Fault Location Method Based On Natural Frenquencies For Power Transmission Lines And GRID

It is the important period of accelerating industrialization and urbanization at present, so the demand of electricity has maintained rapid growth. With the increasing distribution range of power grid, man-made damages often occurred in the operation and the power supply equipment is easily failure for the long time running. Therefore, quickly and accurately fault location is of enormous social and economic benefits.Existing time-domain fault location methods using travelling wave have kinds of defects. The fault location method based on natural frequencies which this paper choose could not only provide a new solution to issue the fault location, avoid the influence of picking travelling wave front, accurately calculate the velocity of the travelling wave, but also has important theoretical and practical significance. However, the power transmission lines and grid widely used such types of lines as double-circuit transmission lines, hybrid overhead-cable transmission lines. It is little to find how the fault location method based on natural frequencies applied to these types of lines. Therefore, it is quite necessary to discuss how to put the method into these types of transmission lines and how is the adaptability of it.After respectively analyzing mechanisms of failures in general transmission lines, double-circuit transmission lines, hybrid overhead-cable transmission lines and transmission grid, this paper discusses the fault location methods for these transmission lines and grid.In the aspect of picking and spotting the dominant frequency of natural frequencies of the travelling wave, this paper integrates the functions of recording waves, filtering waves, phase mode transformation, choosing mode components and identifying the dominant natural frequency within Natural Frequency Measurement Unit (NFMU). Various simulation results show that the spectra estimating using Multiple Signal Classification (MUSIC) within NFMU is of high noise immunity and performances well in distinguishing the signals.In terms of fault location for the general transmission lines, this paper firstly obtains the fault location method using two-terminal date based on natural frequencies. This method adds the data measured by two-terminal on the original single-ended fault location method, and carries on the fault location according to the two-terminal data to eliminating the bias error of the system. Simulation results reveal that the method is ranging more precise. In the second place, this paper proposed a fault location method based on natural frequencies for the double-circuit transmission lines. This method adapts similar-Clarke phase to mode transformation and different characteristics of failure reflection matrix, selects appropriate modulus, completes the spectrum estimation and calculates the fault distance. Simulation results indicate that this method is of high precision and not affected by the transition resistances, fault types and initial phase angles, etc. However, accurate results could not be obtained when the fault type is synonyms-phase cross-line fault due to'mould hybrid'.In respect of fault location for hybrid overhead-cable transmission lines, this paper constructed a fault location scheme based on Empirical Mode Decomposition (EMD) and natural frequencies. The proposed scheme firstly decomposes the initial fault travelling wave which is mixed with different frequencies waves using EMD, then estimates the spectrum of the signal to be analyzed to spot the dominate natural frequency and completes the fault location. Amount of simulations demonstrate that the proposed scheme is of high accuracy in the ideal hybrid transmission lines and a hybrid transmission lines constructed realistically. Because there is'mixing mode'in EMD, so errors of fault location are occasionally large. But this demerit could be made up by artificial line patrol and does not affect the approach.In terms of fault location for the power grid, in the first place, this paper studies on the fault location method for a simple topology power grid and proposes a fault location method based on ordering dominant natural frequencies. This method formats a fault location database using the relations between the travelling wave paths corresponding to its own dominant natural frequencies and the fault position, then constructs a criterion for judging fault segment and rejecting disturbance, and locates the fault in the end. Additionally, a fault location method based on networked natural frequencies for general topology power grid is also discussed. This method forms a criterion for judging fault segment by comparing the lengths of travelling wave paths to the lengths of the lines'own to determine the fault segment and calculate the fault distance. Extensive simulations make clear that these methods achieve favorable fault location results in transmission grid.Overall, this paper finally forms a fault location based on natural frequencies framework for different types of transmission lines from general transmission lines (including the double-circuit transmission lines) to the hybrid overhead-cable transmission lines, and then to power transmission grid, which is expected to have a certain prospect.