A fault location method for single-circuit T-type transmission line without pre-identification of faulty branch

Abstract

The present invention relates to a single-loop T-type transmission line fault location method without pre-identifying the fault branch. First, the three-phase voltage and current at each end of the single-loop T-type transmission line are collected using the power transformer at the protection installation location. Then, the collected fundamental wave components are decomposed using the symmetrical component method, and the positive sequence components and positive sequence fault components at each end of the T-type line are calculated. Finally, the positive sequence components and positive sequence fault components at each end of the single-loop T-type transmission system are used to construct the fault distance measurement functions of the three branches respectively, and the fault location is screened out by judging the rationality of the results of the three distance measurement functions. The present invention is simple and practical in principle, and accurate distance measurement results can be obtained after only a small number of iterations. There is no need to pre-identify the fault branch, and there is no need to perform tedious full-line search and pseudo-root identification. The required amount of calculation is small and easy to implement.

Description

Technical Field

[0001] The invention belongs to the field of power system protection and control, and proposes a single-circuit T-type transmission line fault location method without pre-identifying a fault branch based on consideration of the effect of the single-circuit T-type transmission line on ground capacitance. Background Art

[0002] With the development of the national economy and the improvement of industrial level, the electricity demand of various industries is increasing. In order to improve the use efficiency of transmission lines, save line corridor land and investment costs, T-type transmission lines have been widely used in power systems. When a T-type transmission line fails, rapid and accurate fault location is not only conducive to reducing the workload of operators' line inspections, timely repairing faulty lines and ensuring power supply reliability, but also plays a very important role in the safety, stability and economic operation of the power system.

[0003] Existing fault location methods for T-type transmission lines can be divided into two categories: traveling wave location method and fault analysis method.

[0004] The traveling wave location method calculates the fault distance through the relationship between the time it takes for the reflected traveling wave to reach the three ends after the fault and the wave speed. In order to accurately identify the wave head of the traveling wave, special high-speed sampling equipment is required, which requires a large investment.

[0005] Fault analysis methods are mainly divided into single-end ranging method and double-end ranging method. Due to the particularity of the T-type transmission line structure, the single-end ranging method that only uses single-end data is difficult to perform fault ranging. The double-end ranging method also has the problem of being difficult to directly apply to T-type line fault ranging, and further improvement is needed before it can be used.

[0006] Existing fault distance measurement methods for single-loop T-type transmission lines often require the determination of the fault branch before fault distance measurement can be performed. However, the fault branch determination may fail in the case of high-resistance faults, which greatly affects the reliability of fault distance measurement. Moreover, many existing distance measurement methods require iterative searches and pseudo-root identification within the entire line, which requires large amounts of calculation and is not conducive to meeting the requirements of rapid and accurate fault location. Summary of the invention

[0007] The purpose of the present invention is to propose a single-circuit T-type transmission line fault location method without pre-identifying the fault branch based on the shortcomings of the existing fault location technology by deeply analyzing the fault characteristics of the single-circuit T-type transmission line.

[0008] The present invention solves the technical problem by the following technical solutions:

[0009] A single-loop T-type transmission line fault location method without pre-identifying the fault branch is characterized by: firstly, using the power transformer at the protection installation location to collect the three-phase voltage and current at each end of the single-loop T-type transmission line, then using the symmetrical component method to decompose the collected fundamental wave components, and calculate the positive sequence components and positive sequence fault components at each end of the T-type line, and finally using the positive sequence components and positive sequence fault components at each end of the single-loop T-type transmission system to construct the fault distance measurement functions of the three branches respectively, and by judging the rationality of the results of the three distance measurement functions, the fault location is screened out, and the steps of the method are:

[0010] (1) First, the three-phase voltage and three-phase current at the three ends of the single-circuit T-type transmission line are collected using the power transformer at the protection installation site. The collected data are decomposed using the symmetrical component method to obtain the positive sequence components at each end of the single-circuit T-type transmission system, and the positive sequence fault components are further calculated;

[0011] (2) Then, based on the solved three-terminal positive sequence component and positive sequence fault component, combined with the π-type equivalent circuit of the three lines, the positive sequence component and positive sequence fault component of the T end are calculated according to the normal operation; the fault distance measurement function is constructed for the three branches respectively, and the positive sequence component and positive sequence fault component of the T end of the analyzed branch can be obtained by the positive sequence component and positive sequence fault component of the T end calculated according to the normal operation of the other two branches; since the fault location is unknown, it is difficult to directly apply the π-type equivalent circuit to the lines on both sides of the fault point on the fault branch, so the effect of the capacitance to the ground cannot be considered. Therefore, when performing the initial fault distance measurement, the method of not considering the effect of the branch capacitance to the ground is adopted to calculate the initial fault distance measurement result.

[0012]

[0013] Where: They represent the positive sequence voltage, positive sequence current, positive sequence voltage fault component and positive sequence current fault component at terminal i respectively;

[0014] It represents the positive sequence voltage, positive sequence current, positive sequence voltage fault component and positive sequence current fault component at the T end of the iT branch obtained from the other two branches;

[0015] L i Indicates the length of the iT branch;

[0016] In order to pursue higher distance measurement accuracy, the initial fault distance measurement result is taken as the fault location, and the π-type equivalent circuit of the lines on both sides of the fault point is considered. The k-th iterative fault distance measurement result is obtained by iterative calculation.

[0017]

[0018] In the formula, Respectively represent the capacitance current to ground at the i-terminal and the T-terminal;

[0019] Let ε = 0.001, when When , it indicates that the iteration has converged, and the iteration result is output Otherwise, repeat the above iterative process until convergence, and the fault location process of the other two branches is similar to the above;

[0020] (3) Finally, whether the distance measurement results calculated according to the three fault distance measurement functions satisfy x i ∈[0,L i ] conditions, thereby determining the branch where the fault point is located, and the fault distance measurement result of the corresponding branch is the fault location, thereby realizing the direct determination of the fault location of a single-loop T-type transmission line without prior identification of the fault branch.

[0021] The advantages and beneficial effects of the present invention are:

[0022] 1. All derivation processes of the present invention adopt positive sequence components. Therefore, the proposed fault location method is applicable to all fault types of single-circuit T-type transmission lines.

[0023] 2. The present invention does not limit the transition resistance, fault location, etc. during the derivation process. Therefore, the proposed fault location method is not affected by the transition resistance and the fault location and has a higher ranging accuracy.

[0024] 3. The principle of the present invention is simple and practical. It can obtain accurate distance measurement results after only a small number of iterations. There is no need to determine the fault branch in advance, nor is there any need to perform tedious full-line search and pseudo-root identification. The required amount of calculation is small and easy to implement. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a schematic diagram of a positive sequence network of a single-loop T-type transmission line of the present invention;

[0026] Figure 2 It is a π-type equivalent circuit diagram of the iT branch under normal operation of the present invention;

[0027] Figure 3 This is the π-type equivalent circuit diagram of the fault distance measurement branch of the present invention, (a) is the fault state, (b) is the normal state, and (c) is the fault component state. DETAILED DESCRIPTION

[0028] The technical solution of the invention will be described in detail below with reference to the examples shown in the accompanying drawings.

[0029] 1. Principle description

[0030] Firstly, the collected three-terminal electrical quantities are decomposed into positive sequence, negative sequence and zero sequence components by using the symmetrical component method. In order to make the proposed distance measurement method applicable to all fault types of single-loop T-type transmission lines, the present invention uses the positive sequence network of the single-loop T-type transmission line for fault location.

[0031] Using the obtained three-terminal positive sequence components and positive sequence fault components, combined with the π-type equivalent circuits of the three branches, the positive sequence components and positive sequence fault components of the T node are calculated respectively. The T node positive sequence components and positive sequence fault components of the iT branch are calculated assuming that there is no fault point on the iT branch, and the MT branch is used as an example for explanation. For the MT branch, according to the attached Figure 2 We can get:

[0032]

[0033] Simplifying, we get:

[0034]

[0035] In the formula, They represent the positive sequence voltage and positive sequence current at terminal M respectively; It represents the calculated positive sequence voltage and current at the T terminal of the MT branch; Respectively represent the positive sequence capacitive current to ground on the M side and T side of the MT branch; Represents the positive sequence current flowing through the line impedance; L M Indicates the length of the MT branch; Z1, B M Indicates the positive sequence impedance and admittance to ground per unit length of the line. Similarly, the positive sequence component at the T end of the NT branch and the PT branch can be derived, and its symbolic meaning is similar to the above:

[0036]

[0037]

[0038] The analysis of the positive sequence fault component network is similar to the above, so the positive sequence fault component at the T end of the MT branch is:

[0039]

[0040] In the formula, They represent the positive sequence voltage fault component and the positive sequence current fault component at the M terminal respectively; It represents the calculated positive sequence voltage fault component and positive sequence current fault component at the T end of the MT branch. The T end positive sequence fault component of the NT branch and the PT branch has a similar form and will not be described in detail.

[0041] When fault location is performed on the MT branch, the positive sequence component and positive sequence fault component at its T end can be obtained from the positive sequence component and positive sequence fault component at the T end of the NT branch and the PT branch:

[0042]

[0043]

[0044] In the formula, They represent the positive-sequence voltage, positive-sequence current, positive-sequence voltage fault component and positive-sequence current fault component at the T end of the MT branch calculated from the NT branch and the PT branch respectively.

[0045] Considering that the location of the fault point is unknown, it is difficult to directly apply the π-type equivalent circuit on the branches on both sides of the fault point, so the effect of the ground capacitance cannot be taken into account. Therefore, when performing the initial fault distance measurement, the effect of the ground capacitance is not considered, so as to obtain the initial fault distance measurement result.

[0046] At the fault point f, the voltages solved by the positive sequence components and the positive sequence fault components at the M and T terminals should be equal:

[0047]

[0048] Simplifying the two equations in equation (8) and dividing them, the initial fault location result can be obtained as:

[0049]

[0050] According to the initial fault location results, the kth fault location is performed considering the effect of the line-to-ground capacitance on both sides of the fault point on the MT branch. First, calculate the ground capacitance current at the M and T terminals:

[0051]

[0052] After considering the ground capacitance current, equation (8) can be changed to:

[0053]

[0054] Simplified, we can get the k-th fault location result:

[0055]

[0056] Let ε = 0.001, when When the iteration converges, the iterative distance measurement result is output If it is not satisfied, repeat the iterative process from (9) to (11) until convergence.

[0057] Similarly, the iterative distance measurement results x of the NT branch and the PT branch can be obtained.N 、x P .

[0058] Now we analyze the properties of the iterative distance measurement results of the three branches and screen out the actual fault location. Assuming that the fault point is located on the MT branch, the T node positive sequence component and positive sequence fault component calculated by the NT branch and the PT branch are accurate, so the fault distance measurement result of the MT branch is correct, and its range is x M ∈[0,L M ]. Since the single-circuit T-type line is symmetrical, only the non-fault branch NT is analyzed, and the PT branch has the same properties. Because the fault point is located in the MT branch, the calculated value is based on the assumption that the fault point is not in the MT branch. will be smaller than the actual voltage value at the fault point, and the actual voltage at the T end is greater than the voltage at the fault point, so the actual voltage at the T end must be greater than Therefore, the amplitude of the voltage at the T end calculated by the MT branch and the PT branch will be smaller than the actual voltage amplitude of the T node. Since there is no fault point in the NT branch, the actual voltage at the T end can be accurately calculated based on the electrical quantity at the N end, and the voltage changes evenly on the NT branch. The fault distance measurement algorithm proposed in the present invention is based on the principle that the voltage calculated by the electrical quantities at both ends of the branch at the fault point is equal, as shown in equations (8) and (10). However, since the actual voltage at the T end on the NT branch is greater than the calculated voltage at the T end calculated by the other two branches, and the actual current at the T end in the NT branch is in the opposite direction to the calculated current, the N-end electrical quantity and the T-end calculated electrical quantity cannot obtain a point where the voltage is equal on the NT branch. This point can only exist at x. N >L N area, so x N ∈[L N ,+∞]. The ranging result of the PT branch is the same.

[0059] Therefore, from the above analysis, it can be seen that the iterative distance measurement result of the fault branch is less than the length of the fault branch, while the iterative distance measurement result on the non-fault branch is greater than the length of the fault branch. Therefore, the following fault branch judgment criteria and fault distance measurement results are proposed: 1) If the distance measurement result of the iT branch (i = M, N, P) satisfies x i ∈[0,0.999L i ], it indicates that the fault point is located in this branch, x i That is the location of the fault point; 2) If the distance measurement result of the iT branch satisfies x i ∈[1.001L i ,+∞], it indicates that the fault point is not located in this branch and this line is a non-fault branch; 3) If the distance measurement results of the three branches all meet x i ∈[0.999Li ,1.001L i ], it indicates that the fault point is located at the T node.

[0060] 2. Simulation verification

[0061] For attachment Figure 1 The single-circuit T-type transmission line shown in the figure is simulated. M , L N , L P The lengths are 120km, 80km, and 60km respectively. The power supply potentials of the three terminals M, N, and P are 110∠0°kV, 110∠30°kV, and 110∠60°kV respectively. The transient data sampling frequency is 10kHz, and a bandpass filter is used to filter and the full-wave Fourier algorithm is used to extract the fundamental component. The calculation formula for defining the relative ranging error is:

[0062]

[0063] The parameters of a single-loop T-type transmission line are: unit positive-sequence impedance: Z1=0.0082+j0.2548Ω / km; unit zero-sequence impedance: Z0=0.1590+j0.8970Ω / km; unit positive-sequence admittance: jωC1=j4.6178uS / km; unit zero-sequence admittance: jωC0=j2.5360uS / km.

[0064] Table 1 lists the distance measurement results of the distance measurement function when different faults occur at different locations of each branch.

[0065] Table 1 Ranging results of different fault types at different locations on each branch

[0066]

[0067] It can be seen from the results in Table 1 that the present invention can accurately determine the branch where the fault is located and accurately locate the fault point.

[0068] Table 2 lists the effects of different transition resistances on the distance measurement results when a phase A ground fault occurs at different locations of the MT branch.

[0069] Table 2 Influence of transition resistance when phase A ground fault occurs at different positions of MT branch

[0070]

[0071]

[0072] The simulation results show that the fault distance measurement algorithm proposed in the present invention can obtain the fault branch judgment result and the fault distance measurement result at the same time, and the fault branch judgment is accurate, and the distance measurement result is not affected by factors such as fault location, fault type and transition resistance, and has high distance measurement accuracy.

[0073] Although the embodiments and drawings of the present invention are disclosed for illustrative purposes, those skilled in the art will appreciate that various substitutions, changes and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the scope of the present invention is not limited to the contents disclosed in the embodiments and drawings.

Claims

1. A method for locating a single-circuit T-type transmission line fault without pre-identifying the faulty branch, characterized in that: Firstly, the three-phase voltage and current at each end of a single-loop T-type transmission line are collected by using the power transformer at the protection installation location, and then the collected fundamental wave components are decomposed by using the symmetrical component method, and the positive sequence components and positive sequence fault components at each end of the T-type line are calculated. Finally, the fault distance measurement functions of the three branches are constructed respectively by using the positive sequence components and positive sequence fault components at each end of the single-loop T-type transmission system, and the fault location is screened out by judging the rationality of the results of the three distance measurement functions. The steps of the method are as follows: (1) First, the three-phase voltage and three-phase current at the three ends of the single-circuit T-type transmission line are collected using the power transformer at the protection installation site. The collected data are decomposed using the symmetrical component method to obtain the positive sequence components at each end of the single-circuit T-type transmission system, and the positive sequence fault components are further calculated; (2) Then, based on the solved three-terminal positive sequence component and positive sequence fault component, combined with the π-type equivalent circuit of the three lines, the positive sequence component and positive sequence fault component of the T end are calculated according to the normal operation; the fault distance measurement function is constructed for the three branches respectively, and the positive sequence component and positive sequence fault component of the T end of the analyzed branch can be obtained by the positive sequence component and positive sequence fault component of the T end calculated according to the normal operation of the other two branches; since the fault location is unknown, it is difficult to directly apply the π-type equivalent circuit to the lines on both sides of the fault point on the fault branch, so the effect of the capacitance to the ground cannot be considered. Therefore, when performing the initial fault distance measurement, the method of not considering the effect of the branch capacitance to the ground is adopted to calculate the initial fault distance measurement result. Where: They represent the positive sequence voltage, positive sequence current, positive sequence voltage fault component and positive sequence current fault component at terminal i respectively; It represents the positive sequence voltage, positive sequence current, positive sequence voltage fault component and positive sequence current fault component at the T end of the iT branch obtained from the other two branches; L i Indicates the length of the iT branch; In order to pursue higher distance measurement accuracy, the initial fault distance measurement result is taken as the fault location, and the π-type equivalent circuit of the lines on both sides of the fault point is considered. The k-th iterative fault distance measurement result is obtained by iterative calculation. In the formula, Respectively represent the capacitance current to ground at the i-terminal and the T-terminal; Let ε = 0.001, when When , it indicates that the iteration converges, and the iteration result is output Otherwise, repeat the above iterative process until convergence, and the fault location process of the other two branches is similar to the above; (3) Finally, whether the distance measurement results calculated according to the three fault distance measurement functions satisfy x i ∈[0,L i ] conditions, thereby determining the branch where the fault point is located, and the fault distance measurement result of the corresponding branch is the fault location, thereby realizing the direct determination of the fault location of a single-loop T-type transmission line without prior identification of the fault branch.

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