IEEE Power & Energy Magazine - March/April 2020 - 34

CEPEL, together with the Brazilian utility Eletrobras and its
subsidiaries Companhia Elétrica do Rio São Francisco and
Furnas, has been developing EXB applications.
After the distances between conductors and the support
structure are determined, a mechanical optimization is
used that includes selection of towers and poles. In this
step, the support total weight is minimized, with several
loadings considered, including longitudinal, transversal,
and vertical forces under nominal and contingency modes,
that is, a conductor falling. Indirectly, the foundations are
also optimized.
At the beginning of compact line development, the
design focus was on the transmission of large blocks of
energy over long distances. However, in the following
years, CEPEL, together with the Brazilian utility Eletrobras and its subsidiaries Companhia Elétrica do Rio São
Francisco (CHESF) and Furnas, has been developing EXB
applications for new high-capacity transmission lines and to
uprate the transmission capacity of existing transmission

lines. Additionally, combining compact line designs and the
use of EXB (HSIL/EXB) may provide advantages from the
system viewpoint, including
✔✔ the reduction or avoidance of series compensation, allowing direct economic benefits, such as the absence
of subsynchronous resonance (SSR) problems as well
as the elimination of maintenance and replacement
costs of additional network equipment
✔✔ an increase in voltage support due to its electrical
characteristics, reflected in the increased power-transfer capacity of the transmission line.
For the design of a new transmission line, the optimization of EM parameters can achieve a better field distribution and a higher SIL, resulting in an increased transmission
capacity compared to traditional designs for the same voltage level. For refurbished transmission lines, HSIL technology also provides opportunities for increasing transfer
capabilities that depend on the transmission-line design.
Options may exist for rearranging conductor configurations
or adding one or more conductors per phase, which need
not necessarily be of the same type as the original conductor. The latter approach provides all of the advantages of
HSIL design by increasing transmission capacity, including
thermal limits. In addition, the adjustment of line parameters in the same transmission corridor can improve voltage
levels in strategic buses, eliminate economic dispatch constraints related to SSR, reduce voltage sags, and improve
stability performance.

Field Experience

figure 3. An EXB convertible line of 2 × 230 kV and
500-kV structure. (Source: CEPEL; used with permission.)
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ieee power & energy magazine

CHESF was an early adopter of HSIL technology. The Brazilian company focused on the EXB technique and adopted
it in new and uprated transmission lines, which played an
important role in meeting the utility's needs. The first commercial application of the EXB technique was employed
in the city of Fortaleza in 1995. At that time, the city was
served by three 230-kV lines from the Paulo Afonso hydro
plant, which was 660 km away. The increase in demand in
Fortaleza required a generation upgrade and a new 500-kV
line from the North region of the Brazilian grid, called the
North-Northeast (N-NE) interconnection. This planned line
would have completed a 500-kV ring to improve reliability
of the local system.
Repeated delays in the construction of the N-NE circuit,
coupled with growing demand, led to a critical situation in
Fortaleza. The problem was successfully resolved through
application of EXB, using a "convertible" technique. A
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IEEE Power & Energy Magazine - March/April 2020

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