LOW SAG CONDUCTORS

Introduction

- There is a growing need to increase the power handling

capacity of existing power transmission assets.

- At the same time there is fierce opposition to the

construction of new lines and the ability of obtaining right of
ways is became more and more difficult.

As a result of these conflicting pressures, increasing the

thermal rating of existing overhead transmission lines is seen
as a valid alternative to the construction of new lines.
 Methods of increasing lines capacity

- Increment of the line voltage: very expensive solution due to

necessity of new project, adaptation of installations to new voltage,..
- Increment conductor tension: that solution might cause problems in
towers – tower reinforce needed, new foundations, aeolian vibration, ..
- Increment of conductor section: that solution might cause problems
in towers – tower reinforce needed, new foundations. New project and
permissions,..
- Installation of bundle conductor - High cost. That solution cause
problems in towers - necessity of reinforce tower, foundations,
permissions, higher right of ways,..
 Methods of increasing lines capacity

- Real-time monitoring system: it is used to determine the position of a

conductor in space thereby determining the rating of the line in real
time, to avoid design sags violation.

- Electrical clearances (sags) re-asses with the possibility that the rated
temperature of the line can be increased. Such physical modification
might be done: moving suspension clamps, re-tensioning, raising
conductor attachment heights, adding new structures in long spans.

-Replacement of the existing conductor with a new conductor that

has either lower electrical resistance and/or is capable of operation at
high temperature within the existing line limits on sag and tension -
LOW SAG CONDUCTORS.
 Ta rgets of low sa g conductor reconductoring

• Increment of line ca pa city (a mpa city)

- supporting the sea sona l or occa siona l dema nd pea ks a s

well a s emergency overloa ds required by the grid
opera tion during line life.

- continuous opera tion a t higher tempera tures tha t existing

conductor increa sing the electrica l loa d.

• Do not modify the structures (towers a nd founda tions)

• Ma inta in a dequa te electrica l clea ra nces (ma ximum sa gs)

 LOW SAG CONDUCTORS

TECHNOLOGY:

Increa se theca pa city (a mpa city) of the line with respect

to its equiva lent conductor, ba sed on the increment of
the working tempera ture, ma inta ining the electrica l
clea ra nces due to low therma l expa nsion.
 Conventiona l Aluminium Ba sed Conductors
Overhea ting = Loss of mecha nica l properties

- ACSR c o nd uc to rs: ma d e of steel c ore + Al 1350 w ires

- If working tem p era ture > 90ºC w ill lose sig nific a nt tensile
streng th (“ a nnea l” ) over tim e
- Ac c umula tive effec t
- As the c o nd uc to r tem p era ture inc rea ses, the ra te o f
a nnea ling inc rea ses ra p id ly
- Ga lva nized steel c ore is a ffec ted a t 170 ºC
- Alum inium Cla d steel c ore it is not a ffec ted b elow 300ºC
 Conventiona l Conductors
Typica l a nnea ling curves for a luminium wires
 Low Sa g Conductors
Therma l-Resista nt Aluminium Alloys

TENSILE Ma x. Tem p era ture Op era tion

CONDUCTIVITY
ALLOY STRENGTH
(% IACS) Continuous Em erg enc y
Min (Kg / m m 2)

HAl 16,2 61,0 90 120

58TAl 16,2 50,0 150 180

60TAl 16,2 60,0 150 180

KTAl 22,9 55,0 150 180

UTAl 16,2 57,0 200 230

ZTAl 16,2 60,0 210 240

XTAl 16,2 58,0 230 310

 “Knee Point Tempera ture”

Definition
- The conductor temperature above which the aluminium strands of a
composite conductor have no tension or go into compression caused by
different material elongation when heated.
- Knee point temperature is not a fixed value and depends of many factors like
span length and mechanical tension.
- Low sag conductors have different physical behaviour 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 Knee Point temperature.
- There are some technologies that reduces the knee point temperatures
improving conductor performance.
Knee Point Temperature
Conductor Cores performance comparison
Low Sag Conductor Types
 HiTLS Conductor Types

1.- GAP type Conductor (G(Z)TACSR). Fig 1

Co nstituted b y a hig h m ec ha nic a l resista nc e steel c o re a nd
severa l therma l resista nt a lum inium la yers tha t, b ec a use o f the
g a p b etween the steel c o re a nd the inner a lum inium la yer, it’ s
Fig 1
free to m ove.

2.- TACSR Conducto Fig 2. Ma d e of a ny kind of steel c o re a nd

severa l therma l resista nt a lum inium la yers . No t a low sa g
c o nd uc to r.

3.- ZTACIR Conductor Fig 2. Ma d e o f a inva r a lum inium

Fig 2
c la d d ed c o re o r g a lva nized a nd severa l therma l resista nt
a lum inium la yers

4.- ACSS Conductor Fig 2. Ma d e of a ny kind o f steel c o re

(severa l typ es) a nd severa l a nnea led a lum inium la yers

5.- ACCR (Fig. 2) a nd ACCC Conductors (Fig. 3). Ma d e of

c om p osite c o res a nd therma l resista nt a lum inium o r a nnea led
a lum inium la yers . Fig 3
Pros & Cons of HTLS conductors
GAP TYPE CONDUCTORS
G(Z)TACSR
 Why Gype Type Conductor?

TREFINASA/SAPREM has selected Gap Type Conductor, by different reasons that make it
the best choice for the replacement of existing conductors.

Gap Type Conductor is produced with conventional materials (aluminium and steel),
that have been used in the production of conductors for more than a century.
Metallurgy and behaviour it is perfectly known. No material risk.

Due to its unique installation methodology, conductor’s KNEE POINT is located at

installation temperature without pre-tensioning. This is a very important fact because in
other type of conductors knee point is located in the range of 100ºC, then conductor
does not work like low sag conductor below this temperature. In the case of the Gap
type conductors, because knee point is located at installation temperature, it works like
low sag conductor from this temperature, providing a superior performance in the
“intelligent” working temperature range (60ºC to 120ºC) where the losses are not too
significant.

Best ratio price /performance

 Why TREFINASA Ga p Conductor?

- The Gap type conductor installation system has been improved by TREFINASA/SAPREM,
in such a way that no longer installation is a handicap. By means of the use of a system
patented by SAPREM, the installation costs have been reduced and the security of pay-off
and sagging tasks have been enhanced appreciably.

- TREFINASA uses Aluminium Clad Steel Wire for production of gap conductor steel core
because of its demonstrated advantages against zinc and mischmetal coating based steel
cores.
 Superior corrosion resistance
 Lighter weight
 Improves conductivity of steel core
 Long term stability in high temperature operation (ACS wire can withstand 300⁰C
continuous operation without degradation)
 Even it is not recommended usage of zinc coating based steel core for
temperatures higher than 170⁰C (there is literature confirming it), many
manufacturers still supplies this kind of material.
 An internal TREFINASA study demonstrated that both galvanized and mischmetal
steel wires suffered deterioration after heating samples at 300 ⁰C for 5 weeks,
while ACS wire kept all initial characteristics.
 Gap Type Conductor

Round or
tra pezoid Hea t
resista nt Al Wires
Specia l
Therma l
Resista nce
Grea se

Tra pezoid Hea t

resista nt Al Wires

High Strength Aluminium Spa ce (Ga p)

Cla d Steel Core
Gap Type Conductor (Fundamentals)

- In it’s initia l sa gging condition, the

mechanica l stress is only a pplied to the steel
core. The a luminium la yers a re inert (no
tension) - KNEE POINT IS AT SAGGING
TEMPERATURE
- The spa ce (ga p) between the steel core a nd
the first a luminium la yer contributes to steel
core movement; grea se a lso contributes.
- Therefore, conductor’s therma l expa nsion
coefficient is only a luminium cla d steel core’s
(11,9 x 10-6)
- In the ca se of an ACSR conductor,
coefficient’s va lue is a lmost double (20 x 10-
6), beca use the a luminium wires contribution.
 SAG AND TENSION CALCULATION for GTACSR

Remember!
•In initia l sa gging condition, mecha nica l stress is only a pplied to the steel core.
•The a luminium la yers a re inert (no tension)
•Knee Point Tempera ture is a t sa gging tempera ture

BELOW KNEE-POINT ABOVE KNEE-POINT

 Conductor Situation: Conductor Situation:
Low Temp. and Overload Conditions High Temperatures
- Mechanical Condition: -Mechanical Condition:
Tensile Load > Tensile load at KPT Tensile Load ≤ Tensile load at KPT
- Aluminium with tensile load (no inert) -Aluminium without tensile load (inert)
- Conductor behaves like an ACSR -Conductor behaves like an Low Sag Cond

Conductor parameters for calculation Conductor parameters for calculation

 E (Modulus of elasticity): composite E (Modulus of elasticity): steel core

 α (Coef. of thermal expansion): composite α (Coef. of thermal expansion): steel core
 S (Conductor area); Aluminium + Steel S (Conductor area); only steel core
 SAG AND TENSION CALCULATION for GTACSR

INSTALLATION ACSR

Knee-Point
GTACSR

GTACSR

LOW SAG CONDUCTOR

AS CONVENTIONAL
CONDUCTOR
WHAT COMPETITORS SAID ABOUT GAP?
 GAP CONDUCTOR SAGGING
To adjust the conductor to the final sag just
pull it from the steel core
 SAPREM®METHOD
for GAP TYPE CONDUCTOR SAGGING
G(Z)TACSR FITTINGS
 GTACSR FITTINGS

COMPRESSION CLAMP SUSPENSION CLAMP

TESTS
 Principal Standards for gap testing

•IEC 6240 Ed1.0 - Concentric lay stranded overhead electrical

conductors cointaining one or more gap(s)

•EN 50182 - Conductors for overhead lines - Round wire concentric lay
stranded conductors

•EN 61395 - Creep Test procedures for stranded conductors

•IEC 62004 - Thermal-resistant aluminium alloy wire for overhead line

conductor

•EN 61232-96 - Aluminium clad steel wires for electrical purposes

•EN 61284 - Overhead lines. Requirements and tests for fittings

 CONDUCTOR TEST

•Surface condition; Diameter; Inertness; Lay ratio

•Mass per unit length
•Cross sectional area
•Gap Measurement
•Resistance
CONDUCTOR TEST

Strain-Stress and Creep Test

 CONDUCTOR TEST

SLIP & BREAKING LOAD TEST

 CONDUCTOR TEST

GAP

Sag/Tension
ACSR vs. Temperature
TEST
 CONDUCTOR TEST

CONDUCTOR SELF-DAMPING AND AEOLIAN VIBRATION TESTS

 THERMAL-RESISTANT ALUMINIUM
ALLOY WIRE TEST

•Diameter •Tensile Strenght

•Electrical Resistivity •Elongation
•Thermal-Resistant Property
 ALUMINIUM-CLAD STEEL WIRE TEST

•Diameter
•Torsional Test
•Thickness of Aluminium Test
•Tensile Stress Test
•Stress at 1% Elongation Test
•Elongation Test
GREASE TEST

•Mass per unit Length

•Drop Point
 FITTINGS TEST
Suspension Clamp Slipping and Breaking Test

Compression Clamp Tensile Stress Test

 FITTINGS TEST

THERMAL BEHAVIOUR OF INSULATOR AND FITTINGS

 ALL IN ONE SOLUTION

TREFINASA/SAPREM offers whole support to finalise

the Project, from the design to the installation stage:
•Conductor design according to Customer needs
•Technical uprating study
•Special fittings proposal
•Technical support for calculation and installation
•Installation tools can be provided
•Installation training to Contractors
•Supervision on site for installation
 ALL IN ONE SOLUTION

ORGANISATIONAL CHART

HIGH TEMPERATURE LOW SAG CONDUCTORS

Conductor Conductor Engineering Fittings

design manufacturing
Technical Installation
support method
THANKS FOR YOUR ATTENTION