Power distribution network protection method and system based on transient traveling wave timing domain characteristic quantity matching

Abstract

The invention relates to the technical field of power distribution network protection, and discloses a power distribution network protection method and system based on transient traveling wave timing domain characteristic quantity matching, and the method comprises the steps: collecting three-phase voltage data and three-phase current data on a line in real time at a protection installation part, and calculating a current front traveling wave and a current reverse traveling wave; performing wavelet transformation on the current forward traveling wave and the current backward traveling wave, determining the arrival time of the wave head of the first traveling wave in the current forward traveling wave and the current backward traveling wave by adopting a maximum value method, and determining the fault direction; if the fault direction is a forward line fault, acquiring a wavelet transform coefficient of a current backward traveling wave in a preset time period to determine a fault area; and protecting the power distribution network according to the fault area. According to the method, the transient characteristic quantity, namely the fault transient traveling wave, after the fault occurs is adopted, the fault transient traveling wave is only related to the fault and is not influenced by the distributed power supply, and the fault area can be effectively identified under inter-phase non-grounding short circuit and symmetrical metal short circuit faults.

Description

Technical Field

[0001] The present invention relates to the technical field of distribution network protection, and in particular to a distribution network protection method and system based on transient traveling wave time domain feature quantity matching. Background Art

[0002] With the influx of distributed power sources (DGs) connecting to the power grid, the traditional radial distribution network has evolved into an active distribution network with multiple power sources. When the power system experiences a fault disturbance, the DGs exhibit complex fault characteristics, such as weak infeed, limited amplitude, and unstable internal impedance, that differ significantly from those of traditional synchronous generators. This presents significant challenges to the adaptability of existing distribution network protection systems.

[0003] Regarding the existing single-ended traveling wave distance protection methods for distribution networks, such as the single-ended traveling wave distance protection method based on the time difference coordination line between the first traveling wave of the fault and the secondary reflected wave, and the single-ended traveling wave distance protection method based on the time difference of the first traveling wave of the zero-mode fault, this method is affected by the distributed power supply characteristics of the distribution network. Under the conditions of phase-to-phase non-grounding short circuit and symmetrical metallic short circuit faults, it is difficult to effectively identify faults within and outside the zone, and therefore cannot provide effective protection for the distribution network. Summary of the Invention

[0004] In order to overcome the problem that in the single-ended traveling wave distance protection of the distribution network, due to the influence of the distributed power supply characteristics of the distribution network, it is difficult to effectively identify the faults within and outside the zone under the phase-to-phase non-grounding short circuit and symmetrical metallic short circuit faults, and thus it is impossible to provide effective protection for the distribution network, the present invention provides a distribution network protection method and system based on transient traveling wave time domain feature matching.

[0005] In a first aspect, in order to solve the above technical problems, the present invention provides a distribution network protection method based on transient traveling wave time domain feature matching, comprising:

[0006] Collect three-phase voltage data and three-phase current data at a preset location of the distribution network within a preset time period at a preset sampling frequency, and calculate the current forward wave and current reverse wave corresponding to the current sampling frequency based on the three-phase voltage data and three-phase current data corresponding to the current sampling frequency;

[0007] Perform wavelet transform on the current forward wave and the current reverse wave corresponding to the current sampling frequency, and use the maximum value method to determine the first arrival time of the first wave head in the current forward wave and the second arrival time of the first wave head in the current reverse wave;

[0008] Determine the fault direction corresponding to the current sampling frequency according to the difference between the first arrival time and the second arrival time corresponding to the current sampling frequency;

[0009] If the fault direction corresponding to the current sampling frequency is a forward line fault, obtaining the first wavelet transform coefficient of the current reverse wave within a preset time period, and determining the fault area corresponding to the current sampling frequency based on the first wavelet transform coefficient;

[0010] The distribution network is protected according to the fault area corresponding to the current sampling frequency.

[0011] In a second aspect, the present invention provides a distribution network protection system based on transient traveling wave time domain feature matching, comprising:

[0012] A traveling wave determination module is used to collect three-phase voltage data and three-phase current data at a preset location of the distribution network within a preset time period at a preset sampling frequency, and calculate the current forward traveling wave and current reverse traveling wave corresponding to the current sampling frequency based on the three-phase voltage data and three-phase current data corresponding to the current sampling frequency;

[0013] An arrival time determination module is used to perform wavelet transform on the current forward wave and the current reverse wave corresponding to the current sampling frequency, and use the maximum value method to determine the first arrival time of the first wave head in the current forward wave and the second arrival time of the first wave head in the current reverse wave;

[0014] A fault direction determination module is used to determine the fault direction corresponding to the current sampling frequency based on the difference between the first arrival time and the second arrival time corresponding to the current sampling frequency;

[0015] a fault area determination module, configured to obtain a first wavelet transform coefficient of a current reverse traveling wave within a preset time period if the fault direction corresponding to the current sampling frequency is a forward line fault, and determine the fault area corresponding to the current sampling frequency based on the first wavelet transform coefficient;

[0016] The distribution network protection module is used to protect the distribution network according to the fault area corresponding to the current sampling frequency.

[0017] The beneficial effects of the present invention are as follows: by collecting three-phase voltage data and three-phase current data at a preset position on the distribution network, the traveling wave data (current forward traveling wave and current backward traveling wave) can be calculated, and then by calculating the first arrival time of the first traveling wave head in the current forward traveling wave and the second arrival time of the first traveling wave head in the current backward traveling wave, the fault direction can be obtained. If the fault direction is a forward line fault, the fault area can be obtained by obtaining the first wavelet transform coefficient of the current reverse traveling wave within a preset time period, and then the distribution network can be protected according to the fault area. The present application uses the transient characteristic quantity after the fault occurs, namely the fault transient traveling wave. The fault transient traveling wave is only related to the fault itself and is not affected by the distributed power supply. It can effectively identify the fault area under phase-to-phase non-grounding short circuit and symmetrical metallic short circuit faults. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the present invention is further described below with reference to the accompanying drawings and embodiments.

[0019] Figure 1 Schematic diagram of the flow of a distribution network protection method based on transient traveling wave time domain feature matching according to an embodiment of the present invention;

[0020] Figure 2 This is a simulation diagram of a 10kV power distribution system;

[0021] Figure 3 The waveforms of the forward and reverse current waves within 50 μs after a fault occurs 2 km outside the reverse zone.

[0022] Figure 4 is the wavelet coefficient of the current forward wave and the current reverse wave occurring 2 km outside the reverse zone;

[0023] Figure 5 The waveforms of the forward and reverse current waves within 50 μs after a fault occurs at 2 km in the area;

[0024] Figure 6 are the wavelet coefficients of the forward and reverse current waves after a fault occurs at 2 km in the area;

[0025] Figure 7 These are the waveforms of the current forward wave and the current reverse wave after a fault occurs 2 km outside the forward zone;

[0026] Figure 8 are the wavelet coefficients of the forward and reverse current waves after a fault occurs 2 km outside the forward zone;

[0027] Figure 9 Schematic diagram of the structure of a distribution network protection system based on transient traveling wave time domain feature matching according to an embodiment of the present invention. DETAILED DESCRIPTION

[0028] The following examples are provided to further explain and supplement the present invention and do not constitute any limitation to the present invention.

[0029] The following describes a distribution network protection method and system based on transient traveling wave time domain feature matching according to an embodiment of the present invention with reference to the accompanying drawings.

[0030] like Figure 1 As shown, the present invention provides a distribution network protection method based on transient traveling wave time domain feature matching, including:

[0031] S1. Collect three-phase voltage data and three-phase current data within a preset time period at a preset location of the distribution network at a preset sampling frequency, and calculate the current forward wave and current reverse wave corresponding to the current sampling frequency based on the three-phase voltage data and three-phase current data corresponding to the current sampling frequency.

[0032] S2. Perform wavelet transform on the current forward wave and the current reverse wave corresponding to the current sampling frequency, and use the maximum value method to determine the first arrival time of the first wave head in the current forward wave and the second arrival time of the first wave head in the current reverse wave.

[0033] S3. Determine the fault direction corresponding to the current sampling frequency according to the difference between the first arrival time and the second arrival time corresponding to the current sampling frequency.

[0034] S4. If the fault direction corresponding to the current sampling frequency is a forward line fault, obtain the first wavelet transform coefficient of the current reverse wave within a preset time period, and determine the fault area corresponding to the current sampling frequency according to the first wavelet transform coefficient.

[0035] S5. Protect the distribution network according to the fault area corresponding to the current sampling frequency.

[0036] In this embodiment, by collecting three-phase voltage data and three-phase current data at a preset location on the distribution network, the traveling wave data (current forward traveling wave and current backward traveling wave) can be calculated. Then, by calculating the first arrival time of the first traveling wave head in the current forward traveling wave and the second arrival time of the first traveling wave head in the current backward traveling wave, the fault direction can be obtained. If the fault direction is a forward line fault, the fault area can be obtained by obtaining the first wavelet transform coefficient of the current reverse traveling wave within a preset time period, and then the distribution network can be protected according to the fault area. This application uses the transient characteristic quantity after the fault occurs, namely the fault transient traveling wave. This fault transient traveling wave is only related to the fault itself and is not affected by the distributed power supply. It can effectively identify the fault area under phase-to-phase non-grounding short circuit and symmetrical metallic short circuit faults.

[0037] In this embodiment, there may be multiple preset locations, that is, distribution network protection is performed simultaneously at multiple locations.

[0038] In this embodiment, the sampling frequency may be 1 MHz, and the preset time length may be 50 μs.

[0039] Optionally, calculating the current forward wave and the current reverse wave corresponding to the current sampling frequency based on the three-phase voltage data and the three-phase current data corresponding to the current sampling frequency includes:

[0040] According to the three-phase voltage data and three-phase current data corresponding to the current sampling frequency, the filtered three-phase voltage data and three-phase current data corresponding to the current sampling frequency are determined by the 10th-order high-pass filtering algorithm. The formula is as follows:

[0041]

[0042] Among them, u a ( t-k) 、u b (tk) represents the three-phase voltage data of the tkth order corresponding to the current sampling frequency, i a (tk ) 、i b (tk) represents the three-phase current data of the tkth order corresponding to the current sampling frequency, u a F (t),u b F (t) represents the filtered three-phase voltage data corresponding to the current sampling frequency, i a F (t), i b F (t) represents the filtered three-phase current data corresponding to the current sampling frequency, N is the order of the filter, f c is the cutoff frequency, which indicates the lowest frequency allowed to pass through in the signal, w(t) is the preset window function, and t represents the time;

[0043] According to the filtered three-phase voltage data and three-phase current data corresponding to the current sampling frequency, the current forward wave and current reverse wave corresponding to the current sampling frequency are calculated. The formula is as follows:

[0044]

[0045] Among them, i Q (t) represents the current forward wave corresponding to the current sampling frequency, i F (t) represents the current reverse wave corresponding to the current sampling frequency.

[0046] This embodiment matches the characteristics of traveling waves that propagate back and forth along the entire length of the protected line. This effectively addresses the difficulty of existing single-ended traveling wave distance protection methods in effectively identifying internal and external faults in phase-to-phase non-ground faults and symmetrical metallic short circuits. Furthermore, this embodiment utilizes transient characteristics after a fault occurs. These characteristics are specific to the fault itself and are unaffected by distributed power sources. This effectively addresses the issues of refusal and false tripping that plague existing distribution network protection systems.

[0047] In this embodiment, c The preferred value is 10KHz.

[0048] Optionally, performing wavelet transform on the current forward wave and the current reverse wave corresponding to the current sampling frequency, and using a maximum method to determine a first arrival time of a wave head of the first wave in the current forward wave and a second arrival time of a wave head of the first wave in the current reverse wave, includes:

[0049] Perform wavelet transform on the current forward wave and the current reverse wave corresponding to the current sampling frequency to determine the second wavelet transform coefficient of the current forward wave within the preset time length corresponding to the current sampling frequency and the third wavelet transform coefficient of the current reverse wave. The formula is as follows:

[0050]

[0051] Among them, w iQ (a，b) (t), W F (a，b) (t) represents the second wavelet transform coefficient and the third wavelet transform coefficient within the preset time length corresponding to the current sampling frequency, where a is the scale factor, b is the translation factor, and ψ a，b (t) represents the preset wavelet basis function;

[0052] The time corresponding to the maximum value is found from the second wavelet transform coefficient as the first arrival time, and the time corresponding to the maximum value is found from the third wavelet transform coefficient as the second arrival time; wherein, the calculation formula of the maximum value is as follows:

[0053]

[0054] Among them, M and M2 represent the first arrival time and the second arrival time, and represents the maximum value in the second wavelet transform coefficient, Represents the maximum value in the third wavelet transform coefficient.

[0055] In this embodiment, the scale factor a is preferably set to 1, 2, 4 or 8, and the translation factor b is preferably set to 1.

[0056] In this embodiment, when calculating the transformation coefficient within the preset time length, in order to avoid the maximum value of the obtained transformation coefficient being too small, resulting in inaccuracy, a threshold of 0.001 is added, that is, the maximum value of the transformation coefficient within the preset time length must be greater than 0.001 (corresponding to the value in this application). and ).

[0057] Optionally, determining the fault direction corresponding to the current sampling frequency according to the difference between the first arrival time and the second arrival time corresponding to the current sampling frequency includes:

[0058] If the difference between the first arrival time and the second arrival time corresponding to the current sampling frequency is greater than a preset value, the fault direction corresponding to the current sampling frequency is a forward line fault;

[0059] If the difference between the first arrival time and the second arrival time corresponding to the current sampling frequency is less than a preset value, the fault direction corresponding to the current sampling frequency is a reverse line fault;

[0060] The default value is Among them, f s Indicates the preset sampling frequency.

[0061] In this embodiment, the comparison between the difference between the first arrival time and the second arrival time corresponding to the current sampling frequency and the preset value can be expressed as the following formula:

[0062]

[0063] Among them, t Q =M1 represents the first arrival time, t F =M2 represents the second arrival time.

[0064] Optionally, obtaining a first wavelet transform coefficient of the current reverse wave within a preset time segment and determining a fault area corresponding to a current sampling frequency according to the first wavelet transform coefficient includes:

[0065] Record and save the fourth wavelet transform coefficient of the current reverse traveling wave within the subsequent preset time window starting from the second arrival time; wherein, the calculation formula of the preset time window is as follows:

[0066]

[0067] Among them, T p represents the preset time window, k1 represents the reliability coefficient of the preset time window length, L1 represents the length of the protected line, and v represents the speed of the traveling wave;

[0068] The wavelet transform coefficients within a preset time segment are selected from the fourth wavelet transform coefficients as the first wavelet transform coefficients; wherein the calculation formula of the preset time segment is:

[0069] [t F +2L1 / v-τ t F +2L l / v+τ]

[0070] Among them, τ represents the matching tolerance, and the calculation formula is f s represents the preset sampling frequency, k2 represents the preset matching tolerance reliability coefficient;

[0071] The first wavelet transform coefficient is compared with the detection threshold to determine the fault area corresponding to the current sampling frequency.

[0072] In this embodiment, the preset time window reliability coefficient k1 is preferably set to 1.05-1.2, the traveling wave velocity v is preferably set to 297500 km / s, and the preset matching tolerance reliability coefficient k2 is preferably set to 1-2.

[0073] In this embodiment, the preset time window is relatively short, so as to achieve rapid and reliable removal of line faults and ensure the safe and stable operation of the distribution network.

[0074] Optionally, comparing the first wavelet transform coefficient with a detection threshold to determine a fault area corresponding to a current sampling frequency includes:

[0075] If the first wavelet transform coefficients are all less than the detection threshold, the fault area corresponding to the current sampling frequency is an internal fault;

[0076] If any first wavelet transform coefficient is greater than the detection threshold, the fault area corresponding to the current sampling frequency is an out-of-area fault.

[0077] In this embodiment, the comparison between the first wavelet transform coefficient and the detection threshold can be written as the following formula:

[0078]

[0079] Among them, w iF P (t) represents the first wavelet transform coefficient, W iFset represents the detection threshold, k3 is the preset detection threshold reliability coefficient, W iQmax Represents the maximum value in the second wavelet transform coefficient, W iFmax Represents the maximum value in the third wavelet transform coefficient.

[0080] Optionally, protecting the distribution network according to the fault area corresponding to the current sampling frequency includes:

[0081] If the fault corresponding to the current sampling frequency is an internal fault, the protection of the distribution network is started;

[0082] If the fault corresponding to the current sampling frequency is an out-of-zone fault, the distribution network will be protected and locked.

[0083] In this embodiment, by determining whether the fault corresponding to the current sampling frequency is an internal fault or an external fault, different distribution network protection modes are selected to protect the distribution network.

[0084] Optionally, if the fault direction corresponding to the current sampling frequency is a forward line fault, calculating a first wavelet transform coefficient of a current reverse traveling wave within a second preset time length starting from the second arrival time, and determining a fault area corresponding to the current sampling frequency based on the first wavelet transform coefficient, further comprising:

[0085] If the fault direction corresponding to the current sampling frequency is a reverse route fault, the distribution network will be protected and locked.

[0086] In this embodiment, protection needs to be activated only when the fault occurs on the forward route. Therefore, if it is determined to be a reverse route fault, the protection is locked and the distribution network protection judgment is continued at the next sampling frequency.

[0087] Optionally, a distribution network protection method based on transient traveling wave time domain feature matching is described with a specific embodiment, as follows:

[0088] Build a simulation platform such as PSCAD / EMTDC Figure 2 The 10kV distribution network model shown has a system impedance of j0.416Ω, a transformer ratio of 110 / 10kV, a Y0-Δ connection, and a capacity of 6.3MVA; L1, L2, L3, L4, L5, and L6 are overhead lines with lengths of 5km, 6km, 3.5km, 4km, 4km, and 4.9km, respectively. The positive sequence impedance is (0.345+j0.27)Ω / km; L7 is a cable line with a length of 4.9km and a positive sequence impedance of (0.069+j0.34)Ω / km; (P1+jQ1) to (P4+jQ4) are loads, all of which are 0.4MVA, with a power factor of 0.85. Taking line L1 as the object, that is, the preset position in this embodiment, the proposed protection K1 is located on the left side of line L1, and the sampling rate of the protection device is set to f s =1MHz. The present invention is verified by setting internal and external faults in the model.

[0089] A BC two-phase short circuit fault is set at 2 km on the reverse direction line L5, 2 km on the line L1, and 2 km on the forward direction lower level line L2 for example analysis.

[0090] Case 1:

[0091] A BC two-phase short circuit fault occurred at 2 km on the reverse direction line L5, and the fault occurred at a time of 3 μs.

[0092] Step 1:

[0093] Step 1: Collect the three-phase voltage data and three-phase current data on the line in real time at the local protection installation. The sampling rate is 1MHz, and the sampling data of 50μs is stored. The data length is 50, and the sampled three-phase voltage data u is obtained. a,u b , and the sampled three-phase current data i a ,i b .

[0094] Step 2: Filter using a 10th-order high-pass filter algorithm to obtain the corresponding filtered voltage data u a F (t),u b F (t) and current data i a F (t), i b F (t), the calculation formula is as follows:

[0095]

[0096] Step 2:

[0097] Step 1: Calculate the current forward wave i Q (t) is opposite to the current wave i F (t), and the current forward wave i is obtained Q (t) is opposite to the current wave i F (t), such as Figure 3 The figure shows the current forward wave and current reverse wave waveform within 50μs after the fault occurs 2km outside the reverse zone, where i Q (t) and i F (t) is calculated as follows:

[0098]

[0099] Step 2: Take the scale factor a=2 and the translation factor b=1, and get the wavelet basis function as follows:

[0100]

[0101] Based on the above wavelet basis function, the current forward wave i Q (t) is opposite to the current wave i F (t) Perform wavelet transform to obtain the corresponding wavelet coefficient w iQ (a，b) (t), W iF (a，b) (t), such as Figure 4 Shown are the wavelet coefficients of the current forward wave and the current reverse wave after a fault occurs 2 km outside the reverse zone.

[0102]

[0103] Step 3: Detect Therefore, the first wave in the current forward wave arrives at time t Q=10μs; the arrival time of the first wave in the current reverse wave is t F =43μs.

[0104] Step 4: Calculate |t Q -t F |=33μs, obviously |t Q -t F |=33μs>1μs. According to the fault direction discriminant formula, the fault occurs on the line in the opposite direction, and the protection is locked.

[0105] Fault direction discriminant:

[0106] Case 2:

[0107] A BC two-phase short circuit fault occurred at 2 km on line L1, and the fault occurred at a time of 3 μs.

[0108] Step 1:

[0109] Step 1: Collect the three-phase voltage data and three-phase current data on the line in real time at the local protection installation. The sampling rate is 1MHz, and the sampling data of 50μs is stored. The data length is 50, and the sampled three-phase voltage data u is obtained. a ,u b , and the sampled three-phase current data i a ,i b .

[0110] Step 2: Filter using a 10th-order high-pass filter algorithm to obtain the corresponding filtered voltage data u a F (t),u b F (t), and current data i a F (t), i b F (t), the calculation formula is as follows:

[0111]

[0112] Step 2:

[0113] Step 1: Calculate the current forward wave i Q (t) is opposite to the current wave i F (t), and the current forward wave i is obtained Q (t) is opposite to the current wave i F (t), such as Figure 5 The figure shows the current forward wave and current reverse wave waveform within 50μs after the fault occurs at 2km in the area, where i Q (t) and i F(t) is calculated as follows:

[0114]

[0115] Step 2: Take the scale factor a=2 and the translation factor b=1, and get the wavelet basis function as follows:

[0116]

[0117] Based on the above wavelet basis function, the current forward wave i Q (t) is opposite to the current wave i F (t) Perform wavelet transform to obtain the corresponding wavelet coefficient w iQ (a，b) (t), W iF (a，b) (t), such as Figure 6 Shown are the wavelet coefficients of the current forward wave and the current reverse wave after a fault occurs 2 km in the area.

[0118]

[0119] Step 3: Detect Therefore, the first wave in the current forward wave arrives at time t Q =10μs; the arrival time of the first wave in the current reverse wave is t F =43μs.

[0120] Step 4: Calculate |t Q -t F |=0μs, obviously |t Q -t F |=0μs<1μs. According to the fault direction discriminant formula, the fault occurs on the line in the positive direction and the protection is activated.

[0121] Fault direction discriminant:

[0122] Step 3:

[0123] Step 1: Take the time window reliability coefficient k1 = 1.1 and calculate the protection criterion time window length T P =36μs, then the current reverse traveling wavelet transform coefficient data from 10μs to 46μs is saved and recorded as w iF P (t).

[0124] Step 2: Take the matching tolerance reliability coefficient k2=2, and calculate the protection criterion matching tolerance to be τ=1μs.

[0125] Step 3: Take the detection threshold reliability coefficient k3 = 0.1 and calculate the detection threshold W iFsetis 0.00601, in the time period [42 μ s, 44 μ The current inverse traveling wavelet transform coefficient W on s] iF p (42:44) = [0 0 0 0 0 0 0] is always less than the detection threshold W iFset 0.00601; According to the internal and external fault discrimination formula, the fault is an internal fault and the protection is activated.

[0126]

[0127] Case 3:

[0128] A BC two-phase short circuit fault occurred at 2 km on the forward line L2, and the fault occurred at a time of 7 μs.

[0129] Step 1:

[0130] Step 1: Collect the three-phase voltage data and three-phase current data on the line in real time at the local protection installation. The sampling rate is 1MHz, and the sampling data of 50μs is stored. The data length is 50, and the sampled three-phase voltage data u is obtained. a ,u b , and the sampled three-phase current data i a ,i b .

[0131] Step 2: Filter using a 10th-order high-pass filter algorithm to obtain the corresponding filtered voltage data u a F (t),u b F (t), and current data i a F (t), i b F (t), the calculation formula is as follows:

[0132]

[0133] Step 2:

[0134] Step 1: Calculate the current forward wave i Q (t) is opposite to the current wave i F (t), and the current forward wave i is obtained Q (t) is opposite to the current wave i F (t), such as Figure 7 The following are the waveforms of the forward and reverse current waves after a fault occurs 2 km outside the forward zone:

[0135]

[0136] Step 2: Take the scale factor a=2 and the translation factor b=1, and get the wavelet basis function as follows:

[0137]

[0138] Based on the above wavelet basis function, the current forward wave i Q (t) is opposite to the current wave i F (t) Perform wavelet transform to obtain the corresponding wavelet coefficient w iQ (a，b) (t), W iF (a，b) (t), such as Figure 8 Shown are the wavelet coefficients of the current forward wave and the current reverse wave after a fault occurs 2 km outside the forward zone.

[0139]

[0140] Step 3: Detect Therefore, the first wave in the current forward wave arrives at time t Q = 27μs; the arrival time of the first wave in the current reverse wave is t F =27μs.

[0141] Step 4: Calculate |t Q -t F |=0μs, obviously |t Q -t F |=0μs<1μs. According to the fault direction discriminant formula, the fault occurs on the line in the positive direction and the protection is activated.

[0142] Fault direction discriminant:

[0143] Step 3:

[0144] Step 1: Take the time window reliability coefficient k1 = 1.1 and calculate the protection criterion time window length T P =36μs, then the current reverse traveling wavelet transform coefficient data of 27μs to 63μs is saved and recorded as w iF P (t).

[0145] Step 2: Take the matching tolerance reliability coefficient k2 = 1.5, and calculate the protection criterion matching tolerance to be T = 1μs.

[0146] Step 3: Take the detection threshold reliability coefficient k3 = 0.1 and calculate the detection threshold w iFset The current inverse traveling wavelet transform coefficient w in the time interval [59μs, 61μs] is 0.00185. iF P(59:61) = [0 0 0 -0.003 0 0 0] is always less than the detection threshold W iF (60)=-0.0030 is greater than 0.00185; according to the internal and external fault discrimination formula, the fault is an external fault and the protection is locked.

[0147]

[0148] like Figure 9 As shown, the present invention provides a distribution network protection system based on transient traveling wave time domain feature matching, including:

[0149] A traveling wave determination module is used to collect three-phase voltage data and three-phase current data at a preset location of the distribution network within a preset time period at a preset sampling frequency, and calculate the current forward traveling wave and current reverse traveling wave corresponding to the current sampling frequency based on the three-phase voltage data and three-phase current data corresponding to the current sampling frequency;

[0150] An arrival time determination module is used to perform wavelet transform on the current forward wave and the current reverse wave corresponding to the current sampling frequency, and use the maximum value method to determine the first arrival time of the first wave head in the current forward wave and the second arrival time of the first wave head in the current reverse wave;

[0151] A fault direction determination module is used to determine the fault direction corresponding to the current sampling frequency based on the difference between the first arrival time and the second arrival time corresponding to the current sampling frequency;

[0152] a fault region determination module configured to obtain a first wavelet transform coefficient of a current reverse traveling wave in a preset time segment if the fault direction corresponding to the current sampling frequency is a forward line fault, and determine the fault region corresponding to the current sampling frequency based on the first wavelet transform coefficient;

[0153] The distribution network protection module is used to protect the distribution network according to the fault area corresponding to the current sampling frequency.

[0154] Optionally, the traveling wave determination module is specifically configured to:

[0155] According to the three-phase voltage data and three-phase current data corresponding to the current sampling frequency, the filtered three-phase voltage data and three-phase current data corresponding to the current sampling frequency are determined by the 10th-order high-pass filtering algorithm. The formula is as follows:

[0156]

[0157] Among them, u a (t-k) 、u b (t-k) Indicates the three-phase voltage data of the tkth order corresponding to the current sampling frequency, i a(t-k) 、i b (t-k) Indicates the three-phase current data of the tkth order corresponding to the current sampling frequency, u a F (t),u b F (t) represents the filtered three-phase voltage data corresponding to the current sampling frequency, i a F (t), i b F (t) represents the filtered three-phase current data corresponding to the current sampling frequency, N is the order of the filter, f c is the cutoff frequency, which indicates the lowest frequency allowed to pass through in the signal, w(t) is the preset window function, and t represents the time;

[0158] According to the filtered three-phase voltage data and three-phase current data corresponding to the current sampling frequency, the current forward wave and current reverse wave corresponding to the current sampling frequency are calculated. The formula is as follows:

[0159]

[0160] Among them, i Q (t) represents the current forward wave corresponding to the current sampling frequency, i F (t) represents the current reverse wave corresponding to the current sampling frequency.

[0161] Optionally, the arrival time determination module is specifically configured to:

[0162] Perform wavelet transform on the current forward wave and the current reverse wave corresponding to the current sampling frequency to determine the second wavelet transform coefficient of the current forward wave within the preset time length corresponding to the current sampling frequency and the third wavelet transform coefficient of the current reverse wave. The formula is as follows:

[0163]

[0164] Among them, W iQ (a，b) (t), W iF (a，b) (t) represents the second wavelet transform coefficient and the third wavelet transform coefficient within the preset time length corresponding to the current sampling frequency, where a is the scale factor, b is the translation factor, and ψ a，b (t) represents the preset wavelet basis function;

[0165] The time corresponding to the maximum value is found from the second wavelet transform coefficient as the first arrival time, and the time corresponding to the maximum value is found from the third wavelet transform coefficient as the second arrival time; wherein, the calculation formula of the maximum value is as follows:

[0166]

[0167] Among them, M1 and M2 represent the first arrival time and the second arrival time, and represents the maximum value in the second wavelet transform coefficient, Represents the maximum value in the third wavelet transform coefficient.

[0168] Optionally, the fault direction judgment module is specifically configured to:

[0169] If the difference between the first arrival time and the second arrival time corresponding to the current sampling frequency is greater than a preset value, the fault direction corresponding to the current sampling frequency is a forward line fault;

[0170] If the difference between the first arrival time and the second arrival time corresponding to the current sampling frequency is less than a preset value, the fault direction corresponding to the current sampling frequency is a reverse line fault;

[0171] The default value is Among them, f s Indicates the preset sampling frequency.

[0172] Optionally, the fault area determination module is specifically configured to:

[0173] Record and save the fourth wavelet transform coefficient of the current reverse traveling wave within the subsequent preset time window starting from the second arrival time; wherein, the calculation formula of the preset time window is as follows:

[0174]

[0175] Among them, T P represents the preset time window, k1 represents the reliability coefficient of the preset time window length, L1 represents the length of the protected line, and v represents the speed of the traveling wave;

[0176] The wavelet transform coefficients within a preset time segment are selected from the fourth wavelet transform coefficients as the first wavelet transform coefficients; wherein the calculation formula of the preset time segment is:

[0177] [t F +2L1 / v-τ t F +2L1 / v+τ]

[0178] Among them, τ represents the matching tolerance, and the calculation formula is f s represents the preset sampling frequency, k2 represents the preset matching tolerance reliability coefficient;

[0179] The first wavelet transform coefficient is compared with the detection threshold to determine the fault area corresponding to the current sampling frequency.

[0180] Optionally, the fault area determination module is specifically configured to:

[0181] If the first wavelet transform coefficients are all less than the detection threshold, the fault area corresponding to the current sampling frequency is an internal fault;

[0182] If any first wavelet transform coefficient is greater than the detection threshold, the fault area corresponding to the current sampling frequency is an out-of-area fault.

[0183] Optionally, the distribution network protection module is specifically used to:

[0184] If the fault corresponding to the current sampling frequency is an internal fault, the protection of the distribution network is started;

[0185] If the fault corresponding to the current sampling frequency is an out-of-zone fault, the distribution network will be protected and locked.

[0186] Optionally, the fault area determination module is further configured to:

[0187] If the fault direction corresponding to the current sampling frequency is a reverse route fault, the distribution network will be protected and locked.

[0188] Those skilled in the art will appreciate that the present invention may be implemented as a system, method, or computer program product. Therefore, the present disclosure may be specifically implemented in the following forms, namely: in the form of complete hardware, complete software (including firmware, resident software, microcode, etc.), or a combination of hardware and software, generally referred to herein as a "circuit," "module," or "system." Furthermore, in some embodiments, the present invention may also be implemented in the form of a computer program product in one or more computer-readable media, the computer-readable media containing computer-readable program code. Computer-readable storage media may be, for example, but not limited to, electrical, magnetic, optical, electromagnetic, infrared, or semiconductor systems, devices, or components, or any combination thereof.

[0189] In the description of this specification, the reference terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and features of different embodiments or examples without contradiction.

[0190] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. A distribution network protection method based on matching of transient traveling wave time domain characteristics, characterized in that: include: Collecting three-phase voltage data and three-phase current data at a preset location of the power distribution network within a preset time period at a preset sampling frequency, and calculating a current forward wave and a current reverse wave corresponding to the current sampling frequency based on the three-phase voltage data and the three-phase current data corresponding to the current sampling frequency; Performing wavelet transformation on the current forward wave and the current reverse wave corresponding to the current sampling frequency, and using a maximum method to determine a first arrival time of a wave head in the current forward wave and a second arrival time of a wave head in the current reverse wave; determining a fault direction corresponding to the current sampling frequency according to a difference between the first arrival time and the second arrival time corresponding to the current sampling frequency; If the fault direction corresponding to the current sampling frequency is a forward line fault, obtaining a first wavelet transform coefficient of the current reverse traveling wave within a preset time segment, and determining the fault area corresponding to the current sampling frequency according to the first wavelet transform coefficient; The distribution network is protected according to the fault area corresponding to the current sampling frequency.

2. The method according to claim 1, characterized in that Calculating a current forward wave and a current reverse wave corresponding to the current sampling frequency according to the three-phase voltage data and the three-phase current data corresponding to the current sampling frequency includes: According to the three-phase voltage data and the three-phase current data corresponding to the current sampling frequency, filtering is performed using a 10th-order high-pass filtering algorithm to determine the filtered three-phase voltage data and three-phase current data corresponding to the current sampling frequency. The formula is as follows: Among them, u a (tk),u b (tk) represents the three-phase voltage data of the tkth order corresponding to the current sampling frequency, i a (tk), i b (tk) represents the three-phase current data of the tkth order corresponding to the current sampling frequency, u a F (t),u b F (t) represents the filtered three-phase voltage data corresponding to the current sampling frequency, i a F (t), i b F (t) represents the filtered three-phase current data corresponding to the current sampling frequency, N is the order of the filter, f c is the cutoff frequency, which indicates the lowest frequency allowed to pass through in the signal, w(t) is the preset window function, and t represents the time; According to the filtered three-phase voltage data and three-phase current data corresponding to the current sampling frequency, the current forward wave and current reverse wave corresponding to the current sampling frequency are calculated. The formula is as follows: Among them, i Q (t) represents the current forward wave corresponding to the current sampling frequency, i F (t) represents the current reverse wave corresponding to the current sampling frequency.

3. The method according to claim 2, characterized in that Performing wavelet transform on the current forward wave and the current reverse wave corresponding to the current sampling frequency, and using a maximum method to determine a first arrival time of a wave head of the first wave in the current forward wave and a second arrival time of a wave head of the first wave in the current reverse wave, including: Perform wavelet transform on the current forward wave and the current reverse wave corresponding to the current sampling frequency to determine the second wavelet transform coefficient of the current forward wave within the preset time length corresponding to the current sampling frequency and the third wavelet transform coefficient of the current reverse wave. The formula is as follows: Among them, W iQ (a，b) (t), W iF (a，b) (t) represents the second wavelet transform coefficient and the third wavelet transform coefficient within the preset time length corresponding to the current sampling frequency, where a is the scale factor, b is the translation factor, and ψ a，b (t) represents the preset wavelet basis function; The time corresponding to the maximum value is found from the second wavelet transform coefficient as the first arrival time, and the time corresponding to the maximum value is found from the third wavelet transform coefficient as the second arrival time; wherein, the calculation formula of the maximum value is as follows: Among them, M1 and M2 represent the first arrival time and the second arrival time, and represents the maximum value in the second wavelet transform coefficient, Represents the maximum value in the third wavelet transform coefficient.

4. The method according to claim 1, wherein Determining a fault direction corresponding to the current sampling frequency according to a difference between the first arrival time and the second arrival time corresponding to the current sampling frequency includes: If the difference between the first arrival time and the second arrival time corresponding to the current sampling frequency is greater than a preset value, the fault direction corresponding to the current sampling frequency is a forward line fault; If the difference between the first arrival time and the second arrival time corresponding to the current sampling frequency is less than a preset value, the fault direction corresponding to the current sampling frequency is a reverse line fault; The preset value is Among them, f s Indicates the preset sampling frequency.

5. The method according to claim 1, wherein The obtaining of a first wavelet transform coefficient of the current reverse traveling wave within a preset time segment and determining a fault area corresponding to a current sampling frequency according to the first wavelet transform coefficient includes: Record and save the fourth wavelet transform coefficient of the current reverse traveling wave within a subsequent preset time window starting from the second arrival time; wherein the calculation formula of the preset time window is as follows: Among them, T P represents the preset time window, k1 represents the reliability coefficient of the preset time window length, L1 represents the length of the protected line, and v represents the speed of the traveling wave; The wavelet transform coefficients within a preset time segment are selected from the fourth wavelet transform coefficients as the first wavelet transform coefficients; wherein the calculation formula of the preset time segment is: [t F +2L1 / v-τ t F +2L1 / v+τ] Among them, τ represents the matching tolerance, and the calculation formula is f s represents the preset sampling frequency, k2 represents the preset matching tolerance reliability coefficient; The first wavelet transform coefficient is compared with a detection threshold to determine a fault area corresponding to a current sampling frequency.

6. The method according to claim 5, characterized in that Comparing the first wavelet transform coefficient with a detection threshold to determine a fault area corresponding to a current sampling frequency includes: If the first wavelet transform coefficients are all less than the detection threshold, the fault area corresponding to the current sampling frequency is an internal fault; If any of the first wavelet transform coefficients is greater than a detection threshold, the fault area corresponding to the current sampling frequency is an out-of-area fault.

7. The method according to claim 5, characterized in that The detection threshold is: Among them, W iFset represents the detection threshold, k3 is the preset detection threshold reliability coefficient, W iQmax Represents the maximum value in the second wavelet transform coefficient, W iFmax Represents the maximum value in the third wavelet transform coefficient.

8. The method according to claim 1, characterized in that The distribution network is protected according to the fault area corresponding to the current sampling frequency, including: If the fault corresponding to the current sampling frequency is an internal fault, the protection of the distribution network is started; If the fault corresponding to the current sampling frequency is an out-of-zone fault, the distribution network will be protected and locked.

9. The method according to any one of claims 1 to 8, characterized in that If the fault direction corresponding to the current sampling frequency is a forward line fault, calculating a first wavelet transform coefficient of a current reverse traveling wave within a second preset time length starting from the second arrival time, and determining a fault area corresponding to the current sampling frequency based on the first wavelet transform coefficient, further comprising: If the fault direction corresponding to the current sampling frequency is a reverse route fault, the distribution network is protected and locked.

10. A distribution network protection system based on transient traveling wave time domain feature matching, characterized in that: include: a traveling wave determination module, configured to collect three-phase voltage data and three-phase current data at a preset location of the power distribution network within a preset time period at a preset sampling frequency, and calculate a current forward traveling wave and a current reverse traveling wave corresponding to the current sampling frequency based on the three-phase voltage data and the three-phase current data corresponding to the current sampling frequency; an arrival time determination module, configured to perform wavelet transform on the current forward wave and the current reverse wave corresponding to the current sampling frequency, and determine a first arrival time of the first wave head in the current forward wave and a second arrival time of the first wave head in the current reverse wave by using a maximum value method; a fault direction determination module, configured to determine the fault direction corresponding to the current sampling frequency according to a difference between the first arrival time and the second arrival time corresponding to the current sampling frequency; a fault area determination module, configured to obtain a first wavelet transform coefficient of a current reverse traveling wave in a preset time segment if the fault direction corresponding to the current sampling frequency is a forward line fault, and determine the fault area corresponding to the current sampling frequency based on the first wavelet transform coefficient; The distribution network protection module is used to protect the distribution network according to the fault area corresponding to the current sampling frequency.

Images