CIGRE: 1984 Session
PRESENT LIMITS OF VERY LONG DISTANCE TRANSMISSION
SYSTEMS
By L. Paris, G. Zini, M. Valtorta, G. Manzoni,
and N. De Franco
Summary
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:
1. Introduction
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great distances today no longer represent a fundamental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.
8. Conclusions
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.)
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