A method and system for determining arc grounding fault of distribution cable based on harmonic components

Abstract

The present invention relates to a method for determining arc grounding fault of distribution cable based on harmonic components, including: collecting three-phase voltage, zero-sequence voltage and zero-sequence current signals of the monitored distribution cable, and collecting arc signals of arc sensors at the same time; judging the starting conditions; finding the segments with the largest amplitude of each line with a window of 100ms, comparing them to find the maximum value, and considering the line where the segment with the maximum value is located as the fault line; retrieving the record of the acquired arc signal, and comparing its time with the time of the marked fault line; and judging the arc grounding fault. The present invention obtains the arcing information and voltage and current transient signals of the arc grounding fault in real time, extracts the harmonic change judgment criteria of the arc, realizes the judgment of arc grounding of the distribution line, improves the reliability and selectivity of line protection, and reduces the equipment loss caused by arcing.

Description

Technical Field

[0001] The present invention relates to the technical field of ground fault identification of distribution network, and in particular to a method and system for determining arc ground fault of distribution cable based on harmonic components. Background Art

[0002] There are three types of neutral point grounding methods in my country's existing power grids: direct neutral point grounding, neutral point grounding through arc suppression coils, and neutral point non-grounding, that is, neutral point insulation. The overvoltage caused by single-phase arc grounding mainly occurs in power grids with non-direct neutral point grounding. Single-phase grounding is the most frequent and common fault form in power grid operation. Most of the neutral point operation modes of my country's 6-66kV power grids use neutral point non-grounding or neutral point grounding through arc suppression coils. In the operation of these power grids, the operating regulations stipulate that after single-phase grounding occurs, the time allowed to operate with grounding points is generally not more than 120 minutes. However, with the expansion of medium and low voltage power grids, the number of outgoing line loops of power supply buses has increased, the line length has increased, and especially the large-scale use of power cable lines has greatly increased the single-phase grounding capacitive current. When the capacitive current increases to a certain extent, the single-phase contact grounding arc cannot be automatically extinguished, and an unstable state of the grounding point arc burning and extinguishing may occur. This intermittent process of arc reignition and extinguishing leads to electromagnetic oscillation of the inductance and capacitance loops in the power grid.

[0003] Due to technical limitations, the early identification of arc grounding faults was mainly based on fault signals extracted by the protection and fault recording or small current line selection device in the substation. When the fault location is far away from the substation, the fault characteristics, especially the small current arc grounding fault, such as the characteristics of the small current grounding system and arc high resistance fault, are often very weak and difficult to accurately identify and extract. Summary of the invention

[0004] The primary purpose of the present invention is to provide a distribution cable arc grounding fault determination method based on harmonic components, which realizes the integration of small current arc grounding judgment criteria by comprehensively analyzing the information of arc sensors and the transient signals of system voltage and current during arc grounding, thereby improving the reliability and selectivity of arc grounding judgment.

[0005] To achieve the above object, the present invention adopts the following technical solution: a method for determining arc grounding fault of distribution cable based on harmonic components, the method comprising the following steps in order:

[0006] (1) Collect the three-phase voltage, zero-sequence voltage and zero-sequence current signals of the monitored distribution cable, and collect the arc signal of the arc sensor at the same time;

[0007] (2) The collected voltage and current signals and arc light signals are judged for the starting conditions. If the starting conditions are not met, the subsequent collected signals are judged; if the conditions are met, the next step is entered;

[0008] (3) Take the zero-sequence current signal of the monitored distribution cable after startup for 1000ms, perform bandpass filtering, and obtain the harmonic content in the frequency band of 50Hz to 1500Hz. Use 100ms as a window to find the segment with the largest amplitude of each line, compare them to find the maximum value, and consider the line where the segment with the maximum value is located as the fault line;

[0009] (4) Take 1000ms of the zero-sequence current signal of the fault line, perform bandpass filtering and calculate the average amplitude, and use 1ms as a window to find the time window that is greater than 1.2 times the average amplitude, and mark its start and end time points;

[0010] (5) Retrieve the record of the acquired arc signal, compare its time with the time of marking the fault line, and obtain the time difference; if the number of recorded arc signals is consistent with the number of time points of marking the fault line, and there is only one time difference, and the time difference is less than 200μs, it is judged as instantaneous arc grounding; if the number of recorded arc signals is consistent with the number of time points of marking the fault line, and is greater than 1 time, and the time difference is less than 200μs, it is judged as intermittent arc grounding; if the number of recorded arc signals is greater than the number of time points of marking the fault line, it is judged as an intermittent arc grounding fault; if the number of recorded arc signals is less than the number of time points of marking the fault line, it is judged as a non-arc grounding fault.

[0011] The starting conditions are: zero-sequence voltage greater than 15V, zero-sequence current greater than 0.05A, and arc signal received continuously for 1ms. Meeting the starting conditions means starting when any one of the three conditions is met.

[0012] Another object of the present invention is to provide a system for determining a distribution cable arc grounding fault based on harmonic components, comprising:

[0013] The cloud virtual server processes the received data and determines the arc grounding fault;

[0014] The intelligent monitoring terminal processes the received signals and sends the processed data to the cloud virtual server;

[0015] Arc sensor, used to collect arc signals;

[0016] Voltage transformer, used to collect the three-phase voltage and zero-sequence voltage of the monitored distribution cable;

[0017] Current transformer, used to collect the zero-sequence current signal of the monitored distribution cable;

[0018] The signal output ends of the arc sensor, voltage transformer and current transformer are connected to the signal input end of the intelligent monitoring terminal, and there is two-way communication between the intelligent detection terminal and the cloud virtual server.

[0019] It can be seen from the above technical scheme that the beneficial effects of the present invention are as follows: the present invention obtains the arcing information and voltage and current transient signals of arc grounding faults in real time, extracts the harmonic change judgment criteria of the arc, realizes the judgment of arc grounding of distribution lines, improves the reliability and selectivity of line protection, and reduces equipment losses caused by arcing. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is a flow chart of the method of the present invention;

[0021] Figure 2 This is a schematic diagram of the structure of this system. DETAILED DESCRIPTION

[0022] like Figure 1 As shown, a method for determining arc grounding fault of distribution cable based on harmonic components comprises the following steps in sequence:

[0023] (1) Collecting the three-phase voltage, zero-sequence voltage and zero-sequence current signals of the monitored distribution cable, and collecting the arc signal of the arc sensor 3 at the same time;

[0024] (2) The collected voltage and current signals and arc light signals are judged for the starting conditions. If the starting conditions are not met, the subsequent collected signals are judged; if the conditions are met, the next step is entered;

[0025] (3) Take the zero-sequence current signal of the monitored distribution cable after startup for 1000ms, perform bandpass filtering, and obtain the harmonic content in the frequency band of 50Hz to 1500Hz. Use 100ms as a window to find the segment with the largest amplitude of each line, compare them to find the maximum value, and consider the line where the segment with the maximum value is located as the fault line;

[0026] (4) Take 1000ms of the zero-sequence current signal of the fault line, perform bandpass filtering and calculate the average amplitude, and use 1ms as a window to find the time window that is greater than 1.2 times the average amplitude, and mark its start and end time points;

[0027] (5) Retrieve the record of the acquired arc signal, compare its time with the time of marking the fault line, and obtain the time difference; if the number of recorded arc signals is consistent with the number of time points of marking the fault line, and there is only one time difference, and the time difference is less than 200μs, it is judged as instantaneous arc grounding; if the number of recorded arc signals is consistent with the number of time points of marking the fault line, and is greater than 1 time, and the time difference is less than 200μs, it is judged as intermittent arc grounding; if the number of recorded arc signals is greater than the number of time points of marking the fault line, it is judged as an intermittent arc grounding fault; if the number of recorded arc signals is less than the number of time points of marking the fault line, it is judged as a non-arc grounding fault.

[0028] The starting conditions are: zero-sequence voltage greater than 15V, zero-sequence current greater than 0.05A, and arc signal received continuously for 1ms. Meeting the starting conditions means starting when any one of the three conditions is met.

[0029] like Figure 2 As shown, the system includes:

[0030] The cloud virtual server processes the received data and determines the arc grounding fault;

[0031] The intelligent monitoring terminal processes the received signals and sends the processed data to the cloud virtual server;

[0032] Arc sensor 3, used for collecting arc signals;

[0033] Voltage transformer 2, used to collect the three-phase voltage and zero-sequence voltage of the monitored distribution cable;

[0034] Current transformer 1, used to collect the zero-sequence current signal of the monitored distribution cable;

[0035] The signal output ends of the arc sensor 3, the voltage transformer 2 and the current transformer 1 are connected to the signal input end of the intelligent monitoring terminal, and there is two-way communication between the intelligent detection terminal and the cloud virtual server.

[0036] In summary, the present invention obtains the arcing information and voltage and current transient signals of arc grounding faults in real time, extracts the harmonic change judgment criteria of the arc, realizes the judgment of arc grounding of distribution lines, improves the reliability and selectivity of line protection, and reduces equipment losses caused by arcing.

Claims

1. A method for determining arc grounding faults in distribution cables based on harmonic components, characterized in that: The method comprises the following steps in order: (1) Collect the three-phase voltage, zero-sequence voltage and zero-sequence current signals of the monitored distribution cable, and collect the arc signal of the arc sensor at the same time; (2) The collected voltage and current signals and arc light signals are judged for the starting conditions. If the starting conditions are not met, the subsequent collected signals are judged; if the conditions are met, the next step is entered; (3) Take the zero-sequence current signal of the monitored distribution cable after startup for 1000ms, perform bandpass filtering, and obtain the harmonic content in the frequency band of 50Hz to 1500Hz. Use 100ms as a window to find the segment with the largest amplitude of each line, compare them to find the maximum value, and consider the line where the segment with the maximum value is located as the fault line; (4) Take 1000ms of the zero-sequence current signal of the fault line, perform bandpass filtering and calculate the average amplitude. Use 1ms as a window to find the time window that is greater than 1.2 times the average amplitude and mark its start and end time points. (5) Retrieve the record of the acquired arc signal, compare its time with the time of marking the fault line, and obtain the time difference; if the number of recorded arc signals is consistent with the number of time points of marking the fault line, and there is only one time difference, and the time difference is less than 200μs, it is judged as instantaneous arc grounding; if the number of recorded arc signals is consistent with the number of time points of marking the fault line, and is greater than 1 time, and the time difference is less than 200μs, it is judged as intermittent arc grounding; if the number of recorded arc signals is greater than the number of time points of marking the fault line, it is judged as an intermittent arc grounding fault; if the number of recorded arc signals is less than the number of time points of marking the fault line, it is judged as a non-arc grounding fault; The starting conditions are: zero-sequence voltage greater than 15V, zero-sequence current greater than 0.05A, and arc signal received continuously for 1ms. Meeting the starting conditions means starting when any one of the three conditions is met.

2. A system for implementing the method for determining arc grounding fault of distribution cable based on harmonic components according to claim 1, characterized in that: include: The cloud virtual server processes the received data and determines the arc grounding fault; The intelligent monitoring terminal processes the received signals and sends the processed data to the cloud virtual server; Arc sensor, used to collect arc signals; Voltage transformer, used to collect the three-phase voltage and zero-sequence voltage of the monitored distribution cable; Current transformer, used to collect the zero-sequence current signal of the monitored distribution cable; The signal output ends of the arc sensor, voltage transformer and current transformer are connected to the signal input end of the intelligent monitoring terminal, and there is two-way communication between the intelligent detection terminal and the cloud virtual server.

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