Research On The Key Issues Of Transmission Network Fault Location Method Based On Natural Frequencies Of Traveling Waves

With the accelerated construction of power grid, it is becoming increasingly prominent for high-voltage power transmission network being the pivotal role, which has important economic value and social benefits to quickly and accurately locate fault and restore power. In this paper, the fault location algorithm based on natural frequencies of traveling wave, compared with the existing traveling wave method based on the time domain, has most notable advantage in avoiding the difficult problem of wave-head identification, and can accurately calculate the wave velocity. But the practical application of this method in transmission network exists several problems, such as the difficulty to obtain accurate equivalent impedances in local system, and the problem of fault branch location in multiterminal system of transmission network.In view of the influence of system equivalent impedance to the fault location, this article proposed the impedance identification method of measuring end in fault location based on natural frequencies of traveling wave. Firstly, the local system resistance and inductance are considered as parameters to be identified, then multi-objective nonlinear functions are constructed using multiple natural frequencies of fault traveling wave, again by Nelder-Mead, namely simplex search algorithm, to solve the local optimal value to obtain the equivalent impedance satisfying the requirement of fault location. Because of the multiple solutions in multi-objective functions, the obtained local optimal equivalent impedance is not representative of the actual system impedance value, but it can correctly calculate the reflection angle of fault traveling wave, and finally get accurate fault distance, which make improvements to fault location method based on traveling wave natural frequencies in evading the influence of system equivalent impedance. This method eliminates the need to add other electrical parameters, and consistents on the form of original location algorithm, which has good portability. A large number of simulation experiments verify that the fault location results are not affected by the change of fault distance, fault type and transition resistance, and the iterative algorithm is not sensitive to the initial iterative. In addition, it can realize evaluation of location accuracy during the fault distance calculation, also can significantly increase the reliability of the fault location method based on the natural frequencies of traveling wave, to avoid extract the error natural frequencies.For T type structure usually appearing in transmission network, this paper presents the fault location based on traveling wave natural frequencies in the T type line solution. In this paper, through the analysis of the wave propagation path reflected by busline current considering different fault positions in T-line, it is revealed that the natural frequencies measured by the fault branch busline has a regular harmonic characteristic. Moreover, further study of the natural frequencies of the spread between the fault point and busline has been proofed by mathematical derivation of the trend of fault generated traveling waves in different system boundary conditions, with which the fault discrimination criterion has been structured. After determining the fault branch, extract the branch busline current, then use the existing single-end fault locating method based on natural frequencies to calculate fault distance, finally the complete T-line fault location method can be achieved. Simulation results show that the location results are not affected by the fault distance and the fault type, especially the fault branch can be reliably determined when single-phase faults near the T-node. Fault location dead zone is near the proximal busline, which is caused by the traveling wave frequencies positioning principle itself.This article addresses the traveling wave fault location method based on natural frequencies dependent on the accurate system equivalent impedance, meanwhile mathematical expressions are proposed to reveal the trend of natural frequencies of the traveling wave, and to achieve reliable fault branch discrimination and fault location in T-line. These above improvements are laid a theoretical foundation for the practical application of the method for fault location in transmission network.