IEEE Power & Energy Magazine - January/February 2014 - 63

To accommodate higher penetrations of variable renewable
energy resources, changes to traditional system restoration
methodologies will be required.
capacity. Some standards do not allow the reconnection of
variable energy resources at the beginning of system restoration. Disconnection of wind generation units connected to
the distribution grid is usually less strict than for units connected to the transmission grid, i.e., units on the transmission
grid are disconnected at a smaller frequency deviation. When
the frequency deviation reaches the threshold values of the
units' protection, they are automatically disconnected from
the grid. Smart grid technologies, however, may permit utilities to use variable renewable resources for black starts.
Load Restoration

After the system is restored with sufficient strength, variable renewable energy resources can be used for load pickup.
Variable energy resources could provide power to restore
load as long as they satisfy all general requirements, i.e.,
those regarding voltage regulation, low- and high-voltage
ride-through, effective inertia, controllability for ramping
and curtailing output, and frequency control.
A sophisticated operating methodology should be established to meet the recent dramatic development of variable
renewable generation, mainly in the form of wind farms.
Otherwise, the integration of uncontrollable wind generation
may have a negative impact on system restoration under the
current system operation methodology. A European Union
report on the coordination of transmission of an electricity
disturbance on 4 November 2006 shows that the unexpected
reconnection of uncontrollable wind capacity had a very
negative impact, preventing the dispatchers in both areas
from managing the situation effectively.
The following two suggestions therefore make sense
from the point of view of power system restoration after a
major outage.
✔ Sophisticated control methods should be used to
improve the frequency and voltage response performance of renewable energy resources before they can
be used in system restoration.
✔ Since the system is much weaker during system restoration, standards that are different from the regular
operating conditions should be established to meet
these critical requirements.

Other Considerations
The growing interconnections among different elements of
the infrastructure (e.g., communications, economic markets, and transportation) and their complex interdependencies could cause a blackout and affect more than one critical
january/february 2014

infrastructure. Addressing this interconnected nature of infrastructure requires an even more integrated approach than is
presently possible. A good example is the dependencies that
exist among power, communications, and IT infrastructures.

Conclusions
Effective system restoration is an important step toward a
self-healing smart grid. In the future energy paradigm, with
a high penetration of renewable resources and responsive
demands, variability and uncertainty will affect power system operating and recovery technologies. Smart restoration
provides an adaptive and optimized strategy with which to
make restoration decisions, one that will reduce restoration
time while maintaining system integrity.
With the implementation of such decision support tools,
the power grid will be better prepared and equipped to
handle extreme events. They enable the streamlining of
communication among all stakeholders, and they preserve
knowledge and experience for future engineers.

For Further Reading
ERGEG Final Report. (2007). The lessons to be learned
from the large disturbance in the European power system on
the 4th of November 2006. [Online]. Available: http://www.
energy-regulators.eu/portal/page/portal/EER_HOME/
EER_PUBLICATIONS/CEER_PAPERS/Electricity/2007/
E06-BAG-01-06_Blackout-FinalReport_2007-02-06.pdf
C.-C. Liu, W. Sun, Y. Hou, and S. Liu. (2011). Putting
into practice the dream of a self-healing smart grid. [Online].
Available: http://smartgrid.ieee.org/september-2011/53-puttinginto-practice-the-dream-of-a-self-healing-smart-grid
R. Podmore. Smart grid restoration concepts. presented
at 2010 IEEE Power and Energy Society General Meeting, Minneapolis, MN, pp. 25-29, July 2010. [Online].
Available:
http://ieeexplore.ieee.org/xpl/mostRecentIssue.
jsp?punumber=5577387

Biographies
Shanshan Liu is with the Electric Power Research Institute
(EPRI), Palo Alto, California.
Yunhe Hou is with the University of Hong Kong.
Chen-Ching Liu is with Washington State University,
Pullman, Washington.
Robin Podmore is with Incremental Systems Corporation, Washington.
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