high temperature –low sag (htls) conductors...tension in theconductorspan. • cores may be of...

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وزارة الكهرباء والطاقة المتجددة

Egypt

High Temperature – Low Sag

(HTLS) Conductors

Professor Ahdab Elmorshedy

President of the Egyptian CIGRE

National Committee

Ministry of Electricity and

Renewable Energy

1Professor Ahdab Elmorshedy


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1. Introduction

2. Methods of Increasing Lines Capacity

3. Transmission Conductors

• Conventional Types of Conductors

• High Temperature Low Sag (HTLS) Conductors

4. Types of HTLS Conductors

5. Advantages of HTLS Conductors

6. Gap and Invar Conductors

• Design Concept of Gap and Invar Conductors

• Supply Record of JPS HTLS Conductors

• Gap type conductor: Maintenance

7. Disadvantages of HTLS Conductors2

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1. Introduction

• There is a growing need to increase the power

handling capacity of existing power

transmission assets.

• There is fierce opposition to the construction

of new lines and the ability of obtaining right

of ways is more and more difficult.



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• As a result: increasing the thermal rating of

existing overhead transmission lines is seen as

a valid alternative to the construction of new

lines.

• One of the prime physical limits on overhead

transmission lines is conductor sag.


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• Sag is limited to meet the clearance requirements

� of the line,

� between the line and ground, and

� between conductors, under maximum load

conditions.

• If the sag is too large, it may cause

� a short circuit between the line and objects below it or

� a short circuit between lines in extremely windy

conditions.



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Professor Ahdab Elmorshedy 6

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• Conductor sag in a transmission line span is

affected by both temperature and ice, which

increases the weight on the span.

• In Egypt, conductor temperature is the most

influential factor on sag.

• This limits the amount of current which is

allowed to flow in the transmission line.



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Conductor temperature

The temperature of a conductor depends on a

number of factors including:

• Current flowing in the conductor

• Ambient temperature

• Solar radiation level

• Wind speed


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Temperature Effects on Aluminum

Conductors

• Standard overhead conductors are made from hard

drawn aluminum (HDA), which increases the tensile

strength over that of aluminum rod by a factor of

almost three.

• However this limits the temperature, as above 100°C

the HDA starts to anneal and lose its tensile strength.

Anneal: to make metal or glass soft by heating

and then cooling it slowly to free from internal

stress.



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1. Introduction












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• Increment of the line voltage

• Increment conductor tension

• Increment of conductor section

• Installation of bundle conductor

- very expensive solutions, cause problems in

towers, necessity of reinforce tower,

foundations, permissions, higher right of ways.



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1. Introduction












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Conventional Types of Conductors

• There is no unique process by which all transmission

and/or distribution lines are designed.

• The major cost components of line design depend upon

the conductor electrical and mechanical parameters.

• There are four major types of overhead conductors used

for electrical transmission and distribution.

1. AAC - All Aluminum Conductor

2. ACSR - Aluminum Conductor Steel Reinforced

3. AAAC - All Aluminum Alloy Conductor

4. ACAR - Aluminum Conductor Aluminum-Alloy

ReinforcedProfessor Ahdab Elmorshedy 14

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1- ACSR conductor (Aluminum conductor steel-

reinforced cable)

ACSR (Aluminum Conductor Steel Reinforced) -

Conventional Conductors With Steel Core



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AAAC formation

2- AAAC Conductors (All Aluminum Alloy Conductor)

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Conventional Aluminum Based Conductors

Overheating = Loss of mechanical properties

• ACSR conductors: made of steel core + Al 1350

wires (a non-treated heatable alloy that is hardened by

cold working)

• If working temperature > 90ºC will lose significant

tensile strength (“anneal”) over time

• As the conductor temperature increases, the rate of

annealing increases rapidly

• Galvanized steel core is affected at 170 ºC

• Aluminum Clad steel core is not affected below

300ºCProfessor Ahdab Elmorshedy 17


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Conventional Conductors

Typical annealing curves for Aluminum wires


Aluminum Cables 1350-H19

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High Temperature Low Sag (HTLS)

Conductors

• HTLS conductors solve the challenges of

higher temperature and higher tensile

strength.

• HTLS uses annealed aluminum or aluminum

alloy conductors and a high tensile strength

core which carries both the weight and the

tension in the conductor span.

• Cores may be of metallic or composite

material construction.Professor Ahdab Elmorshedy 19


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• HTLS conductors make use of an inner core

with higher tensile strength than the aluminum

conductors.

• This allows higher tension to be applied to the

conductor which allows reduced sag.

• Several materials have been used.


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Why HTLS Conductors

• Supporting the seasonal or occasional demand peaks

as well as emergency overloads required by the grid

operation during line life.

• Continuous operation at higher temperatures thus,

increasing the electrical load.

• Do not modify the structures (towers and

foundations)

• Maintain adequate electrical clearances (maximum

sags)

• Increase the current capacity 1.6-2.0 times of ACSR.



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Power Line Reconductoring Project Video

The Pacific Gas and Electric Company (PG&E)

crew working on a power line.

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Egypt Conventional versus HTLS Conductors

Material characteristics:

•Thermal coefficient of expansion of Invar (alloy of steel and

nickel) is 1/3 of steel

•Annealing temperatures of aluminum 930ᵒF


Conventional HTLS

Inner Core Steel Steel alloy

Composite (carbon

or aluminum)

Outer Strands Aluminum Circular Annealed

Aluminum

Aluminum Alloy

Trapezoidal

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1. Introduction













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1-Aluminium conductor steel support (ACSS),

Southwire, USA

2-Aluminum conductor composite reinforced (ACCR),

3M, USA

3-Aluminum conductor composite core (ACCC), CTC,

USA

4-Gap type thermal resistant aluminum alloy conductor

steel reinforced, J-Power, JAPAN- LS Cable, KOREA

5- Invar Core Conductor, LS Cable, KOREA


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Knee Point Temperature (KPT)

• KPT is a temperature at which Aluminum layers do

not bare any tension due to its thermal expansion in

ACSR conductor.

• Above KPT the Tension is on the Steel core only.

• Knee point temperature depends on many factors like

span length and mechanical tension.



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Knee Point Temperature

• HTLS conductors have different physical behavior

when working below or above the knee point

temperature.

• The conductor’s core thermal expansion coefficient is

a key factor in the conductor performance, when it is

working above KPT.

• There are some technologies that reduces the knee

point temperatures improving conductor

performance.


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1-Aluminium conductor steel support (ACSS)

• The outer conductor is annealed aluminum

with an inner core of high tensile steel.

• The HTS core carries the tension in the cable.


Aluminum conductor steel

support (ACSS)

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ACSS/TW Conductor


CenterPoint Energy Houston, Texas


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2-Aluminum conductor composite reinforced

(ACCR)


Aluminum conductor composite reinforced (ACCR)

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• The core is stranded from wires of high purity

aluminum reinforced with alumina fiber.

• The outer, current carrying wires are a

hardened aluminum zirconium alloy.

• The resulting conductor has the same strength

as similar size steel core conductors, but is

much lighter and sags less.



Egypt 3M Metallic Matrix Composite Core

ACCR (Aluminum Conductor Composite Reinforced)


San Diego Gas & Electric- California

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3M™ ACCR - Protecting Grid Integrity-Video


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3-Aluminum conductor composite core

(ACCC)

• The conductor consists of an outer core of

trapezoidal conductors with an inner carbon

fiber/fiber glass composite core.


Aluminum conductor composite core (ACCC)


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• It is able to carry approximately twice as much

current as a conventional aluminum-conductor steel-

reinforced cable (ACSR) cable of the same size and

weight.

• It is popular for retrofitting an existing electric power

transmission line without needing to change the

existing towers and insulators.


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CTC Carbon Fiber Composite Core Conductor

Aluminum conductor composite core (ACCC)

Installed at APS (Arizona Public Service)



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Sag Comparison Test Data: temperature vs. sag of various

conductor types on a 215' test span.

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Sag comparison at 180°C


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• In 2010, demand for electricity in southern Texas

reached an all-time high during a peak winter season.

• Power provided to this region was supplied by two

345 kV lines 193 km long.

• In 2013 American Electric Power (AEP) began

upgrading the existing lines.

• Using a live-line technique, they replaced over 2300

km of double-bundled aluminum conductor steel-

reinforced cable (ACSR) with double-bundled

aluminum conductor composite core (ACCC) lines.


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• ACCC replaced the conventional steel wires with a

single composite core strand.

• The composite core’s lighter weight allows it to

incorporate 28% more aluminum using trapezoidal

shaped strands without a weight or diameter penalty.

• The ACCC Conductor hybrid core is not only twice

as strong as steel, it is also 70% lighter.



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Example of sag differences in the field (UK)

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Live-line technique Video


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Ice loaded tress failed to damage ACCC, Kansas (US),

2007.


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ACCC power plant upgrade

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Conductor comparison showing ampacity capabilities.


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• GAP-Type Conductors is composed

of layers of thermal resistant

aluminum alloy wires around a high

strength steel core.

• Grease is filled in the gap to make

the steel core move freely, giving the

conductor its special characteristics.


4-Gap type thermal resistant aluminum alloy

conductor steel reinforced

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Gap HTLS conductor


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Gap Conductor Installed at HydroOne

( Canadian province of Ontario)

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Principal behind small sag



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Issues with Gap conductor

Difficult to use mid-span connectors

– If Gap breaks then the internal steel core immediately

contracts down the conductor core and so a mid-span

joint cannot be made.

– The only alternative is reconductoring the section


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Gap relies on the grease staying put

– Oman, Ireland, UK have all experienced Gap losing

its grease

– Sometimes dripping onto people's roofs and cars

– Commonly burning off on the surface and causing

black marks

– The steel is then not protected.



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• Gap knee point is at erection temperature, so if

sections are erected at different temperatures then

their sag/temperature behavior will be different in the

different sections and this can put stresses on tension

towers.

• Because the aluminum is not connected with the steel

core, the whole conductor can be twisted easily by

hand


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• Wet snow can twist the conductor and hence Gap

accretes higher snow loads than, for example, CCC

(CopperClad Composite Conductors).

• It is very slow to erect as the steel core has to be

stripped bare and pre-tensioned for 12 hours.



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LS Cable and System Gap conductor

Video

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5- Invar Core Conductors (TACIR, KTACIR,

ZTACIR)

Invar Conductor Installed at

HydroOne ( Canadian province

of Ontario)

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Invar conductors use a special steel alloy: Iron–

nickel (Fe-Ni) which main characteristic is the

very low thermal expansion coefficient.

Invar is covered by a thin layer of aluminum

extruded on it which prevent the corrosion and

the wire is identified by the acronym ACI

(Aluminum Clad Invar).



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1. Introduction













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1-Higher Current Carrying Capacity

• HTLS conductors can be operated at elevated

temperatures around 150°C-250°C.

• The amount of current rating of these conductors is

high compared to the conventional conductors.

• Based on the manufacturers’ information, GTACSR

conductors are able to handle 1.6 times the same size

ACSR while GZTACSR can handle 2.0 times the

CCC of similar size ACSR conductors


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2- ROW saving

• HTLS conductors can be used to transfer bulk power

from one stations to other, so it has the potential to

reduce number of transmission lines being

constructed.

• Conventional conductors are restricted to low

capacities, so a requirement of multiple transmission

lines is needed and hence ROW requirements will be

large.

• HTLS becomes handy in such situations where they

can eliminate the requirement of multiple lines by a

single tower line.Professor Ahdab Elmorshedy 67


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3- Thermal Uprating of Existing Lines

• One of the main advantages of HTLS conductors is to

use them as a medium for thermal uprating of

existing transmission lines.

• With the increasing demand, older transmission lines

are unable to supply the required power demand and

construction of new overhead lines became a

challenge given the unavailability of ROW.

• Use of higher cross section line in the existing towers

is not an option as the existing towers are not

designed for additional forces.


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• Even if conductors with higher cross section is

used, the thermal sag of conductors will violate

the required ground clearances.

• The best option is to use a suitable HTLS

conductor with similar mechanical properties

where:

• the existing towers can be used without

violating tower safety requirements as well as

minimum ground clearances.



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4- Energy Efficiency

• Using HTLS conductors achieves energy efficiency

during power transmission.

• Conductivity of the conductors can be improved by

the proper composition of elements and proper heat

treatment methods.

• Energy loss (I2R) during transmission can be reduced

by the use of HTLS conductors.

• This will in turn reduce the amount of power

generation requirements to be met and will save fuel

and CO2.


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5- Long Span Crossing

• HTLS conductors can be used for longer spans

crossings.

• This remained a great challenge with ACSR

conductors due to its higher thermal expansion

coefficient.

• At the same time, UTS (Ultimate Tensile Strength)

of conventional conductors is low compared to the

HTLS.



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• With conventional conductors, taller towers are

required to obtain the ground clearance.

• This also results in the need of additional steel as well

as larger foundations.

• Conventional conductors cannot be tensioned to

higher values as there is a risk of being subjected to

fatigue failure due to wind vibration.

• With lower expansion values and higher UTS values,

HTLS conductors have become a good solution for

long span crossing.


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1. Introduction













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Design Concept of Gap and Invar Conductors

• Gap: Shift the Knee Point Temperature (KPT)

to lower side

• Invar: very small thermal expansion at

temperatures above KPT


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Design Concept

• Gap: Shift the Knee Point Temperature (KPT)

to lower side

• Invar: very small thermal expansion at

temperatures above KPT


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Gap conductors need Special Tensioning Method

(only Tension Tow.)



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Gap type conductor: Maintenance

• Repair Sleeve: same as ACSR:

in case of damage less than 10% of AL wires

• Mid Span joint: same as ACSR:

in case of damage more than 11% of AL wires

• Tension load at repaired portion shall have

more than 95% tension load of original

conductor


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Required current capacity: 1250A

GTACSR 448SQ at 115 deg C: 1250A, (Sag 20.36m)

ACSR 435/55SQ at 60 deg C: 643A, (Sag 19.83m)



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1. Introduction












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1- Low Service Experience

• ACSR conductors have more than hundred years

of service experience.

• ACSR conductors are being used all over the

world by thousands of contractors and utilities.

• HTLS conductors came to the world of

transmission line construction at a later stage

where no utility or contractor has that much

service experience regarding its use.

• In case of ACCC conductors, it was first

developed in 2005 and commercialized in 2006.



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• Presently over 100 utilities in more than 30 countries

are using ACCC over 24,000km span.

• GTACSR conductor first immerge in nineteen

seventies in Japan.

• Use of Gap conductors was merely limited to Japan

until the start of 2000.

• Then it started spreading all over the world and

currently more than 11,000km of supply record is

there.

• All other HTLS conductors such as ACSS, ZTACIR,

ACCC have limited experience regarding the service

life.


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2- Difficulties can arise in constructing new lines

with HTLS conductors for a variety of reasons:

• HTLS conductors such as ACCC and ACSS utilize

fully annealed aluminum strands which are more

vulnerable to bird-caging during installation.

• Pulling annealed aluminum HTLS conductors under

tension can be difficult unless the core is part of the

tension grip.



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Bird-caging of Annealed Aluminum Conductor after

Compressing Dead-end

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• With bundled conductors, the use of HTLS sub-

conductors can cause unequal thermal elongation at

everyday temperatures since the knee-point

temperature of the sub-conductors may not be equal.

• Use of composite cores can result in installation

damage since these materials are very sensitive to

shear stress.

• Connectors and dead-ends are unique to each type of

HTLS conductor.

• This presents a potential problem of standardization

and emergency repairs.



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3- Special Stringing Requirements and Spares

• One of the main disadvantages of some of the HTLS

conductors is the requirement of specialized stringing

methods.

• As an example, ACCC and Gap conductors require

special trained staff on stringing.

• Stringing procedure is different from conventional

methods used with ACSR.


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• Especially the dead ends used with ACCC and Gap

conductors shall be compression type to tackle

thermal expansion of Aluminum layer at elevated

temperatures.

• They require special mid span joints unlike in the

case of ACSR.

• They must be handled very carefully during stringing

and cannot be subjected to rough and rigid handling.



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Unusual Properties Requires Special

Handling


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4- High Price of HTLS

• Unit cost of HTLS conductors are considerably

higher compared to the cost of ACSR and AAAC, 2-3

times.

• Most of the utilities in the world have very strict

investment plans on their power systems and

additional cost bearing will cause a great challenge.



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• Therefore still in case of a new line construction, use

of HTLS will cost additional amount other than the

saving of ROW.

• However in situations where existing line uprating,

HTLS has the ability to cut down the cost of new

transmission line only by restring conductors.


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5- Reconductoring with HTLS Limitations

• As power flow increases, the voltage at the

receiving end of the line decreases, power

flow is limited to that which yields a 5% drop

• The flow through particular circuit is limited

in order to avoid overheating a power

transformer or underground cable in series

with OHL, reconductoring with HTLS will not

help.


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• Replacing existing power conductor while

preserving the original structure, typically

leaves electric and magnetic fields unchanged

as the physical spacing and their geometric

arrangement remain unchanged.

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Giza Systems Awarded INVAR Thermal

Conductor Project

• The Egyptian Electricity Transmission Company

(EETC) awarded Giza Systems the project for Cairo

500/ Sadat 220 kV OHTL – Thermal Conductor –

INVAR, March 2015.

• Giza Systems successfully executed Sadat-Cairo 500

INVAR project in significant low outage time, 58 kM.

• Installation of 30 kM Thermal conductor “GAP” for

Wadi Houf / El Tebbin 220 kV.



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high temperature –low sag (htls) conductors...tension in theconductorspan. • cores may be of...

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