Fault section determination method and system for distribution network based on positive sequence component of fault current

Abstract

Disclosed is a power distribution network fault section determination method and system based on fault current positive sequence component, the method being: installing fault current monitoring devices on each line section of the power distribution network, collecting fault current information, and performing symmetrical transformation to obtain each phase positive sequence component; according to the fault characteristics of the fault current positive sequence component, using the additional positive sequence fault current difference of the fault current in the fault area and the non-fault area to screen out possible fault sections; then further according to the difference between the additional positive sequence fault current amplitude and phase of the fault section and the non-fault section, further determining the fault section position. The present application can use fault current monitoring information to quickly determine the fault, and has important theoretical and practical application value.

Description

TECHNICAL FIELD

[0001] The present application relates to a power distribution network fault section determination method, in particular to a fault current positive sequence component fault characteristic identification. BACKGROUND

[0002] According to the fault information collected by the power grid, it can be seen that the power outage accidents caused by the fault of the power distribution network account for 98% of all accidents. Therefore, it is particularly important to determine the fault location. However, the access of distributed generation (DG) has changed the power distribution network from a single-source radial network to a bidirectional flow network, and the topology is more complex.

[0003] The existing solutions are divided into two categories, including methods based on power distribution network automation information and methods based on wide-area information. The method based on power distribution network automation information is only applicable to power distribution networks with low penetration (not more than 25%). The method based on wide-area information includes methods based on graph theory and artificial intelligence, wavelet coefficient comparison method, power direction comparison method, etc. Due to the complex topology of the power distribution network, the iteration process is prone to errors and the calculation time is long. SUMMARY

[0004] The present application provides a power distribution network fault section determination method and system based on fault current positive sequence component, according to the fault characteristics of the fault current positive sequence component amplitude ratio and the phase angle difference, simplifies the fault determination process, quickly distinguishes the fault area and the non-fault area, and improves the efficiency of fault determination.

[0005] According to a first aspect of the embodiment of the present application, a power distribution network fault section determination method based on fault current positive sequence component is provided, comprising: collecting the additional positive sequence fault current amplitude and phase angle of each section of the power distribution network; screening out the section with an additional positive sequence fault current amplitude greater than a current threshold value as a possible fault section set; and further screening out the fault section from the possible fault section according to the amplitude and phase difference of the additional positive sequence fault current before and after the fault section.

[0006] According to a second aspect of the embodiment of the present application, a power distribution network fault section determination system based on fault current positive sequence component is provided, comprising: a fault current monitoring device for collecting the additional positive sequence fault current amplitude and phase angle of each section of the power distribution network; and a processing module for screening out the section with an additional positive sequence fault current amplitude greater than a current threshold value as a possible fault section set, and further screening out the fault section from the possible fault section according to the amplitude and phase difference of the additional positive sequence fault current before and after the fault section.

[0007] The present application has the beneficial effect that the monitoring information of the existing fault monitoring device can be used for fault identification, and the fault point area can be quickly determined step by step, thereby improving the efficiency of fault determination and the stability of power grid operation. BRIEF DESCRIPTION OF DRAWINGS

[0008] The application will be described in further detail below in conjunction with the accompanying drawings and specific embodiments.

[0009] Figure 1 A structural diagram of a power distribution network fault section determination system provided for an embodiment of the application.

[0010] Figure 2 A flowchart of a power distribution network fault section determination method provided for an embodiment of the application.

[0011] Figure 3 A positive sequence component equivalent network diagram of a power distribution network fault section determination system provided for an embodiment of the application, wherein Z1-Z n Z1-Zn are positive sequence impedances of branch 1-branch n, S Z1-Zn are positive sequence impedances of branch 1-branch n, DG Z1-Zn are positive sequence impedances of branch 1-branch n, S E' is a positive sequence electromotive force of the main power supply, D E' is a positive sequence electromotive force of the main power supply, λ is a ratio of a length from the fault point to a head of the section to a total length of the section. DETAILED DESCRIPTION

[0012] The power distribution network fault section determination method based on the positive sequence component of the fault current of the application uses a fault current monitoring device (referred to as a monitoring device) to collect current signals of line sections, performs symmetric transformation on the current signals in the abc coordinate system to obtain positive sequence components, and uses an FFT algorithm to extract the positive sequence components of the fault current. According to the characteristics of the positive sequence fault current, the differences in the amplitudes and phases of the positive sequence components of the fault region and the non-fault region are obtained; and considering the influence of the distributed power supply on the fault characteristics, the amplitude ratio and the phase angle difference of the positive sequence components of the fault currents at the head and the tail of the fault section are obtained by using the limit rules of the capacity of the distributed power supply, so that the fault section can be identified. According to the characteristics of the complex topology structure of the power distribution network, the fault current monitoring devices at the heads of all sections are used to determine the fault currents, and a possible fault section set is screened out, and then the section where the fault point is located is determined step by step.

[0013] Figure 1 A structural diagram of a power distribution network fault section determination system is shown, which includes three parts: a fault current monitoring device installed on each line section of the power distribution network; the fault current monitoring device transmits the collected fault current information to the database of the fault section determination system, and the database of the fault section determination system also stores the topology structure information of the power distribution network; and the processing module of the fault section determination system determines the fault section according to the fault current information and the topology structure information received by the database.

[0014] As Figure 2The flowchart shown is a fault determination process of a fault section determination system, which mainly includes the following three steps.

[0015] Step 1: The fault current monitoring device collects the amplitude and phase angle of the positive sequence component of the fault current in each section of the distribution network.

[0016] like Figure 3 The positive sequence component equivalent network diagram shown, and the fault current monitoring devices at both ends of each feeder section, i.e., M 1,in -M n,in and M 1,out -M n,out (n represents the number of fault current monitoring devices, which is also the number of sections), used to monitor fault current. According to the superposition theorem, the current at each fault current monitoring device after a distribution network fault can be considered as the superposition of the normal operating current and the additional current under the fault. Subtracting the three-phase current before the fault from the three-phase current after the fault, we can obtain the additional three-phase current under the fault as follows:

[0017]

[0018]

[0019] Among them: i=1,2,…,n; i′ a,i,in 、i′ b,i,in 、i′ c,i,in Let i′ be the additional three-phase currents (a, b, c) collected under the condition of a fault in the monitoring device at the beginning of the i-th section. a,i,out 、i′ b,i,out 、i′ c,i,out The additional a, b, c three-phase currents collected under the condition of a fault in the end monitoring device of the i-th section; i a,i,in i b,i,in i c,i,in Let i be the three-phase currents (a, b, c) after the fault detected by the monitoring device at the beginning of the i-th section; as,i,in i bs,i,in i cs,i,in Let i be the three-phase currents (a, b, c) before the fault, as monitored by the monitoring device at the beginning of the i-th section; a,i,out i b,i,out i c,i,out Let i be the three-phase currents (a, b, c) after the fault detected by the monitoring device at the end of the i-th section; as,i,out i bs,i,out i cs,i,out Let be the three-phase currents a, b, and c before the fault, as monitored by the end monitoring device of the i-th section.

[0020] The positive sequence components of the three-phase currents a, b, and c under fault conditions at the monitoring devices at the beginning and end of the i-th segment are obtained through symmetrical transformation:

[0021]

[0022] where is the positive sequence component of the additional a, b, c three-phase current at the head of the i-th section under fault; is the positive sequence component of the additional a, b, c three-phase current at the end of the i-th section under fault; a is the complex transformation factor of symmetrical component transformation, a = e j120 .

[0023] Further using fast Fourier transform technology, according to and the amplitude and the phase angle of the power frequency component of the additional positive sequence current at the head of the i-th section under fault can be obtained. and the phase angle of the power frequency component of the additional positive sequence current at the end of the i-th section under fault can be obtained.

[0024] The amplitude and the phase angle of the power frequency component of the additional positive sequence current of all monitoring devices are sent to the database of the fault section determination system through the communication network.

[0025] Step 2: Screening of possible fault sections

[0026] According to the fault current information and the topological structure information received by the database, the screening of possible fault sections is first performed to improve the efficiency of fault section determination. There is additional positive sequence fault current when the fault current flows through the line section; there is no additional positive sequence fault current when the fault current does not flow through the non-fault section. Therefore, the section through which the fault current flows, i.e. the possible fault section, can be screened according to the amplitude of the additional positive sequence fault current collected by the fault current monitoring device. The screening steps are as follows:

[0027] (1) Initialize the set A of positive integers as an empty set; set the positive integer j = 1;

[0028] (2) If then A = A U {j}; otherwise, keep the set A unchanged; in the formula, I th is the current threshold value, which is usually set as 5% of the rated current of the distribution network line;

[0029] (3) j = j + 1; if j > n, the screening is ended; otherwise, repeat step (2);

[0030] After the screening is ended, the elements in the set A obtained are the numbers of all possible fault sections.

[0031] Step 3: Determination of fault section

[0032] Figure 3 This is a positive-sequence network model for a ground fault at point f on distribution network segment k. Since the fault current is a through-current in non-faulty segments, the amplitude and phase of the positive-sequence additional fault current flowing into and out of these segments remain almost unchanged. However, in the faulty segment, the positive-sequence additional fault current only flows in and not out. Therefore, step 3 further filters segments potentially prone to faults based on the difference in amplitude and phase of the additional positive-sequence fault current before and after the faulty segment. The filtering steps are as follows:

[0033] (1) Set k = 1, i = 1, m = |A|, that is, m represents the number of elements in set A;

[0034] (2) Let k = A[i], that is, assign the i-th element in set A to k. The physical meaning of k represents the number of the section that may have a fault. and Whether the criterion is met depends on Kirchhoff's theorem and its appendix. Figure 3 From the orthogonal equivalent network, the criterion is as follows:

[0035]

[0036] (3) i = i + 1; if the criterion is met, then output segment k as the fault segment; otherwise, further judge i. If i > m, then stop the location program; otherwise, return to step (2).

[0037] In addition, Figure 2 Each block in the flowchart can represent a module, segment, or portion of code containing one or more executable instructions for implementing the specified logical function. It should also be noted that in some alternative implementations, the functions indicated in the blocks may occur in a different order than those shown in the figures. For example, two consecutively indicated blocks may actually execute substantially in parallel, or sometimes in reverse order, depending on the functions involved. Furthermore, each block and combination of blocks in the flowchart can be implemented using a dedicated hardware-based system that performs the specified function or operation, or using a combination of dedicated hardware and computer instructions.

Claims

1. A method for fault section identification in a power distribution network based on positive sequence component of fault current, characterized by, The method comprises the following steps: collecting the amplitude and phase angle of the additional positive sequence fault current of each section of the power distribution network; filtering out the sections with the amplitude of the additional positive sequence fault current greater than a current threshold value as a set of possible fault sections, and the filtering method comprises the following steps: 1.1, initializing a set of positive integers A as an empty set; setting a positive integer j = 1; 1.2, if then A = A U {j}, otherwise keep set A unchanged, where I th is the current threshold, is the positive sequence fault current amplitude at the beginning of the jth section. 1.3, j = j + 1; if j > n, the filtering ends, otherwise, repeat 1.2, wherein n is the number of sections; further filtering out the fault section from the possible fault sections according to the amplitude and phase difference of the additional positive sequence fault current before and after the fault section, and the filtering steps comprise the following steps: 2.1, setting k = 1, i = 1, and m = |A|, that is, m represents the number of elements in set A; 2.2 Let k = A[i], that is, assign the i-th element in set A to k. The physical meaning of k represents the number of the section that may have a fault. and Whether the criterion is met is determined by Kirchhoff's theorem and the topology information of the distribution network, as shown in the following formula: wherein is the kth segment end and end additional positive sequence fault current amplitude, respectively, is the kth segment end and end additional positive sequence fault current amplitude, respectively, is the kth segment end additional positive sequence fault current phase 2.3, i = i + 1; if the criterion is met, output section k as the fault section; otherwise, further judge i, if i > m, stop the positioning program, otherwise, return to step 2.

2.

2. The power distribution network fault section determination method of claim 1, wherein, The method for collecting the amplitude and phase angle of the additional positive sequence fault current of each section of the power distribution network comprises the following steps: obtain the additional a, b, c three-phase currents under fault according to the following formulas (1), (2): wherein: i = 1, 2, …, n; i' a,i,in , i' b,i,in , i' c,i,in is the additional a, b, c three-phase current at the beginning of the i-th section under fault; i' a,i,out , i' b,i,out , i' c,i,out is the additional a, b, c three-phase current at the end of the i-th section under fault; i a,i,in , i b,i,in , i c,i,in is the a, b, c three-phase current after fault at the beginning of the i-th section; i as,i,in , i bs,i,in , i cs,i,in is the a, b, c three-phase current before fault at the beginning of the i-th section; i a,i,out , i b,i,out , i c,i,out is the a, b, c three-phase current after fault at the end of the i-th section; i as,i,out , i bs,i,out , i cs,i,out is the a, b, c three-phase current before fault at the end of the i-th section; obtain the positive sequence components of the additional a, b, c three-phase currents at the first end and the end of the i-th section under fault through symmetry transformation: wherein is the positive sequence component of the a, b, c three-phase current added under the first end fault of the i-th section; is the positive sequence component of the a, b, c three-phase current added under the last end fault of the i-th section; a is a complex transformation factor of the symmetrical component transformation, a = e j120° ; Using the fast Fourier transform algorithm, the amplitude and the phase angle of the fundamental frequency component of the additional positive sequence current at the head end and the amplitude and the phase angle of the fundamental frequency component of the positive sequence current at the end of the ith section under fault can be obtained 3. A power distribution network fault section determination system based on positive sequence component of fault current, characterized by, The method comprises the following steps: a fault current monitoring device for collecting the amplitude and phase angle of the additional positive sequence fault current of each section of the power distribution network; a processing module for filtering out the sections with the amplitude of the additional positive sequence fault current greater than a current threshold value as a set of possible fault sections, and further filtering out the fault section from the possible fault sections according to the amplitude and phase difference of the additional positive sequence fault current before and after the fault section, the filtering method of the possible fault sections comprises the following steps: 1.1, initializing a set of positive integers A as an empty set; setting a positive integer j = 1; 1.2, if then A = A U {j}, otherwise keep set A unchanged, where I th is the current threshold, is the positive sequence fault current amplitude at the beginning of the jth section. 1.3, j = j + 1; if j > n, the filtering ends, otherwise, repeat 1.2, wherein n is the number of sections; the method for further filtering out the fault section from the possible fault sections comprises the following steps: 2.1, setting k = 1, i = 1, and m = |A|, that is, m represents the number of elements in set A; 2.2 Let k = A[i], that is, assign the i-th element in set A to k. The physical meaning of k represents the number of the section that may have a fault. and Whether the criterion is met is determined by Kirchhoff's theorem and the topology information of the distribution network, as shown in the following formula: wherein and are the additional positive sequence fault current amplitude at the beginning and end of the kth section, respectively, is the additional positive sequence fault current phase at the beginning of the kth section 2.3, i = i + 1; if the criterion is met, output section k as the fault section; otherwise, further judge i, if i > m, stop the positioning program, otherwise, return to step 2.

2.

4. The power distribution network fault section determination system of claim 3, wherein, The method for collecting the amplitude and phase angle of the additional positive sequence fault current of each section of the power distribution network by the fault current monitoring device comprises the following steps: obtain the additional a, b, c three-phase currents under fault according to the following formulas (1), (2): wherein: i = 1, 2, …, n; i a,i,in , i b,i,in , i c,i,in = a, b, c phase current of the first section after the fault at the beginning; i a,i,out , i b,i,out , i c,i,out = a, b, c phase current of the first section after the fault at the end; i a,i,in , i b,i,in , i c,i,in = a, b, c phase current of the first section before the fault at the beginning; i as,i,in , i bs,i,in , i cs,i,in = a, b, c phase current of the first section before the fault at the end; i a,i,out , i b,i,out , i c,i,out = a, b, c phase current of the first section after the fault at the end; i as,i,out , i bs,i,out , i cs,i,out = a, b, c phase current of the first section before the fault at the end; obtain the positive sequence components of the additional a, b, c three-phase currents at the first end and the end of the i-th section under fault through symmetry transformation: wherein is the positive sequence component of the a, b, c three-phase current added under the first end fault of the i-th section; is the positive sequence component of the a, b, c three-phase current added under the end fault of the i-th section; a is a complex transformation factor of the symmetrical component transformation, a = e j120° ; Using the fast Fourier transform algorithm, the amplitude and the phase angle of the fundamental frequency component of the additional positive sequence current at the head end and at the end of the ith section with a fault can be obtained and

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