A power distribution network single-phase ground fault active defense method

Abstract

The application discloses a kind of power distribution network single-phase ground fault active defense method and system.The method utilizes intelligent monitoring terminal and main control unit to implement whole-process active defense: before fault occurs, by analyzing the change trend of line-to-ground insulation resistance, generating insulation deterioration early warning and locating hidden danger section;At the moment of fault occurrence, control neutral point active grounding compensation device injects compensation current equal to fault current amplitude, opposite in phase, and quickly extinguishes fault arc;After arc extinguishing, by injecting low-frequency characteristic signal with monitoring terminal, precise positioning and isolation of fault section are realized.The application changes passive defense into active intervention, effectively solves the problem of traditional arc extinction incompleteness and line selection difficulty, significantly improves the power supply reliability and safety of power distribution network.

Description

Technical Field

[0001] This invention relates to an active defense method for single-phase grounding faults in power distribution networks, belonging to the field of power grid fault analysis technology. Background Technology

[0002] In my country's 10kV-35kV distribution network system, single-phase grounding faults are the most frequent type of fault, accounting for over 80% of all network faults. Currently, my country's distribution network mainly uses low-current grounding methods (including ungrounded neutral systems or systems grounded via arc suppression coils). Because the fault current is relatively small when a single-phase grounding fault occurs, the system can usually operate with the fault for 1 to 2 hours, which to some extent ensures power supply reliability. However, existing single-phase grounding fault handling technologies still have the following significant drawbacks: 1) Existing technologies mainly rely on "line selection" and "location" after the fault occurs, and cannot detect the fault in its early stages (i.e., the insulation degradation period), which is a typical "post-event handling" and cannot effectively prevent the occurrence of faults. There is a passive response mode problem. 2) Traditional arc suppression coils (such as tuned inductors) can only compensate for power frequency capacitive current and cannot compensate for resistive components and harmonic currents. When the grounding current is large or contains high-frequency components, the arc is difficult to self-extinguish, and intermittent arc grounding overvoltages are easily generated, which can break down equipment insulation, induce phase-to-phase short circuits, or even fires. There are limitations in arc suppression effectiveness. 3) Traditional fault location often relies on manual circuit searching or simple signal detection, resulting in low location accuracy and long processing time. For permanent faults, the process from discovery to isolation often involves large-scale, long-term power outages, severely affecting the continuity of power supply. There is also the problem of low handling efficiency.

[0003] Therefore, how to develop a technology that can cover the entire process of fault incubation, occurrence, and elimination, transforming passive response into proactive defense, and taking into account both early warning and millisecond-level precise handling, is a key issue that urgently needs to be addressed in the field of safe operation of power distribution networks. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide an active defense method for single-phase grounding faults in power distribution networks, so as to overcome the shortcomings of the prior art.

[0005] The technical solution of this invention is: to provide an active defense method for single-phase grounding faults in a power distribution network, the method comprising the following steps:

[0006] By deploying intelligent monitoring terminals at each node of the power distribution line, the zero-sequence current data of each feeder and the zero-sequence voltage data of the busbar are collected in real time and synchronously. The main control unit continuously analyzes the trend of the line's insulation resistance to ground based on the data. When the insulation resistance is detected to be continuously decreasing and has not reached the fault alarm threshold, an insulation degradation early warning signal is generated and the section is located.

[0007] When a sudden change in the zero-sequence voltage of the bus is detected and exceeds the preset first threshold, it is determined that a ground fault has been initiated; the main control unit retrieves the transient zero-sequence current waveform before and after the fault initiation time;

[0008] After identifying the faulty phase, the main control unit controls the active grounding compensation device installed at the neutral point of the substation to inject compensation current; the compensation current has the same amplitude and opposite phase as the grounding capacitor current of the system.

[0009] After the arc is extinguished, the active grounding compensation device is switched to signal injection mode to inject a low-frequency characteristic signal into the system. Based on the sensing results of the characteristic signal by each intelligent monitoring terminal, the precise location of the fault is determined. If it is determined to be a permanent fault, the automatic tripping isolation of the faulty section and the load transfer of the non-faulty section are executed.

[0010] Furthermore, the main control unit, each intelligent monitoring terminal, and the bus voltage transformer are sampled and synchronized using a synchronous clock.

[0011] Furthermore, the conditions for generating the insulation degradation early warning signal also include: the amplitude or frequency of the partial discharge signal is detected to be increasing.

[0012] Furthermore: In the active arc suppression intervention step, the active grounding compensation device adopts a voltage source inverter based on an insulated gate bipolar transistor (IGBT), and calculates the current system grounding capacitance current by real-time acquisition of the bus zero-sequence voltage and neutral point current. And control the inverter output compensation current. .

[0013] Further: The low-frequency characteristic signal is a 20Hz characteristic current signal; the determination of the precise location of the fault specifically involves: based on the abrupt change point of the characteristic signal amplitude at adjacent intelligent monitoring terminals along the line, locating the fault to a specific tower section or cable well section.

[0014] The beneficial effects of this invention are as follows: Compared with the prior art, this invention achieves full current compensation and zero voltage arc suppression by utilizing the active control characteristics of power electronic devices. It can not only compensate for reactive current, but also compensate for active and harmonic current, achieving true "zero residual current" and "zero voltage" for the fault phase, thus fundamentally suppressing arc reignition.

[0015] This invention achieves 100% fault location accuracy, transforming passive detection into active injection. By injecting a location signal with controllable amplitude and distinct characteristics, the fault characteristics are no longer affected by transition resistance and system operating mode, completely solving the problem of difficult fault location in low-current grounding systems.

[0016] This invention also achieves full life-cycle protection, adds an early warning function, can identify early signs of insulation degradation, moves the accident handling point forward, and changes "fault repair" to "condition-based maintenance". Attached Figure Description

[0017] Figure 1 This describes the overall system workflow of the present invention. Detailed Implementation

[0018] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that the following embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention.

[0019] Example 1: Reference Figure 1 An active defense method for single-phase ground faults in a power distribution network, the method comprising the following steps:

[0020] By deploying intelligent monitoring terminals at each node of the power distribution line, the zero-sequence current data of each feeder and the zero-sequence voltage data of the busbar are collected in real time and synchronously. The main control unit continuously analyzes the trend of the line's insulation resistance to ground based on the data. When the insulation resistance is detected to be continuously decreasing and has not reached the fault alarm threshold, an insulation degradation early warning signal is generated and the section is located.

[0021] When a sudden change in the zero-sequence voltage of the bus is detected and exceeds the preset first threshold, it is determined that a ground fault has been initiated; the main control unit retrieves the transient zero-sequence current waveform before and after the fault initiation time;

[0022] After identifying the faulty phase, the main control unit controls the active grounding compensation device installed at the neutral point of the substation to inject compensation current; the compensation current has the same amplitude and opposite phase as the grounding capacitor current of the system.

[0023] After the arc is extinguished, the active grounding compensation device is switched to signal injection mode to inject a low-frequency characteristic signal into the system. Based on the sensing results of the characteristic signal by each intelligent monitoring terminal, the precise location of the fault is determined. If it is determined to be a permanent fault, the automatic tripping isolation of the faulty section and the load transfer of the non-faulty section are executed.

[0024] Furthermore, the main control unit, each intelligent monitoring terminal, and the bus voltage transformer are sampled and synchronized using a synchronous clock.

[0025] Furthermore, the conditions for generating the insulation degradation early warning signal also include: the amplitude or frequency of the partial discharge signal is detected to be increasing.

[0026] Furthermore: In the active arc suppression intervention step, the active grounding compensation device adopts a voltage source inverter based on an insulated gate bipolar transistor (IGBT), and calculates the current system grounding capacitance current by real-time acquisition of the bus zero-sequence voltage and neutral point current. And control the inverter output compensation current. .

[0027] Further: The low-frequency characteristic signal is a 20Hz characteristic current signal; the determination of the precise location of the fault specifically involves: based on the abrupt change point of the characteristic signal amplitude at adjacent intelligent monitoring terminals along the line, locating the fault to a specific tower section or cable well section.

[0028] In practical use

[0029] 1. On the power distribution lines, install intelligent monitoring terminals with high-precision zero-sequence current measurement capabilities at the beginning, middle, and end points of the lines. Install high-precision zero-sequence voltage transformers on the 10kV busbars of substations. Data from all intelligent monitoring terminals and high-precision zero-sequence voltage transformers are synchronously sampled at the microsecond level via a high-speed synchronous clock.

[0030] 2. The main control unit receives zero-sequence current data (i) synchronously uploaded by each intelligent monitoring terminal in real time. 01 i 02 i 03 , ..., i 0n The data includes the zero-sequence voltage data (u0) of the high-precision zero-sequence voltage transformer on the bus. Based on the uploaded data, the following characteristic quantities are analyzed and calculated: (1) the amplitude and phase of the zero-sequence current of each line. (2) the estimated value of the system's ground capacitance current. (3) the high-frequency transient components of the waveform at each monitoring point.

[0031] 3. The main control unit has the function of storing and continuously analyzing historical data, comparing real-time data with historical data. When the system detects a continuous downward trend in the insulation resistance to ground of a certain line or section, or a steady increase in the amplitude and frequency of partial discharge signals, but the zero-sequence voltage does not exceed the alarm threshold, the system generates an "insulation degradation early warning" signal and accurately locates the corresponding tower section or cable well section. At the same time, it pushes an early warning work order to the operation and maintenance management system, prompting preventive maintenance.

[0032] 4. When the high-precision zero-sequence voltage transformer on the bus detects a sudden change in the zero-sequence voltage and the amplitude exceeds the preset first threshold (e.g., 15% of the phase voltage), the main control unit determines it as "suspected ground fault start" and records this moment as T0.

[0033] 5. Therefore, the main control unit immediately retrieves the transient zero-sequence current waveforms of all intelligent monitoring terminals within one cycle before and after time T0. By comparing the initial polarity, amplitude, and high-frequency characteristics of the transient current of each line, the faulty line and faulty phase are accurately identified within 20 milliseconds.

[0034] 6. Upon identifying the faulty phase (within T0+20ms), the main control unit sends a start command to the active grounding compensation device installed at the neutral point of the substation.

[0035] 7. The core of the active grounding compensation device is a voltage source inverter composed of IGBTs. It performs the following operations: (1) Real-time acquisition of bus zero-sequence voltage u0 and neutral point current i 0n (2) Based on the instantaneous signal detection algorithm, the grounding capacitance current i of the current system is calculated. c(t) (3) Control the voltage source inverter to generate a voltage source inverter with i c(t) Compensation currents i with equal amplitude and opposite phase x(t) , i.e. i x(t) =-i c(t) (4) The compensation current i is transferred through the injection transformer connected between the output terminal and the neutral point of the voltage source inverter. x(t) Injected into the power distribution system.

[0036] 8. Compensation current i x(t) After injection, the ground capacitance current at the fault point -i c(t) The current cancels out each other out, causing the actual current flowing through the fault point to drop below 5A. The fault arc extinguishes rapidly within 100 milliseconds due to insufficient energy. At this point, the bus zero-sequence voltage returns to normal, the three-phase voltage of the system returns to balance, and the entire distribution network maintains uninterrupted power supply.

[0037] 9. After confirming that the arc has been extinguished and the system is stable (T0+1s), the main control unit controls the active grounding compensation device to switch to "signal injection mode". The voltage source inverter generates a unique, low-frequency (e.g., 20Hz) characteristic current signal and injects it into the system.

[0038] 10. Each intelligent monitoring terminal along the line monitors this characteristic signal. Based on the abrupt change in signal amplitude at each intelligent monitoring terminal along the line, the main control unit accurately determines which two adjacent intelligent monitoring terminals the fault point is located between, with a positioning accuracy reaching the distance of a pole or cable well section.

[0039] 11. The main control unit uploads fault information (line, phase, precise location, fault nature (instantaneous / permanent)) to the distribution automation master station. For instantaneous faults, only an early warning report is generated, and planned inspections are scheduled. For permanent faults, the distribution automation master station automatically generates the optimal "fault isolation-load transfer" solution, remotely controls the intelligent pole-mounted switches or ring main units on both sides of the faulty section to trip and isolate the fault, and closes the tie switch, restoring power to the non-faulty section within 3 minutes.

[0040] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A method for active defense against single-phase grounding faults in a power distribution network, characterized in that, The method includes the following steps: By deploying intelligent monitoring terminals at each node of the power distribution line, the zero-sequence current data of each feeder and the zero-sequence voltage data of the busbar are collected in real time and synchronously. The main control unit continuously analyzes the trend of the line's insulation resistance to ground based on the data. When the insulation resistance is detected to be continuously decreasing and has not reached the fault alarm threshold, an insulation degradation early warning signal is generated and the section is located. When a sudden change in the zero-sequence voltage of the bus is detected and exceeds the preset first threshold, it is determined that a ground fault has been initiated; the main control unit retrieves the transient zero-sequence current waveform before and after the fault initiation time; After identifying the faulty phase, the main control unit controls the active grounding compensation device installed at the neutral point of the substation to inject compensation current; the compensation current has the same amplitude and opposite phase as the grounding capacitor current of the system. After the arc is extinguished, the active grounding compensation device is switched to signal injection mode to inject a low-frequency characteristic signal into the system. Based on the sensing results of the characteristic signal by each intelligent monitoring terminal, the precise location of the fault is determined. If it is determined to be a permanent fault, the automatic tripping isolation of the faulty section and the load transfer of the non-faulty section are executed.

2. The active defense method according to claim 1, characterized in that: The main control unit, each intelligent monitoring terminal, and the bus voltage transformer are sampled and synchronized through a synchronous clock.

3. The active defense method according to claim 1, characterized in that: The conditions for generating the insulation degradation early warning signal also include: the amplitude or frequency of the partial discharge signal is detected to be increasing.

4. The active defense method according to claim 1, characterized in that: In the active arc suppression intervention step, the active grounding compensation device uses a voltage source inverter based on an insulated gate bipolar transistor (IGBT). It calculates the current system grounding capacitance current by real-time acquisition of the bus zero-sequence voltage and neutral point current. And control the inverter output compensation current. .

5. The active defense method according to claim 1, characterized in that: The low-frequency characteristic signal is a 20Hz characteristic current signal; the precise location of the fault is determined by: based on the abrupt change point of the characteristic signal amplitude at adjacent intelligent monitoring terminals along the line, locating the fault to a specific tower section or cable well section.

Images