IEEE Power & Energy Magazine - March/April 2020 - 44

The solutions are part of the corporate strategic objective to be at
the forefront of eco-design, which aims to reduce the company's
global environmental footprint.

44	

This article presents some of the latest innovations that
have been put into operation and are about to be implemented.
The solutions are part of the corporate strategic objective to
be at the forefront of eco-design, which aims to reduce the
company's global environmental footprint. This includes the
consideration of greenhouse-gas emissions, the use of raw
materials, and the impact on biodiversity. Eco-design can be
considered at a grid level that fully utilizes existing assets to
limit the unnecessary development of new infrastructure and
in the design of grid-related equipment.
Increasing the power-flow capability of the existing transmission system must recognize that the system should be
secure at all times under N-1 criteria. Operating near the real
maximum circuit ampacity can be achieved by monitoring
weather conditions and utilizing dynamic line ratings (DLRs)
for overhead lines (OHLs). Underground-cable designs with
embedded optical fibers that sense conductor temperatures can
be used to establish ratings and monitor the line's conditions,
which reduces the number of outages. Another way to increase
the power flow uses adaptive and flexible electronic devices
(SmartModules). The last example in this category presents the
use of battery energy storage at the subtransmission level to
reduce potential local congestion, particularly the excess flows
that result from local renewable generation. The development
and installation of a sulfur hexafluoride (SF6)-free substation
provides a means of decreasing use of one of the worst greenhouse gases in terms of its global warming potential (GWP).

Main Use Cases Identified and First Results

DLRs for OHLs

Delivery of Electricity Generated by Wind Farms

Electrical and mechanical constraints limit the permissible
power flows across OHLs. Historically, operators employed
a static rating based on unfavorable weather conditions to
ensure that conductor temperatures remained within design
specifications. DLRs can be established by monitoring realtime meteorological parameters, such as wind speed, ambient
temperature, and solar radiation. Applying DLR technology
helps to fully utilize the potential of existing OHLs.
Since 2009, different DLR applications have been tested
to determine the potential use of this technology. Several
trial installations were implemented to
✔✔ estimate the benefits offered by DLRs compared to
static ratings for all use cases
✔✔ resolve the main operational issues:
*	deciding when to implement DLRs on an OHL
*	equipping an OHL with a DLR
*	using DLRs in operations
*	determining what maintenance is necessary.

In France, wind turbines are usually built in rural areas,
away from inhabited locations where the electrical grid is
more developed (meshed, with lines that have high static ratings). Thus, the aggregation of the wind turbines may require
the addition of new lines to enable the delivery of all of the
electricity produced. Wind speed is one of the most influential factors for cooling conductors. The times when line currents are very high coincide with periods when wind power
generation is at its peak, meaning that, at the same moment,
wind is blowing on the conductors to help cool them. This
suggests that DLR applications may avoid a major capital
investment in new transmission lines.
Since the beginning of 2018, two OHLs have been monitored as use cases: one at 63 kV and another at 90 kV. Based
on a one-year analysis, the use of dynamic ratings provided
an additional 50% wind-power capacity connection. Indeed,
without DLRs, connecting wind power plants would have
been infeasible due to insufficient transmission capacity.

ieee power & energy magazine	

Ski Resort Supplied by Two OHLs
With Low Static Ratings

During winter, the demand for electricity at ski resorts in the
French Alps increases to the extent that some of the transmission lines operate at or very close to their static limits. One
solution to this problem would be to build a new transmission line. An option to avoid such a significant investment is
to use DLRs and operate the transmission line closer to its
true limit. Indeed, the high load demand in winter correlates
with low ambient temperatures. Moreover, the conductor's
exposure to the wind chill at this time would also increase
the maximum current-carrying capability of the line above
its static rating, which is based on more conservative ambient assumptions.
From 2013 to 2017, one OHL in the French Alps was
equipped with DLR sensors to confirm the theoretical application of this technology. Based on the static-rating value, during periods of low winter temperatures, operators must change
the network topology and feed the substation with a single line
to comply with the N-1 criteria. Since the area is exposed to
power outages from faults on a nearby line, a new underground
line was installed in 2017. Before the new line was commissioned, the use of dynamic ratings enabled the operators to
avoid changing the grid topology, which could have detrimentally impacted reliability for approximately 200 h/year.

march/april 2020



IEEE Power & Energy Magazine - March/April 2020

Table of Contents for the Digital Edition of IEEE Power & Energy Magazine - March/April 2020

Contents
IEEE Power & Energy Magazine - March/April 2020 - Contents
IEEE Power & Energy Magazine - March/April 2020 - Cover2
IEEE Power & Energy Magazine - March/April 2020 - 1
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IEEE Power & Energy Magazine - March/April 2020 - Cover3
IEEE Power & Energy Magazine - March/April 2020 - Cover4
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