IEEE Power & Energy Magazine - May/June 2021 - 16

diesel, or small hydroelectric generators.
Among the significant differences are
the limited fault-current capacity of the
inverters and the disparate design considerations of the DER controllers. The
resulting performance is highly variable
and dependent on the design and implementation choices.
This issue presents
the complexities and specific protection requirements that are unique to
microgrid systems, in
both connected and islanded operating modes
as well as the transition
between them. Adaptive
protection is one of the
solutions to these complexities discussed in the
articles. Fault conditions
arising from the power
electronic grid interfaces
of fast energy converters used for DERs and
the coordination of communication schemes are
some of the complexities
for microgrid protection that the authors explain.

project. In this article, the authors offer
a unique perspective on microgrid protection informed by lessons learned and
insights gained from a long tradition of
experience in microgrid technology
worldwide. More specifically, the article explores the effects of different
operational transitions
of microgrids. It reviews
the characteristics of
power electronics-based
generation on the performance of conventional
protection schemes in
internal fault cases as
well as the pros and cons
of various protection
methods. The promising prospects of adaptive
protection and the importance of hardware-inthe-loop testing for the
acceptance of microgrid
protection solutions are
also highlighted.
The next article is
" Influence of InverterBased Resources on
Microgrid Protection, " by Matthew
Reno and Michael Ropp from Sandia
National Laboratories, Sukumar Brahma from Clemson University, and Ali
Bidram from the University of New
Mexico. Since this is a topic of overarching importance, it was prepared in
two parts- " Part 1: Microgrids in Radial Distribution Systems " and " Part
2: -Secondary Networks and Microgrid
Protection. " Advanced microgrids
today include IBRs, and many microgrids have modes or conditions
under which they are entirely energized by them. The authors explain
the behavior of IBRs under faulted
conditions that present challenges for
microgrid protection system design.
There are special problems concerning the fault-current profile between
grid-connected and microgrid-islanded modes and between IBR-dominant
or rotating-machine-dominant configurations. Protection for IBR-based
microgrids and solutions with different controls for IBRs are identified
as key issues in the integration of mi-

The authors
explain the
behavior of
IBRs under
faulted
conditions
that present
challenges
for microgrid
protection
system design.

Microgrid Protection: The
Scope of the Articles
The articles in this issue are dedicated to
exploring the topic of microgrid protection. The authors are leaders in the field;
they are active in R&D with the national laboratories in the United States and
the European Union, the studies of the
IEEE Power & Energy Society (PES)
Power System Relaying and Control
Committee, the IEEE Standards Association (SA), and CIGRE C6 Distribution. As guest editors, we are delighted
that they agreed to share their insights
and research with us.
The first article is " Microgrid Protection Against Internal Faults, " by
Dimitris Lagos, Vasileios Papaspiliotopoulos, George Korres, and Nikos
Hatziargyriou. Hatziargyriou was a key
contributor to one of the first microgrids
in Europe on Kythnos Island in 2001,
and we offer our congratulations on
the 20th anniversary of this microgrid
16

ieee power & energy magazine

crogrids in both radial and secondary networks.
In the fourth article, " Practical Microgrid Protection Solutions, " authors
Scott Manson, engineering services
technology director at Schweitzer Engineering Laboratories, Inc., and Ed
McCullough, senior manager for Tesla
Energy application engineering, present a new set of challenges to protection in microgrids from the perspective
of the impacts of IBR-connected systems on protection design principles.
The authors offer a set of solutions that
uses the computing platform embedded in programmable protective relays
to achieve adaptability. The article
explains technical challenges, such as
supplying simulated inertia, limited
current contributions, and other firmware-based inverter behavior. It offers
several common techniques to overcome them with programmable protective relays.
The fifth article is " North Bay
Hydro Microgrid, " by Michael Higginson, Keith Moses, and Peter Curtiss
of S&C Electric, Matt Payne, president
and chief operating officer of North Bay
Hydro Services, Ontario, and Stephen
Costello of CIMA+. The authors present their operational experiences for a
microgrid that was retrofitted from a
distribution system that was not engineered to support microgrids. The article describes what protection challenges were expected in the design phase
and how the protection system operates
in the field. It also discusses the major
challenges in devising a robust protection plan that included bidirectional
and variable fault current, power-export
restrictions, and a need for fast protection operation, including the ability to
reliably detect utility events promptly
and protect the equipment from closing
out of phase. This article is a real-life
example of the realities and importance
of protection for microgrids that are interconnected with the grid.
Any discussion of microgrid protection would be incomplete without an
understanding of the role of standards.
In the sixth article, " Status of Microgrid
Protection and Related Standards and
may/june 2021

IEEE Power & Energy Magazine - May/June 2021

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