Abstract
When generators are connected through long transmissions lines, a characteristic of the Western Interconnection (WI), low frequency oscillations can be observed between generator groups. These low frequency oscillations are referred to as inter-area oscillations and occur between generators in one part of the system oscillating against generators in other parts of the system. The WI is characterized by recognizable modes, a term for distinct oscillation patterns. When electro-mechanical modes in the power system are excited, combined with insufficient damping, they can have a destabilizing effect, leading to major system disturbances.
The East West A (EWA) Mode of the WI is identified by generators in Colorado and Eastern Wyoming oscillating against generators in the rest of the interconnection but, although it is identifiable, requires further study to provide sufficient characterization to identify reliability risks to the Bulk Electric System (BES). Through simulation of realistic operating scenarios, combined with application of a system disturbance of the loss of different generation and transmission elements, this thesis utilizes ringdown analysis to analyze the system response to provide characterization of its modal properties. It found that, under various stressed conditions and excitation events, the mode's frequency, damping, and participating generators can vary depending on system conditions.
This research analyzes the impact to the EWA Mode from the retirement of synchronous generation as states within the WI role out plans to integrate renewable resources and retire their coal fire generation stations. Transmission infrastructure is extremely costly to build, and many developers have capitalized on the retirement of fossil fired generation by using the existing infrastructure to integrate wind and solar generation. As a result of the changing generation profile, the modal properties of the EWA Mode are significantly impacted. This research quantifies the impact of the changing generation profile to the EWA Mode by assessing changes to its shape, frequency, and damping when synchronous generation is replaced by typical, grid following, Inverter Based Resources (IBRs). The analysis uses an iterative approach to determine how the location of replacement of synchronous generation with IBRs has on its modal characteristics and provides recommendations to industry professionals on how to address the changing generation profile in the future to ensure the reliability of the BES is maintained.