Traveling wave switch based on a secondary fusion on-column switch and application thereof

Abstract

The application discloses a design and application of a traveling wave type switch of a primary and secondary fusion pole switch, relates to the technical field of power distribution network fault positioning, and the current sensor built in the traveling wave type switch is connected with a traveling wave current sensor, the output end of the voltage sensor built in the traveling wave type switch is connected with a voltage traveling wave sampling circuit, and a traveling wave processing module is built in the power distribution terminal of the traveling wave type switch; the traveling wave current sensor and the voltage traveling wave sampling circuit adopt coaxial cables; the traveling wave current sensor is used for collecting traveling wave current data, the voltage traveling wave sampling circuit is used for collecting traveling wave voltage data, and the traveling wave processing module is used for processing the traveling wave current data and the traveling wave voltage data, so that the problem that the current primary and secondary fusion pole switch cannot effectively capture the traveling wave high-frequency component generated by a fault and leads to a large positioning error is solved.

Description

Technical Field

[0001] This invention relates to the field of distribution network fault location technology, specifically to the design and application of a traveling wave switch based on a primary and secondary integrated pole-mounted switch. Background Technology

[0002] The integrated primary and secondary pole-mounted switch possesses high-precision fault diagnosis capabilities, accurately identifying fault types and automatically isolating faults when necessary to ensure uninterrupted power supply to non-faulty areas, thereby improving power supply reliability. Currently, integrated primary and secondary pole-mounted switches typically collect information such as current, voltage, and traveling wave data, and use methods like traveling wave localization for fault detection and location.

[0003] However, the transient traveling wave signal of a single-phase ground fault has a duration in milliseconds and a high frequency in MHz. The current sensor built into the primary and secondary fusion pole-mounted switch usually adopts a traditional electromagnetic current sensor, whose frequency response range is usually limited to the power frequency (50 / 60Hz). The response to high frequency signals above several kilohertz is significantly attenuated, which makes it impossible to accurately detect the high frequency component of the traveling wave (usually in the kHz to MHz range), resulting in a large positioning error. Summary of the Invention

[0004] To address the problem that current integrated primary and secondary pole-mounted switches cannot effectively capture the high-frequency components of traveling waves generated by faults, leading to large positioning errors, this invention provides a traveling wave type switch based on an integrated primary and secondary pole-mounted switch. The traveling wave type switch has a built-in current sensor connected to a traveling wave current sensor, and the output terminal of a built-in voltage sensor connected to a voltage traveling wave sampling circuit. The power distribution terminal of the traveling wave type switch has a built-in traveling wave processing module. The traveling wave current sensor and the voltage traveling wave sampling circuit use a coaxial cable. The traveling wave current sensor is used to collect traveling wave current data, the voltage traveling wave sampling circuit is used to collect traveling wave voltage data, and the traveling wave processing module is used to process the traveling wave current data and the traveling wave voltage data.

[0005] A high-frequency current sensor is designed inside the primary and secondary fusion pole. This sensor has high-frequency characteristics and can effectively capture the high-frequency components of the traveling wave generated by the fault. At the same time, it can transmit the traveling wave current signal to the acquisition circuit according to a certain ratio. Proportional transmission results in smaller data volume and faster acquisition speed. A high-pass filter sampling circuit is connected in series at the lower end of the primary and secondary fusion pole voltage sensor. A hardware differentiating circuit with a specific frequency bandwidth is selected to extract the fault feature signal with high fidelity. This circuit can filter out the line power frequency signal and amplify the high-frequency feature signal to accurately obtain the fault signal on the line. The traveling wave voltage and traveling wave current signals are led out with coaxial cables to reduce interference during signal transmission. The traveling wave processing module is built into the distribution terminal. After filtering and sampling the traveling wave voltage and traveling wave current signals, more accurate distribution network data is obtained, thereby reducing the location error. Combined with the traveling wave positioning method, the accurate fault location is obtained.

[0006] Currently, the zero-sequence voltage and current threshold method is commonly used to identify ground faults. However, in the case of high-resistance ground faults, the current may be as low as milliamperes, which can be drowned out by noise. In the early stages of a fault, before the circuit breaker trips, no obvious zero-sequence path is formed at the fault point, and the zero-sequence voltage rises slowly. This means that only after the upstream circuit breaker trips will obvious zero-sequence characteristics (such as a sudden increase in zero-sequence voltage and current) form downstream of the fault point, at which point the fault location can be determined. Furthermore, the above method has a simple judgment logic, usually using voltage and current to obtain the direction of zero-sequence power. The direction of the fault is determined solely by the direction of zero-sequence power. Single-point direction determination can only roughly determine that the fault is downstream, but it cannot distinguish the specific location in multiple downstream sections. For example, if a 10kV line has 5 sectionalizing switches, the above method can only determine that the fault is downstream of the tripped circuit breaker, but it cannot identify whether the fault is in the 2nd or 3rd section.

[0007] To address the issue that the aforementioned methods rely on circuit breaker tripping and can only determine that the fault is downstream of the circuit breaker, failing to achieve precise section location, this invention utilizes a traveling wave switch combined with a ground fault location method to solve the above problem. The method is based on a traveling wave switch with integrated primary and secondary pole-mounted switches, collecting distribution network data and impedance frequency curves of the lines under fault-free conditions from each section switch. The distribution network data includes zero-sequence voltage, zero-sequence current, transient current, and transient traveling wave.

[0008] Based on the zero-sequence voltage and the zero-sequence current, the steady-state zero-sequence component is obtained;

[0009] Based on the transient traveling wave, the transient traveling wave characteristics and the arrival time of the traveling wave front are obtained;

[0010] Based on the impedance frequency curve, the impedance trajectory offset under fault conditions is obtained.

[0011] The fault point is obtained based on the steady-state zero-sequence component, the arrival time of the traveling wave front, and the impedance trajectory offset.

[0012] A composite feature system combining transient high-frequency traveling wave, steady-state zero-sequence component, and impedance characteristics is constructed. Utilizing the high-frequency component (1-50kHz) of the traveling wave generated instantaneously during a ground fault, wavelet transform is used to extract characteristic parameters such as the arrival time and polarity of the traveling wave front. This allows for the capture of initial fault characteristics without circuit breaker operation, improving response speed. Each section switch records the impedance-frequency curve under normal line conditions. During a fault, the impedance trajectory offset is calculated in real time, enabling autonomous positioning at the equipment end. This eliminates dependence on information from upstream circuit breakers. Furthermore, a two-dimensional spatiotemporal positioning method is employed: a time dimension recording the arrival timestamp of the transient traveling wave, and a spatial dimension acquiring the line impedance spectrum. Real-time comparison of impedance trajectory offsets before and after the fault is performed. By integrating transient high-frequency traveling wave signals and steady-state zero-sequence components, transient traveling wave time difference positioning and impedance spectrum spatial positioning are achieved. This spatiotemporal joint positioning results in higher accuracy. Combined with topological relationships, precise section-level positioning is achieved. Moreover, through impedance spectrum mutation analysis and traveling wave time sequence fusion, autonomous positioning without upstream switch operation is realized, solving the positioning problem when no circuit breaker operation is required.

[0013] Furthermore, the specific steps for obtaining the fault point include:

[0014] The time difference of arrival of the traveling wave is obtained based on the arrival time of the traveling wave front and the preset arrival time;

[0015] If the arrival time difference of the traveling wave is less than a first preset threshold and the impedance trajectory offset is greater than a second preset threshold, then several abnormal switches are obtained based on the segmented switch.

[0016] Based on the line topology diagram, obtain a number of first switches adjacent to the abnormal switch;

[0017] First data is obtained by acquiring the distribution network data of each of the first switches, and first traveling wave arrival time, first zero-sequence power direction and first impedance change frequency band are obtained based on the first data;

[0018] The distribution network data of each abnormal switch is obtained to obtain second data, and the second traveling wave arrival time, the second zero-sequence power direction, and the second impedance change frequency band are obtained based on the second data;

[0019] Based on the arrival time of the first traveling wave and the arrival time of the second traveling wave, the arrival time sequence of the traveling wave is obtained, and based on the arrival time sequence of the traveling wave, the first zero-sequence power direction and the second zero-sequence power direction, the fault direction is obtained;

[0020] The fault point is obtained based on the first impedance change frequency band, the second impedance change frequency band, and the fault direction.

[0021] A two-level decision-making mechanism is constructed, consisting of local rapid judgment and interactive verification with adjacent terminals. Each switch has a built-in fault feature rapid matching engine. Abnormal switches are marked by traveling wave arrival time difference and impedance trajectory offset to complete the initial judgment. Through a preset line topology diagram, adjacent terminals are initiated for collaborative verification. In the transient stage, the fault direction is initially determined by the traveling wave arrival time sequence. In the steady-state stage, the fault direction is verified by the zero-sequence power direction and the consistency of electrical quantities is checked. In the confirmation stage, the topology verification is completed by the interaction information of adjacent switches, thereby achieving accurate section location.

[0022] Furthermore, the specific steps for obtaining the impedance change frequency band include:

[0023] A sinusoidal sweep frequency signal is injected into the first switch, and the first voltage and first current of the first switch are collected. The steady-state zero-sequence impedance at different frequency points is obtained based on the first voltage and the first current. An impedance spectrum is generated based on the steady-state zero-sequence impedance.

[0024] Based on the impedance spectrum, the impedance mutation factor at different frequency points is calculated, and several abnormal mutation points are obtained based on the impedance mutation factor.

[0025] Cluster the abnormal mutation points to obtain several abnormal frequency bands, obtain several spacings of the abnormal frequency bands, obtain the abnormal frequency band corresponding to the largest spacing, and obtain the impedance mutation frequency band.

[0026] When a ground fault occurs on a line, the impedance characteristics upstream and downstream of the fault point show significant differences. The upstream section exhibits power supply-side impedance characteristics (low impedance state), while the downstream section exhibits load-side impedance characteristics (high impedance state). At the fault point, the impedance trajectory undergoes abrupt changes in a specific frequency band. This invention injects a sinusoidal sweep frequency signal, synchronously measures the voltage / current response, calculates the impedance at each frequency point, generates the current impedance spectrum, calculates the impedance abrupt change factor using a sliding window differential, obtains abnormal abrupt change points, clusters them, aggregates them into continuous frequency bands, and selects the frequency band corresponding to the largest inter-cluster spacing as the effective abrupt change frequency band. This can reduce misjudgment of isolated abrupt change points caused by random noise, improve reliability, and the frequency band range is related to the fault distance (high-frequency attenuation characteristics), providing a basis for spatial positioning.

[0027] Furthermore, the formula for calculating the impedance mutation factor is:

[0028] ;

[0029] ;

[0030] in, Indicates the impedance mutation factor. Indicates the window width. Represents frequency The impedance offset, Indicates the position number of the frequency point within the window. Indicates the frequency point number. This represents the impedance spectrum under fault conditions. This represents the impedance spectrum under normal conditions. Indicates the high-frequency attenuation coefficient. express The frequency of the position.

[0031] Furthermore, the specific steps for obtaining several anomalous mutation points include:

[0032] Obtain the ratio of the impedance abrupt change factor at the current frequency point to that at the previous frequency point;

[0033] If the impedance mutation factor is greater than a third preset threshold and the ratio is greater than a fourth preset threshold;

[0034] The current frequency point is then marked as the abnormal mutation point.

[0035] The criteria for determining the sudden change point are set. The impedance sudden change caused by the fault has a steep leading edge characteristic. Its rate of change is much higher than that of normal operating condition fluctuations. It generates an impedance step response in a specific frequency band. The impedance sudden change factor is greater than the third preset threshold to ensure that the sudden change intensity exceeds the background noise and achieves effective differentiation. The ratio is greater than the fourth preset threshold to filter out slowly changing interference.

[0036] Furthermore, the specific steps for obtaining the fault point based on the first impedance change frequency band, the second impedance change frequency band, and the fault direction include:

[0037] If the first impedance change frequency band and the second impedance change frequency band have overlapping frequency bands, then obtain the switches corresponding to the first impedance change frequency band and the second impedance change frequency band, and obtain the first fault switch and the second fault switch respectively.

[0038] The time difference is obtained based on the arrival times of the traveling waves of the first fault switch and the second fault switch;

[0039] The distance difference is obtained based on the time difference and the traveling wave propagation speed;

[0040] The fault point is obtained based on the second fault switch, the fault direction, and the distance difference.

[0041] The spatial positioning cross-verification mechanism integrates the spatial distribution of impedance mutations and the time difference of traveling waves to achieve cross-verification of dual physical quantities. The frequency band of impedance mutation determines the fault boundary. That is, if two adjacent terminals detect overlapping frequency bands of mutation, the fault is located between the two. The distance difference is calculated by using the time difference of traveling waves and combined with the fault direction to achieve accurate positioning.

[0042] Furthermore, the specific steps for obtaining the arrival time of the traveling wavefront include:

[0043] S1. Based on wavelet transform, calculate the wavelet transform coefficients of each sampling point of the transient traveling wave; calculate the modulus maxima of the wavelet transform coefficients, and obtain several candidate wavefronts based on the modulus maxima;

[0044] S2. Obtain the first waveform within the time window based on the candidate wavefront, obtain the correlation coefficient based on the first waveform and the standard wavefront template, and obtain the peak-to-peak value based on the first waveform;

[0045] S3. If the correlation coefficient is greater than the fifth preset threshold and the peak-to-peak value is greater than the sixth preset threshold, then obtain the candidate wavefront to obtain a valid wavefront, obtain the arrival time of the valid wavefront, and obtain the arrival time of the traveling wavefront; otherwise, mark the candidate wavefront as noise, return to S2, and update the next candidate wavefront of the candidate wavefront to the candidate wavefront.

[0046] By calculating the modulus maxima for each sampling point using wavelet transform, points that meet the threshold condition are marked as candidate wavefronts. Combined with time window correlation verification, the system distinguishes between real fault traveling waves and noise pulses, enhances anti-interference capabilities, obtains effective wavefronts, and improves positioning accuracy.

[0047] Furthermore, before performing S2, the method further includes:

[0048] Based on the candidate wavefront, a preset number of sampling points are obtained, and several verification points are obtained. The polarity of each verification point is obtained. If the polarities are different, the candidate wavefront is deleted, and the process returns to S1, where the next candidate wavefront is updated to the candidate wavefront.

[0049] Polarity verification requires that a preset number of sampling points before and after the wavefront maintain the same polarity to eliminate oscillation interference.

[0050] Furthermore, each segment switch is equipped with a smart terminal unit, which is used to collect the power distribution network data and the impedance frequency curve.

[0051] The IEDs deployed in each sectionalizing switch integrate a high-frequency signal acquisition module, which can acquire the high-frequency components of traveling waves.

[0052] One or more technical solutions provided by this invention have at least the following technical effects or advantages:

[0053] 1. A high-frequency current sensor is designed inside the primary and secondary fusion pole. This sensor has high-frequency characteristics and can effectively capture the high-frequency components of the traveling wave generated by the fault. At the same time, it can transmit the traveling wave current signal to the acquisition circuit according to a certain ratio. Proportional transmission results in smaller data volume and faster acquisition speed. A high-pass filter sampling circuit is connected in series at the lower end of the primary and secondary fusion pole voltage sensor. A hardware differentiating circuit with a specific frequency bandwidth is selected to extract the fault feature signal with high fidelity. This circuit can filter out the line power frequency signal and amplify the high-frequency feature signal to accurately obtain the fault signal on the line. The traveling wave voltage and traveling wave current signals are led out with coaxial cables to reduce interference during signal transmission. The traveling wave processing module is built into the distribution terminal. After filtering and sampling the traveling wave voltage and traveling wave current signals, more accurate distribution network data is obtained, thereby reducing the location error. Combined with the traveling wave positioning method, the accurate fault location is obtained.

[0054] 2. A composite feature system is constructed, consisting of transient high-frequency traveling wave, steady-state zero-sequence component, and impedance characteristics. Utilizing the high-frequency component (1-50kHz) of the traveling wave generated instantaneously during a ground fault, wavelet transform is used to extract characteristic parameters such as the arrival time and polarity of the traveling wavefront. This allows for the capture of initial fault characteristics without circuit breaker operation, improving response speed. Each section switch records the impedance-frequency curve under normal line conditions. During a fault, the impedance trajectory offset is calculated in real time, enabling autonomous positioning at the equipment end. This eliminates dependence on information from upstream circuit breakers. Positioning is achieved using a two-dimensional spatiotemporal approach: a time dimension recording the arrival timestamp of the transient traveling wave, and a spatial dimension acquiring the line impedance spectrum. Real-time comparison of impedance trajectory offsets before and after the fault is performed. By integrating transient high-frequency traveling wave signals and steady-state zero-sequence components, transient traveling wave time difference positioning and impedance spectrum spatial positioning are achieved. This spatiotemporal joint positioning results in higher accuracy. Combined with topological relationships, precise section-level positioning is achieved. Furthermore, through impedance spectrum mutation analysis and traveling wave time sequence fusion, autonomous positioning without upstream switch operation is realized, solving the positioning problem when no circuit breaker operation is required.

[0055] 3. Construct a two-level decision-making mechanism of local rapid judgment + adjacent terminal interactive verification. Each switch has a built-in fault feature rapid matching engine. Abnormal switches are marked by traveling wave arrival time difference and impedance trajectory offset to complete the initial judgment. Adjacent terminal collaborative verification is initiated by using a preset line topology diagram. In the transient stage, the fault direction is initially judged by the traveling wave arrival time sequence. In the steady state stage, the fault direction is verified by the zero-sequence power direction and the electrical quantity consistency is checked. In the confirmation stage, the topology verification is completed by the interaction information of adjacent switches, thereby achieving accurate section location.

[0056] 4. Inject a sinusoidal sweep frequency signal, synchronously measure the voltage / current response, calculate the impedance at each frequency point, generate the current impedance spectrum, calculate the impedance mutation factor using a sliding window differential, obtain abnormal mutation points, cluster them, aggregate them into continuous frequency bands, select the frequency band corresponding to the largest inter-class spacing as the effective mutation frequency band, which can reduce the misjudgment of isolated mutation points caused by random noise, improve reliability, and the frequency band range is related to the fault distance (high frequency attenuation characteristics), providing a basis for spatial positioning.

[0057] 5. Set the criteria for determining the sudden change point. The impedance sudden change caused by the fault has a steep leading edge characteristic. Its rate of change is much higher than that of normal operating condition fluctuations. It generates an impedance step response in a specific frequency band. The impedance sudden change factor is greater than the third preset threshold to ensure that the sudden change intensity exceeds the background noise and achieves effective differentiation. The ratio is greater than the fourth preset threshold to filter out slowly changing interference.

[0058] 6. Spatial positioning cross-verification mechanism: It integrates the spatial distribution of impedance mutation and the time difference of traveling wave to achieve cross-verification of dual physical quantities. The frequency band of impedance mutation determines the fault boundary. That is, if two adjacent terminals detect overlapping frequency bands of mutation, the fault is located between the two. The distance difference is calculated by using the time difference of traveling wave propagation, and the fault direction is combined to achieve accurate positioning.

[0059] 7. The modulus maxima are calculated for each sampling point by wavelet transform. Points that meet the threshold condition are marked as candidate wavefronts. Combined with time window correlation verification, the actual fault traveling wave is distinguished from noise pulses, which enhances anti-interference, obtains effective wavefronts, and improves positioning accuracy. Attached Figure Description

[0060] The accompanying drawings, which are provided to further illustrate embodiments of the invention and constitute a part of this invention, are not intended to limit the scope of the invention.

[0061] Figure 1 This is a schematic diagram of the traveling wave switch in this invention, wherein A, B, and C represent any one of the three phases, Ia, Ib, and Ic represent the currents of phases A, B, and C in the current sensor, Iax, Ibx, and Icx represent the currents of phases A, B, and C in the traveling wave current sensor, In and Inx represent the currents of the current sensor and the traveling wave current sensor, respectively, Ua, Ub, and Uc represent the voltages of phases A, B, and C in the voltage sensor, and Uax, Ubx, and Ucx represent the voltages of phases A, B, and C in the voltage traveling wave sampling circuit.

[0062] Figure 2 This is a flowchart illustrating a grounding fault location method according to the present invention;

[0063] Among them, 1-traveling wave switch, 2-current sensor, 3-traveling wave current sensor, 4-power distribution terminal, 5-traveling wave processing module, 6-voltage sensor, 7-voltage traveling wave sampling circuit, and 8-coaxial cable. Detailed Implementation

[0064] To better understand the above-mentioned objectives, features, and advantages of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that, where there is no conflict, the embodiments of the present invention and the features thereof can be combined with each other.

[0065] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and therefore the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0066] Example 1

[0067] refer to Figure 1 This embodiment provides a traveling wave switch based on a primary and secondary fusion pole-mounted switch. The current sensor 2 built into the traveling wave switch 1 is connected to the traveling wave current sensor 3. The output terminal of the voltage sensor 6 built into the traveling wave switch 1 is connected to the voltage traveling wave sampling circuit 7. If a hardware differentiating circuit with a specific frequency bandwidth is selected, the fault feature signal can be extracted with high fidelity. The power distribution terminal 4 of the traveling wave switch 1 has a built-in traveling wave processing module 5.

[0068] The traveling wave current sensor 3 and the voltage traveling wave sampling circuit 7 adopt coaxial cable 8; the traveling wave signal transmission line adopts coaxial cable 8 and is integrated with the original cable design to achieve the transmission of all relevant signals by one cable, realize the overall design, and make the traveling wave type primary and secondary integrated circuit breaker output by one cable, which is simple in structure and easy to construct.

[0069] The traveling wave current sensor 3 is used to collect traveling wave current data, the voltage traveling wave sampling circuit 7 is used to collect traveling wave voltage data, and the traveling wave processing module 5 is used to process the traveling wave current data and the traveling wave voltage data.

[0070] In this embodiment, the transmission signal line uses a special TNC connector to combine with the aviation plug of the power distribution terminal, and the whole thing is connected to the power distribution terminal with a single cable and a single plug.

[0071] Example 2

[0072] refer to Figure 2Based on Embodiment 1, this embodiment provides a ground fault location method. The method is based on a traveling wave type switch with integrated primary and secondary pole-mounted switches. It collects distribution network data and impedance frequency curves of the line under fault-free conditions from each segment switch. The distribution network data includes zero-sequence voltage, zero-sequence current, high-frequency transient current, and transient traveling wave. Each segment switch is equipped with an intelligent terminal unit (IED) that integrates a high-frequency signal acquisition module (100kHz sampling rate). The intelligent terminal unit is used to collect the distribution network data and the impedance frequency curves.

[0073] Based on the zero-sequence voltage and the zero-sequence current, the steady-state zero-sequence component is obtained;

[0074] Based on the transient traveling wave, the transient traveling wave characteristics and the arrival time of the traveling wave front are obtained;

[0075] Based on the impedance frequency curve, the impedance trajectory offset under fault conditions is obtained.

[0076] The fault point is obtained based on the steady-state zero-sequence component, the arrival time of the traveling wave front, and the impedance trajectory offset.

[0077] In this embodiment, the transient traveling wave characteristics may include relevant data such as polarity, amplitude, and entropy.

[0078] The specific steps for obtaining the fault point include:

[0079] The time difference of arrival of the traveling wave is obtained based on the arrival time of the traveling wave front and the preset arrival time;

[0080] If the arrival time difference of the traveling wave is less than a first preset threshold and the impedance trajectory offset is greater than a second preset threshold, then several abnormal switches are obtained based on the segmented switch.

[0081] Based on the line topology diagram, obtain a number of first switches adjacent to the abnormal switch;

[0082] First data is obtained by acquiring the distribution network data of each of the first switches, and first traveling wave arrival time, first zero-sequence power direction and first impedance change frequency band are obtained based on the first data;

[0083] The distribution network data of each abnormal switch is acquired to obtain second data, and the second traveling wave arrival time, the second zero-sequence power direction, and the second impedance change frequency band are obtained based on the second data; for example, the zero-sequence power direction is obtained according to the steady-state zero-sequence component.

[0084] The arrival time sequence of the traveling wave is obtained based on the arrival time of the first traveling wave and the arrival time of the second traveling wave, and then sorted according to the arrival time.

[0085] The fault direction is obtained based on the traveling wave arrival time, the first zero-sequence power direction, and the second zero-sequence power direction.

[0086] The fault point is obtained based on the first impedance change frequency band, the second impedance change frequency band, and the fault direction.

[0087] The specific steps for obtaining the impedance change frequency band include:

[0088] The first switch is injected with a 0.1-5kHz sinusoidal sweep frequency signal, and the first voltage and first current of the first switch are collected. The steady-state zero-sequence impedance at different frequency points is obtained based on the first voltage and the first current. An impedance spectrum is generated based on the steady-state zero-sequence impedance.

[0089] Based on the impedance spectrum, the impedance mutation factor at different frequency points is calculated, and several abnormal mutation points are obtained based on the impedance mutation factor.

[0090] K-means clustering is performed on the abnormal mutation points to obtain several abnormal frequency bands, several spacings of the abnormal frequency bands are obtained, and the abnormal frequency band corresponding to the largest spacing is obtained to obtain the impedance mutation frequency band.

[0091] The formula for calculating the impedance mutation factor is as follows:

[0092] ;

[0093] ;

[0094] in, Indicates the impedance mutation factor. Indicates the window width. Represents frequency The impedance offset, Indicates the position number of the frequency point within the window. Indicates the frequency point number. This represents the impedance spectrum under fault conditions. This represents the impedance spectrum under normal conditions. Indicates the high-frequency attenuation coefficient. express The frequency of the position.

[0095] The specific steps for obtaining several abnormal mutation points include:

[0096] Obtain the ratio of the impedance jump factor at the current frequency point to that at the previous frequency point, i.e., the ratio = impedance jump factor at the current frequency point / impedance jump factor at the previous frequency point;

[0097] If the impedance mutation factor is greater than a third preset threshold and the ratio is greater than a fourth preset threshold;

[0098] The current frequency point is then marked as the abnormal mutation point.

[0099] The specific steps for obtaining the fault point based on the first impedance change frequency band, the second impedance change frequency band, and the fault direction include:

[0100] If the first impedance change frequency band and the second impedance change frequency band have overlapping frequency bands, then obtain the switches corresponding to the first impedance change frequency band and the second impedance change frequency band, and obtain the first fault switch and the second fault switch respectively.

[0101] The time difference is obtained based on the arrival times of the traveling waves of the first fault switch and the second fault switch;

[0102] The distance difference is obtained based on the time difference and the traveling wave propagation speed;

[0103] The fault point is obtained based on the second fault switch, the fault direction, and the distance difference.

[0104] For example, the outputs of each terminal are shown in Table 1:

[0105] Table 1 Terminal Information Table

[0106] terminal Sudden change frequency band Traveling wave arrival time Zero-sequence power direction A 1.2-1.8kHz t=312.7μs positive B 0.8-1.4kHz t=312.7μs Reverse C No mutation - -

[0107] Intersection of abrupt frequency bands: The intersection of A and B is 1.2-1.4kHz → The fault is between A and B;

[0108] Time difference = 312.7μs - 312.7μs = 160.4μs;

[0109] Distance difference = time difference * traveling wave propagation speed; in this embodiment, the traveling wave propagation speed can be the speed of light * wave speed correction factor;

[0110] Then, the fault direction is determined based on the zero-sequence power direction, and the distance between the fault point and terminal A is the distance difference.

[0111] The specific steps for obtaining the arrival time of the traveling wavefront include:

[0112] S1. Based on wavelet transform, calculate the wavelet transform coefficients of each sampling point of the transient traveling wave; calculate the modulus maxima of the wavelet transform coefficients, and obtain several candidate wavefronts based on the modulus maxima; for example, using db4 wavelet for 6-level decomposition, calculate the modulus maxima at scale s=5, and select points with modulus maxima greater than a preset threshold to obtain candidate wavefronts;

[0113] S2. Based on the candidate wavefront, obtain the first waveform within the time window, use the Pearson correlation coefficient, obtain the correlation coefficient based on the first waveform and the standard wavefront template, and obtain the peak-to-peak value based on the first waveform;

[0114] S3. If the correlation coefficient is greater than the fifth preset threshold and the peak-to-peak value is greater than the sixth preset threshold, then obtain the candidate wavefront to obtain a valid wavefront, obtain the arrival time of the valid wavefront, and obtain the arrival time of the traveling wavefront; otherwise, mark the candidate wavefront as noise, return to S2, and update the next candidate wavefront of the candidate wavefront to the candidate wavefront.

[0115] The method further includes:

[0116] Based on the candidate wavefront, a preset number of sampling points are obtained, such as obtaining 3 sampling points before and after the wavefront, and several verification points are obtained. The polarity of each verification point is obtained. The polarity can be obtained according to the wavelet transform coefficients, and the positive / negative value indicates the polarity of the traveling wave.

[0117] If the polarities are not the same, the candidate wavefront is deleted, and the process returns to step S1, where the next candidate wavefront is updated to the candidate wavefront.

[0118] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of the invention.

[0119] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method of ground fault location, characterized by, The row wave type switch based on a secondary fusion column switch collects power distribution network data and line impedance frequency curves in a non-fault state of each sectional switch, and the power distribution network data includes zero sequence voltage, zero sequence current, transient current and transient row wave; Based on the zero sequence voltage and the zero sequence current, the steady-state zero sequence component is obtained; Based on the transient row wave, the transient row wave characteristic and the row wave head arrival time are obtained; Based on the impedance frequency curve, the impedance trajectory offset in a fault state is obtained; Based on the steady-state zero sequence component, the row wave head arrival time and the impedance trajectory offset, the fault point is obtained; The current sensor in the row wave type switch is connected with the row wave current sensor, the output end of the voltage sensor in the row wave type switch is connected with the voltage row wave sampling circuit, and the row wave processing module is built in the power distribution terminal of the row wave type switch; The row wave current sensor and the voltage row wave sampling circuit adopt coaxial cables; The row wave current sensor is used for collecting row wave current data, the voltage row wave sampling circuit is used for collecting row wave voltage data, and the row wave processing module is used for processing the row wave current data and the row wave voltage data; The specific steps for obtaining the fault point include: Based on the row wave head arrival time and the preset arrival time, the row wave arrival time difference is obtained; If the row wave arrival time difference is less than a first preset threshold value, and the impedance trajectory offset is greater than a second preset threshold value, a plurality of abnormal switches are obtained based on the sectional switches; Based on the line topology graph, a plurality of first switches adjacent to the abnormal switches are obtained; The power distribution network data of each first switch is obtained to obtain first data, and based on the first data, the first row wave arrival time, the first zero sequence power direction and the first impedance mutation frequency range are obtained; The power distribution network data of each abnormal switch is obtained to obtain second data, and based on the second data, the second row wave arrival time, the second zero sequence power direction and the second impedance mutation frequency range are obtained; Based on the first row wave arrival time and the second row wave arrival time, the row wave arrival time sequence is obtained, and based on the row wave arrival time sequence, the first zero sequence power direction and the second zero sequence power direction, the fault direction is obtained; Based on the first impedance mutation frequency range, the second impedance mutation frequency range and the fault direction, the fault point is obtained.

2. The method of claim 1, wherein, The specific steps for obtaining the impedance mutation frequency range include: The first switch injects a sinusoidal sweep signal, the first voltage and the first current of the first switch are collected, the steady-state zero sequence impedance at different frequency points is obtained based on the first voltage and the first current, and the impedance spectrum is generated based on the steady-state zero sequence impedance; The impedance mutation factor at different frequency points is calculated based on the impedance spectrum, and a plurality of abnormal mutation points are obtained based on the impedance mutation factor; The abnormal mutation points are clustered to obtain a plurality of abnormal frequency ranges, a plurality of intervals of the abnormal frequency ranges are obtained, the abnormal frequency range corresponding to the maximum interval is obtained, and the impedance mutation frequency range is obtained.

3. A method of locating a ground fault according to claim 2, wherein, The calculation formula of the impedance mutation factor is: ； ； wherein, denotes the impedance mutation factor, denotes the window width, denotes the frequency of the impedance offset, denotes the position number of the frequency point within the window, denotes the frequency point number, denotes the impedance spectrum in the fault state, denotes the impedance spectrum in the normal state, denotes the high-frequency attenuation coefficient, denotes the frequency of the position.

4. The method of claim 2, wherein, The specific steps for obtaining a plurality of abnormal mutation points include: The ratio of the impedance mutation factor of the current frequency point to the last frequency point is obtained; If the impedance mutation factor is greater than a third preset threshold and the ratio is greater than a fourth preset threshold, the current frequency point is marked as the abnormal mutation point. Based on the first impedance mutation frequency band, the second impedance mutation frequency band and the fault direction, the specific steps of obtaining the fault point include:

5. The method of claim 1, wherein, If the first impedance mutation frequency band and the second impedance mutation frequency band overlap, the switches corresponding to the first impedance mutation frequency band and the second impedance mutation frequency band are obtained, and the first fault switch and the second fault switch are obtained respectively. Based on the traveling wave arrival time of the first fault switch and the second fault switch, a time difference is obtained. Based on the time difference and the traveling wave propagation speed, a distance difference is obtained. Based on the second fault switch, the fault direction and the distance difference, the fault point is obtained. The specific steps of obtaining the traveling wave head arrival time include:

6. The method of claim 1, wherein, S1, based on wavelet transform, the wavelet transform coefficient of each sampling point of the transient traveling wave is calculated, the modulus maximum value of the wavelet transform coefficient is calculated, and a plurality of candidate wave heads are obtained based on the modulus maximum value; S2, based on the candidate wave head, the first waveform in the time window is obtained, the correlation coefficient is obtained based on the first waveform and the standard wave head template, and the peak-peak value is obtained based on the first waveform; S3, if the correlation coefficient is greater than a fifth preset threshold and the peak-peak value is greater than a sixth preset threshold, the effective wave head is obtained based on the candidate wave head, the arrival time of the effective wave head is obtained, and the traveling wave head arrival time is obtained; if not, the candidate wave head is marked as noise, the S2 is returned, and the next candidate wave head of the candidate wave head is updated as the candidate wave head. Before performing the S2, the method further includes:

7. A method of ground fault location according to claim 6, wherein, Based on the candidate wave head, a preset number of sampling points are obtained, a plurality of check points are obtained, the polarity of each check point is obtained, if the polarity is not the same, the candidate wave head is deleted, the S1 is returned, and the next candidate wave head of the candidate wave head is updated as the candidate wave head. The segmented switch deployment intelligent terminal unit is used to collect the power distribution network data and the impedance frequency curve.

8. The method of claim 1, wherein, ​

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