Method for recognizing internal fault and external fault of ultrahigh voltage alternating current transmission line

Abstract

The invention relates to a method for recognizing an internal fault and an external fault of an ultrahigh voltage alternating current transmission line. The method comprises the following steps of: after an alternating current line fails, starting a starting element, selecting the voltage of a fault component at the moment of 0.2ms before the fault and 0.8ms after the fault, and decoupling by using new phase mode transformation to acquire line mode voltage; performing S-transformation on the line mode voltage to acquire a result which is a time frequency complex matrix in a row -m and a column n; solving the modulus of each element in the complex matrix to acquire a modular matrix; calibrating the arrival time Tn of an initial voltage travelling wave according to an amplitude-time characteristic in the modular matrix; extracting the total high-frequency energy and the total low-frequency energy of the line mode voltage corresponding to 100 sampling points after the Tn from the modular matrix, and solving the ratio k of high-frequency energy to low-frequency energy; and distinguishing the internal fault from the external fault according to the ratio of the high-frequency energy to the low-frequency energy. In the method, sampling frequency is 250kHz, the length of a sampling sequence is 250 sampling points, the required data length is relatively short, calculated amount is low, and a real time property is relatively high. Whether the faults occur in a region is judged only by using single end amount without the usage of channels, so that the method is relatively high in applicability. A large number of simulation results prove that the method is high in transition resistance endurance capacity, is suitable for different fault types and has an obvious effect.

Description

technical field [0001] The invention relates to the technical field of electric power system relay protection, in particular to a method for identifying internal and external faults of ultra-high voltage AC transmission lines based on the conversion energy ratio of line-mode voltage S. 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, and TA saturation), and it is difficu...

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Problems solved by technology

[0004] The existing non-channel transient protection mainly selects the ratio of high and low frequency energy to constitute the criterion, but the selection of high and low frequency bands lacks basis, and the energy of high and low frequencies is often represented by wavelet coefficients after binary wavelet transform. When the sampling rate is fixed, the frequency bands divided by the binary wavelet transform are fixed, which is not conducive to the flexible selection of high and low frequency bands.

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