Analysis And Application Of Traveling Wave Fault Location For Hybrid Transmission Lines

Transmission line fault location is of great significance for improving the reliability of power system operation,reducing the time of power failure and reducing economic losses.The traveling wave fault location method has received continuous attention in power grid fault location because of its simplicity,reliability,wide adaptability and high fault location accuracy.However,the continuous expansion of power grid scale and the increasing shortage of urban land resources make the application of overhead line-cable hybrid transmission lines more and more widely,but the movement process of transient traveling wave generated by the fault is extremely complicated in the hybrid transmission due to the discontinuity of the wave impedance at the cable connection,which makes single-ended traveling wave fault location method difficult to effectively detect and identify the reflected wave at the fault point and counter-reflected wave.At the same time,the inconsistency of wave speed also increases the fault location difficulty of hybrid transmission lines.Wavelet transform can effectively deal with power system transient high-frequency signals in the time-frequency domain.Therefore,this paper uses the wavelet transform modulus maxima to detect the singularity of the traveling wave signal to identify the arrival time of the traveling wave head to the measuring end,and then establish a double-ended traveling wave fault location model of the hybrid transmission line based on time search.The main research contents of this paper include the following three aspects:1)Study the traveling wave generation principle and the catadioptric process,and analyze the traveling wave motion equations in pure overhead and cable hybrid transmission lines respectively,which provides the basis for the subsequent effective identification of fault transient traveling wave heads.At the same time,the simulation model is built to study the influence of various factors such as fault type,fault initial angle and transition resistance on the traveling wave waveform.2)Study the basic principles of wavelet transform and modulus maxima,and apply the wavelet transform modulus maxima to the detection and identification of the fault transient traveling wave head arriving at the measuring end.The validity of the wavelet transform is verified by constructing a 220 kV pure overhead transmission line model,and the effects of fault type,fault distance and transition resistance on the fault location accuracy of single-ended traveling wave are analyzed.3)The double-ended traveling wave fault location algorithm based on time variable for hybrid transmission line is studied and established.The maximum value of the wavelet transform modulus is used to accurately identify the time when the fault initial traveling wave reaches the measuring end for the first time.The approximate location of the fault point is determined according to the fault time and the traveling time of the traveling wave in each section,and then combines the wave velocity to achieve fault location.