Power distribution network fault traveling wave detection method and device based on capacitive electronic voltage transformer

Abstract

The application discloses a kind of based on capacitive electronic voltage transformer's distribution network fault travelling wave detection method and device, method: in the ground wire of capacitive electronic voltage transformer increases voltage travelling wave signal acquisition extraction unit and constitutes travelling wave sensor, using its collection travelling wave signal;From travelling wave collection signal, real-time screening meets the fault travelling wave signal of amplitude-frequency requirement;According to the power frequency signal of real-time acquisition, using half-wave increment difference polarity method judges whether distribution network line is fault, and marks fault time period;If there is the travelling wave signal screened out in fault time period, then the travelling wave signal is effective fault voltage travelling wave signal;By comparing the energy slope size of effective fault voltage travelling wave signal in continuous adjacent time window, determine the first half-wave interval of effective fault voltage travelling wave signal;By increment difference ratio method, the initial moment of wave head arrives is positioned.The application realizes the arrival time of distribution network fault travelling wave signal to be identified and calibrated quickly and accurately.

Description

Technical Field

[0001] This invention belongs to the field of signal acquisition and identification in power distribution networks, and specifically relates to a method and device for detecting traveling waves of power distribution network faults based on capacitive electronic voltage transformers. Background Technology

[0002] Medium-voltage distribution networks directly face users, and rapid, accurate, and safe fault location is crucial for shortening power outage time and improving power supply reliability. However, domestic medium-voltage distribution networks operate with a neutral point that is not effectively grounded. Because the distribution network is close to the user side, the line corridors are complex and variable, making it prone to faults, especially single-phase grounding faults. Currently, fault location products for distribution networks are generally ineffective, especially for high-resistance grounding faults, where there are almost no ranging methods. This leads to lines operating with faults for extended periods, increasing the risk of fires and personal safety issues. A traveling wave-based location method, unaffected by grounding methods, is gradually being applied to distribution networks. The key to accurate location lies in precisely finding the first half-wave and start time of the traveling wave reaching the device. The reliability of this method depends on its ability to effectively identify fault traveling wave signals in the line and eliminate interference signals. Therefore, correctly extracting and identifying the first half-wave and start time of the fault traveling wave signal, and distinguishing between interference and faults, is one of the key issues for rapid and accurate fault location.

[0003] Various methods exist for traveling wave front identification both domestically and internationally, including the reciprocal method, instantaneous power method, mathematical morphological gradient method, instantaneous capability curve peak method, and wavelet transformation method. While these methods have limitations, they have shown some effectiveness in power transmission networks, and their anti-interference performance is generally average. However, these methods are not suitable for distribution networks. Due to the complex network structure and severe mixing of cables and overhead lines, distribution network lines have many points of impedance discontinuity, causing attenuation and distortion of the traveling wave signal waveform. Furthermore, distribution networks have many branches and short lines, resulting in short traveling wave propagation times and severe transient traveling wave signal aliasing. This makes it difficult for existing traveling wave devices in distribution networks to identify the first half-wave and start time of the traveling wave arriving at the device. In addition, the presence of discharge phenomena on distribution network lines can easily cause false initiation of traveling wave detection. Existing high-impedance identification methods are mainly based on steady-state methods, often requiring multiple cycles to determine whether a line is faulty, and cannot quickly solve the interference problem of traveling wave methods. Therefore, how to extract usable power frequency signals and traveling wave signals using electronic voltage transformers becomes the key to achieving rapid interference removal and reliable location.

[0004] Currently, most methods for identifying traveling wave fronts are based on computer processing. Devices that detect traveling waves do not have the function of identifying traveling wave fronts. As a result, these devices have difficulty distinguishing between interference and traveling wave signals, making it impossible to quickly and accurately locate line faults. Summary of the Invention

[0005] This invention provides a method and device for detecting traveling waves of distribution network faults based on capacitive electronic voltage transformers, thereby improving fault location accuracy.

[0006] To achieve the above technical objectives, the present invention adopts the following technical solution:

[0007] A method for detecting traveling waves of distribution network faults based on capacitive electronic voltage transformers includes the following steps:

[0008] A traveling wave sensor is constructed by adding a voltage traveling wave signal acquisition and extraction unit to the grounding wire of a capacitive electronic voltage transformer, and the traveling wave signal is acquired using this traveling wave sensor.

[0009] From the traveling wave signals collected by the traveling wave sensor, the traveling wave signals that meet the amplitude and frequency requirements of the fault traveling wave are selected in real time.

[0010] Based on the real-time collected power frequency signals, the half-wave incremental difference polarity method is used to determine whether a fault has occurred in the distribution network line, and the fault time period is marked.

[0011] If the selected traveling wave signal exists within the fault period, then the traveling wave signal within the fault period is a valid fault voltage traveling wave signal.

[0012] The first half-wave interval of the effective fault voltage traveling wave signal is determined by comparing the energy slope of the effective fault voltage traveling wave signal in consecutive adjacent time windows; then the initial moment when the wavefront arrives at the traveling wave sensor is located by using the incremental difference ratio method.

[0013] Furthermore, the voltage traveling wave signal acquisition and extraction unit includes a resistor R, a capacitor C3, and a filter circuit. The resistor R is connected in series with the grounding wire of the capacitive electronic voltage transformer, the capacitor C3 is connected in parallel across the two ends of the resistor R, and the filter circuit is set at the output end of the capacitor C3. The output end of the filter circuit is used to acquire the traveling wave signal.

[0014] Furthermore, the filter circuit includes a resistor R4, a capacitor C4, a capacitor C5, and a resistor R5; the resistor R4 is connected in series with the capacitor C4 and then in parallel with the capacitor C3, and the capacitor C4 is located at the ground terminal; the resistor R5 is connected in series with the capacitor C5 and then in parallel with the capacitor C4, and the connection point of the resistor R5 and the capacitor C5 serves as the output terminal of the filter circuit.

[0015] Furthermore, the formula for acquiring traveling wave signals using a traveling wave sensor is as follows:

[0016]

[0017]

[0018] Wherein, U1 is the primary side voltage, U2 is the fault signal acquired by the voltage traveling wave signal acquisition and extraction unit, and U0 is the traveling wave signal output by the filtering circuit in the voltage traveling wave signal acquisition and extraction unit, which is the acquired traveling wave signal; Z C1 Z C2 Z represents the capacitive reactance of the two capacitors C1 and C2 inside the capacitive electronic voltage transformer; C3 Z R Z C4 Z C5 Z R4 Z R5 Here are the impedance values ​​of capacitor C3, resistor R, capacitor C4, capacitor C5, resistor R4, and resistor R5.

[0019] Furthermore, the method of using half-wave incremental difference polarity to determine whether a fault has occurred in a distribution network line specifically involves:

[0020] The three-phase voltage signal is collected by a capacitive electronic voltage transformer. Based on the high-resistance fault criterion shown in equation (3) and the non-high-resistance fault criterion shown in equation (4), it is determined whether a high-resistance fault or a non-high-resistance fault has occurred.

[0021]

[0022]

[0023] Where j is the sampling point, U a(j) U b(j) U c(j) U represents the voltage amplitude of phases A, B, and C at the current sampling point j. a(j-T / 2) U b(j-T / 2) U c(j-T / 2) Let A(j), B(j), and C(j) be the voltage amplitudes of phases A, B, and C at half a cycle time jT / 2 before the current sampling point j, where T is the power frequency cycle, SING[*] represents the polarity corresponding to a certain number, γ is the threshold value for judging high-resistance fault conditions, and λ is the increment ratio threshold value; & represents logical AND, and || represents logical OR; A(j), B(j), and C(j) are the increment differences between the current time and half a cycle ago, as detailed below:

[0024] A (j) =[U a(j) +U a(j-T / 2) ]×SIGN[U a(j) (5)

[0025] B (j) =[U b(j) +U b(j-T / 2) ]×SIGN[U b(j) (6)

[0026] C (j)=[U c(j) +U c(j-T / 2) ]×SIGN[U c(j) (7)

[0027] If N consecutive sampling points meet the high-resistance fault criterion, then the distribution network is considered to have experienced a high-resistance fault; if N consecutive sampling points meet the non-high-resistance fault criterion, then the distribution network is considered to have experienced a non-high-resistance fault.

[0028] For both high-resistance and non-high-resistance faults, the N sampling points and the previous N sampling points, totaling 2N sampling points, are marked as the fault time period.

[0029] Furthermore, the step of determining the first half-wave interval of the effective fault voltage traveling wave signal by comparing the energy slope of the effective fault voltage traveling wave signal within consecutive adjacent time windows specifically involves:

[0030] Calculate the energy of the effective fault voltage traveling wave signal within each time window, and construct the formula for the maximum increment based on the energy:

[0031]

[0032]

[0033] Where Δ is the time window scale, p(i) is the energy of the effective fault voltage traveling wave signal x(i) within the time window 2Δ, τ is the energy threshold value, and T(i) is the corresponding time.

[0034] If the energy of the effective fault voltage traveling wave signal is greater than the energy threshold value τ in M' time windows out of M consecutive time windows, then the energy slope value in each two adjacent time windows in the M consecutive time windows is compared, that is, the ratio of the energy difference to the time difference in two adjacent time windows. If the largest energy slope value is greater than the energy slope threshold value δ, then the M consecutive time windows are determined to be the effective first half-wave interval; otherwise, it is a normal transient disturbance.

[0035] Furthermore, the method of locating the initial moment of the wavefront arriving at the traveling wave sensor using the incremental difference ratio method specifically involves:

[0036] If a sampling point j within the first half-wave interval satisfies the criterion shown in formula (10), then the sampling point j is determined to be the initial time when the wavefront of the valid fault traveling wave signal arrives at the device:

[0037]

[0038] Where x(j+1), x(j), x(j-1), x(j-2), and x(j-3) are the amplitudes of the effective fault traveling wave signal at the corresponding sampling points j+1, j, j-1, j-2, and j-3, respectively, and k is the threshold value of the incremental difference; S(j), S'(j), and S""j" are the incremental difference ratios at sampling points 1, 2, and 3 apart, respectively.

[0039] A distribution network fault traveling wave detection device based on a capacitive electronic voltage transformer includes:

[0040] A traveling wave sensor is constructed by adding a voltage traveling wave signal acquisition and extraction unit to the grounding wire of a capacitive electronic voltage transformer, and is used to acquire traveling wave signals.

[0041] The traveling wave signal filtering module is used to: filter traveling wave signals that meet the amplitude and frequency requirements of fault traveling waves from the traveling wave signals collected by the traveling wave sensor in real time;

[0042] The fault diagnosis module is used to: determine whether a fault has occurred in the distribution network line based on the real-time collected power frequency signal using the half-wave incremental difference polarity method, and mark the fault time period;

[0043] The valid signal determination module is used to: if the selected traveling wave signal exists within the fault time period, determine that the traveling wave signal within the fault time period is a valid fault voltage traveling wave signal;

[0044] The positioning module is used to: determine the first half-wave interval of the effective fault voltage traveling wave signal by comparing the energy slope of the effective fault voltage traveling wave signal in consecutive adjacent time windows; and then locate the initial moment when the wavefront arrives at the traveling wave sensor by using the incremental difference ratio method.

[0045] The power distribution network fault traveling wave detection device is used to implement any of the power distribution network fault traveling wave detection methods described above.

[0046] Beneficial effects

[0047] This invention designs a traveling wave sensor based on a capacitive voltage transformer to acquire valid traveling wave signals and power frequency signals of power distribution network faults. Based on the acquired power frequency signals and the requirement for rapid processing of traveling waves, an incremental difference polarity method is proposed to determine whether a fault has occurred in the line. Based on the acquired traveling wave signals, an energy interval slope method is proposed to compare the magnitude of the energy slope within two adjacent time windows to find the first half-wave interval, removing interference signals and traveling wave signals from severely aliased segments. Based on the characteristics of abrupt changes in the fault traveling wave, the proposed incremental difference ratio method is used to find the starting point of the fault voltage traveling wave signal arriving at the device, thereby improving the fault location accuracy.

[0048] This invention enables rapid and accurate identification and calibration of the arrival time of traveling wave signals in power distribution networks. Moreover, the identification method of this invention is simple and reliable, easy to operate, highly practical, and not limited by fault grounding resistance, fault type, or operating mode, making it easy to implement. Attached Figure Description

[0049] Figure 1 This is a flowchart of the power distribution network fault traveling wave detection method according to an embodiment of the present invention.

[0050] Figure 2 This is a schematic diagram of a traveling wave sensor based on a capacitive electronic voltage transformer in an embodiment of the present invention;

[0051] Figure 3 It is Figure 2 Circuit diagram of the medium voltage traveling wave signal acquisition and extraction unit when it is represented by components and is unfiltered;

[0052] Figure 4 This is a filter circuit diagram for filtering the extracted fault signal U2;

[0053] Figure 5 This is a circuit diagram of a 10kV real-type distribution network experiment. Detailed Implementation

[0054] The embodiments of the present invention will be described in detail below. These embodiments are based on the technical solutions of the present invention and provide detailed implementation methods and specific operation processes to further explain the technical solutions of the present invention.

[0055] This embodiment provides a method for detecting traveling waves of faults in distribution networks based on capacitive electronic voltage transformers. (Refer to...) Figure 1 As shown, it includes the following steps:

[0056] Step 1, refer to Figure 2 As shown, a traveling wave sensor is constructed by adding a voltage traveling wave signal acquisition and extraction unit to the grounding wire of a capacitive electronic voltage transformer, and the traveling wave signal is acquired using this traveling wave sensor.

[0057] like Figure 3 As shown, the voltage traveling wave signal acquisition and extraction unit includes a resistor R, a capacitor C3, and a filter circuit. The resistor R is connected in series with the grounding wire of the capacitive electronic voltage transformer, the capacitor C3 is connected in parallel across the two ends of the resistor R, and the filter circuit is set at the output end of the capacitor C3. The output end of the filter circuit is used to acquire the traveling wave signal.

[0058] Furthermore, such as Figure 4As shown, the filter circuit includes resistor R4, capacitor C4, capacitor C5 and resistor R5; resistor R4 is connected in series with capacitor C4 and then in parallel with capacitor C3, and capacitor C4 is located at the ground terminal; resistor R5 is connected in series with capacitor C5 and then in parallel with capacitor C4, and the connection point of resistor R5 and capacitor C5 serves as the output terminal of the filter circuit.

[0059] The formula for acquiring traveling wave signals using a traveling wave sensor is:

[0060]

[0061]

[0062] Wherein, U1 is the primary side voltage, U2 is the fault signal acquired by the voltage traveling wave signal acquisition and extraction unit, and U0 is the traveling wave signal output by the filtering circuit in the voltage traveling wave signal acquisition and extraction unit, which is the acquired traveling wave signal; Z C1 Z C2 Z represents the capacitive reactance of the two capacitors C1 and C2 inside the capacitive electronic voltage transformer; C3 Z R Z C4 Z C5 Z R4 Z R5 Here are the impedance values ​​of capacitor C3, resistor R, capacitor C4, capacitor C5, resistor R4, and resistor R5.

[0063] Step 2: Select traveling wave signals that meet the amplitude and frequency requirements of the fault traveling wave from the traveling wave signals collected by the traveling wave sensor in real time.

[0064] Step 3: Based on the real-time acquired power frequency signal, use the half-wave incremental difference polarity method to determine whether a fault has occurred in the distribution network line, and mark the fault time period. Specifically:

[0065] The three-phase voltage signal is collected by a capacitive electronic voltage transformer. Based on the high-resistance fault criterion shown in equation (3) and the non-high-resistance fault criterion shown in equation (4), it is determined whether a high-resistance fault or a non-high-resistance fault has occurred.

[0066]

[0067]

[0068] Where j is the sampling point, U a(j) U b(j) U c(j) U represents the voltage amplitude of phases A, B, and C at the current sampling point j. a(j-T / 2) U b(j-T / 2) U c(j-T / 2)Let A(j), B(j), and C(j) be the voltage amplitudes of phases A, B, and C at half a cycle time jT / 2 before the current sampling point j, where T is the power frequency cycle (20ms), SING[*] represents the polarity corresponding to a certain number, γ is the threshold value for judging high-resistance fault conditions, λ is the increment ratio threshold value, which is set to 15% in this embodiment; & represents logical AND, || represents logical OR; A(j), B(j), and C(j) are the increment differences between the current time and half a cycle ago, as detailed below:

[0069] A (j) =[U a(j) +U a(j-T / 2) ]×SIGN[U a(j) (5)

[0070] B (j) =[U b(j) +U b(j-T / 2) ]×SIGN[U b(j) (6)

[0071] C (j) =[U c(j) +U c(j-T / 2) ]×SIGN[U c(j) (7)

[0072] If N consecutive sampling points meet the high-resistance fault criterion, then the distribution network is considered to have experienced a high-resistance fault; if N consecutive sampling points meet the non-high-resistance fault criterion, then the distribution network is considered to have experienced a non-high-resistance fault.

[0073] Regardless of whether it is a high-impedance fault or a non-high-impedance fault, the time period between the fault occurrence at the N sampling points and the previous N sampling points is marked as the fault time period. In this embodiment, N is 5, so the fault time period is [j(-5),j(4)].

[0074] Step 4: If the selected traveling wave signal exists within the fault time period, then the traveling wave signal within the fault time period is a valid fault voltage traveling wave signal.

[0075] Step 5: By comparing the energy slope of the effective fault voltage traveling wave signal within consecutive adjacent time windows, the first half-wave interval of the effective fault voltage traveling wave signal is determined; then, the initial moment when the wavefront arrives at the traveling wave sensor is located using the incremental difference ratio method.

[0076] (1) The first half-wave interval of the effective fault voltage traveling wave signal is determined by comparing the energy slope of the effective fault voltage traveling wave signal in consecutive adjacent time windows, specifically:

[0077] Calculate the energy of the effective fault voltage traveling wave signal within each time window, and construct the formula for the maximum increment based on the energy:

[0078]

[0079]

[0080] Where p(i) is the energy of the effective fault voltage traveling wave signal x(t) within time window i, τ is the energy threshold value; T(i) is the time corresponding to time window i;

[0081] If the energy of the effective fault voltage traveling wave signal is greater than the energy threshold value τ in M' time windows out of M consecutive time windows, then the energy slope value in each two adjacent time windows in the M consecutive time windows is compared, that is, the ratio of the energy difference to the time difference in two adjacent time windows. If the largest energy slope value is greater than the energy slope threshold value δ, then the M consecutive time windows are determined to be the effective first half-wave interval; otherwise, it is a normal transient disturbance.

[0082] In this embodiment, the values ​​are M=5 and M'=4.

[0083] (2) The initial moment of the wavefront arriving at the traveling wave sensor is determined by the incremental difference ratio method, specifically as follows:

[0084] If a sampling point j within the first half-wave interval satisfies the criterion shown in formula (10), then the sampling point j is determined to be the initial moment when the wavefront of the valid fault traveling wave signal arrives at the traveling wave sensor:

[0085]

[0086] Where x(j+1), x(j), x(j-1), x(j-2), and x(j-3) are the amplitudes of the effective fault traveling wave signal at the corresponding sampling points j+1, j, j-1, j-2, and j-3, respectively, and k is the threshold value of the incremental difference; S(j), S'(j), and S""j" are the incremental difference ratios at sampling points 1, 2, and 3 apart, respectively.

[0087] This embodiment uses the actual fault traveling wave identification of a 10kV distribution network experimental line as an example. There are a total of three sets of traveling wave sensors based on capacitive voltage transformers in the line to collect fault signals, such as... Figure 5 As shown; the overhead line between two adjacent monitoring points is 3km long, and the cable line is 90m long. The distribution of the overhead line and cable line is as follows: every 1km of overhead line is connected to the next 1km of overhead line by a 30m cable; there is a 200m cable line outside prototype No. 1 at the power supply point, and a 1.5km cable line at the end outside prototype No. 3. The location of the fault point overlaps with the location of prototype No. 2. When a fault occurs in the 10kV real-type distribution network, the traveling wave signal generated at the fault point propagates along the line to both ends of the fault. The prototype installed in the line constantly detects the fault signal in the line and deduces the initial time of the traveling wave signal of the fault voltage reaching the detection prototype.

[0088] According to the power frequency signal differential polarity method proposed in this invention, it is possible to quickly determine whether a line fault has occurred.

[0089] Taking a 1kΩ C-phase high-resistance grounding fault as an example, since it is a high-resistance fault, the analysis is based on the high-resistance fault criteria. Furthermore, the power frequency utilization rate is low, and the time scale is calculated in milliseconds (ms). Therefore, only the power frequency signal collected by prototype No. 2 needs to be analyzed. According to formulas 3-5 in this invention, and with γ calculated as 0.01, five consecutive points A(j), B(j), and C(j) are selected where γ exceeds γ, and each group has different polarities. This satisfies the requirements of this invention patent for rapid line fault identification. The specific calculation results are as follows:

[0090] A(0)=0.0160 B(0)=-0.0202 C(0)=-0.0817

[0091] A(1)=0.0238 B(1)=0.0278 C(1)=-0.1059

[0092] A(2)=0.0341 B(2)=0.0381 C(2)=-0.1255

[0093] A(3)=0.0466 B(3)=0.0506 C(3)=-0.1384

[0094] A(4)=0.0631 B(4)=0.0661 C(4)=-0.1475

[0095] Based on data analysis, it was determined from the five data points j∈[0,4] that a line fault had occurred, and the fault occurred in the time segment j between [-5,4]. The traveling wave signal detected by the prototype during this time segment was a valid traveling wave signal.

[0096] Using the traveling wave signal acquired by the traveling wave sensor based on the capacitive voltage transformer, the traveling wave signal recorded by the device in the valid fault interval is searched. The first half-wave interval of the traveling wave is determined by energy comparison, with τ set to 0.1, δ set to 0.1, and k set to 2. The specific calculation process is as follows:

[0097] Analysis of Prototype No. 1:

[0098] According to Formula 8 of the present invention, the energy value can be obtained:

[0099] P(-1) = 0.0153 P(0) = 1.3123

[0100] P(1) = 0.6210 P(2) = 0.7897

[0101] P(3) = 0.3635 P(4) = 1.0486

[0102] According to Formula 9 of this invention, the energy slope is:

[0103]

[0104]

[0105]

[0106]

[0107] Analysis shows that the maximum slope of [T(0),T(-1)] is greater than the threshold value δ, and P(0) is greater than the threshold value τ, so the first half of the traveling wave is determined to be in the T(0) interval.

[0108] According to formula 10 of the present invention, the incremental difference ratio is:

[0109] Analysis of the original data shows that the requirement is met when i = -3;

[0110]

[0111]

[0112]

[0113] When i = -3, the above three conditions are met, that is, y(-3) is the starting point of the fault voltage traveling wave signal arriving at the device.

[0114] Similarly, we can conclude that:

[0115] Analysis of Prototype No. 2:

[0116] According to Formula 8 of the present invention, the energy value can be obtained:

[0117] P(-1) = 0.0232 P(0) = 1.1895

[0118] P(1) = 0.6050 P(2) = 0.6229

[0119] P(3) = 0.7751 P(4) = 0.785613

[0120] According to Formula 9 of this invention, the energy slope is:

[0121]

[0122]

[0123]

[0124]

[0125] The first half of the traveling wave is in the T(0) interval. This is obtained from the analysis of the original data. The requirement is met when i = -36.

[0126]

[0127]

[0128]

[0129] When i = -36, the above three conditions are met, meaning y(-36) is the starting point of the fault voltage traveling wave signal arriving at the device. Analysis of prototype No. 3:

[0130] According to Formula 8 of the present invention, the energy value can be obtained:

[0131] P(-1) = 0.0305 P(0) = 0.9220

[0132] P(1) = 0.9002 P(2) = 0.8735

[0133] P(3) = 0.8175 P(4) = 0.8339

[0134] According to Formula 9 of this invention, the energy slope is:

[0135]

[0136]

[0137]

[0138]

[0139] The first half of the traveling wave is in the T(0) interval. This is obtained from the analysis of the original data. The requirement is met when i = -21.

[0140]

[0141]

[0142]

[0143] When i = -21, the above three conditions are met, that is, y(-21) is the starting point of the fault voltage traveling wave signal arriving at the device.

[0144] To verify whether the found fault traveling wave starting point is accurate, a dual-end positioning method is used for fault location verification.

[0145] 1) Positioning of Prototype 1 and Prototype 2

[0146] The initial arrival times of the traveling wave at the device are: Prototype 1: t1 = 21.6 μS; Prototype 2: t2 = 10.8 μS; The cable lines of Prototypes 1 and 2 are equivalent to overhead lines:

[0147]

[0148] The entire process for prototype No. 1 and prototype No. 2 is as follows:

[0149] l 12 =180+3000=3180m

[0150] Then the fault location L 12f for:

[0151]

[0152] Positioning error:

[0153] d 12f =l 12 -L 12f =3180-3193.8=13.8m

[0154] 2) Positioning of Prototype No. 2 and Prototype No. 3

[0155] The initial arrival times of the traveling wave at the device are: Prototype 2: t2 = 10.8 μS; Prototype 3: t3 = 21.0 μS; The cable lines of Prototypes 2 and 3 are equivalent to overhead lines:

[0156]

[0157] The entire process for prototype No. 1 and prototype No. 2 is as follows:

[0158] l 23 =180+3000=3180m

[0159] Then the fault location L 12f for:

[0160]

[0161] Positioning error:

[0162] d 23f =0-L 12f =0 -75.3 = -75.3m

[0163] The positioning error between prototype 1 and prototype 2, and between prototype 2 and prototype 3, is a maximum of 75.3m, which meets the requirements for precise positioning.

[0164] The above embodiments are preferred embodiments of this application. Those skilled in the art can make various changes or improvements based on them. Without departing from the overall concept of this application, these changes or improvements should fall within the scope of protection claimed in this application.

Claims

1. A method for detecting traveling waves of distribution network faults based on capacitive electronic voltage transformers, characterized in that, Includes the following steps: A traveling wave sensor is constructed by adding a voltage traveling wave signal acquisition and extraction unit to the grounding wire of a capacitive electronic voltage transformer, and the traveling wave signal is acquired using this traveling wave sensor. From the traveling wave signals collected by the traveling wave sensor, the traveling wave signals that meet the amplitude and frequency requirements of the fault traveling wave are selected in real time. Based on the real-time collected power frequency signals, the half-wave incremental difference polarity method is used to determine whether a fault has occurred in the distribution network line, and the fault time period is marked. If the selected traveling wave signal exists within the fault period, then the traveling wave signal within the fault period is a valid fault voltage traveling wave signal. The first half-wave interval of the effective fault voltage traveling wave signal is determined by comparing the energy slope of the effective fault voltage traveling wave signal in consecutive adjacent time windows; then the initial moment when the wavefront arrives at the traveling wave sensor is located by using the incremental difference ratio method.

2. The method for detecting traveling waves in a distribution network fault according to claim 1, characterized in that, The voltage traveling wave signal acquisition and extraction unit includes a resistor R, a capacitor C3, and a filter circuit. The resistor R is connected in series with the grounding wire of the capacitive electronic voltage transformer, the capacitor C3 is connected in parallel across the two ends of the resistor R, and the filter circuit is set at the output end of the capacitor C3. The output end of the filter circuit is used to acquire the traveling wave signal.

3. The method for detecting traveling waves in a distribution network fault according to claim 2, characterized in that, The filter circuit includes a resistor R4, a capacitor C4, a capacitor C5, and a resistor R5; the resistor R4 is connected in series with the capacitor C4 and then in parallel with the capacitor C3, and the capacitor C4 is located at the ground terminal; the resistor R5 is connected in series with the capacitor C5 and then in parallel with the capacitor C4, and the connection point of the resistor R5 and the capacitor C5 serves as the output terminal of the filter circuit.

4. The method for detecting traveling waves in a distribution network fault according to claim 3, characterized in that, The formula for acquiring traveling wave signals using a traveling wave sensor is: Wherein, U1 is the primary side voltage, U2 is the fault signal acquired by the voltage traveling wave signal acquisition and extraction unit, and U0 is the traveling wave signal output by the filtering circuit in the voltage traveling wave signal acquisition and extraction unit, which is the acquired traveling wave signal; Z C1 Z C2 Z represents the capacitive reactance of the two capacitors C1 and C2 inside the capacitive electronic voltage transformer; C3 Z R Z C4 Z C5 Z R4 Z R5 Here are the impedance values ​​of capacitor C3, resistor R, capacitor C4, capacitor C5, resistor R4, and resistor R5.

5. The method for detecting traveling waves in a distribution network fault according to claim 1, characterized in that, The method of using half-wave incremental difference polarity to determine whether a fault has occurred in a distribution network line is as follows: The three-phase voltage signal is collected by a capacitive electronic voltage transformer. Based on the high-resistance fault criterion shown in equation (3) and the non-high-resistance fault criterion shown in equation (4), it is determined whether a high-resistance fault or a non-high-resistance fault has occurred. Where j is the sampling point, U a(j) U b(j) U c(j) U represents the voltage amplitude of phases A, B, and C at the current sampling point j. a(j-T / 2) U b(j-T / 2) U c(j-T / 2) Let A(j), B(j), and C(j) be the voltage amplitudes of phases A, B, and C at half a cycle time jT / 2 before the current sampling point j, where T is the power frequency cycle, SING[*] represents the polarity corresponding to a certain number, γ is the threshold value for judging high-resistance fault conditions, and λ is the increment ratio threshold value; & represents logical AND, and || represents logical OR; A(j), B(j), and C(j) are the increment differences between the current time and half a cycle ago, as detailed below: If N consecutive sampling points meet the high-resistance fault criterion, then the distribution network is considered to have experienced a high-resistance fault; if N consecutive sampling points meet the non-high-resistance fault criterion, then the distribution network is considered to have experienced a non-high-resistance fault. For both high-resistance and non-high-resistance faults, the N sampling points and the previous N sampling points, totaling 2N sampling points, are marked as the fault time period.

6. The method for detecting traveling waves in a distribution network fault according to claim 1, characterized in that, The method of determining the first half-wave interval of the effective fault voltage traveling wave signal by comparing the energy slope of the effective fault voltage traveling wave signal within consecutive adjacent time windows is as follows: Calculate the energy of the effective fault voltage traveling wave signal within each time window, and construct the formula for the maximum increment based on the energy: Where Δ is the time window scale, p(i) is the energy of the effective fault voltage traveling wave signal x(i) within the time window 2Δ, τ is the energy threshold value, and T(i) is the corresponding time. If the energy of the effective fault voltage traveling wave signal is greater than the energy threshold value τ in M' time windows out of M consecutive time windows, then the energy slope value in each two adjacent time windows in the M consecutive time windows is compared, that is, the ratio of the energy difference to the time difference in two adjacent time windows. If the largest energy slope value is greater than the energy slope threshold value δ, then the M consecutive time windows are determined to be the effective first half-wave interval; otherwise, it is a normal transient disturbance.

7. The method for detecting traveling waves in a distribution network fault according to claim 1, characterized in that, The method of locating the initial moment of the wavefront arriving at the traveling wave sensor using the incremental difference ratio method is as follows: If a sampling point j within the first half-wave interval satisfies the criterion shown in formula (10), then the sampling point j is determined to be the initial time when the wavefront of the valid fault traveling wave signal arrives at the device: Where x(j+1), x(j), x(j-1), x(j-2), and x(j-3) are the amplitudes of the effective fault traveling wave signal at the corresponding sampling points j+1, j, j-1, j-2, and j-3, respectively, and k is the threshold value of the incremental difference; S(j), S'(j), and S""j" are the incremental difference ratios at sampling points 1, 2, and 3 apart, respectively.

8. A distribution network fault traveling wave detection device based on a capacitive electronic voltage transformer, characterized in that, include: A traveling wave sensor is constructed by adding a voltage traveling wave signal acquisition and extraction unit to the grounding wire of a capacitive electronic voltage transformer, and is used to acquire traveling wave signals. The traveling wave signal filtering module is used to: filter traveling wave signals that meet the amplitude and frequency requirements of fault traveling waves from the traveling wave signals collected by the traveling wave sensor in real time; The fault diagnosis module is used to: determine whether a fault has occurred in the distribution network line based on the real-time collected power frequency signal using the half-wave incremental difference polarity method, and mark the fault time period; The valid signal determination module is used to: if the selected traveling wave signal exists within the fault time period, determine that the traveling wave signal within the fault time period is a valid fault voltage traveling wave signal; The positioning module is used to: determine the first half-wave interval of the effective fault voltage traveling wave signal by comparing the energy slope of the effective fault voltage traveling wave signal in consecutive adjacent time windows; and then locate the initial moment when the wavefront arrives at the traveling wave sensor by using the incremental difference ratio method. The power distribution network fault traveling wave detection device is used to implement the power distribution network fault traveling wave detection method according to any one of claims 1-7.

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