IEEE Electrification Magazine - March 2016 - 20

Enhancing the
physical vulnerability
of communication
links,
instrumentation,
and control centers
is of paramount
importance to
the security of the
electricity grid.

credible contingencies. Here, the main
focus of reliability enhancement is on
N-1 and N-2 outages (i.e., events in
which one or two system components
would be on outage). Such outages
could be followed by insufficient
awareness or preparedness for more
severe disturbances. Hurricane Sandy,
for instance, was an N-90 contingency.
Long Island, New York, lost the entirety
of its tie lines to Connecticut and New
Jersey, and New York City lost all its
ties to New Jersey. The hurricane left
about 7.5 million people without
power across 15 states. At the same
time, the only sections of the area that
remained energized were the ones
that were equipped with controllable
microgrids. The widespread outages in
the wake of such natural disasters cast light on the fact that
the resilience cannot be ensured, but deterioration can
often be controlled locally at a tolerable level until full services are recovered at the large grid level.
Although continuous efforts have been devoted to
strengthening the components of resilience, blackouts are
deemed to happen again. Consequently, the resilience of

Figure 1. New York City-13 October 2012: On the second night without
power, the lower Manhattan skyline appears as a silhouette over the East
River from the Brooklyn Heights promenade. A few emergency-generatorpowered lights can be seen in some office windows of the Financial District. The Hurricane Sandy storm surge combined with spring tides at the
full moon caused the East River to flood and disable vital power-supply
equipment at the 14th Street Con Edison plant. Power was immediately
cut off to Manhattan from 42nd Street southward.

Fault Tolerance

Recovery

Resilient Electricity Grid
Fast Response

Reliability

Figure 2. The components of resilience in the electricity grid.

I E E E E l e c t r i f i cati o n M agaz ine / March 2016

the power system is inevitably dependent not just on reducing the number
of outages but also on how the grid
will respond to such events. In this
regard, rapid and effective restoration
plans are required to support the
recovery of electricity grids in resilient
power systems.

What Is the Impact
of Microgrids?

The potential for building a resilient
electric grid can be realized by
expanding the role of autonomous
microgrids. Microgrids, as basic elements of future smart grids, could
pave the way for improving the grid
resilience. A microgrid, as shown in
Figure 3, represents interconnected
loads and distributed energy resources (DERs) with
defined electrical boundaries and acts as a single controllable entity with respect to the main grid. Generally,
microgrids can improve the resilience of the electric
infrastructure in several ways, from providing customers
with a reliable and secure source of energy to preparing
the grid for a prompt response to disasters. Microgrids
can be operated in either grid-connected or island
modes. In the grid-connected mode, which is used during normal operating conditions, the power transacted
between the upstream grid and the microgrid may be in
either direction. In the island mode, used in the event of
faults in the main grid, microgrid loads are supplied by
the local distribution resources. Here, the focus is to
identify strategies that make the power grid sufficiently
robust for handling inevitable failures without disastrous
consequences. Microgrids have profound effects on
power system planning, security, reliability, restoration,
and the market, to name a few. The majority of these
issues have not been fully investigated yet, and more
work is required to demonstrate the impact of distributed control and operation on the electricity grid.

Microgrid-assisted recovery
Although microgrid operations can impact the resilience
components of a power grid, depicted in Figure 2, they can
mostly improve the third component, i.e., recovery and
restoration of the electricity grid. Conventionally, a restoration plan can be categorized into three steps: 1) preparation, 2) system restoration, and 3) load restoration. The
ultimate goal of these steps is to recover the system loads
safely, efficiently, and as expeditiously as possible. Myriad
problems such as cold load pickup handling, reactive
power balancing, and restorable load prediction will arise
during the restoration process. Moreover, the devastating
effects of blackouts will be escalated exponentially as outage durations are prolonged. During the restoration

Table of Contents for the Digital Edition of IEEE Electrification Magazine - March 2016