During the last decade of the 20th century we have witnessed unprecedented changes to the electricity industry on a global basis. Deregulation of the industry and the creation of energy markets have promoted the expansion of large interconnected electricity highways, which are no longer constrained by national and political boundaries. The combination of computer modeling and innovative technology has enabled utilities to optimize their generation and transmission assets. In addition, they are able to manage infrastructure investment more efficiently by participating in international energy-trading agreements.

This article presents reports on five major transmission projects around the world that are either in the planning stages or that currently are in progress. Each project demonstrates the application of innovative technologies that the industry continues use to satisfy demands for a more abundant and less expensive supply of electrical energy. The challenge for the 21st century is to secure a reliable and inexpensive source of electrical energy for the world's population achieved without undue adverse effect on the environment.

Italy-Greece 400-kV HVDC Interconnector The interconnection of the 380-kV ac transmission systems in Italy and Greece was initiated in 1989 with a feasibility study conducted by the two utility partners in the project, ENEL S.p.A. (Italy) and the Public Power Corporation of Greece. A 500-MW HVDC interconnector crossing the Channel of Otranto was proposed, a decision supported by the positive service experience acquired by the previously commissioned Sardinia-Corsica-Italy link, a project that incorporated many new technical features.

A 400-kV monopolar system with sea current return was selected, as this requires a lower level of initial investment compared to other systems but allows for an upgrade in transfer capacity by installing a second pole (for example, conversion to a bipolar scheme in the future).

System Details The route of this interconnector, which comprises a 43.5-km (27-mile) underground cable section on the Italian mainland, a 163-km (101-mile) submarine cable section across the Otranto Channel and an 110-km (68-mile) transmission line section in Greece. Briefly, the configuration of the interconnector is as follows: 1. HVAC/HVDC converter stations located at Galatina in southeast Italy and at Arachthos in northwest Greece. 2. A +/-400-kV dc cable system comprising: n Self-contained fluid-filled cable that runs from Galatina to the land-sea transition joint at the Otranto route n Submarine mass-impregnated cable crossing the Otranto Channel and Corfu Strait n Short section [500 m (1640 ft)] of mass-impregnated cable from the land-sea transition joint to the underground/overhead station at Aetos. 3. A HVDC transmission line between Aetos and Arachthos. 4. Sea electrodes and related cables and accessories; the cathode-installed near the Italian coast and the anode installed in Greece.

Cable Specifications Land Sections-A fluid-filled cable was selected for the Italian section to address the higher operating temperatures.

Initially, the scheme was planned on the basis on an overhead line section between Galatina and Port Badisco, but for environmental reasons, this section had to be placed underground and the landing point in Italy was moved to Otranto.

Submarine Cable Special consideration had to be given to the design of the armour as the cable will be laid at a depth of 1000m (3280 ft)-the deepest in the world.

The main features of the high-tensile steel-armour design include: n Torque balanced to avoid cable rotation under tension n Compactness of design to minimize cable weight and size n Long lay pitch to reduce cable elongation under tension. To incorporate these characteristics, a double-counter helical armour of high-tensile galvanized steel flat wires [3 mm by 10 mm (0.024 in by 0.393 in)] were developed.

Project Contracts and Timetable As a first stage of the contract, prior to production, Pirelli, according to ENEL's technical specification, had to submit prototypes of actual cables and accessories for a rigorous qualification program.

This focussed specifically on two aspects of this HVDC project on which previous service experience was limited, namely the extreme water depth and the number of polarity reversals during the lifetime of the interconnector. Pirelli conducted the test program in conjunction with Centro Elettrotechnico Sperimentale Italiano in Milan, according to the CIGRE recommendations. In addition, a full-scale sea trial was performed with the cable ship "Giulio Verne" to demonstrate the ability to laythe cable at the maximum water depth of 1000 m (3280 ft).

In 1998, ENEL awarded turnkey contracts to ABB for the Galatina and Arachthos converter stations and to Pirelli for the land and submarine cable sections in 1998. Pirelli started installing the land cable from Galatina to Otranto in September 1998 using mechanized laying techniques designed to minimize environmental disturbance. This equipment installs a base backfill, followed by the cable and a covering backfill. The 163-km (101-mile) submarine cable is being manufactured in two lengths, Pirelli's cable laying vessel the "Giulio Verne" will start laying the first section in January 2000 and the second section in June 2000. These dates are in accordance with the project's schedule that specifies commissioning by the end of the year 2000.

This is the first energy project in the European Union's program to develop the Trans-European power networks.

Croatia-Hungary 380-kV Interconnection Line The construction of a 380-kV transmission line between Hungary and the Zagreb area of Croatia was considered in the late 1980s to facilitate power transfer from the former USSR to Italy. At that time, this power exchange had to consider the interconnection of two large unsynchronous systems. Hungary and the USSR formed part of the East European Interconnected Power Systems of CMEA, and the former Yugoslavia and Italy were connected to the former UCPTE, now UCTE (West European Union for Coordination of Transmission of Electricity.

Since then, we have seen political changes in the former USSR and the former Yugoslavia, and a decision was made to interconnect Hungary and the three other CENTREL countries (Slovakia, Czech Republic and Poland) to the UCTE before the end of the century. These events have not removed the need for a 380-kV interconnection between Hungary and Croatia, but it now has a different and strategically important role for the power utilities involved.

Hungary-Croatia-Slovenia Interconnection Croatia is now an independent state, and the utility, Hrvatska Elektropriveda (HEP), has two local 120/110-kV lines that are joined to the Hungarian system, which is operated by Magyar Villamos Muvek Rt (MVM). The S"jt"r-Nedeljanec line in the Zagreb area was built in 1958, and the Siklos-D. Miholjac circuit in the Osijek area was constructed in 1995. These circuits have insufficient capacity to enable Croatia to participate in the UCTE/CENTREL electricity-trading market.

The agreed route for the new 380-kV double-circuit line is from Heviz, Hungary, to the triangle of the Hungary-Croatia-Slovenia border, then proceeding as a 380-kV single-circuit line to Zerjavinec (Zagreb East) in Croatia. The other circuit is planned to proceed to the Elektro-Slovenia's (ELES) Substation in Slovenia, but, at present, the route of this second circuit of the interconnection is still under consideration by ELES.

This 380-kV interconnection, therefore, offers the partner utilities the following benefits: n Allows MVM to have existing ties to the northern and western sector of UCTE/CENTREL, this interconnection gives a new link to the southern sector. n Secures the supplies to the Zagreb area, which has almost half the total consumption of the Croatian network and secures the Croatian network, providing a beneficial parallel connection between the east and west. n Optimizes the use of the existing generation capacity in Hungary, which is almost exclusively thermal, and Croatia with 50/50-hydro/thermal generation. n Offers a similar opportunity to the utilities in Bosnia and Herzegovina.

Load Transfer Capacities Feasibility studies for this "H-HR-SI" interconnected system have confirmed that the new line increases short-circuit current at the busbars of the terminal substations, but they remain below the 30-kA permissible level. It also impacts the dynamic conditions of the two nuclear plants and a thermal power plant in the region. Studies confirm that the Hungary-Croatia-Slovenia line connection improves stability conditions at these power plants.

The full potential of the interconnection, in terms of load exchanges and transits, also has been studied to confirm the following scenarios: n Export of 300 MW from Hungary to Slovenia n Export of 600 MW from Ukraine to Italy (injection in Mukacevo/Ukraine) n Export of 1200 MW from Ukraine (injection in Mukacevo) n 300 MW for Croatia, 300 MW for Slovenia, 600 MW for Italy.

The Project The 380-kV double-circuit transmission line has a route length of 70 km (44 miles) from Heviz to the triple-border point. A double-circuit lines 161 km (100 miles) long is constructed from the border to Zerjavinec in Croatia, the route for the Slovenian section remains undecided. ACSR Conductors will be used throughout the project, 3 x [2 x 500/65 mm2 (2 x 0.78/ 0.10 in2 )] on the Hungarian side and, 3 x [2 x 490/65 mm2 (2 x 0.75/0.10 in2)] for the circuits in Croatia (and Slovenia in future), enabling a power loading of 2000 MW. Optical fibres are incorporated in the 120/70 mm2 (0.19/0.11 in2) ground wire.

Project Timetable and Construction The first stage of negotiations between HEP and MVM required reviving the plan to construct the 380-kV interconnection. This stage began under the new political conditions in 1993. The construction agreement was signed in 1996, with a scheduled operational date of summer/autumn 1999.

Each utility was responsible for the contracts for their own section of the interconnection, and MVM started construction using mainly Hungarian components in 1997. Site work commenced on the Croatian section in May 1998. The turnkey contractor for the Croatian section was Dalekovod (Zagreb). The components being sourced internationally include steel towers (Mitas-Turkey), conductors (Elka-Zagreb), OPGW (Alcatel) and isolators (Fidenza-Italy). Site construction on the Croatian contract continued for 12 months, completing the border to Tumbri Substation 129-km (80-mile) section at a rate of 11 km (97 miles) per month.

The 380-kV interconnection between Hungary and Croatia was energized on Nov. 12, 1999, and commissioned formally by Croatia's Prime Minister Zlatko Matesa and Hungary's Prime Minister Viktor Orban on Nov. 18, 1999. HEP General Director Damir Begovic said, "The transmission line will mean a quality connection between Croatia and Hungary with Western Europe, making Croatia a transit country in the European electricity market solving the energy transit bottleneck problem."

Initially, the interconnection will be used as a single-circuit link to Croatia, terminating at Tumbri 380/110-kV Substation (Zagreb-South) due to the delay in the completion of Zerjavinec Substation (Zagreb-East). The second circuit on the new 380-kV line in Croatia will operate temporarily at 220 kV.

Future Benefits This 380-kV Hungary-Croatia transmission line has a long history and, in spite of all the changes to the original objectives, the strategic importance of this link has remained. Additionally, the value of this interconnection has been increased by industry deregulation and creation of electricity trading that has transpired since the project was discussed in 1993. This reinforcement of the interconnected European network provides a new longitudinal transfer route providing an urgently required north-to-south transmission corridor whose value was proven by the load flows that followed the circuit commissioning. This fact, in addition to being the first new line between CENTREL and UCTE, ranks this interconnection on the highest level of European reinforcements in 1999.

Namibia-South Africa 400-kV Interconnector In 1995, NamPower, the National Utility of Namibia, commissioned a System Expansion Study to determine the future electricity demand in Namibia and the potential sources of supply. The study confirmed the need to strengthen the transmission system with a new 400-kV interconnection to South Africa. At present, the NamPower transmission system comprises a 330-kV transmission line, that measures 500 km (311 miles), interconnecting its Ruacana Hydro Power Station, 240-MW capacity (3-MW by 80-MW units) on the border with Angola, to the capital city and main load centre Windhoek. A 220-kV double-circuit transmission line, 840 km (520 miles) with six intermediate 220-kV substations, links Windhoek to the National Utility of South Africa's (Eskom) 220-kV system at Aggeneis.

The construction agreement for the new 400-kV interconnection between the two countries was signed by NamPower and Eskom in September 1996. This circuit will supply NamPower with 380 MW in 2000, increasing to 585 MW by 2015.

International Interconnection Project The 400-kV International Interconnection Project consists of the construction of a 900-km (560-mile) 400-kV single-circuit transmission line and two new 400/220-kV substations. The transmission line is a compact design with an inverted delta phase configuration resulting in an economical design with high surge impedance loading. The line will be strung with quad "TERN" ACSR 431.6 mm2 (0.67 in2) conductors giving the circuit a thermal capacity of 1685 MVA at 70 degrees C (158 degrees F). A 24-core fiber-optic ground wire is installed for remote monitoring and control while the additional fibers suitable for high-speed quality data communication can be utilized by Telecom Namibia or other users.

Construction of the 400-kV transmission line commenced in mid-March 1998, and the first section comprising 420 km (261 miles) from Aries Substation to Kokerboom Substation was successfully energized on May 31, 1999. The second section of 470 km (292 miles) from Kokerboom to Auas Substation currently is under construction, with completion scheduled for February 2000.

The 400-kV substations at Kokerboom and Auas will include the installation of 630-MVA capacity, 400/220-kV transformers, several 400-kV, 100-MVAr line-compensation reactors and other associated high-voltage equipment. Construction work on the extension to Aries Substation and the new Kokerboom Substation is complete, and civil construction work is in progress at Auas Substation.

The transmission-line contractor is a consortium of ABB and Cegelec (Alstom). ABB Powertech (South Africa) is the contractor for the 400/220-kV transformers and shunt reactors. The total cost of this International Intercon- nection Project is US$146 million, a figure that includes the contract value of the transmission line (US$60 million).

System Operational Characteristics During the system studies, it became evident that the NamPower system parameters, together with the new 400-kV line, were such that a resonance condition is prevalent close to the fundamental 50 Hz, in the event Ruacana has one generator in operation or being off-load. This resonance condition will produce severe power frequency overvoltages and, subsequently, result in damage to equipment.

The project, therefore, includes a sophisticated resonance control device in the form of a fast-reacting static var compensator (SVC). This equipment, supplied by ABB Power Systems, Sweden, will be installed at Auas Substation before the next section of the transmission line can be energized. The application of this SVC is unique in that the controller must be robust and fast in operation, being capable of changing the system impedance whenever the resonance condition occurs. The nominal rating of the SVC is 80-MVAr capacitive to 250-MVAr inductive at 1-pu (400-kV) system voltage.

The SVC consists of four 110-MVAr thyristor-controlled reactors (TCR) and two double-tuned 40-MVAr filter-capacitor banks. One TCR is an energized standby unit. The compensator is connected to the 400-kV grid via a bank of three single-phase power transformers. A fourth unit is installed as a strategic spare.

Detailed simulation studies have shown that the low system eigen frequency, characteristic of the NamPower system (due to the long line and low system short-circuit level), can be controlled by using power electronic devices.

Baltic Sea Cable Replacement Project-Technology for the New Millennium The Aland archipelago is a group of Finnish Islands in the Baltic Sea, situated between Sweden and Finland, currently supplied from Sweden via three single-phase 185 mm2 (0.30 in2) copper-cored 77-kV cables, which were laid on the seabed 25 years ago. The transmission capacity of these cables is 35 MW, and ?land has experienced both power shortages and cables damaged by pack ice movement and ship's anchors. Also, power losses due to the high loads are rather high. Following feasibility studies in 1995, the local power company, Kraftn,t ?land Ab (K?) considered the construction of a new power plant to supply the increasing demand, but opted for the technical viability, flexibility and reduced investment offered by submarine cable replacement.

From the Finnish mainland, there is a small cross-section 45-kV submarine-cable connection along islands of the Aland archipelago, however, there is no interconnection with the Swedish network due to a small phase difference.

Aland Island Reinforcement Project To optimize system power losses KA decided to upgrade the voltage of the submarine cable to 100 kV and to increase the transfer capacity of the link to 80 MW, decisions that also required the construction of new substations at both ends. In Sweden, a new substation equipped with a 77/110-kV transformer will be constructed at Senneby. In Aland, a new 110-kV, 15-km (9.3-mile) transmission line will link the new cable to Aland's 45-kV distribution system via a 110/45-kV transformer at Tingsbacka Substation.

Cable Contract NK Energy, a subsidiary of NK Cables, was awarded a turnkey contract to manufacture and lay the submarine and underground cable link from Vaddo, Sweden, to Tellholmen, Aland. This contract includes the supply of 63 km (39 miles) of 110-kV submarine cable and 6 km (3.7 miles) of underground cable, joints and accessories. The cable for this project will be one of the world's first 110-kV three-core submarine cables and will comprise 240 mm2 (0.37 in2) copper conductors and 36 optical fibers for data transmission. This cable provides significant savings in cable-laying costs and will reduce transmission losses.

The value of this contract is about FIM 60 million (US$10.7 million). NK Energy has previously supplied 45-kV submarine cables to K? for distribution within the ?land islands.

The submarine cable will have solid copper conductors, a design that makes the cable longitudinally watertight, and a semi-conducting swelling tape under the lead sheath, making an effective barrier against water penetration in the event of cable damage.

SZ-stranding of the power cable cores has been used whereby they are twisted first clockwise and then counterclockwise a laying-up technique that prevents the use of traditional stranding machines.

NK Cable's Spiral Space design will be used for the optical unit in this cable. It was created to be a simple, cost-efficient and reliable optic cable to fulfill a range of applications from direct-buried usage to indoor, submarine and optical ground wire cables. The Spiral Space core has several properties that make it ideal for data transmission particularly within a dual-purpose power cable: n Nonmetallic core n High crush strength (ideally suited where the cable is subjected to underwater pressures n Extra sheath n Small diameter n Easy to manufacture and install. The Spiral Space plastic tube in the Aland cable has a diameter of 7.5 mm (0.30 in) containing the 36 optical fibers, allowing a data-transmission rate in excess of 30,000 telephone messages per fiber.

Pre-installation Testing A test cable was manufactured in May 1999, followed by type testing during the summer. Three factory joints for the submarine cable have been subjected to mechanical and electrical tests in accordance with the international CIGRE recommendations, IEC standards and customer specifications. Longitudinal water penetration tests were performed at maximum 27 bar pressure corresponding to the maximum water depth [270m (900 ft)] along the route in addition to satisfying tests in accordance with KA's technical specification. Optical fibers also have been measured during and after each test results confirming, no evidence of increased attenuation. Tensile and electrical tests for the repair joint are currently in progress.

Submarine-Cable Installation A new route has been selected for the submarine cable to avoid rocky coastal areas and this increased the overall length by some 5 km (3.1 miles). During the installation, a ROV camera will be used to check the cable touch-down points in critical areas. The cable will be buried to 10-m (32.8 ft) water depth in Sweden and 5-m (16.4 ft) water depth in Aland to provide protection from pack ice. Manufacture of the contracted submarine cable began in August 1999, in preparation for an April/May 2000 installation.

Keeping the Power and Data Flowing This submarine-cable project will restore a reliable cost-effective power supply to the Aland Islands and the added benefits of optical-fiber data transmission will give Kraftnat Aland Ab technology for the next millennium.

Expansion of the Peru's Transmission System The Peruvian power system, consisting of two 220-kV isolated electricity systems and operating in the Centre-North and South regions of the country, is owned by two utilities. Etecen operates the interconnected system in the Centre-North (SICN), managing a system totalling 5900 km (3667 miles), and in the South, Etesur operates and manages the 1460-km (907-mile) interconnected system (SISUR). A major project is in progress to increase generation capacity and expand and increase the capacity of the transmission system. By the end of the year 2000, a new 220-kV line will interconnect the two existing systems.

Peruvian Southern System Energia del Sur S.A. (Enersur), the Peruvian branch of Tractebel (Belgium), is one of the utilities responsible for the generation of electrical energy to the southern region of Peru. Enersur operates the existing Ilo thermal power plant (installed capacity 207 MW), which is located in the Moquegua region of Ilo province. This plant is connected to the 138-kV transmission system and 13.8-kV distribution system owned by Southern Peru Ltd. This plant supplies the local demands of Ilo and Moquegua and via two 138-kV single-circuit lines, the Southern Copper Corporation Mines at Toquepala and Botiflaca (Cuajone).

Expansion of the Generating Capacity To satisfy the increasing demand for energy from all sectors of the economy, Enersur is constructing a new power plant, Ilo 2, on the Pacific coast, south of Ilo city, some 1225 km (761 miles) south of Lima. The contract for this 250-MW thermal power plant was awarded to Hitachi (Japan).

The New Transmission System In parallel with the construction of this power plant, in September 1998, Enersur awarded a turnkey contract to a consortium formed by ALSTOM and Ingenieros Consultores y Ejecutores S.A. (ICE) to reinforce and increase the capacity of the existing transmission system. The contract includes new transmission lines, construction of an additional 220/138-kV substation, and modifications to two existing 138-kV substations. The six elements of work within this contract are: n Construction of a new 220-kV double-circuit transmission line between Ilo 2 power plant and a new substation to be constructed at Moquegua a route length of 72.3 km. The circuits comprising bundled phase conductors [2 x 236 mm2 (0.37 in2 ) AAAC "Cairo" Conductors] with a single ground conductor, [159mm2 (0.25in2) AAAC "Butte" conductor] will each have a load transfer capacity of 400 MVA. n Construction of a new 138-kV, 30.5-km (19-mile) single-circuit transmission line between the new Moquegua Substation and the existing Botiflaca Substation in Cuajone will be constructed using conductors [470 mm2 (0.73 in2) AAAC "Greeley" conductors] that will give the circuit a 196-MVA rating n Deviation and interconnection of the existing 138-kV single circuit line into the Moquegua Substation. n Stringing of a second circuit on the existing single-circuit 138-kV line between Moquegua Substation and the existing substation at Toquepala (38.7 km or 24 miles). The new circuit will increase the power transfer capacity between these two substations by 100 MVA. n Construction of a new 220/138-kV substation near Moquegua city. The substation will be equipped with two new 300/300/50-MW autotransformers, these being the largest transformers to be installed on Peru's transmission system. SF6-insulated circuit breakers (rating of 3150 A) will be used to control the 220-kV and 138-kV circuits. n The two existing 138-kV substations at Botiflaca, installed capacity three 58-MVA transformers, and Toquepala, installed capacity two 33-MVA transformers, will be expanded to accommodate the circuit breakers protection and SCADA telecontrol for the additional transmission lines.

ALSTOM, the consortium leader, is responsible for the electrical and mechanical engineering, the supply of all equipment and materials, and supervision of the project. ICE are responsible for the execution of the works using locally based staff for the civil works, erection of the transmission lines and substation construction.

Project Timetable This completion date for this contract that was awarded in September 1998 is January 2000, and at the end of November 1999, all transmission line towers were erected and conductor stringing on the three circuits was almost complete. The new substation installation near Moquegua was 80% complete and work at the Botiflaca Substation and the Toquepala Substation was on schedule.

Project Funding The complete project is partially financed by a US$300 million loan from the Inter American Bank of Development, approximately US$33 million of this loan is being invested in reinforcing Peru's transmission system.

Future Development of Peru's Transmission System. This contract forms part of Peru's strategic long-term development plan for the transmission systems in north, central and south Peru. The proposed north-south, 600-km 220-kV transmission line between Mantaro and Socabaya, which is also under construction, will interconnect the country's two isolated transmission systems by the end of 2000.