Redistribution of Reactive Power Flow in Contingency Studies

During recent years, problems associated with reactive power flow and bus voltages have acquired greater importance. The transmission capacity may sometimes be limited by reactive power considerations. In a few instances collapse of transmission network has been attributed to abnormal reactive power flow patterns. Some recent papers have addressed the question of improving the contingency study techniques for the reactive power flow problem. A commonly used method for contingency analysis is based upon the use of distribution factors. The distribution factor method of contingency analysis is very fast in its execution time, and for this reason is widely used in real time applications as well as planning studies. This technique is known to be particularly suited to the study of real power redistribution following an outage. It is not as accurate in dealing with problems of reactive power flow redistribution and accompanying effects on bus voltages. The inaccuracies are particularly significant when voltage controlled buses are present in the power system. The distribution factors are based on approximating active power injections by current injections under the assumption that voltage magnitudes throughout the system are kept constant. This is an unacceptable assumption for reactive power. This paper develops a new formulation of distribution factors which is suitable for the analysis of the reactive power problem. The new formulation is based on the S-E (complex power - complex bus voltage) representation of a power network instead of the usual I-E (complex current - complex bus voltage) formulation.