In this paper, a non-linear 7 th order dynamic model and a linearized 3 rd order dynamic model of a synchronous generator connected to an infinite bus are presented and compared in details. Parameters and equations of the both models are explained and summarized. They represent a useful starting point for work in areas of synchronous generators' construction, analysis, control systems design and synthesis. Novelty of this work represents a detailed research of applicability of the linearized model in an entire operating range. Established theoretical conclusions were confirmed with numerical results. Restrictions of utilizing the linearized model are presented. On a basis of the analysis for the synchronous generators of different power, their applicability with feasibility and accuracy was evaluated by certain objective criteria.
This paper analyzes the influence of inverter-interfaced distributed generations’ (IIDGs) response during transmission network faults. The simplest and safest solution is to switch IIDGs off during network faults without impacting the network voltages. A more elaborate and efficient concept, required by national grid codes, is based on controlling the IIDGs’ currents, involving positive- and negative-sequence voltage measured at the connection point. In this way the magnitude and phase of the injected currents can be adjusted, although the generated power will depend on the actual line voltages at the connection point. Therefore, an improved concept is proposed to adjust IIDGs’ fault current injection through the required active and reactive power, employing the same voltage characteristics. The proposed, i.e., power-based concept, is more definite than the current-based one, since the required power will always be generated. The discussed concepts for the fault current injection by IIDGs were tested in different 110-kV networks with loop and radial topologies, and for different short-circuit capabilities of the aggregated network supply. Based on extensive numerical calculations, the power-based concept during transmission networks faults generates more reactive power compared to the current-based concept. However, the voltage support by IIDGs during transmission networks faults, regardless of the concept being used, is influenced mainly by the short-circuit capability of the aggregated network supply. As regards distance protection operation, it is influenced additionally by the network topology, i.e., in radial network topology, the remote relay’s operation can be delayed due to a largely seen impedance.
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