CIGRE: 1984 Session
PRESENT LIMITS OF VERY LONG DISTANCE TRANSMISSION SYSTEMS
By L. Paris, G. Zini, M. Valtorta, G. Manzoni, and N. De Franco
Energy resources available at sites far away from load centres can become competitive as a result of the present high cost of the energy available at nearby sites, and of the recent development of transmission technology.
The paper gives a thorough analysis of the conditions that determine the competitiveness of electric energy transmission over very-long-distance (VLD) transmission exceeding 2000 kilometers, by means of technical and economic assessments, based on the present state of the art and on the developments expected in the short term.
Investment cost, efficiency and reliability of VLD transmission system (TS), both AC and DC, have accordingly been determined.
A further stage deals with the optimization of system variables, based on the minimum cost of the energy delivered, which renders the characteristics of the transmission system independent of those of the receiving system. The consequences for the receiving system of the different reliability of the various TS considered, are taken into account by adding risk-cost.
Based on this, the competitiveness limits of remote energy resources are then determined as a function of:
Some parts of the world have hydraulic resources that can be exploited at low cost for the production of electricity. Examples of this are the Amazon basin, the River Zaire (Inga) , South-West of China, etc. There are also coalbeds that could be exploited in the vicinity of the mines to provide low-cost electric power.
One of the reasons why these resources have never been utilized is their great distance from any consumer areas. The increased cost of electricity generated by power stations located in consumer areas plus the progress achieved in transmission technology means that the exploitation of these remote resources is now becoming competitive.
We therefore decided to produce a technical and economical assessment that would, as far as possible, have general validity, and serve as an instrument for the rapid evaluation of the competitiveness of remote energy sources, at the same time showing that great distances today no longer represent a fundamental obstacle to the exploitation of those sources.
The exploitation of remote energy sources at low cost (e.g. hydro or mine-mouth, coal-fired plant suitable for producing electricity at a cost of the order of 10 - 25 mills/kWh) is now feasible and economical for distances never before entertained. For example, transmission systems can be set-up over a distance of as much as 7000 km in d.c and 3000-4000 km in a.c. such that, by offering an acceptable reliability level for the receiving system concerned, present costs small enough (from 5 to 20 mills/kwh) as to make advantageous the exploitation of those sources, when compared to generation at 30 - 35 mills/kWh located in the vicinity of load centers.
The unit cost of the electric power, transmitted by d.c, shows only small increases when increasing transmission distance: for every additional 1000 km the increase is of the order of 1.5 and 2.6 mills/kWh for transmission of 10 GW and 2.5 GW respectively. By consequence, variations in the cost of energy produced close to consumption centers (as determined by market prices) that may even be smaller than those registered during the past ten years, results in shifts of hundreds (or thousands) of km in the competitive distances of remote sources.
The effect of scale on transmission cost is - at least up to 10 GW - considerable: unit costs decrease approximately proportionally to p-0.4.
Although the above-mentioned transmission costs were obtained with reference to transmission schemes with two lines (two bi-poles in the case of d.c.), they are nevertheless representative also of the cost of different schemes (see 6.1), since the effect of transmission reliability has been costed and included.
Finally it may be interesting to note that for transmission systems similar to those above described advanced studies are being carried out in Brazil. Those studies, out of which some preliminary information has been here used, confirm the feasibility of the transmission from Amazon region over a distance of about 2500 km, being the implementation foreseen for the mid-nineties, hinging on the growth rate of electricity consumption in the country.
**Only Summary, Introduction and Conclusions are included above. Click here for a pdf version of the entire paper (5 MB download).