Research On Fault Location Method For Multi-terminal Transmission Lines

Transmission line plays a decisive role in the power system,and it is easier to fail compared with other components.When fault occurs,detecting the fault location accurately is very important for power system to restore the lines' transmission service timely and ensure the stable operations.As there are many defects in the existing transmission line fault location methods,especially for the multi-terminal transmission lines,so this paper makes an in-depth study of multi-terminal transmission lines.When fault occurs,the fault traveling wave suffers from attenuation or distortion,which will cause the detection of wave front be false.Therefore,a new fault location method based on phase comparison is presented.In this method,it is practicable to install multiple current measuring points on the circuit,which can decrease the fault range and improve the detection precision of the wave front.Firstly,the phase differences are determined by comparing the phase between two measurements which installed in the lines using Kaiser windows Fast Fourier Transform(FFT).Secondly,the wave velocity of the fault current is obtained by the ratio of the length of healthy line to time delay that the wave travels through this segment.Based on double-terminal traveling wave theory,the final fault distance can be achieved.This method can judge the fault interval and fault phase exactly,remedy the defect of the dead zone near the teed node and conquer the influence of traveling wave velocity.The fault location method based on natural frequency of traveling wave for transmission lines can accurately determine the fault position without identifying the wave front of traveling wave and is not restricted by synchronous clock,so it has great advantages,and its core issue is the extraction of natural frequency.When fault occurs,the fault traveling wave will refract or reflect in fault point and bus bar.As a result,it is difficult to extract the principle component of natural frequency due to the frequency spectrum aliasing.To solve above problem,a fault location method based on traveling wave natural frequency for teed-circuits is presented in this paper.This method is based on the method of Variational Mode Decomposition(VMD).It overcomes the influence of spectrum aliasing effectively compared with traditional methods,and has good modal stability.Then by comparing the value of natural frequency component reflecting fault point and T node correspondingly,the fault interval will be determined.Therefore this method can greatly reduce the complexity of fault interval judgement.Due to the complex structure of the multi-terminal transmission lines,it is difficult to determine the fault location accurately.A fault location method for multi-terminal transmission lines based on traveling wave natural frequency is presented in this paper.By combining the VMD algorithm and Multiple Single Classification(MUSIC)algorithm,the spectrums of corresponding modes will be got.Then the propagation paths of the fault current traveling wave are analyzed in depth,and the natural frequency components reflecting the fault distances can be extracted.Finally the fault distance can be determined.So this method can effectively solve the difficult problem of fault location for multi-terminal transmission lines due to the complex structure.