Defining power system resilience

30 September 2019

The definition of resilience has alluded utilities and standard authorities. Resilience is more than just “bouncing back”. CIGRE Working Group SC C4.47 has researched and formulated a definition as well as key actionable measures as an integral part of the definition. This paper covers the process and derivation of the definition as well as the actionable measures. It compares reliability to resilience and discusses application of the definition in the electricity sector.

Despite several attempts by organisations worldwide in the power and energy engineering communities to define resilience, there is no universally accepted definition. Resilience is a multi-dimensional and dynamic concept. Resilience is more than simply “the ability to bounce back”.

In 2017 CIGRE SC C4 formed a Working Group consisting of experts from 19 countries. The purpose was to formulate a standard definition and approach to resilience. An international survey was undertaken and the inputs consolidated into an internationally agreed definition. The group also discussed the difference between reliability and resilience as these terms are often confused.

Reliability refers to the probability of the satisfactory provision of power and energy to meet load demands and ability to withstand disturbances.
Resilience, as a concept, adds a new dimension to system management and reliability. The concept is intended to assist utilities and regulators to encourage prudent investments to enhance resilience capabilities of the interconnected power system in case of extreme events that are characterised by their low frequency of occurrence but with significant consequences.

The definition of resilience as determined by the group is as follows:

Power system resilience is the ability to limit the extent, severity, and duration of system degradation following an extreme event.

An integral part of the definition is the following key actionable measures;

Power system resilience is achieved through a set of key actionable measures to be taken before, during, and after extreme events, such as:

anticipation
preparation
absorption
sustainment of critical system operations
rapid recovery; and
adaptation
application of lessons learnt.

The new definition clearly separates the definition of the properties from the key actionable measures that can be deployed [Before (B), During (D) and After (A) events] to achieve or enhance resilience.

The process of “anticipation” (B) refers to evaluating and/or monitoring the onset of foreseeable scenarios that could have disastrous outcomes
Preparation” (B) is the process required by decision-makers to advance the knowledge gained during the anticipation phase from the resilience strategies to clear objectives to guide the deployment of measures
The process of “absorption” (D) is to meet defined objectives by means of which a system can absorb the impacts of extreme events and can minimise or avoid consequences.
The “sustainment of critical system operations” (D, A) refers to the process of maintaining the operational capability of the impaired power system
The “rapid recovery” (D, A) process requires the operational response to contain or limit the consequence to the disruptive events.
In the “adaptation” (A) process, changes are carried out in the power system management, defence and operational regimes, to contain and/or limit the undesirable situations.

This reference paper defines resilience within the electricity sector. It should be read in conjunction with the technical papers and/or brochures to be published by the WG.