Method for judging internal and external faults of alternating current transmission line based on fractal dimension
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A fractal dimension, fault discrimination technology, applied in the direction of measuring electricity, measuring electrical variables, measuring devices, etc., can solve the problem of indistinguishable internal and external faults, etc.
Inactive Publication Date: 2012-07-11
KUNMING UNIV OF SCI & TECH
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The existing non-channel transient protection mainly selects the ratio of high and low frequency energy to form the criterion, but when a small angle fault occurs and the high resistance is grounded, the high ground energy attenuates faster, and it is impossible to clearly distinguish internal and external faults
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Embodiment 1
[0066] Example 1: The transmission line is at a distance of 70km from the protection installation place (F 1 ) A phase-to-ground fault occurs, the transition resistance is 10Ω, the time window length is 1ms, and the sampling frequency is 1MHz.
[0067]The specific steps of the AC transmission line fault discrimination method based on the fault voltage fractal dimension are as follows:
[0068] 1.1 After the high-voltage AC transmission line fails, the starting element starts immediately, and within a short time window, the fault voltage at the line protection is measured U i [ k ]; then use the differential filter method to obtain the phase voltage fault component Δ U i [ k ]:
[0069] ;
[0070] In the formula, i =A,B,C; N T is the number of sampling points corresponding to the power frequency cycle, k Indicates the 1st, 2nd, 3rd... N sampling points, U i [ k ] is the collected voltage, Δ U i [ k ] is the phase voltage fault component;
[0071] 1.2 The fa...
Embodiment 2
[0085] Example 2: The transmission line is 220km away from the M-end busbar (F- 2 ) A phase-to-ground fault occurs, and the transition resistance is 10Ω.
[0086] Through the same method as embodiment 1, find the fractal dimension of the line mode voltage D =1.08037, satisfying the criterion D≤ 1.2, it is determined that this fault is an out-of-area fault.
[0087] In the present invention, different fault distances, different grounding resistances and different angles are simulated and verified, and the fractal dimension is obtained D c (F), the result of which is as Figure 7 , 8 , as shown in 9. Figure 7 is the simulation fractal dimension diagram under different fault distances; the vertical coordinate D c (F) is the box dimension, the abscissa is the fault distance L, and the unit is kM. Figure 8 is the simulation fractal dimension diagram under different transition resistances; the ordinate D c (F) is the box dimension, the abscissa is the fault transition re...
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Abstract
The invention relates to a method for judging internal and external faults of an alternating current transmission line based on a fractal dimension, and belongs to the technical field of relay protection of electric power systems. The method comprises the following steps of: when an alternating current line fails, selecting fault component voltage, and decoupling by new phase-mode transformation to obtain line mode voltage, wherein sampling frequency is 1MHz, and a time window is 1ms; selecting a discrete line mode voltage signal with the sampling sequence length of 1,000 points; fracturing by a sampling box dimension method to obtain a fractal dimension D of the fault component voltage; and distinguishing the internal and external faults according to the fractal dimension, determining that the fault is the external fault when the D is less than or equal to 1.2, and determining that the fault is the internal fault when the D is more than 1.2. The sampling frequency is 1MHz, the time window is 1ms, required data has a small length, and the method is low in calculated amount and high in real-time performance; and whether the faults occur in an area is only judged by single end amount without channels, and the method is relatively high in practicability. A large number of simulation results prove that the method is high in transition resistance tolerating capacity, is suitable for different fault types and has an obvious effect.
Description
technical field [0001] The invention relates to a fractal dimension-based method for distinguishing faults inside and outside an AC transmission line, and belongs to the technical field of electric power system relay protection. Background technique [0002] With the continuous construction of ultra-high voltage and ultra-high voltage transmission lines, large-capacity units have been put into operation one after another. After a line fault, quickly and reliably clearing the fault is an effective measure to increase the transmission capacity of the line and improve the transient stability of the power grid. At present, power frequency mutation characteristics are widely used in power systems to form relay protection devices, which have problems such as slow action speed and easy to be affected by power frequency phenomena (such as power frequency oscillation, transition resistance, TA saturation), and are difficult to meet the current line requirements. protection requiremen...
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