IEEE Power & Energy Magazine - September/October 2014 - 81

Distributed resources by and large
can provide many of the same energy and ancillary services
that central resources can provide.

Demand Response

Maximizing Resource Availability During VLSEs

today, most demand response programs are designed to
reduce peak demand or avoid system emergencies. these
programs are mostly designed for system-wide participation
of load and are not specific to a certain distribution feeder.
some utilities (e.g., Progress energy and Pacific Gas and
electric) are evaluating locational-based Dr within their
Dr notification systems. some wholesale power markets
also allow demand aggregators and large customers to contribute certain ancillary services through Dr. there are also
reported applications of Dr in managing transmission congestion by transpower in new Zealand.
all of the above Dr applications are targeted for normal operating conditions or to avoid emergencies. the
best-known application of Dr during emergency operating conditions is voluntary load reduction. as is the case
with the Der resources, current regulations for franchises granted to public utilities do not allow a customer's
Dr resources to be leveraged to help another customer
during outage conditions. For example, a customer's capability to adjust load to provide frequency regulation to the
system cannot be leveraged if that customer is islanded
during an outage.

Utilities defer discretionary maintenance of central generation units to maximize resource availability if they predict
a vLse. they also coordinate with neighboring utilities to
increase reserve margins.
currently there is little or no communication between utilities and Der owners related to distribution network operation during and after vLses. Increased communications
could help the utility and the Der owners better plan and
coordinate their response. For example, emergency condition
alerts in media outlets could include some recommendations
for Der owners and their neighbors. customers could ensure
that their backup generators are ready to come on line and
their batteries are fully charged, if the utility is anticipating a
critical event. In conjunction with these actions, Der owners
could communicate the status of their resources to the utility,
and allow, for example, the coordinated disconnection and
islanding of local microgrids from at-risk feeders.

Leveraging Distributed Resources
for Grid Resilience
the current state of the art is largely the result of engineering
standards and interconnection agreements that were developed when the penetration of distributed resources was low.
Given the significant amount of distributed resources that
already exists at many utilities and the forecast growth in
distributed resources, it is prudent to explore whether utilities could further leverage these resources in response to
vLses. Below, we present some examples of distributed
resources applications. In many cases, further research is
needed to explore viability or to address current technical
and nontechnical barriers. existing engineering standards
and interconnection agreements would need to evolve to
make some of these applications possible. while it may seem
bold to suggest such changes, it is worth noting how dramatically today's landscape of renewable resource integration
already differs from the situation one or two decades ago.
the proposed applications are analogous to the coordinated
operation of interconnections, in which neighboring utilities
cooperate and cooptimize their resources for the benefit of
the interconnection.
september/october 2014

Riding Through Faults
Ieee standard 1547, which is central to most interconnection agreements, requires DG to cease to energize the grid
for all faults or major disturbances on the grid to which it is
connected. this requirement may not be optimal when there
is a large penetration of distributed resources that could all
disconnect simultaneously, causing an unintended adverse
impact on the grid. the standard should be modified to
allow for different requirements under conditions mutually
agreeable to the grid operator and the DG owner, especially
during a vLse. the grid operator may then, in some cases,
want distributed resources to ride through a fault to avoid
bigger issues. smarter protection and automation schemes
will need to be devised for such ride-through capability.

Optimizing Restoration Prioritization
most utilities prioritize the restoration of loads based on
their importance to public health and safety, giving higher
priority to loads designated as critical (e.g., hospitals, police
facilities). this prioritization is normally a static process
and does not take into account the real-time conditions in
the field. the prioritization could be optimized, however, if
the utilities were made aware of the status of the distributed
resources. as an example, if a utility knew that a certain customer had islanded, was supplying his own critical load, and
was able to continue to do so for 24 h, the utility could then
focus its effort on other critical loads that were completely
ieee power & energy magazine

Table of Contents for the Digital Edition of IEEE Power & Energy Magazine - September/October 2014