Research On Accurate Location Method Of Single Phase To Earth Fault In Medium Voltage Distribution Network

Medium voltage distribution network plays a key role as the intermediate link between transmission network and power consumers. It is very important for improving power supply reliability and realizing highly efficient economic operation of distribution network to locate the fault point quickly and accurately and repair the power supply line when single-phase earth fault happened. Traveling-wave fault location method, which would not be influenced by factors such as system parameters, transition resistance and system oeration mode, has been successful applied, but reliability of location under noise environment need to be improved. For the numerous line branch and complex structure of distribution network, it is difficult to make single-ended traveling wave fault location and double-ended traveling wave fault location work in the precise location of single-phase earth fault. Therefore, this paper is devoted to study accurate traveling wave location method of single-phase ground fault in distribution network.A new method based on modulus transmission time difference is came with to locate fault point for multi-terminal distribution network, on the strength of the gap between on the zero mode and aerial mode traveling wave propagation time of Single-end positioning method. Firstly, wavelet transform modulus maxima is used to calibrate the moment of zero line mode inceptive travelling wave reaching detection point, and iterative location formula is established on relationship between wave velocity of zero module and fault distance as well as modulus transmission time difference. Segment layering principle of distribution network is proposed, and distribution line is layered. Then calculate fault distance between endpoint of each layer and fault point using iterative location formula. Distribution segment layering principle has been proposed, and it is used to layer distribution line. Fault distance between end point and fault point is computed through ranging iterative formula, and the fault branch decision matrix of each layer is formed, and fault section is obtained by it to get fault distance. Simulation shows the proposed method is correct and effective.Noise may submerge singularity of weak traveling wave signal, leading to the calibration failure of inceptive travelling wave. The different noise and its effects on the wavefront calibration analysis is proposed, and mathematical morphology filter is used to filter out impulse noise of traveling wave signal. Wavelet transform is used to transform traveling wave signal filtered impulse noise wavelet transform, and calibrate line model travelling wave head under the combined scale wavelet coefficients, making sensitivity higher and corresponding features more pronounced. Simulation shows that the method enhanced anti-interference performance of the calibration of noising traveling wave head.Without the need of time synchronization, it has proposed online zero mode wave velocity algorithm using fused information of the two ends. It also put forward single phase-to-ground fault traveling wave location method in distribution networks based on single ended positioning principle of modulus transmission time difference. Firstly, the arrival time of inceptive travelling wave under s-transform to detection point is demarcated, when traveling wave frequency of zero line is kHz or 500kHz, to ensure the unity of wave velocity about each detection point. The correlation of zero-mode wave velocity and single ended traveling wave ranging formula is deduced, and located the minimum zone of fault point. Then line sectioning contained by the minimum zone is decomposed into T type to fault location. The results show that the zero-mode wave velocity and location method are accurate and highly engineering significant.