IEEE Power & Energy Magazine - July/August 2017 - 84

abnormal conditions by interrupting and isolating faulted or
failed components from the system. They also provide safety
for electrical workers and the public. These systems operate
in a decentralized manner to achieve a high level of reliability, speed, sensitivity, and selectivity. The microgrid protection system should be able to deal with:
✔ external faults
✔ internal faults
✔ ride-through capability.
Microgrid Overcurrent Protection Requirement

Overcurrent protection must respond to the utility grid and
microgrid faults.
✔ Utility grid faults: Microgrid overcurrent protection
isolates the microgrid from the utility grid as rapidly
as necessary to protect the microgrid loads.
✔ Microgrid faults: Microgrid overcurrent protection
isolates the smallest possible section of the feeder to
eliminate the fault.
The challenge with the microgrid overcurrent protection
design is that it should be able to clear faults for both islanded
and grid-connected operation modes. In the grid-connected
mode, the fault current is very high, reinforced by the grid
supply, whereas during islanding condition, the fault current
is not as high. The protection system should be able to adapt
itself to be able to detect faults with a high degree of accuracy
regardless of the fault current.
Variable Generation Low Voltage Ride-Through

Variable generation resources normally have inverters that
cease to operate when there are voltage sags. It is important
that these devices are equipped with protection devices that
enable them to ride through low-voltage conditions without
shutting down.

Layer 2: Automation and Control
The automation control system on the South Campus deals
with fast remedial actions that are needed under different
conditions. These conditions include islanding, resynchronization to the grid, maintenance of equipment, a substation
section, or different loads.
In general, automation control provides three modes of
control:
✔ Automated: The control actions are predetermined
and executed by the automation control system.
✔ Manual control: The control actions are executed
by the operator.
✔ Remote control: The control actions are executed by
another external controller, such as a layer 3 controller.
The actions under automated control include the following:
✔ Islanding: Under islanding conditions, the system
needs to cater to frequency and voltage variations. A
generator needs to be assigned as the main generation
source and respond appropriately to frequency and
voltage variations.
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✔ Resynchronization: Once the grid is energized, the

islanded microgrid will get prepared to resynchronize
with the grid. Once the conditions necessary have
been reached, the automated control will resynchronize to the grid.
✔ Maintenance: Under maintenance conditions, the
automated control is programmed to pass on the responsibilities of the maintenance equipment to other
members. For example, if a part of the substation
needs servicing, the automated control will automatically reconfigure all the feeders from this segment to
other segments of the substation.
✔ System shut down: Under this control, the microgrid
is shut down methodically, respecting the system and
component requirements.
✔ System cold start: Under this control, the microgrid
is restarted, bringing units up one by one and energizing the substation, respecting all the system and component requirements and standards.

Layer 3: Monitoring, Optimization,
Scheduling, and Dispatch
Layer 3 schedules the microgrid resources to optimize the
microgrid based upon the mode of operations and current conditions. For example, the schedules and optimization schemes
will vary based upon environmental conditions (Is the sun
shining?), utility availability (Is the grid tie available? Is natural
gas flowing?), time of day and day of the week (Is the building
occupied?), and other conditions. Layer 3 views the microgrid
holistically and assigns schedules to the lower layers on a longer time horizon (typically 1, 5, or 15 min). Layers 3 and 4 are
necessary to transform a typical microgrid into an advanced
microgrid. A microgrid master controller solution has been
developed that provides monitoring, scheduling, optimization,
and dispatch. Further details are provided in the section "South
Campus Optimization Strategies."

Layer 4: Energy Market, Grid,
and Transactive Operations
Layer 4 functions will enhance, and if desired maximize, the
economic benefits of microgrid resources by scheduling and
optimizing generation, storage, and dispatchable loads against
dynamic electric supply rates and market opportunities for the
supply of grid services. Layer 4 provides for incorporation of
time of use, real-time power, and demand charge tariffs in
its scheduling and optimization functions. More importantly,
it provides for assessing market opportunities for supply of
capacity, energy, and various ASs and capabilities to offer
and deliver these services to the distribution grid operator and
to independent system operator (ISO)/regional transmission
operator (RTO) markets. This includes data interfaces to utility and ISO/RTO markets for available capability nomination,
telemetry, bidding, scheduling, dispatch, and settlements.
The power industry is moving decisively toward utilization of DERs for improved system economics and grid
july/august 2017

Table of Contents for the Digital Edition of IEEE Power & Energy Magazine - July/August 2017