IEEE Power & Energy Magazine - March/April 2015 - 23

feeder. Dispersed, customer-based generation has a quite different impact, even though the same amount of electricity
may be produced.

Distribution Feeder Response Characteristics
Even though feeders may appear to have similar characteristics (such as voltage class, topology, and load), analyses performed by the Electric Power Research Institute (EPRI) have
shown that easily observed feeder characteristics alone cannot definitively and accurately determine how many DERs
a feeder can accommodate. A distribution feeder's response
characteristics (like its voltage profile and short-circuit
strength) can be used, however, to help determine what level
of DERs can be accommodated and where.

DER Technologies
Variable generation such as wind and solar can have
widely varying impacts on voltage and capacity value
compared with forms of generation that are dispatchable. The differences primarily emanate from the timing
in which the electricity is generated and the character of
the energy output. Rotating machines and static inverter
interfaces have different impacts on system protection,
for example.
Considering all of these factors can be rather challenging,
particularly due to:

0

1
Normalized Power
Production

Normalized Power
Production

0.5

0

V (pu)

1.05

1

0.95
0
5
10
15
Distance from Substation (km)

0.5

0

1.05

V (pu)

Normalized Power
Production

0.5

1.05

V (pu)

entire systems
✔✔ limited manpower and data with which to perform
detailed analysis of an entire distribution system
✔✔ the reduced visibility in terms of what is happening at the edge of the grid (important for models and
measurements)
✔✔ the wide range of results that can be seen based on the
particular scenarios investigated (location, PV size,
control, and so on).
To work around these challenges, planners have tried to
estimate DERs impacts based on load levels alone or have
simplified the problem by limiting the analysis to only a few
"typical" distribution feeders. For the latter solution, feeders
are chosen using clustering, or the grouping of feeders by
topological characteristics. The downside of this approach
is that it does not take into account the unique distribution
system response as a whole, since each individual feeder dictates how the distribution system responds and changes as
the system evolves over time.
These complex associations are the reason why one
feeder can host more DERs than another. The hosting capacity of a feeder is defined as the amount of DERs a feeder can
support under its existing topology, configuration, and physical response characteristics. When this hosting capacity is
reached, any further additions will result in a deterioration

1

1

Total Power
Production (kw)

✔✔ the sheer number of feeders associated with analyzing

1

0.95
0
5
10
15
Distance from Substation (km)

1

0.95
0
5
10
15
Distance from Substation (km)

3,236

108

0

100

200

300
400
Relative Time (min)

500

600

700

figure 2. Time and location impacts of variable solar PV on voltage control.
march/april 2015

ieee power & energy magazine

23
Table of Contents for the Digital Edition of IEEE Power & Energy Magazine - March/April 2015
