IEEE Power & Energy Magazine - March/April 2017 - 30

when and how they consume grid-supplied electricity. Collectively, these demand-altering measures are referred to as
distributed energy resources (DERs).
Regulatory and state initiatives are also looking at DER
integration policies and practices. In 2014, extensive reform
activities emerged in California and New York, with each having the potential to substantially alter the status quo of utility business landscapes. They advocate similar goals that will
move utilities toward full integration of DERs into their distribution system planning, operations, and investment. A component of that integration is to identify optimal locations where
DERs can be best integrated to provide the greatest benefit to
the entire electric system. This will require that utilities balance
daily and long-term strategies to ensure that existing assets perform effectively, while adapting to the changing character of the
grid and the new technologies that are interconnected.
To meet this need, the Electric Power Research Institute
(EPRI) launched a research effort with Consolidated Edison
of New York (Con Edison) and Southern California Edison
(SCE) to derive evidence-based insights and inform the temporal and spatial impacts of DERs on both radial and network
distribution systems. This study is distinctive in that it focuses
first and foremost on portraying how DERs impact distribution, which is where they are interconnected. This approach
acknowledges that electricity flows are determined by physical

relationships. By understanding the physical principles of
how power flows, practices and policies can be informed to
achieve specific goals using the local distribution system.
The results highlight "what matters most" in assessing the
locational value of DERs. Findings underscore how systematic and detail-driven approaches can add critical insights to
such inquiries and lead to more robust practices, programs,
and policies. The numerical findings provide examples; however, they are not intended for extrapolating the impacts
widely nor interpreted as a comparison of the relative value
of DERs across two utilities.

Two Different Systems
An important factor in studying DER impacts is the type of
system. This study selected distribution circuits to reflect the
diversity of system designs employed in the United States,
mindful that systems have distinct architectures that may
influence how DERs are accommodated and utilized. Con
Edison selected a mesh network, and SCE selected its flexible radial system.
Most utility distribution systems in North America are radial,
employing a hub-and-spoke configuration to transfer power from
high-voltage lines to low-voltage customer premises. Figure 1 is a
schematic for a typical radial distribution feeder. There is a single
path from the substation (the hub, marked with a red triangle) to
each load along the spokes or circuit radii. The thickness of the
lines is proportional to the power flowing so that the radial topology is clearly evident in the figure.
Densely populated urban areas are served by extensive,
low-voltage networks (Figure 2). Network systems are designed
so that they can withstand two coincident failures (hence the

138-kV Transmission Supply
26.4-kV
Distribution

Load

Feeders

Low-Voltage
Grid Network
(Meshed)

figure 1. A typical radial distribution feeder.
30

ieee power & energy magazine

figure 2. A typical urban network distribution system.
march/april 2017

Table of Contents for the Digital Edition of IEEE Power & Energy Magazine - March/April 2017