Impact of location and composition of dynamic load on the severity of SSR in meshed power systems

Abstract

This paper evaluates the impact of dynamic loads (induction motors) on the damping of Subsynchronous Resonance (SSR) based on load location and aggregate load inertia for the IEEE 68 bus network simulated in DIgSILENT. The severity of SSR oscillations is shown to increase in the presence of Subsynchronous Resonance Load Interactions (SSRLI), whereby dynamic loads may contribute towards negative damping under certain network topologies. This change in severity is investigated for each load location by replacing the static (constant impedance) load model, traditionally used in SSR studies, with a 50% static and 50% dynamic load model. The paper shows that the torsional damping and thus the severity of SSR is sensitive to the location and aggregate inertia of the dynamic load. These results establish the sensitivity of torsional damping to dynamic load location, size and aggregate inertia. In the absence of accurate knowledge of load composition, 50% static and 50% dynamic load composition can be used as a recommendation for the modelling of load during EMT studies of SSR, to avoid conservative results and over/under design of protection or mitigation strategies.