IEEE Power & Energy Magazine - March/April 2020 - 37

also featured midspan bundle expansions: near the tower,
the bundles are smaller, with a special spacer used to enlarge
the bundle size midspan. This gives an "average bundle"
performance without enlarging the structures. Figure 5 shows
the test setup for this line.
The development of new geometries cannot be limited to
a theoretical model. Following the R&D cycle, laboratory
tests are conducted using tower mockups and normalized
voltage sources under controlled conditions. Since its conception, CEPEL has provided a full range of laboratories.
The newest addition of an ultrahigh voltage (UHV) laboratory (Figure 6) can perform tests up to 1,100 kV ac and
800 kV for dc lines.

Dynamic Line-Rating Techniques
The HSIL concept is well suited for application in the case
of long lines. Shorter lines will have power transfer limited
by the conductors' thermal rating, which demands a different approach.
Increased transmission capacity can generally be achieved
using dynamic line-rating (DLR) techniques, which is now
a mature technology that uses current/temperature sensors
(Figure 7) and real-time monitoring to establish the true
transmission-line limit. However, this solution should be
used with caution because of of differences along the line in
atmospheric conditions, span lengths, and vegetation growth,
all of which have a direct influence on conductor temperature, which can vary widely along the line. A transmission
line may be limited by a single critical span or by a few spans
that require the adoption of special measures.
Since conductor temperature may affect line integrity
and also, more importantly, endanger safety due to potential
fires, DLR uprating must be used very carefully. Transmission-line static line ratings are normally established with
conservative assumptions due to these safety considerations.
Cases in which less conservative assumptions are used can
result in DLRs being lower than the static ratings some of
the time.
There are some special conditions under which the application of DLR is both safe and efficient. A real-life example
is presented in which the combined application of modeling tools and real-time monitoring allowed for an increased
transmission-line capacity in the connection of wind-power
generation plants to Brazil's national grid.
A huge potential for wind-power generation was identified
in the Northeast region of Brazil, and several wind plants are
being developed in the region. Expanding the transmission
system to collect this energy production and connect it to the
national network has been a challenge. Transmission lines
of 69, 138, 230, and 500 kV are being designed and built to
allow for proper flow of the energy generated in these wind
farms to load centers.
Due to problems associated with the legal schedules for
environmental licensing and acquisition of land-use rights,
including indemnities, the construction and operation of
march/april 2020	

(a)

(b)

figure 7. Examples of the sensors used for real-time monitoring (a) before installation and (b) on the line. (Source:
CEPEL/CHESF; used with permission.)

important connection lines to these generation plants were
being delayed, while, at the same time, more wind plants
were being installed. This posed two important problems.
First, without new transmission lines, the potential output
of power produced by the wind farms would be wasted at
a time when hydraulic generation was constrained due to
reduced reservoir levels and low inflows. Second, the contracts ensured that generators would be paid as soon as the
generation equipment was available, even if the transmission grid could not accommodate their production.
In the case presented here, a wind farm was installed
on the coast near Natal, and the scheduled transmission
ieee power & energy magazine 	

37



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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