STUDY OF FORCED OSCILLATIONS IN TWO AREA POWER SYSTEM

Abstract

The demand for electricity is increasing day by day leading to integration of renewable energy and increasing stability problems in the power grid. In today‟s scenario, small signal stability has been become an area of great interest for the researchers in dealing with stability problems of the power grid. The approach to study poorly damped low frequency oscillations for electromechanical modes is based on two different methods: Modal analysis method in power system depends upon linearized equations of system model, and Measurement based methods that are useful for monitoring power system oscillations in real time from Phasor measurement Units (PMU). Ring down analysis and ambient data analysis are the two different approaches under the measurement based method. Ring down analysis is preferred for sudden large disturbance when subjected in power system, whereas ambient analysis is observed when the power system is subjected for small continuous random fluctuations in loads and its operation is considered when it is in Quasi-Steady state. In the recent past years, with increased installation of PMUs in power grids, modal analysis techniques which are based on real time measurement data from the PMU is a preferred method for stability analysis of power system. Apart from natural electromechanical modes which are operated by load variations in power system the electromechanical modes can be excited by forced oscillations from apparent mechanism serving as from cyclic loads or mechanical aspects of generators. They can have adverse effects on system by resonance, named as forced resonance oscillations. When the forced oscillation frequency is close to system mode frequency or Inter area mode whichever poorly damped at location for which Inter area mode is associated, system oscillations at much higher value, as compare to source can appear leading to collapse of the system. This dissertation studies a recent event in power system installation during summer season of 2013 reported several instances for the damping level of 0.37Hz, inter area mode of western power grid obtain below 3% for several hours. The present work deals with the study about forced oscillations in power system with the popular Kundur‟s two area test system. The test system consists of 12 buses illustrates WECC transmission system for simulation and its transient stability and its long term dynamics. Here dissertation gives a complete description of modelling a forced oscillation from V

governor of generator in two area system leading to Interarea resonance in the tie lines. Further, this work compares the PMU based measurement techniques of ring down method: Prony Analysis method and ambient method: Frequency domain decomposition (FDD) method to detect the presence of forced oscillation in power system.