Although load growth in Asia remains the highest in the world, distribution of energy resources in many of the continent's large countries is remote from the centers of population and industrial development. Thus, significant investment is needed to fund projects designed to satisfy increasing demand, improve system reliability and extend the power networks to those areas still lacking a connection to a source of electrical energy.

Technology is now available to meet these challenges. A review of major projects in Asia and Australia recently completed, currently in progress and planned for the future indicates the increasing use of high-voltage direct current (HVDC) systems. The advantages of HVDC, which offers the most efficient and economic means of transmission over long distances, also include lower losses, improved system control as dc technology enables full power flow control and environmental benefits.

The projects presented in this article provide insight into the applications of new technology and the continual investments being made by utilities in developed and developing countries to ensure consumers receive a reliable supply and to extend this source of energy to those millions still without a connection to a distribution network.

India's East-South HVDC Transmission Line

In the spring of 2000, the Power Grid Corporation of India awarded Siemens a turnkey contract to deliver and commission the two converter stations at each end of the East-South HVDC transmission line. With a transfer capacity of 2000 MW, this ±500-kV HVDC link is the sixth longest in India and the second longest HVDC circuit in the world. The 1400-km (870-mile) transmission line links the coal-fired power plants near Talcher, in the state of Orissa, to the industrial regions located in the vicinity of Bangalore, in the state of Karnatake.

Because India's five regional electrical networks are not mutually compatible, and the distances between power plants and centers of population are great, HVDC technology offers a solution to overcoming the technical and economic constraints associated with ac transmission systems. Hence, India's transmission system is dependent on the benefits of HVDC transmission technology to ensure power exchanges via an interconnected system that, on a national scale, are both reliable and flexible.

The two converter stations are each equipped with power thyristors, switch-gear, converter transformers and control technology supplied and commissioned by Siemens to convert the ac to dc in the (East) transmitting station and transform from dc to ac in the (South) converter station (Fig. 1). India's largest energy transmission project went into commercial operation in February 2003, three months ahead of schedule.

India's Vizag II Project

ABB was awarded a US$48 million contract in September 2002 by the Power Grid Corporation of India to design, build and install a new 500-MW HVDC power system to supply millions of consumers in eastern and southern India. The Vizag II project will be installed at Gazuwaka, located at Vishakhapatnam on India's southeast coast. Located adjacent to an existing HVDC converter station, this interconnection between two regional grids will increase the capacity for power exchange by 500-MW and also will provide voltage and frequency support for both grids during power disturbances. The contract includes project management, civil works, buildings erection and commissioning, as well as equipment, including thyristor valves, converter transformers, and control and protection systems.

Scheduled for completion and commercial operation in early 2005, this project is a further stage of Power Grid's phased development of the National Grid that will improve regional power reliability.

Thailand

One of the world's first gas-insulated transmission line (GIL) with N2 and SF₆ gas mixture at a voltage level of 550 kV is now in operation in Bangkok, Thailand. The Electricity Generating Authority of Thailand (EGAT) built a new 550-kV gas-insulated switchgear (GIS) in Sai Noi Substation (Fig. 2), with eight line feeders and two connection bays to an existing GIS. Long-distance interconnections were necessary between the GIS bays and the overhead line gantry, but because of insufficient space for air-insulated bus bars, GIL was chosen.

The current rating of 4000 A makes this GIL one of the largest high-power transmission systems worldwide, with 3800-MVA load-transfer capability. The GIL is operated under severe ambient conditions with high sun radiation and high ambient temperatures.

The second-generation GIL was selected for this project, with an insulation gas mixture of SF₆ and nitrogen. This GIL is designed and tested according to IEC 61640, and is suitable for energy transmission over long distances. All GIL components were shipped separately to reduce the risk of transport damages. Furthermore, the assembly was performed in a temporary working tent in order to achieve the necessary cleanliness. The GIL tubes for this 3.5 km (2.2 miles) installation were machined, cleaned, assembled and then jointed by welding, and then placed into the final position within the substation.

Laos

Electricité du Laos (EDL), the state-owned utility, awarded ABB a contract valued at US$17 million to design and build a 340-km (211-mile) 115-kV double-circuit transmission line and a 282-km (175-mile) 34.5-kV distribution network, including high-/low-voltage distribution transformers.

The underdeveloped state of the rural infrastructure in Laos was a major constraint to economic growth and poverty alleviation. With the assistance of the Asian Development Bank, which financed the project, ABB's experience and expertise in rural electrification and an accelerated construction program, this project was completed in 2003.

The transmission system has been extended in the northern Laos provinces of Luang Prabang, Xayaburi, Vientiane, Xaisomboun and Xieng-Khonuang, and the reinforced 34.5-kV distribution network has increased the number of villages in Laos afforded an electricity supply by about 3%.

Vietnam

The Southern Vietnam Power project Management Board (SPPMB), a unit of the Electricity of Vietnam (EVN), awarded ABB a US$16 million contract in March 2004 for the design, manufacture, testing and commissioning of a 500/220/110-kV substation to reinforce supplies in the south of the country.

The order includes a 500-kV series compensator, 500-kV and 220-kV power transformers, a 500-kV reactor and primary equipment, including switchgear at all three voltage levels. The proposed substation, scheduled for completion within 12 months, will improve the transmission system's efficiency and increase the reliability of supply in Ho Chi Minh City and other areas in the south.

China

Many countries in the Far East are still building interconnected national systems. Of these countries, China has the fastest growth in power demand. From 1990 to 2000, its installed generation capacity rose more than 130%, from 135 GW to 319 GW. The main energy resources in the country are hydro in the central and southern areas and coal in the north. Also, some nuclear power stations have been built near the load centers. Because of the great distances that have to be covered in China, smaller, isolated regional systems were built in the early stages of system development. These small systems evolved into seven large regional power networks and several smaller local systems in the less-populated areas of Tibet and Xinjiang (Fig. 3).

The main ac transmission voltage levels used in China are 330 kV and 500 kV. Large power blocks produced by hydro power stations must be transmitted to the load centers over distances of 1000 km (622 miles) and more. Although HVDC transmission typically is used for this task, 500-kV ac also is common for transmission within the regional systems.

Although some coal-fired power stations have been built closer to the load, they are concentrated in the northern part of the country. Power exchange among the regional systems is still at a relatively low level in relation to the installed capacity of the systems. Thus, just a few ac lines would be sufficient for the interconnections needed to handle power exchange. However, because of various problems and the additional investments needed to adapt the systems to enable synchronous operation, HVDC transmission now is used for most interconnections.

In the future, the seven existing regional power networks will be merged to form three large interconnected systems: the north, center and south power grids. Interconnection among these grids will be handled primarily by HVDC. In addition to the existing four HVDC's links, another 14 HVDC transmission links are planned. Connection by ac to the larger regional grids only will be used for smaller and remote local networks — probably using 765 kV because of the distances involved.

Taiwan's Mai Liao Industrial Park

Siemens designed, supplied and installed on a turnkey project basis the complete power supply system for the coal-fired generating station of the Mai Liao Industrial Park in Taiwan. The operator of the Industrial Park, Formosa Petrochemical Corp. (FPCC), had to be considered during the execution of the project, along with other special requirements.

For example, the 345-kV GIS was designed to withstand the short-circuit current for three times the normally specified duration. The 8DQ1 switchgear is a key element in the power supply system through which energy is provided for all the factories in the Industrial Park and to the tie lines that supply Taiwan Power Corp. (TPC).

The 345-kV substation is equipped with two 937.5 MVA transformers — the largest three-phase autotransformers ever supplied by the Siemens manufacturing plant in Nuremberg. Siemens designed the control system for the 345-kV substation, which can be remotely controlled from various locations in the Industrial Park to allow power flow in both directions. Fig.4 shows the 345-kV GIS installed in Mai Liao Industrial Park Substation.

The 345-kV substation remote control facilities are afforded by a sophisticated SCADA system. The communications and control data is transmitted via a 28-km (17.4 miles) fiber-optic network at the Mai Liao site. Communication with the substation at the TPC termination of the 72-km (45-mile) overhead line is via optical fibers in the earth wire. The project also includes the monitoring and complete protective system for the power transmission and distribution. The substation and all associated components were commissioned in 2003, and the complex combination of 345-kV switchgear, multiple control systems and fiber-optic interconnection can be remotely controlled via the switching cubicles installed in the Chung Liao tie-line substation, which is located 72 km (45 miles) from the Industrial Park.

Australia's MetroGrid Project

The goal of the MetroGrid Project in Sydney is to give Australia's largest city the modern reliable energy network it needs to meet increased demand and to put in place the infrastructure needed for the next century.

Commissioned in July 2004, the challenge of this project was to get the job done safely, cost effectively and on time without disrupting the city or the surrounding environment. Now in the final commissioning phase, the MetroGrid Project has set new standards in safety and management of impacts for CBD developments. It included several major engineering projects, each of which presented its own challenges, giving rise to innovative solutions implemented in a diverse range of environments and in a tight time frame. These included:

• Installing a new AUS$90 million (US$61 million) TransGrid substation at Haymarket.

• Laying 330-kV cable in a 28-km (17-mile) route from the TransGrid Sydney South Substation to Haymarket, the last 3.5 km (2.2 miles) in a tunnel with other shared services, at a cost of AUS$200 million (US$136 million).

• Incorporating significant distribution developments by EnergyAustralia, including two indoor 132-kV GIS substations, a tunnel and 132-kV cables.

Haymarket Substation has three 400-MVA gas-insulated transformers from TM T&D Systems (Toshiba). There is a 330-kV ring arrangement of four bays and a 132-kV double bus bar with 24 bays of GIS from Siemens. The proximity of office buildings, a pedestrian plaza, a university campus and the likelihood of a high-rise residential building dictated the substation have a low environmental impact in terms of noise, visibility, EMF and consequence of failure.

The choice of transformer technology was critical. The technology that could provide a proven satisfactory level of public safety and environmental impact as a consequence of transformer failure in the Haymarket location was SF₆ gas-insulated transformers and shunt reactor. The gas-insulated transformers installed at Haymarket are the highest voltage and largest capacity gas-insulated transformers installed worldwide thus far.

The location and capacity requirements of this project have presented many challenges to the designers and suppliers. The cost-effective management of the environmental and community impacts in a close to CBD location required innovative designs and engineering solutions to meet the numerous expectations of stakeholders and the community.

Murraylink HVDC Light Connection

The Murraylink transmission system is the world's longest HVDC Light underground cable interconnection between the Riverland region of South Australia and the Sunraysia region of Victoria.

The AUS$100 million (US$ 68 million) project took just 39 months from concept to commissioning — a major feat that included laying two ±150kV dc cables along a route length of 176 km (109 miles) in less than 10 months. The 200-MW interconnector, running between Red Cliffs Converter Station in Victoria and Berri Converter Station in South Australia, will supply enough energy for about 120,000 homes.

TransEnergie Australia, a subsidiary of Hydro-Québec (Québec, Canada), awarded the project construction contract to ABB, who employed its HVDC Light technology to transmit the power from one state to the other.

HVDC Light technology converts current from ac to dc and uses special extruded cable, laid in bipolar pairs, to transmit the power underground. Anti-parallel currents eliminate magnetic fields. The converter stations built at either end of the HVDC cable system handle power flow in either direction. The advantage of HVDC compared to conventional ac transmission lines is that it uses fewer cables and can be laid underground. The components of the converter stations are compact and modular, allowing for relatively short lead and construction times on projects.

The Murraylink installation comprises two HVDC cables laid 100-mm (4 inches) apart in a trench dug within a 3- to 4-m wide easement. A key criteria for this type of project is to have backfill material of the appropriate resistivity level to allow the cables correct heat dissipation during operation. As a result, 300 test holes were dug along the cable route.