Single-phase grounding fault indication method and system in distribution network three-core cable small-current grounding system

Abstract

The invention belongs to the technical field of distribution network detection, and particularly relates to a single-phase grounding fault indication method and system in a distribution network three-core cable small-current grounding system, and the system comprises an electrical collection module, a signal processing module, a fault point parameter calculation module, a fault point parameter analysis module, a display alarm module, a communication module and a power module. According to the invention, through the electrical acquisition module installed on the grounding copper braid, the electrical quantity on the grounding copper braid can be acquired in real time, and through the processing of the signal processing module and the fault point parameter calculation module, the related parameters of the fault point can be rapidly and accurately calculated. Therefore, the real-time performance of fault positioning is improved, the positioning accuracy is remarkably improved, and powerful support is provided for rapid fault processing.

Description

Technical Field

[0001] The invention belongs to the technical field of distribution network detection, and in particular relates to a single-phase grounding fault indication method and system in a three-core cable small current grounding system of a distribution network. Background Art

[0002] In the power system, the three-core distribution cable, as a key power transmission medium, has become the preferred material in the construction and transformation of urban and rural power grids due to its excellent insulation performance and high transmission efficiency. These cables can not only withstand the impact of high voltage and high current, but also maintain stable power transmission under harsh environmental conditions, thus ensuring the stable operation of the power grid.

[0003] However, with the continuous expansion of the scale of the power grid and the continuous accumulation of operating time, the pressure and load on the cable lines are also increasing. This pressure comes not only from the growth of power load, but also from the combined effect of multiple complex factors such as environmental factors and equipment aging. Therefore, the incidence of single-phase grounding faults in cable lines has also shown an increasing trend year by year.

[0004] Once a single-phase grounding fault occurs, it will pose a great threat to the safe and stable operation of the power grid. It may cause power outages and affect the normal power consumption of users; more seriously, it may also cause safety accidents such as fires, posing a serious threat to people's lives and property. Therefore, quickly and accurately locating and handling single-phase grounding faults is of vital importance to ensure the safe and stable operation of the power grid.

[0005] Traditionally, the location of single-phase grounding faults in three-core cables in distribution networks mainly relies on manual inspections and traditional measuring instruments, such as megohmmeters and multimeters. Although these methods can locate the fault point to a certain extent, they are time-consuming, labor-intensive, and have limited positioning accuracy. They are no longer able to meet the needs of modern power grids for rapid response and accurate positioning of faults. With the continuous development of smart grid technology, higher requirements have been placed on the real-time and accuracy of fault positioning, and traditional fault positioning methods are obviously no longer able to meet the needs. Summary of the invention

[0006] In view of the above-mentioned deficiencies in the prior art, the present invention provides a single-phase grounding fault indication method and system in a three-core cable low-current grounding system of a distribution network to solve the above-mentioned technical problems.

[0007] In a first aspect, the present invention provides a single-phase grounding fault indication method in a three-core cable low-current grounding system of a distribution network, comprising: The electrical quantity on the grounding copper braid is collected by an electrical collection module installed on the grounding copper braid; The electrical acquisition module transmits the collected electrical quantities to the signal processing module, and the electrical quantities are processed by the signal processing module and transmitted to the fault point parameter calculation module; The fault point parameter calculation module calculates the parameters of the electrical quantity after signal processing, and transmits the calculated parameters to the fault point parameter analysis module. The calculated parameters include the fault point electrical quantity, the fault location voltage and the fault traveling wave distance; The fault point parameter analysis module performs fault point location analysis based on the received calculation parameters, stores the analysis results and the collected electrical quantities, and transmits the analysis results to the display alarm module; The display alarm module displays the analysis results and issues a fault alarm in combination with the fault point location information on the grounding copper braid in the analysis results.

[0008] A further improvement of the technical solution is that the electrical quantity on the grounding copper braid is collected by an electrical collection module installed on the grounding copper braid, and the method specifically includes: collecting the positive and negative zero-sequence current and voltage at the electrical quantity collection point on the grounding copper braid respectively through a current transformer and a voltage transformer installed on the grounding copper braid.

[0009] A further improvement of the technical solution is that the positive and negative zero-sequence currents and positive and negative zero-sequence voltages at the electrical quantity collection points on the grounding copper braid detected by the current transformer and the voltage transformer respectively are amplified and filtered.

[0010] A further improvement of the technical solution is to calculate the parameters of the electrical quantity after signal processing, and the method specifically includes: The positive and negative zero-sequence current values ​​and positive and negative zero-sequence voltage values ​​at the electrical quantity collection point after amplification and filtering are input into the pre-established line parameter model, and the positive and negative zero-sequence current values ​​and positive and negative zero-sequence voltage values ​​at the fault position on the grounding copper braid are calculated; Calculate the voltage at the fault location based on the positive and negative zero-sequence current values ​​and positive and negative zero-sequence voltage values ​​at the electrical quantity collection point after amplification and filtering; The fault traveling wave distance is calculated based on the detected traveling wave characteristics on the grounding copper braid.

[0011] A further improvement of the technical solution is that the formula for calculating the positive and negative zero-sequence current values ​​at the fault position on the grounding copper braid is: ; The formula for calculating the positive and negative zero-sequence voltage values ​​at the fault location on the grounding copper braid is: ; in, is the positive and negative zero-sequence current value at the fault position on the grounding copper braid, To amplify the positive and negative zero-sequence current values ​​at the electrical quantity collection point after filtering, To amplify the positive and negative zero-sequence voltage values ​​at the electrical quantity collection point after filtering, is the constant value during the positive and negative zero sequence transmission process in the grounding copper braid, is the distance between the fault location and the electrical collection point, is the impedance of the current traveling wave of the grounding copper braid during the positive and negative zero sequence transmission process, It is the positive and negative zero-sequence voltage value at the fault location on the grounding copper braid.

[0012] A further improvement of the technical solution is to calculate the fault traveling wave distance based on the detected traveling wave characteristics on the grounding copper braid, and the specific calculation formula is: ; in, is the fault traveling wave distance, is the speed of the grounded copper braid during the traveling wave transmission process, is the time difference between the initial wave and the reflected wave arriving at the electrical quantity collection point, is the time when the initial wave of the traveling wave reaches the electrical quantity collection point when a fault occurs, It is the time it takes for the reflected wave to reach the electrical quantity collection point when a fault occurs.

[0013] A further improvement of the technical solution is that the fault point parameter analysis module performs fault point location analysis according to the received calculation parameters, and the specific method is: performing fault point location analysis by combining the calculated fault traveling wave distance with the proportional factor.

[0014] In a second aspect, the present invention provides a single-phase grounding fault indication system in a three-core cable low-current grounding system of a distribution network, comprising: The electrical data collection module is installed on the grounding copper braid and is used to collect the electrical quantities on the grounding copper braid; A signal processing module is used to perform signal processing on the electrical quantities on the grounding copper braid collected by the electrical collection module; The fault point parameter calculation module is used to calculate the parameters of the electrical quantity after signal processing. The calculation parameters include the electrical quantity of the fault point, the voltage at the fault location and the fault traveling wave distance. The fault point parameter analysis module is used to perform fault point location analysis based on the received calculation parameters and store the analysis results and the collected electrical quantities; Display alarm module, used to display the analysis results and issue fault alarm in combination with the fault point location information on the grounding copper braid in the analysis results; Communication module, used to realize signal transmission between systems; The power module is used to supply power to the entire system.

[0015] A further improvement of the technical solution is that the signal processing module includes an amplifying circuit and a filtering circuit; The amplification circuit includes an amplifier U1, a resistor R1, a resistor R2, a resistor R3, a resistor R4, an amplifier U2 and a diode D1. The non-inverting input terminal of the amplifier U1 is connected to the output terminal of the electrical acquisition module and the first end of the resistor R1, the second end of the resistor R1 is grounded, the inverting input terminal of the amplifier U1 is grounded through the resistor R2, the output terminal of the amplifier U1 is connected to the first end of the resistor R3 and the first end of the resistor R4, the second end of the resistor R3 is connected to the inverting input terminal of the amplifier U1, the second end of the resistor R4 is connected to the non-inverting input terminal of the amplifier U2, the output terminal of the amplifier U2 is connected to the inverting input terminal of the amplifier U2 and the input terminal of the filter circuit, the power supply terminal of the amplifier U1 and the power supply terminal of the amplifier U2 are both connected to the cathode of the diode D1, and the anode of the diode D1 is connected to a 5V power supply.

[0016] A further improvement of the technical solution is that the filtering circuit includes an inductor L1, a capacitor C1, an inductor L2 and a capacitor C2, the first end of the inductor L1 is connected to the output end of the amplifier U2, the second end of the inductor L1 is connected to the input end of the fault point parameter calculation module, the first end of the inductor L2 and the first end of the capacitor C2 through the capacitor C1, and the second end of the inductor L2 and the second end of the capacitor C2 are both grounded.

[0017] The beneficial effects of the present invention are: Improved real-time performance and accuracy: The electrical data acquisition module installed on the grounding braid can collect the electrical data on the grounding braid in real time, and after being processed by the signal processing module and the fault point parameter calculation module, the relevant parameters of the fault point can be quickly and accurately calculated. This not only improves the real-time performance of fault location, but also significantly improves the accuracy of location, providing strong support for rapid fault handling.

[0018] Intelligence and automation: This method realizes the intelligence and automation of fault location, without manual inspection and manual measurement, which greatly reduces the workload of operation and maintenance personnel. At the same time, through the display alarm module, the analysis results and fault location information can be intuitively displayed, which is convenient for operation and maintenance personnel to quickly respond to and handle faults.

[0019] High-precision positioning: By accurately calculating the positive and negative zero-sequence current and voltage values ​​at the fault location, as well as the fault traveling wave distance, this method can achieve high-precision fault point positioning. This helps operation and maintenance personnel to quickly and accurately find the fault point, reduce troubleshooting time, and improve the operation efficiency of the power grid.

[0020] In addition, the invention has a reliable design principle, a simple structure and a very broad application prospect. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0022] Figure 1 The present invention is a schematic flow chart of a method according to an embodiment of the present invention.

[0023] Figure 2 A schematic block diagram of a system according to an embodiment of the present invention.

[0024] Figure 3 This is the schematic diagram of the amplifier circuit.

[0025] Figure 4 This is the schematic diagram of the filter circuit.

[0026] 210 is an electrical acquisition module, 220 is a signal processing module, 230 is a fault point parameter calculation module, 240 is a fault point parameter analysis module, 250 is a display alarm module, 260 is a communication module, and 270 is a power supply module. DETAILED DESCRIPTION

[0027] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only 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 should fall within the scope of protection of the present invention.

[0028] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0029] Figure 1 The present invention provides a schematic flow chart of a single-phase grounding fault indication method in a three-core cable low-current grounding system of a distribution network. Figure 1 The execution entity may be a single-phase grounding fault indication system in a three-core cable low-current grounding system of a distribution network.

[0030] like Figure 1 As shown, the method includes: Step 110, collecting electrical quantities on the grounding copper braid by means of an electrical collection module installed on the grounding copper braid; Step 120, the electrical acquisition module transmits the collected electrical quantities to the signal processing module, and the electrical quantities are processed by the signal processing module and then transmitted to the fault point parameter calculation module; Step 130, the fault point parameter calculation module performs parameter calculation on the electrical quantity after signal processing, and transmits the calculated parameters to the fault point parameter analysis module, the calculated parameters including the fault point electrical quantity, the fault position voltage and the fault traveling wave distance; Step 140, the fault point parameter analysis module performs fault point location analysis according to the received calculation parameters, stores the analysis results and the collected electrical quantities, and transmits the analysis results to the display alarm module; Step 150: the display alarm module displays the analysis result, and generates a fault alarm in combination with the fault point location information on the grounding copper braid in the analysis result.

[0031] To facilitate understanding of the present invention, the following is a further description of the single-phase grounding fault indication method in a distribution network three-core cable low-current grounding system provided by the present invention based on the principle of the single-phase grounding fault indication method in the distribution network three-core cable low-current grounding system of the present invention, combined with the process of indicating the single-phase grounding fault in the distribution network three-core cable low-current grounding system in the embodiment.

[0032] Specifically, the electrical quantity on the grounding copper braid is collected by an electrical collection module installed on the grounding copper braid, and the method specifically includes: collecting the positive and negative zero-sequence current and voltage at the electrical quantity collection point on the grounding copper braid respectively through the current transformer and voltage transformer installed on the grounding copper braid.

[0033] In addition, the positive and negative zero-sequence currents and positive and negative zero-sequence voltages at the electrical quantity collection points on the grounding copper braid detected by the current transformer and the voltage transformer are amplified and filtered.

[0034] In addition, the parameters of the electrical quantities after signal processing are calculated, and the method specifically includes: S131, inputting the positive and negative zero-sequence current values ​​and the positive and negative zero-sequence voltage values ​​at the electrical quantity collection point after amplification and filtering into a pre-established line parameter model, and calculating the positive and negative zero-sequence current values ​​and the positive and negative zero-sequence voltage values ​​at the fault position on the grounding copper braid; S132, calculating the voltage at the fault location according to the positive and negative zero-sequence current values ​​and the positive and negative zero-sequence voltage values ​​at the electrical quantity collection point after amplification and filtering; S133. Calculate the fault traveling wave distance based on the detected traveling wave characteristics on the grounding copper braid.

[0035] Specifically, the formula for calculating the positive and negative zero-sequence current values ​​at the fault location on the grounding copper braid is: ; The formula for calculating the positive and negative zero-sequence voltage values ​​at the fault location on the grounding copper braid is: ; in, is the positive and negative zero-sequence current value at the fault position on the grounding copper braid, To amplify the positive and negative zero-sequence current values ​​at the electrical quantity collection point after filtering, To amplify the positive and negative zero-sequence voltage values ​​at the electrical quantity collection point after filtering, is the constant value during the positive and negative zero sequence transmission process in the grounding copper braid, is the distance between the fault location and the electrical collection point, is the impedance of the current traveling wave of the grounding copper braid during the positive and negative zero sequence transmission process, It is the positive and negative zero-sequence voltage value at the fault location on the grounding copper braid.

[0036] In addition, the fault traveling wave distance is calculated based on the traveling wave characteristics detected on the grounding copper braid. The specific calculation formula is: ; in, is the fault traveling wave distance, is the speed of the grounded copper braid during the traveling wave transmission process, is the time difference between the initial wave and the reflected wave arriving at the electrical quantity collection point, is the time when the initial wave of the traveling wave reaches the electrical quantity collection point when a fault occurs, It is the time it takes for the reflected wave to reach the electrical quantity collection point when a fault occurs.

[0037] Furthermore, the fault point parameter analysis module performs fault point location analysis based on the received calculation parameters. Specifically, the fault point location analysis is performed by combining the calculated fault traveling wave distance with the proportional factor. The actual fault location is: ;in, is the scale factor.

[0038] like Figure 2 As shown, the present invention provides a single-phase grounding fault indication system in a three-core cable low-current grounding system of a distribution network, including an electrical acquisition module 210, a signal processing module 220, a fault point parameter calculation module 230, a fault point parameter analysis module 240, a display alarm module 250, a communication module 260 and a power supply module 270.

[0039] Among them, the electrical acquisition module is installed on the grounding copper braid and is used to collect electrical quantities on the grounding copper braid; the signal processing module is used to perform signal processing on the electrical quantities on the grounding copper braid collected by the electrical acquisition module; the fault point parameter calculation module is used to perform parameter calculation on the electrical quantities after signal processing, and the calculation parameters include the electrical quantities at the fault point, the voltage at the fault location and the fault traveling wave distance; the fault point parameter analysis module is used to perform fault point location analysis based on the received calculation parameters, and store the analysis results and the collected electrical quantities; the display alarm module is used to display the analysis results, and perform fault alarm in combination with the fault point location information on the grounding copper braid in the analysis results; the communication module is used to realize signal transmission between systems; the power supply module is used to power the entire system.

[0040] like Figure 3 As shown, the signal processing module includes an amplifying circuit and a filtering circuit; wherein the amplifying circuit includes an amplifier U1, a resistor R1, a resistor R2, a resistor R3, a resistor R4, an amplifier U2 and a diode D1, the in-phase input terminal of the amplifier U1 is connected to the output terminal of the electrical acquisition module and the first terminal of the resistor R1, the second terminal of the resistor R1 is grounded, the inverting input terminal of the amplifier U1 is grounded through the resistor R2, the output terminal of the amplifier U1 is connected to the first terminal of the resistor R3 and the first terminal of the resistor R4, the second terminal of the resistor R3 is connected to the inverting input terminal of the amplifier U1, the second terminal of the resistor R4 is connected to the in-phase input terminal of the amplifier U2, the output terminal of the amplifier U2 is connected to the inverting input terminal of the amplifier U2 and the input terminal of the filtering circuit, the power supply terminal of the amplifier U1 and the power supply terminal of the amplifier U2 are both connected to the cathode of the diode D1, and the anode of the diode D1 is connected to a 5V power supply.

[0041] like Figure 4 As shown, the filtering circuit includes an inductor L1, a capacitor C1, an inductor L2 and a capacitor C2. The first end of the inductor L1 is connected to the output end of the amplifier U2, the second end of the inductor L1 is connected to the input end of the fault point parameter calculation module, the first end of the inductor L2 and the first end of the capacitor C2 through the capacitor C1, and the second end of the inductor L2 and the second end of the capacitor C2 are both grounded.

[0042] Although the present invention has been described in detail with reference to the accompanying drawings and in combination with the preferred embodiments, the present invention is not limited thereto. Without departing from the spirit and essence of the present invention, a person of ordinary skill in the art may make various equivalent modifications or substitutions to the embodiments of the present invention, and these modifications or substitutions shall be within the scope of the present invention. Any person of ordinary skill in the art may easily think of changes or substitutions within the technical scope disclosed by the present invention, and these shall be within the scope of protection of the present invention.

Claims

1. A single-phase grounding fault indication method in a three-core cable low-current grounding system of a distribution network, characterized in that: include: The electrical quantity on the grounding copper braid is collected by an electrical collection module installed on the grounding copper braid; The electrical acquisition module transmits the collected electrical quantities to the signal processing module, and the electrical quantities are processed by the signal processing module and transmitted to the fault point parameter calculation module; The fault point parameter calculation module calculates the parameters of the electrical quantity after signal processing, and transmits the calculated parameters to the fault point parameter analysis module. The calculated parameters include the fault point electrical quantity, the fault location voltage and the fault traveling wave distance; The fault point parameter analysis module performs fault point location analysis based on the received calculation parameters, stores the analysis results and the collected electrical quantities, and transmits the analysis results to the display alarm module; The display alarm module displays the analysis results and issues a fault alarm in combination with the fault point location information on the grounding copper braid in the analysis results.

2. The single-phase grounding fault indication method in the three-core cable low-current grounding system of the distribution network according to claim 1 is characterized in that: The electrical quantity on the grounding copper braid is collected by an electrical collection module installed on the grounding copper braid. The method specifically includes: collecting the positive and negative zero-sequence current and voltage at the electrical quantity collection point on the grounding copper braid respectively through a current transformer and a voltage transformer installed on the grounding copper braid.

3. The single-phase grounding fault indication method in the three-core cable low-current grounding system of the distribution network according to claim 2 is characterized in that: The positive and negative zero-sequence currents and positive and negative zero-sequence voltages at the electrical quantity collection points on the grounding copper braid detected by the current transformer and the voltage transformer are amplified and filtered.

4. The single-phase grounding fault indication method in the three-core cable low-current grounding system of the distribution network according to claim 3 is characterized in that: The method for calculating the parameters of the electrical quantity after signal processing includes: The positive and negative zero-sequence current values ​​and positive and negative zero-sequence voltage values ​​at the electrical quantity collection point after amplification and filtering are input into the pre-established line parameter model, and the positive and negative zero-sequence current values ​​and positive and negative zero-sequence voltage values ​​at the fault position on the grounding copper braid are calculated; Calculate the voltage at the fault location based on the positive and negative zero-sequence current values ​​and positive and negative zero-sequence voltage values ​​at the electrical quantity collection point after amplification and filtering; The fault traveling wave distance is calculated based on the detected traveling wave characteristics on the grounding copper braid.

5. The single-phase grounding fault indication method in the three-core cable low-current grounding system of the distribution network according to claim 4 is characterized in that: The formula for calculating the positive and negative zero-sequence current values ​​at the fault location on the grounding copper braid is: ； The formula for calculating the positive and negative zero-sequence voltage values ​​at the fault location on the grounding copper braid is: ； in, is the positive and negative zero-sequence current value at the fault position on the grounding copper braid, To amplify the positive and negative zero-sequence current values ​​at the electrical quantity collection point after filtering, To amplify the positive and negative zero-sequence voltage values ​​at the electrical quantity collection point after filtering, is the constant value during the positive and negative zero sequence transmission process in the grounding copper braid, is the distance between the fault location and the electrical collection point, is the impedance of the current traveling wave of the grounding copper braid during the positive and negative zero sequence transmission process, It is the positive and negative zero-sequence voltage value at the fault location on the grounding copper braid.

6. The single-phase grounding fault indication method in the three-core cable low-current grounding system of the distribution network according to claim 4 is characterized in that: The fault traveling wave distance is calculated based on the detected traveling wave characteristics on the grounding copper braid. The calculation formula is as follows: ； in, is the fault traveling wave distance, is the speed of the grounded copper braid during the traveling wave transmission process, is the time difference between the initial wave and the reflected wave arriving at the electrical quantity collection point, is the time when the initial wave of the traveling wave reaches the electrical quantity collection point when a fault occurs, It is the time it takes for the reflected wave to reach the electrical quantity collection point when a fault occurs.

7. The single-phase grounding fault indication method in the three-core cable low-current grounding system of the distribution network according to claim 6 is characterized in that: The fault point parameter analysis module performs fault point location analysis according to the received calculation parameters, and the specific method is: performing fault point location analysis by combining the calculated fault traveling wave distance with the proportional factor.

8. A single-phase grounding fault indication system in a three-core cable low-current grounding system of a distribution network, characterized in that: include: The electrical data collection module is installed on the grounding copper braid and is used to collect the electrical quantities on the grounding copper braid; A signal processing module is used to perform signal processing on the electrical quantities on the grounding copper braid collected by the electrical collection module; The fault point parameter calculation module is used to calculate the parameters of the electrical quantity after signal processing. The calculation parameters include the electrical quantity of the fault point, the voltage at the fault location and the fault traveling wave distance. The fault point parameter analysis module is used to perform fault point location analysis based on the received calculation parameters and store the analysis results and the collected electrical quantities; Display alarm module, used to display the analysis results and issue fault alarm in combination with the fault point location information on the grounding copper braid in the analysis results; Communication module, used to realize signal transmission between systems; The power module is used to supply power to the entire system.

9. A single-phase grounding fault indication system in a three-core cable low-current grounding system of a distribution network according to claim 8, characterized in that: The signal processing module includes an amplifying circuit and a filtering circuit; The amplification circuit includes an amplifier U1, a resistor R1, a resistor R2, a resistor R3, a resistor R4, an amplifier U2 and a diode D1. The non-inverting input terminal of the amplifier U1 is connected to the output terminal of the electrical acquisition module and the first end of the resistor R1, the second end of the resistor R1 is grounded, the inverting input terminal of the amplifier U1 is grounded through the resistor R2, the output terminal of the amplifier U1 is connected to the first end of the resistor R3 and the first end of the resistor R4, the second end of the resistor R3 is connected to the inverting input terminal of the amplifier U1, the second end of the resistor R4 is connected to the non-inverting input terminal of the amplifier U2, the output terminal of the amplifier U2 is connected to the inverting input terminal of the amplifier U2 and the input terminal of the filter circuit, the power supply terminal of the amplifier U1 and the power supply terminal of the amplifier U2 are both connected to the cathode of the diode D1, and the anode of the diode D1 is connected to a 5V power supply.

10. A single-phase grounding fault indication system in a three-core cable low-current grounding system of a distribution network according to claim 9, characterized in that: The filtering circuit includes an inductor L1, a capacitor C1, an inductor L2 and a capacitor C2. The first end of the inductor L1 is connected to the output end of the amplifier U2. The second end of the inductor L1 is connected to the input end of the fault point parameter calculation module, the first end of the inductor L2 and the first end of the capacitor C2 through the capacitor C1. The second end of the inductor L2 and the second end of the capacitor C2 are both grounded.

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