Resiliency of Power Systems to Black Swan Hazards: How Ready Are We?

One might claim that these weather events are due to climate change, and, as such, their severity and frequency will further increase in the future. Irrespectively, these weather events as well as natural hazards are becoming a reality. In fact, in some occasions (e.g. Chile which is hit by more than 450 earthquakes per year of intensity larger than 4.5R), we may have to think twice before we characterize these events as of high-impact and low-probability (or frequency), since they, actually, occur increasingly frequently. It is, thus, becoming more critical than ever to consider these black swan events in the operational and reinforcement planning of power systems, if we want to keep the lights on under probable and less probable events. However, the assessment and planning tools that we have used so far may be inappropriate to deal with these new challenges.

Motivated by the above real-world experiences and considerations, recent joint work from the authors has provided insights into the need for developing advanced risk-based probabilistic multi-spatial and multi-temporal tools for assessing the impact of disastrous events on power systems resiliency. These tools go beyond the traditional N-1/N-2 security assessment, which is key when analysing the impacts of events that could result in the simultaneous loss of multiple assets, possibly in a very short period. These tools have been effectively and consistently used to assess the impact of windstorms and floods on the Great Britain transmission network as well as the impact of earthquakes on the Chilean transmission network. Our work has also highlighted the need for suitable resiliency metric systems, for example based on the so-called multi-phase resiliency trapezoid: this trapezoid describes the phases that a power system might reside during a disturbance, namely, disturbance progression, post-disturbance degraded state, and restorative state. By using these metric systems, bottlenecks in the response and recovery of a power system can be identified and the effectiveness of different resiliency enhancement strategies can be compared. Overall, the results clearly demonstrate that the use of traditional reliability indices in such studies, which do not take into proper account risk considerations, can significantly underestimate the severity of the problem.

Hence, the resiliency trilemma arises as to whether we should make the electrical infrastructure bigger, stronger or smarter. In fact, in many occasions it may be more efficient to have a smarter and more responsive strategy to accelerate the recovery of the system, rather than the “expected” solution of making the system bigger, i.e. more redundant. Once again, this has been shown for case studies in Chile through a risk-based planning approach that minimizes risk exposure to large earthquakes (above 7R) subject to budget constraints. The results indicate that an optimal planning portfolio should consider a wide-range set of investments, including: new transmission lines (to provide redundancy), substation reinforcement (to provide robustness), and an array of distributed energy resources organized in microgrids (to provide rapid restoration to critical zones in the system). Indeed, a more risk-based planning approach would naturally recommend a diversified set of measures that allow network operators to deal with unforeseen events in a more flexible manner, better adapting power system operation to the remaining power infrastructure resulting from extreme events. In this outlook, our results also suggest that flexible transmission systems (FACTS and HVDC) that can better manage and re-route power flows after a catastrophic event occurs, utilizing more efficiently the remaining power infrastructure, can successfully improve the resiliency of the power network.

However, how ready is the power engineering industry to make the shift from the traditional reliability-oriented paradigm to a more resiliency-oriented, risk-based engineering? The need for this shift is becoming even more critical considering significant changes and uncertainties in the power systems landscape, such as the increasing penetration of intermittent renewable sources, as for example demonstrated in the South Australia blackout of September 2016. There is clearly still a lot to do, and building a resilient electrical power infrastructure is a truly daunting task that involves technical and commercial considerations. Regulation and market mechanisms should in fact be in place to incentivize the power industry to consider resiliency issues in its long-term planning, as well as to enable and maximize the utilization of the benefits of emerging technologies. Yes, there are challenges to overcome with many of these technologies, but there are also several benefits which are still to be fully exploited. The roadmap towards resilient power systems should eventually be a collective effort by all the key actors, from the increasingly active end-users and distribution system operators, all the way up to regulators and policy-makers, as we advocate the use of risk-aware tools to successfully enable this transition.

This article was edited by Jose Medina