| Summary: | 碩士 === 國立臺灣科技大學 === 電機工程系 === 102 === Traditionally, the distribution system is radial type. The fault current presents in top-dowm direction; hence, a non-direction overcurrent relay may apply for feeder protection. Nowaday, Distributed Generations (DG) have been widely installed and fed into the distribution system. The system with DG may form as Microgrid and operate in Grid-Connected Mode or Islanded Mode. However, the fault current in Microgrid no longer presents in one-way. The directional function relay must be introduced instead of non-directional one. It will increase the installation cost since the additional Protecntial Transfomers (PT) are required to provide the reference quantity.
In case of the Microgrid operation in Island Mode, the fault location is close to the PT installation. The refrence quantity may be too low to provide the direction check for relay. To avoid this possibility a DSP-based Current-Only algorithm has been propsed. It can simply and easily apply feeder protection on Microgrids. Basically, the algorithm is base on modified DFT inherent in high calculation speed and fast filtering ability, the exponential decaying DC component in initial fault current can easily be removed within one more cycle. In addition, the more DGs and modern electronic loads in Microgrids the more harmonic issues need to be concerned. To monitor the power quality, the harmonic analysis function also be included in the proposed relay. Finally, the proposed relay is succeddfully tested and varified by Matlab/Simulink and Doble emulator. It concluded that the proposed relay is good for feeder protection in Microgrids.
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