Abstract

The paper presents some important principles to be taken into consideration in the analysis of possibilities for the creation of the global electric network. The prospects for this global electric network in the near future are considered and 'moderate' and 'optimistic' hypotheses for the development of a global electric network in the distant future given. In these hypotheses, consideration is given to the possibilities far the utilisation of the economic component of renewable energy resources and the different conditions of interstate and interregional cooperation in electric power systems.

1. Introduction

Numerous studies have been performed on the analysis of the efficiency of components for interconnecting electric power systems (EPS), the technical limits of their intercon- nection, and other aspects which are linked with the assessment of possibilities for creating a global electric network (Paris et al 1984; Antimenko et al 1992; Mueller et al 1992; Voropai et al 1992; Meslier 1993). There is a wide range of views in these works. Much experience has been gained on the design and operation of large national, international, and intercontinental interconnections (Antimenko et al 1992; Straub 1993).

Some important principles to be taken into consideration in the analysis of the possibilities for the creation of the global electric network are formulated below:

1. There are few technical limits for the interconnection of EPSs for parallel operation with AC. Possible problems caused by the undesirable properties of large extended interconnections (low-frequency weakly damped oscillations, higher probability of large-scale systems emergencies, etc), can be identified by suitable studies and suppressed by the rational selection of the EPS structure, use of new controlled elements of an electric network (controlled VAR compensators, FACTs, DC back-to- back stations, SMES, etc), and the choice of the corresponding principles and means of control, including emergency control. The technical possibilities for EPS interconnection are even more increased when DC lines and DC back-to-back stations are used to connect individual parts of the interconnection.
   
   
2. In terms of the economic efficiency of interconnecting EPSs there exists a view that tbere is saturation in economic growth with continuing increase of interconnection size (Mueller et al 1992). This view, however, is not shared by all researchers. It would be more correct to say that there is a limit on the economic efficiency of long-distance power exchange, but this is not a restriction for the interconnection of EPSs.
   
   
3. Energy independence of states and power utilities, in the stimulation of market relations between EPSs, and a rejection of stringent centralised management in interconnection development and operation, are important factors. These factors impose constraints on the value of power exchanges, and the use of an interconnected system is greatly affected if the political relations between the partners is unstable. At the same time, large interstate interconnections intensify the economic integration of the participating countries to allow a more rational use of energy and other natural resources and, in the long run, promote political stabitisation in the region.
   
   
4. Experience in EPS development shows that although discussion on the large-scale power transmission at sufficiently large distances is under way, in some cases at the design level, in practice the planned transmission scales are much lower. Nonetheless, thetrends in EPS development demonstrate that, with the growth of power consumption and generating capacities, the interconnections extend and the fraction of intersystem exchanges rise with respect to the EPS capacities of the partners.
   
   
5. The electric utility industry has already acquired the functions of an infrastructural industry in many respects and will be able to perform them over an even greater extent in the future. This is a factor which will facilitate the interconnection of EPSs, the creation of large international and intercontinental interconnections, and the formation of a global electric network in the future.
   
   
6. In the distant future, the technical possibilities for long-distance power transmission and improved efficiency of interconnecting EPSs should increase owing to the appearance of new technologies (high-temperature superconductivity, super-high- frequency power transmission, etc).

Thus, the laws and trends in EPS development, technological progress in power transmission, and the transformation of the requirements of society to the electricity industry will lead to a gradual closing-up of the boundaries between individual interconnections and EPSs. This process will be supplemented by the power supplied by large power plants according to contracts.

Analysis of possible limits to the EPS interconnection allows the conditional separation of two extreme hypotheses on the development of the global network:

1. A moderate hypothesis, where there is a small use of intersystem (interregional) effects, basically for emergency assistance at the initial period of an emergency and some optimisation of power plant use. In principle, this corresponds to the existing scales of interaction between EPSs in an interconnection; therewith it is supposed that conditions for large-scale power transmission from some region to another at large distances do not appear, possibly except for the use of hydro energy resources. The internal networks in the countries and regions develop on the basis of their own demands.
   
   
2. An optimistic hypothesis where, first, the potential intersystem effects are realised to a greater measure than in the moderate hypothesis, and, second, this is achieved through possible power transmission from some region to another, in particular as a result of the introduction of nonconventional renewable energy resources and power from space. This will lead to new technical potentials in long-distance power transmission. The internal demands and the necessity to distribute power from large power plants will determine the development of the internal electric networks of the countries and regions.

These two hypotheses determine a range of possibilities for the development of a global electric network.

2. Prospects for the development of a global electric network in the near future

Different national and international electric power organisations have analysed the propects for electric network development for the next 15-20 years. At the international level the leading role belongs to CIGRE. Figure 1 presents the zones (shaded areas) which are serviced by existing and planned main grids with a voltage of 330 kV (and higher) for different countries and regions of the world which are separated on the basis of CIGRE information. There are suggestions on the creation of new interconnections in some world regions and countries such as China, India, on the territories of some Arabian countries, the countries of the Persian Gulf, south of Africa from Zaire and Tanzania to the South-African Republic, Central America, East Asia, and some others.

Figure 1. Service zones (shaded areas) of a network operating at 330 kV and higher and possible interregional power flows (straight lines) for the moderate hypothesis (all figures in GW).

3. The moderate hypothesis for the development of a global electric network for the distant future

Estimates of the possible growth in power consumption in the world regions for the years 2025 and 2050 (Slavin and Filippov 1993) underly the formation of the scenario considered here for the development of the global electric network. Power production and generating capacities in world regions are determined from these estimates (table 1). Noticeable growth in power production in 2050 against that in 2025 in the regions comprising the developing countries is stipulated by the population growth in these regions and the levelling of the per capita energy consumption in the world regions.

Figure 1 also presents the estimates of the transfer capabilities of main transmission lines in terms of the moderate hypothesis. It is assumed that the electric ties between the adjacent regions should be able to transmit power equal to 50% of the component of the operating reserve that is put into operation automatically for a duration of 5 -15 s and is referred to as the fast reserve (Dubitskii et al 1988), ie about 2% of the load maximum. Hence, the electric ties between the regions should transmit power equal to 1% of the generating capacity of the larger region of two adjacent ones. In addition, consideration was given to the constraint that situations where the total transfer capability of all electric ties coming into some region exceed 15% of the capacity of power plants in this region (the total capacity reserve of the region) should be regarded as inexpedient, unless the situation arises for special reasons, such as the long-distance transport of electricity from large power plants.

Based on knowledge of the growth in power consumption and generating capacities, territorial peculiarities, and specific features in the location of energy resources in some regions, one can expect the formation of AC electric networks of a voltage level of 1100-1200 kV. Such transmission lines can be developed in Russia and created in China, Brazil, India, Southern Africa, and possibly in other places.

Experts attract attention to the possible development and use of the hydro resources of the rivers in Russia, China, Africa (basin of the Congo), South America (basin of the Amazon), and others (Bohlin et al 1991; Praca et al 1991). The potential power transmission from hydro power plants in this case is reflected in figure 1 in the transfer capabilities of interregional ties connecting the former Soviet Union (SU) to the USA and Canada (NA); Western Europe (WE); Japan and South Korea (JK); China, Mongolia, North Korea, Taiwan, and Hong Kong (CMK); and those connecting the Middle and Near East and North Africa (MENA) to Western Europe and Central and South Africa (AF), see table 1. Other large power sources were not considered in this hypothesis.

The interregional ties can be realised as AC transmission lines of 500 or 1100-1200 kV or DC back-to-back stations, and DC lines can be used depending on their transfer capabilities.

Table 1. Future production of electricity (E, in TWh)
and generating capacities (P, in GW) in the world regions.

4. The optimistic hypothesis for the development of a global electric network for the distant future

Possibilities for the formation of the. optimistic scenario are considerably less certain now in comparison with the moderate one. The key factors which will determine the optimistic scenario are caused by the following aspects:

• the scales of use of nonconventional renewable energy sources, especially new ones:
  • terrestrial solar power plants,
  • power from space, etc;
    
    
• the degree of use of intersystem effects in the joint operation of electric power systems;
  
  
• the technological progress in the means of long-distance power transmission and distribution, such as
  • new designs of transmission lines of higher transfer capability,
  • high-temperature superconductivity, and
  • super-high-frequency power transmission.

All these aspects require additional detailed studies. Hence only separate fragments of the optimistic scenario of the global electric network development can be formulated. We will analyse them on the basis of estimates of the world's energy resources from Filippov (1994).

Among all the types of renewable energy resources, hydro, wind, and solar energy are of practical concern. Table 2 presents estimates of the maximum capacity of power plants which can use the economic component of these renewable energy resources (Filippov 1994).

Analysis of tables 1 and 2 reveals the expediency in separating out the following: hydro resources in the regions of SU (Siberia and Far East), CMK, and SSEA (the western and eastern slopes of Tibet), LA (basically Brazil); wind energy resources in the regions of NA, SU, and LA; solar energy resources in the regions of ANZ, MENA, AF, LA (figure 2).

Of these three types of energy resources the hydro energy resources are the most technologically developed and convenient in terms of conditions of use. At the same time attention is paid (Filippov 1994) to the problem that the water reservoirs of hydro power plants in the equatorial zone are being severely affected by intensive processes of biomass growth and decomposition. The use of solar energy is connected with daily cycles and so requires backing-up by the capacities of other types of power plants or the use of energy storage systems. In addition, the possible environmental consequences of constructing solar conversion plants on vast areas of the deserts are not clear. The wind energy in some regions is localised in almost inaccessible and remote northern areas. Moreover, the large-scale use of wind plants on a vast territory along a coast can lead to irreversible

Table 2,Maximum capacity (in GW) of power plants for utilisation of the economic component of renewable energy resources.

climatic changes in the mainland and also to other unfavourable environmental damage (Fillipov 1994). To estimate the probable scale of practical use of renewable energy resources it seems advisable to develop only a certain fraction of cheap hydro, wind, and solar energy systems, with the ideas mentioned above and the existing experience and possible technological progress in the use of these resources taken into account. This fraction can most probably comprise 10% -20% of the cheap portion of energy resources as given in table 2.

Some comments are required concerning the possible demand for commissioning new generating capacities in different world regions for the considered period. On the one hand, as was indicated above, high growth rates of power consumption are probable in the developing countries of Asia, Africa, and Latin America, though these rates can be substantially limited by the lack of financial resources. On the other hand, despite much lower growth of power consumption in the developed countries of Europe, Asia, North America, and Australia, the existing generating facilities that have used up their resource should be replaced on a large scale with a shift of emphasis from fossil fuels to renewable energy resources. Hence, possibilities for the mass use of renewable energy resources will arise in all world regions.

Thus, it may be expected that wind energy will develop primarily in most regions. Interregional power flows from hydro power plants will probably be the same for both the optimistic and the moderate hypotheses. Power transmission to other regions can be expected from solar power plants in North Africa and Arabia as well as in Australia.

As for power production from space, its appreciable production will probably be possible towards the end of the considered period. However, possible designs cause some constraints on the location of the rectennas. Therefore, at this stage, it is accepted that in order to receive power from space, the rectennas will be located near the power consumption centres and thus will not influence the development of the global electric network.

From the above, and with consideration of the possibilities of the use of some alternative energy resources in a region, power consumption growth, a certain increase in the scales of realisation of intersystem effects and other factors, figure 2 presents estimates of possible power flows between individual regions for the remote future.

The values of power flows show that an electricity network of 1 100 - 1200 kV C These estimates underly the optimistic scenario for the global electric network. possibly higher) can develop widely in many regions and new designs will be needed in the area of power transmission in some directions. All these problems should be further investigated.

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