Dissertation > Industrial Technology > Electrotechnical > High Voltage Engineering > Overvoltage and Its Protection > Over-voltage protection devices

Study on a new type earthing distance protection

Author CaiWeiWei
Tutor DuHongJi
School Nanjing University of Technology and Engineering
Course Proceedings of the
Keywords Ground impedance relay transition resistance steady-state overreach systempower swing MATLAB simulation
Type Master's thesis
Year 2013
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When ground faults occur in the EHV or UHV system, it’s not generally due to the metal contact ground faults, but because there are transient resistances. The existence of transient resistances will seriously affect the performance of the distance protection, which are mainly embodied in the following three aspects:1) when external faults occur, distance protection may overreach;2) when internal faults occur, the zone of distance protection may decrease;3) when line outlet faults occur, distance protection will lose direction. Therefore, the research of the endurance ability of ground distance protection on transient resistances has practical significance to improve the performance of the distance protection.This new kind of ground impedance relay takes the difference between positive sequence voltage and voltage of ground fault phase (UMA1-UMA) as polarization voltage. The relay cannot adapt to different fault resistance. First, we can add a phase-shift to improve its ability of enduring fault resistance. Second, the paper takes a zero sequence delay to avoid overreach. Last, the modified criterion has explitic direction and high sensitivity without voltage dead zone. Adopt three point DFT algorithm and forward propulsion DFT algorithm to collect voltage and current data so as to prevent the impact of system power swing.Calculating simulation data of various cases, such as sending terminal, receiving terminal, phase shift and different voltage of both ends. Simulation analysis with MATLAB proves that, this new kind of relay has excellent operating characteristic on110kV、500kV and750kV line.

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