Research On The Adaptive Reclosure Of Single-circuit Transmission Line

In all the breakdowns of electrical power system, majority of breakdowns stem from transmission line (particularly overhead line). In order to enhance the reliability of transmission line, reduce the power cut time, lessen the economic loss, the reclosure technology has been widely used in electrical power system. According to the statistics, the success ratio is generally about 60%~90%. Due to the reclosure technology, giant economy and the social efficiency has been brought to the electrical power system, but the disability to differentiate the permanent breakdown and the instantaneous one makes relosure very blindness, easy to ruin the stability of electrical power system, endanger the electrical power system seriously.In order to avoid the harm of reclosing blindly, so many domestic and foreign scholars have conducted a massive research to adaptive auto-relosure technology. The so-called adaptive auto-relosure just adds function of the distinction of fault nature and the block of the system breakouts in the permanent situation contrast to the convention reclosing.Along with UHV/EHV transmission line gradually becomes the important constituent part in the entire electrical power system, studies of auto-reclosure for the application on UHV/EHV transmission line has the vital significance, especially to the stability of the fast developing electrical power system. But the high voltage rank always means the problem of over-voltage. Therefore, UHV/EHV transmission line often install the parallel reactors to suppresses the influence of over-voltage, the improve voltage distribution along the route. Consequently, this article will carry on the comprehensive discussion and analysis on the reclosure of single-circuit transmission line from two aspects, including single-phase auto-reclosure and three-phase reclosure.The single-phase earth fault is one of the most frequent faults in the electric power transmission line. Therefore, single-phase reclosure has extremely important research value in the single-circuit transmission line. Massive theoretical analysis and proof on the single-phase reclosing has been carried on in this paper. The production mechanism of free oscillation component in the restored voltage and the factors which influent the oscillation frequency has also been stated. And a new criterion has been proposed to discriminate permanent breakdown and the instantaneity breakdown by the way of extraction the free oscillation component. Although the proportion of two or three-phase breakdown in the transmission line short circuit breakdown is not very big, when three-phase reclosing on two or the three-phase permanent breakdown, Very serious danger will be caused in the electrical power system. Because it is very difficult to obtain enough information to discriminate the fault nature after the three-phase trip, three-phase reclosure at present does not have a quite satisfactory plan. A preliminary discussion analysis on the reason of the appearance of beat frequency signal and its frequency characteristic has been carried on in this article.