IEEE Power & Energy Magazine - May/June 2015 - 66

number and location of repair crews. The latter refers to the contribution of each component to restoring operational resilience
under different operational scenarios. However, the influence of
these two aspects on decision making is not independent, but it
is in contrast strongly correlated. For example, if a component is
ranked first of the most critical components in restoring operational resilience, but under specific circumstances it may be very
difficult or lengthy to restore, then it might not be highly ranked
in the priority list. Other components, possibly less "operationally" critical, may be restored first.

Hybrid Grids: Stronger, Bigger, Smarter
It can be clearly seen that understanding and enhancing grid
resilience is still an open challenge. Hardening/reinforcement schemes may come at a significantly higher cost than
the smart/operational measures. On the other hand, operational measures without sufficient strengthening of the network may not be enough for keeping the lights on in the
face of a disaster. In addition, some of these actions, such as
moving overhead lines underground or making use of adaptive protections that may not be sufficiently reliable, may
have controversial effects on the key features of resilience.
A hybrid network might be the solution for boosting the
resilience of future power systems in an economically feasible way. The term "hybrid" can be interpreted here in two
different, but related, ways. The first refers to the combination of hardening and smart measures for meeting the resilience and cost-efficiency targets. The second refers to the
coexistence of large, interconnected traditional grids (with
centralized control) and smaller balancing areas (with distributed and decentralized control) that could be operated as
microgrids if needed. Such a hybrid system would offer the
advantages of both bigger and more robust networks as well
as more operational flexibility and security.

Conclusions
Building a power infrastructure that is reliable to known and
credible threats, but also resilient to the high-impact low-probability events, is very challenging. To achieve this, we need first
to have a good understanding of what resilience is. Resilience is
not a static concept, but it is a dynamic, ongoing procedure for
adapting (and possibly transforming) the structure and operation
of power systems to be better prepared to external, unforeseeable shocks. A resilient network must thus be robust and operationally flexible but must also possess the adaptation capacity
to plan, facilitate, and implement the actions and measures
required for preparing to similar or new events in the future.
In general, reinforcing the network (i.e., making it bigger or
stronger) may not always have the desired effect, while it usually requires a significant investment. A hybrid network with
built-in synergy between hardening and "smart" measures is
thus likely to achieve a good tradeoff between resilience and
cost efficiency. This needs to be assessed through cost/benefit
analysis that compares different potential resilience measures

66

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and risk-based approaches. In this respect, from this work several research questions emerge that are only now starting to be
addressed, including how smart grid measures can cost effectively and reliably enhance resilience when compared to hardening and reinforcement actions, what metrics should be used to
assess the multiple dimensions of resilience, and what type of
tools are appropriate to make resilience-related, cost-effective
decisions taking into account the relevant uncertainties and risks.

Acknowledgments
This work was supported by the Resilient Electricity Networks for Great Britain (RESNET) project, which is funded
by the Engineering and Physical Sciences Research Council
(EPSRC), United Kingdom.

For Further Reading
M. Panteli and P. Mancarella, "Modelling and evaluating
the resilience of critical electrical power infrastructure to
extreme weather events," IEEE Syst. J., pp. 1-10, 2015, doi:
10.1109/JSYST.2015.2389272.
M. Panteli and P. Mancarella, "Influence of extreme
weather and climate change on the resilience of power systems: Impacts and possible mitigation strategies," Electric
Power Syst. Res., to be published.
A. R. Berkeley and M. Wallace. (2010, Oct.). A framework for establishing critical infrastructure resilience goals:
Final report and recommendations by the council. National
Infrastructure Advisory Council, USA. [Online]. Available: http://www.dhs.gov/xlibrary/assets/niac/niac-a-framework-for-establishing-critical-infrastructure-resiliencegoals-2010-10-19.pdf
M. Chaudry, P. Ekins, K. Ramachandran, A. Shakoor, J.
Skea, G. Strbac, X. Wang, and J. Whitaker, "Building a resilient UK energy system," Working paper, Ref. UKERC/
WP/ES/2009/023, UK Energy Research Centre, Mar. 2009.
Cabinet Office. (2011, Oct.). Keeping the country running: Natural hazards and infrastructure. [Online]. Available:
https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/61342/natural-hazards-infrastructure.pdf
Executive Office of the President. (2013, Aug.). Economic
benefits of increasing electric grid resilience to weather outages. White House Office of Sci. and Technol., Washington, D.C. [Online]. Available: http://energy.gov/sites/prod/
files/2013/08/f2/Grid%20Resiliency%20Report_FINAL.pdf
C. S. Holling, "Resilience and stability of ecological systems," Annual Review of Ecology and Systematics, vol. 4, pp.
1-23, Nov. 1973, doi: 10.1146/annurev.es.04.110173.000245.

Biographies
Mathaios Panteli is with The University of Manchester,
United Kingdom.
Pierluigi Mancarella is with The University of Manchester, United Kingdom.
p&e

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http://www.dhs.gov/xlibrary/assets/niac/niac-a-frame https://www.gov.uk/government/uploads/system/uploads/at http://www.energy.gov/sites/prod/

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