A new method for detecting arc high resistance fault of power distribution network

Abstract

The present application relates to a kind of new methods for detecting arc high resistance fault of power distribution network.The method is as follows: first, obtain each feeder zero sequence current, calculate the kurtosis value of each feeder zero sequence current in the quarter cycle after fault occurs, when the kurtosis value of any one feeder is greater than the set threshold, start the arc high resistance fault detection method;Second, obtain bus zero sequence voltage, carry out trapezoidal sliding window integration on bus zero sequence voltage, then carry out differential calculation on the integrated bus zero sequence voltage, obtain characteristic zero sequence voltage;Then, carry out low-pass filtering on each feeder zero sequence current, obtain each feeder characteristic zero sequence current;Finally, calculate the transient characteristic power ratio of each feeder using the obtained characteristic zero sequence voltage and each feeder characteristic zero sequence current, and realize arc high resistance fault detection according to the positive and negative difference of transient characteristic power ratio.

Description

TECHNICAL FIELD

[0001] The application relates to a new arc high-resistance fault detection method for a power distribution network and belongs to the technical field of relay protection of a power distribution network. BACKGROUND

[0002] In medium-voltage power distribution network faults, high-resistance faults account for 5% to 20%, such faults are often accompanied by arcs and are prone to cause major accidents such as fires due to high transition resistance and weak fault signals, and the detection of arc high-resistance faults is particularly difficult. In China, the neutral point of the power distribution network is mostly not grounded or grounded through an arc suppression coil, and the arc suppression coil further weakens the fault characteristics, which adds obstacles to arc high-resistance fault line selection. The existing transient power direction method is difficult to effectively detect due to the weak arc high-resistance fault characteristics. In order to break through this technical bottleneck, it is urgent to improve the transient characteristic power direction method and construct a new arc high-resistance fault detection method to accurately extract fault information and improve detection reliability and ensure the safe and stable operation of the power distribution network. SUMMARY

[0003] The application aims to provide a new arc high-resistance fault detection method for a power distribution network, which solves the problem that the existing transient power direction method cannot effectively detect arc high-resistance faults due to weak characteristics.

[0004] The technical solution adopted by the application is a new arc high-resistance fault detection method for a power distribution network based on an improved transient characteristic power direction method, which specifically comprises the following steps:

[0005] Step 1: Obtain the zero sequence current i 0h (t e ) of each feeder, h is the feeder number, h = 1, 2, 3…, n, e is the sampling point number, and the kurtosis value K h of the zero sequence current of each feeder in the first quarter cycle after the fault occurs is calculated. When the kurtosis value of any one feeder is greater than the set threshold value beta, the protection device is started, and then step 2 is entered.

[0006] Step 2: Obtain the zero sequence voltage u0(t e ) of the bus, perform trapezoidal sliding window integration on the bus zero sequence voltage to obtain u 0J (t e ), and then perform differential calculation on the integrated bus zero sequence voltage u 0J (t e ) to obtain the characteristic zero sequence voltage u 0W (t e ).

[0007] Step 3: Perform low-pass filtering on the zero sequence current i 0h (t e ) of each feeder to obtain the characteristic zero sequence current i lh (t e ) of each feeder.), and the characteristic zero-sequence voltage u0(t 0W (t e ) of each feeder is calculated h , and the arc high-resistance fault is detected according to the positive and negative differences of the transient characteristic power ratio T h .

[0008] Preferably, the specific process of constructing the starting criterion using the zero-sequence current of each feeder in step 1 is as follows:

[0009] Step 1.1: Obtain the zero-sequence current i 0h (t e ), h = 1, 2, 3,..., n, and calculate the kurtosis value K h of the zero-sequence current of each feeder within a quarter period after the fault occurs h The specific calculation formula of the kurtosis value K

[0010]

[0011] In the formula, i j is the zero-sequence current sampling value corresponding to the jth sampling point, n is the number of zero-sequence current sampling points within a quarter period after the fault occurs, μ is the mean value of the zero-sequence current within a quarter period after the fault occurs, σ is the standard deviation of the zero-sequence current within a quarter period after the fault occurs,

[0012] Step 1.2: When the kurtosis value of any feeder is greater than the set threshold β, the protection device is started, and then step 2 is entered;

[0013] The selection principle of the threshold β is as follows: when the system is normally operated, the current waveform is a standard sine wave, and the kurtosis value is 1.5; after the fault occurs, the waveform will have a transient process, resulting in a sudden increase in the kurtosis value of the waveform. Since the system actually exists three-phase asymmetric operation or noise, a margin of 2-3 times is considered, and the value of β is set to 4.5, that is, when K h > 4.5, the protection device is started.

[0014] Preferably, the step 2 includes the following specific steps:

[0015] Step 2.1: Obtain the bus zero-sequence voltage u0(t e ), and integrate the bus zero-sequence voltage by using a sliding trapezoidal window with a size of 7 sampling points, which is specifically shown in the following formula:

[0016]

[0017] In the formula, f sis the sampling rate, k is the first sampling point in the sampling window, l = 1, 2, 3, 4, 5 is the corresponding different sampling point in the sampling window, u0(t k ) is the bus zero sequence voltage sampling value corresponding to the kth sampling point in the sampling window, u0(t k+l ) is the bus zero sequence voltage sampling value corresponding to the k+1th sampling point to the k+5th sampling point in the sampling window, u0(t k+6 ) is the bus zero sequence voltage sampling value corresponding to the k+6th sampling point in the sampling window;

[0018] Step 2.2: Central difference processing is performed on the integral result u 0J (t e ) to obtain the characteristic zero sequence voltage u 0W (t e ), which is specifically shown in the following formula:

[0019]

[0020] In the formula, Δt is the time interval of adjacent sampling points.

[0021] Preferably, the specific process of step 3 is as follows:

[0022] Step 3.1: Low-pass filtering is performed on each feeder zero sequence current i 0h (t e ) to obtain each feeder characteristic zero sequence current i lh (t e );

[0023] Step 3.2: The transient characteristic quantity of one-fourth power frequency period is extracted from the characteristic zero sequence voltage u 0W (t e ) in step 2 and the feeder characteristic zero sequence current i lh (t e ) in step 3.1 to obtain the transient characteristic zero sequence voltage and the feeder transient characteristic zero sequence current The feeder transient characteristic power Q h is calculated, which is specifically shown in the following formula:

[0024]

[0025] In the formula, T is one power frequency period, and h = 1, 2, 3, …, n;

[0026] Step 3.3: The feeder transient characteristic power ratio T h is defined as the ratio of the feeder transient characteristic power Q h to the absolute value of the product of all feeder transient characteristic powers, h = 1, 2, 3, …, n, and the specific calculation formula of T h is shown in the following formula:

[0027]

[0028] When there is a transient characteristic power ratio T of a certain feeder h If the sign is opposite to that of other feeders, it is determined that the feeder has an arcing high-resistivity fault.

[0029] Working principle of the invention

[0030] 1. Equivalent circuit for arc flash high-resistance grounding fault

[0031] When a high-resistance arc fault occurs, the feeder inductance, feeder resistance, and arc suppression coil resistance can be ignored. Therefore, the zero-sequence equivalent network of the resonant grounding system can be simplified to... Figure 2 As shown in the figure. L p The system has n feeders, where the y-th feeder is assumed to be faulty and m is a healthy feeder, with m = 1, 2, ..., y-1, y+1, ..., n. C 0h Let h be the zero-sequence capacitance to ground of the h-th feeder, where h = 1, 2, ..., n, and R be the arc-damped high-resistance grounding resistance; i 0h Let i be the zero-sequence current of the h-th feeder. 0f with i L Let u represent the fault point current and the neutral point current, respectively. 0f u0(t) represents the phase voltage at the fault point and the zero-sequence voltage of the bus, respectively.

[0032] according to Figure 2 For the network shown, write the differential equations:

[0033]

[0034] In the formula, This is the sum of the capacitances of each feeder to ground.

[0035] Solving the above equations simultaneously, we can establish the differential equation as follows:

[0036]

[0037] The characteristic roots of the above equation are:

[0038]

[0039] When the system is in an underdamped state, R satisfies:

[0040]

[0041] At this time, the attenuation factor δ and the damped oscillation angular frequency ω f The following equation is satisfied.

[0042]

[0043] When high resistance grounding fault occurs in resonant grounding system, the system is generally in under-damped state, set u 0f = U ms sin(ω0t1+θ), U ms and θ are the amplitude and initial phase of the pre-fault voltage at the fault point, ω0 is the angular frequency of power frequency. At this time, the current i L flowing through the neutral point is:

[0044]

[0045] Where B, A1, A2 are the coefficients set for solving the differential equation of neutral point current. And the transient component i L_z of the neutral point current is:

[0046] i L_z e -δt (A1cos(ω f t1)+A2sin(ω f t1))

[0047] The first and second derivatives of i L are derived, and the specific results are:

[0048]

[0049] The initial conditions of i L are:

[0050] i L (0 - )=i L (0 + )=0

[0051] From the above derivation formula, when t=0, we can get:

[0052]

[0053] The calculation can be obtained:

[0054]

[0055] Further, the bus zero sequence voltage u0(t) is:

[0056]

[0057] Where the transient component u 0_z (t) of the bus zero sequence voltage is:

[0058] u 0_z (t)=L p e -δt [(A2ωf -A1δ)cos(ω f t)-(A1ω f +A2δ)sin(ω f t)]

[0059] Therefore, the zero-sequence current i of a healthy feeder can be obtained. 0m for:

[0060]

[0061] In the formula, m = 1, 2, ..., y-1, y+1, ..., n.

[0062] Improve the transient component of zero-sequence current in the feeder. 0m_z for:

[0063]

[0064] Furthermore, based on Figure 2 The direction of current flow can be used to calculate the zero-sequence current i of the faulty feeder y. 0y for:

[0065]

[0066] The transient component of the zero-sequence current of the fault feeder is i 0y_z for:

[0067]

[0068] 2. Applicability Analysis of Transient Power Direction Method in High-Resistance Grounding Faults of Resonant Grounding Systems

[0069] The basic principle of the transient current power direction method is: the zero-sequence current at the outlet of a healthy line has the same polarity as the derivative of the zero-sequence voltage of the bus, and the polarity is opposite to that of the transient zero-sequence current at the outlet of a faulty line. The line with a negative direction coefficient Q is selected as the faulty line. Define the transient zero-sequence current i at the outlet of a certain outgoing line x. x The directional coefficients of the zero-sequence voltage u0(t) and the zero-sequence voltage u0(t) are Q. x Its expression is:

[0070]

[0071] Let Q be the transient power direction factor of the m-th healthy line. m The transient power directional coefficient of the faulty line is Q. y We can conclude that:

[0072]

[0073] In the formula, m = 1, 2, ..., y-1, y+1, ..., n.

[0074] The above formula is divided into two parts, wherein:

[0075]

[0076] Q y1 and Q y2 are calculated respectively:

[0077]

[0078] As can be seen from the above formula, the positive and negative of the transient power of the fault feeder is related to A1, A2, the attenuation factor δ and the damped oscillation angular frequency ω f , and the polarity positive and negative cannot be obtained only by the formula, so the transient power direction method may fail in some working conditions.

[0079] 3, kurtosis

[0080] Kurtosis is a statistical quantity used to describe the characteristics of data distribution, which reflects the deviation of data distribution from the normal distribution, and the calculation formula of the kurtosis value of each feeder zero sequence current of the application is as follows:

[0081]

[0082] In the formula, i j is the zero sequence current sampling value corresponding to the jth sampling point, n is the number of zero sequence current sampling points in the quarter cycle after the fault occurs, μ is the mean value of the zero sequence current in the quarter cycle after the fault occurs, σ is the standard deviation of the zero sequence current in the quarter cycle after the fault occurs,

[0083] When the system is normally operated, the current waveform is a standard sine wave, and the kurtosis value is 1.5; after the fault occurs, the transient process appears, which causes the kurtosis value to suddenly increase at this time, and since there is three-phase asymmetric operation or noise in the actual system, the application considers a margin of 2-3 times, and sets the value of β to 4.5, that is, when the kurtosis value of any feeder is greater than the set threshold β, the protection device is started.

[0084] Compared with the prior art, the application has the following advantages:

[0085] 1) In terms of high resistance fault detection starting: the traditional zero sequence voltage starting method has insufficient sensitivity to weak faults, needs to sample data for more than one cycle, has slow response, is prone to misoperation due to transient overvoltage interference, and is often ineffective in a small current grounding system due to insufficient increase of zero sequence voltage. The existing method calculates the kurtosis of each feeder zero sequence current in the quarter cycle after the fault, and starts when the kurtosis of any feeder is greater than 4.5, which can accurately capture the transient fault through the non-normal distortion of the current waveform, shorten the response time, enhance the anti-interference ability, especially suitable for small current grounding systems, and improve the protection speed, reliability and adaptability.

[0086] 2) In signal processing: the advantages of integrating and then differentiating the bus zero sequence voltage are obvious. Integration can accumulate the zero sequence voltage energy of weak faults, convert small voltages such as high resistance grounding into identifiable energy increments, suppress high frequency noise, and reduce false operation; differentiation can capture the voltage rate of change at the moment of fault, amplify the transient mutation characteristics, and achieve fast response. The combination of the two breaks through the traditional amplitude dependence, enhances the detection sensitivity and anti-interference, and balances the sensitivity, speed and reliability of the protection in high resistance fault and other scenarios. BRIEF DESCRIPTION OF DRAWINGS

[0087] Figure 1 Flow chart of arc high resistance fault detection method in the application;

[0088] Figure 2 Zero sequence equivalent network of resonant grounding system in the application;

[0089] Figure 3 Simulation model schematic diagram of 10kV resonant grounding system in the application;

[0090] Figure 4 Emanuel arc working condition model in the application;

[0091] Figure 5 (a) Bus zero sequence voltage u0(t) under case 1 in the application; e );

[0092] Figure 5 (b) Trapezoidal sliding window integration u(t) of bus zero sequence voltage under case 1 in the application; 0J (t e );

[0093] Figure 5 (c) Characteristic zero sequence voltage u(t) under case 1 in the application; 0W (t e );

[0094] Figure 6 (a) Zero sequence current waveform i(t) of each feeder under case 1 in the application; 0h (t e );

[0095] Figure 6 (b) Transient characteristic zero sequence current i(t) of each feeder under case 1 in the application; DETAILED DESCRIPTION

[0096] The application will be described in detail below in combination with the drawings and specific embodiments.

[0097] A new method for detecting arc high resistance faults in distribution networks:

[0098] Step 1: Obtain the zero-sequence current i of each feeder 0h (t e ), h is the feeder number, h = 1, 2, 3, ..., n, e is the sampling point number, calculate the kurtosis value K of the zero-sequence current of each feeder within one-quarter of the cycle after the fault occurs. h When the kurtosis value of any feeder is greater than the set threshold β, the protection device is activated, and then the process proceeds to step 2.

[0099] Step 2: Obtain the zero-sequence voltage u0(t) of the bus. e The zero-sequence voltage of the bus is integrated using a trapezoidal sliding window to obtain u. 0J (t e Then, the integrated zero-sequence voltage u of the bus is... 0J (t e Perform differential calculations to obtain the characteristic zero-sequence voltage u. 0W (t e );

[0100] Step 3: Calculate the zero-sequence current i of each feeder. 0h (t e Low-pass filtering is performed to obtain the characteristic zero-sequence current i of each feeder. lh (t e ), and the characteristic zero-sequence voltage u in step 2 0W (t e Calculate the transient characteristic power ratio T for each feeder. h And based on the transient characteristic power ratio T h The positive and negative differences enable arc light high-resistivity fault detection.

[0101] Specifically, the process of constructing the start-up criterion using the zero-sequence current of each feeder in step 1 is as follows:

[0102] Step 1.1: Obtain the zero-sequence current i of each feeder 0h (t e Given h = 1, 2, 3, ..., n, calculate the kurtosis value K of the zero-sequence current of each feeder within a quarter-cycle after the fault occurs. h kurtosis value K h The specific calculation formula is shown below:

[0103]

[0104] In the formula, i j Let be the zero-sequence current sample value corresponding to the j-th sampling point, n be the number of zero-sequence current sampling points within a quarter-cycle after the fault occurs, μ be the mean of the zero-sequence current within a quarter-cycle after the fault occurs, and σ be the standard deviation of the zero-sequence current within a quarter-cycle after the fault occurs.

[0105] Step 1.2: When the kurtosis value of any feeder is greater than the set threshold β, the protection device is started, and then step 2 is entered.

[0106] The selection principle of the threshold β is: when the system is normally operated, the current waveform is a standard sine wave, and the kurtosis value is 1.5; after a fault occurs, the waveform will appear a transient process, resulting in a sudden increase of the kurtosis value of the waveform. Since there is three-phase asymmetric operation or noise in the actual system, a margin of 2-3 times is considered, and the value of β is set to 4.5, that is, K h >4.5, the protection device is started.

[0107] Specifically, the step 2 includes the following specific steps:

[0108] Step 2.1: Obtain the bus zero sequence voltage u0(t e ), and integrate the bus zero sequence voltage by using a sliding trapezoidal with a window size of 7 sampling points, which is specifically shown in the following formula:

[0109]

[0110] In the formula, f s is a sampling rate, k is a first sampling point in a sampling window, and l=1, 2, 3, 4, 5 are different sampling points in the sampling window, u0(t k ) is a bus zero sequence voltage sampling value corresponding to the kth sampling point in the sampling window, u0(t k+l ) is a bus zero sequence voltage sampling value corresponding to the k+1th to k+5th sampling points in the sampling window, and u0(t k+6 ) is a bus zero sequence voltage sampling value corresponding to the k+6th sampling point in the sampling window.

[0111] Step 2.2: Perform central difference processing on the integration result u 0J (t e ) to obtain a characteristic zero sequence voltage u 0W (t e ), which is specifically shown in the following formula:

[0112]

[0113] In the formula, Δt is a time interval of adjacent sampling points.

[0114] Specifically, the specific process of the step 3 is as follows:

[0115] Step 3.1: Perform low-pass filtering on each feeder zero sequence current i 0h (t e ) to obtain each feeder characteristic zero sequence current i lh (te );

[0116] Step 3.2: For the characteristic zero-sequence voltage u from Step 2... 0W (t e and the characteristic zero-sequence current i of each feeder in step 3.1 lh (t e Extracting the transient characteristic quantity of one-quarter of the power frequency cycle yields the transient characteristic zero-sequence voltage. and the transient characteristic zero-sequence current of each feeder Calculate the transient characteristic power Q of each feeder h The specific formula is as follows:

[0117]

[0118] In the formula, T is one power frequency cycle, and h = 1, 2, 3, ..., n.

[0119] Step 3.3: Define the transient characteristic power ratio T of the h-th feeder. h The transient characteristic power Q of this feeder h The ratio of the absolute value of the product of the transient characteristic power of all feeders, h = 1, 2, 3, ..., n, T h The specific calculation formula is shown below:

[0120]

[0121] When there is a transient characteristic power ratio T of a certain feeder h If the sign is opposite to that of other feeders, it is determined that the feeder has an arcing high-resistivity fault.

[0122] Example

[0123] like Figure 3 As shown in Table 1, a neutral-point arc-suppression coil distribution network is constructed, with four feeders l1 to l4. The line parameters are shown in Table 1. The system sampling rate is 10kHz. The system employs overcompensation with an overcompensation degree of 5%, and the arc-suppression coil inductance L... p =0.547H, damping resistance r L =5.1557Ω, i1, i2, i3, i4 are the currents flowing through each feeder. The arcing high-resistivity fault is set to occur at 5km of l1 in 0.2s.

[0124] Table 1. Specific parameters of the line

[0125]

[0126] The Emanuel arc model is used to simulate high-resistance faults. The Emanuel arc model consists of two diodes connected to two anti-parallel DC sources and two asymmetrical resistors, as shown below. Figure 4 As shown: Two DC sources Vp , V n and diode D p , D n composes positive and negative half-cycle current path; two DC sources V p , V n simulates arc voltage, whose value depends on voltage level of system and asymmetric modeling, and changes randomly and independently according to time. When instantaneous value V s > V p , current flows to ground, when V s < V n , current reverses, and during V n < V s < V p , no current flows. Changing V p and V n size increases randomness and extinction time of asymmetric fault, while simulating asymmetric current by taking different values of two nonlinear resistors R p and R n , specific parameters as shown in Table 2.

[0127] Table 2 Arc model parameters of three types

[0128] Arc V p / kV]]> V n / kV]]> [R p / Ω]] [R n / Ω]] Step / ms Case 1 2.2±20.45％ 2.0±20％ 800 750 0.1 Case 2 3.8±10％ 3.6±10％ 400 350 0.1 Case 3 1.2±10％ 1.0±10％ 1200 1100 0.1

[0129] Taking arc model of case 1 as an example, first, the bus zero sequence voltage u0(t e ) is integrated by trapezoidal sliding window to obtain u 0J (t e ), as shown in Fig. Figure 5 (b), it can be seen from the figure that the zero sequence voltage energy of weak fault accumulates, and small amplitude voltage is converted into identifiable energy increment. Then the integrated bus zero sequence voltage u 0J (t e ) is differentiated to obtain the characteristic zero sequence voltage u 0W (t e ), as shown in Fig. Figure 5 (c), it can be seen that the differential captures the voltage rate of change at the moment of fault, and amplifies the transient mutation characteristics. Finally, the low-pass filter is performed on each feeder zero sequence current i 0h (t e ) to obtain the transient characteristic zero sequence current , as shown in Fig. Figure 6 (b), it can be seen from the figure that the characteristic band filter maximally reduces signal distortion, and the high-frequency noise and low-frequency interference in each feeder zero sequence current are filtered out, providing pure and effective characteristic quantity input for subsequent fault detection.

[0130] Using the obtained transient characteristic zero sequence voltage and each feeder transient characteristic zero sequence current The transient characteristic power ratio T of each feeder is calculated h The transient characteristic power ratio T of each feeder is calculated respectively for the three types of arc models h The results are shown in Table 3.

[0131] Table 3 Arc high resistance fault detection conditions of three types

[0132] Arc [T1 / var] [T2 / var] [T3 / var] [T4 / var] Detection situation Case 1 -2.3196 0.0316 0.8306 0.4329 Valid Case 2 -35.1973 0.2325 7.1184 3.4210 Valid Case 3 -1.1796 0.0190 0.4898 0.2568 Valid

[0133] As can be seen from Table 3, in the arc high resistance fault detection conditions of the three types, the transient characteristic power ratio T1 of feeder 1 is negative, while the transient characteristic power ratios of the other feeders are positive, which can determine that feeder 1 is the fault feeder, and the accurate detection of arc high resistance fault can be achieved.

Claims

1. A new method for detecting arc light high resistance fault of power distribution network, characterized in that: Step 1: Obtain each feeder zero sequence current i 0h (t e ), h is the feeder number, h = 1, 2, 3…, n, e is the sampling point number, calculate the kurtosis value K of each feeder zero sequence current in the first quarter cycle after the fault occurs h When the kurtosis value of any one feeder is greater than the set threshold β, the protection device is started, and then step 2 is entered; Step 2: Obtain bus zero sequence voltage u0(t e ), carry out trapezoidal sliding window integration on the bus zero sequence voltage to obtain u 0J (t e ), and then carry out differential calculation on the integrated bus zero sequence voltage u 0J (t e ) to obtain characteristic zero sequence voltage u 0W (t e ); Step 3: low-pass filter each feeder zero sequence current i 0h (t e ) to obtain each feeder characteristic zero sequence current i lh (t e ), and calculate each feeder transient characteristic power ratio T 0W with the characteristic zero sequence voltage u e (t h ) in step 2, and realize arc light high resistance fault detection according to the positive and negative difference of the transient characteristic power ratio T h . The specific process of step 3 is as follows: Step 3.1: Low-pass filtering of each feeder zero-sequence current i 0h (t e ) to obtain each feeder characteristic zero-sequence current i lh (t e ) Step 3.2: For the characteristic zero-sequence voltage u from Step 2... 0W (t e and the characteristic zero-sequence current i of each feeder in step 3.1 lh (t e Extracting the transient characteristic quantity of one-quarter of the power frequency cycle yields the transient characteristic zero-sequence voltage. and the transient characteristic zero-sequence current of each feeder Calculate the transient characteristic power Q of each feeder h The specific formula is as follows: In the formula, T is a power frequency cycle, h = 1, 2, 3…, n; Step 3.3: Define the feeder transient characteristic power ratio T h For the feeder transient characteristic power Q h The ratio of the absolute value of the product of all feeder transient characteristic powers, h = 1, 2, 3…, n, T h The specific calculation formula is as follows: When the transient feature power ratio T h If the other feeders are opposite in sign, then it is judged that the arc light high resistance fault occurs in the feeder.

2. The new method for detecting arc light high resistance fault of power distribution network according to claim 1, characterized in that, The specific process of constructing the starting criterion using the zero sequence current of each feeder in step 1 is as follows: Step 1.1: Obtain the zero sequence current i of each feeder 0h (t e ), h = 1, 2, 3…, n, calculate the kurtosis value K of the zero sequence current of each feeder in the first quarter cycle after the fault occurs h , the specific calculation formula of the kurtosis value K h is shown in the following formula: In the formula, i j is the zero sequence current sampling value corresponding to the jth sampling point, n is the number of zero sequence current sampling points in the quarter cycle after the fault occurs, μ is the mean value of the zero sequence current in the quarter cycle after the fault occurs, and δ is the standard deviation of the zero sequence current in the quarter cycle after the fault occurs. Step 1.2: When the kurtosis value of any one feeder is greater than the set threshold β, the protection device is started, and then step 2 is entered; The selection principle of the threshold β is: when the system is normally operated, the current waveform is a standard sine wave, and the kurtosis value is 1.5; after a fault occurs, the waveform appears a transient process, which leads to a sudden increase of the kurtosis value of the waveform at this time. Since there is three-phase asymmetric operation or noise in the actual system, a margin of 2-3 times is considered, and the value of β is set to 4.5, that is, when K h >4.5, the protection device is started.

3. The new method for detecting arc high resistance fault of power distribution network according to claim 1, characterized in that, The step 2 includes the following specific steps: Step 2.1: Obtain the bus zero-sequence voltage u0(t e ), and integrate the bus zero-sequence voltage using a sliding trapezoidal window with a size of 7 sampling points, as shown in the following formula: wherein, f s is a sampling rate, k is the first sampling point in the sampling window, l = 1, 2, 3, 4, 5 is the corresponding different sampling point in the sampling window, u0(t k ) is the bus zero sequence voltage sampling value corresponding to the kth sampling point in the sampling window, u0(t k+l ) is the bus zero sequence voltage sampling value corresponding to the k+1th sampling point to the k+5th sampling point in the sampling window, u0(t k+6 ) is the bus zero sequence voltage sampling value corresponding to the k+6th sampling point in the sampling window. Step 2.2: Central difference processing is performed on the integration result u 0J (t e ) to obtain the characteristic zero sequence voltage u 0W (t e ), as shown in the following formula: In the formula, Δt is the time interval of adjacent sampling points.

Images