07-10-2010, 12:54 PM
Abstract
A transmission line trip during a power swing may cause instability of a power system. It is necessary to recognize the power swing from fault. Based on stability boundary, the power swing blocking relays must be set. To do that, first power swing should be analyzed. Second a way of probability of occurrence of fault must be found. Third, the critical condition under which the stability of a power system hasn’t been disturbed is recognized. Finally the settings of the power swing relays are calculated. In this paper analysis of the power swing occurrence has been made. By defining transmission s and generators sensitivities coefficients, the way of making the line under consideration full load is found. The way of minimization of distance between load impedance and the last zone of distance protection is given and the settings of the power swing relays are calculated.
Introduction
After clearance of a fault on a line of a power system network, the line is isolated and power swing may occur. As an example it can be mentioned the isolation of Azarbayjan network from Iran power system because of occurrence of power swing. In this example short circuit fault occurred on Rajaee-Tabriz line and the protection on this line ordered to isolate the line, then two transmission lines named Poonel-Taghidize and Miane-Zanjan tripped by distance relays. Finally one unit ofTabriz Power Station tripped and Azarbayjan network became unelectricited[1]. In order to prevent such unwanted protection, it is necessary to specify faults from power swing. In other word power swing blocking elements must be set such that the distance relays are allowed to operate the fault and prevented to operate the power swing. Many attempts have been made in the past to analyze the power system stability and compute the settings of power swing relays .
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