Frequency dependent hybrid equivalents of large networks

grantor: University of TorontoFor the digital time-domain analysis of electromagnetic transients in an interconnected power system, the system is artificially divided into two sections: (i) the study zone, in which the transient phenomenon occurs and where the component models must be represented in detail, including physical and mathematical nonlinearities, and (ii) the external system which encompasses the rest of the network, and due to its electrical distance to the location of the transient phenomenon, can be represented by a linear network in the whole frequency range of interest. This thesis develops a new methodology to obtain a frequency dependent equivalent for an external network. The main motivation behind development of an equivalent for the external system is to minimize computation resources, i.e., CPU time and memory, for the analysis of realistic size systems. The required computational resources are the bottleneck in real-time simulation and application of off-line software packages for the analysis of high-frequency electromagnetic transients. The salient feature of the proposed approach, as compared with the other methods for deducing external network equivalent, is that it provides a simpler model (lower-order mathematical model) with the required accuracy. Furthermore, the proposed methodology ensures positive-realness of the equivalent. The proposed equivalent is referred to as the hybrid equivalent since it relies on a combination of (i) simplified distributed line models and (ii) lumped element models, to generate a frequency response equivalent of the external system. This thesis also expands the proposed approach to develop a multi-port equivalent and to consider the impact of sources (generators and harmonic sources) on the equivalent. The proposed concept has been applied to a realistic size interconnected 500 kV study system to obtain a single-port and a two-port equivalent with respect to pre-specified observation points. The validity and accuracy of the proposed approach is verified based on comparing the simulation results with those obtained from the simulation of the original system using the ElectroMagnetic Transients Program (EMTP).Ph.D