Translated Abstract
Electric energy is an important secondary energy source for the development of industry and the lives of residents. Electric energy, as a secondary energy, is transformed from primary energy source. The primary energy source is mainly located in the west part of our country, while the load center is in the east part of our country, so that the electic energy need transporting from west ti east. Transmisson lines are the only way for power transporting. The voltage of transmisson line is high, the distance is long and the capacity is large. The connection of two equivalent systems at the ends of a long-distance transmisson line is weak. A tiny disturb may lead to power system oscillation.
Power system oscillation have an effect on power system in many aspects. One of them is the effect on distance protection. Distance protection is a widely used transmisson line protection. Power oscillation may cause the maloperation of distance protection. In order to avoid this kind of maloperation, the short time on-limits strategy is put into use. In practical, the maloperation is not primarily caused by power oscallation, but the entrance of the oscillation center in distance protection zone.
This paper did a research on the changing parttern of electric parameters during power oscillation, and especially made an analysis on the difference of electric parameters when oscillation center is inside and outside of distance protection zone. A oscillation center location method is put forward based on sigle end electric parameters, and the method can be used when oscillation center migration happens. The simulation results in two-equivalent sources and three-equivalent sources demonstrate correctness of this method.
Based on the provided method, this paper supplements the power oscillation blocking logic of distance protection. Currently, the distance protection will have a short time, which is 150ms, on-limits after activated, but if distance protection is not tripped during this short time, it will be blocked to avoid maloperation that may caused by oscillation. This stategy doesn’t take the location of oscillationg center into consideration. If the oscillationg center can be identified using the same end electric parameters as distance protection does, the oscillation block can be more selective, which in turns improve the performance of distance protection during power oscillation.
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