device information, fault information, line operation information, etc. in real time. The indicator lights include a status indicator light, a power indicator light, a communication indicator light, a fault indicator light, an operation indicator light, a self-test indicator light, etc. The optocoupler isolator model used is TLP112, which ensures the stability and anti-interference of the input and output state quantities and analog signals.

[0093] Please continue reading Figure 3Furthermore, the communication unit includes a remote communication interface and a USB debugging interface. The remote communication interface is used for remote communication connection with the master station system; the USB debugging interface is used to connect to an external computer to set threshold parameters or update programs for the central processing unit. The remote communication interface is an RJ45 interface, which is connected to the remote master station system, sends information to the remote master station system, and receives various instructions from the master station system. The USB debugging interface is connected to an external computer to update the program or set threshold parameters for the fault analysis device. The RS232 and RS485 interfaces are local communication connection interfaces with other intelligent devices.

[0094] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, a person of ordinary skill in the art should understand that the technical solutions described in the aforementioned embodiments can still be modified, or some or all of the technical features therein can be replaced by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application, and they should all be included in the scope of the claims and specification of the present application. In particular, as long as there is no contradiction or conflict, the various technical features mentioned in the embodiments can be combined in any way. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions that fall within the scope of the claims.

Claims

1. A method for determining a single-phase grounding fault in an overhead distribution line, characterized in that: The following steps are involved: S1, collects the power frequency current signal and power frequency zero sequence voltage signal of the distribution line; S2, determine whether the power frequency current mutation value exceeds the power frequency current mutation threshold, if it exceeds, go to step S3, otherwise go to step S4; S3, judging whether the power frequency zero-sequence voltage value exceeds the first power frequency zero-sequence voltage threshold value, if so, judging it as a permanent single-phase grounding fault, otherwise judging it as a power grid disturbance; S4, collecting the transient current signal of the distribution line, and determining whether the transient current mutation value exceeds the transient current mutation threshold value, if not, returning to step S2, otherwise proceeding to step S5; S5, judging whether the power frequency zero-sequence voltage value exceeds the second power frequency zero-sequence voltage threshold value, if not, judging it as a power grid disturbance, otherwise proceeding to step S6; S6, simultaneously calling three transient analysis algorithms, namely, the fifth harmonic method, the first half-wave method and the characteristic frequency band method, to make a judgment. When any of the transient analysis algorithms judges that it is a ground fault, the process proceeds to step S7, otherwise it returns to step S2; S7, collecting the high-frequency transient traveling wave current signal of the distribution line, and determining whether the high-frequency transient traveling wave current value exceeds the high-frequency transient traveling wave current threshold value, if not, returning to step S2, otherwise entering step S8; S8, judging whether the power frequency zero-sequence voltage value exceeds the third power frequency zero-sequence voltage threshold value, if so, judging it as a permanent single-phase grounding fault, otherwise judging it as a transient single-phase grounding fault.

2. A system for determining a single-phase grounding fault of an overhead distribution line, based on a method for determining a single-phase grounding fault of an overhead distribution line according to claim 1, characterized in that: include: The power frequency zero-sequence voltage sensor is used to collect the power frequency zero-sequence voltage signal of the distribution line; Three-phase power frequency current sensor, used to collect three-phase power frequency current signals of distribution lines; Three-phase transient current sensor, used to collect three-phase transient current signals of distribution lines; Three-phase high-frequency transient traveling wave current sensor, used to collect three-phase high-frequency transient traveling wave current signals of distribution lines; The fault analysis device is electrically connected to the power frequency zero-sequence voltage sensor, the three-phase power frequency current sensor, the three-phase transient current sensor, and the three-phase high-frequency transient traveling wave current sensor, respectively, and is used to judge whether a single-phase grounding fault occurs in the distribution line and the type of the fault based on the collected power frequency zero-sequence voltage signal, the three-phase power frequency current signal, the three-phase transient current signal, and the three-phase high-frequency transient traveling wave current signal.

3. The single-phase grounding fault analysis and judgment system for overhead power distribution lines according to claim 2 is characterized in that: The fault analysis and judgment device comprises a data acquisition unit, a signal processing and storage unit, a central processing unit and a communication unit connected in sequence, and the central processing unit is also connected to a display unit and an operation unit; The data acquisition unit is electrically connected to the power frequency zero-sequence voltage sensor, the three-phase power frequency current sensor, the three-phase transient current sensor, and the three-phase high-frequency transient traveling wave current sensor, respectively, and is used to convert the collected signals and transmit them to the signal processing and storage unit; The signal processing and storage unit is used to preprocess and store the converted signal and transmit the preprocessed data to the central processing unit; The central processing unit analyzes the pre-processed data to determine whether a single-phase grounding fault occurs in the distribution line and the type of the fault; The display unit is used to display fault information of the power distribution line; The operating unit is used for human-computer interaction with the central processing unit; The communication unit is used to communicate with the remote master station system, transmit the fault information of the distribution line to the master station system, and receive various instructions sent by the master station system.

4. The single-phase grounding fault analysis and judgment system for overhead power distribution lines according to claim 3 is characterized in that: The data acquisition unit includes an overvoltage protection module, a signal conditioning module and an analog-to-digital conversion module which are connected in sequence; The overvoltage protection module is connected to a power frequency zero-sequence voltage sensor, a three-phase power frequency current sensor, a three-phase transient current sensor or a three-phase high-frequency transient traveling wave current sensor, and is used to perform overvoltage protection on the data acquisition unit; The signal conditioning module is used to convert the voltage signal that has passed the overvoltage protection into a current signal; The analog-to-digital conversion module is used to convert the current signal conditioned by the signal conditioning module into a digital signal and transmit it to the signal processing and storage unit.

5. The single-phase grounding fault analysis and judgment system for overhead power distribution lines according to claim 3 is characterized in that: The signal processing and storage unit includes an FPGA chip and a static memory and a clock management module connected to the FPGA chip. The FPGA chip is used to preprocess the converted signal, the static memory is used to store the preprocessed data, and the clock management module is used to add an accurate time stamp to the preprocessed data.

6. The overhead distribution line single-phase grounding fault analysis system according to claim 3 is characterized in that: The operating unit includes a plurality of operating buttons, and the plurality of operating buttons are connected to the central processing unit via an optical coupling isolator.

7. The overhead distribution line single-phase grounding fault analysis and judgment system according to claim 3 is characterized in that: The display unit comprises a display screen and a plurality of indicator lights, and the display screen and the plurality of indicator lights are respectively connected to the central processing unit via optical coupling isolators.

8. The overhead distribution line single-phase grounding fault analysis system according to claim 3 is characterized in that: The communication unit includes a remote communication interface and a USB debugging interface. The remote communication interface is used for remote communication connection with the main station system; the USB debugging interface is used for connecting to an external computer to set threshold parameters or update programs for the central processing unit.

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