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Subject: POWER/EUROPEAN GRID - Consolidating European power
Date: Wed, 4 Nov 92 10:20:19 EST
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POWER/EUROPEAN GRID - Consolidating European power

Henri Persoz,     Electricite de France
Jean Remondeulaz, SA Energie de l'Ouest-Suisse


     Synchronous coupling of the power grids on either side of
the former iron curtain makes economic sense ore than any other
consumer good or service, electric energy flowing through a large
interconnected multinational system makes for solidarity among
the countries that use it. In Europe, this solidarity will
develop and broaden in scope the next few years, as the plans to
increase the electric energy exchange between its eastern and
western halves go into effect. The reciprocal solidarity ranges
from the very long term to a few seconds--from the design of the
architecture of the system to the prevent ion of serious
incidents that could have repercussions throughout the continent.
The potential benefit from such an exchange, if done
economically, is substantial--all the participating countries
together could save up to a total of a few hundred million
European Currency Units every year. (There is about 0.7 ECU to
the 1992 U.S. dollar.)
     ELECTRIC CURTAIN. After World War II, the iron curtain came
down, dividing Europe into two blocs. The Cold War mentality
affected the electric systems in Europe, and energy exchanges
between the blocs fell to practically nil. The political iron
curtain became also an electric curtain.
     However, the allure of safer and cheaper energy from
electric interconnection was strong. In the east as in the west,
national grids were beginning to operate in parallel with their
neighbors.
     On the western side, the German, Swiss, and French networks
began operating in parallel in 1957, others joined later, and
today, members of the Union for the Coordination of Production
and Transmission of Electricity (UCPTE) are operating
synchronized systems--working at the same frequency. The union,
now based in Arnhem, the Netherlands, has 12 members: Portugal,
Spain, and France, with Belgium, the Netherlands, and Luxembourg,
plus West Germany, Switzerland, Austria, Italy, Yugoslavia, and
Greece.  Albania and the continental part of Denmark (Jutland)
have joined the synchronized system, but not the UCPTE. The whole
list represents a peak demand of 220 000 MW.
     Meanwhile, in eastern Europe, Hungary was connected to
Czechoslovakia in 1953, and in 1962 East Germany, Hungary,
Czechoslovakia, Poland, and the western part of Ukraine were
synchronized. Romania joined them a year later, followed by
Bulgaria in 1967. And in 1988, the Soviet system linked up with
the Ukrainian system; the result resembles the UCPTE in power
level but not in geographical coverage--it spans over 7000 km to
Lake Baikal.
     As for northern Europe, Finland, Sweden, Norway, and
Seeland, an island part of Denmark, are interconnected today. But
the sea blocks any thought of synchronous interconnection with
the rest of the continent. Several high-voltage dc (HVDC) links
join Norway and Sweden to the UCPTE system.
     Because of the political barrier between Eastern and Western
Europe, which lasted for nearly half a century, exchanges between
them even in terms of electric energy were discouraged.
Consequently, the two blocs developed separately at the same
rated frequency of 50 Hz, but not in synchronism, that is, with
no power lines linking the two systems directly.
     Synchronized operation means that all generators producing
the same frequency operate at exactly the same speed (rotation
speed determines frequency) and that the angular positions of the
rotors are linked by a synchronizing electric torque.  Control of
the speed of all generators must be well coordinated. It must
also be consistent with the way in which each country undertakes
its fair share of the tight maintenance of frequency, that is, in
the construction of a balance between total demand an d supply.
Frequency remains at 50 Hz only if supply equals demand. If, for
instance, the instantaneous consumption goes up, the missing
energy is taken from the rotating machines--turbines and the
generators--and the machines slow down, causing a drop in
frequency until additional power is supplied to the turbines.
     As the years went by, the two systems became more at odds
technologically, a state of affairs reflected in sizeable
differences in operating standards. Frequency control, in
particular, which realizes a permanent matching of supply and
demand, conformed to a much higher standard on one side than the
other.  These differences prevented the systems' parallel
operation.
     Around 1975, many discussions took place in Geneva,
Switzerland, as part of the United Nations' Economic Commission
for Europe, to advance the synchronization of both parts of
Europe, but to no avail. In fact, though, since experts on either
side of a border always find great technical and economic
interest in trading electric energy, two types of barter
developed along the iron curtain: exchanges in pockets and by
ac/dc converter stations.
     EXCHANGES IN POCKETS. A pocket is an enclave in a system
belonging territorially to synchronized system A but connected
electrically with another synchronized system B. Part of the
production or consumption of system A is therefore synchronized
with system B [Fig. 1]. Naturally, this enclave is not
electrically connected to the remainder of A. Pockets of
production or consumption or a mixture of both can be imagined.
This problem of pockets explains why a fair number of electric
lines cross the old iron curtain today. However, the effective
power transmitted is nowhere near line capacity, because the
pockets are quite difficult to manage electrically.
     AC/DC EXCHANGES. When ac at 50 Hz is converted to dc and
back again at the same frequency, the link formed is
asynchronous, in that the two electric systems thus joined are
not synchronized. This technique is used for some energy
exchanges between, on the one hand, Czechoslovakia and Austria
(550 MW) and on the other, Russia and Finland (1000 MW). Other
converter station projects are presently under way, between
Austria and Hungary and between Germany and Czechoslovakia.
Unfortunately, the high cost of these stations inhibits the
natural desire to exchange electric energy over borders. In
contrast, the pocket is cost free (except the ac lines), but
allows exchanges only on a limited scale and over short
distances.
     PRESENT PROBLEM. The Cold War is at last over, and Europeans
to the west and east are envisioning new relationships. One
upshot should be a surge in the flow of electric energy between
both parties. The problem is whether to continue these exchanges
over dc converter stations or whether it is possible and
desirable to synchronize the systems to ensure least-cost energy
exchanges and greater political and economic solidarity between
the nations involved.
     Today, the topology of the flows of electric energy (ac and
dc) indicates four typical groups of national borders of
particular interest: to the east, the border between the former
Soviet Union (most of which is now the Commonwealth of
Independent States) and Central European countries; next, the old
iron curtain; then, a border running through roughly the middle
of Western Europe; and finally, the border between the France-
Spain-Portugal block and the remainder of Europe [Fig. 2]. The
figure prompts several observations. First, the influence of
large exporters of energy such as France or the former Soviet
Union is obvious. Curiously enough, both countries export similar
quantities, although for radically different reasons: commercial
in the West, mutual economic cooperation in the East.
     The mid-West-European border is a normal one between
countries that have signed no large import or export contracts,
but conduct classical emergency exchanges (in the event of
temporary shortages) or economic exchanges (to reduce the overall
cost of the energy produced by drawing on another's production
facilities or demand curves). This border therefore gives an idea
of the flow of exchanges that the countries are naturally
inclined to foster, to benefit from the compensation phenomena
possible through interconnection. It is not chance that exchanges
are nearly balanced on both sides.
     Because the four types of frontiers have different lengths,
it makes good electrical sense to illustrate the density of
exchanges in terms of megawatthours per kilometer of border [Fig.
3]. Compensation phenomena tend to link exchange densities to
 production and consumption densities. (The higher of the two
flows is taken each time because it represents the exchange
capacity between systems.)
     As East European economies and industries rise to about the
same level as in Western Europe, they will need to exchange ever
higher power densities with the western countries, until these
exchanges have reached a level at least 10 times that of to
day. This level simply reflects the quest for the benefit
provided by the classical phenomenon of the interconnection of
systems. Additional exchanges could arise from time differences
between countries. And if these countries become large exporters
to or importers from the West, the volume of exchanges could be
markedly higher.
     EAST-WEST CONTRACTS LIKELY? The key question is whether it
is likely that large trade contracts will in the future be signed
throughout Europe, especially across the old iron curtain. It is
well known that it costs more to transmit electric energy
 than to transport primary fuel, and it is also sometimes more
difficult to transmit electric energy because few people enjoy
the eyesore of extrahigh-voltage (EHV) lines.
     Nevertheless, popular opposition makes it difficult to build
generating plants, whether nuclear, thermal or hydroelectric, in
some countries, notably Italy and Switzerland. These nations are
therefore forced to buy electric energy, in far from negligible
quantities, from other countries and are presently hoping to turn
to central or east European countries for their supplies.
     As things stand, the last countries lack adequate installed
capacity because many power plants there are obsolete. Nor are
they organized, either financially or industrially, to build the
missing generating facilities rapidly. They are envisioning
collaboration with West European utilities, which would provide
capital and know-how in return for sending part of the new
generated power to Western Europe.
     Although not a certainty today, it can be predicted that
long-term electric energy exchange contracts will be signed
between Eastern and Western Europe, increasing the need for
exchanges between these two regions. Some specific projects--for
example, between Russia and Germany--are under study.
     However, these projects are somewhat contrived in that
transmitting electricity over long distances is expensive and
difficult, and the importing country must worry about the safety
of the energy supply. In addition, it poses general security
problems for European countries at large: the sudden outage of an
important transmission line in Europe would subject more than one
country to instantaneous repercussions, events that utilities are
unsure they can fully master. In the long term, the most likely
thing is that collective wisdom should prevail, with each country
resuming a policy of self-sufficiency, and with national electric
output roughly meeting national demand.
     Despite the above, the East-West electric energy flows are
bound to increase in the future by at least a factor of 10. If
so, planners will have to determine whether this increase will
have to be carried by costly ac/dc converter stations or whether
the synchronization of both systems would obviate the need for
them.
     AC AND DC INTERCONNECTION. Schematically, the dc technique
can be used in two ways: without or with dc lines. The first is
the way it is done today, using back-to-back stations along the
old border between Eastern and Western Europe, with one and
the same building housing both ac/dc and dc/ac conversion
stations, so that no dc line is needed. These stations would be
strung along the border between the synchronized systems. The
other approach is to build one or several dc lines, penetrating
some distance into both synchronized systems to form so-called
"staples." The conversion stations are then at either end of the
line and also, if necessary, at intermediate points, forming a
multi-terminal configuration.
     One advantage of back-to-back converter stations is their
total control over electric power flowing through the two
electric systems they join, while in the event of a serious
incident, they provide an additional degree of freedom in
preventing cascading collapses. Each of the systems connected by
back-to-back converter stations must be responsible for its own
frequency control.
     To some extent, these converter stations, insofar as they
are not too numerous, uncouple the problems and simplify the
necessary real-time coordination of system management. Their main
drawback is their cost. For example, the energy cost penalty due
to the use of these stations is approximately 0.5 percent of an
ECU per kilowatthour. Consequently, only a few countries can
afford them. East-West transfers would then flow through rather
few points--an undesirable situation for both technical and
political reasons. Free trade in electricity would be markedly
reduced and European solidarity would suffer.
     STAPLED SYSTEMS. Like the back-to-back configuration, the
stapling together of two systems by dc lines gives good control
of power flow between the systems. Also, dc lines themselves are
cheaper than ac lines because the insulation voltage for the dc
lines is lower by a factor of the square root of 2--the ratio of
maximum (peak) to effective voltage. And when dc lines are at
least 700 km long, the expense associated with the converter
stations can be justified. Another advantage is the option of
laying relatively short dc transmission cables underground in
those areas where the topography is extremely unsuited to
overhead lines. Because of the high cost involved, however, this
option should be limited to only a few locations. All of the
above make stapled systems adequate for long-distance power
exchanges.
     The construction of long high-power lines, however, hinges
on accurate knowledge of the trend of electric energy flows in
Europe over the next 20 years. Such a forecast is not readily
available. Nor are long high-power dc lines very suitable for
natural compensation flows of the kind mentioned earlier, since
these flows vary over time in both magnitude and direction. The
meshed system, comprising many interlinked meshes, is far better
adapted to these flows.
     Stapled systems also are expensive, and difficult technical
problems are encountered in building intermediate conversion
stations along the dc transmission lines, wherever power
exchanges are needed. Without these intermediate stations, the
risk is that electric energy will be transmitted unnecessarily
from one end of the line to the other and some or all of it will
have to be sent part of the way back over the underlying network.
     Then there is the security of the general system. When the
sudden outage of a transeuropean transmission line causes
disruptions, it must be possible to control it fully.  Finally,
the high level of power concentration required for the economic
viability of the project--typically at least 3000 MW--is even
more obvious than in the case of back-to-back stations. This
concentration is not helpful either to general security or to the
organization of energy flows from any point in Europe to another.
     EXISTING AC LINES. Most of the ac transmission lines that
would be used in East-West power exchanges are in place. It will
be possible, at reasonable cost, to organize electricity
exchanges between all regions on either side of the former East-
West border.  In general, the existing ac transmission lines
allow a better coordination between systems on both sides of the
border, at optimized cost, and in a far more flexible manner than
the dc systems would allow.
     Ac connection would conduce to the creation of a very large
synchronous system. As a result, utilities on both sides of the
border would have to overcome the increased complexity of the
organizations of the different utilities.
     COLLABORATION.  International collaboration on this
important technical issue is essential. Within an interconnected
electric system, a stable frequency is a common resource that
must be managed collectively. Patient, joint development of
general guidelines is a must.
     Once general guidelines have been set, the modalities of
implementation of East-West power exchanges are subject to
bilateral negotiations between countries with common frontiers.
The Paris-based International Union of Producers and Distributors
of Electrical Energy (Unipede), speaking through its Large
Systems and International Interconnections Study Committee, in
March 1990 agreed with UCPTE to create an ad hoc working group,
common to both organizations. This group is responsible for
examining the whole issue, and more particularly, for indicating
whether ac connection is technically possible, and if so, when
and under what conditions.
     This group was the first extraordinary exchange forum for
experts from both sides of the former iron curtain. They were
unaccustomed to speaking to each other, let alone to exchanging
technical views on how their systems operate. In addition to We
stern and Northern European representatives, this group comprises
representatives from Czechoslovakia, Hungary, Poland, the
Commonwealth of Independent States (the former Soviet Union),
Bulgaria, Romania, Yugoslavia, and Turkey.
     From the many discussions that took place, it became clear
that synchronous interconnection of Europe as a whole is
desirable after the following points have been solved:
  * The Commonwealth of Independent States (CIS) is at present
handling frequency control for the whole East European system.
The interconnection of UCPTE and East European countries, unaided
by CIS, would therefore require the Easterners to implement a
frequency control as efficient as that of the UCPTE. Doing this
could involve the construction of additional generating sets.
More generally, countries that are candidates for entry into the
synchronized system should offer the same reliability and same
standard of service as those of Western countries.
  * Given the magnitude of the new Commonwealth's electric system
(the power level of its grid is equivalent to that of all UCPTE
countries put together), the system forms a special case that
needs to be examined separately. This study has not yet been
finished by the group. Because the extension to the synchronous
system will have to be organized progressively, initial couplings
are unlikely to include the Commonwealth.
  * That situation underscores the problem of such countries as
Hungary and Bulgaria. As part of old contracts, they continuously
receive a share of their electric energy from the CIS. They
cannot be synchronized with both the UCPTE and the Commonwealth.
 The problem of imports from the Commonwealth is therefore a
little annoying. It could be solved by preserving the pockets in
countries such as Hungary, Bulgaria, and to a far lesser extent,
Czechoslovakia, letting them remain synchronized with the
Commonwealth grid; then the rest of the country could be
synchronized with the UCPTE, by installing back-to-back dc
stations at the end of the lines coming from the Commonwealth.
The ideal situation would of course be to dismantle the stations
located near the present UCPTE border and to re-assemble them
closer to the old USSR border line, an act that may save
approximately 50 percent of the cost. However, this problem is
temporarily less acute, due to the decline in consumption in
Hungary and Bulgaria .
  * Although there are numerous transmission lines that connect
Eastern and Western Europe [Fig. 4], the eastern and western
systems have each been structured to meet the exchanges specific
to them. The interconnection of the two grids could cause
undesirable loop transfers (transfers due to the Kirchoff law
rather than the will of the dispatcher) and necessitate a change
in the internal structure of these systems. This possibility is
presently under study. Austria has already undertaken initial
calculations that show how a power flow through Europe is
distributed amongst countries.
  * The general security of the interconnected system should be
examined and adequate protection installed to prevent a major
incident from sweeping Europe from end to end.
     The working group made its initial report to the Unipede
Copenhagen Congress in June 1991. It concluded that synchronous
coupling between the Eastern and Western Europe is possible
provided that the technical problems mentioned earlier be solved
beforehand. The group estimated the time needed to find solutions
at 5-10 years.
     THREE STAGES. A progressive approach is essential in this
field, so that synchronization may have to follow three stages.
First would come Czechoslovakia, Poland, and Hungary. Next would
come countries like Bulgaria, Rumania, and Turkey.  Finally,
extensions would be possible into yet other countries.
     The working group is continuing its studies and refining its
analyses. It will be presenting its final conclusions within the
next few months, because Europe is making history very quickly
today, and those involved in electric power cannot afford
to be left behind.
     The question of the long-term future of the European
electric system is also posed in parallel to the problem of East-
West interconnection. Will there really be large transfers of
energy across Europe? How far can the synchronous system go? For
example, the present intention is to extend it into North Africa.
Is it now time to examine the usefulness of a higher voltage
level? Should dc play a new role? Or will the 400-kV meshed
system remain for now the basis of the European system? Another
Unipede-UCPTE group is proposing to examine these issues, taking
over from the initial group, but from the long-term point of
view.
     In conclusion, no one should underestimate the difficulties
caused by the technical and cultural gap between the two parts of
Europe or the self-interest with which each country views the
problems. Much work has already been done, but the hardest
part lies ahead. However, the interest of electric
interconnections and the solidarity it represents is too great
for experts in electricity not to achieve their goal, despite the
upheavals yet to be expected from history.
     TO PROBE FURTHER. The source paper for this article,
"Cooperation in the field of electric systems and between Eastern
and Western Europe," will appear in the multi-volume proceedings
of the 15th World Energy Council (WEC) Congress. WEC scheduled
this congress for Madrid, Sept. 20-25, 1992, on the theme of
energy and life. For more information on the copyrighted article,
contact WEC at 34 St. James's St., London SW1A 1HD, United
Kingdom; (44+71) 930 3900; fax, (44+71) 925 0452.
     ABOUT THE AUTHORS. Henri Persoz (F) is general inspector for
the generation and transmission system of Electricit{x,q}e de
France. He is also the chairman of the Large Systems and
International Interconnections Study Committee of the
International Union of Producers and Distributors of Electrical
Energy (Unipede).
     Jean Remondeulaz is chairman of the East West
Interconnection mixed group of Unipede and the Union for the
Coordination of Production and Transmission of Electricity
(UCPTE). He is also the director of SA L'Energie de l'Ouest-
Suisse


Copyright 1992, IEEE Spectrum.

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