IEEE Power & Energy Magazine - January/February 2016 - 51

simple question: across all these cases, why would a given
component ever be represented in a different way? in current
practice, where different models are maintained by different
parties, this is commonplace. the result, however, is more
engineering labor, greater difficulty in validating data, and
difficulty in comparing results generated by different parties.
this observation leads to two more key requirements:
3) in designing model parts, the aspects of models that
should be invariant over all the cases should be separated from those that change.
* these invariant aspects correspond to the characteristics that are inherent in the system "as constructed"
and don't change except in the case of new construction events.
* the remaining variant aspects make up the hypothesis every study has about the particular operating
condition for the grid being studied.
4) component identification must be consistent across
all studies, forming a reliable basis for comparing the
content of analytical results and tracing all data back
to original sources.
the largest number of network cases study the present
state of the grid. Many operating studies, though, look at
future conditions ranging from an hour ahead out to a year
ahead; in planning contexts, studies may project as much as
ten years into the future. studies of past conditions are also
sometimes required. these differing time frames give us an
fifth key requirement:
5) Model parts must be able to represent the changes in
the network over time.
different parts of the grid are owned by or the responsibility of different parties, and these parties are usually the
logical source for data about their area of responsibility.
there is no party that could logically be assigned responsibility for all of the grid. hence, a sixth requirement:
6) the design of model parts must allow partitioning of
like data according to the data's logical model authority.
the most common divisions are regional (by ownership
or operating responsibility) and electrical (as in transmission versus subtransmission versus distribution).
different studies cover different parts of the grid. No
study ever analyzes the entire grid in detail: each one has a
focus and models that part in depth, while simplifying its
view of the rest of the grid. to take two extremes of this as
examples: a bulk power analysis might represent all highvoltage lines and large generating plants but simplify all
subtransmission and distribution to net substation "load"-
while, at the other end of the voltage scale, a distribution
feeder analysis might represent every customer transformer,
but simplify the transmission to a single power source.
all studies begin by selecting the parts of the network that
must be represented and selecting the time frame being represented. others aspects of studies may be very specialized,
such as setting up a generation pattern based on outcomes
of a specific market. in all cases, though, the ciM goal is to
january/february 2016

enable automation that reduces the need for manual babysitting of the process. this implies a seventh requirement:
7) the design of model parts must enable the creation of
appropriate automated procedures for each different
network analysis business process.
Finally, no significant revision of network modeling practice could possibly be accomplished all at once. any practical plan for change will have to involve an evolution from
current state, which leads to a final requirement:
8) the future vision for network model management
design must also support present practice and any
intermediate stages required for migration to that
future vision.
in sum, the ciM pursues a revolutionary vision: a framework of nonoverlapping plug-together model parts representing the grid and its operating characteristics through
all voltages levels, across all participants, and over all time
frames while also serving all analytical requirements.

The CIM Building Block
Network Data Architecture
this section provides highlights of the ciM approach to network model management. (a basic overview is all that space
allows here; for more information, see the suggestions in the
"For Further reading" section.)

Model Part Basics
a ciM model part is a set of ciM data objects with these
minimum characteristics:
✔ the model part objects are governed by a subset of
the ciM information model for power systems operations. (the specific information model subset defines
the model part's "type.")
✔ together, the model part object instances satisfy some
holistic purpose, such as describing "the equipment
that makes up the bulk power grid of belgium" or "the
schematic diagram of objects for the anytown airport
substation."
✔ the model part data come from one source, such as
"the belgian transmission system operator (tso)" or
"anytown energy."
this core definition of the model part is loose enough so
that, as per our eighth requirement, today's network analysis
processes-which are primarily based on exchange of complete
power flow cases-can be expressed as exchange of model
parts. the ciM building block vision, however, is based on two
other important and innovative aspects of ciM model parts:
✔ a model part may contain objects that define associations to objects in other model parts. these "dangling
references" are the essential mechanism for defining
how the model part will connect with other model parts.
✔ a model part may also have an association to a model
framework that defines the role of the model part-
e.g., "my role is to cover the belgian territory" or "my
role is to cover my town's distribution network."
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Table of Contents for the Digital Edition of IEEE Power & Energy Magazine - January/February 2016