Centre for Science and Technology for Development

Advanced Technology Assessment System
Issue 6 Autumn 1991

Energy Systems,
Environment and Development

A Reader

United Nations New York, 1991

The Advanced Technology Assessment System (ATAS) Bulletin is a recurrent publication of the Centre for Science and Technology for Development, United Nations Secretariat, New York.

TECHNICAL EDITOR: Martin J. Bernard III
MANAGING EDITOR: Mary Pat Williams Silveira

The views expressed in the papers are those of the individual authors and do not imply the expression of any opinion on the part of the United Nations Secretariat. Papers have been edited and consolidated in accordance with United Nations practice and requirements.

The designations employed and the presentation of the material in this publication do not imply the expression of any opinion whatsoever on the part of the United Nations Secretariat concerning the legal status of any country, territory, city or area or of its authorities, or concerning the delimitation of its boundaries.

Mention of firms and commercial products does not imply the endorsement of the United Nations.

UNITED NATIONS PUBLICATION Sales No. E.91.II.A.4 ST/STD/ATAS/6
ISBN 0257-9373 ISSN 92-1-104364-6
Cover design by Graphic presentation Unit, United Nations
Desktop publishing by M. J. Bernard III
ATAS Bulletin

Advanced Electric Power Transmission Technologies

Sergio O. Frontin, Archer Mossé and Helio D. Porangaba

Introduction

The aim of this paper is to provide a global overview of the technological advances in power transmission, outlining the implications and future policy options for developing countries. There are several ways to improve power transmission technologies, ranging from the introduction of new concepts, such as half-wave, higher phase order, or microwave transmission, to improved applications of old concepts, such as high voltage direct or alternating current. Some of the improvements come from the need to reduce costs while maintaining overall reliability-others from the need to overcome technological barriers, and-might be related to the use of new materials or equipment and/or to a better use of the land and protection of the environment. Several materials and electronic equipment technologies are being introduced in the transmission networks of industrialized countries, increasing reliability and lowering costs.

Basically there is no difference between industrialized and non-industrialized countries with respect to new transmission technology needs. The needs are dictated by specific applications in each power transmission scenario. For example, countries like Brazil, China, India, and the Soviet Union are pursuing improvements in ultra-high voltage technology in order to maintain more economic and reliable transmission links from their remote natural resources to the main load centres in the country. In the United States and Europe, direct current (DC) technology has been used in asynchronous connections of regional grids, as well as in the transfer Of power from remote coal reserves, power imports from neighbouring countries and underwater crossings. [Editor's note: The electrical engineering jargon will be defined presently.]

In developing nations, almost everything remains to be done in order to maintain an adequate supply of electricity and ensure economic growth. Power networks are weak (low short-circuit capacity), sparsely distributed and weakly interconnected. Development of strong inter-regional alternating current (AC) or DC interconnections is a common trend to improve system operation. Problems of voltage fluctuation, reactive power management and systems stability derived from weak and sparsely distributed power systems may be reduced by the introduction of high voltage DC (HVDC) transmission schemes.

Electricity market rates of growth in developing countries usually are higher than those in industrialized countries. Average electricity growth rate in developing countries in the last decade was between 11 percent and 15 percent/yr. If the first few years of the eighties are included, the average value drops somewhat, but is still higher than in most industrialized nations. To meet the growing demand, large hydro and thermal generations plants must be built and the power transported to the load centres. Usually, there are no shortages of primary energy resources, but they are unevenly distributed with respect to the main load centres in the country. A related problem is the explosive growth of population, mainly in the urban arms, bringing the need for high capacity transmission into the cities.

Worth noting is that coal, oil, or even nuclear fuel can be transported by some permanent infrastructure other than the electricity transmission network. This is not the case for site-specific hydro and other renewable sources of energy, where the resultant power must be transported as electricity.

Developing nations, with few exceptions, are major exporters of raw materials. Electrical system expansion programmes have been carried out using foreign-based technologies, even if, as in Some cases, equipment and facilities are manufactured and built in the country by subsidiaries of transnational companies.

One result is that developing nations' power system expansions consume promising commercial markets. At the same time, plagued by huge foreign debts, internal economic and political crises, and lack of technology, developing nations do not always make the best possible decisions on how to implement needed expansion programmes without aggravating those problems.

The major constraints for the implementation of new technologies are centred in the financial requirements of new projects and the availability of affordable technology in the country or elsewhere. In this respect developing countries have both an advantage, due to the stage of development of their electrical Systems, and a drawback, due to the lack of manufacturing industries and home-based technology.

State-of-the-art Power Transmission Technologies

UHVAC Transmission Systems (>1,000 kV)

Electric power transmission at voltages >l000-kV AC is one alternative to be considered in the transfer of large blocks of power and/or over long distances. For this reason, countries such as Brasil, Mexico, India, China, Italy, Japan, the United States, and the Soviet Union have been conducting research programmes to develop the related technology. From the results obtained, it is possible to say that UHVAC transmission technology is presently available and awaiting commercial applications.

The question for countries like Brasil is to determine if the existing technology is adequate or if higher voltage levels should be implemented. To date the highest AC and DC voltages in commercial use in the world are the 1200-kV AC Soviet line from Siberia to the Urals and the +/-600-kV DC Brasilian Line from the Itaipu power plant to the industrial southeast. Other possible solutions for the problem are higher phase order and half-wavelength transmission, but there are not yet lines operating with these technologies.

Compact Transmission Lines

If the intent is to go through a transmission corridor of reduced width, it is possible to design Several circuits in the same vertical plane. More than four circuits in the same support have been reported. Another alternative is to explore the reduction of the geometric mean distance of phases, which increases the surge impedance loading and the power transmission capacity. The results of an economic evaluation of l,500-kV AC transmission towers of conventional and non-conventional self-supporting and guyed configurations (see sketch on previous page as an example) are that compact towers are more economical than the conventional types and the cross-rope is the most economical. Another possibility is to Convert AC lines to DC, thus increasing the transfer capacity of the lines.

Higher Phase Order Transmission

Siting transmission lines (with high and extra/ultra high voltages) is becoming more difficult, mainly in more densely populated areas due to problems in acquiring rights-of-way and to the environmental impact. As a consequence, the need to transmit much more power requires the investigation of new concepts. Using higher phase order to increase line power rate without substantial changes in right-of-way requirements lines is one alternative that has attracted growing interest in recent years. A double 138-kV (three-phase) circuit converted to a single six-phase circuit of the same voltage would result in a 73 per cent increase in thermal Capacity within the same right-of-way, with only a minimal additional environmental impact. To date, there is no higher phase order transmission operation, but the existent studies and prototype projects have demonstrated the feasibility of using this concept for long distance high capacity transmission.

Half-wave-length Power Transmission

The first theoretical analysis of the application of the half-wave-length concept of power Transmission was published in 1940 in the Soviet Union. It is based on the operation of a transmission line whose electrical length is equivalent to a half-wave at system frequency (180 electrical degrees). This mode of operation can be achieved naturally or artificially. In the natural half-wave-power transmission, the electrical length is equal to the physical length (3,000 km at 50 Hz or 2,500 km at 60 Hz).

UHV DC Transmission Systems (+/-600 kV)

At present the highest voltage/capacity system in the world is the Itaipu+/-600-kV, 6,300-MW transmission Line from Foz do Igua'u, at the border of Brasil and Paraguay, To Sao Paulo, Brasil, over a distance of approximately 800 km. The design and implementation of this project is a joint effort of ASEA/Sweden and ASEA/Brasil, the equipment manufacturers: PROMON, a Brasilian engineering firm; FURNAS, the utility in charge of the project; and CEPEL, the Brasilian electric power research centre.

For very long distance/high capacity transmission, the DC alternative of voltages above +/-600-kV (UHVDC) can be economically attractive, and research on bipolar lines and converter station equipment is being pursued. The information obtained has demonstrated that no major problem is expected for the design and construction of HVDC bipolar lines of voltage up to +/-1,500-kV.

Between 1982 and 1985, the Electric Power Research Institute (EPRI) in the United States, with CEPEL/ELETROBRAS (Brasil), sponsored research to determine the critical problems in developing HVDC converter station equipment for voltages in the range +/-600 to +/-l,200-kV. The work was assigned to Them, a Brasilian engineering consulting firm, and to Institute de Recherché de l'Hydro-Quebec, Canada, and consisted of engineering studies and the identification of research and development needs. The conclusion was that converter stations at voltage +/-800-kV DC are technically feasible with existing knowledge, although some R&D effort is still needed for the design and construction of outdoor bushings. For voltages above +/-800-kVDC, substantial R&D effort is still required. The economics and reliability of DC transmission may be enhanced in the future by some of the new developments in DC technology, such as HVDC circuit breakers, SF6 insulated valves, modern thyristors and new materials for converter transformers.

HVDC multi-terminals

By 1965 the basic principles of multi-terminal DC (MTDC) systems were already well developed, but more than 20 years elapsed before the first MTDC system was in operation; it was the 1987 expansion of the link connecting the three separated networks of Sardinia, Corsica and Continental Italy. This system, with the inclusion of the power tap supplying Corsica, is an expansion of the two terminals DC Link Sardinia-Italy. The Corsica station has a 50-MW rating, which represents 25 per cent of the original Link rating. Due to the lower Cost of electricity from the continent, the tap alternative showed a 40 per cent advantage in cost over local hydro or thermal generation. The Quebec-to-New England HVDC transmission interconnection will be the largest One in the world and the second design scheme to operate as MTDC.

MTDC application as an alternative for point-to-point systems or AC networks could improve the flexibility of system operation and may be economically attractive. In some developing countries the application of this technology could be useful in order to utilize generation from remote hydro resources and at the same time supply different load centres along the way.

Shunt and Series HVDC Taps

Small power tapping from HVDC point-to-point schemes would increase The attractiveness Of The DC transmission in comparison with AC alternatives. This type of tap could result in substantial benefits for the areas crossed by the Long distance transmission trunks, supplying small loads along the route. The technical and economic feasibility of implementation of small tap schemes depends on the particular application under analysis. Cost comparisons with possible local generation supply, impact on the reliability of the main transmission trunks and local tap control are among the factors that need to be evaluated.

Asynchronous Interconnections

An AC interconnection implies that the frequencies of the two systems are the same in normal steady-state operation. HVDC technology using static converters assures the possibility to connect AC networks not in phase and/or with different frequencies. Asynchronous links for inter-regional connections may improve the overall performance of the two networks.

Unit Connections

Several technical and economic reasons strongly suggest that in certain HVDC applications it may be advantageous to simplify the rectifier station, via a direct connection of Each machine Set to a separate Converter group. With any series-parallel combination made on the DC side. Studies have shown cost, space, and reliability benefits of unit connections, but none have been used in major projects.

Microwave Transmission

A solar satellite system for the generation of electric power was proposed in 1968 by Dr. Peter Glaser (United States). A very Large power satellite would be placed in stationary Earth orbit to generate electricity from the sun and beam the power as microwaves to Earth to be converted in electricity. The microwave transmission system is one of the key elements of the power satellite. Although all required technology seems to be available for the implementation of such a system, significant advances still have to be made before it becomes technically feasible and economically competitive with other energy alternatives.

Future Needs for New Technology: The Case of Brasil

Brasil's total installed capacity is approximately 43 gW. With energy consumption growth rates in The range of 4.3 to 7.6 percent, it will be necessary to install 120 gW more through the year 2010.

The Brasilian hydro potential located in the south, southeast and northeast regions will soon be exhausted. Low-cost. large-scale hydro resources are in the major right-bank tributaries of the Amazon River, but these are in the north and far distant from The population centres. Roughly 100 gW can be developed at a relatively low cost ($44/MWh, including long distance transmission), which is competitive with the alternative of building smaller hydro, coal and nuclear plants near the load centres. By the year 2010, large blocks of power (20 to 25 gW) may be transmitted over distances up to 2,400 km from the north to the other regions.

Planning studies and economic evaluations were performed considering application of ultra-high voltage AC and DC. One result Of the present-worth cost estimation for the transmission of a power block of 8 gW over 2,400 km is summarized in Table 1. Investment cost includes substation and line costs for each optimized system (two bipoles for the DC alternatives, and three series and shunt-compensated lines for the AC case). The cost of losses refers to equipment and joule and corona Line losses. The new technology of +/-800-kVDC has the lowest total cost.

Conclusions and Recommendations

A developing country must decide how it will tap its primary energy resources. Should electricity be transported to existing load centres or should industrial development be promoted at or near the generation sites? Should electricity be restricted to specific sites Or should it be dispersed based on alternate energy sources? Answers will vary by country, because they relate more to economics than to the electrical System planning, and to the nature and size of the energy resources.

Now, more than ever, it is important for developing countries to start a concerted effort to bridge the technology gap. One of the major fields where this could take place is in energy technology, affecting the way transmission technologies are introduced in the developing nations-the problems are there to be solved and the electric utility Industry is one of the few organizations that can tackle the problems. Such effort might include:

• joint ventures in R&D,
• demonstration programmes, and
• equipment nationalization on a regional level.

To reduce the gap, in addition To local or regional R&D incentives and either north-south or south-south co-operation, a new kind of human resource is needed, deep commitment to regional development and acquisition of the adequate technical knowledge.

The origins of the electrical system, American and/or European, and the lack of financial resources needed to face the large investments in the expansion Of the transmission system, coupled with the availability of suppliers and other international financing, brought to developing countries a mix of influences and, as a result, both European and American standards are sometimes in use in the same region, the same country and even the same grid. A common example is the different frequency standards used in South America, which hinder the interconnections between neighbouring countries. A regional power industry development effort might alleviate such problems, and increase the chances for the future build-up of continental power pools, at least in South America. Some African nations are already electrically interconnected, but technology is usually supplied from European countries that still hold substantial control over the technological development of their former colonies.

In conclusion:

• Developing countries have both the need and, roost often, the natural resources for the expansion of their electrical Systems.
• Due to the incipient state of their industrial development, much is still to be done and electricity rates of growth are high.
• The attractive part is that they can still make technological choices because their electrical Systems are in an early stage of development.
• The distribution of natural resources, away from the main load centres, and of population in and around major cities in the country suggests large investments in the design and construction of long-distance/high-capacity power transmission trunks.
• There is also a need to improve and expand electricity distribution networks at the destination, in major cities and in industrial regions.
• Electric power research and development must be a concern of developing nations, because in many cases they have both the problems and engineering skills To Solve the problems.
• As the power system expands, it becomes more complex to operate and, as a consequence of the delayed investments, more prone to suffer from power failures. A further consequence is the operation at reduced safety margins, i.e., closer to the limits of both equipment and facilities.
• There is no way to decouple power system expansion from large amounts of financing needs. Even if electricity conservation measures, which have their own costs, reduce the rate of investments in generation and transmission, the latter will still be needed in the future.
• The major question that remains is how to finance the needed expansion. Electricity rate increases are limited by the buying power of the population and, sometimes, by the need to curb inflation growth; therefore they cannot be the sole source of power expansion funds. The question becomes even more difficult if the borrowing potential of the country-access to international financing from world/regional organizations and other governments-is severely restricted by already existing foreign debt. As a result, investments in construction and operation of generation and transmission facilities are not always compatible with the needs of the country.

We recommend a few measures To ease the path to improving the country's industrial development and attending to the social needs of the population.

• Achieve technological development through in-house research or Joint ventures (or informal associations) with industrial nations (vertical technical co-operation) or other countries under development (horizontal co-operation). For instance, develop a working knowledge of local and regional meteorological and other conditions to produce adequate transmission system design. Such Joint ventures/associations may take the form of R&D or demonstration programmes.
• Invest in power system planning and operation methodology. Using modern software for expansion planning and systems operation leads to substantial savings by either maximizing returns on new projects or delaying future investments.
• Look at the local/regional industrial park organizations, using the buying power of the utility industry to boost the number and quality of products in the country.
• The countries must make good use of their utility industries' buying potential, in more than one sense. They might for instance, preserve their power expansion markets for local industrial development.
• Practice, as much as possible, realistic electricity tariffs, for both the industrial/commercial and residential consumers.

Bibliography

UHV AC Transmission System (>1,000 kV)

Belyakov. N. N., L. M. Bortinil, and A. F. Djakov, "1,200-kV Transmission Line in the U.S.S.R.: The First Results of Operation," CIGRE (1988 Session).

Morrissy, C. A., A. Vian, J. M. Bressane and A. V. Ferraz, "1,000-kVAC Alternatives for the 8 gW/2,400 km Transmission System from the Amazon Basin to the South-Eastern Region," Workshop on Very Long Distance AC Transmission Systems, Pisa (1984).
 

Compact Transmission Lines

Hajdu, E. M., R. Cardoso and F. Teiveilis, "Evaluation of Various Conductor Support Systems for 1,500-kV Transmission Lines," CIGRE Open Conference Study Committee 22, Rio de Janeiro (1983).
 

Higher Phase Order Transmission

Grant, I. S., et al., "Higher Phase Order Transmission Line Research, "CIGRE Symposium, Stockholm, Sweden (1981).

Guyker, W. C., "Six-phase Protection Hurdle Cleared," Electrical World (Jan. 1981).

Stewart, J. R. et al., "HPO Line Practical for Limited R/W," Transmission and Distribution (Oct. 1985).
 

Half-wave-length Power Transmission

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Prabhakara, F. S., K. Partharathy, and H. N. Ranachandra, "Analysis of Natural-Half-wave-length Power Transmission Lines", and "Performance of Tuned Half-wave-length Power Transmission Lines," IEEE (Dec. 1968)

Pouel, C. O., "Half-wave Transmission," VI SNPTEE, Santa Catarina (1981).
 

UHV DC Transmission System (+/-600-kV)

Campos Barros, J. G., S. O. Frontin, J. A. Jardini and L. B. Ries, "Engineering Studies for HVDC Above +/-600-kV with a View to its Applications to the Transmission of Large Blocks of Power over Very Long Distance," CIGRE(1988 Session).

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HVDC Multi-terminals

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Shunt and Series HVDC Taps

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Krishnayya, P. C. S., et al., "Simulator Study of Multiterminal HVDC System with Small Parallel Tap and Weak AC System," IEEE/PES 1984 Winter Meeting, Dallas (Jan. 1984).

Morissy, C. A., et al., "Some Aspects of the Energy Supply to Small Loads Located Near Long Distance Transmission Trunks," CIGRE, Paris(1986 Session).
 

Asynchronous Interconnections

Clark, H. K., and F. P. Melo, "Enhancement of AC Systems by Application of DC Technology," First Symposium of Specialists to Electrical Operational Planning, Rio de Janeiro (Aug. 1987).
 

Unit Connections

Krishnayya, P. C. S., et al., "A Review of Unit Generator Converter Connections for HVDC Transmission," IEEE/CSEE Joint Conference, Beijing(Oct. 1987).
 

Microwave Transmission

Denman, O. S., et al., "A Microwave Power Transmission System for Space Satellite Power," and G. M. Hartley, "Evolution of Satellite Power System Concepts", both at 13th Intersociety Energy Conversion Engineering Conf., United States (1978).
 

Itaipu Transmission Project

Peaxow, C. A. 0., "Itaipu 6,300 MW HVDC Transmission System Feasibility and Planning Aspects," Symp. Incorporation HVDC Power Transmissionin System Planning, Phoenix (Mar. 1980).

Madzarevic, V., C. A. 0. Peixoto, and L. Hagloef, "General Description and Principal Charicteristics of the Itaipu HVDC Transmission System," Proc. International Symposium on HVDC Technology, Rio de Janeiro (Mar. 1983).