Page 40 - Impiantistica Italiana

been developed and ap- transmission capacities may help to select
plied for many hundreds of power from cheaper (including environmen-
km in Italy, Switzerland and tal costs) units located in another region or
Egypt (the figure 8 shows country and to capture the best of renewables
an OHTL arriving at the sources;
Cairo South substation) • both AC and DC technologies are available
in the voltage level range for systems above 1000 kV for OHTL’s (1200
from 145 to 400 kV. This is kV AC in India and 1100 kV DC in China) and
a cheap alternative to tu- up to 600 kV for sea / underground cables.
bular poles by presenting Sea cables have been developed for depths
light bi-dimensional towers exceeding 3000 m. The DC transmission up
and small foundations. to 3500 km in length is under construction in
Among the tubular pole China. FACTS technologies have had great
types, the one in figure 9 improvements in AC systems. There are no
is of interest with the use limits for technologies but the key issue is the
of post type insulators to increasingly strong opposition to building new
minimize the impact on the OHTLs and the very long times to implement
environment and minimum them.
RoW width. • The average time in the EU from the concep-
Some interesting new line tual engineering of a new HV OHTL of some
sections are reported in fi- dozens of kilometers to its commissioning
gure 10. phase, is longer than 10 years and sometimes
Also in this area there are becomes infinite, when it is impossible to arrive
no limits to imagination for at the final completion. The Spain – France in-
improvements but not only terconnection, now in operation, has taken 25
Capex costs should be years to complete, the Matera – Santa Sofia in
carefully analyzed, but also Italy has required 18 years, while in China less
Fig. 7 - Varieties of AC lines O&M costs which are becoming critical in some of than 4 years were needed from initial thinking
to increase transfer capacity the above mentioned solutions. For all the above to commissio-
with lower impact on the en- towers/lines, insulator assemblies and types of in- ning of a 2000
vironment [5] sulators play a fundamental role. km long ± 800
kV UHVDC
2.3 Dynamic loading of OHTL’s line carrying
7000 MW.
The possible increase of power transfer on an Interconnectors
OHTL in specific and not rare favorable atmosphe- are also a mean to
ric conditions (low temperatures, or no sun or pre- fostering a higher
sence of rain or wind to dissipate the heat), with penetration of RES
the aid of line monitoring of conductor current/tem- with consequent
perature/ambient conditions allows larger transfer reduction of GHG
capacity in the great majority of hours with respect (Greenhouse Gas Fig. 8 - A cheap alternative for
to a deterministic limit of maximum current valid in Emissions). Sub- compact lines as applied in Cairo
extreme / very rare conditions. Adequate sensors Sahara Africa has suburbs (Egypt)
and communication facilities, already well develo-
ped, are involved.

2.4 Interconnections between
countries and transmission
of bulk powers from remote /
economic sources

The interconnection benefits are political, technical,
economic and environmental:
• the development of interconnections capacity
between countries (or regions) allows greater
electrical system reliability and flexibility in the
generation mix and operations, improving se- Fig. 9 - Tubular pole line with two conductors per phase,
curity of energy supply; no ground wires and arrester to protect from lightning faults
• the availability of cross-border/cross region on the top phase

38 Impiantistica Italiana - Marzo-Aprile 2018