Low current line selection method, device and storage medium

Abstract

The present invention relates to the field of electrical technology, and provides a small current line selection method, device, and storage medium. The small current line selection method includes: when determining to start the small current line selection, obtaining a zero-sequence voltage mutation derivative filter value and a zero-sequence current mutation filter value based on the zero-sequence voltage mutation derivative value, the zero-sequence current mutation instantaneous value, and a bandpass filter; obtaining the first sampling data of the zero-sequence current mutation instantaneous value and the zero-sequence voltage mutation instantaneous value within one cycle after the small current line selection is started, the second sampling data within the first half-wave short window, and the third sampling data within the first half-wavelength window, and obtaining the fourth sampling data of the zero-sequence voltage mutation derivative filter value and the zero-sequence current mutation filter value within the filter algorithm data window; and judging whether to execute the line selection action based on the first to fourth sampling data. Whether to execute the line selection action is comprehensively judged by the data within the first half-wave short window, the first half-wavelength window, and the filter algorithm data window, thereby improving the line selection accuracy.

Description

Technical Field

[0001] The present invention relates to the field of electrical technology, and in particular to a low-current line selection method, device and storage medium. Background Art

[0002] Low-current line selection, also known as a low-current grounding line selection device (also known as a low-current line selection device), is a type of protective device used in the power industry. It is suitable for distribution networks, such as those with ungrounded neutral points and those with neutral points grounded via arc suppression coils, where the short-circuit current is low in the event of a single-phase fault.

[0003] Currently, algorithms for low-current line selection include signal injection method, zero-sequence active component method, zero-sequence reactive power method, etc. However, the accuracy of line selection is low, and the adaptability and reliability are poor. Summary of the Invention

[0004] The present invention provides a low-current line selection method, equipment and storage medium, which improve the accuracy, adaptability and reliability of line selection.

[0005] In a first aspect, the present invention provides a low current line selection method, comprising:

[0006] Obtain the instantaneous values ​​of the three-phase current and three-phase voltage of the line;

[0007] Determine the instantaneous value of the zero-sequence current mutation amount according to the instantaneous value of the three-phase current, and determine the instantaneous value of the zero-sequence voltage mutation amount according to the instantaneous value of the three-phase voltage;

[0008] If it is determined that the start-up condition for small current line selection is met based on the instantaneous value of the zero-sequence current mutation and the instantaneous value of the zero-sequence voltage mutation, the derivative value of the zero-sequence voltage mutation and the instantaneous value of the zero-sequence current mutation are respectively input into a band-pass filter to obtain a zero-sequence voltage mutation derivative filtered value and a zero-sequence current mutation filtered value; the derivative value of the zero-sequence voltage mutation is the value of the instantaneous value of the zero-sequence voltage mutation after first-order difference;

[0009] Obtain first sampling data of the instantaneous value of the zero-sequence current mutation and the instantaneous value of the zero-sequence voltage mutation within one cycle after the small current line selection is started, second sampling data within the first half-wave short window after the small current line selection is started, and third sampling data within the first half-wavelength window after the small current line selection is started, and obtain fourth sampling data of the derivative filtered value of the zero-sequence voltage mutation and the filtered value of the zero-sequence current mutation within the filtering algorithm data window; wherein the first half-wave short window, the first half-wavelength window, and the filtering algorithm data window are all related to the duration of the first half-wave;

[0010] Whether to execute a line selection action is determined according to the first sampling data, the second sampling data, the third sampling data, and the fourth sampling data.

[0011] Optionally, the bandpass filter adopts a 6th-order Chebyshev II type digital bandpass filter, the cutoff frequencies of the bandpass filter include 300 Hz and 1500 Hz, and the sampling frequency is 12 kHz.

[0012] Optionally, the reverse polarity ratio coefficient of the bandpass filter is 0.59.

[0013] Optionally, the first half-wave short window is the first 1 / 40 of the cycle, the first half-wavelength window is the first 1 / 8 of the cycle, and the filtering algorithm data window is the remaining length after subtracting the first half-wave short window from the first half-wavelength window.

[0014] Optionally, the determining whether to perform a line selection action according to the first sampling data, the second sampling data, the third sampling data, and the fourth sampling data includes:

[0015] Obtaining a first result according to whether the first sampling data satisfies a sampling value mutation counting condition;

[0016] obtaining a second result according to whether the second sampling data satisfies a first half-wave short window forward action condition;

[0017] Obtaining a third result according to whether the third sampling data satisfies a first half-wavelength window forward action condition;

[0018] obtaining a fourth result according to whether the second sampling data and the third sampling data satisfy a first half-wave reverse action condition;

[0019] obtaining a fifth result according to whether the fourth sampling data satisfies a reliable operation condition of the filtering algorithm;

[0020] obtaining a sixth result according to whether the fourth sampling data satisfies an unreliable action condition of the filtering algorithm;

[0021] Whether to execute a line selection action is determined according to the first result, the second result, the third result, the fourth result, the fifth result, and the sixth result.

[0022] Optionally, the first sampling data includes X current sampling values ​​of the instantaneous value of the zero-sequence current mutation and X voltage sampling values ​​of the instantaneous value of the zero-sequence voltage mutation; X is the number of sampling points determined according to the sampling frequency of the bandpass filter and the period of the cycle;

[0023] The sampling value mutation counting conditions include:

[0024] The first voltage count value is greater than or equal to the first voltage count threshold; or,

[0025] The first voltage count value is greater than or equal to a second voltage count threshold, and the first current count value is greater than or equal to a first current count threshold;

[0026] The first voltage count threshold is greater than the second voltage count threshold; the first voltage count value is the number of voltage sampling values ​​greater than the voltage threshold among the X voltage sampling values, and the voltage threshold is related to the secondary rated value of the system voltage; the first current count value is the number of current sampling values ​​greater than the current threshold among the X current sampling values, and the current threshold is related to the secondary rated value of the system current.

[0027] Optionally, the second sampling data includes M current sampling values ​​and M voltage sampling values ​​within the first half-wave short window, where M is the number of sampling points determined according to the sampling frequency of the bandpass filter and the first half-wave short window;

[0028] The third sampling data includes N current sampling values ​​and N voltage sampling values ​​within the first half-wavelength window, where N is the number of sampling points determined according to the sampling frequency of the bandpass filter and the first half-wavelength window;

[0029] The positive action condition of the first half-wave short window includes: within the first half-wave short window,

[0030] The number of sampling points whose first product is less than 0 is greater than or equal to M; or,

[0031] The number of sampling points where the first product is less than 0 is greater than or equal to M-1, and the number of sampling points where the first product is greater than 0 is equal to 0;

[0032] The forward action condition of the first half-wavelength window includes: within the first half-wavelength window,

[0033] The number of sampling points where the first product is less than 0 is greater than or equal to the first product threshold; and

[0034] The proportion of sampling points whose first product is less than 0 is greater than or equal to the first proportion threshold;

[0035] The first half-wave reverse action condition includes the first half-wave short window reverse action condition or the first half-wave wavelength window reverse action condition;

[0036] The reverse action condition of the first half-wave short window includes: within the first half-wave short window,

[0037] The number of sampling points where the first product is greater than 0 is greater than or equal to M; or,

[0038] The number of sampling points where the first product is greater than 0 is greater than or equal to M-1, and the number of sampling points where the first product is less than 0 is equal to 0;

[0039] The reverse action condition of the first half-wavelength window includes: within the first half-wavelength window,

[0040] The number of sampling points where the first product is greater than 0 is greater than or equal to the first product threshold; and

[0041] The proportion of sampling points whose first product is greater than 0 is greater than or equal to the first proportion threshold;

[0042] The first product is the product of the current sampling value and the voltage sampling value corresponding to the current sampling value.

[0043] Optionally, the fourth sampling data includes Y current filtering sampling values ​​of the zero-sequence current mutation amount filtering value and Y voltage filtering sampling values ​​of the zero-sequence voltage mutation amount derivative filtering value; Y is the number of sampling points determined according to the sampling frequency of the bandpass filter and the filtering algorithm data window;

[0044] The reliable operation conditions of the filtering algorithm include:

[0045] The number of sampling points where the second product is less than 0 is greater than or equal to the high value of the filtering algorithm action; and

[0046] The proportion of the sampling points where the second product is less than 0 is greater than or equal to the reverse polarity proportion coefficient of the band-pass filter;

[0047] The unreliable action conditions of the filtering algorithm include:

[0048] The number of sampling points where the second product is less than 0 is greater than or equal to the low value of the filtering algorithm action; and

[0049] The proportion of the sampling points where the second product is less than 0 is greater than or equal to the reverse polarity proportion coefficient of the band-pass filter;

[0050] The second product is the product of the current filtering sampling value and the voltage filtering sampling value corresponding to the current filtering sampling value.

[0051] In a second aspect, the present invention provides a low-current line selection device, comprising: a module for implementing the low-current line selection method provided by the present invention.

[0052] In a third aspect, the present invention provides a low current line selection device, comprising: a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the low current line selection method provided by the present invention when executing the computer program.

[0053] In a fourth aspect, the present invention provides a computer-readable storage medium having a computer program stored thereon, wherein the computer program, when executed by a processor, implements the low-current line selection method provided by the present invention.

[0054] The present invention provides a low-current line selection method, device and storage medium, which comprehensively utilize the first half-wave short window, the first half-wavelength window and the statistics of sampling points with polarity satisfying characteristics in the filtering algorithm data window to form a comprehensive line selection criterion, utilize more dimensions of fault electrical quantities, overcome the shortcomings of a single criterion, have strong anti-interference ability and adaptability, and improve the accuracy, adaptability and reliability of line selection. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0056] Figure 1 A diagram of an application scenario of low-current line selection provided by an embodiment of the present invention;

[0057] Figure 2 A flow chart of a low current line selection method provided by an embodiment of the present invention;

[0058] Figure 3 A flow chart for determining whether a low-current line selection start condition is met according to an embodiment of the present invention;

[0059] Figure 4 A schematic diagram of an amplitude-frequency response curve of a bandpass filter provided in an embodiment of the present invention;

[0060] Figures 5A to 5C A schematic diagram of the bandpass filtering effect provided by an embodiment of the present invention;

[0061] Figure 6 A schematic diagram of a reverse polarity ratio curve and a same polarity ratio curve after bandpass filtering provided by an embodiment of the present invention;

[0062] Figure 7 Another flow chart of the low current line selection method provided by an embodiment of the present invention;

[0063] Figure 8 A schematic diagram of the line selection logic within the first half-wave short window and the first half-wavelength window provided by an embodiment of the present invention;

[0064] Figure 9 A schematic diagram of the line selection logic within the data window of the filtering algorithm provided by an embodiment of the present invention;

[0065] Figure 10 A schematic diagram of the line selection logic within one cycle after the low-current line selection is started according to an embodiment of the present invention;

[0066] Figure 11 A schematic diagram of the integrated line selection logic provided by an embodiment of the present invention;

[0067] Figure 12 A schematic diagram of the main wiring of the RTDS dynamic mold system provided in an embodiment of the present invention;

[0068] Figure 13A A schematic diagram of the waveforms of u0(t) and i0(t) of a simulation example provided in an embodiment of the present invention;

[0069] Figure 13B A schematic diagram of the waveforms of dΔu0(t) / dt_F and Δi0(t)_F of a simulation example provided in an embodiment of the present invention;

[0070] Figure 14 A schematic structural diagram of a low-current line selection device provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0071] In order to make the purpose, technical solutions and advantages of this application more clear, the following further describes this application in detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0072] It will be understood that the terms "first", "second", "third", "fourth", etc. (if any) in the embodiments of the present application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence.

[0073] The low current line selection method, device and storage medium provided by the present invention are applicable to the scenario of determining whether to perform line selection in the distribution network. Figure 1 This is an application scenario diagram of the low current line selection provided by the embodiment of the present invention. Figure 1 As shown, the low-current line selection device obtains the grid data of the distribution network, determines whether to start the low-current line selection according to the grid data, and determines whether to perform the line selection action after starting the low-current line selection, so as to protect the distribution network through the line selection action when a fault occurs in the distribution network.

[0074] In related technologies, the algorithms for small current line selection mainly include signal injection methods by injecting DC voltage and AC current, current increment, zero-sequence current, etc. into the system, as well as line selection algorithms that utilize the system's transient and steady-state voltage and current signals, such as the zero-sequence active component method, zero-sequence reactive power method, first half-wave algorithm, transient zero-sequence direction method, etc.

[0075] The signal injection method requires the installation of additional signal injection equipment. For intermittent arc grounding, the injected signal is variable and discontinuous, and the line selection accuracy is low.

[0076] The zero-sequence active component method uses zero-sequence voltage and current to calculate the magnitude and direction of each line's zero-sequence active power to identify the fault line. However, considering overcompensated, undercompensated, and ungrounded neutral systems, the angular thresholds for zero-sequence current lagging / leading zero-sequence voltage and the thresholds for active power are difficult to determine, resulting in a low accuracy rate for line selection in actual operation.

[0077] The zero-sequence reactive power method uses wavelet transform / wavelet packet transform to select lines based on the phase-frequency characteristics of transient zero-mode current. However, wavelet analysis is very sensitive to singularities and easily affected by interference signals, which in turn affects the line selection results and leads to low line selection accuracy.

[0078] The first half-wave algorithm uses the phase opposition between the first half-wave of the transient zero-sequence current and zero-sequence voltage to select a line. However, in practice, its anti-interference capability is weak, the judgment data window is small, and the inaccurate first half-wave positioning results in low line selection accuracy.

[0079] The transient zero-sequence direction method uses the polarity between the derivatives of the transient zero-sequence current and the transient zero-sequence voltage within the characteristic frequency band to select the line. However, in the case of high-resistance grounding of the arc suppression coil grounding system, the ratio of the transient zero-sequence current to the voltage derivative changes with time, and the two are not in a linear relationship, resulting in a low line selection accuracy.

[0080] The low-current line selection method provided by the present invention optimizes the transient zero-sequence direction method by designing a bandpass filter and a filtering algorithm data window. The first half-wave algorithm is optimized by proposing a first half-wave short window and a first half-wavelength window. By comprehensively utilizing the statistics of sampling points with polarity-satisfactory characteristics within the first half-wave short window, the first half-wavelength window, and the filtering algorithm data window, a comprehensive line selection criterion is formed. This utilizes fault electrical quantities from multiple dimensions, overcomes the shortcomings of a single criterion, and possesses strong anti-interference capabilities and adaptability, thereby improving line selection accuracy and reliability.

[0081] The technical solution of the present invention is described in detail below with reference to specific embodiments.

[0082] Figure 2 This is a flow chart of a low current line selection method provided by an embodiment of the present invention. The low current line selection method provided by this embodiment can be performed by a low current line selection device. Figure 2 As shown, the low current line selection method provided in this embodiment may include:

[0083] S201. Obtain the instantaneous values ​​of the three-phase current and the three-phase voltage of the line.

[0084] Specifically, the current transformer can be used to collect the instantaneous value i of the three-phase current corresponding to the current time t of the line in real time. A (t), i B (t), i C(t), using voltage transformer to collect the instantaneous value u of the three-phase voltage of the busbar connected to the line in real time A (t),u B (t),u C (t).

[0085] S202. Determine the instantaneous value of the zero-sequence current mutation amount according to the instantaneous values ​​of the three-phase currents, and determine the instantaneous value of the zero-sequence voltage mutation amount according to the instantaneous values ​​of the three-phase voltages.

[0086] Formula (1) can be used to calculate the instantaneous value of zero-sequence current i0(t) and the instantaneous value of zero-sequence voltage u0(t).

[0087]

[0088] Formula (2) is used to calculate the instantaneous value of the zero-sequence current mutation △i0(t) and the instantaneous value of the zero-sequence voltage mutation △u0(t).

[0089]

[0090] T represents the duration of one cycle, also known as the period. For example, for an alternating current with a frequency of 50 Hz, T is 20 ms.

[0091] S203. Determine whether a start condition for small current line selection is met according to the instantaneous value of the zero-sequence current mutation amount and the instantaneous value of the zero-sequence voltage mutation amount.

[0092] If it is determined that the start-up conditions for low-current line selection are met, S204 to S206 are executed.

[0093] If it is determined that the start condition for low-current line selection is not met, the process returns to and re-executes S203 .

[0094] Optional, Figure 3 A flow chart for determining whether the low current line selection start condition is met is provided in an embodiment of the present invention. Figure 3 As shown, in S203, determining whether the starting condition for small current line selection is met according to the instantaneous value of the zero-sequence current mutation amount and the instantaneous value of the zero-sequence voltage mutation amount may include:

[0095] S301. Obtain the real-axis component and the imaginary-axis component of the fundamental component of the zero-sequence current mutation according to the instantaneous value of the zero-sequence current mutation and the number of sampling points per cycle of the fundamental signal; obtain the real-axis component and the imaginary-axis component of the fundamental component of the zero-sequence voltage mutation according to the instantaneous value of the zero-sequence voltage mutation and the number of sampling points per cycle of the fundamental signal.

[0096] Alternatively, the Fourier algorithm can be used to obtain the real axis component a of the fundamental component of the zero-sequence current mutation through formula (3): i0 and the imaginary axis component bi0 , and the real axis component a of the fundamental component of the zero-sequence voltage mutation u0 and the imaginary axis component bu0.

[0097]

[0098] Wherein, N represents the number of sampling points per cycle of the fundamental signal, △i0(n) is the n-th sampling value of the instantaneous value of the zero-sequence current mutation, and △u0(n) is the n-th sampling value of the instantaneous value of the zero-sequence voltage mutation.

[0099] S302. Obtain an effective value of the fundamental component of the zero-sequence current mutation according to the real axis component and the imaginary axis component of the fundamental component of the zero-sequence current mutation, and obtain an effective value of the fundamental component of the zero-sequence voltage mutation according to the real axis component and the imaginary axis component of the fundamental component of the zero-sequence voltage mutation.

[0100] Optionally, formula (4) may be used to obtain the effective value of the fundamental component of the zero-sequence current mutation amount and the effective value of the fundamental component of the zero-sequence voltage mutation amount.

[0101]

[0102] S303: If the effective value of the fundamental component of the zero-sequence current mutation is greater than the zero-sequence current mutation start threshold, and the effective value of the fundamental component of the zero-sequence voltage mutation is greater than the zero-sequence voltage mutation start threshold, it is determined that the start condition for small current line selection is met.

[0103] Among them, the zero-sequence current mutation startup threshold can be expressed as △I 0set The zero-sequence voltage mutation threshold can be expressed as △U 0set , this embodiment is for △I 0set and △U 0set There is no restriction on the specific value of .

[0104] S204: Input the derivative value of the zero-sequence voltage mutation and the instantaneous value of the zero-sequence current mutation into a bandpass filter to obtain a filtered value of the derivative of the zero-sequence voltage mutation and a filtered value of the zero-sequence current mutation. The derivative value of the zero-sequence voltage mutation is the value of the instantaneous value of the zero-sequence voltage mutation after first-order difference.

[0105] In relay protection logic judgment, discrete digital quantities are usually used. Therefore, the first-order derivative calculation of the instantaneous zero-sequence voltage mutation △u0(t) can be simulated by differential calculation. The gain value after differential calculation of two discrete adjacent sampling points, that is, the ratio of the fault current amplitude after differential calculation to the fault current amplitude before differential calculation, is Where t1 and t2 represent the moments of two adjacent sampling points respectively.

[0106] Optionally, formula (5) can be used to calculate the derivative value of the zero-sequence voltage sudden change d△u0(t) / dt.

[0107]

[0108] Here, d△u0(t2) / dt represents the value of △u0(t) after primary differentiation at time t2, △u0(t1) and △u0(t2) represent the instantaneous values ​​of the zero-sequence voltage mutation at times t1 and t2, respectively, k represents the differential proportional coefficient, and ω represents the zero-sequence voltage angular frequency. For example, for a power frequency of 50 Hz, ω is 100π.

[0109] S205. Obtain first sampling data of the instantaneous value of the zero-sequence current sudden change and the instantaneous value of the zero-sequence voltage sudden change within one cycle after the low-current line selection is enabled, second sampling data within the first half-wave short window after the low-current line selection is enabled, and third sampling data within the first half-wave window after the low-current line selection is enabled. Obtain fourth sampling data of the derivative filtered value of the zero-sequence voltage sudden change and the filtered value of the zero-sequence current sudden change within the filtering algorithm data window. The first half-wave short window, the first half-wave window, and the filtering algorithm data window are all related to the duration of the first half-wave.

[0110] Specifically, the transient first half-wave algorithm uses the characteristic that the transient zero-sequence current and the zero-sequence voltage have opposite phases during the first half-wave to select the line. This algorithm does not show a clear transient process when the fault occurs at the zero-crossing point of the phase voltage, and only a few sampling points can be used after startup. The data window for logical judgment is very small, and in the event of partial faults or data disturbances, it is very easy to make misjudgments or missed judgments. Therefore, in this embodiment, the first half-wave algorithm is optimized by proposing a first half-wave short window and a first half-wavelength window. The length of the first half-wavelength window is greater than the length of the first half-wave short window, and the first half-wavelength window includes the first half-wave short window.

[0111] Optionally, the duration of the transient first half-wave under various working conditions, such as a neutral point ungrounded system, a neutral point grounded system via an arc suppression coil, a metallic grounding fault, a grounding fault via a transition resistor, and an intermittent arc grounding fault, can be comprehensively considered. The duration of the first half-wave can be from several hundred microseconds to several milliseconds.

[0112] Optionally, the first half-wave short window is the first 1 / 40 of the cycle, and the first half-wavelength window is the first 1 / 8 of the cycle. Optionally, the filtering algorithm data window is the remaining length after subtracting the first half-wave short window from the first half-wavelength window. For example, for an alternating current with a frequency of 50Hz, the cycle period is 20ms. The first half-wave short window can be 0~20ms*(1 / 40), that is, 0~0.5ms. The first half-wavelength window can be 0~20ms*(1 / 8), that is, 0~2.5ms. The filtering algorithm data window can be 0.5ms~2.5ms.

[0113] The first half-wave algorithm was optimized by setting the first half-wave short window and the first half-wave wavelength window, and the transient zero-sequence direction method was optimized by setting the filtering algorithm data window, thereby improving the accuracy of line selection using the first half-wave algorithm and the transient zero-sequence direction method.

[0114] Moreover, in order to prevent the execution of line selection action due to disturbing sudden changes in zero-sequence voltage or zero-sequence current, data within one cycle after the start of small current line selection is also referenced to improve the accuracy of line selection.

[0115] The sampling frequencies of the first sampling data, the second sampling data, the third sampling data and the fourth sampling data are related to the sampling frequency of the bandpass filter.

[0116] S206 : Determine whether to execute a line selection action according to the first sampling data, the second sampling data, the third sampling data, and the fourth sampling data.

[0117] As can be seen, the low-current line selection method provided in this embodiment optimizes the first half-wave algorithm by proposing a first half-wave short window and a first half-wavelength window, and optimizes the transient zero-sequence direction method through the filtering algorithm data window. This method uses the sampled data within the first half-wave short window, the first half-wavelength window, and the filtering algorithm data window to form a comprehensive line selection criterion. This utilizes fault electrical quantities from multiple dimensions, overcomes the shortcomings of a single criterion, and provides strong anti-interference capabilities and adaptability, thereby improving line selection accuracy and reliability.

[0118] Next, the design of the bandpass filter in this embodiment is described.

[0119] The transient zero-sequence direction method utilizes the opposite polarity between the derivatives of the transient zero-sequence current and the transient zero-sequence voltage within a characteristic frequency band to select a line. For ungrounded systems and low-resistance grounding systems with arc suppression coils, the zero-sequence current and the zero-sequence voltage derivative of the fault line exhibit a positive proportional relationship with a negative proportionality coefficient. However, for high-resistance grounding systems, the ratio of the transient zero-sequence current to the voltage derivative of the fault line varies over time, and the relationship is not linear. The ratio of the zero-sequence current to the zero-sequence voltage derivative can fluctuate between positive and negative values. To improve line selection accuracy, the transient zero-sequence direction must be optimized.

[0120] In this embodiment, considering both ungrounded neutral point systems and arc suppression coil-grounded systems, the frequency range of the transient zero-mode capacitive current free oscillation is generally 300-1500 Hz. Therefore, the cutoff frequencies of the bandpass filters are set to 300 Hz and 1500 Hz, respectively. Based on the Nyquist sampling theorem and with a certain margin, the sampling frequency can be set to 12 kHz.

[0121] At this point, the time difference between two adjacent sampling points is 1 / 12kHz, or approximately 0.0833ms. For an AC power supply with a frequency of 50Hz, the cycle period is 20ms. The number of sampling points in one cycle is approximately 20ms / 0.0833ms, which is an integer of 240. Therefore, the number of sampling points in one cycle is N = 240.

[0122]

[0123]

[0124] In this embodiment, the bandpass filter can be a 6th-order Chebyshev II digital bandpass filter. According to the cutoff frequency and sampling frequency of the bandpass filter, the transfer function coefficient of the 6th-order Chebyshev II digital bandpass filter is as follows:

[0125] NUM[7]={0.0256507425545,-0.08426336168964,0.09193306863013,0,-0.09193306863013,0.08426336168964,-0.0256507425545}.

[0126] DEN[7]={1,-5.033580000106,10.86438327579,-12.85681954856,8.796060072236,-3.299510726317,0.5309351754304}.

[0127] Optionally, in S204, formula (7) can be used to obtain the zero-sequence voltage mutation derivative filtered value d△u0(t) / dt_F according to the zero-sequence voltage mutation derivative value, and formula (8) can be used to obtain the zero-sequence current mutation filtered value △i0(t)_F according to the instantaneous value of the zero-sequence current mutation.

[0128] For example, Figure 4 A schematic diagram of an amplitude-frequency response curve of a bandpass filter provided in an embodiment of the present invention, Figures 5A to 5C A schematic diagram illustrating the bandpass filtering effect provided by an embodiment of the present invention.

[0129] like Figure 4 As shown, the solid line represents the amplitude response curve, and the dotted line represents the phase response curve.

[0130] like Figure 5A As shown in , the solid line represents the original waveform of the instantaneous value of zero-sequence voltage u0(t), and the dotted line represents the original waveform of the instantaneous value of zero-sequence current i0(t). Figure 5BAs shown in the figure, the solid line represents the waveform of the instantaneous value of the zero-sequence voltage mutation △u0(t), and the dotted line represents the waveform of the instantaneous value of the zero-sequence current mutation △i0(t). Figure 5C As shown, the solid line represents the waveform of the derivative filter value of the zero-sequence voltage mutation d△u0(t) / dt_F, and the dotted line represents the waveform of the zero-sequence current mutation filter value △i0(t)_F. Figures 5A to 5C It can be seen that the time window length in which the derivative filter value of the zero-sequence voltage mutation d△u0(t) / dt_F and the filter value of the zero-sequence current mutation △i0(t)_F have an inverse polarity relationship has been greatly improved compared to the time window length in which the instantaneous value of the zero-sequence voltage mutation △u0(t) and the instantaneous value of the zero-sequence current mutation △i0(t) have an inverse polarity relationship. This can expand the data window for line selection logic judgment to one cycle, thereby improving the accuracy of line selection.

[0131] Still Figure 4 、 Figures 5A to 5C Taking the waveform data shown as an example, the reverse polarity ratio curve and the same polarity ratio curve after band-pass filtering are statistically obtained as follows Figure 6 As shown. Figure 6 In the figure, the solid line represents the reverse polarity ratio curve after band-pass filtering, and the dotted line represents the same polarity ratio curve after band-pass filtering.

[0132] To obtain more comprehensive percentage data, the reverse polarity percentage statistics after bandpass filtering were obtained based on dynamic model experimental data for the ungrounded system and the arc suppression coil grounded system under the conditions of metallic grounding, transition resistance grounding, and intermittent arc grounding, as shown in Table 1. Five data points were collected for each case.

[0133] Table 1 Statistics of reverse polarity ratio after bandpass filtering

[0134]

[0135] Combine Figure 6 From the data in Table 1, we can see that under various operating conditions, the sampling points where the fault line polarity meets the characteristics are greater than 60%. Considering a certain margin, the reverse polarity ratio coefficient of the bandpass filter can be determined to be 0.59.

[0136] Optionally, the sampling frequency of the bandpass filter based on the above design is 12kHz. The first half-wave short window is the first 1 / 40 of the cycle and can include 6 sampling points. That is, the first 1 to 6 points within one cycle after the low-current line selection is activated are the first half-wave short window. The first half-wavelength window is the first 1 / 8 of the cycle and can include 30 sampling points. That is, the first 1 to 30 points within one cycle after the low-current line selection is activated are the first half-wavelength window.

[0137] The data window of the filtering algorithm includes 30-6+1=25 sampling points, that is, the 6th to 30th sampling points within one cycle after the small current line selection is started.

[0138] Optional, in Figure 2 Based on the illustrated embodiment, another embodiment of the present invention provides a low-current line selection method. Figure 7 Another flow chart of the low current line selection method provided by the embodiment of the present invention. Figure 7 As shown, in S206, judging whether to perform a line selection action based on the first sampled data, the second sampled data, the third sampled data, and the fourth sampled data may include:

[0139] S701: Obtain a first result based on whether first sampling data meets a sampling value mutation counting condition.

[0140] S702. Obtain a second result according to whether the second sampling data meets the first half-wave short window forward action condition.

[0141] S703 : Obtain a third result according to whether the third sampling data meets the first half-wavelength window forward action condition.

[0142] S704 , obtaining a fourth result according to whether the second sampling data and the third sampling data meet the first half-wave reverse action condition.

[0143] S705 : Obtain a fifth result based on whether the fourth sampling data meets a reliable operation condition of the filtering algorithm.

[0144] S706 : Obtain a sixth result based on whether the fourth sampling data satisfies an unreliable action condition of the filtering algorithm.

[0145] S707 : Determine whether to execute the line selection action according to the first result, the second result, the third result, the fourth result, the fifth result, and the sixth result.

[0146] This embodiment does not limit the execution order of S701 to S706.

[0147] As can be seen, in this embodiment, the first result reflects the sudden change in sampling values ​​within one cycle after the low-current line selection is initiated. The second to fourth results, based on the first half-wave algorithm, reflect the opposite phase characteristics of the transient zero-sequence current and zero-sequence voltage within the first half-wave short window and the first half-wavelength window. The fifth and sixth results, based on the transient zero-sequence direction method, reflect the opposite polarity characteristics between the derivatives of the transient zero-sequence current and transient zero-sequence voltage within the filtering algorithm data window. By comprehensively utilizing the statistics of sampling points with polarity that meet the characteristics within the first half-wave short window, the first half-wavelength window, and the filtering algorithm data window, and determining their respective correlation coefficients, a comprehensive line selection criterion is formed. This utilizes more dimensions of fault electrical quantities, overcomes the shortcomings of a single criterion, has strong anti-interference capabilities and adaptability, and improves the accuracy, precision, and reliability of line selection.

[0148] Next, the line selection logic within the first half-wave short window and the first half-wavelength window is explained.

[0149] The second sampling data includes M current sampling values ​​and M voltage sampling values ​​within the first half-wave short window, where M is the number of sampling points determined according to the sampling frequency of the bandpass filter and the first half-wave short window.

[0150] The third sampling data includes N current sampling values ​​and N voltage sampling values ​​within the first half-wavelength window, where N is the number of sampling points determined according to the sampling frequency of the bandpass filter and the first half-wavelength window.

[0151] The positive action conditions of the first half-wave short window include: within the first half-wave short window,

[0152] The number of sampling points where the first product is less than 0 is greater than or equal to M. Or,

[0153] The number of sampling points where the first product is less than 0 is greater than or equal to M-1, and the number of sampling points where the first product is greater than 0 is equal to 0.

[0154] The first half-wavelength window positive action conditions include: within the first half-wavelength window,

[0155] The number of sampling points where the first product is less than 0 is greater than or equal to the first product threshold.

[0156] The proportion of sampling points whose first product is less than 0 is greater than or equal to the first proportion threshold.

[0157] The first half-wave reverse action condition includes a first half-wave short window reverse action condition or a first half-wave length window reverse action condition.

[0158] The reverse action conditions of the first half-wave short window include: within the first half-wave short window,

[0159] The number of sampling points where the first product is greater than 0 is greater than or equal to M. Or,

[0160] The number of sampling points where the first product is greater than 0 is greater than or equal to M-1, and the number of sampling points where the first product is less than 0 is equal to 0.

[0161] The reverse action conditions of the first half-wavelength window include: within the first half-wavelength window,

[0162] The number of sampling points where the first product is greater than 0 is greater than or equal to the first product threshold.

[0163] The proportion of sampling points whose first product is greater than 0 is greater than or equal to the first proportion threshold.

[0164] The first product is the product of the current sampling value and the voltage sampling value corresponding to the current sampling value.

[0165] Optionally, the first product threshold is related to N. The first product threshold may be a value obtained by rounding 1 / N.

[0166] For example, Figure 8 Schematic diagram of line selection logic within the first half-wave short window and the first half-wavelength window provided by the embodiment of the present invention. Figure 8 In the example, the first product is represented by △u0△i0, where △u0 represents the voltage sampling value corresponding to the instantaneous value of the zero-sequence current mutation △u0(t) (also denoted as △u0(n)), and △i0 represents the current sampling value corresponding to the instantaneous value of the zero-sequence voltage mutation △i0(t) (also denoted as △i0(n)). The symbol "&" represents an AND relationship, and the symbol "≥" represents an OR relationship. M = 6, N = 30, the first product threshold = 15, and the first proportion threshold = 0.8.

[0167] Meet the first half-wave short window forward action conditions, meet the first half-wavelength window forward action conditions, meet the first half-wave short window reverse action conditions, meet the first half-wavelength window reverse action conditions, meet the first half-wave reverse action conditions can refer to Figure 8 shown.

[0168] For example, for the first half-wave short window positive action condition, the first half-wave short window includes 6 sets of voltage and current sampling values. If the number of sampling points in the first half-wave short window where △u0△i0<0 is ≥6, the first half-wave short window positive action condition is met. If the number of sampling points in the first half-wave short window where △u0△i0<0 is ≥5, and the number of sampling points where △u0△i0>0 is equal to 5, the first half-wave short window positive action condition is met.

[0169] For another example, for the first half-wavelength window positive action condition, the first half-wavelength short window includes 30 sets of voltage and current sampling values. If the number of sampling points with △u0△i0<0 in the first half-wavelength window is ≥15, and the proportion of sampling points with △u0△i0<0 is ≥0.8, then the first half-wavelength window positive action condition is met.

[0170] Optionally, since the first half-wavelength window is very likely to contain a zero crossing point, in order to prevent inaccurate polarity discrimination caused by zero drift, the following conditions can be added to the discrimination logic of the first half-wavelength window, that is, for the forward action condition of the first half-wavelength window and the reverse action condition of the first half-wavelength window:

[0171] In the first half-wavelength window, the effective value of the fundamental component of the zero-sequence current mutation △I0 is greater than the zero-sequence current threshold value △I 0set’ , and the effective value of the fundamental component of the zero-sequence voltage mutation △U0 is greater than the zero-sequence voltage threshold value △U 0set’ In this embodiment, the zero-sequence current threshold value △I 0set’ and zero-sequence voltage threshold △U 0set’ The value of is not limited.

[0172] The effective value △I0 of the fundamental component of the zero-sequence current mutation and the effective value △U0 of the fundamental component of the zero-sequence voltage mutation can be referred to formula (4).

[0173] Next, the line selection logic within the filtering algorithm data window is explained.

[0174] The fourth sampling data includes Y current filter sampling values ​​of the zero-sequence current sudden change amount filter value and Y voltage filter sampling values ​​of the zero-sequence voltage sudden change amount derivative filter value. Y is the number of sampling points determined according to the sampling frequency of the bandpass filter and the data window of the filtering algorithm.

[0175] Reliable action conditions for filtering algorithms include:

[0176] The number of sampling points where the second product is less than 0 is greater than or equal to the high value of the filtering algorithm action.

[0177] The proportion of the number of sampling points whose second product is less than 0 is greater than or equal to the reverse polarity proportion coefficient of the band-pass filter.

[0178] Unreliable action conditions for the filtering algorithm include:

[0179] The number of sampling points where the second product is less than 0 is greater than or equal to the low value of the filtering algorithm. In addition, the proportion of the sampling points where the second product is less than 0 is greater than or equal to the reverse polarity proportion coefficient of the bandpass filter.

[0180] The second product is the product of the current filtered sampling value and the voltage filtered sampling value corresponding to the current filtered sampling value.

[0181] Optionally, the low value of the filtering algorithm action may be the number of sampling points M determined according to the sampling frequency of the bandpass filter and the first half-wave short window.

[0182] Optionally, the high value of the filtering algorithm action is related to Y. The high value of the filtering algorithm action may be a value obtained by rounding 1 / Y.

[0183] For example, Figure 9 Schematic diagram of the line selection logic within the filtering algorithm data window provided by an embodiment of the present invention. Figure 9 In the example, the second product is expressed as d△u0 / dt_F*△i0_F, where d△u0 / dt_F represents the voltage filter sample value corresponding to the derivative filter value of the zero-sequence voltage mutation d△u0(t) / dt_F (also denoted as d△u0(n) / dt_F), and △i0_F represents the current filter sample value corresponding to the zero-sequence current mutation filter value △i0(t)_F (also denoted as △i0(n)_F). The symbol "&" represents an AND relationship. Y = 25, filter algorithm action high value = 12, filter algorithm action low value = 6, and the reverse polarity ratio coefficient of the bandpass filter = 0.59.

[0184] The reliable action conditions of the filtering algorithm and the unreliable action conditions of the filtering algorithm can be found in Figure 9 shown.

[0185] For example, if the filtering algorithm's reliable operation condition includes 25 sets of voltage and current filter sampling values ​​within the filtering algorithm data window, the reliable operation condition is met if the number of sampling points where d△u0 / dt_F*△i0_F < 0 within the filtering algorithm data window is ≥12, and the percentage of sampling points where d△u0 / dt_F*△i0_F < 0 is ≥0.59.

[0186] Next, the line selection logic within one cycle after the low-current line selection is started is explained.

[0187] The first sampling data includes X current sampling values ​​of the instantaneous value of the zero-sequence current mutation and X voltage sampling values ​​of the instantaneous value of the zero-sequence voltage mutation, where X is the number of sampling points determined according to the sampling frequency of the bandpass filter and the period of the cycle.

[0188] Sampling value mutation counting conditions include:

[0189] The first voltage count value is greater than or equal to the first voltage count threshold. Or,

[0190] The first voltage count value is greater than or equal to the second voltage count threshold, and the first current count value is greater than or equal to the first current count threshold.

[0191] The first voltage count threshold is greater than the second voltage count threshold. The first voltage count value is the number of voltage sampling values ​​greater than the voltage threshold among X voltage sampling values, and the voltage threshold is related to the secondary voltage rating of the system. The first current count value is the number of current sampling values ​​greater than the current threshold among X current sampling values, and the current threshold is related to the secondary current rating of the system.

[0192] For example, Figure 10A schematic diagram of the line selection logic within one cycle after the low current line selection is started provided by an embodiment of the present invention. Figure 10 In the equation, the symbol “≥” indicates an or relationship. △u0 indicates the voltage sampling value corresponding to the instantaneous value of the zero-sequence voltage mutation △u0(t), which can also be recorded as △u0(n). △i0 indicates the current sampling value corresponding to the instantaneous value of the zero-sequence current mutation △i0(t), which can also be recorded as △i0(n). U n Indicates the secondary rated value of the system voltage, I n Indicates the secondary rated value of the system current. First voltage count threshold = 90, second voltage count threshold = 54, first current count threshold = 42. Voltage threshold = 0.03U n , current threshold = 0.04I n .

[0193] exist Figure 10 After the medium and small current line selection is started, 240 sets of voltage sampling values ​​and current sampling values ​​are included in one cycle. If △u0>0.03U n If the first voltage count value of ≥90, the sampling value mutation count condition is met. n The first voltage count value is ≥54, and △i0>0.04I n If the first current count value is ≥42, the sampling value mutation count condition is met.

[0194] Optionally, in S707, judging whether to perform the line selection action according to the first result, the second result, the third result, the fourth result, the fifth result, and the sixth result may include:

[0195] Obtain a seventh result according to the second result, the third result, the fourth result, the fifth result, and the sixth result;

[0196] Whether to execute the line selection action is determined according to the first result and the seventh result.

[0197] For example, Figure 11 This is a schematic diagram of the integrated line selection logic provided by an embodiment of the present invention, illustrating the line selection action conditions. When the line selection action conditions are met, the line selection action is executed. The symbol "&" represents an AND relationship, and the symbol "≥" represents an OR relationship.

[0198] The technical effects of the low-current line selection method provided by the present invention are described below.

[0199] For example, Figure 12 The diagram of the main wiring of the RTDS dynamic model system provided by the embodiment of the present invention is shown in FIG. The real-time digital simulation system RTDS, system version 4.007.4, is used to simulate and test the method of the present invention. Figure 12As shown in the simulation model, S represents the 110 kV equivalent power source. The secondary 35 kV busbar of main transformer T has three outgoing lines: branch 01, branch 02, and branch 03. K1 represents the fault point on the busbar, and K2 through K7 represent the fault points at the beginning, midpoint, and end of each branch. The busbar voltage is measured from the voltage transformer PT. Circuit breakers SK1 through SK3 measure the current from current transformers CT1 through CT3, respectively. R represents resistance, and L represents inductance. When the neutral point is ungrounded, both circuit breakers SKA and SKB are open. When the neutral point is grounded via an arc suppression coil, circuit breaker SKA is open and circuit breaker SKB is closed. A protective device is installed on branch 01. The protective device determines when line selection is to be executed.

[0200] The system parameters are set as follows: the short-circuit capacity of the equivalent infinite power source S is 500MVA, the capacity of the transformer T is 10MVA, the transformation ratio is 115kV / 36.5kV, the secondary neutral point grounding resistance is 1000Ω, the grounding inductance is 28.66H, the line positive-sequence resistance is 0.1Ω / km, the line positive-sequence inductance is 0.4Ω / km, the line positive-sequence capacitive reactance is 0.33052MΩ*km, the line zero-sequence resistance is 0.5Ω / km, the line zero-sequence inductance is 1.2Ω / km, the line zero-sequence capacitive reactance is 0.4863MΩ*km, and the lengths of branches 01 to 03 are 20km, 15km, and 10km, respectively.

[0201] Table 2 Summary of dynamic model test line selection results

[0202]

[0203] Table 2 summarizes the line selection results under various simulated operating conditions. It can be seen that the low-current line selection method provided by the present invention can reliably operate for in-zone faults and reliably remain inoperative for out-of-zone faults. This verifies the adaptability and reliability of the low-current line selection method provided by the present invention.

[0204] Taking the case of a ground fault at K3 in a neutral point ungrounded system with a 1000Ω transition resistance as an example, the simulation data is analyzed. Figure 13A As shown in , the solid line represents the original waveform of the instantaneous value of zero-sequence voltage u0(t), and the dotted line represents the original waveform of the instantaneous value of zero-sequence current i0(t). Figure 13B As shown, the solid line represents the waveform of the derivative filtered value of the zero-sequence voltage mutation d△u0(t) / dt_F, and the dotted line represents the waveform of the zero-sequence current mutation filtered value △i0(t)_F.

[0205] according to Figure 13A and Figure 13BIt can be concluded that: within the first half-wave short window after the fault is started (the number of sampling points with △u0(n)△i0(n)<0) = 5; (the number of sampling points with △u0(n)△i0(n)>0) = 0; within the first half-wavelength window (the number of sampling points with △u0(n)△i0(n)<0) = 29; within the filtering algorithm data window (the number of sampling points with d△u0(n) / dt_F*△i0(n)_F<0) = 25; within the data window of one cycle after startup (the number of sampling points with △u0(n)>0.03Un) = 235; within the data window of one cycle after startup (the number of sampling points with △i0(n)>0.04In) = 191. Figures 8 to 11 It can be seen from the line selection logic diagram that the line selection action conditions are met.

[0206] Figure 14 This is a schematic diagram of the structure of the low current line selection device provided by the embodiment of the present invention. Figure 14 As shown, the low-current line selection device provided in this embodiment may include a processor 1402, a memory 1404, and a communication interface 1403 connected to a system bus 1401. The processor 1402 is used to provide computing and control capabilities. The memory 1404 includes a non-volatile storage medium and an internal memory. The non-volatile storage medium stores an operating system and a computer program. The internal memory provides an environment for the operation of the operating system and the computer program in the non-volatile storage medium. The communication interface 1403 of the detection device is used to communicate with other devices. When the computer program is executed by the processor 1402, the low-current line selection method provided by the present invention is implemented.

[0207] Those skilled in the art will understand that Figure 14 The structure shown in the figure is only a block diagram of a part of the structure related to the scheme of the present application, and does not constitute a limitation on the small current line selection device provided by the present application. The specific detection device may include more or fewer components than shown in the figure, or combine certain components, or have a different component arrangement.

[0208] It should be clear that the process of executing the computer program by the processor in the embodiment of the present application is consistent with the execution process of each step in the above method. For details, please refer to the description above.

[0209] In one embodiment, a computer-readable storage medium is provided, on which a computer program is stored. When the computer program is executed by a processor, the low-current line selection method provided in the above method embodiment of the present application can be implemented.

[0210] Those skilled in the art will appreciate that all or part of the processes in the above-mentioned embodiments can be implemented by instructing the relevant hardware through a computer program. The computer program can be stored in a non-volatile computer-readable storage medium. When the computer program is executed, it can include the processes of the embodiments of the above-mentioned methods. Among them, any reference to memory, storage, database or other media used in the embodiments provided in this application can include non-volatile and / or volatile memory. Non-volatile memory can include read-only memory (ROM), programmable ROM (PROM), electrically programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM) or flash memory. Volatile memory can include random access memory (RAM) or external cache memory. By way of illustration and not limitation, RAM is available in various forms, such as static RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), double data rate SDRAM (DDRSDRAM), enhanced SDRAM (ESDRAM), synchronous link (Synchlink) DRAM (SLDRAM), memory bus (Rambus) direct RAM (RDRAM), direct memory bus dynamic RAM (DRDRAM), and memory bus dynamic RAM (RDRAM).

[0211] The technical features of the above embodiments can be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0212] The above-described embodiments merely represent several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art could make various modifications and improvements without departing from the spirit of the present application, all of which fall within the scope of protection of the present application. Therefore, the scope of protection of the present patent application shall be determined by the appended claims.

Claims

1. A low current line selection method, characterized in that: include: Obtain the instantaneous values ​​of the three-phase current and three-phase voltage of the line; Determine the instantaneous value of the zero-sequence current mutation amount according to the instantaneous value of the three-phase current, and determine the instantaneous value of the zero-sequence voltage mutation amount according to the instantaneous value of the three-phase voltage; If it is determined that the start-up condition for small current line selection is met based on the instantaneous value of the zero-sequence current mutation and the instantaneous value of the zero-sequence voltage mutation, the derivative value of the zero-sequence voltage mutation and the instantaneous value of the zero-sequence current mutation are respectively input into a band-pass filter to obtain a zero-sequence voltage mutation derivative filtered value and a zero-sequence current mutation filtered value; the derivative value of the zero-sequence voltage mutation is the value of the instantaneous value of the zero-sequence voltage mutation after first-order difference; Obtain first sampling data of the instantaneous value of the zero-sequence current mutation and the instantaneous value of the zero-sequence voltage mutation within one cycle after the small current line selection is started, second sampling data within the first half-wave short window after the small current line selection is started, and third sampling data within the first half-wavelength window after the small current line selection is started, and obtain fourth sampling data of the derivative filtered value of the zero-sequence voltage mutation and the filtered value of the zero-sequence current mutation within the filtering algorithm data window; wherein the first half-wave short window, the first half-wavelength window, and the filtering algorithm data window are all related to the duration of the first half-wave; Determining whether to perform a line selection action according to the first sampling data, the second sampling data, the third sampling data, and the fourth sampling data includes: Obtaining a first result according to whether the first sampling data satisfies a sampling value mutation counting condition; Obtaining a second result according to whether the second sampling data satisfies the first half-wave short window forward action condition; obtaining a third result according to whether the third sampling data satisfies the first half-wavelength window forward action condition; According to whether the second sampling data and the third sampling data meet the first half-wave reverse action condition, the first half-wave reverse action condition is obtained. Four results; obtaining a fifth result according to whether the fourth sampling data satisfies a reliable operation condition of the filtering algorithm; obtaining a sixth result according to whether the fourth sampling data satisfies an unreliable action condition of the filtering algorithm; Whether to execute the line selection action is determined according to the first result, the second result, the third result, the fourth result, the fifth result, and the sixth result.

2. The method according to claim 1, characterized in that The bandpass filter adopts a 6th-order Chebyshev II type digital bandpass filter, the cutoff frequencies of the bandpass filter include 300 Hz and 1500 Hz, and the sampling frequency is 12 kHz.

3. The method according to claim 1, characterized in that The reverse polarity ratio coefficient of the bandpass filter is 0.

59.

4. The method according to claim 1, wherein The first half-wave short window is the first 1 / 40 length of the cycle, the first half-wavelength window is the first 1 / 8 length of the cycle, and the filtering algorithm data window is the remaining length after subtracting the first half-wave short window from the first half-wavelength window.

5. The method according to any one of claims 1 to 4, characterized in that The determining whether to execute the line selection action according to the first sampling data, the second sampling data, the third sampling data, and the fourth sampling data includes: Obtaining a first result according to whether the first sampling data satisfies a sampling value mutation counting condition; obtaining a second result according to whether the second sampling data satisfies a first half-wave short window forward action condition; Obtaining a third result according to whether the third sampling data satisfies a first half-wavelength window forward action condition; obtaining a fourth result according to whether the second sampling data and the third sampling data satisfy a first half-wave reverse action condition; obtaining a fifth result according to whether the fourth sampling data satisfies a reliable operation condition of the filtering algorithm; obtaining a sixth result according to whether the fourth sampling data satisfies an unreliable action condition of the filtering algorithm; Whether to execute a line selection action is determined according to the first result, the second result, the third result, the fourth result, the fifth result, and the sixth result.

6. The method according to claim 5, characterized in that The first sampling data includes X current sampling values ​​of the instantaneous value of the zero-sequence current mutation and X voltage sampling values ​​of the instantaneous value of the zero-sequence voltage mutation; X is the number of sampling points determined according to the sampling frequency of the bandpass filter and the period of the cycle; The sampling value mutation counting conditions include: The first voltage count value is greater than or equal to the first voltage count threshold; or, The first voltage count value is greater than or equal to a second voltage count threshold, and the first current count value is greater than or equal to a first current count threshold; The first voltage count threshold is greater than the second voltage count threshold; the first voltage count value is the number of voltage sampling values ​​greater than the voltage threshold among the X voltage sampling values, and the voltage threshold is related to the secondary rated value of the system voltage; the first current count value is the number of current sampling values ​​greater than the current threshold among the X current sampling values, and the current threshold is related to the secondary rated value of the system current.

7. The method according to claim 5, characterized in that The second sampling data includes M current sampling values ​​and M voltage sampling values ​​within the first half-wave short window, where M is the number of sampling points determined according to the sampling frequency of the bandpass filter and the first half-wave short window; The third sampling data includes N current sampling values ​​and N voltage sampling values ​​within the first half-wavelength window, where N is the number of sampling points determined according to the sampling frequency of the bandpass filter and the first half-wavelength window; The positive action condition of the first half-wave short window includes: within the first half-wave short window, The number of sampling points whose first product is less than 0 is greater than or equal to M; or, The number of sampling points where the first product is less than 0 is greater than or equal to M-1, and the number of sampling points where the first product is greater than 0 is equal to 0; The forward action condition of the first half-wavelength window includes: within the first half-wavelength window, The number of sampling points where the first product is less than 0 is greater than or equal to the first product threshold; and The proportion of sampling points whose first product is less than 0 is greater than or equal to the first proportion threshold; The first half-wave reverse action condition includes the first half-wave short window reverse action condition or the first half-wave wavelength window reverse action condition; The reverse action condition of the first half-wave short window includes: within the first half-wave short window, The number of sampling points where the first product is greater than 0 is greater than or equal to M; or, The number of sampling points where the first product is greater than 0 is greater than or equal to M-1, and the number of sampling points where the first product is less than 0 is equal to 0; The reverse action condition of the first half-wavelength window includes: within the first half-wavelength window, The number of sampling points where the first product is greater than 0 is greater than or equal to the first product threshold; and The proportion of sampling points whose first product is greater than 0 is greater than or equal to the first proportion threshold; The first product is the product of the current sampling value and the voltage sampling value corresponding to the current sampling value.

8. The method according to claim 5, characterized in that The fourth sampling data includes Y current filtering sampling values ​​of the zero-sequence current mutation amount filtering value and Y voltage filtering sampling values ​​of the zero-sequence voltage mutation amount derivative filtering value; Y is the number of sampling points determined according to the sampling frequency of the bandpass filter and the filtering algorithm data window; The reliable operation conditions of the filtering algorithm include: The number of sampling points where the second product is less than 0 is greater than or equal to the high value of the filtering algorithm action; and The proportion of the sampling points where the second product is less than 0 is greater than or equal to the reverse polarity proportion coefficient of the band-pass filter; The unreliable action conditions of the filtering algorithm include: The number of sampling points where the second product is less than 0 is greater than or equal to the low value of the filtering algorithm action; and The second product is the product of the current filtering sampling value and the voltage filtering sampling value corresponding to the current filtering sampling value.

9. A low current line selection device, characterized in that: include: A memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the method according to any one of claims 1 to 8 when executing the computer program.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the method according to any one of claims 1 to 8 is implemented.

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