The interconnection between Spain and Morocco,
across the Straight of Gibralter, represents an
outstanding example of cooperation between neighboring
countries. The first electrical connection between
the two countries — a 400-kV submarine cable link
28 km (17.5 miles) long laid at a depth of 615
m (2000 ft) — was commissioned in 1997. Commercial
operation of the interconnector began in May 1998,
supplying energy market agents on the basis of
bilateral short-term energy contracts.
Since 1998, however, significant regulatory changes
have occurred on both sides of the link. The European
Union (EU) has deployed policies to strengthen
cross-border transmission lines and to further
develop the European electricity markets. In Spain,
structural changes have been introduced and an
electricity market has been in place for several
years now. During the past three years, agents,
operators and regulators have taken steps to launch
the Iberian Electric Markets.
The Maghribian network, comprising Morocco, Algeria
and Tunisia, is now being reinforced. This is
part of an expansion plan conceived within a more
ambitious Mediterranean Electricity Ring (MedRing)
project. MedRing will interconnect the electrical
networks of all Mediterranean countries: France,
Spain, Morocco, Algeria, Turkey, Greece, Italy,
Libya, Egypt and Jordan. With this new plan in
place, the role of the submarine link between
Spain and Morocco becomes an outstanding issue
in terms of ensuring high-quality and secure grid
connections.
The direction of power flow through the submarine
cable has been substantially from Spain to Morocco
since the line was commissioned (Table 1). However,
the network stability and security contribution
of the times of energy flow from Morocco to Spain
has been of great value. These transfers have
removed network constraints on the Spanish grid
in the area of close proximity to the Mediterranean.
The maximum transmission capacity through the
interconnector is reduced from 700 MW to 400 MW,
taking into consideration the neighboring network
configuration and operational restrictions. This
is known as the commercial rating of the link.
This limit is reached several hours daily at times
of system peak demand; hence, an increased rating
would be valuable because there would be more
opportunity for larger energy exchanges.
To increase the benefits available from this
interconnection, the two system operators and
owners, Red Eléctrica de España (REE; Spain) and
Office National De L'Electricité, (ONE; Morocco),
launched a project in 2001 to reinforce the existing
link. This resulted in the design and installation
of a second 400-kV ac submarine-cable link to
operate in parallel with the existing circuit.
This cable circuit provides the additional exchange
capacity required and makes a significant contribution
to system security and operational performance
improvements. These two key objectives are vitally
important when considered within the framework
of the MedRing project, because the link between
Spain and Morocco is the only Western transmission
system interconnection between the northern and
southern Mediterranean systems.
LAUNCHING THE PROJECT
REE and ONE jointly conducted research that
defined and specified the reinforcement project.
Their work revealed that the existing substations
and transition stations located near the coasts
had to be extended and a new submarine cable route
on the rough sea bottom of the Straight of Gibraltar
was needed. A new cable route corridor some 2
km (1.25 miles) wide westward of the existing
circuit was studied and surveyed in 2002 (Fig.
2). These specialized survey vessels were equipped
to identify the and seabed features with the aim
of finding cable routes that would offer maximum
stability, use sandy seabeds, optimize the significant
number of cable crossings and minimize cable lengths.
The new cable routes proved to be longer than
those used for the first cable link, but they
satisfied most of the search objectives and solved
the difficult task of the rocky Moroccan inshore
approach. The total length of the new interconnector
is 31 km (19.3 miles), including land sections
at both ends, with 2 km (1.2 miles) in Spain and
0.25 km (0.16 miles) in Morocco. The maximum depth
at which the submarine cable is laid is some 629
m (2064 ft), the sea depth in the middle of the
straight.
With the experience gained from the first interconnector
and the existing infrastructure available in each
utility, the project was limited to the land and
submarine cable sections, as the two utilities
were able to manage the extension and adaptation
of existing network facilities. An international
invitation for tenders was launched in 2002 to
attract the best and most experienced cable suppliers
and contractors. Following assessment and evaluation
of the bids received, a consortium comprising
Prysmian Cables & Systems (Italy) and Nexans (France)
were awarded the turnkey contract to design and
install the second 400-kV ac circuit of the Spain-Morocco
submarine electrical interconnection, with the
value of this contract being 115 million euros
(US$157 million).
A common-objective team, incorporating suppliers'
and clients' project managers, formed in the execution
phase during the second quarter of 2004, brought
together the experience and enthusiasm to push
forward this challenging project. The new circuit
was commissioned in June 2006. After the new line
successfully passed all contractual commissioning
tests, the second interconnector was energized.
DESIGN AND CONSTRUCTION
Multinational projects require additional coordination
because they are split by various disciplines
that are being carried out in different countries
by specialized engineering teams. A detailed project
plan outlined at the beginning of this project
served as a common guideline for all the engineers
and specialists who contributed to the success
of this project.
An initial detailed engineering phase allowed
the confirmation of the pre-engineering performed
by each utility and allowed the start of manufacturing
activities that have a relatively long lead time
for this type of project. Extra-high-voltage and
fiber-optic cable (submarine and land) installation
procedures, control and protection systems — including
a temperature-monitoring system with distributed
temperature sensing and oil-feeding systems —
were designed and cross-checked before manufacturing
actually began. Special efforts were made to maximize
the interoperability of both links using modern
electronic control systems, as they share one
spare power cable. Changes to the original control
system were necessary to achieve this objective.
The interconnector is designed to transmit 700
MW with a thermal overload capability to allow
a 900-MW load for 20 minutes. The general features
of this double-circuit link are listed in Table
2.
Inshore and offshore operations are of great
sensitivity in this type of project, as they involve
specialized cable-laying vessels, equipment and
personnel for a relatively short period of time.
Two specialized power cable-laying vessels, Skagerrak
(Nexans) and Giulio Verne (Prysmian), were used
to lay the submarine cables in two separate laying
campaigns in November 2005 and February 2006,
respectively. As winter is not the best period
of the year for offshore operations in the Straight
of Gibraltar, the two campaigns had to cope with
high winds and strong currents, increasing the
challenge of these outstanding tasks.
The required support for the marine activities,
landing operations and cable protection and burial
were secured with the presence of very experienced
marine contractors such as Impresub D&MC (Italy),
Asso Divers (Greece) and Mika (Norway). Figure
1 shows the Skagerrak cable-laying vessel and
the onshore cable installation at Tarifa (Spain),
and Fig. 3 shows the cable-laying vessel Giulio
Verne used to install the first cable. The seabed
cable protection is undertaken by jetting (Fig.
4) and the use of cast-iron shells (Fig. 5).
Onshore, the extension of the transition terminal
stations at Tarifa (Spain) and Fardioua (Morocco)
and the land sections of the cable link had to
be completed before the submarine cables were
installed, because the oil-feeding-system continuity
was required on a 24-hour basis. The completion
of this task was ensured by the contributions
of contractors Nexans, Elecnor (Spain), Cegelec
(Morocco) and Arco Beton (Morocco). The overall
coordination of skilled workers within the two
locations in the south of Spain and north of Morocco,
geographically close but at the same time distant
from each other, was one of the keys to the success
of this project.
ENVIRONMENT AND CORPORATE RESPONSIBILITY
Life-cycle assessment of new electrical infrastructures
and social acceptance of project stakeholders
are increasingly important topics for utilities
worldwide. The Straight of Gibraltar is a site
of great environmental value, representing the
link of two continents, two cultures and one project.
It is now one of the world's major bird-watching
locations, because it serves as the main migration
corridor between Europe and Africa. EU directives
such as “Sites of Community Interest within Natura
2000 Network” protect some special areas of the
straight. Within their respective countries, the
two utilities have undertaken a large number of
actions to promote community participation in
the preparation, discussion and final approval
of environmental impact assessment reports.
Ramón Granadino earned his degree in industrial
engineering in 1990 at the Polytechnic University
of Madrid, Spain, and his M.Sc.ECE degree in 1993
from the University of Massachusetts at Amherst
(U.S.). He has worked at Red Eléctrica de España
since 1994, managing projects for the development
of the 220- and 400-kV Spanish networks. rgranadino@ree.es
Fatima Mansouri graduated in electricity
and electrotechnical engineering at the National
Higher School for Electricity and Mechanics (Casablanca,
Morocco). Working with Office National De L'Electricité
since 1992, she has been involved in managing
projects for the development of the 60-, 225-
and 400-kV Moroccan transmission networks. mansouri@one.org.ma
Table 1. Energy exchanges through the interconnection.
Period 2000-2003 2004 2005
Spain to Morocco (MWh) 6,639,295 1,567,641 898,367
Morocco to Spain (MWh) 59,153 21,190 110,405
Table 2. General features of the 400-kV ac interconnector.
Rated voltage (ac/dc) 400/450 kV
Maximum transmission capacity (ac) 2 × 700 MW
Maximum overload capacity 2 × 900 MW (for 20 minutes)
Maximum sea depth 620 m (2016 ft)
Number of submarine power cables 7 (6 +1 spare)
Number of submarine fiber-optic cables 4
Submarine route length 26 km (16 miles) 29 km
(18 miles)
Land section length
Spanish side
Moroccan side 2.1 km (1.3 miles) 0.25 km (0.16
miles)
