IEEE Power & Energy Magazine - March/April 2020 - 50

Battery Energy Storage as a Grid Component
Plans call for installing three energy-storage systems with
large batteries. The size of each battery system will be 12 MW
(the power rating) and 24 MWh (the energy rating). The batteries will be connected to the 63-kV grid in two locations
and to the 90-kV grid in one location. All three projects
are expected to be in operation by the end of 2020. They
were designed for two main applications. First, they can
act quickly (0-12 MW in 1 s) and be used for fast remedial
actions. After a fault or an outage, if there is an overload on
a line, the battery will start charging (because it is upstream
of the overload), and the overload will be removed rapidly.
The second application is more energy oriented. Under conditions when renewable-energy generation is very high (possibly resulting in congestion), the battery will store energy.
The stored energy will be discharged when the renewable
generation declines and there is no congestion in the local
sub-transmission system.

Simulations for Optimized Localization
Large studies were conducted to find the optimal location on
the grid for the three batteries. Beginning with 15 potential
sites, two years of archived hourly grid data were modified
for 2021 conditions and generation profiles. Grid simulations were conducted, and the optimal use of the batteries
for congestion management was determined. The total quantity of renewable-generation curtailment was calculated to
provide an indication of the batteries' impact at the possible
locations. In conjunction with technical feasibility studies
that were conducted in parallel, locations in the Southern
Alps, West Atlantic Coast, and Northeast regions of France
were chosen.

Need for Battery and
Generation Curtailment Coordination
Since the lines are expected to be severely congested in
the three locations that were selected, the batteries, despite
their scale, may not have the capacity to fully relieve the
strain. As such, some degree of renewable-generation curtailment is expected. To properly manage and coordinate
the batteries and curtailment, a new controller is being
developed to perform autonomous congestion management
in these subtransmission areas; its three levels are presented next.

Higher Level: Centralized Slow Controls
In the considered areas, congestion results from large volumes of generation. To compensate for the overloads, the
batteries would need to charge to absorb some of the generation. Centralized slow controls (CSCs) will run in the
control rooms every 5 min to operate each battery. Based
on deterministic forecasts, the CSCs will compute the reference trajectory to ensure that the battery is fully discharged
when congestion occurs and ready to manage the excess by
charging. Using grid simulations, the CSCs will also com50

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pute capacity bandwidths for each battery, which will forecast security domains (in power and energy). Operating the
batteries within those bandwidths ensures that they will be
able to optimally manage congestion without creating any
new excess.

Real-Time Controller: Area Slow Controls
In each zone, an area slow control real-time controller
will be deployed based on distributed implementation.
This c- losed-loop control receives measurements of the grid
flows every second. Every 5 s it computes actions to be sent
automatically to controlled devices: battery installations to
charge or discharge, renewable-generation curtailment for
each substation in the managed area, switch opening for
node splitting, and, in some cases, line opening. The mathematical framework uses model predictive control with
embedded dc linear modeling and optimization.

Last Resort: Substation Fast Controls
According to the optimize-control-protect operating scheme,
fast and purely local controls ensure last-resort protection of
equipment and people.

Changing Framework
When no congestion is foreseen in these zones, stakeholders in the energy sector could make the batteries available
for other uses. The concept of battery-capacity bandwidths
identifies good candidates for installations that can provide
multiple services.
Researchers predict that, in the near future, line overloads will not be based on current ratings (that is, the maximum value for amperage) but use maximum values for the
temperature and sag, whatever the amperage value. This will
be possible through real-time sag and temperature measurements and substation fast controls that open lines on the
basis of the measurements. This method differs from the
DLR performance described previously since it does not rely
on current measurements and limitations.

SF6-Free Substation: Next-Generation
Initiative
A Long-Standing Practice Reaches Its Limits
SF6 has been widely used in the electric-power industry for
40 years as the best and least expensive material for gasinsulated substations (GISs) and circuit breakers. However,
SF6 is now recognized for its poor GWP performance when
leaks occur in aging components. The Kyoto protocol listed
it among the six most harmful greenhouse gases. According
to the Greenhouse-Gas Protocol GWP table values (based
on the 2014 Intergovernmental Panel on Climate Change's
fifth assessment report), SF6 has the strongest GWP computed for a 100-year normalized reference period. SF6 is
equivalent to 23,500 kg of carbon dioxide (CO 2) and has a
lifetime of approximately 3,200 years due to its exceptional
march/april 2020

IEEE Power & Energy Magazine - March/April 2020

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