Wide-Area Oscillation Assessment and Trending Analysis

Understanding the potential impact of the on-going power system transition on system modal properties and wide-area oscillatory behavior.

Windmills at sunset in Turlock, United States.

Photo by American Public Power Association on Unsplash

Background

The electric power grid evolves at an accelerated pace with a significant new mix of generation and consumption such as smart loads and power electronic-based devices. As a result, the grid is seeing more renewable energy penetration and more active consumers (Figure 1). The new uncertainties and dynamics they bring in have significant impact on the grid behaviors. Figure 2 shows the grid’s frequency responses to both emergency and normal operation situations. Especially the trending shown in Figure 2(b) is worth further studies to see if there are any correlations to the grid evolution in generation mix and consumer participation.

Of great concern is the inter-area low-frequency oscillation that usually propagate through a large region and has a system-wide impact. Such oscillations may lead to unnecessary or inadvertent tripping of generators that may be simply reacting to the oscillations originating from geographically remote sites. Such tripping of generators can lead to cascading outages, system split and load loss events. In recent years, several system-wide oscillation events have been observed across all three North American interconnections.

fig 1
Figure 1. Stochastics and uncertainty increase with more renewable and consumer participation: (a) Solar generation increases require a significant ramp when solar is not available in the evening time (credit: CAISO); and (b) US electricity trends toward significantly higher penetration of uncertain resources (credit: U.S. Energy information Administration).

 

fig 2
Figure 2. Power grid trending to have more dynamic content: (a) Frequency significantly deviates from the nominal 60 Hz during emergency operation like the August 14, 2003 Northeast Blackout; (b) Frequency trends of larger and more frequent deviations from the nominal 60 Hz during normal operation.