A New Coherence Approach of Generators for Investigation of Slow and System Wide Oscillations in Large Power Systems

Abstract

A new technique is described for aggregation of generators in a large power system. The technique focuses on slow and system wide oscillations. The reduced order models have many applications in analysis of large power systems. The equivalent parameters for the turbine governors and synchronous machines are calculated as weighted mean values of the parameters of included governers and machines in the coherent group. Model parameters for voltage control, power system stabilizers etc., have the same control characteristics as the largest machine in the coherent group.The primary advantage of this procedure is that the definition of coherent machines can easily be interpreted physically and the definition is independent of the excitation of the system. This definition may be used for small disturbance stability analysis, (SDSA). Similar approach is used by Geeves,1988. Other definitions of coherency (Berg et. al.,1983; Oshawa et. al.,1978; Podmore,1978; Zhou et. al.,1985) are not suitable for the analysis of slow and system wide power oscillations. These definitions are mainly used for large disturbance stability analysis, (LDSA). The coherency, based on the LDSA - definition, of generators will depend on where the disturbances are applied in the power system and will also depend the frequency spectrum of the disturbances.