The power grid’s hazard landscape has changed. Widely accepted power system reliability metrics, long regarded as exemplary models of contingency planning, are no longer enough to prepare for the many new challenges emerging as the grid evolves.
Changes in power demand, the influx of renewables, and the growing adoption of new technologies and grid-connected devices are redefining “normal” grid operations. Meanwhile, the increasing frequency of severe weather events and cyber-attacks represent new threats that need to be addressed as organizations seek to prevent and respond to disturbances on the modern grid.
As a result, the electricity sector has sought to define new practices for improving its ability to recover from these low-probability but extremely disruptive events, while accounting for changes in grid operations and power system dynamics. This effort is both informing and being informed by the concept of power systems resilience, which, lacking a universal definition, is ultimately about a system’s ability to withstand and recover from a disturbance.
The next step for industry stakeholders is to align on a common definition and develop actionable measures to build resilience into their systems and organizations. There is some promising headway on this front; the U.S. DOE-funded Metrics Analysis for Grid Modernization project is seeking to “define, develop, and validate metrics that can be used to measure progress towards…resilience.”¹
In fact, the United States Department of Defense might have the most straight forward definition of resilience available. Paraphrasing their work in energy resilience, a reasonable definition of resilience is “…the ability to prepare for and recover from energy disruptions that impact your mission.”² An energy provider’s mission is to deliver energy to the end user. However, assuring 100% availability of the utility-level energy supply may not, in fact, be the most cost-effective way to provide resilient energy services to an end user. Resiliency is really driven by individual use cases and therefore it is difficult to broadly quantify or develop metrics for. A common understanding of resilience will require that qualitative metrics be considered as well as quantitative metrics.
Meanwhile, CIGRE Working Group C4.47 – Power System Resilience is seeking to set a standardized approach to resilience thinking and practices in the electricity sector. PSC Technical Director Zia Emin is the Chair of CIGRE Study Committee C4. He explains:
“WG C4.47 is tasked to explore how a number of resilience conceptual models are utilized to demonstrate the application of resilience thinking in the electrical sector starting with the conceptual difference between traditional reliability engineering and resilience engineering techniques.
As part of the work, a comprehensive questionnaire has been developed and a consensus has been reached in terms of defining power system resilience as ‘the ability to limit the extent, severity and duration of system degradation following an extreme event.’³
It is important to distinguish severity of event from severity of the event consequences and here it is the consequences that are relevant. The working group has also identified six actionable measures where resilience is achieved through these key actionable measures taken before, during and after extreme events. These measures are anticipation, preparation, absorption, adaptation, rapid recovery and sustainment of critical system operation. The work is progressing in developing methods, metrics and planning that can be used for resilience purposes, as well as regulatory frameworks that can encourage and incentivize resilience reinforcement.”
While a fully defined set of globally accepted practices around resilience might be too much to ask for by Dec 31, 2020, increasing coordination and emphasis on the topic shows we are heading toward a more common understanding of resilience.
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¹ https://prod-ng.sandia.gov/techlib-noauth/access-control.cgi/2017/171493.pdf
² https://www.energy.gov/sites/prod/files/2017/06/f34/5_Storage%20and%20Microgrids%20Panel%20-%20Ariel%20Castillo%2C%20DoD.pdf
³ E Ciapessoni, D Cirio, A Pitto, M Panteli and M Van Harte, “Defining power system resilience”, CIGRE Electra No:306“, October 2019, pp. 32- 34