IEEE Power & Energy Magazine - July/August 2016 - 42

Generation
Plants
Interconnections

HV
Transmission
Grid

HV
Substations

HV
Substations
Distribution
Grid

Medium
Consumers

Very Large
Consumers

Large
Consumers

Distributed
Generation

Small
Consumers

figure 1. The traditional power system representation.

the direction of the power flows, anything is possible regarding the sizes and connection points of some of the technologies that comprise the broad category of DeRs. attempting
to establish sharply outlined classifications is a hopeless
task. In this article, any resources connected in the distribution network-another ambiguous term-will be considered
to be DeRs.
The second-and last-key message is that the answer
to the question of the impact of DeRs on transmission networks is obvious: the impact could be anything. In fact, if
the contribution of DeRs to meeting the total demand of a
power system, including exports, can be as large or more than
what the centralized generation plants could contribute, the
flows in the transmission network due to DeRs could be as
large as the customary ones created by the large conventional
generators. alternatively, there could be near -zero flows on
transmission should all demand be met by local generation.
The end of the trickling down paradigm most likely also
means that the physical, organizational, functional, and regulatory differentiation that, until now, has existed between
transmission and distribution has to be reconsidered. figure 2 tries to convey the new perspective. We shall have to
rethink how to define the roles of transmission system operators (Tsos) and distribution system operators (Dsos), the
boundary between distribution and transmission, how to
july/august 2016

allocate the network costs, and how to allow the DeRs to
provide electricity services and participate in markets that
are presently restricted to large actors.
The role of transmission, with its move from a humble
ancillary of generation to a preeminent position as the
meeting point of the wholesale electricity market with
the unbundling and liberalization of the 1990s, is poised
for another major transformation. The always-ambiguous
division between transmission and distribution will become
fuzzier, the roles of the system operators for the two networks will become closer, and the regulation of the distribution network will likely gradually incorporate many of
the features that have been developed during the last two
decades at the bulk power system level: locational marginal
prices (lMPs), management of congestions, ancillary services, advanced cost allocation schemes, or unbundling of
network and commercial activities. The boundary between
transmission and distribution networks may be determined
by the legacy of ownership, but the functional divide will
probably separate the mostly meshed network (typically,
transmission and high-voltage distribution) and the mostly
radial network (medium- and low-distribution voltages).
from a pragmatic standpoint, a large transmission infrastructure will likely continue to be examined one by one by
regulatory authorities, while the innumerable distribution
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Table of Contents for the Digital Edition of IEEE Power & Energy Magazine - July/August 2016
