Lightweight low-voltage fault point positioning method and device

Abstract

The invention relates to a lightweight low-voltage fault point positioning method and device, and belongs to the technical field of low-voltage electrical fault detection. By adopting the light-weight low-voltage fault point positioning method and the light-weight low-voltage fault point positioning device, through input conditioning of three-phase voltage and current alternating current signals, AD conversion and real-time acquisition of an MCU, instantaneous values of three-phase voltage and current at a current device installation position are obtained, and through corresponding data storage and operation processing, the positioning accuracy of the light-weight low-voltage fault point is improved. Obtaining a break variable instantaneous value of the three-phase voltage and current, a half-cycle sliding window effective value of the three-phase voltage and the three-phase voltage break variable, and a transient active break variable, and carrying out analysis and processing by utilizing the calculation results; whether a voltage sag event occurs in a power grid or not, the occurrence time of the voltage sag event and the position of a fault point causing the voltage sag event can be conveniently identified. Therefore, guidance suggestions can be provided for subsequent improvement of electric energy quality, and technical support is provided for accident repair and planned maintenance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of low-voltage electrical fault detection, in particular to the technical field of fault point positioning when the power grid is disturbed, and specifically refers to a lightweight low-voltage fault point positioning method and device. BACKGROUND

[0002] In the power system, some voltage sag or fluctuation events often occur, which are often caused by power grid short-circuit faults, heavy load switching, large capacitor bank non-zero switching, etc. For some precision running equipment and some frequency conversion equipment, the power supply quality of the power grid is more sensitive, and when a voltage sag event occurs, the voltage of the power grid fluctuates greatly, which may cause the equipment to run abnormally or even shut down. Therefore, these power users are very concerned about the location of the sag source or disturbance source that causes the voltage sag event, and quickly determining the fault point position of the voltage sag event has very important guiding significance for efficient organization of accident repair and subsequent planned maintenance.

[0003] At present, there is a method for realizing voltage sag and disturbance source judgment by applying a deep learning algorithm, which has a complex model and a large amount of calculation, and requires high hardware performance, and cannot be applied in low-power embedded devices with limited performance.

[0004] Therefore, how to quickly, accurately and low-costly identify the location of the sag source or disturbance source when the voltage of the power grid fluctuates greatly or a sag event occurs, i.e. to locate the fault point causing the sag or disturbance, has become a problem to be solved in the field. SUMMARY

[0005] The purpose of the present application is to overcome the shortcomings of the prior art, provide a method and device capable of accurately recording voltage sag events and positioning fault points when the power grid fails or is disturbed, and provide guidance and suggestions for subsequent power quality improvement, and technical support for accident repair and planned maintenance.

[0006] In order to achieve the above purpose, the lightweight low-voltage fault point positioning method of the present application comprises:

[0007] (A) installing a plug-and-play monitoring device on the power supply line between the public power grid and the internal power grid of the user;

[0008] (B) the monitoring device collects three-phase voltage and current signals of the alternating current power grid to obtain instantaneous values of three-phase voltage and current at the installation position;

[0009] (C) a data operation processing device calculates the instantaneous values of the three-phase voltage and current to obtain instantaneous values of the three-phase voltage and current, half-cycle sliding window effective values of the three-phase voltage and three-phase voltage mutation, and transient active mutation;

[0010] (D) The data operation processing device finds the maximum value among the effective values of the sudden change variables of all the three-phase voltages in the half-cycle sliding window, records the phase type of the maximum value, and determines whether the maximum value meets the voltage sag condition specified in the power quality standard. If yes, step (E) is entered. If no, step (B) is returned to.

[0011] (E) The data operation processing device determines, according to the transient active sudden change variable corresponding to the maximum value, whether the fault point is upstream or downstream of the installation location and the corresponding data of the fault point.

[0012] In the lightweight low-voltage fault point positioning method, step (B) is specifically:

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

[0014] In the lightweight low-voltage fault point positioning method, step (C) includes:

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

[0016] Δx(j) = x(j) - x(j-N);

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

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

[0019]

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

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

[0022] .

[0023] The step (D) comprises:

[0024] (D-1) Analyze the half-cycle sliding window effective values ΔUA(j), ΔUB(j), ΔUC(j) of the three-phase voltage mutation in the latest two cycles by using the following formula, and find the maximum values ΔUAm(j-r), ΔUBm(j-s), ΔUCm(j-t) of the voltage mutation half-cycle sliding window effective values in the latest two cycles in each phase and the corresponding sampling time j-r, j-s, j-t:

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

[0026] In the above formula, j-n is the sampling time when the maximum value ΔXm of the variable ΔX appears in the latest two cycles;

[0027] (D-2) Find the maximum value ΔUm(j-h) of the voltage mutation effective value among the maximum values ΔUAm(j-r), ΔUBm(j-s), ΔUCm(j-t) of the voltage mutation half-cycle sliding window effective values in the three phases in step (D-1) by using the following formula, and record the phase type,

[0028] ΔUm(j-h)=max{ΔUAm(j-r), ΔUBm(j-s), ΔUCm(j-t)}

[0029] Wherein, j-h is the sampling time when the maximum value of the phase mutation effective value appears, and j-h is also one of the sampling times j-r, j-s, j-t when the maximum values of the voltage mutation half-cycle sliding window effective values of the three phases appear;

[0030] (D-3) Determine whether the voltage mutation half-cycle sliding window effective value of the phase where the maximum value ΔUm(j-h) of the mutation effective value is located satisfies the following condition:

[0031] ΔUm(j) < 0.25 * ΔUm(j-h)

[0032] And

[0033] ΔUm(j-h) > 0.05 * Un

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

[0035] If yes, go to step (D-5), if no, go to step (D-4);

[0036] (D-4) Determine whether Um(j-h) corresponding to the maximum value of the half-cycle sliding window effective value of the voltage sudden change quantity ΔUm(j-h) satisfies the voltage sag condition stipulated by the power quality standard by using the following formula,

[0037] Um(j-h)>0.92*Un

[0038] If yes, clear the sag flag of the phase, and return to step (B);

[0039] (D-5) Determine whether the phase has been set with a sag flag, if yes, return to step (B), if no, go to step (D-6);

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

[0041] Um(j-h)<0.99*Um(j-h-N)

[0042] and

[0043] Um(j-h) ≤0.90*Un

[0044] In the formula, Um(j-h-N) is the half-cycle sliding window effective value of the phase voltage at the sampling time j-h one cycle before Um(j-h) corresponding to the maximum value of the half-cycle sliding window effective value of the voltage sudden change quantity ΔUm(j-h),

[0045] If no, return to step (B), if yes, go to step (E).

[0046] The light-weight low-voltage fault point positioning method, wherein the step (E) comprises:

[0047] (E-1) Take out the transient active sudden change quantity ΔP(j-h) at the sampling time j-h corresponding to the phase where the maximum value of the half-cycle sliding window effective value of the voltage sudden change quantity ΔUm(j-h) is located, if the ΔP(j-h)>0, the fault point is located upstream of the installation position, that is, the fault causing this time of sag occurs at the power supply side, if ΔP(j-h)<0, the fault point is located downstream of the installation position, that is, the fault causing this time of sag occurs at the load side;

[0048] (E-2) Set a voltage sag mark for the phase where the maximum value of the half-cycle sliding window effective value of the voltage sudden change quantity ΔUm(j-h) is located, record the time point of the voltage sag event, that is, the specific time of the time corresponding to the sampling point j-h, and record the half-cycle sliding data window effective values of the three-phase voltages UA(j-h), UB(j-h) and UC(j-h) at the time;

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

[0050] The application also provides a lightweight low-voltage fault point positioning device, which comprises:

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

[0052] The data operation processing device is connected with the monitoring device in data to calculate instantaneous values of sudden change quantities of the three-phase voltage and current, half-cycle sliding window effective values of the three-phase voltage and sudden change quantities of the three-phase voltage, and transient active sudden change quantities by using the instantaneous values of the three-phase voltage and current; the device is also used to find the maximum value among the half-cycle sliding window effective values of the sudden change quantities of the three-phase voltage, record the phase of the maximum value, judge whether the maximum value meets the voltage sag condition specified in the power quality standard, and if yes, determine the upstream or downstream of the fault point at the installation position and the corresponding data of the fault point according to the transient active sudden change quantity corresponding to the maximum value.

[0053] The lightweight low-voltage fault point positioning method and the plug-and-play positioning device adopt the application, through input conditioning, AD conversion and real-time collection of the MCU of the three-phase voltage and current AC signals, instantaneous values of the three-phase voltage and current at the installation position of the device are obtained, and through corresponding data storage and operation processing, instantaneous values of sudden change quantities of the three-phase voltage and current, half-cycle sliding window effective values of the three-phase voltage and sudden change quantities of the three-phase voltage, and transient active sudden change quantities are obtained, and then the calculation results are analyzed and processed, so that whether the power grid has a voltage sag event and the time of the voltage sag event and the position of the fault point causing the voltage sag event can be easily identified. Thus, guidance suggestions for subsequent improvement of power quality can be provided, and technical support for accident repair and planned maintenance can be provided. BRIEF DESCRIPTION OF DRAWINGS

[0054] Figure 1 It is a flowchart of the lightweight low-voltage fault point positioning method of the application;

[0055] Figure 2 It is a functional module structure diagram of the lightweight low-voltage fault point positioning device of the application;

[0056] Figure 3 A detailed flowchart of the lightweight low-voltage fault point positioning method in actual application is shown in the figure. DETAILED DESCRIPTION

[0057] In order to make the technical content of the present application more clearly understood, the following examples are described in detail.

[0058] Please refer to Figure 1 A flowchart of the lightweight low-voltage fault point positioning method is shown in the figure.

[0059] In an embodiment, the lightweight low-voltage fault point positioning method comprises:

[0060] (A) installing a plug-and-play monitoring device on a power supply line between a public power grid and a user internal power grid;

[0061] (B) the monitoring device collects three-phase voltage and current signals of the alternating current power grid to obtain instantaneous values of three-phase voltage and current at the installation position;

[0062] (C) a data operation processing device calculates instantaneous values of three-phase voltage and current, half-cycle sliding window effective values of three-phase voltage and three-phase voltage sudden change, and transient active sudden change using the instantaneous values of three-phase voltage and current;

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

[0064] (E) the data operation processing device determines the upstream or downstream of the fault point at the installation position and the corresponding data of the fault point according to the transient active sudden change corresponding to the maximum value.

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

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

[0067] Step (C) comprises:

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

[0069] Δx(j) = x(j) - x(j-N);

[0070] wherein Δx(j) is the instantaneous value of the jth sampling time of the abrupt change of the variable x, x(j) is the instantaneous value of the jth sampling time of the variable x, x(j-N) is the instantaneous value of the j-Nth sampling time of the variable x, and N is the number of sampling points per cycle, and the 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 of the three-phase voltages UA(j), UB(j), UC(j) and the latest half-cycle sliding data window effective values of the three-phase voltage abrupt changes ΔUA(j), ΔUB(j), ΔUC(j) are obtained based on the following formula,

[0072]

[0073] In the above formula, X(j) is the half-cycle sliding data window effective value of the jth sampling time of the variable x, x(j-k) is the instantaneous value of the j-kth sampling time of the variable x, and the variable x is one of the three-phase voltages ua, ub, uc and the three-phase voltage abrupt changes Δua, Δub, Δuc;

[0074] (C-3) the transient active abrupt change ΔP(j) caused by the three-phase voltage abrupt change in the latest half-cycle sliding data window is calculated according to the following formula,

[0075] .

[0076] The step (D) comprises:

[0077] (D-1) the half-cycle sliding window effective values of the three-phase voltage abrupt changes ΔUA(j), ΔUB(j), ΔUC(j) in the latest two cycles are analyzed by using the following formula to find the maximum values ΔUAm(j-r), ΔUBm(j-s), ΔUCm(j-t) of the voltage abrupt change half-cycle sliding window effective values in each phase in the latest two cycles and the corresponding sampling time j-r, j-s, j-t:

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

[0079] In the above formula, j-n is the sampling time at which the maximum value ΔXm of the abrupt change of the variable ΔX appears in the latest two cycles;

[0080] (D-2) Find the maximum value of the voltage sudden change effective value ΔUm(j-h) among the maximum values of the voltage sudden change effective values ΔUAm(j-r), ΔUBm(j-s), ΔUCm(j-t) of the three phases in step (D-1) by using the following formula, and record the phase type,

[0081] ΔUm(j-h) = max{ΔUAm(j-r), ΔUBm(j-s), ΔUCm(j-t)}

[0082] where j-h is the sampling time at which the maximum value of the voltage sudden change effective value of the phase occurs, and j-h is one of the sampling times j-r, j-s, j-t at which the maximum values of the voltage sudden change effective values of the three phases occur;

[0083] (D-3) Determine whether the voltage sudden change effective value of the phase in which the maximum value of the voltage sudden change effective value ΔUm(j-h) occurs satisfies the following condition by using the following formula:

[0084] ΔUm(j) < 0.25 * ΔUm(j-h)

[0085] and

[0086] ΔUm(j-h) > 0.05 * Un

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

[0088] If it is satisfied, go to step (D-5), if it is not satisfied, go to step (D-4);

[0089] (D-4) Determine whether Um(j-h) corresponding to the maximum value of the voltage sudden change effective value ΔUm(j-h) satisfies the voltage sag condition specified by the power quality standard by using the following formula,

[0090] Um(j-h) > 0.92 * Un

[0091] If yes, clear the sag flag of the phase, and return to step (B);

[0092] (D-5) Determine whether the phase in which Um(j-h) corresponding to the maximum value of the voltage sudden change effective value ΔUm(j-h) is set with a sag flag, if yes, return to step (B), if no, go to step (D-6);

[0093] (D-6) Determine whether Um(j-h) corresponding to the maximum value of the voltage sudden change effective value ΔUm(j-h) satisfies the following condition:

[0094] Um(j-h) < 0.99 * Um(j-h-N)

[0095] and

[0096] Um(j-h) ≤0.90*Un

[0097] wherein Um(j-h-N) is the half-cycle sliding window effective value of the phase voltage one cycle before the sampling time j-h corresponding to Um(j-h) at which the maximum value of the voltage mutation half-cycle sliding window effective value ΔUm(j-h) occurs,

[0098] If not, return to step (B), and if yes, go to step (E).

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

[0100] (E-1) taking out the transient active mutation ΔP(j-h) at the sampling time j-h corresponding to the maximum value of the voltage mutation half-cycle sliding window effective value ΔUm(j-h), and if the ΔP(j-h) > 0, then the fault point is located upstream of the installation position, i.e. the fault causing the current transient is on the power supply side, and if the ΔP(j-h) < 0, then the fault point is located downstream of the installation position, i.e. the fault causing the current transient is on the load side;

[0101] (E-2) setting a transient mark for the phase at which the maximum value of the voltage mutation half-cycle sliding window effective value ΔUm(j-h) occurs, recording the time point of the current transient event, i.e. the specific time of the time corresponding to the sampling point j-h, and recording the half-cycle sliding data window effective values UA(j-h), UB(j-h), UC(j-h) of the three-phase voltage at the time;

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

[0103] The present application also provides a lightweight low-voltage fault point positioning device, as shown in Figure 2 In an embodiment, the device comprises:

[0104] a monitoring device which is installed on the power supply line between the public power grid and the internal power grid of the user in a plug-and-play manner, and is used to collect the three-phase voltage and current signals of the alternating current grid to obtain the instantaneous values of the three-phase voltage and current at the installation position;

[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] where Δx(j) is the instantaneous value of the jth sampling time of the variable x, x(j) is the instantaneous sampling value of the jth sampling time of the variable x, x(j-N) is the instantaneous sampling value of the j-Nth sampling time of the variable x, and N is the number of sampling points per cycle. Here, the variable x can be replaced by ua, ub, uc and ia, ib, ic, respectively, to solve the instantaneous value of the three-phase voltage, three-phase current and the sudden change variable.

[0114] The effective value of the latest half-cycle sliding data window of three-phase voltage, three-phase voltage sudden change variable is calculated. The calculation formula is as follows:

[0115]

[0116] where X(j) is the half-cycle sliding data window effective value of the jth sampling time of the variable x, and the variable x can be replaced by ua, ub, uc and Δua, Δub, Δuc to solve the current half-cycle sliding data window effective value UA(j), UB(j), UC(j), ΔUA(j), ΔUB(j), ΔUC(j) of three-phase voltage, three-phase voltage sudden change variable. In the formula, the capital variable represents the effective value and the lowercase variable represents the instantaneous value.

[0117] The transient active sudden change variable caused by three-phase voltage sudden change in the latest half-cycle sliding data window, i.e. the transient disturbance energy injected due to voltage disturbance, is calculated. The calculation formula is as follows:

[0118] .

[0119] The half-cycle sliding window effective value of three-phase voltage sudden change variable in the last two cycles is analyzed to find the maximum value in each phase in the last two cycles and the corresponding sampling time ΔUAm(j-r), ΔUBm(j-s), ΔUCm(j-t), where j-r, j-s, j-t are the sampling times when the maximum value of the corresponding phase appears. The calculation method is as follows:

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

[0121] Here j-n is the sampling time when the maximum value ΔXm of the variable ΔX appears in the last two cycles.

[0122] The maximum value ΔUm(j-h) among the maximum values of the three voltage sudden change variable half-cycle sliding window effective values is found, and the phase is recorded. Where j-h is the sampling time when the maximum value of the phase appears, and j-h is also one of the sampling times when the maximum values of the three phases j-r, j-s, j-t appear.

[0123] ΔUm(j-h) = max{ΔUAm(j-r), ΔUBm(j-s), ΔUCm(j-t)}

[0124] If the current time voltage mutation half-cycle sliding window effective value of the phase where ΔUm(j-h) is located satisfies:

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

[0126] then go to the next step, otherwise go to the next step to determine whether the voltage sag flag has been set. In the formula, Un is the rated value of the grid phase voltage.

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

[0128] If the voltage sag flag has been set for the phase where ΔUm(j-h) is located, return to real-time sampling of instantaneous values of three-phase voltage and current. Continue to determine whether the following conditions are satisfied:

[0129] Um(j-h) < 0.99 * Um(j-h-N) and Um(j-h) ≤ 0.90 * Un

[0130] In the formula, Um(j-h-N) is the voltage sliding half-cycle effective value one cycle before the sampling time j-h where the maximum value Um(j-h) is located.

[0131] If the above formula is not satisfied, return to real-time sampling of instantaneous values of three-phase voltage and current. If it is satisfied, it indicates that the voltage amplitude of the phase has decreased due to this voltage fluctuation, and the cumulative decrease has reached the voltage sag threshold specified in the power quality standard.

[0132] Take the active transient mutation ΔP(j-h) corresponding to the sampling time j-h of the phase ΔUm(j-h). If the sampling point corresponds to ΔP(j-h) > 0, it indicates that the voltage sag source is located upstream of the monitoring device installation point, i.e. the fault that caused this voltage sag occurred on the power supply side. If ΔP(j-h) < 0, it indicates that the fault source is located downstream of the monitoring device installation point, i.e. the fault that caused this voltage sag occurred on the load side.

[0133] The device sets a flag for the voltage sag of the phase where ΔUm(j-h) is located, and records the time point of the voltage sag event, i.e. the specific time of the sampling point j-h corresponding to the time, as well as the three-phase voltage half-cycle sliding window effective values UA(j-h), UB(j-h), and UC(j-h) at that time. Then return to real-time sampling of instantaneous values of three-phase voltage and current.

[0134] The light-weight low-voltage fault point positioning method and the plug-and-play positioning device adopt the input conditioning, AD conversion and real-time collection of three-phase voltage and current AC signals, obtain the instantaneous values of three-phase voltage and current at the installation position of the device, and obtain the instantaneous values of sudden change variables of three-phase voltage and current, the half-cycle sliding window effective values of three-phase voltage and three-phase voltage sudden change variables, and the transient active sudden change variable through corresponding data storage and operation processing, so that the occurrence of voltage sag event, the time of voltage sag event and the position of the fault point causing the voltage sag event can be easily identified by analyzing and processing the calculation results, thereby providing guidance suggestions for subsequent power quality improvement and technical support for accident repair and planned maintenance.

[0135] In this specification, the application has been described with reference to its particular embodiments. It is clear, however, that various modifications and changes can be made without departing from the spirit and scope of the application. 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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