Low-resistance grounding system high-resistance fault detection method based on sampling value vector included angle

Abstract

The invention discloses a low-resistance grounding system high-resistance fault detection method based on a sampling value vector included angle, and belongs to the field of power system relay protection. The method is characterized by comprising the following steps: step a, collecting zero-sequence current in a line; b, judging whether the zero-sequence current break variable exceeds a preset threshold value or not; c, three-phase voltage and zero-sequence current of the outlet side of each line are collected; step d, carrying out data interception on the three-phase voltage and the zero-sequence current; e, calculating a vector included angle between the three-phase voltage and the zero-sequence current; f, whether the vector included angle is smaller than a preset vector included angle threshold value or not is judged; and g, judging a fault phase and a fault section. According to the low-resistance grounding system high-resistance fault detection method based on the sampling value vector included angle, high-resistance grounding fault detection is achieved through the relation between the three-phase voltage after the fault and the zero-sequence current sampling value vector included angle, the problem that a traditional protection method depends on zero-sequence voltage is solved, and the transition resistance resistance capacity is improved.

Description

Technical Field

[0001] The invention discloses a high-resistance fault detection method for a small-resistance grounding system based on the angle of a sampling value vector, belonging to the field of relay protection of power systems. Background Art

[0002] Single-phase grounding fault is a common fault in the power distribution system. After a single-phase fault occurs, the low-resistance grounding system has the advantages of obvious fault characteristics, easy and fast experiment of relay protection, and can suppress system resonant overvoltage. However, my country's low-resistance grounding system generally adopts time-limited zero-sequence current protection, and the current setting value is set according to the maximum capacitance current of the line, which is generally not more than 40A. The 10kV system has a transition resistance resistance of less than 150Ω, and cannot cut off high-resistance faults such as electric shock to the human body, wire falling to the ground, and hitting a tree. High-resistance faults not only affect normal power supply, but also may develop into phase-to-phase faults over time, causing greater harm.

[0003] In the prior art, the main methods for detecting high-resistance grounding faults in low-resistance systems are:

[0004] (1) A method based on zero-sequence power variation (such as the technical solution disclosed in Chinese invention patent publication number CN117200155A).

[0005] (2) Waveform similarity method based on the differential value of line zero-sequence current and bus zero-sequence voltage.

[0006] (3) The following technical solutions also disclose their respective detection methods, such as the technical solutions disclosed in Chinese invention patents with publication numbers CN113419139A, CN114113913A, CN117856184A, and CN117728346A.

[0007] However, a common problem in the prior art including the above-mentioned scheme is that under a high-resistance fault in a low-resistance grounding system, the bus zero-sequence voltage is small, resulting in a large calculation error of the above-mentioned method and a weak ability to withstand transition resistance.

[0008] The applicant of this application disclosed a Chinese invention patent with application number 202210177708.9 and patent name “A method for locating high-resistance grounding faults in a low-resistance grounding system” on February 25, 2022. A technical solution is recorded in this technical solution. In this technical solution, the phase difference between the three-phase voltage and the zero-sequence current phase is used to realize high-resistance grounding fault detection, which reduces the influence of zero-sequence voltage on the reliability of protection action and improves the ability to withstand transition resistance. However, in this technical solution, the calculation of the phase difference using Fourier transform requires the use of data of more than 3 cycles, so the amount of data to be processed is large and the calculation is more cumbersome.

[0009] Therefore, designing a technical solution that can optimally improve the transition resistance capability while reducing the amount of data that needs to be processed to reduce the complexity of the calculation has become an urgent problem to be solved in the text field. Summary of the invention

[0010] The technical problem to be solved by the present invention is: to overcome the shortcomings of the prior art and provide a method for high-resistance grounding fault detection based on the angle relationship between the three-phase voltage and the zero-sequence current sampling value vector after the fault, thereby getting rid of the problem that the traditional protection method relies on the zero-sequence voltage and improving the transition resistance resistance. The method has a low-resistance grounding system high-resistance fault detection capability based on the sampling value vector angle.

[0011] The technical solution adopted by the present invention to solve the technical problem is: the high-resistance fault detection method of a low-resistance grounding system based on the angle of a sampling value vector is characterized by comprising the following steps:

[0012] Step a, collecting zero-sequence current in the line;

[0013] Step b, determining whether the zero-sequence current mutation exceeds a preset threshold value, if it exceeds the preset threshold value, executing step 1003, if it does not exceed the preset threshold value, returning to step a;

[0014] Step c, collecting the three-phase voltage and zero-sequence current at the outlet side of each line and filtering them;

[0015] Step d, capturing data of three-phase voltage and zero-sequence current;

[0016] Step e, calculating the vector angle between the three-phase voltage and the zero-sequence current;

[0017] Step f, respectively determining whether the vector angle between the phase voltage and the zero-sequence current of each phase is less than a preset vector angle threshold, if it is less than the preset vector angle threshold, executing step g, if it is greater than or equal to the preset vector angle threshold, returning to step a;

[0018] Step g, determine the fault phase and fault section.

[0019] Preferably, when executing step d, the data interception length is greater than one quarter of the power frequency cycle, with any maximum value of the zero-sequence current as the center, and the three-phase voltage and zero-sequence current after interception are u phaseAx_cut (t),u phaseBx_cut (t) and u phaseCx_cut (t) and i 0x_cut (t), x = 1 ~ N, N is the total number of outgoing lines in the system.

[0020] Preferably, when executing step e, the intercepted three-phase voltage and zero-sequence current are first discretized to obtain the discretized value u of the three-phase voltage phaseAx_cut (n),uphaseBx_cut (n),u phaseCx_cut (n), and the discretized value of zero-sequence current i 0x_cut (n), n is the length of discrete signal data.

[0021] Preferably, the discretized zero-sequence current i 0x_cut (n) is the reference vector, and the reference vector is the discretized three-phase voltage u phaseAx_cut (n),u phaseBx_cut (n) and u phaseCx_cut (n) vector angle: θ A ,θ B ,θ C :

[0022]

[0023] Among them, u phaseAx_cut (n),u phaseBx_cut (n) and u phaseCx_cut (n) are the discretized voltages of phase A, phase B and phase C, i 0x_cut (n) is the discretized zero-sequence current.

[0024] Preferably, in step f, the vector angle threshold is 4°.

[0025] Preferably, when executing step f, a phase whose vector angle is smaller than a vector angle threshold is a faulty phase, and a line where the faulty phase is located is a faulty line.

[0026] Preferably, when executing step f, in the fault line, the section between the distribution automation device that meets the fault criterion and the adjacent distribution automation device that meets the sound criterion is the fault section.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] In this high-resistance fault detection method for a low-resistance grounding system based on the sampling value vector angle, the angle relationship between the three-phase voltage and the zero-sequence current sampling value vector after the fault is used to realize high-resistance grounding fault detection, which gets rid of the problem that the traditional protection method relies on zero-sequence voltage. It has strong resistance to transition resistance, which can reach more than 12kΩ, and improves the sensitivity and reliability of protection.

[0029] This high-resistance fault detection method for a low-resistance grounding system based on the sampling value vector angle intercepts the three-phase voltage and zero-sequence current sampling values ​​that are greater than a quarter of the power frequency cycle after the fault, and further uses the vector angle relationship to realize high-resistance grounding fault detection. It uses a small amount of data, is simple to calculate, has a short running time, and has high engineering practicality.

[0030] This high-resistance fault detection method for a low-resistance grounding system based on the angle of sampling value vectors utilizes the angle relationship between the three-phase voltage and zero-sequence current sampling value vectors after the fault to realize high-resistance grounding fault detection, and can realize the fault line selection, positioning and phase selection functions at the same time, thereby reducing the fault finding time, reducing the fault power outage time, and improving the power supply reliability.

[0031] In this high-resistance fault detection method for a low-resistance grounding system based on the angle of a sampling value vector, the three-phase voltage can be directly obtained through a phase voltage transformer or indirectly obtained using two line voltages and a zero-sequence voltage. The transient zero-sequence current signal can be acquired through traditional power frequency sensor collection or three-phase synthesis. There is no need to add additional primary equipment or cooperate with other primary equipment, and the practical application value is high. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 The flowchart of the high-resistance fault detection method for a low-resistance grounding system based on the angle of the sampling value vector is shown in FIG.

[0033] Figures 2 to 4 They are the three-phase voltage waveforms of A, B and C after filtering.

[0034] Figure 5 This is the zero-sequence current waveform after filtering.

[0035] Figure 6 This is a schematic diagram of the installation location of the power distribution terminal. DETAILED DESCRIPTION

[0036] Figures 1 to 6 The best embodiment of the present invention is shown below in conjunction with the attached Figures 1 to 6 The present invention is further described.

[0037] like Figure 1 As shown, the high-resistance fault detection method of a low-resistance grounding system based on the sampling value vector angle includes the following steps:

[0038] Step 1001, start;

[0039] The three-phase voltage and zero-sequence current are collected in real time through the substation or line protection terminal. The three-phase voltage can be directly obtained through the phase voltage transformer, or indirectly obtained by using two line voltages and the zero-sequence voltage. The zero-sequence current can be directly obtained through the zero-sequence current transformer or indirectly obtained through the three-phase current synthesis.

[0040] Step 1002, determining whether the zero-sequence current mutation exceeds a preset threshold;

[0041] Determine whether the amplitude or mutation amount of the zero-sequence current collected in step 1001 is greater than or equal to a preset threshold. If the zero-sequence current exceeds the preset threshold, execute step 1003. If the zero-sequence current is less than the preset threshold, return to step 1001.

[0042] Step 1003, collecting three-phase voltage and zero-sequence current at the outlet side of each line;

[0043] The distribution automation device collects the three-phase voltage and zero-sequence current at the line outlet side. The three-phase voltage at the line outlet side is recorded as u phaseAx (t),u phaseBx (t) and u phaseCx (t), the zero-sequence current at the line outlet is recorded as i 0x (t), x = 1 ~ N, N is the total number of outgoing lines in the system, and the three-phase voltage and zero-sequence current are filtered. The waveform of the filtered three-phase voltage is as follows Figures 2 to 4 As shown, the zero-sequence current waveform after filtering is as follows Figure 5 shown.

[0044] Step 1004, capturing data of three-phase voltage and zero-sequence current;

[0045] The distribution automation device takes the fault initiation time as the starting point, and intercepts the three-phase voltage and zero-sequence current at the line outlet side in step 1003. The data interception length is greater than one quarter of the power frequency cycle, with a certain maximum value of the zero-sequence current as the center. After interception, the three-phase voltage and zero-sequence current are u phaseAx_cut (t),u phaseBx_cut (t) and u phaseCx_cut (t) and i 0x_cut (t), after discretizing the three-phase voltage and zero-sequence current, we can get: phaseAx_cut (n),u phaseBx_cut (n) and u phaseCx_cut (n) and i 0x_cut (n), where n is the length of discrete signal data, which depends on the sampling frequency of the distribution automation device and the length of the interception time window.

[0046] The sampled value vector of the intercepted three-phase voltage and zero-sequence current is: U A (n)=(u a1 ,u a2 ,…,u an ), U B (n)=(u b1 ,u b2 ,…,u bn ), U C (n)=(u c1 ,u c2 ,…,u cn ), I 0(n)=(i 01 ,i 02 ,…,i 0n ).

[0047] Among them, U A (n), U B (n), U C (n) are the three-phase voltage sampling value vectors, I 0 (n) is the zero-sequence current sampling value vector, u a1 ,u a2 The first and second sampling values ​​of the A phase voltage in the interception interval are taken, and the rest are the same.

[0048] Step 1005, calculating the vector angle between the three-phase voltage and the zero-sequence current;

[0049] The calculation formula of the vector angle between the voltage and current sampling value vectors is:

[0050]

[0051] Where θ is the vector angle between two sample value vectors.

[0052] Specifically, the discretized zero-sequence current i 0x_cut (n) is the reference vector, and the reference vector is the discretized three-phase voltage u phaseAx_cut (n),u phaseBx_cut (n) and u phaseCx_cut (n) vector angle: θ A ,θ B ,θ C :

[0053]

[0054] Among them, u phaseAx_cut (n),u phaseBx_cut (n) and u phaseCx_cut (n) are the discretized voltages of phase A, phase B and phase C, i 0x_cut (n) is the discretized zero-sequence current.

[0055] Step 1006, determining whether the vector angle is less than a preset threshold;

[0056] It is determined whether any one of the vector angles of the three-phase voltages A, B, and C and the zero-sequence current calculated in step 1005 is less than a preset threshold value, if less than the threshold value, step 1008 is executed, if greater than or equal to the threshold value, step 1007 is executed. In the present method for detecting high-resistance faults in a low-resistance grounding system based on the sampling value vector angle, the threshold value of the vector angle is set to 4°.

[0057] Step 1007, the line is a sound line;

[0058] When the vector angles between the three-phase voltage and the zero-sequence current of the line do not exceed the preset threshold, it indicates that the current line is a sound line, and the process returns to step 1001 .

[0059] Step 1008, determining the fault phase;

[0060] If any one of the vector angles between the three-phase voltages A, B, and C and the zero-sequence current exceeds the pre-examination threshold, it indicates that a high-resistance grounding fault occurs in the phase line corresponding to the vector angle exceeding the threshold, which is the faulty phase.

[0061] Step 1009, determining the fault section;

[0062] After determining the faulty line, the distribution automation device on the line repeats steps 1003 to 1006. In the faulty line, the section between the distribution automation device that meets the fault criterion and the adjacent distribution automation device that meets the sound criterion is the fault section.

[0063] The following further describes the high-resistance fault detection method for a low-resistance grounding system based on the angle of a sampling value vector according to an example:

[0064] For example Figure 6 The schematic diagram of the installation position of the distribution terminal is shown, and the feeder L1, feeder L2 and feeder L3 are led out from the busbar. The distribution terminals are set on the feeder L1: device L11 ~ device L14, the distribution terminals are set on the feeder L2: device L21 ~ device L23, and the distribution terminals are set on the feeder L3: device L31 ~ device L34.

[0065] The zero-sequence current in the line is collected, and a high-resistance grounding fault occurs in the line by comparing the amplitude or mutation value of the zero-sequence current with the threshold, and then a high-resistance fault detection method for a small-resistance grounding system based on the angle of the sampling value vector is started, corresponding to steps 1001 to 1002.

[0066] The distribution automation device collects the three-phase voltage and zero-sequence current at the line outlet side. The three-phase voltage at the line outlet side is recorded as u phaseAx (t),u phaseBx (t) and u phaseCx (t), the zero-sequence current at the line outlet is recorded as i 0x(t), x=1, N is the total number of outgoing lines in the system. The distribution automation device takes the fault initiation time as the starting point, intercepts the three-phase voltage and zero-sequence current at the outlet side of the line in step 1003, and takes a certain maximum value of the zero-sequence current as the center. The data interception length is greater than one quarter of the power frequency cycle. The three-phase voltage and zero-sequence current are intercepted and discretized to obtain the discretized values ​​of the three-phase voltage and zero-sequence current: u phaseAx_cut (n),u phaseBx_cut (n) and u phaseCx_cut (n) and i 0x_cut (n), corresponding to step 1003 to step 1004.

[0067] The discretized zero-sequence current i 0x_cut (n) is the reference vector, and the reference vector is the discretized three-phase voltage u phaseAx_cut (n),u phaseBx_cut (n) and u phaseCx_cut (n) vector angle: θ A ,θ B ,θ C After calculation, we get: θ A =1.53°,θ B =138.56°,θ C =142.56°, which corresponds to step 1005.

[0068] It can be seen that the vector angle of phase A in feeder L1 is less than the preset threshold of 4°, so it can be determined that a high-resistance grounding fault occurs in feeder L1 and the fault phase is phase A. This corresponds to steps 1006 to 1008.

[0069] The distribution terminals in the feeder L1: device L11 to device L14, respectively execute steps 1003 to step 1007, and finally conclude that the high-resistance grounding fault occurs between device L11 and device L12.

[0070] The above is only a preferred embodiment of the present invention, and does not limit the present invention in other forms. Any technician familiar with the profession may use the above disclosed technical content to change or modify it into an equivalent embodiment with equivalent changes. However, any simple modification, equivalent change and modification made to the above embodiment according to the technical essence of the present invention without departing from the technical solution of the present invention still belongs to the protection scope of the technical solution of the present invention.

Claims

1. A high-resistance fault detection method for a low-resistance grounding system based on the angle of a sampling value vector, characterized in that: The steps include: Step a, collecting zero-sequence current in the line; Step b, determining whether the zero-sequence current mutation exceeds a preset threshold value, if it exceeds the preset threshold value, executing step 1003, if it does not exceed the preset threshold value, returning to step a; Step c, collecting the three-phase voltage and zero-sequence current at the outlet side of each line and filtering them; Step d, capturing data of three-phase voltage and zero-sequence current; Step e, calculating the vector angle between the three-phase voltage and the zero-sequence current; Step f, respectively determining whether the vector angle between the phase voltage and the zero-sequence current of each phase is less than a preset vector angle threshold, if it is less than the preset vector angle threshold, executing step g, if it is greater than or equal to the preset vector angle threshold, returning to step a; Step g, determine the fault phase and fault section.

2. The method for detecting high-resistance faults in a low-resistance grounding system based on the angle of sampling value vectors according to claim 1 is characterized in that: When executing step d, the data interception length is greater than one quarter of the power frequency cycle, with any maximum value of the zero-sequence current as the center. After interception, the three-phase voltage and zero-sequence current are u phaseAx_cut (t),u phaseBx_cut (t) and u phaseCx_cut (t) and i 0x_cut (t), x = 1 ~ N, N is the total number of outgoing lines in the system.

3. The method for detecting high-resistance faults in a low-resistance grounding system based on the angle of sampling value vectors according to claim 1 is characterized in that: When executing step e, the three-phase voltage and zero-sequence current after interception are first discretized to obtain the discretized value u of the three-phase voltage phaseAx_cut (n),u phaseBx_cut (n),u phaseCx_cut (n), and the discretized value of zero-sequence current i 0x_cut (n), n is the length of discrete signal data.

4. The method for detecting high-resistance faults in a low-resistance grounding system based on the angle of sampling value vectors according to claim 3 is characterized in that: The discretized zero-sequence current i 0x_cut (n) is the reference vector, and the reference vector is the discretized three-phase voltage u phaseAx_cut (n),u phaseBx_cut (n) and u phaseCx_cut (n) vector angle: θ A ,θ B ,θ C : Among them, u phaseAx_cut (n),u phaseBx_cut (n) and u phaseCx_cut (n) are the discretized voltages of phase A, phase B and phase C, i 0x_cut (n) is the discretized zero-sequence current.

5. The method for detecting high-resistance faults in a low-resistance grounding system based on the angle of sampling value vectors according to claim 1 is characterized in that: In step f, the vector angle threshold is 4°.

6. The method for detecting high-resistance faults in a low-resistance grounding system based on the angle of sampling value vectors according to claim 1, characterized in that: When executing step f, a phase whose vector angle is smaller than the vector angle threshold is a faulty phase, and a line where the faulty phase is located is a faulty line.

7. The method for detecting high-resistance faults in a low-resistance grounding system based on the angle of sampling value vectors according to claim 6 is characterized in that: When executing step f, in the fault line, the section between the distribution automation device that meets the fault criterion and the adjacent distribution automation device that meets the sound criterion is the fault section.

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