Factors in the resilience of electrical power distribution infrastructures

One measure of the resilience of any dynamical system is the speed of return to equilibrium following perturbation. In electrical power distribution systems this may be approximated by the duration of unscheduled outages due to failure of the distribution system (i.e., excluding outages due to failure of the generation or transmission systems). We hypothesize that the resilience of power distribution systems depends on two main factors. One is the power distribution infrastructure, the biophysical environment within which it operates, and interactions between the two. The other is the priority given to restoration by the power company, and the effectiveness of the power company's response. To test this we modeled outage duration in the residential electrical power distribution system in part of the City of Phoenix, Arizona between 2002 and 2005. We found that while the type of infrastructure did not have a significant effect on outage duration, the interaction between infrastructure (overhead lines) and the biophysical environment (vegetation) did. We also found strong evidence that proximity to particular high priority emergency assets (i.e., hospitals) confers resilience on residential distribution systems. More generally, residential outage duration was found to be most spatially dependent up to around 1000 feet from an outage location. Overall, a spatial outage duration model provided a better fit to the data than a non-spatial model.