IEEE Power & Energy Magazine - March/April 2018 - 60

✔ at the continental level, the development of intermit-

figure 5. A modular approach.

Tools to Ensure a Safe System
The new ems enables
✔ monitoring the system and the level of risk
✔ studying and ensuring the security in anticipation
(a tool called iTesla)
✔ submitting orders to the sCaDa system
✔ optimizing the global system
✔ publishing reports
✔ improving cooperation and helping the mobility of operators between control centers but also with coordination center, field workers, and other entities.

Focus on the Uncertainties in the
Short-Term Operations Planning Process
The project aims at orienting the management of the system
toward prediction rather than reaction. in such a framework,
taking uncertainties into account in the decision process is a
key point. Within the power systems field, stochastic optimization is often used for generation dispatch and historically
for the management of hydropower. on the grid management
side, operators implicitly deal with stochastic optimization
concepts to handle the tradeoff between the decrease of
uncertainties as real-time approaches and the increased cost
(or unavailability) of resources. For power grid management,
risk concept is still widely based on n-K contingency analysis using a deterministic grid state forecast.
in europe, several drivers push toward changing the multidecade status quo:
✔ The unbundling of the electric utility created a situation in which Tsos naturally focus on the optimization of their own asset use, i.e., the grid, while the
generation optimization side is handled by the market.
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tent generation and use of electric power markets have
increased cross-border exchanges and their volatility, resulting in dynamics too fast to be faced without forecasting functions (for instance, if the French
export position varies by more than 3 GW within 10 min
of the hour). The easy valuation of additional crossborder capacity through price spreads demonstrates
the advantages of a more sophisticated use of the existing assets.
✔ at the local level, the integration of distributed intermittent generation also triggered a need for a more
sophisticated short-term operation. indeed, as the value
of curtailed generation is much lower than the value of
lost load and intermittent generation rarely produces
at its nominal output, the system will no longer be developed to transmit all the producible power at any one
time. as a result, part of the costs has switched from
capital expenses to operating expenses, thus increasing
the willingness to make the operations more complex
to gain additional transmission capacity with a minimal
amount of investment. This complexity results in a more
active management of the grid (such as phase-shifter
transformer tap settings, substation topology changes,
and special protection schemes) combined with a better
assessment of uncertainties that reduce the operational
margins while controlling risk levels.
This uncertainty framework will need some extensions,
especially to improve the simulations, which we assumed to
be simple load flows.
✔ The simulations may return more complex information than safe/unsafe. For example, they may compute
the amount of unserved load resulting from a contingency. However, operators typically have only discrete
choices in that they may be unable to use information
not aggregated to the simple form of safe (i.e., nothing
to do) versus unsafe (i.e., find a solution to mitigate this
unacceptable risk).
✔ The simulations may need to be in multiple time scales.
rTe's current security analysis process generates one
forecasted grid state per hour up to the end of the next
day, plus one special point for the 19:00 hour (which
corresponds to peak load in France). They are all individually analyzed. increasing the sampling during the
next hours is likely to occur soon, but there is no plan
yet to assess the security over several samples at once.
However, some time-coupling constraints are appearing. some cables can be overloaded up to 4 h, and some
storage can be used to handle congestion conditions for
a few hours. as a result, simulations will need to go
through several samples both to model the actions and
to evaluate the secure system states. The first step will
be to include state variables in the grid states (past time
duration during which the cable has been overloaded,
actual state of charge of the storage, etc.).
march/april 2018

Table of Contents for the Digital Edition of IEEE Power & Energy Magazine - March/April 2018