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rejection, using the battery energy storage system as
a replacement load to avoid a power-export protection trip.
✔✔ Once the load rejection has been replaced by the
load of the battery energy storage system charging,
the microgrid controller can slowly adjust both the
battery energy storage charging set point and the
CHP power output to maintain the net power import within the minimum and maximum limits. This
permits the CHPs to slowly ramp to their new set
points without risking a power-export trip, and, at
the same time, it allows the net power import to be
as close to the limit as possible, thus reducing overall utility charges.

Asset Availability
The protective devices on individual DERs will protect
DERs during faults. In a fashion similar to that of powerexport protection, the microgrid controller also acts as a
proactive protection device to avoid energizing a DER when
it is likely to experience an issue. The microgrid controller
performs this proactive protection by reading error conditions from the DER and using an internal and user-settable
flag to mark a DER as available or unavailable.
While grid connected, the DER may report an error that
does not cause a protective trip but may be indicative of a
future problem. These errors include a lost communication connection, the operator marking the DER as unavailable, and the DER's failure to respond to issued commands.
Upon recognizing that error, the microgrid controller can
act quickly to remove the DER from the microgrid. Once
removed, additional DERs may be energized to replace the
functionality, if additional assets are available. For the two
CHP generators, that would mean dispatching one generator
to replace the loss of another.
This functionality also extends to user-settable values. In
the case where microgrid operators determine that one DER
must be curtailed for maintenance or other runtime considerations, they can set the availability flag in the microgrid
controller and allow the microgrid controls to spin up additional resources and curtail the unavailable DER.
In the North Bay CEP microgrid, there is only one
battery energy storage system, and its important functions cannot be replaced by any of the other DERs. To
avoid the risk of a protective-export protection trip, the
microgrid controller automatically adjusts the minimum
and maximum net power-import limits when the battery
energy storage system is marked as unavailable. This
allows for routine maintenance work to happen while
other DERs are still providing power, reducing overall
costs for microgrid operators.
DER availability is an important consideration, but
equally important is switch availability. The microgrid
controller reads specific information from each relay
to determine whether the switch it controls is openable,
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closable, or otherwise usable. For example, if the relay is
being operated locally and does not permit remote signals, the microgrid controller will not attempt to open
or close it and will also not attempt to energize DERs
downstream of the switch.

Conclusion
The North Bay CEP microgrid incorporates many protection strategies typical of microgrids and addresses several unique challenges. These challenges were overcome
using innovative microgrid protection techniques, and
this microgrid system provides key considerations to help
improve microgrid protection strategies for future projects. The CEP microgrid's protection system uses adaptive
relaying, directional overcurrent, IEC 61850 GOOSE messaging, a fast directional overcurrent blocking scheme, and
other techniques to protect the microgrid. The microgrid
controls and protection work together to fulfill some of
the microgrid use-case objectives. The sophisticated North
Bay CEP microgrid protection enables this innovative
microgrid to operate safely and resiliently while supplying
continuous power to the community it serves.

For Further Reading
" Microgrid protection systems, " IEEE Power & Energy
Society, Piscataway, NJ, Tech. Rep. PES-TR71, July 2019.
" Impact of IEEE 1547 standard on smart inverters and
the applications in power systems, " IEEE Power & Energy
Society, Piscataway, NJ, Tech. Rep. PES-TR67, Aug. 2020.
M. Higginson, K. Moses, B. Harwig, P. Curtiss, and H.
Tiwari, " Microgrid seamless transitions between grid-tied
and islanded operation: A case study, " in Proc. 2020 IEEE/
PES Transm. Distrib. Conf. Exposi. (T&D), pp. 1-5. doi:
10.1109/TD39804.2020.9299920.
M. R. Islam and H. A. Gabbar, " Analysis of Microgrid
protection strategies, " in Proc. 2012 Int. Conf. Smart Grid
(SGE), pp. 1-6. doi: 10.1109/SGE.2012.6463969.
A. Bernstein, J. L. Boudec, L. Reyes-Chamorro, and
M. Paolone, " Real-time control of microgrids with explicit
power setpoints: Unintentional islanding, " in Proc. IEEE
Eindhoven PowerTech, July 2015, pp. 1-6. doi: 10.1109/
PTC.2015.7232750.

Biographies
Michael Higginson is with S&C Electric Company, Chicago,
Illinois, 60626, USA.
Matt Payne is with North Bay Hydro Services Inc., North
Bay, Ontario, P1A 0B4, Canada.
Keith Moses is with S&C Electric Company, Chicago,
Illinois, 60626, USA.
Peter Curtiss is with S&C Electric Company, Chicago,
Illinois, 60626, USA.
Stephen Costello is with CIMA+, Sudbury, Ontario, P3G
117, Canada.
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