چكيده به لاتين
This dissertation presents a study on two types of travelling wave based fault location in HVDC systems including DC links and offshore wind farms. Travelling wave methods, despite the higher sampling rate, are widely used for fault location in transmission lines, and in general are highly accurate.
The first presented fault location method is based on the natural frequencies of the travelling wave in a CSC-HVDC system including an overhead transmission line and interconnection of two AC systems. Travelling wave spectrum of fault at single end measurement contains information from the fault distance that can be identified by using the dominant frequency of the fault generated waveform, the angle of the voltage reflection coefficient at the measuring terminal, and the wave velocity at its prevailing frequency. The multiple signal classification (MUSIC) tool has been used to detect the dominant frequency of the fault signal. Simulation is done in PSCAD software for different fault types and fault resistance. The results in MATLAB software show the accuracy of this method in fault location.
The second method is a proposed a single end fault location using time-frequency characteristic of the travelling wave. This fault location method is for underground cable lines in MMC-HVDC system interconnecting offshore wind farms and AC networks. The discrete wavelet transform is first applied to the transient fault current at one terminal to obtain first and second fronts of the travelling waves. Then, the dominant natural frequency of the transmission line is extracted using multiple signal classification method and the travelling wave velocity on the line is calculated. Finally, according to the polarity of first and second fronts of the travelling waves, location of the fault is estimated using the proposed algorithm. Considering different fault types and resistances, the proposed method is evaluated by simulating the HVDC test system in PSCAD. Simulation results show the effectiveness of the method in fault location in different fault conditions.
