IEEE Power & Energy Magazine - May/June 2021 - 14

guest editorial

Jim Reilly and S.S. (Mani) Venkata

microgrid protection
its complexities & requirements

MICROGRIDS AROUND THE WORLD
are evolving at a quick pace. They come
in many sizes and types, for a -v ariety
of uses. With the integration of smart,
digital devices and technologies, realtime, automated grid operation with
the human in the loop is a daunting
task. Eight years ago, this topic was
the theme of the July/August 2013
issue of IEEE Power & Energy Magazine. Two years later, the related topic
of grid and microgrid resiliency was
given comprehensive treatment i n
the May/June 2015 issue. Continuing this theme on the development of
m icrog r id tech nologies, t he July/
August 2017 issue covered microgrid
controllers, which define the micro--
grid's operations and functionality.
This 2021 issue further continues the
microgrid theme with the challenging
topic of protection.
Microgrid protection has become a
topic of great interest as the number
of microgrids with prominent levels
of inverter-based resources (IBRs),
storage, and managed loads has grown
greatly along with the trend toward
new generation being connected to distribution networks. Microgrids themselves are no longer diesel generators
connected to specific building loads
in case of power outages. They have
evolved into complex entities that operate in parallel with the grid and provide
grid support services. As their importance in serving critical loads has
Digital Object Identifier 10.1109/MPE.2021.3057949
Date of current version: 19 April 2021

ieee power & energy magazine

risen and their impact on grid reliability
has become a reality, microgrids have
become a serious consideration for
utility system protection schemes. Microgrids may not lead to greater reliability and resiliency than that already
delivered by existing networks, especially mesh, unless protection is taken
into consideration.

System Protection:
Art and Science
System protection is both an art and
a science involving protective equipment, which is like a silent sentinel.
The protection of even a classical, passive, and radial distribution system has
always been incredibly challenging.
Practices vary widely even within a
utility and especially so among utilities. Practices for microgrids are even
more fluid and challenging.

Consider System
Protection: Integration
Complexities
As modern technologies and distributed energy resources (DERs) with
energy storage and renewable generating resources become more prevalent
in electric power systems, operational
complexity increases. Attention to system protection is a critical issue to pave
the way for achieving safe, efficient,
and effective means of managing this
emerging complex system. The challenges in microgrid protection design
result from the combination of a high
penetration of DERs using power electronic interfaces and the absence of a

connection to the larger distribution
grid in islanded operation. Also, the
protection schemes, or at a minimum
the protection system settings, must be
changed and adapted when transitioning from grid-connected to islanded
modes of operation. These transitions
include those that require the design
of adaptive protection systems. The
combination of a large penetration of
inverter-based DERs and an absence
of a strong grid in islanded operation
mode results in a microgrid protection
design that significantly departs from
the conventional power system protection philosophy.
To allow islanded and autonomous
operations, microgrids need to incorporate local DERs, which include
renewable energy resources (wind
and solar), and the associated electrical storage required for balancing
and firming intermittent generation.
From this perspective, a microgrid is
a means to aggregate DERs. In the microgrid islanded operation, the local
distribution system is no longer connected to the larger power grid provided by central generation. This makes
the design of protection systems in an
islanded mode different from that in
grid-connected mode.
DERs are mostly interconnected
to the distribution grid using power
electronic-based energy converters.
The presence of these types of DERs
requires approaches to protection that
are different from those for conventional rotating-machine-based DERs,
such as combined heat and power,
may/june 2021

IEEE Power & Energy Magazine - May/June 2021

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