Threshold-based monitoring of cascading outages with PMU measurements of area angle

TL;DR

This paper introduces a method using synchrophasor measurements of area angles to quickly assess the severity of multiple line outages in power grids, enabling faster response to prevent cascading failures.

Contribution

It proposes a threshold-based monitoring procedure utilizing area angle measurements to evaluate outage severity and guide operational decisions in real time.

Findings

Area angle effectively indicates outage severity.

Thresholds correlate with maximum power transfer limits.

Method applied successfully to Northwestern USA grid data.

Abstract

When power grids are heavily stressed with a bulk power transfer, it is useful to have a fast indication of the increased stress when multiple line outages occur. Reducing the bulk power transfer when the outages are severe could forestall further cascading of the outages. We show that synchrophasor measurements of voltage angles at all the area tie lines can be used to indicate the severity of multiple outages. These synchrophasor measurements are readily combined into an "area angle" that can quickly track the severity of multiple outages after they occur. We present a procedure to define thresholds for the area angle that relate to the maximum power that can be transferred through the area until a line limit is reached. Then in real time we would monitor the area angle and compare it to the thresholds when line outages occur to determine the urgency (or not) of actions to reduce the bulk transfer of power through the area. The procedure also identifies exceptional cases in which separate actions to resolve local power distribution problems are needed. We illustrate the thresholds and monitoring with the area angle across several states of Northwestern USA.