Smart utilization and upgrading
of existing transmission assets
Compact lines with high SIL
A.Clerici
Senior Corporate Advisor CESI SpA Italy
Honorary Chairman WEC Italy--Vice President IEC Italy
UPME - Bogotá – November 10, 2013
INDEX
1. A global energy view
2. The electrical system &Smart Grids
3. Transmission & upgrading of
existing assets
4. Compact lines with high SIL
5. Compact Lines for Suburban Areas
6. Conclusions
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1. A global energy view
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• World population now 7 billion people: (300,000 births/day).
• In the last 20 years: population +27%; primary energy +48%;
electricity +76% (from WER of WEC)
• 1.3 billion human beings with no electricity.
• Electric Energy consumption in 2030 will be about double
quantity of 2007 with 44% of primary energy resources for
its production (36% in 2007).
Worldwide 40% of CO2 emissions connected to energy are
caused by production of electricity : 12 billion t/year.
Electricity is more and more important.
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Patterns of primary energy demand: elaboration of IEA data
Current Policies (BAU)
2000
2010
2020
2035
New Policies
2020
2035
450 Scenario
2020
2035
COAL
23,6%
27,3%
28,8%
29,6%
27,4%
24,5%
25,2%
15,8%
OIL
36,2%
32,3%
29,6%
27,1%
29,9%
27,1%
30,2%
24,9%
GAS
20,5%
21,5%
21,8%
23,5%
21,9%
23,9%
21,7%
22,3%
NUCLEAR
6,7%
5,6%
5,8%
5,5%
6,0%
6,6%
6,6%
10,5%
HYDRO
2,2%
2,3%
2,5%
2,5%
2,6%
2,8%
2,8%
3,6%
10,2%
10,0%
9,8%
9,3%
10,3%
10,9%
11,1%
15,1%
0,6%
0,9%
1,7%
2,7%
2,0%
4,1%
2,4%
7,8%
10097
12730
15332
18676
14922
17197
14176
14793
BIOENERGY
OTHER RENEWABLES
TOTAL (Mtoe)
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Conventional fossil fuel resources have a reserve (R) to present
consumption (C) ratio R/C
(from WER 2013 of WEC)
118 years for coal,
60 years for natural gas
56 years for oil.
But the technology developments and the high price of oil at around
100$/barrel make convenient also the use of huge reserves of
unconventional oil and unconventional gas (see the shale gas revolution
in USA) which are around 3 times those of the conventional fuels.
Fossil fuels availability is therefore not a real problem for around 200
years; the key issues are:
• their reserves are unevenly distributed between production and
consumption areas with the well-known socio-political implications;
• the impact on environment for their extraction, production and
“burning”.
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Electricity installed capacity and energy production worldwide
(source Terna and CESI elaborations)
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Trend over the first decade of 3rd millennium for the power production
worldwide from different primary resources
(CESI elaborations from IEA data)
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2. The electrical system
& Smart Grids
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An Electrical system ranges from power
generation, transmission, distribution to final
consumption.
Key issue is the reliable and economic flow of
energy at any time from any generating plant to
any load.
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Deregulation and the opening of markets have
pushed for unbundling of:
•
•
•
•
Production
Transmission
Distribution
Sales
P
T
D
S
and this with proliferation of entities, split
responsibilities, different / conflicting interests.
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On the other hand:
•
•
•
•
Environmental issues.
Increase of RES penetration (both large/bulk and distributed).
Increased request of demand response systems.
The always increasing difficulty to build new transmission lines
and substations.
• The development of Technologies in both the electric “power
industry” and in the ICT arena.
are pushing for a better and indispensable integration of
the operation of P - T – D and clients/”prosumers”.
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Main impacts of an high % of nonprogrammable RES generation on the
power system
•
•
•
•
•
•
•
Impact on the day-ahead power market
Load following
Risk of “overgeneration”
Need for additional reserve
Network congestions
Risk of RES generating unit cascade disconnection
Dynamic stability and quality of supply
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Everything is becoming “smart”. Some titles of newspapers:
“SMART DOMESTIC
APPLIANCES”
“SMART
PRICING”
“SMART
PRODUCTION”
“SMART
HOME”
“SMART TRANSPORTS”
“SMART DISTRIBUTION”
“SMART
CITIES”
“SMART
BUILDINGS”
“SMART
HARBOURS”
Smart… smart… smart…
When a real concern on smart transmission systems?
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For smart grids:
• Advanced hardware (power system infrastructures)
• Advanced ICT’s (and a terrific number of data are
involved) are the key ingredients
ICT is an asset but… without adequate infrastructures
does not solve the problem; ICT cannot control the flow of
electrons if there are no adequate overhead lines (OHTL’s)
and substations.
But also vice versa, there is no optimum utilization of
power system infrastructures without ICT.
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MY DEFINITION
A smart grid (or better a smart electrical system) is an
evolved system from any type of production to consumers
that manages the electricity production, transmission,
distribution
and
demand
through
measuring,
communicating, elaborating and controlling all the on line
quantities of interest with transparent info accessible to all
the involved stakeholders; this to optimize the valorization
of assets and the reliable and economic operation
allowing adequate global savings with smart sharing of
costs and benefits among all the involved.
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3 .Transmission &
upgrading of existing
assets
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Interconnection benefits:
political, technical, economical
and environmental
•
New interconnections between different areas /countries, can
help achieve global, regional and national primary energy goals
improving security of energy supply
• The development of interconnection capacity between countries
(or areas) allows greater electrical system reliability and
flexibility in the generation mix and operations
• The availability of cross-border/cross areas transmission capacity,
may help select power from cheaper (including environmental
costs) units located in another area, country or region and to
“capture” the best of renewables
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Interconnections:
key role of technologies
OHTL
Underground and undersea cables
AC substations
AC/DC converters
Back-to-back stations
Power electronics (FACTS)
Protections
Controls
ICT
Smart Grids
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Strong opposition and very long times to
implement OHTL’s
From the conceptual engineering of a new OHTL of
some dozens of km to its commissioning, the average
time in EU is above 10 years… and disregarding those
cases of infinite time (impossibility to arrive at final
completion).
And we have the 25 years of the Spain – France
interconnection now in construction, and we have the
18 years of the Matera – Santa Sofia in Italy
..In China less than 4 years from initial thinking to
commissioning of a 2000 km + 800 kV UHVDC line
carrying 7000 MW
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OHTL’s :the most critical subsystem of the
electrical power system for environmental concerns
OHTL’s are becoming even more critical than Power
Plants;they involve:
- many countries,regions municipalities
- many authorities(PTT,Railways,Highways/roads,…etc)
-many land owners,nice landscapes, populated area
+ EMF
Underground cables:yes but
cost + technical limits for AC
No new lines,no power upgrading----no new loads –no new
generation-no development of the country
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Control and actions of FACTS devices
to increase line power transfer limited by external system
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FACTS: Flexible Alternating Current Trans. Systems
• A variety of power electronic equipment for
application in transmission systems has been
developed over the last few decades. The incentive
has been the need for:
• better load flow control;
• improved system dynamics;
• and better voltage control.
• FACTS devices help in increasing transport capacity,
in avoiding loop power flows,in improving transient
and dynamic stability etc but do not increase the
inherent transmission capacity of a line or trafo
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Considering the key bottle neck in electrical power
systems is transmission, the quick application of smart
grid concepts to transmission should be implemented
as soon as possible .
smart grid concepts must include
“smart upgrading” of existing assets with
And
special reference to transmission line corridors and
optimum utilization of substations with relevant
transformers.
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Upgrading of existing Right of Way (RoW) corridors
Many alternatives:
use of new conductors (eg. ACCC, etc.) which allow a 1.5-2
power transfer increase with no changes in towers/foundations;
voltage upgrading of an AC line maximizing use of present
towers/conductors with application of horizontal V insulators;
transformation of an existing AC line with a DC one making
maximum use of conductors and towers with up to 4 times
transfer capacity increase;
substitution of an existing AC line with a compact one at higher
voltage or with a DC one (no limit to power transfer with poles
in vertical position).
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Transformation of an ac line to a new one at higher voltage
The Figure shows the study performed on a 230 kV Italian double circuit line
equipped with single ø 31 mm conductor per phase.On existing tower body
and foundations, substituting the 6 arms with “horizontal V” pivoted insulator
assemblies you get a 400 kV circuit with 2 conductors per phase . Both the
mechanical stresses to the tower and foundations and electrical problems (RIV,
corona, electric and magnetic fields, etc.) have been deeply investigated and solved.
The power increase got was of 1.7 times .
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Transformation of an existing line from AC operation to
DC operation
Studies have been performed since the 90’s (ref. Clerici, Paris) to utilize as
much as possible the components of an existing line (conductors, towers,
foundations) in order to increase transmissible power in a HVDC mode .
Clearly the AC insulators must be substituted by special DC ones; type and
numbers of DC insulators depend on contamination conditions and on
maximum DC voltage level applicable in the specific case.
The type of tower of the existing AC lines which is the best for
transformation is the double circuit one with one circuit in vertical
disposition on both sides of the tower.
According to the length/type of the AC insulator strings and according to
clearances to tower and ground, the easiest transformation is the one
implying the simple substitution of AC insulators with the maximum
possible length of the DC ones; this determines the maximum DC voltage
and therefore the DC power got. The maximum upgrading is given by
eliminating the arms of existing AC towers and substituting them with two
new arms in suitable position to match mechanical and electrical stresses.
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Possible transformation of Italian 220 kV AC lines to HVDC
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Transformation of an existing line from AC operation to DC operation
Study performed on a 230 kV Latin American line to get the maximum
power increase. In the specific case, the transformation to DC ±500 kV not
only improves the power transfer on the specific line; the DC control of
terminal stations is useful to damp system oscillations due to faults on the
parallel 400 kV system and in addition to improve the transfer capacity on
the 400 kV system itself.
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CONVERSION OF A DOUBLE CIRCUIT 230 kV AC LINE
TO A +/- 500 kV DC ONE
UPME - Bogotá – November 10, 2013
Transformation of a line from AC to DC operation
Study performed on a double circuit 400 kV AC line of a ME country; only
one of the 2 circuits is transformed to DC and possible “hot line
transformation” has been investigated with the remaining AC circuit in
operation. Detailed studies have been performed for mutual interactions
of DC and AC circuit both in steady state and transient conditions (induced
voltages and currents from one circuit to the other one). The studies have
shown a global increase of transferred power on the AC/DC line about 3
times that of the previous AC one with the additional advantages above
mentioned relevant to the special controls of DC terminals.
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Replacing in the same
corridor an AC line with a
bipolar DC one
No special limits for power
increase with the new
designed DC line. The limits
are imposed by the electric
field at the border of the
ROW (right of way). To
minimize these problems the
new line could be built with
vertical position of the two
poles as shown in the figure.
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Upgrading Transmissible power in existing corridors
Replacing in the same corridor some existing AC lines
with new compact AC ones in higher number and/or voltage
Study performed (by Clerici and Paris) on a corridor entering Rio de Janeiro. The 2
conventional double circuit 138 kV lines could be substituted by 3 parallel compact
double circuit lines, 2 at 138 kV and one at 500 kV with a very substantial power
increase (more than 10 times).
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Upgrading Transmissible power in existing corridors
Conclusions
There are no limits to imagination for possible solutions to improve the power
transfer capability of existing transmission lines or transmission line corridors.
Different possible solutions with different power increase/costs can be
considered.
Clearly the key issues are :
• the actual possibility to take out of service the specific AC line and for how
much time during the “transformation period”;
• specific problems relevant to existing anchor towers, angle towers, etc.;
• the length of line involved even if entering/exit from substations could
consider a new transformed line as a series of 2-3 original AC ones;
• the cost/space of DC stations in case of transformation of AC into DC lines;
• the actual “power increase” acceptable by the networks at both ends of the
line;
• the local standards (including possible hot line maintenance, RIV, AN, EMF
limits, etc.) and conditions posed by technical problems (e.g. local
contamination), by accesses and logistics and by local costs including cost of
losses.
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Better utilization of existing OHTL’s
(dynamic loading)
OHTL’s have:
• a summer current limit (and consequent power) valid for all the summer
months/hours;
• a winter current limit valid for all the winter months/hours.
based on critical / extreme ambient wind / temperature to avoid
excessive sags of conductors.
An on line monitoring of conductor current/ temperature, sags and
ambient conditions (LTM Line Thermal Monitoring):
• allows larger transfer capacity in the great majority of hours;
• allows an alleviation of N-1 conditions (to be reconsidered).
Effect on standards and operating rules
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Better utilization of trafos
• Also trafos have pass-through power limits depending from
ambient conditions and actual hot spot temperature.
• 2 interconnecting trafos are usually working in parallel at 50% of
load to avoid overloading of the parallel one in case of a trafo
fault.
• Adequate monitoring and diagnostics systems and control of
ambient and winding hot spot temperature would increase the
utilization of the machines both in normal and emergency
conditions; this minimizes:
− Possible consequences on the transmission system from
transformer faults;
− Restrictions of operation for possible overloads that are not
overloads in many specific conditions.
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4.
Compact lines with high SIL
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Simple formulas for the electrical behaviour of AC OHTL’s
The transmission power over an OHTL is a function of the main line
parameters and of the voltage at sending and receiving ends. Simple
formulas can be derived for EHV transmission where series and shunt
losses are negligible
.
For a lossless OHTL, the electric power transferred from A to B in a
transmission system is given by:
dlim is the phase angle between VA and VB which for stability problems must
be limited to 25°-30°
XAB is the equivalent series reactance between A and B that for a lossless
OHTL is equal to:
L, C = phase inductance/capacitance per km
A = line length in km
w = 2pf
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Simple formulas for the electrical behaviour of AC OHTL’s
GMD = Geometric Mean Distance between the phases;
Req = equivalent Radius of phase bundle conductors.
Considering in first approximation VA = VB = V
where V2/Zs is the so-called Surge Impedance Loading (SIL) of the line.
TO INCREASE SIL ONE MUST DECREASE SURGE IMPEDANCE
VALUE
-- LOWER GMD (DISTANCE BETWEEN PHASES)
-- INCREASE THE EQUIVALENT RADIUS OF THE BUNBLE
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COMPACT LINES FOR LONG TRANSMISSION
GMD
ROW
SIL
SIL/ROW
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COMPACT LINES FOR LONG TRANSMISSION
GMD
ROW
SIL
SIL/ROW
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Transmissible power as a function of voltage and of OHTL length
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4
HVAC Compact Lines
Brazil
500 kV AC line
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1050 kV ITALIAN PROJECT
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OHTL WITH EXPANDED BUNDLE
CONDUCTORS CONFIGURATION
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LARGE BUNDLE CONDUCTORS
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KEY ISSUE – STRINGING TECHNOLOGIES AND
EQUIPMENT
1000 kV line – China
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STRINGING OF LARGE BUNDLE CONDUCTORS
Four machines connected working as puller guaranteed the simultaneous stringing of 8
bundled conductors with 8 independent pulling ropes at the max total force of 360 kN.
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BRAZIL – RIO MADEIRA DC +/- 600 kV line
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BRAZIL – RIO MADEIRA DC +/- 600 kV line
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5. COMPACT LINES FOR
SUBURBAN AREAS
You can meet
Compact
Line in
Florence
Area
La nuova soluzione
SAE-Saldemi “Open
Welded Tubes”
composed by a pair of
cold-formed sections
connected by round
bars welded thru robots
Egitto: Cairo South 2 doppie terne 230 kV compatte
6. Conclusions
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 Many things, can be called “smart”, but discussions of
“smart grids” are often limited to distribution
systems.
 The development of new bulk and distributed RES
generation and the difficulties for new corridors for
transmission lines are pushing for quick application
of “smart” technologies to transmission systems.
 “Smart Grid” concept must include and give special
attention to transmission.
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• A correct «smart grid approach» must consider the
complete electrical power system,that is :
generation,transmission , distribution and the final
clients.
• Final scope of a smart grids should be that to
optimize the reliable and economic utilization of
present(with appropriate upgradings) and future
assets with fare sharing of the benefits and
information between the involved stakeholders
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Smart Grids
• The data in real time would not be only electrical but
also associated with weather conditions (temperature
and sags of line conductors, possible transformer
overloads due to actual temperature, etc.) and data
relevant to diagnostics.
• ICT
will clearly contribute to the successful
introduction of modern “smart” systems but it cannot
replace the need for development of key power
system infrastructures.
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• For an effective and inherently gradual
application of smart grid concepts,a more
practical vision is necessary with clear steps
of implementations based on detailed
technical and economical analyses and
financing structures.
• Let us stop a lot of bla,bla,bla and an abuse of
the term smart
• Let us avoid the usual approach of long term
incentives using the final clients as a
«bancomat»
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Smart Grids
The smart grid approach must for each specific
application define
WHO IS INVESTING AND WHO IS PAYING
• SMART GRIDS CANNOT BE THE ONLY
PANACEA SOLVING ALL THE PROBLEMS
• SMART TRANSMISSION, including
upgrading of existing assets, is the best
renewable energy source available today
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Thank you for listening!
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