| High voltage transmission line is an important part of power system. It bears the important task of power transmission. As the development of power system, teed circuit has been widely applied to high voltage power network. Teed circuit is generally applied to500kV or higher voltage levels. Once a fault occurs, it not only can shorten the recovery time of power supply, but also reduce economic losses if the fault position is quickly and accurately located. It also has a very important significance to the power system’s reliability and security. The main work of the thesis is as follows,Give an analysis of the factors that influence the ranging accuracy of power frequency method. Under the distributed parameter model, a frequency domain equation of uniform transmission line was deduced. When there is a three-phase asymmetrical fault, the realization of three phase decoupling is by phase mode transformation. The full wave Fourier algorithm is used to extract fundamental component from fault transient component of voltage and current which contains a lot of harmonic components.An algorithm of teed circuit that based on power frequency data of three-terminals is presented. This algorithm needs to distinguish the fault branch firstly and then calculate the fault distance. At the same time, because of the sampling data from three-terminals may out of sync, a formula is deduced to calculate the asynchronous angle by the data of one cycle before occurring of fault. The parameter of transmission line is changing with the external environment and its value can influence the precision of distance measurement. In view of this, an algorithm is put forward to revise the parameters of line. Calculating the wave impedance and propagation coefficient of circuit in real time through iterative calculation, then the given value is modified. Simulation shows that the method can accurately reflect the real time parameters of transmission line and can obviously improve the location accuracy. It has the value of application. An algorithm of fault location that is based on the relative relationship between branch length and fault distance of teed circuit is given. This algorithm does not need to identify the fault section firstly and can carry out fault location directly. It has an advantage compared with other algorithm.The theory of traveling wave and wavelet transform is of transmission line is introduced. The characteristics and ranging principle of raveling wave is analyzed and the influence that time, velocity and the length of transmission has on ranging precision is presented. The method that using wavelet transform can extract the singularity of traveling wave is presented. The algorithm does not require have a priority to judge the fault branch and can use the solutions of equations to realize fault location directly. Comparing with the method that only need single terminal data and the method that needs of branch identification of travelling wave, this algorithm is better than them. This algorithm also has a higher precision when compared with the algorithm that base on power frequency. At the same time, when the fault happens at the moment that the voltage is very low this would lead to the identification of wave head unavailable. So a combination algorithm that’s based on multi sensor is put forward. The algorithm can make full use of a variety of sampling data and can determine the weighted coefficient according to actual situation. This algorithm can overcome the shortcomings of single data source. Simulation results show that this is a simple and practical scheme and has a very high reliability. |
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