IEEE Power & Energy Magazine - March/April 2017 - 31

designation as designed to an N-2 contingency) without interrupting loads. The result is reliability up to two orders of magnitude better than can be achieved with radial systems.
DERs interconnected along a radial system can result in power flows (when DER production is in excess of the site's load) that
oppose the traditional direction of load flow from feeder head to
load. As a result, it offsets the upstream power flow directly. In
some cases, overloads on the upstream line sections and transformers are relieved directly by power injected by the DERs.
Conversely, overloads downstream of the DERs are unlikely to
benefit from the DERs.
Networks are generally more complex to model and especially to identify DER impacts. The effect of DERs installed
in the path to counter an overload current depends on the location (in any direction) of the DERs relative to the overload.
In a network, the power injected by the DERs can be quickly
dispersed by the multiple junctions in the meshed grid and by
power flows going in multiple directions.

Study Approach
The EPRI Integrated Grid Benefit-Cost Framework, depicted in Figure 3, provides a method, consisting of system
modeling and benefit-cost protocols, for assessing the time
and locational value of DERs. It provides objective, reproducible, and substantive insights into the methods and applications that will be needed to evaluate the physical and
economic implications of DERs on both radial and network
system configurations. It begins by specifying the core assumptions: market conditions, DER adoption rates, and
system assumption (base case), which are used to define scenarios which portray possible outcomes. Energy, capacity,

and reliability analyses are undertaken to identify designs
and approaches that take advantage of the DER benefits
while avoiding adverse reliability impacts.
The benefit-cost step is where the accumulated impacts
are processed and measures of net benefits are constructed.
It requires a reference case to establish a basis for comparing DER interconnection scenarios. The study stipulates
a level (or levels) of DER interconnection and determines
the impacts that result. Its goal is to expose the implications
of different levels and locations of DERs (or portfolios of
DERs) on circuits as well as different approaches for the
related system design modifications.
Through the effective modeling of the distribution system, a broad range of potential benefits are realized, such
as improved confidence in DER impact assessments, greater
visibility into the detail of the physical operation of the system, and better utilization of existing assets. Models allow
utilities to better evaluate solutions to accommodating
DERs and perform value determinations. Variations in grid
and DER conditions can be evaluated to allow for distribution
engineers to consider a wide range of possible conditions by
which they can interact with the grid. However, to provide
the proper analytical perspective, features must be spatially
and temporally comprehensive and enable value assessments
that consider the potential to utilize DERs. Figure 4 shows
the power system criteria that should be considered in these
modeling and simulation studies. Utilizing these, distribution
planners can assess DER interconnection impacts as well as
how the system's operation may change over time.
Each utility system was modeled in EPRI's OpenDSS
or commercial software package and calibrated to system

Distribution System
Hosting

Energy

Capacity

Reliability
Benefit-Cost

Scenario Definition
Market
Conditions

DER
Adoption

System
Assumptions

System
Cost
Changes
Bulk System
Resource
Transmission
Adequacy
Performance
Flexibility

Societal
Costs/Benefits
Customer or
Owner
Cost/Benefits

Transmission
Expansion

Operational Practices and Simulation

figure 3. The EPRI Integrated Grid framework.
march/april 2017

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