A lightweight low-voltage fault location method and device

Abstract

This invention relates to a lightweight low-voltage fault location method and device, belonging to the field of low-voltage electrical fault detection technology. The lightweight low-voltage fault location method and device of this invention obtains the instantaneous values ​​of the three-phase voltage and current at the current device installation location through input conditioning, AD conversion, and real-time acquisition by an MCU of the three-phase voltage and current AC signals. Through corresponding data storage and processing, the instantaneous values ​​of the sudden changes in three-phase voltage and current, the effective values ​​of the half-cycle sliding window of the three-phase voltage and its sudden changes, and the transient active power change are obtained. Further analysis using these calculation results can easily identify whether a voltage sag event has occurred in the power grid, the time of the voltage sag event, and the location of the fault point that triggered it. This provides guidance for subsequent power quality improvement and technical support for emergency repairs and planned maintenance.

Description

Technical Field

[0001] This invention relates to the field of low-voltage electrical fault detection technology, and particularly to the field of fault location technology when the power grid is disturbed, specifically to a lightweight low-voltage fault location method and device. Background Technology

[0002] In power systems, voltage sags or fluctuations frequently occur, often caused by grid short-circuit faults, heavy load connections, or non-zero-crossing closing of large capacitor banks. Some precision-operating equipment and frequency converters are particularly sensitive to grid power quality. When voltage sags occur, the significant voltage fluctuations can sometimes lead to equipment malfunctions or even shutdowns. Therefore, these power users are highly attentive to the location of the sag or disturbance source. Quickly identifying the fault location is crucial for efficiently organizing emergency repairs and conducting planned maintenance.

[0003] Currently, there are methods in the industry that use deep learning algorithms to identify voltage sags and interference sources. However, these methods are complex, computationally intensive, and have high hardware performance requirements, making them unsuitable for use in low-power embedded devices with limited performance.

[0004] Therefore, how to quickly, accurately, and cost-effectively identify the source of the voltage sag or disturbance when large fluctuations or sag events occur in the power grid, that is, to locate the fault point that causes the sag or disturbance, has become an urgent problem to be solved in this field. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method and apparatus for accurately recording voltage dip events and locating fault points when a power grid fault or disturbance occurs, providing guidance for subsequent power quality improvement and technical support for emergency repairs and planned maintenance.

[0006] To achieve the above objectives, the lightweight low-voltage fault location method of the present invention includes:

[0007] (A) Install plug-and-play monitoring devices on the power supply lines between the public power grid and the user's internal power grid;

[0008] (B) The monitoring device acquires the three-phase voltage and current signals of the AC power grid to obtain the instantaneous values ​​of the three-phase voltage and current at the installation location;

[0009] (C) The data processing device uses the instantaneous values ​​of the three-phase voltage and current to calculate the instantaneous value of the sudden change in the three-phase voltage and current, the effective value of the half-cycle sliding window of the three-phase voltage and the sudden change in the three-phase voltage, and the transient active power change.

[0010] (D) The data processing device finds the maximum value among the effective values ​​of the half-cycle sliding window of all the sudden changes in the three-phase voltage, records the phase of the maximum value; determines whether the maximum value meets the voltage sag condition specified in the power quality standard. If yes, proceed to step (E); if no, return to step (B).

[0011] (E) The data processing device determines whether the fault point is upstream or downstream of the installation location and the corresponding data of the fault point based on the transient active power change corresponding to the maximum value.

[0012] In this lightweight low-voltage fault location method, step (B) specifically includes:

[0013] The monitoring device acquires the instantaneous values ​​of three-phase voltage ua(j), ub(j), uc(j) and three-phase current ia(j), ib(j), ic(j) at the installation location.

[0014] In this lightweight low-voltage fault location method, step (C) includes:

[0015] (C-1) The instantaneous values ​​of the three-phase voltage surges Δua(j), Δub(j), and Δuc(j) and the instantaneous values ​​of the three-phase current surges Δia(j), Δib(j), and Δic(j) are calculated based on the following formula.

[0016] Δx(j) = x(j) - x(jN);

[0017] In the formula, Δx(j) is the instantaneous value of the sudden change at the j-th sampling time of variable x, x(j) is the instantaneous value at the j-th sampling time of variable x, x(jN) is the instantaneous value at the jN-th sampling time of variable x, and N is the number of sampling points per cycle. Variable x is one of the three-phase voltages ua, ub, uc and the three-phase currents ia, ib, ic.

[0018] (C-2) The latest half-cycle sliding data window effective values ​​UA(j), UB(j), UC(j) of the three-phase voltage and the latest half-cycle sliding data window effective values ​​ΔUA(j), ΔUB(j), ΔUC(j) of the three-phase voltage mutation are calculated based on the following formula.

[0019]

[0020] In the above formula, X(j) is the effective value of the sliding data window of the half-cycle of variable x at the j-th sampling time, x(jk) is the instantaneous value of variable x at the jk-th sampling time, and variable x is one of the three-phase voltages ua, ub, uc and the three-phase voltage mutations Δua, Δub, Δuc.

[0021] (C-3) Calculate the transient active power change ΔP(j) caused by the three-phase voltage change within the latest half-cycle sliding data window according to the following formula.

[0022] .

[0023] In this lightweight low-voltage fault location method, step (D) includes:

[0024] (D-1) Analyze the effective values ​​of the half-cycle sliding window for the voltage surges in the three phases within the most recent two-wave period using the following formula, ΔUA(j), ΔUB(j), and ΔUC(j). Find the maximum effective values ​​of the half-cycle sliding window for the voltage surges in each phase within the most recent two-wave period, ΔUAm(jr), ΔUBm(js), and ΔUCm(jt), and the corresponding sampling times jr, js, and jt:

[0025] ΔXm(jn)=max{ΔX(j-2N+1), ΔX(j-2N+2),…, ΔX(j-1), ΔX(j)}

[0026] In the above formula, jn is the sampling time when the maximum value of the abrupt change of variable ΔXm occurs in the most recent two cycles;

[0027] (D-2) Using the following formula, find the maximum effective value of the voltage surge in the three phases in step (D-1) among the maximum effective values ​​of the half-cycle sliding window ΔUAm(jr), ΔUBm(js), and ΔUCm(jt), and record the phase.

[0028] ΔUm(jh)=max{ΔUAm(jr), ΔUBm(js), ΔUCm(jt)}

[0029] Where jh is the sampling time when the maximum effective value of the voltage change in the phase occurs, and jh is also one of the sampling times jr, js, jt when the maximum effective value of the half-cycle sliding window of the voltage change in each of the three phases occurs;

[0030] (D-3) Using the following formula, determine whether the effective value of the half-cycle sliding window of the voltage change at the current moment of the phase containing the maximum effective value ΔUm(jh) of the change satisfies the following condition:

[0031] ΔUm(j) < 0.25 * ΔUm(jh)

[0032] and

[0033] ΔUm(jh)>0.05*Un

[0034] In the above formula, Un is the rated value of the phase voltage of the power grid.

[0035] If satisfied, proceed to step (D-5); otherwise, proceed to step (D-4).

[0036] (D-4) Using the following formula, determine whether the Um(jh) corresponding to the maximum effective value ΔUm(jh) of the half-cycle sliding window of the voltage surge meets the voltage sag condition specified in the power quality standard.

[0037] Um(jh)>0.92*Un

[0038] If so, clear the temporary descent mark of that phase and return to step (B);

[0039] (D-5) Determine whether the phase has been temporarily slumped. If yes, return to step (B); otherwise, proceed to step (D-6).

[0040] (D-6) Determine whether the Um(jh) corresponding to the maximum effective value ΔUm(jh) of the half-cycle sliding window of the voltage change satisfies the following condition:

[0041] Um(jh) < 0.99 * Um(jhN)

[0042] and

[0043] Um(jh) ≤0.90*Un

[0044] In the formula, Um(jhN) is the effective value of the half-cycle sliding window of the phase voltage at the sampling time jh corresponding to the maximum effective value ΔUm(jh) of the voltage mutation.

[0045] If the condition is not met, return to step (B); if the condition is met, proceed to step (E).

[0046] In this lightweight low-voltage fault location method, step (E) includes:

[0047] (E-1) Take out the transient active power change ΔP(jh) at the corresponding sampling time jh where the maximum effective value of the half-cycle sliding window of the voltage change is ΔUm(jh). If ΔP(jh)>0, the fault point is located upstream of the installation location, that is, the fault that caused this sag occurs on the power supply side. If ΔP(jh)<0, the fault point is located downstream of the installation location, that is, the fault that caused this sag occurs on the load side.

[0048] (E-2) Set a temporary drop marker for the phase where the maximum effective value of the half-cycle sliding window of the voltage change is ΔUm(jh), record the time point of this temporary drop event, that is, the specific time corresponding to the sampling point jh, and record the effective values ​​of the three-phase voltage half-cycle sliding window UA(jh), UB(jh), UC(jh) at that time.

[0049] (E-3) Return to step (B).

[0050] The present invention also provides a lightweight low-voltage fault location device, the device comprising:

[0051] The monitoring device is plug-and-play installed on the power supply line between the public power grid and the user's internal power grid to collect the three-phase voltage and current signals of the AC power grid and obtain the instantaneous values ​​of the three-phase voltage and current at the installation location.

[0052] The data processing device is connected to the monitoring device and is used to calculate the instantaneous values ​​of the sudden changes in the three-phase voltage and current, the effective values ​​of the half-cycle sliding window of the three-phase voltage and the sudden changes in the three-phase voltage, and the transient active power change using the instantaneous values ​​of the three-phase voltage and current. It is also used to find the maximum value among all the effective values ​​of the half-cycle sliding window of the sudden changes in the three-phase voltage, record the phase of the maximum value, and determine whether the maximum value meets the voltage sag conditions specified in the power quality standard. If so, it determines whether the fault point is upstream or downstream of the installation location and the corresponding data of the fault point based on the transient active power change corresponding to the maximum value.

[0053] This invention employs a lightweight low-voltage fault location method and a plug-and-play location device. Through input conditioning, AD conversion, and real-time acquisition by the MCU of three-phase voltage and current AC signals, the instantaneous values ​​of the three-phase voltage and current at the current device installation location are obtained. Through corresponding data storage and processing, the instantaneous values ​​of the sudden changes in three-phase voltage and current, the effective values ​​of the half-cycle sliding window of the three-phase voltage and its sudden changes, and the transient active power change are obtained. Using these calculation results for analysis, it is possible to easily identify whether a voltage sag event has occurred in the power grid, the time of the voltage sag event, and the location of the fault point that triggered it. This provides guidance for subsequent power quality improvement and technical support for emergency repairs and planned maintenance. Attached Figure Description

[0054] Figure 1 This is a flowchart illustrating the lightweight low-voltage fault location method of the present invention.

[0055] Figure 2 This is a schematic diagram of the functional module structure of the lightweight low-voltage fault location device of the present invention;

[0056] Figure 3 This is a detailed flowchart illustrating the application of the lightweight low-voltage fault location method of the present invention. Detailed Implementation

[0057] To better understand the technical content of this invention, the following embodiments are provided for detailed explanation.

[0058] Please see Figure 1 The diagram shown is a flowchart illustrating the lightweight low-voltage fault location method of the present invention.

[0059] In one embodiment, the lightweight low-voltage fault location method includes:

[0060] (A) Install plug-and-play monitoring devices on the power supply lines between the public power grid and the user's internal power grid;

[0061] (B) The monitoring device acquires the three-phase voltage and current signals of the AC power grid to obtain the instantaneous values ​​of the three-phase voltage and current at the installation location;

[0062] (C) The data processing device uses the instantaneous values ​​of the three-phase voltage and current to calculate the instantaneous value of the sudden change in the three-phase voltage and current, the effective value of the half-cycle sliding window of the three-phase voltage and the sudden change in the three-phase voltage, and the transient active power change.

[0063] (D) The data processing device finds the maximum value among the effective values ​​of the half-cycle sliding window of all the sudden changes in the three-phase voltage, records the phase of the maximum value; determines whether the maximum value meets the voltage sag condition specified in the power quality standard. If yes, proceed to step (E); if no, return to step (B).

[0064] (E) The data processing device determines whether the fault point is upstream or downstream of the installation location and the corresponding data of the fault point based on the transient active power change corresponding to the maximum value.

[0065] In a preferred embodiment, step (B) specifically includes:

[0066] The monitoring device acquires the instantaneous values ​​of three-phase voltage ua(j), ub(j), uc(j) and three-phase current ia(j), ib(j), ic(j) at the installation location.

[0067] Step (C) includes:

[0068] (C-1) The instantaneous values ​​of the three-phase voltage surges Δua(j), Δub(j), and Δuc(j) and the instantaneous values ​​of the three-phase current surges Δia(j), Δib(j), and Δic(j) are calculated based on the following formula.

[0069] Δx(j) = x(j) - x(jN);

[0070] In the formula, Δx(j) is the instantaneous value of the sudden change at the j-th sampling time of variable x, x(j) is the instantaneous value at the j-th sampling time of variable x, x(jN) is the instantaneous value at the jN-th sampling time of variable x, and N is the number of sampling points per cycle. Variable x is one of the three-phase voltages ua, ub, uc and the three-phase currents ia, ib, ic.

[0071] (C-2) The latest half-cycle sliding data window effective values ​​UA(j), UB(j), UC(j) of the three-phase voltage and the latest half-cycle sliding data window effective values ​​ΔUA(j), ΔUB(j), ΔUC(j) of the three-phase voltage mutation are calculated based on the following formula.

[0072]

[0073] In the above formula, X(j) is the effective value of the sliding data window of the half-cycle of variable x at the j-th sampling time, x(jk) is the instantaneous value of variable x at the jk-th sampling time, and variable x is one of the three-phase voltages ua, ub, uc and the three-phase voltage mutations Δua, Δub, Δuc.

[0074] (C-3) Calculate the transient active power change ΔP(j) caused by the three-phase voltage change within the latest half-cycle sliding data window according to the following formula.

[0075] .

[0076] Step (D) includes:

[0077] (D-1) Analyze the effective values ​​of the half-cycle sliding window for the voltage surges in the three phases within the most recent two-wave period using the following formula, ΔUA(j), ΔUB(j), and ΔUC(j). Find the maximum effective values ​​of the half-cycle sliding window for the voltage surges in each phase within the most recent two-wave period, ΔUAm(jr), ΔUBm(js), and ΔUCm(jt), and the corresponding sampling times jr, js, and jt:

[0078] ΔXm(jn)=max{ΔX(j-2N+1), ΔX(j-2N+2),…, ΔX(j-1), ΔX(j)}

[0079] In the above formula, jn is the sampling time when the maximum value of the abrupt change of variable ΔXm occurs in the most recent two cycles;

[0080] (D-2) Using the following formula, find the maximum effective value of the voltage surge in the three phases in step (D-1) among the maximum effective values ​​of the half-cycle sliding window ΔUAm(jr), ΔUBm(js), and ΔUCm(jt), and record the phase.

[0081] ΔUm(jh)=max{ΔUAm(jr), ΔUBm(js), ΔUCm(jt)}

[0082] Where jh is the sampling time when the maximum effective value of the voltage change in the phase occurs, and jh is also one of the sampling times jr, js, jt when the maximum effective value of the half-cycle sliding window of the voltage change in each of the three phases occurs;

[0083] (D-3) Using the following formula, determine whether the effective value of the half-cycle sliding window of the voltage change at the current moment of the phase containing the maximum effective value ΔUm(jh) of the change satisfies the following condition:

[0084] ΔUm(j) < 0.25 * ΔUm(jh)

[0085] and

[0086] ΔUm(jh)>0.05*Un

[0087] In the above formula, Un is the rated value of the phase voltage of the power grid.

[0088] If satisfied, proceed to step (D-5); otherwise, proceed to step (D-4).

[0089] (D-4) Using the following formula, determine whether the Um(jh) corresponding to the maximum effective value ΔUm(jh) of the half-cycle sliding window of the voltage surge meets the voltage sag condition specified in the power quality standard.

[0090] Um(jh)>0.92*Un

[0091] If so, clear the temporary descent mark of that phase and return to step (B);

[0092] (D-5) Determine whether the phase where the maximum effective value ΔUm(jh) of the half-cycle sliding window corresponding to the voltage change has been set with a temporary sag flag. If yes, return to step (B); otherwise, proceed to step (D-6).

[0093] (D-6) Determine whether the Um(jh) corresponding to the maximum effective value ΔUm(jh) of the half-cycle sliding window of the voltage change satisfies the following condition:

[0094] Um(jh) < 0.99 * Um(jhN)

[0095] and

[0096] Um(jh) ≤0.90*Un

[0097] In the formula, Um(jhN) is the effective value of the half-cycle sliding window of the phase voltage at the sampling time jh corresponding to the maximum effective value ΔUm(jh) of the voltage mutation.

[0098] If the condition is not met, return to step (B); if the condition is met, proceed to step (E).

[0099] In a more preferred embodiment, step (E) includes:

[0100] (E-1) Take out the transient active power change ΔP(jh) at the corresponding sampling time jh where the maximum effective value of the half-cycle sliding window of the voltage change is ΔUm(jh). If ΔP(jh)>0, the fault point is located upstream of the installation location, that is, the fault that caused this sag occurs on the power supply side. If ΔP(jh)<0, the fault point is located downstream of the installation location, that is, the fault that caused this sag occurs on the load side.

[0101] (E-2) Set a temporary drop marker for the phase where the maximum effective value of the half-cycle sliding window of the voltage change is ΔUm(jh), record the time point of this temporary drop event, that is, the specific time corresponding to the sampling point jh, and record the effective values ​​of the three-phase voltage half-cycle sliding window UA(jh), UB(jh), UC(jh) at that time.

[0102] (E-3) Return to step (B).

[0103] This invention also provides a lightweight low-voltage fault location device, such as... Figure 2 As shown, in one embodiment, the device includes:

[0104] The monitoring device is plug-and-play installed on the power supply line between the public power grid and the user's internal power grid to collect the three-phase voltage and current signals of the AC power grid and obtain the instantaneous values ​​of the three-phase voltage and current at the installation location.

[0105] The data processing device is connected to the monitoring device and is used to calculate the instantaneous values ​​of the sudden changes in the three-phase voltage and current, the effective values ​​of the half-cycle sliding window of the three-phase voltage and the sudden changes in the three-phase voltage, and the transient active power change using the instantaneous values ​​of the three-phase voltage and current. It is also used to find the maximum value among all the effective values ​​of the half-cycle sliding window of the sudden changes in the three-phase voltage, record the phase of the maximum value, and determine whether the maximum value meets the voltage sag conditions specified in the power quality standard. If so, it determines whether the fault point is upstream or downstream of the installation location and the corresponding data of the fault point based on the transient active power change corresponding to the maximum value.

[0106] In a preferred embodiment, the data processing device is an MCU, and the monitoring device includes a pluggable open-type current transformer and a voltage sampling terminal. The data processing device and the monitoring device are integrated into a miniaturized DIN rail structure, which can be plugged and played and installed on the power grid.

[0107] In a more preferred embodiment, the system is self-powered by the AC voltage sampling input signal obtained from the voltage sampling terminal.

[0108] In practical applications, the lightweight low-voltage fault location device of this invention is an online monitoring device for 0.4kV power systems. It adopts a miniaturized rail-mounted structure design and features a pluggable open-type current transformer and voltage sampling terminals, facilitating installation and plug-and-play functionality. Furthermore, this fault location device can be self-powered by an AC voltage analog sampling input signal. Compared to most existing machine learning-based fault location algorithms, the algorithm of this invention is designed based on the physical characteristics of power grid operation, resulting in lower computational load and higher speed.

[0109] The fault location device has certain hardware conditions, which can realize real-time sampling of AC voltage and current analog quantities, storage of historical data and events, and sufficient arithmetic operation capabilities. The device samples the instantaneous values ​​of three-phase voltage and current in real time to obtain the current instantaneous sampled values ​​of three-phase voltage and current ua(j), ub(j), uc(j) and ia(j), ib(j), ic(j).

[0110] like Figure 3 As shown, in practical applications, the lightweight low-voltage fault location method of the present invention may include the following steps:

[0111] Calculate the instantaneous values ​​of the three-phase voltage and current abrupt changes: Δua(j), Δub(j), Δuc(j), Δia(j), Δib(j), Δic(j). These instantaneous values ​​can be obtained by comparing the current instantaneous sampled value with the instantaneous sampled value one cycle before the wavefront. That is:

[0112] Δx(j) = x(j) - x(jN);

[0113] In the formula, Δx(j) is the instantaneous value of the abrupt change at the j-th sampling time of variable x, x(j) is the instantaneous sampled value at the j-th sampling time of variable x, x(jN) is the instantaneous sampled value at the jN-th sampling time of variable x, and N is the number of sampling points per cycle. Here, variable x can be replaced by ua, ub, uc and ia, ib, ic respectively to solve for the instantaneous values ​​of the abrupt changes in three-phase voltage and three-phase current.

[0114] Calculate the latest half-cycle sliding data window RMS value of the three-phase voltage and the three-phase voltage fluctuation. The calculation formula is as follows:

[0115]

[0116] In the formula, X(j) is the effective value of the half-cycle sliding data window of variable x at the j-th sampling time. Variable x can be replaced by ua, ub, uc and Δua, Δub, Δuc to solve for the current effective values ​​of the half-cycle sliding data window of three-phase voltage and three-phase voltage abrupt change, respectively: UA(j), UB(j), UC(j), ΔUA(j), ΔUB(j), ΔUC(j). In the formula, uppercase variables represent effective values ​​and lowercase variables represent instantaneous values.

[0117] The transient active power surge caused by the three-phase voltage surge within the latest half-cycle sliding data window, i.e., the transient disturbance energy injected due to voltage disturbance, is calculated using the following formula:

[0118] .

[0119] Analyze the effective values ​​of the three-phase voltage surges within the sliding window of the most recent two-week waveform. Find the maximum value of each phase within the most recent two-week waveform and the corresponding sampling times ΔUAm(jr), ΔUBm(js), and ΔUCm(jt), where jr, js, and jt are the sampling times when the maximum value of the corresponding phase occurs. The calculation method is as follows:

[0120] ΔXm(jn)=max{ΔX(j-2N+1), ΔX(j-2N+2),…, ΔX(j-1), ΔX(j)}

[0121] Here, jn is the sampling time when the maximum value ΔXm of the variable ΔX occurs in the most recent two cycles.

[0122] Find the maximum value ΔUm(jh) among the maximum values ​​of the effective values ​​of the three voltage surges in the half-cycle sliding window, and record the phase. Here, jh is the sampling time when the maximum value of this phase occurs, and therefore jh is also one of the sampling times of the maximum values ​​of the three phases jr, js, and jt.

[0123] ΔUm(jh)=max{ΔUAm(jr), ΔUBm(js), ΔUCm(jt)}

[0124] If the effective value of the half-cycle sliding window of the voltage change at the current moment of the phase containing ΔUm(jh) satisfies:

[0125] ΔUm(j)<0.25*ΔUm(jh) and ΔUm(jh)>0.05*Un

[0126] If the condition is met, proceed to the next step; otherwise, proceed to the next step to determine whether a temporary sag flag has been set. In the formula, Un is the rated value of the grid phase voltage.

[0127] If Um(jh) > 0.92 * Un, clear the phase sag flag where ΔUm(jh) is located and return the instantaneous values ​​of the real-time sampled three-phase voltage and current.

[0128] If the phase containing ΔUm(jh) has a temporary sag flag set, then return the instantaneous values ​​of the real-time sampled three-phase voltage and current. Continue to determine if the following conditions are met:

[0129] Um(jh)<0.99*Um(jhN) and Um(jh) ≤0.90*Un

[0130] In the formula, Um(jhN) is the effective value of the voltage sliding half-cycle at the sampling time jh where the maximum value Um(jh) is located.

[0131] If the above formula is not satisfied, the instantaneous values ​​of the real-time sampled three-phase voltage and current will be returned. If it is satisfied, it indicates that the voltage fluctuation has caused a decrease in the voltage amplitude of that phase, and the cumulative decrease has reached the voltage sag threshold specified in the power quality standard.

[0132] Take out the active transient change ΔP(jh) at the sampling time jh corresponding to the phase ΔUm(jh). If ΔP(jh) > 0 at the sampling point, it indicates that the source of the sag is located upstream of the monitoring device installation point, that is, the fault that caused this sag occurred on the power supply side. If ΔP(jh) < 0, it indicates that the source of the fault is located downstream of the monitoring device installation point, that is, the fault that caused this sag occurred on the load side.

[0133] The device sets a marker for the phase sag where ΔUm(jh) occurs, and records the specific time of this sag event, i.e., the time corresponding to the sampling point jh, as well as the effective values ​​of the three-phase voltage half-cycle sliding window UA(jh), UB(jh), and UC(jh) at that time. Then, it returns the instantaneous values ​​of the real-time sampled three-phase voltage and current.

[0134] This invention employs a lightweight low-voltage fault location method and a plug-and-play location device. Through input conditioning, AD conversion, and real-time acquisition by the MCU of three-phase voltage and current AC signals, the instantaneous values ​​of the three-phase voltage and current at the current device installation location are obtained. Through corresponding data storage and processing, the instantaneous values ​​of the sudden changes in three-phase voltage and current, the effective values ​​of the half-cycle sliding window of the three-phase voltage and its sudden changes, and the transient active power change are obtained. Using these calculation results for analysis, it is possible to easily identify whether a voltage sag event has occurred in the power grid, the time of the voltage sag event, and the location of the fault point that triggered it. This provides guidance for subsequent power quality improvement and technical support for emergency repairs and planned maintenance.

[0135] In this specification, the invention has been described with reference to specific embodiments thereof. However, it will be apparent that various modifications and variations can be made without departing from the spirit and scope of the invention. Therefore, the specification and drawings should be considered illustrative rather than restrictive.

Claims

1. A lightweight low-voltage fault location method, characterized in that, include: (A) Install plug-and-play monitoring devices on the power supply lines between the public power grid and the user's internal power grid; (B) The monitoring device acquires the three-phase voltage and current signals of the AC power grid to obtain the instantaneous values ​​of the three-phase voltage and current at the installation location; (C) The data processing device uses the instantaneous values ​​of the three-phase voltage and current to calculate the instantaneous value of the sudden change in the three-phase voltage and current, the effective value of the half-cycle sliding window of the three-phase voltage and the sudden change in the three-phase voltage, and the transient active power change. (D) The data processing device finds the maximum value among the effective values ​​of the half-cycle sliding window of all the sudden changes in the three-phase voltage, records the phase of the maximum value; determines whether the maximum value meets the voltage sag condition specified in the power quality standard. If yes, proceed to step (E); if no, return to step (B). (E) The data processing device determines whether the fault point is upstream or downstream of the installation location and the corresponding data of the fault point based on the transient active power change corresponding to the maximum value.

2. The lightweight low-voltage fault location method according to claim 1, characterized in that, Step (B) specifically refers to: The monitoring device acquires the instantaneous values ​​of three-phase voltage ua(j), ub(j), uc(j) and three-phase current ia(j), ib(j), ic(j) at the installation location.

3. The lightweight low-voltage fault location method according to claim 2, characterized in that, Step (C) includes: (C-1) The instantaneous values ​​of the three-phase voltage surges Δua(j), Δub(j), and Δuc(j) and the instantaneous values ​​of the three-phase current surges Δia(j), Δib(j), and Δic(j) are calculated based on the following formula. Δx(j) = x(j) - x(jN); In the formula, Δx(j) is the instantaneous value of the sudden change at the j-th sampling time of variable x, x(j) is the instantaneous value at the j-th sampling time of variable x, x(jN) is the instantaneous value at the jN-th sampling time of variable x, and N is the number of sampling points per cycle. Variable x is one of the three-phase voltages ua, ub, uc and the three-phase currents ia, ib, ic. (C-2) The latest half-cycle sliding data window effective values ​​UA(j), UB(j), UC(j) of the three-phase voltage and the latest half-cycle sliding data window effective values ​​ΔUA(j), ΔUB(j), ΔUC(j) of the three-phase voltage mutation are calculated based on the following formula. In the above formula, X(j) is the effective value of the sliding data window of the half-cycle of variable x at the j-th sampling time, x(jk) is the instantaneous value of variable x at the jk-th sampling time, and variable x is one of the three-phase voltages ua, ub, uc and the three-phase voltage mutations Δua, Δub, Δuc. (C-3) Calculate the transient active power change ΔP(j) caused by the three-phase voltage change within the latest half-cycle sliding data window according to the following formula. 。 4. The lightweight low-voltage fault location method according to claim 3, characterized in that, Step (D) includes: (D-1) Analyze the effective values ​​of the half-cycle sliding window for the voltage surges in the three phases within the most recent two-wave period using the following formula, ΔUA(j), ΔUB(j), and ΔUC(j). Find the maximum effective values ​​of the half-cycle sliding window for the voltage surges in each phase within the most recent two-wave period, ΔUAm(jr), ΔUBm(js), and ΔUCm(jt), and the corresponding sampling times jr, js, and jt: ΔXm(jn)=max{ΔX(j-2N+1), ΔX(j-2N+2),…, ΔX(j-1), ΔX(j)} In the above formula, jn is the sampling time when the maximum value of the abrupt change of variable ΔXm occurs in the most recent two cycles; (D-2) Using the following formula, find the maximum effective value of the voltage surge in the three phases in step (D-1) among the maximum effective values ​​of the half-cycle sliding window ΔUAm(jr), ΔUBm(js), and ΔUCm(jt), and record the phase. ΔUm(jh)=max{ΔUAm(jr), ΔUBm(js), ΔUCm(jt)} Where jh is the sampling time when the maximum effective value of the voltage change in the phase occurs, and jh is also one of the sampling times jr, js, jt when the maximum effective value of the half-cycle sliding window of the voltage change in each of the three phases occurs; (D-3) Using the following formula, determine whether the effective value of the half-cycle sliding window of the voltage change at the current moment of the phase containing the maximum effective value ΔUm(jh) of the change satisfies the following condition: ΔUm(j) < 0.25 * ΔUm(jh) and ΔUm(jh)>0.05*Un In the above formula, Un is the rated value of the phase voltage of the power grid. If satisfied, proceed to step (D-5); otherwise, proceed to step (D-4). (D-4) Using the following formula, determine whether the Um(jh) corresponding to the maximum effective value ΔUm(jh) of the half-cycle sliding window of the voltage surge meets the voltage sag condition specified in the power quality standard. Um(jh)>0.92*Un If so, clear the temporary descent mark of that phase and return to step (B); (D-5) Determine whether the phase has been temporarily slumped. If yes, return to step (B); otherwise, proceed to step (D-6). (D-6) Determine whether the Um(jh) corresponding to the maximum effective value ΔUm(jh) of the half-cycle sliding window of the voltage change satisfies the following condition: Um(jh) < 0.99 * Um(jhN) and Um(jh) ≤0.90*Un In the formula, Um(jhN) is the effective value of the half-cycle sliding window of the phase voltage at the sampling time jh corresponding to the maximum effective value ΔUm(jh) of the voltage mutation. If the condition is not met, return to step (B); if the condition is met, proceed to step (E).

5. The lightweight low-voltage fault location method according to claim 4, characterized in that, The step (E) includes: (E-1) Take out the transient active power change ΔP(jh) at the corresponding sampling time jh where the maximum effective value of the half-cycle sliding window of the voltage change is ΔUm(jh). If ΔP(jh)>0, the fault point is located upstream of the installation location, that is, the fault that caused this sag occurs on the power supply side. If ΔP(jh)<0, the fault point is located downstream of the installation location, that is, the fault that caused this sag occurs on the load side. (E-2) Set a temporary drop marker for the phase where the maximum effective value of the half-cycle sliding window of the voltage change is ΔUm(jh), record the time point of this temporary drop event, that is, the specific time corresponding to the sampling point jh, and record the effective values ​​of the three-phase voltage half-cycle sliding window UA(jh), UB(jh), UC(jh) at that time. (E-3) Return to step (B).

6. A lightweight low-voltage fault location device, characterized in that, include: The monitoring device is plug-and-play installed on the power supply line between the public power grid and the user's internal power grid to collect the three-phase voltage and current signals of the AC power grid and obtain the instantaneous values ​​of the three-phase voltage and current at the installation location. The data processing device is connected to the monitoring device and is used to calculate the instantaneous values ​​of the sudden changes in the three-phase voltage and current, the effective values ​​of the half-cycle sliding window of the three-phase voltage and the sudden changes in the three-phase voltage, and the transient active power change using the instantaneous values ​​of the three-phase voltage and current. It is also used to find the maximum value among all the effective values ​​of the half-cycle sliding window of the sudden changes in the three-phase voltage, record the phase of the maximum value, and determine whether the maximum value meets the voltage sag conditions specified in the power quality standard. If so, it determines whether the fault point is upstream or downstream of the installation location and the corresponding data of the fault point based on the transient active power change corresponding to the maximum value.

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