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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

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

INDEX

2 UPME - Bogotá – November 10, 2013

1. A global energy view


• 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.


Patterns of primary energy demand: elaboration of IEA data

2000 2010 2020 2035 2020 2035 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%

BIOENERGY 10,2% 10,0% 9,8% 9,3% 10,3% 10,9% 11,1% 15,1%

OTHER RENEWABLES 0,6% 0,9% 1,7% 2,7% 2,0% 4,1% 2,4% 7,8%

TOTAL (Mtoe) 10097 12730 15332 18676 14922 17197 14176 14793

450 ScenarioCurrent Policies (BAU) New Policies


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”.


Electricity installed capacity and energy production worldwide (source Terna and CESI elaborations)


Trend over the first decade of 3rd millennium for the power production worldwide from different primary resources (CESI elaborations from IEA data)


2. The electrical system & Smart Grids


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.


Deregulation and the opening of markets have pushed for unbundling of:

• Production P

• Transmission T

• Distribution D

• Sales S

and this with proliferation of entities, split responsibilities, different / conflicting interests.


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”.


Main impacts of an high % of non-programmable 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


Smart… smart… smart…

When a real concern on smart transmission systems?

Everything is becoming “smart”. Some titles of newspapers:

“SMART DOMESTIC

APPLIANCES”

“SMART TRANSPORTS”

“SMART DISTRIBUTION”

“SMART

PRODUCTION”

“SMART

BUILDINGS”

“SMART

PRICING”

“SMART

HOME”

“SMART

CITIES” “SMART

HARBOURS”


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.


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.


3 .Transmission & upgrading of existing assets


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


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


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

Strong opposition and very long times to implement OHTL’s


21

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 UPME - Bogotá – November 10, 2013

Control and actions of FACTS devices

to increase line power transfer limited by external system


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


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 .

And smart grid concepts must include “smart upgrading” of existing assets with

special reference to transmission line corridors and optimum utilization of substations with relevant transformers.


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).

Upgrading of existing Right of Way (RoW) corridors


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 .


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.


Possible transformation of Italian 220 kV AC lines to HVDC


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.


CONVERSION OF A DOUBLE CIRCUIT 230 kV AC LINE

TO A +/- 500 kV DC ONE


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.


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.


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).

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.

Upgrading Transmissible power in existing corridors


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).

Better utilization of existing OHTL’s (dynamic loading)

Effect on standards and operating rules


• 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.

Better utilization of trafos


39

4. Compact lines with high SIL


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


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


GMD

ROW

SIL

SIL/ROW

COMPACT LINES FOR LONG TRANSMISSION


COMPACT LINES FOR LONG TRANSMISSION

GMD

ROW

SIL

SIL/ROW


Transmissible power as a function of voltage and of OHTL length

44


HVAC Compact Lines

Brazil

500 kV AC line


1050 kV ITALIAN PROJECT


OHTL WITH EXPANDED BUNDLE

CONDUCTORS CONFIGURATION


LARGE BUNDLE CONDUCTORS


KEY ISSUE – STRINGING TECHNOLOGIES AND

EQUIPMENT 1000 kV line – China


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.


BRAZIL – RIO MADEIRA DC +/- 600 kV line


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


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.


• 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


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.


• 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»


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


Thank you for listening!


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