Civil Engineering Reference
In-Depth Information
The class diagram for an EPN is shown in Fig. 18.5. Both
EPNedge
and
EPNnode
are abstract classes. Edges can be either underground or over-
head lines. Nodes can be generator stations, slack buses, or load stations.
The latter can be either transformation/distribution substations or distribu-
tion substations. The distinction has an infl uence on the function and the
number of buses included in the model.
Examples of the main attributes and methods include, for instance, at the
EPN
level, the
capacityPerCapita
attribute that stores the required power
per person, used by the
computeDemand
method jointly with the popula-
tion in the node tributary cells to estimate the electric power demand. Two
more examples are the
powerFlow
and the
defi neStatCompState
methods.
The former assembles and solves the fl ow equations in the functional model,
while the latter, based on the IM at sites and the components' fragility
curves, samples the damage state for all components (buses, switches, trans-
former, etc.) in the generic substation.
Within an EPN, overhead lines are generally not considered as vulnerable
components (Vanzi, 1996), while underground lines may be modelled as
vulnerable. Components in the substations have point-like fragility models.
Power plants, if considered vulnerable, should be treated as critical facilities
within this model (see Section 18.5.3); however, they can be modelled in a
more simplistic way. In the current implementation, however, no vulnerabil-
ity model is yet available for power plants.
As far as the functional model for the EPN is concerned, a very important
and delicate aspect in the capacitive (fl ow) analysis of an EPN in a seismi-
cally active environment is the determination of the functional portion of
the EPN in the post-earthquake conditions. This does not simply mean what
components are damaged. Indeed, damage to components of a substation
can lead to a short-circuit (SC) that may or may not propagate within the
substation and/or further away from the substation to adjacent others, gen-
erating in extreme cases large-scale black-outs.
Hence, the functional model implemented consists of a sequence of two
models. The analysis of SC propagation, where circuit breakers are active
components playing a key role in arresting the SC spreading, precedes the
power-fl ow analysis to determine voltage and power in all stations as well
as current power and power loss in all transmission lines. The sub-model
for SC propagation (Vanzi, 1996) is the reason why in the presented frame-
work sub-stations are modelled with all their components and internal
(electric) logic, so that SC propagation can be evaluated in each damaged
state. In order to facilitate the modelling work for the analyst, the model
automatically sets up all the components and links within a substation based
on the substation type.
Finally, the set of nonlinear power-fl ow equations is solved for the func-
tional portion of the EPN, which are given by:
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