POWER SYSTEM REDUCTION FOR TRANSIENT STUDIES

Electromagnetic Transient study of power system requires modelling of complicated transmission networks. And modeling the details of a full system requires great amount of computer memory and computation time, specially when statistical analyses are also of interest. In these studies usually just a small portion of power system is modeled in detail and the rest of system is modeled by a simple equivalent circuit based on short circuit studies. some times a relatively better equivalent model by application of line's surge impedance in parallel with the short circuit impedance is employed. Although the recent model increases the accuracy of the first reflections, however Will not provide accurate results for low frequencies, and therefore the steady state response is not valid. In this paper some of the recent reduction methods will be discussed, and the proposed method based on reduction of system discrete equations in z-Domain, and replacing equivalent RL, RC or RLC branches for the reduced Transfer Functions is introduced for single-port and multi-port equivalents. This method is validated perfectly with two case studies.