EXPERIENCE WITH THE MECHANICAL PERFORMANCE OF NON-CONVENTIONAL CONDUCTORS

695
EXPERIENCE
WITH THE MECHANICAL PERFORMANCE
OF NON-CONVENTIONAL CONDUCTORS
WORKING GROUP
B2.48
AUGUST 2017

Members
J.B. WAREING, Convenor GB J. HUANG, Secretary US
P. FIERS AT B. RISSE BE
P. VAN DYKE CA J.M. ASSELIN CA
T. LESKINEN FI J. GARNIER FR
A. MANENTI IT S. KOLOSOV RU
M. LANDEIRA ES D. SUNKLE US
P. TIMBRELL AU A. ANAND IN
T. KAVANAGH IE D. MARGINEAN RO
M. MITO JP D. HORSMAN GB
K. HALSAN NO D. RESHAM NP
T.A. FURTADO BR
Corresponding Members
C. PON CA C. ROZE FR
U. COSMAI IT J. HAVEL US
D. HAVARD CA P. CATCHPOLE US
G. HOWES GB H. DEVE US
N. LAURENTIU RO R. TONG GB
S.M. UEDA BR G. DIANA IT
C. TAMM US F. DELHUMEAU FR
R. PAUVEL BE A. VINOGRADOV RU
L. MAZZOLA IT
WG B2.48
Copyright © 2017
“All rights to this Technical Brochure are retained by CIGRE. It is strictly prohibited to reproduce or provide this publication in
any form or by any means to any third party. Only CIGRE Collective Members companies are allowed to store their copy on
their internal intranet or other company network provided access is restricted to their own employees. No part of this
publication may be reproduced or utilized without permission from CIGRE”.
Disclaimer notice
“CIGRE gives no warranty or assurance about the contents of this publication, nor does it accept any responsibility, as to the
accuracy or exhaustiveness of the information. All implied warranties and conditions are excluded to the maximum extent
permitted by law”.
WG XX.XXpany network provided access is restricted to their own employees. No part of this publication may be
reproduced or utilized without permission from CIGRE”.
Disclaimer notice
“CIGRE gives no warranty or assurance about the contents of this publication, nor does it accept any responsibility, as to the
EXPERIENCE WITH THE MECHANICAL
PERFORMANCE OF NON-
CONVENTIONAL CONDUCTORS
ISBN : 978-2-85873-398-9

EXPERIENCE WITH THE MECHANICAL PERFORMANCE OF NON-CONVENTIONAL CONDUCTORS
3
EXECUTIVE SUMMARY
Electricity transmission and distribution networks around the world are increasingly being required to handle
significant changes in power transfer capability. Increased environmental constraints and public opposition to new
overhead lines has meant that it is the existing assets that are being subjected to ever increasing needs for
increased capacity. Today the cost of obtaining permission for the erection of new overhead lines (OHLs) is a
major consideration in any new development. Non-conventional conductors are needed generally to maintain
overhead lines and allow more ampacity. In cases, the use of new conductors can also be for a need of
refurbishment without reinforcement of towers. Some non-conventional conductor designs resist vibration and
galloping problems more effectively than conventional conductors.
The area of non-conventional conductors has been the subject of several CIGRE Technical Brochures. WG B2.48
was set up to review experience and gather all available data on the mechanical performance of these conductors
(including high temperature low sag (HTLS) conductors). To perform this work, two questionnaires were sent out.
One version went to conductor manufacturers/suppliers world-wide and another version to utilities.
In the absence of a consensus in defining the non-conventional conductor types, and for the purpose of this
brochure, the WG has come up with the following classification:
Type 0 Conductors expected to be operated at "low" temperature not exceeding 95°C for extended periods of
time
Type 1 Conductors consisting of a strength member made of steel, coated steel, or steel alloy, and an envelope
for which the high temperature effects are mitigated by means of thermal-resistant aluminium alloys
Type 2 Conductors consisting of a strength member made of steel, coated steel, or steel alloy, and an envelope
for which the high temperature effects are mitigated by means of annealed aluminium
Type 3 Conductors consisting of a metal-matrix composite (MMC) strength member, and an envelope for which
the high temperature effects are mitigated by means of thermal-resistant aluminium alloys
Type 4 Conductors consisting of a polymer-matrix composite (PMC) strength member, and an envelope for
which the high temperature effects are mitigated by means of annealed aluminium or thermal-resistant
aluminium alloys for HTLS applications
This brochure covers conductor types 0 but restricted to compact conductors and types 1 to 4. Tests on wind/ice
loading and vibration characteristics have been performed at sites in Brazil, Canada, France, UK, USA and data is
also provided by EPRI.
Much data has been accumulated on the effect of HTLS conductors on fittings and, in particular, composite and
porcelain insulators. It indicates that these items should not reach inappropriate temperatures even if the
conductors run at 200°C.
The questionnaire results indicated a high level of satisfaction with HTLS conductors at voltages from 33kV to over
500kV in single and bundled configuration. The performance expectations were generally either met or even
exceeded. The question of economics is often raised but the survey showed that the high capital cost of HTLS
conductors can be re-gained in a few years by avoidance of structure changes and, in some cases, lower line
losses. The TB raises questions about what the vibration fatigue mechanism of HTLS conductors is in practice and
the necessity to review the H/w (tension /weight per unit length) values used in vibration limits for conventional
conductors when applied to HTLS versions. There is also a need for some aid to the handling of composite cored
conductors where bending the conductor can cause core breakage problems. This can be avoided by using trained
linesmen and the utilities' survey indicated that training was given and that any failures were due to mishandling,
commonly by untrained contractors. Since HTLS conductors are relatively new products, except for Type 2
conductors, it was not possible to obtain feedback regarding their long term behaviour.

4
TABLE OF CONTENTS
EXECUTIVE SUMMARY............................................................................................................ 3
1. NEED FOR NON-CONVENTIONAL CONDUCTORS................................................................ 7
INTRODUCTION.......................................................................................................................................................................7
BOTTLENECKS...........................................................................................................................................................................8
CAPACITY INCREASE TECHNOLOGIES ..............................................................................................................................8
COSTS........................................................................................................................................................................................9
UTILITIES’ JUSTIFICATIONS ....................................................................................................................................................9
NEW AND PLANNED INSTALLATIONS ............................................................................................................................12
2. DESCRIPTION OF NON-CONVENTIONAL CONDUCTORS, TYPES AND
CONSTRUCTION .......................................................................................................................................15
TYPES OF CONDUCTOR COVERED .................................................................................................................................15
MATERIAL PROPERTIES OF ENVELOPE WIRES...............................................................................................................17
MATERIAL PROPERTIES OF CORE .....................................................................................................................................17
COMPACT DESIGNS............................................................................................................................................................21
TYPE 1 CONDUCTORS........................................................................................................................................................23
TYPE 2 CONDUCTORS........................................................................................................................................................25
TYPE 3 CONDUCTORS........................................................................................................................................................26
TYPE 4 CONDUCTORS........................................................................................................................................................27
3. CHARACTERISTICS OF NON-CONVENTIONAL CONDUCTORS.................................................29
INTRODUCTION....................................................................................................................................................................29
RELATIVE COST .....................................................................................................................................................................29
KNEE-POINT...........................................................................................................................................................................29
MODULUS OF ELASTICITY..................................................................................................................................................31
CREEP.......................................................................................................................................................................................32
GREASES.................................................................................................................................................................................32
SHORT CIRCUIT.....................................................................................................................................................................33
TESTING OF CONDUCTOR................................................................................................................................................33
AGEING..................................................................................................................................................................................34
EFFECT OF ICE LOADS.........................................................................................................................................................35
RECYCLING............................................................................................................................................................................37
4. INSTALLATION OF NON-CONVENTIONAL CONDUCTORS AND MAINTENANCE.................39
EFFECT OF ERECTION TENSION AND STRINGING ......................................................................................................39
SUPPLIER MANUFACTURERS’ QUESTIONNAIRE SUMMARY.......................................................................................40
IS PRE-TENSIONING REQUIRED AT INSTALLATION?....................................................................................................41
UTILITY QUESTIONNAIRE SUMMARY...............................................................................................................................41
INFORMATION FROM PUBLISHED PAPERS ....................................................................................................................42
SAG CALCULATIONS...........................................................................................................................................................44
MAINTENANCE......................................................................................................................................................................45
5. FITTINGS.................................................................................................................................................47
FITTINGS FOR HTLS CONDUCTORS ................................................................................................................................47
LONGEVITY OF CONNECTORS........................................................................................................................................47
OPERATION OF CONVENTIONAL CONDUCTOR SYSTEMS ABOVE 100ºC [CIGRE TB 643]............................47
MITIGATION ..........................................................................................................................................................................49
ARMOUR RODS ....................................................................................................................................................................49
NON-METALLIC CONDUCTOR HARDWARE ..................................................................................................................50
IMPACT OF USING HIGH TEMPERATURE CONDUCTORS ON INSULATORS.........................................................50

5
CONTRACTS AND GUARANTEES .................................................................................................................52
6. FIELD EXPERIENCE.................................................................................................................................53
7. VIBRATION MITIGATION ....................................................................................................................55
DAMPING SYSTEMS.........................................................................................................................................55
SELF-DAMPING .................................................................................................................................................55
FATIGUE PERFORMANCE................................................................................................................................56
LABORATORY TESTS........................................................................................................................................58
FIELD TESTS ........................................................................................................................................................59
SAFE DESIGN TENSION ..................................................................................................................................65
CONCLUSION............................................................................................................................................67
BIBLIOGRAPHY/REFERENCES..................................................................................................................69
ANNEX A. GLOSSARY..............................................................................................................................71
ANNEX B. UTILITY QUESTIONNAIRE......................................................................................................73
ANNEX C. SUPPLIER QUESTIONNAIRE..................................................................................................77
ANNEX D. EXAMPLE OF A HIGH TEMPERATURE SAG-TENSION TEST AND KNEE-POINT
TEMP. MEASUREMENT ..............................................................................................................................81
TEST OBJECTIVE................................................................................................................................................81
TEST SET-UP .......................................................................................................................................................81

6

7
1. NEED FOR NON-CONVENTIONAL CONDUCTORS
INTRODUCTION
The main focus of this brochure is to present non-conventional conductors and gather all available data on their
mechanical performance as well as field experience. The non-conventional conductors considered are mainly aimed
at increasing capacity of existing overhead lines although other benefits are also considered.
Conductor change becomes an attractive option if a line has reserve strength (or redundancy) in its structures to
carry a larger and heavier conductor, if a non-conventional conductor can offer higher capacity without weight
penalty, or if the existing conductor offers no cost-effective ampacity increase because it is already at or near its
thermal or sag limit. Costs can be limited by avoiding structure changes or at least restricting changes to minor
levels. Some conductor types that offer dramatically higher thermal limits and ampacity limits with limited or no
structure changes can be more expensive than standard conductors, offsetting the benefits of keeping the existing
structure. Therefore, the low cost option within this category is to replace the existing conductor with a standard
conductor of a larger size. An optimizing feature available to maximize the value of a larger conductor of standard
alloy, standard construction and modest cost is to change from round strands to compact (trapezoidal or Z-shaped
wires) or other compact designs. This effectively packs more aluminium into a common overall diameter by
displacing the airspace voids inherent to a round wire conductor type (~30%). Modest weight is added to the
conductor while retaining the same diameter. Since conductor diameter affects wind load on structures which in
turn with the weight affects maximum design tension, it can be advantageous to accept the weight increase and
minimize the diameter. Even so, the ampacity increases related to this type of conductor change are typically
modest.
A problem with adding weight to a conductor is that it will not only increase load (tension) on the towers, it will
also increase the conductor’s sag unless the tension can be raised even further. Thus, overall project costs may
actually be less even though the conductor cost is slightly higher. If power losses are taken into account, then
payback periods for using new high-temperature low-sag (HTLS) conductors can be a matter of only a few years.
Depending on the project and its environmental configuration, the utility will have to compare the total life-cycle
costs of conductor replacement and reinforcement of towers to that with the building of a new line. This can lead
to the use of non-conventional conductors even though feedback and maintenance are not always well known at
present.
Developments and field experience with HTLS conductors, however, mean that these aspects are beginning to be
appreciated for all conductor types. To gain larger ampacity increases, expenditure is necessary on the conductors
or the structures, or both. Ampacity increases associated with a conductor change often do not require raising
structures but rather strengthening them. As with raising structures, the easiest types to strengthen are wood
poles. To avoid structure change, the use of high temperature (HT) conductors with features such as high
ampacity rating, small diameter (to stay below existing wind load limits), light weight and reduced sag
characteristics can be attractive. It is clear that when choosing a particular HT conductor local line design
standards and conditions will need to be taken into account as these will have a significant impact on the type of
HT conductor chosen.
In some cases, the use of non-conventional conductors can also be for refurbishment without reinforcement of
towers and no real increase of ampacity.
The area of non-conventional conductor types has been the subject of several CIGRE Technical Brochures and IEC
documents:
 TB 244 ‘Conductors for the uprating of overhead lines’ 2004 (under revision)
 TB 294 ‘How overhead lines are redesigned for uprating/upgrading - Analysis of the replies to the
questionnaire’ 2006
 TB 331 ‘Considerations relating to the use of high temperature conductors’ 2007
 TB 353 ‘Guidelines for increased utilisation of existing Overhead Transmission Lines’ 2008
 TB 425 ‘Increasing capacity of overhead transmission lines: Needs and solutions’ 2010

8
 TB 426 ‘Guide for qualifying High Temperature Conductors for use on Overhead Transmission Lines’
2010
 IEC TC7 PT 62818 Draft presented to National committees covering: Fibre Reinforced composite core
used as supporting member material in conductors for lines, under preparation
BOTTLENECKS
Bottlenecks in transmission and distribution grids are causing more and more precarious situations in the electrical
energy supply. Initially, at the beginning of the liberalisation of the energy market, commercial consideration was
the main driver for managers to exercise caution in overhead line investments. Today, the cost of obtaining
permission for the erection of new overhead lines (OHLs) is a major consideration in any new development. The
driver for network expansion and strengthening in many countries is the push for renewable energy, in particular
wind and solar farms, in areas where networks are insufficient to carry the load. One method of increasing capacity
without major support structure changes is to use high temperature conductors which can allow higher ampacity at
low sags, thereby not violating ground clearance regulations.
Feeding energy from wind farms, closure of old power stations (for reduction of CO2 considerations) and
alternating power loads (caused through energy trading) are causing instabilities in the grid and so the electrical
upgrading of existing lines is becoming more significant. This means that electricity transmission and distribution
networks around the world are increasingly being required to handle significant changes in power transfer
capability. Increased environmental constraints and public opposition to new overhead lines has meant that it is
the existing assets that are being subjected to ever increasing needs for increased capacity. The same
environmental pressure and public opposition, along with network availability requirements, also restrict the extent
to which existing structures can be modified.
CAPACITY INCREASE TECHNOLOGIES
A recent CIGRE work [CIGRE TB 425, 2010] reports several ways to increase the power capacity of overhead lines:
 Dynamic line ratings (DLR)
Applying dynamic ratings based on real-time monitoring of weather conditions or conductor properties to
determine (by calculations or direct measurement) the ground clearance at any time. This can allow higher
power capacities in 'beneficial' weather conditions [CIGRE WG 22.12, 2001] [Motlis et al, 2000]. The
assumptions about conductor temperatures from weather conditions are covered in CIGRE TB 299 [2006],
which looks at the influence of weather parameters and suggests how the direct measurement of actual
conditions can increase the operational efficiency of a line without making any conductor temperature or
structural changes.
 Probability based ratings (PBR)
Probability based rating (PBR) uses historical or predictive weather conditions to allow a probabilistic
approach to conductor ampacity levels. It has the advantage that no real-time monitoring equipment is
needed.
 Physical changes
Physical modifications to insulator hardware (attachment hardware, use of V-shaped suspension systems,
etc.) can allow for increased sag. V-shaped suspension systems support the conductor by two angled
insulators rather than vertically, so reducing the vertical height of the insulator set and hence increasing
ground clearance. Increasing conductor tension can also help, as long as a possible reduction in conductor
lifetime and implications on tower strength are taken into account.
 Re-conductoring with standard conductors
Re-conductoring with conductors that have a lower electrical resistance and/or are capable of higher
temperature operation while maintaining existing clearance limits, preferably using standard fittings can
offer modest capacity increases. This topic is covered by CIGRE B2.42 'Guide to operation of conventional
conductors above 100°C' [CIGRE TB 643, 2015].
 High temperature conductors
The focus of this report is high temperature conductor use and new material technologies in conductor
construction and design. Whilst this CIGRE brochure was written basically for steel towers, it does have

9
relevance to wood pole lines as well. Re-conductoring based on “high-temperature (HT) conductor”
increases capacity by allowing increased rated temperatures within existing sag limits. Such capacity
increase options should at least maintain, and if possible, improve power line reliability.
 The Solutions
Conductor-based solutions can increase the power capacity of the line in four basic ways:
1. Improve operational techniques to make more efficient use of existing conductor capacity;
2. Raise the thermal limit of existing conductors;
3. Replace the existing conductors with non-conventional conductors of higher capacity.
4. Treat the surface of conductors (black conductors) to change their emissivity or absorptivity to
increase radiation losses allowing higher currents at lower temperatures.
During the development of the “upgrading technology” in the late 1980’s in Austria and Germany,
another method was utilised, which was to paint the finished high temperature conductors black.
At high temperature, this type of surface offers the benefit of better radiation, i.e. better self-
cooling effect due to increased emissivity. This self-cooling effect provides either increased current
carrying capacity or lower operating temperature (10 – 15°C) for a given current.
A side effect of the black surface is to make conductors less visible (camouflage) in nature
which can help in obtaining planning permission. In other circumstances, however,
conductors have to be made more visible to avoid birds and low flying aircraft colliding
with them. The coating, generally, is not permanent and can disappear after years
depending on local climatic conditions. However, a new generation of coloured conductors
is becoming available that claim to be more stable.
Option 2 is being considered in CIGRE TB 643 [2015]. Option 4 is an established technology but available
surface coatings are limited at this time. Conductor retention often requires structure modification and
generally offers only modest ampacity increases, whereas conductor change offers substantial gain. In the
latter there are four options:
 Increase conductor size within structure limitations
 Change to a HTLS type within structure limitations
 Change to a HTLS and reinforce only few structures, typically dead-end or angle towers
 Re-build the line with improved structures and conductors
This report concentrates on making OHL engineers aware of the benefits, characteristics and problems with non-
conventional conductor types so that an informed and economic choice can be made.
COSTS
Several studies have been done [CIGRE TAG04/06, 2013] on the economics of HTLS conductor use and it was the
subject of a question in the Utilities Questionnaire, reported on later in this brochure. These studies compared non-
conventional conductors and the increase of ampacity, with its associated cost (increase of ampacity in %
compared with the cost ratio between a non-conventional conductor and an ACSR). Other studies took into
account the cost savings from the lower temperature operation (of HTLS conductors) compared with standard
conductors at the same current capacity, resulting in a reduction in power losses and introducing a reduced ‘pay-
back’ period of just a few years before recovering the initial higher cost of HTLS conductors.
UTILITIES’ JUSTIFICATIONS
The utility questionnaire is shown in Annex B. There were 34 respondents from Europe, Asia, Australasia and the
Americas. The break-down of the types of Utilities is shown in Table 1.1.
Type of utility No. of
utilities
Investor owned 12

10
State government ownership 8
Municipal/Regional ownership 6
State government ownership plus investors 1
Municipal/Regional ownership plus investors 1
Other forms of ownership including consulting engineers 6
Table 1.1: Type of utilities who answered the questionnaire
Table 1.2 lists the various reasons given by utilities for their planned installations.
Reason for future
installations
No. of
respondents
Increased ampacity 26
Economic* 20
Ground clearance 14
Voltage drop 2
Planning permits and outages 2
Minimise line loss 1
De-icing 1
Less visual impact 1
Optimise (n-1) criteria 1
Table 1.2: Reasons for HTLS use
*
Respondents that indicated “Economic Justification,” were asked to answer four further questions related to it.
The responses, whilst quantitative, required some interpretation. It could be concluded from the responses that
generally utilities that used HTLS, expected costs (i.e. total life-cycle costs) to be around 20 to 50% of the cost of
using a conventional conductor.
All respondents except one who answered this question indicated a significant construction time advantage,
typically ranging from four months to several years.
Six respondents indicated the high importance for regulatory approval through the use of HTLS conductors, four
rated this as being of moderate importance and one as low importance.
Table 1.3 below lists the mains reasons utilities have provided to explain their choice of HTLS on one or more of
their projects.

11
Purpose of choosing HTLS Number of respondents
Upgrade/uprate 29
Construction of new lines 9 (see note)
Trial pilot installations 9
Aged conductor replacement 7
Specific application – (e.g. river crossing) 6
De-icing 1
Note: 8 of the 9 respondents indicated the purpose of the new line was
also upgrade/uprate
Table 1.3: Response frequency to the purpose of choosing an HTLS
The following comments were also received from utilities:
 “Plans to install both single and bundled in range 200 to 300kV” (Single bundled type 1 conductor (TACSR)
installed)
 “Max permissible temperature of fittings. Ageing and durability of new conductor types long time creeping.
Lack of data regarding ageing, durability and long time creep of new conductor types as well as maximum
permissible temperature of fittings.”
 “In the metropolitan area we did not have any area to install new OHTL. Thus the new types of conductors
for ‘reconductoring’ should be a great solution in this case. Another solution could be to install
underground lines but it is too expensive” (Single bundled type 1 conductor (TACSR and GZTACSR)
installed in region 100 – 200kV)
 “At present we are installing type 1 conductor (ZTACIR/AS 191/45mm2
) on our 110kV wood pole system to
good effect. We are proposing to string 40km of double circuit PL16 tower line with type 1 conductor
(GTACSR 240mm2
) next year. ” (Current installs of new conductor in the 100 – 200kV area using
ZTACIR/ACS. Planned future single conductor install in 100 – 200kV region.)
 “For questions 3 - 12, type 0 conductor (AAAC-Z) were not considered as new conductor type as they are
installed as a standard solution for 30 years without any problems. They are used as replacement of aged
conductors or for new installations as well and allow up to 15% increased ampacity.” (Current installation
100 – 200kV Single type 4 conductor. Planned future install of bundle at >300kV)
 “Little experience with new conductor type, grid not too saturated now and so no need for new conductor
type in near future other than for de-icing. Previous discussion with new conductor type suppliers for
possible pilot project. Price of all 5 to 7 times ACSR. Limited install of type 2 conductor for de-icing but
recent developments has created opportunity to consider newest conductor type on river crossing.
Therefore considering 6 km section with alternative to type 2 conductor. Factors to consider include future
transit needs, expected life vs ACSR, existing structure life expectancy, gain of reduced conductor diameter
vs mechanical rating of structures”
 “It is important that utilities apart from prototype testing requirements for new cables, also consider the
engineering design and installation of these new cables from the regulatory point of view” (Current
installation in all voltages from <100kV to 300kV using type 2 and 4 conductors. Future planned
installations at 200 -300 kV)
 “We recently entered a request for quotation allowing several HTLS conductor types to compete for a
project demand. Tower modifications including change to foundations require a building license, which
means additional project time and risk; HTLS conductors may be a quick solution. Needing an upgrade:
generally cost for tower strengthening are lower than the new present value future transport losses” (No
current installs but plan future installations in 100 -200kV region)
 “We have been very pleased with the performance of type 4 conductor and will use it again in the future
as the need arises”. (Current installation 100 – 200kV of type 4 conductor. No future plans reported)

12
Hydro-Québec has installed type 2 conductors to replace the conductors of existing lines on three line sections in
1987, 1999 and 2006 [Van Dyke et al, 2011]. In these cases, the main reasons for choosing Type 2 (ACSS) conductors
were to:
 Increase transit capacity without decreasing ground clearance while keeping most of the towers. In one
case, the ACSS was larger than the ACSR it replaced and dead end towers as well as angle towers had to be
replaced.
 Have the capacity to increase the conductor temperature in order to de-ice it.
 Replace a twin bundle by a single type 2 conductor with the same transit capacity over a new highway in
order to increase the ground clearance without increasing the impact of the climatic load on the dead end
towers. This solution was less expensive than the cost of replacing the adjacent towers with dead end towers
with a higher load capacity.
Moreover, the conductors could be replaced faster than the conductors and the towers, thus mitigating the associated
loss of revenue.
While there are other HTLS conductors available with different specifications than type 2 conductor, type 2 was
chosen on a cost analysis basis, as it was cheaper. It also has the advantage of being a proven technology.
Where higher electrical loads were expected, RTE (France) has also replaced conductors on some existing lines with
prestressed type 2 conductors or type 4 conductors, so to ensure that one circuit would be able to handle the whole
load in case of an emergency [Van Dyke et al, 2011].
Utilities were asked to comment on what features and properties would be desirable from new conductor types
(Table 1.4).
Voltages installed and
planned
Comments
<100 kV and
100 – 200 kV
No increase of mechanical load and sag
100 – 200 kV
Autosensing conductor by means of optical fibre sensing (strain and
temperature)
100 – 200 kV Adequate short circuit performance
100 – 200 kV Less line losses like ACSR
200 – 300 kV Lower price. More suppliers of fittings and clamps for specific conductor types
200 – 300 kV
No detrimental impacts from major ice loading or wind induced conductor motion
- especially galloping.
200 – 300 kV Reduction of conductor losses
No voltage given Predictability and value
Table 1.4: Features and properties wish list from utilities for new conductor types
NEW AND PLANNED INSTALLATIONS
Total length of OHL owned, installation of new conductor types and planned installation of new conductor types in
circuit kilometres (CK) obtained from the questionnaire are listed in Table 1.5. From this table, one can say that
clearly the largest growth area appears to be for bundled-conductor circuits in voltages above 300 kV. As this value
stands out over all others, it should be noted that this seemingly high growth value comes from only three utilities,
with one planning major expansion in this area. None of these utilities claim to have major installations of new
conductor types already installed. All utilities in this group claimed increased ampacity for the need to expand, with
one also claiming economic reasons.

13
OHL currently owned
Current installation
of new conductor
Planned installation
of new conductor
<100 kV 382 052 CK
40.2 CK of single
22 CK of bundled
26.2 CK of single
100 to 200 kV 204 763 CK
1 525 CK single
2.4 CK of bundled
704 CK of single
200 to 300 kV 80 504 CK
922.6 CK of single
221.4 CK of bundled
772 CK of single
100 CK of bundled
>300 kV 97 554 CK
5 CK of single
28.3 CK of bundled
100 CK of single
1 400 CK of bundled
Table 1.5: Owned, installed and planned installations

14

15
2. DESCRIPTION OF NON-CONVENTIONAL
CONDUCTORS, TYPES AND CONSTRUCTION
TYPES OF CONDUCTOR COVERED
In the absence of a consensus in defining the non-conventional conductor types, and for the purpose of this
brochure, the Working Group has come up with the following classification:
Type 0 Conductors expected to be operated at "low" temperature not exceeding 95°C for extended periods
of time
Type 1 Conductors consisting of a strength member made of steel, coated steel, or steel alloy, and an
envelope for which the high temperature effects are mitigated by means of thermal-resistant
aluminium alloys
Type 2 Conductors consisting of a strength member made of steel, coated steel, or steel alloy, and an
envelope for which the high temperature effects are mitigated by means of annealed aluminium
Type 3 Conductors consisting of a metal-matrix composite (MMC) strength member, and an envelope for
which the high temperature effects are mitigated by means of thermal-resistant aluminium alloys
Type 4 Conductors consisting of a polymer-matrix composite (PMC) strength member, and an envelope for
which the high temperature effects are mitigated by means of annealed aluminium or thermal-
resistant aluminium alloys for HTLS applications
Table 2.1 describes each conductor type and provides former or usual acronyms and trademarks.
Conductors may also be classified according to their outer geometry and two main classes may be defined:
 Standard conductors with circular wires and
 Compact conductors with trapezoidal or Z-shaped wires.
The Technical Brochure presents information for the following non-conventional conductors:
 Type 0 but restricted to compact conductors
 Types 1 to 4 High Temperature Low Sag conductors (HTLS) made with the following cores and envelopes:
 Cores
 Types 1 or 2: Galvanized, mischmetal, aluminium clad or invar steel
 Type 3: Metal matrix composite (MMC)
 Type 4: Polymer matrix composite (PMC)
 Envelopes
 Types 2 or 4: Annealed aluminium
 Types 1, 3 or 4: Thermal (zirconium) aluminium alloys AT1, AT2, AT3 or AT4
Because of the variety of products on the market, this document cannot be seen as definitive but instead as a
general guide and reference should always be made to the supplier.
As well as steel cores, some manufacturers offer non-ferrous and non-metallic core materials. The attraction of
these materials is their high strength, low density and sag-temperature characteristics compared to conventional
cores. The detraction is cost and/or limited experience with long-term reliability. However, from a mechanical and
thermal point of view, they offer attractive opportunities for large ampacity increase on existing lines via conductor
change.

16
Type Core Envelope
Acronym or
trademark
Description
0
Galvanized or
aluminium clad
steel
Hard drawn
aluminium and
aluminium alloys
ASC, AAC, AASC,
AAAC, ACSR,
AACSR, ACAR, etc.
Operating at temperature not exceeding
95°C
1
Galvanized,
mischmetal or
aluminium clad
steel
Thermal
aluminium AT1
(TAL or 60TAL)
TACSR
Thermal resistant aluminium alloy
conductor, steel reinforced
Invar steel
Thermal
aluminium AT1
(TAL or 60TAL)
TACIR
Thermal resistant aluminium alloy
conductor, invar reinforced
Galvanized,
mischmetal or
aluminium clad
steel
Thermal
aluminium AT2
(KTAL)
KTACSR
High strength, thermal resistant
aluminium alloy conductor, steel
reinforced
Galvanized or
mischmetal clad
steel
Thermal
aluminium AT3
(ZTAL or UTAL)
GZTACSR
Gap type, ultra thermal resistant
aluminium alloy conductor, steel
reinforced
Galvanized,
mischmetal or
aluminium clad
steel
Thermal
aluminium AT3
(ZTAL or UTAL)
ZTACSR
Ultra thermal resistant aluminium alloy
conductor, steel reinforced
Invar steel or
aluminium clad
invar steel
Thermal
aluminium AT3
(ZTAL or UTAL)
ZTACIR,
ZTACIR⁄HACIN
Ultra thermal resistant aluminium alloy
Invar steel or
aluminium clad
invar steel
Thermal
aluminium AT4
(XTAL)
XTACIR,
XTACIR⁄HACIN
Extra thermal resistant aluminium alloy
2
Galvanized,
mischmetal or
aluminium clad
steel
Annealed
aluminium
1350-0
ACSS Aluminium conductor, steel supported
3
Metal matrix
composite
Thermal
aluminium AT3
(ZTAL or UTAL)
ACCR, ACMR
Thermal-resistant aluminium alloy
conductor, metal matrix composite core
reinforced
4
Polymer matrix
composite
Thermal
aluminium AT1
(TAL or 60TAL)
ACPR
conductor, polymer matrix composite
core reinforced
Thermal
aluminium AT3
(ZTAL or UTAL)
ACCFR, ACFR, ACPR
conductor, polymer matrix composite
core reinforced
Annealed
aluminium
1350-0
ACCC, ACPS, ACCFR,
ACFR, CRAC,
HVCRC, C7
Annealed aluminium conductor,
polymer matrix composite core supported
Table 2.1: Conductors classification
High temperature conductors are made of different materials which can withstand more heat while transmitting up
to 100% more current, compared to a conventional conductor of the same diameter when the aluminium cross-
sectional area is increased by reducing the core diameter and/or the use of trapezoidal wires in replacement of
circular wires on top of running at high temperature. They are also used for refurbishment when reinforcement of
towers is to be avoided even if no real increase in ampacity is required.

17
Aluminium and its alloys have been in use for well over 100 years to provide conductivity to overhead conductors.
Initial line construction often limited the rated temperature of all overhead conductors to 40-50°C. In 1970,
however, the limit set on conductor temperature was removed or raised in many countries with the requirement
that statutory ground clearances be maintained. Re-conductoring, therefore, has to match the profiles of these
existing lines.
MATERIAL PROPERTIES OF ENVELOPE WIRES
Type 0 conductors with aluminium (1350-H19) and its alloys permanently lose mechanical strength (anneal) at
temperatures above about 95°C (CIGRE TB 643 [2015]) (This value is debatable and is based on the type of
rod production). To limit this loss of strength, their rated temperature must be restricted accordingly, taking into
account their likely lifetime temperature exposure. The operation of Type 0 conductors at elevated temperature is
described in CIGRE TB 643 [2015].
When a line needs to be reconductored for the purpose of increasing its transit capacity, one solution is to operate
it at a higher temperature. Some types of high temperature conductors are designed with an aluminium envelope
annealed intentionally in the factory before installation while others are provided with heat-resistant alloy.
In the case of fully annealed aluminium, loss of strength in the aluminium portion of the conductor at high
temperatures will not occur. However, its low strength must be compensated for by means of increased core
strength, either by using a stronger core material, or by simply using a larger core. To anneal the envelope, two
different techniques can be used: annealing the individual wires prior to stranding the conductor or heating the
whole conductor.
In the case of thermo-resistant aluminium alloys, the alloy is formulated (by the addition of Yttrium, Zirconium and
other elements) so that it retains its full strength at temperatures up to and beyond the annealing limit of standard
hard-drawn aluminium. There are various grades of alloys capable of operation up to 150, 210, and 230°C (see
Table 2.2). They all have similar strength to hard-drawn aluminium, removing the need for larger or high-strength
cores.
It should be noted that the electrical resistance of various aluminium alloys typically increases as their strength
increases (Table 2.2). Although actual values vary slightly according to standards used, fully annealed 1350-O (or
1370-O) aluminium, for instance, has a conductivity of 61.8% IACS (International Annealed Copper Standard)
while type A1 used in conventional conductors has a conductivity of 61.2% and alloy A3 is at 52.5%. Thus when
added strength is required, conductivity gains are usually not realized.
MATERIAL PROPERTIES OF CORE
The conductors considered in this brochure utilise several different core materials.
Steel and Invar are the most common ferrous core materials, and both can be either galvanised (zinc or
mischmetal coated), or "metal-cladded" (typically with aluminium). Invar steel is an iron-nickel alloy (Fe-36%Ni)
with a very small coefficient of thermal expansion between 2.8 and 3.6 x10-6
/ºC, depending on temperature (the
core material itself exhibits a knee-point characteristic at about 100°C). Several types of composite materials are
also available commercially including a metal-matrix composite made of alumina fibres in an aluminium matrix and
polymer-matrix composite consisting of a resin matrix and carbon fibre protected by a glass fibre layer integrated
in the resin, or by an aluminium tube. Table 2.3 gives the principal properties of various core materials.

18
IEC
designation
Formerly known as
Tensile
strength
(MPa)
Conductivity
(% IACS)
Maximum
continuous
operating
temperature
(ºC)
Emergency
operating
temperature
(ºC)
A1 1350-H19 160 to 200 61.0 90(2)
A3 6201-T81 315 to 325 52.5 90
(1)
1350-0 (fully annealed) 42 to 98 61.8 200 250
AT1 TAL or 60TAL 159 to 169 60 150 180
AT2 KTAL 225 to 248 55 150 180
AT3 ZTAL or UTAL 159 to 176 60 210 240
AT4 XTAL 159 to 169 58 230 260
(1)
ASTM values
(2)
This is based on the type of rod production. For continuous-cast rod, it could be as high as 125ºC
Table 2.2: Aluminium conducting materials properties (ASTM B609 and IEC 62004)

19
Core Properties as per ASTM Other Properties for Information
Description
ASTM
Standard
(Metric)
Tensile
strength
(MPa)
Density
(kg/m3
)
Modulus
of
elasticity
(GPa)
Thermal
expansion
(10-6
/C)
Maximum
continuous
operating
temp.
(C)
Zinc Coating
Regular
Strength
Steel
B 498 1380 - 1450
7780 200 11.5
200
High
Strength
Steel
B 606 1520 - 1620
Extra-High
Strength
Steel
B 957 1725 - 1825
Ultra-High
Strength
Steel
B 957 1825 - 1965
Invar Steel (see note) 1030 - 1080 8000 162 2.8 - 3.6
Mischmetal
Coating
Regular
Strength
Steel
B 802 1380 - 1450
7780 200 11.5 250
High
Strength
Steel
B 803 1520 - 1620
Aluminium-
Clad
Regular
Strength
Steel
B 502 1103 - 1340
6590 162 13.0
260
High
Strength
Steel
B 502 1340 - 1450
Invar Steel
Class 14
(see note) 1030 - 1080 7100 152 3.7 - 10.8
Invar Steel
Class 17
(see note) 870 - 1040 6750 146 4.1 - 11.2
Composite
Metal-Matrix B 976 1380 3337 210 6.3 300
Regular
Strength
Polymer
Matrix
B 987 1724 1938 124- 150 1.6 180
Note: From IEC TC7 PT 62774
Table 2.3: Core materials properties (ASTM and IEC)
For High Temperature Low Sag conductors (HTLS), considering the increased sag caused by higher temperature,
the use of a core material with low thermal expansion is a must. When the temperature of a composite conductor
is increased, the aluminium (or aluminium alloy) envelope wires usually expand at a higher rate than the core. This
expansion is accompanied by a proportional reduction in its share of the total tensile load on the conductor. At a
given temperature (called the "knee-point"), the envelope becomes mechanically "unloaded", the conductor being
supported only by its core. It is at this point that the sag is governed only by the thermal expansion of the core.
According to IEEE 1283 [2013], laboratory investigations have shown that:
 High-temperature operation of conductors with a standard (100% zinc) galvanized steel core can be
limited by the adherence of zinc coating to steel core wires. Some important generalizations and
observations about high-temperature operation of galvanized steel core wire include:

20
 The steel wires of ACSR and ACSS conductors will run hotter than the aluminium wires. Tests show
temperature differences between the steel core and outer aluminium wires can be as high as 10%
of the conductor surface temperature for new conductors and 20% for old conductors, depending
on stranding, age, and ambient conditions.
 The zinc coating does not adhere well to the core wires at temperatures in excess of 200°C
(392°F). Operating temperatures above this value will decrease the life expectancy of in-service
conductors due to reduced corrosion resistance from subsequent pitting of the steel wires.
 Temperatures in excess of 225°C (437°F) cause the zinc surface layer to alloy with the underlying
steel. This alloying forms brittle compounds, which have a tendency to flake and spall and tend to
lower the corrosion resistance of the galvanized wire. Additionally, brittle cracks in the zinc alloy
layer will greatly increase the underlying steel’s susceptibility to fatigue.
 Steel core wire coated with a zinc alloy, 5% aluminium mischmetal coating, often referred to as
“mischmetal,” is designed to successfully withstand prolonged operating temperatures approaching 300°C
(572°F), allowing conductor temperatures up to about 250°C (482°F).
 The mechanical characteristics of an aluminium-clad steel core are similar to those of a galvanized steel
core because of their comparable steel strength to total core strength ratios (approximately 0.94).
However, the types of degradation described for zinc-coated steel core wires due to elevated temperatures
are not exhibited by aluminium-clad core wires. High temperature effects on aluminium-clad wires are
minimal up to approximately 300°C (572°F), above which the tensile strength of these wires exhibits a
smooth degradation with temperature.
In their standard forms, both steel and invar core wires are galvanised (with zinc or mischmetal) to protect them
from corrosion. An alternative to galvanising is to clad the core wires, typically with aluminium. Aluminium clad
core properties are dependent on cladding thickness which is commonly 22% of the core cross-section for HS
steels and 25% for Invar steels. Mischmetal is a galvanising process with a small amount of aluminium (~5%) in
the zinc bath. Mischmetal is an improved coating with better corrosive protection at high temperature.
It is worth mentioning, that zinc or mischmetal have self-recovering properties in case of a scratch which is not the
case for aluminium clad.
By using clad core wires in place of standard galvanised wires, improvements are made both to the corrosion
resistance of the core and to the conductivity of the conductor as a whole. Since cladding reduces the cross
sectional area of steel (or invar), there can also be a significant weight saving, but also an increase in the thermal
expansion of the core due to the cladding constituent with much higher thermal expansion coefficient. There will
also be a corresponding reduction in the strength of the conductor, but this effect can be offset by using a higher
strength steel (or Invar). The end result is a conductor that is lighter and more conductive than a conductor of the
same strength with a galvanised core. If a standard stringing basis of a fixed proportion of breaking load (typically
20%) at a temperature of 10ºC is used, the result will be a lower initial sag. However, the clad core will typically
have a higher expansion coefficient than the standard one, so the overall thermal expansion of the conductor will
be higher, but the lower initial sag will still mean that a higher rated temperature can be applied. This, coupled
with increased conductivity, can result in a significant rating improvement.
Conductors with clad, rather than galvanised, cores are identified as such by the use of a suffix to their standard
code. For example, ACSR/ACS (In the USA, the suffix “AW” is used instead, giving ACSR/AW), indicating an ACSR
with aluminium-clad steel core wires, and TACIR/HACIN, indicating a TACSR (ACSR with a thermo-resistant alloy)
with a High-strength aluminium-clad invar core.
For the conductors described in this brochure, galvanising or cladding is only applicable to steel and invar cores: it
is not applicable to the metal or polymer matrix composite materials.
An EPRI report [2009] stated that glass-carbon/ organic matrix composites were subjected to a series of tests to
evaluate the physical-chemical impacts on potential service life of composites after accelerated aging. Testing
carried on the composite between 180 and 210ºC shows two co-existing degradation modes under thermal stress -
thermal oxidation and hydrolysis. The core can operate at 150ºC and for short peaks at 180ºC. Conductor core
temperature above 200ºC causes severe thermal instability.

21
The utility questionnaire provided the Maximum Design Temperature for Normal Operation and Emergency shown
in Table 2.4.
Conductor type Normal operation (°C) Emergency operation (°C)
1 TACSR 150, 150, 150, 150, 125 170, 150, 180, 150, 150
TAL 100 100
GZTACSR 165, 95, 175, 210 180, 95, -, 240
XTACIR 230, 230 290, 240
ZTACIR 210, 210 240, 240
HACIN 80 150
2 ACSS 150, 200, 250, 150, 200 150, 200, 250, 200, 250
3 ACCR 240, 210, 200, 210, 210 240, 240, 200, 210, 240
4 ACCC 150, 175, 175, 150, 100, 100, 180 200, 180, 175, 180, 150, 180, 200
Table 2.4: Design temperatures provided by utilities
COMPACT DESIGNS
Changes can also be made to the outer aluminium wires. A standard conductor (Figure 2.1 (a)) is constructed of
layers of wires having a round cross section, resulting in a significant proportion (about 28%) of a conductor’s
cross section without aluminium. By using shaped aluminium wires, a conductor can be constructed with a much
more “solid” cross section, increasing conductivity while maintaining the same outer diameter. The wire shape in
compact conductors is usually trapezoidal (Figure 2.1 (b)) and may be Z-shaped (Figure 2.1 (c)) which makes
slightly more compact conductors.
A compact conductor will be heavier than a standard conductor of the same diameter, resulting in increased tower
loads. This is not necessarily a significant effect though, since peak tower loads are generally a function of
additional climatic (ice and wind) loads, which are in turn a function of conductor diameter rather than weight. The
increase in loads resulting from an increase in weight will be a small proportion of peak load. Peak loads resulting
from the action of wind alone may even be reduced, as the outer surface of a compact conductor is smooth, and
typically exhibits a lower drag coefficient at high wind speeds. Table 2.5 compares standard and compact cross-
sections for type 0 conductors (AAAC and ACSR) designs.
(a) Conventional round-wire
conductor
(b) Compact trapezoidal-wire
conductor
(c) Compact z-shaped wire
conductor
Figure 2.1: Standard and compact conductor cross sections

22
AAAC
ASTER 228
AAAC-Z
AZALEE 261
ACSR
CROCUS 228
ACSS/TW 237.6
Cross section (mm²) 227.83 261.68 227.80 237.60
Outside diameter (mm) 19.6 19.6 19.6 18.06
Mass per unit length (kg/m) 0.62 0.72 0.84 0.88
RTS (daN) 7405 8490 9210 8900
Number of wires x dia. (mm) 37 x 2.80 37 x 2.8 (ZW)
7 x 2.8 (steel)
30 x 2.8
7 x 2.81 (steel)
7+11 x 2.54 (TW)
DC resistance at 20°C (Ω/km) 0.1460 0.128 0.157 0.1446
Modulus of elasticity (GPa) 57 59 75.5 190
Linear expansion coefficient
(10-6
/°C)
23.0 23.0 18.0 11.5
TW: Trapezoidal wires, ZW: Z-shaped wires
Table 2.5: Standard and compact cross-sections for AAAC and ACSR designs
In accordance with ASTM, compact conductors are generally identified by a suffix to their standard code, typically
“TW” for Trapezoidal Wire, e.g. ACSR/TW, ACSS/TW and “Z” for Z-shaped wires, e.g. AAAC-Z. The smooth outer
surface of a compact conductor can, however, be detrimental to its thermal rating, since it can inhibit convective
heat transfer. The effect is not very significant because at higher temperatures the aluminium wires expand which
causes a slight increase in conductor diameter and space between the wires that allows improved heat convection.
Thus, when considering the potential differences in temperatures between the various layers of aluminium wires
and core wires, the difference between round wires and trapezoidal or Z-shaped wires is generally ignored.
All of the conductors described in this brochure can be manufactured either as round-wired or compact versions.
The only exception is the gap-type conductor, which requires that the inner-most aluminium layer, adjacent to the
core, be always of compact construction. The outer layers can be either standard or compact construction
(Figures 2.5 and 2.6).
Z-shaped wires, as well as trapezoidal wires, compact the conductor so that, for the same diameter, considerably
more aluminium is available. Typically, the 261-Z has an identical outer diameter to a typical Lynx conductor but
up to 43% more aluminium cross-section if used in the AAAC format and 20% more if used in the ACSR format. It
is supplied in high conductivity AAAC and ACSR and also high temperature versions. The Z-shaped aluminium wires
were first designed and commercialized in the mid 1970s. Z-shaped cables and conductors have at least the last
layer of wires composed of Z-shaped profiled wires, which overlap each other, the bottom of one wire being placed
under the top of the adjoining wire. This gives them an almost cylindrical outer surface ribbed with helical grooves
(Figure 2.2).
Short circuit tests have been made on conductors with Z-shaped wires at EDF’s Renardière Laboratory. These tests
have shown that up to 4 adjoining Z-wires can be broken and still stay in the outer layer avoiding therefore a
possible contact with another near phase.
The hardware and accessories for compact conductors, as well as the compression techniques, are almost identical
to a standard conductor.
Considering an equal section, compact conductors have a smaller external diameter than standard conductors
which reduces the drag force applied by the wind. Moreover, as shown in Figure 2.3 [Gaudry et al, 1998], the drag
coefficient curves of a standard and compact conductor display significantly different behaviour as a function of
wind velocity: At low wind velocities, a plateau shows up with a drag coefficient (Cd) slightly above 1.2, followed by
a pronounced drop leading to a minimum Cd value and then a slight increase as the wind increases. As a general
rule:
 The minimum Cd value will decrease as the outer layer of the conductor becomes smoother
 The wind velocity at which the minimum Cd value occurs will increase as the outer layer of the conductor
becomes smoother

23
 For the same roughness, the wind velocity at which the minimum Cd value occurs will decrease as the
conductor diameter increases
Consequently, compact conductors have a higher Cd at low wind velocity and a lower Cd (which reduces the drag
load) at high wind velocity as shown in Figure 2.3. While the advantage of a low drag coefficient is significant at
the highest wind speeds, it cannot be taken into account for lower wind speeds nor for combined ice and wind load
(generally with lower wind speed anyway) since the conductor is then covered with ice and its drag coefficient
depends on the ice roughness.
Figure 2.2: Z-shaped conductors
Figure 2.3: Drag coefficients for a standard and compact conductor [Gaudry et al, 1998]
TYPE 1 CONDUCTORS
The "thermo-resistant aluminium conductor steel reinforced", (Z)TACSR, is made from thermo-resistant aluminium-
zirconium alloy, either AT1 or AT3, depending on the operating temperature desired. Figure 2.4 shows the basic
schematic of a (Z)TACSR and (Z)TACSR/ACS conductor. It is geometrically identical to conventional ACSR, with the
only differences being a slightly reduced conductivity and a much increased maximum allowable temperature
(Table 2.2). It is not, by design, a low-sag conductor as it has the same thermal elongation behaviour as ACSR. Its
main advantage is that its aluminium alloy wires do not lose strength at high temperature, allowing the conductor
to be operated at high temperature where electrical clearances allow.
This technology was first developed in Japan where TACSR conductors have been installed since1960 and to date
the vast majority of transmission lines are equipped with HT conductors. It has been used in Europe since the late

24
1980s. Problems of corrosion protection have led to high temperature conductors often being reinforced with
aluminium clad steel (ACS).
Figure 2.4: Cross Section of TACSR/TACSR/ACS Conductor
Type 1 conductors may be produced with an Invar steel core to overcome sag problems. It is commonly known as
(Z)TACIR or (Z)TACIR/HACIN (HACIN is high strength aluminium clad invar). In this form it is often used to replace
ACSR. The cladding offers improvements in conductivity as the aluminium cladding has a higher conductivity than
the steel it replaces, but is detrimental to the expansion coefficient as the aluminium expands more than the steel
it replaces.
Prestressing (Z)TACIR or (Z)TACIR/HACIN can effectively lower the temperature of the knee-point.
A gap type (GTACSR or GZTACSR) conductor makes use of a galvanised steel core, surrounded by a thermo-
resistant aluminium alloy which is typically either AT1 or AT3, depending on the maximum operating temperature
desired.
Although made up of the same combination of materials, what sets the gap-type conductor apart from TACSR is its
construction. The wires of the innermost layer of aluminium are always of trapezoidal shape, and sized such that
the inside diameter of the resulting tube is slightly larger than the external diameter of the core within it. This
radial gap (Figure 2.5) between the core and the aluminium trapezoidal wires allows the core and outer layers to
move independently.
By employing specialised stringing procedures, gap-type conductor are sagged-in in such a way that the entire
conductor stress is carried by the steel core only, effectively setting the knee-point of the conductor at the erection
temperature. The expansion coefficient of the conductor above the knee-point temperature will be that of the steel
core (11.5 x10-6
/ºC), rather than the complete conductor.
Although Figure 2.5 shows a gap-type conductor with a round-wire outer layer, it is also available with all
aluminium layers being of compact construction. The UK National Grid started using 'Matthew' in the late 1990’s, a
620 mm2
conductor that has such a construction (Figure 2.6).
With the exception of the more complex installation procedure, gap-type conductor will exhibit the same properties
(corrosion, electrical, etc.) as a TACSR. However, its low sag behaviour will allow it to be operated at much higher
temperatures than ACSR.
Figure 2.5: Cross-section of a GTACSR Conductor

25
Figure 2.6: 'Matthew' 620mm² Gap conductor used by National Grid [Tunstall et al, 2000]
TYPE 2 CONDUCTORS
ACSS (Aluminium Conductor Steel Supported), developed in North America around 1970, consists of fully annealed
aluminium wires, around a stranded steel core. The core can be HS, EHS, UHS, mischmetal or aluminium Clad
Steel, depending on the RTS required. These conductors can increase the existing current capacity of an OHL and
provide reduced sag, even when operating at up to 250°C, compared to standard conductors. ACSS is mostly
supplied in compact design – designated ACSS/TW indicating the use of trapezoidal shaped wires, as illustrated in
Figure 2.7.
The conductivity of annealed aluminium wires (61.8% IACS) is higher than hard-drawn aluminium wires (61%
IACS) used in ACSR.
The tensile strength of fully annealed aluminium (60 MPa) [IEC TC7 PT 62641] is lower than that for hard-drawn
aluminium (160-200 MPa) [IEC TC7 PT 62641], however, this is offset somewhat through the use of a high
strength steel core.
The reduced capacity of the annealed aluminium wires to carry significant mechanical load results in a relatively
low knee-point for the conductor. This knee-point can be significantly reduced by pre-stressing the conductor,
which has the effect of imparting a permanent plastic deformation to the aluminium wires, such that an even
greater proportion of stress is carried by the steel core. The knee-point of ACSS can therefore vary greatly
depending on installation methods, but could typically be around 60°C, with the expansion coefficient above the
knee-point being essentially that of steel (11.5 x10-6
/ºC).
Provided pre-stressing is applied, the low knee-point leads to very high rated temperature with relatively low sag.
As the aluminium wires are already fully annealed, there is, theoretically, no limit to the temperature that the
conductor can be operated to, as further annealing is impossible. However, other limits apply, the most critical of
which being the ability of the core wires to remain intact. Galvanising is prone to degradation above 200ºC,
however, aluminium-clad or mischmetal (Al-Zinc alloy) clad cores are more robust (Table 2.3) against heat
degradation.
Annealed aluminium wires provide higher mechanical self-damping for ACSS than for standard ACSR of the same
stranding ratio. In theory this should allow higher tensions whilst keeping within required vibration limits (see
chapter 7).
Aluminium Conductor Steel Supported (ACSS) is described in EN 50540 and ASTM B856-95 and Shaped
(Trapezoidal)-Wire aluminium Conductor Steel Supported (ACSS/TW) is described in ASTM B857.
Two processes exist to manufacture ACSS: the first one consists of drawing the wires, stranding the conductor
and annealing it in furnaces. This process is called "batch annealing". This process cannot be used with galvanised
steel cores as the high temperature will damage the zinc coating. It may also lead to thermal stress in the core and
the impact of this is not well known (the annealing is done at 350°C). The second process requires the aluminium

26
wires to be annealed after drawing but before stranding. This process provides more uniform properties but is
more difficult to achieve, as annealed aluminium wires are more prone to damage from the plant equipment during
stranding.
Figure 2.7: Sections of ACSS/TW
TYPE 3 CONDUCTORS
Type 3 conductors are made of a metal matrix composite core (MMC) on which layers of aluminium-zirconium alloy
wires are stranded. A section is shown in Figure 2.8. Its structure is essentially the same as any ACSR and differs
only by the materials used. The core is made of wires composed of alumina fibres in an aluminium matrix, forming
a composite material. Conductor trials have been going on since 2001 and it was introduced commercially in 2003.
The composite core material provides a substantially lower coefficient of thermal expansion above its knee-point
(6.310-6
/ºC) (Table 2.3), compared to a steel core (11.510-6
/ºC), resulting in a significant reduction of the
expansion coefficient of the conductor as a whole. Furthermore, the core material is significantly lighter than steel,
resulting in a lower weight, while at the same time being both stronger and having a higher elastic modulus. The
metal matrix composite core has significantly greater conductivity than steel.
Figure 2.8: Cross section of type 3 conductor
If sufficient clearances are available, a type 3 conductor operating above its knee-point will produce little further
increases in sag (compared to steel) as the temperature is increased further.
Some advantageous properties of the conductor are:
 Improved corrosion resistance: chemically, the conductor is essentially all-aluminium, and the lack of a
steel core removes the possibility of galvanic corrosion. From a corrosion viewpoint, therefore, it should be
very similar to AAAC.
 Exhibits very little creep: tests carried out by the manufacturer indicate that the core material exhibits very
little permanent elongation over time, even at high temperatures.

27
 Has no undesirable magnetic properties: conductors with a ferrous core experience increases in resistance
due to magnetic effects. This magnetic effect is eliminated.
 High temperature, low sag operation: it can be operated continuously at temperatures up to 210°C and
emergency up to 240°C with AT3 alloy wires.
TYPE 4 CONDUCTORS
This conductor type is made of a polymer matrix composite (PMC) core usually made of carbon fibres in a resin or
epoxy resin matrix (depending on the manufacturer). The core is protected against galvanic corrosion; by either an
annular sleeve made up of glass fibres, all in the same resin matrix, or protected by an aluminium alloy welded
tube or other methods. The envelope can be either annealed aluminium or thermal resistant aluminium alloy wires,
round, trapezoidal or Z-shaped.
The polymer matrix can be made with thermoplastic or thermosetting compounds. Since 2002, several companies
have produced various types of PMC, mostly, but not only, thermosetting compounds. Their characteristics are
provided in Table 2.3. Thermosetting compound are more difficult to recycle.
The polymer matrix composite cores are usually solid, rather than stranded (Figure 2.9), but stranded
configuration exists.
PMC cores can have higher strength compared to steel in order to compensate for the lower strength of fully
annealed aluminium wires.
Temperature limitations do not come from the aluminium wires but from the polymer composite core material, as
temperatures approaching the limit or higher can accelerate aging if sustained for long periods of time. Type 4
conductor cores are designed for a specific temperature, typically in the range of 80 to 200°C. Brief excursions to
higher temperatures can be tolerated, but are generally not recommended since they can alter the properties of
the core material and thus the core strength and durability.
Depending on their characteristics, these conductors can be used for uprating requirements, minimizing conductor
sag or for their light weight, preventing increases in tower loads. This feature alone makes it very attractive for
uprating – a substantial increase in conductor ampacity with no increase in tower loads. The conductor’s very low
coefficient of thermal expansion of 1.6 x 10-6
/ºC typically minimizes conductor sag under very high electrical loads.
Under ice loads, special design can be chosen with higher modulus to meet required sags.
Figure 2.9: Cross-section of type 4 conductors showing composite core covered with glass fibres
envelope (left) or welded aluminium tube (right)

28

29
3. CHARACTERISTICS OF NON-CONVENTIONAL
CONDUCTORS
INTRODUCTION
All of the HTLS conductors studied have the following characteristics:
 Low thermal elongation rates
 Possibility to increase the ampacity of an existing conductor
 Capacity to operate continuously at temperatures well above 100°C without any deterioration of
mechanical or electrical properties.
 Usually same or lower resistance as a conductor of the same diameter.
However, it is less clear which of the HTLS conductors will work best in a particular uprating situation. The stress-
strain models for each of the HTLS conductors are available and utility engineers can evaluate each of the choices
in a given uprating problem.
The best conductor choice ultimately depends on the existing clearance buffer, original design margins,
environmental loading conditions, the magnitude of the desired rating increase, and the total life-cycle cost of
installation and operation.
RELATIVE COST
Besides performance, cost is one of the major factors involved when choosing a conductor type. Table 3.1 below
provides an approximate relative cost factor of each type relative to an ACSR. The relative cost factor compares
the acquisition cost of the conductors but does not cover the possible installation or maintenance cost difference.
Conductor type Relative cost
Type 1 ACIR [EPRI, 2008] 5
Type 1 Gap [EPRI, 2008] 2
Type 2 1.5
Type 3 5
Type 4 3
Table 3.1: Relative cost factor of different conductor types relative to an ACSR
KNEE-POINT
One thing that is vital in designing for HT conductors is the ‘knee-point’. This is the point below which the
conductor sag-tension relationship is determined by the whole conductor whereas above this point it is governed
by the core. The knee-point can be altered by the erection procedure or tension history (e.g. severe ice load or
wind event). Above the knee-point, the aluminium envelope may go into compression – a phenomenon not
considered for standard conductors as the aluminium would always be in tension.
The 'knee-point' of a conductor is a phenomenon observed on all composite conductors where the core material
has a lower thermal expansion coefficient than the wires surrounding it. At temperatures below the knee-point, all
wires of a conductor are under tension. Under these conditions, the thermal expansion coefficient of the conductor
as a whole is governed by both materials making up the conductor (higher than the core on its own, but lower
than the outer wires on their own). As the temperature rises, the outer wires will experience a higher rate of
thermal expansion, resulting in mechanical stress being increasingly transferred to the core. Eventually, the outer
wires actually become stress-free, with most of the conductor tension being borne by the core. Under this
condition, the thermal expansion coefficient of the conductor as a whole becomes close to that of the core material
only. The temperature at which this change occurs is known as the knee-point. As mentioned, it depends on the
installation conditions and for some conductor technologies, the knee-point can be shifted to a lower temperature

30
by increasing the mechanical load through high ice or wind loads or pre-tensioning. This is more effective with
conductors containing annealed aluminium. The knee-point is not a fixed value and depends of many factors
like span length, mechanical tension, ruling conditions, conductor constituent characteristics (e.g.
proportion of envelope section over total section, coefficient of thermal expansion, modulus of each
component). It should be further noted that creep in the conductor will also shift the conductor knee-
point to lower temperatures over time, because conductor creep is primarily driven by the aluminium
constituent, and the tensile load in the envelope shifts to the core while it elongates (due to creep). The
knee-point is defined as the point of inflection of the curve in the sag – temperature diagram (Figure 3.1) or
tension – temperature diagram (Figure 3.2).
Figure 3.1: Knee-point
Figure 3.2: Comparison of knee-points of two conductor types
For a HT conductor to be fully effective, the rated temperature of the line needs to be above the knee-point if
there is to be full benefit from having a low-expansion core. Some ACSR may have a knee-point above its normal
operating temperature range (Figure 3.3).
A conductor such as the gap-type GZTACSR takes advantage of a knee-point that is the same as the erection
temperature, allowing the conductor to fully exploit its low coefficient of expansion of the steel core.

31
Some years ago, when the UK National Grid wanted to increase capacity on its 400kV lines, it required a conductor
which could provide the power capacity increase without infringing on the regulatory clearance. At the initial line
design (the line was built in the 1950s), Zebra ACSR for a particular span length had a sag of 12.2 m at the design
temperature of 50°C. Examples of sag-temperature curves for various non-conventional conductors available at
that time and exhibiting high and low temperature knee-points are shown in Figure 3.3 along with the curves for
standard ACSR and AAAC, which do not exhibit knee-points in the working range 10 -100°C [Tunstall and
Hoffmann, 2003].
From the figure, it can be seen that an AAAC conductor (green line) can be operated at 87°C before exceeding
regulatory clearance, so some increase in capacity is available using this route. However, more capacity, including
n-1 capability was required. The ZTACIR (Invar cored) conductor exhibits a lower increase in sag compared with
the ACSR at all temperatures, although the improvement in performance is only really significant above its knee-
point of 90ºC. However, for the case illustrated, this temperature is well in excess of the safe rated temperature of
about 60°C. The advantage of the ‘Matthew’ Gap-type conductor, at 31.5mm diameter, with its assumed knee-
point of 15°C (a typical erection temperature), is clearly seen in this graph. If the line design were different, with
available sags up to a metre greater than that given, the advantage of the gap-type over the invar-cored conductor
becomes less apparent, as the curves are converging above 90°C. Typical Type 3 conductor knee-point is around
70-90°C in most applications. The knee-point of type 2 conductors can vary greatly depending on installation
methods, but could typically be in the range 20-60°C, with the expansion coefficient above the knee-point being
essentially that of steel (11.5x106
/ºC).
Annex D provides an example of a high temperature sag-tension test and knee-point temperature measurement.
Figure 3.3: Standard ACSR and AAAC compared with ZTACIR and Gap type conductors exhibiting high
and low temperature knee-points. This graph is schematic only and should not be used to estimate
sags as sag characteristics are not linear
MODULUS OF ELASTICITY
The most quoted references for testing by suppliers were IEC 61089, EN50540 and the Aluminium Association for
stress strain and E modulus testing.

32
CREEP
One problem with non-conventional conductor types that operate with the aluminium envelope in compression is
that the effect of creep is not necessarily well known. The creep of non-conventional conductors must be studied
to compare to conventional conductors so as to define the temperature correction to use when installing the
conductor. Unlike conventional conductors, conductors with fully annealed aluminium are generally controlled by
the core creep. Moreover, the influence of temperature on creep is not well known at high temperature, since the
load is transferred to the core.
GREASES
Some utilities require additional protection against corrosion especially where the line is exposed to environmental
accelerators like extreme temperatures, exposure to humidity, salt and acidic pollutants. This requirement is
commonly solved with grease. For the application in high temperature conductors with galvanised steel cores,
grease with an elevated drop point has to be used to avoid leakage of grease through the individual layers of the
conductor. This grease penetration can cause corona problems as well as allowing corrosion.
Grease that protects conductors from corrosion can be the limiting constraint for high temperature conductor
operation [IEC 61394, 2011]. Commonly, the grease used in conventional conductors is a lithium soap based type
with strict temperature limitations. If grease is used, the temperature limits of the particular grease should be
determined either by consulting the conductor or grease manufacturers, or by testing. Hot applied greases are
generally unsuitable for operation above 100°C as their melting point is typically around this figure and they will
become fluid and flow out of the conductor at high temperatures. General purpose, soap thickened lubricating
greases may exhibit excessive oil separation at high operating temperatures and may also be unsuitable for use.
For application in conductors run at high temperatures, grease with increased drop point and oil separation point
has to be used to avoid the penetration of grease through the individual layers of the conductor. Grease selection
is important and the properties required must meet the following:
 Retain its properties and performance over the specified temperature range
 Remain within the conductor with no migration to the outer surface
 Provide protection of the multi-metal combinations for the specified life of the conductor
 Be highly effective in environments of high humidity, coastal and industrial regions
 Be of a consistency that can be readily applied to the conductor with standard equipment
 Have a consistency that when applied to the conductor during the stranding process will hold its form to
provide a concentric film on the core prior to the next strand being laid
The grease formulator has the responsibility to not only supply a product which is capable of satisfying all of the
performance requirements and is ultimately fit for purpose, but must also demonstrate compliance with recognised
standards. The internationally recognised standard IEC 61394 should be used to verify compliance of the grease
with the requirements. Particular attention should be given to multi-metal combination conductor construction,
which is the most susceptible to corrosion in service, particularly in coastal regions where the saline nature of the
moisture significantly increases the potential to create a galvanic cell between steel core and the aluminium when
moisture acting as the electrolyte, enters the interstices of the conductor. Moisture can be drawn into the
conductor during energizing, hot and cold cycles or forced in by the wind. With maximum operational temperatures
from 80°C to 230°C, raw material limitations and commercial awareness does not allow the grease formulator to
offer a single universal grease to cover the full temperature range. Raw material limitations are based on the fact
that as mineral oil will start to decompose at temperatures in excess of 180°C; full synthetic technology has to be
employed to ensure stability and reversibility characteristics of the grease are met. In depth testing and raw
material selection has shown the optimum transition point from natural (mineral oil) based technology to full
synthetic technology to be for conductors rated above 150°C.
Although synthetic technology could be used for all conductors with no performance limitations, it would not only
be over engineered but also commercially unacceptable.
To test the maximum temperature rating of either grease technologies two tests are used: Drop point and Oil
separation. Drop point (test method ISO 2176), although essential for the test and control of hot applied grease, it

33
is not as important for cold applied. It does however provide a clear and defined high temperature value and is
commonly used by inspectors when testing complete conductors during manufacture.
Oil separation is an extremely important test as it demonstrates the ability of the grease to retain its form within
the conductor at the maximum specified temperature over time, with absolute minimal oil bleed. When excessive
amounts of oil or components separate from the grease structure in service they migrate to the outer surface of
the conductor, attracting dust, sand and atmospheric pollutants. As these build up, corona discharge could be
produced.
The oil separation test is IP 121 test method. It measures the mass fraction of oil that separates from the grease
when held at the maximum temperature over a given time period. Temperature is simply related to the specified
temperature, however the time period will vary dependant on whether the test is to demonstrate compliance with
a specification.
IEC is in the process of issuing a new version of IEC 61394 which will incorporate all high-temperature tests and
protocols.
The ability of the grease to resist shear and hold its form is required to ensure that its physical properties are not
impaired during multiple applications or while the conductor is in service, where in certain conditions it has to
tolerate mechanical loading generated by oscillation of the conductor.
SHORT CIRCUIT
Tests conducted at Kinectrics [2005] showed that rapid temperature excursions of the aluminium envelope due to
high fault currents can take some time to raise the temperature of the core (Figure 3.4). This process also occurs
in conventional conductors. Short circuit events lead to an instantaneous jump in conductive wire temperature. The
extent of the temperature jump is dependent upon the conductor’s initial temperature, its aluminium content, the
fault current, and the duration of the event. As with any conductor, a short circuit event can cause very rapid
expansion of the envelope which can lead to birdcaging.
TESTING OF CONDUCTOR
Suppliers provided a list of tests for their products. The following tests were listed:
 Electrical tests :
 Resistivity
 DC Resistance
 Corona
 RIV
 Thermal Cycling
 Mechanical tests :
 Tensile
 Elasticity Modulus
 Coefficient of Thermal Expansion
 Transition Point
 Stress Strain Curve
 Creep
 Vibration
 Laboratory fatigue tests
 Self-damping
 Field tests
Tests were conducted according to CIGRE TB 426 [2010], EN50540 [2010], ASTM B856 and ASTM B857.

34
Figure 3.4: Temperature response comparison of a 1020 kcmil Type 4 conductor and 795 kcmil ACSR
Drake Type 0 conductor to a short circuit event
In terms of hardware testing, some manufacturers referenced the users back to the supplier of the hardware and
generally the hardware testing was very similar to that for conventional conductors.
Utilities provided the following information:
 “Do you have a specification or any testing requirements?”
Twenty-four responses said “Yes” and six said “No” to this question. Those that responded in the negative
covered the full voltage spectrum but interestingly all except one is from the Americas.
 “Were tests witnessed by the company?”
Fifteen responses in the affirmative and twelve in the negative. No obvious correlations existed here
 “Have sags been verified after being installed for some time to verify creep?”
There were fourteen positive and fourteen negative responses to this question. In one case the supplier of
the conductor (Type 3) was reported to have performed the check.
 “Were tests done to confirm the modulus and stress-strain data of the new conductor?”
Fifteen positive responses and fourteen negative responses with one response advising the supplier of the
conductor (Type 3) had performed these tests.
AGEING
As shown in Tables 2.2 and 2.3, all conductors will age above a given temperature. The key ageing effect may
relate to the upper temperature the strength member (core) coating can tolerate for type 2 conductors or the
temperature the polymer matrix composite core itself can tolerate for type 4 or it can be the aluminium envelope
for type 4 conductors.

35
For gap (type 1) conductors, the ageing of the galvanised coating on the core is expected at temperatures above
210o
C and 240o
C.
Conductor ageing is expected at temperatures above the maximum temperature at which their core is rated
(Table 2.3).
Ageing tests were performed where the main objective was to compare the performance of ACSR and TACSR at
high temperatures up to 150°C [Nascimento and Ueda, 1998]. The tests were performed on a test line having two
spans of 122 and 89 m, respectively.
The conductors were kept at high temperature for one year and the energisation was made by means of a 300 kVA
transformer and voltage regulators. A weather station registered ambient temperature, wind speed and direction
and solar radiation. The conductor temperature was also continuously registered.
The natural variation of wind speed and temperature made it impossible to keep the cable temperature constant
(and hence the electric current). The histograms of Figure 3.5 show the distribution of the surface temperature of
the conductors over time.
Samples of complete cables were tested for tensile strength determination. The average results (Table 3.2) show
that the TACSR showed no considerable variation of its RTS after one year at high temperatures. In turn, ACSR
showed loss of 9% of its RTS.
Strain tests were also performed on samples of aluminium wires from the cables tested (Table 3.3 and Figure 3.6).
It was demonstrated that TAL strands also lose strength over time, but their residual strength tends to stabilize at
a value higher than conventional 1350-H19 wires.
Metallographic images of samples were also taken from aluminium wires and show that the ageing of the cable
gives rise to the formation of crystals. In alloy "TAL" this phenomenon is less pronounced due to the presence of
zirconium.
EFFECT OF ICE LOADS
To study the effect of ice accretion on type 2 conductors, ice rain was simulated by spraying water on a 100-m
span [Van Dyke et al, 2011]. A comparison was done of ACSS Linnet 336.4 kcmil and Hawk ACSR conductors, both
with circular wires. Figure 3.7 shows the Linnet type 2 conductor after three cycles of icing and de-icing with an
equivalent ice thickness of 25 mm. The elongation of the outer layer wires is clearly visible.
The effect of wet snow accretion was also studied on a 160-m span of a type 2 TW 883R conductor. The conductor
was pre-tensioned at 25% RTS (86 kN) and then the tension was reduced to 10% RTS (34 kN). Six cycles of snow
load and snow melting were obtained using a snow cannon (Figure 3.8). During the snow load cycles, the
conductor tension reached 61 to 70 kN on three occasions. There was no visible deformation of the type 2
conductors at the end of the tests. This result might be an indication that trapezoidal wires, which have a larger
section than circular wires, are less sensitive to ice accretion.
Figure 3.5: Hourly average temperature at the conductor’s surface

36
Conductor Strength
Reference – New
before
experiment
After 4 months
of experiment
After 12 months
of experiment
Type 0 (ACSR)
kN 39.1 37.1 35.7
Loss (%) - 5.3 8.9
Type 1 (TACSR)
kN 37.4 37.5 38.4
Loss (%) - ~0 ~0
Table 3.2: Percentage of conductor strength loss
Wire alloy Strength
Reference – New
before
experiment
After 4 months
of experiment
After 12 months
of experiment
Al 1350
kN 3.16 1.25 1.48
Loss (%) - 60 53
TAL
kN 3.17 2.70 1.99
Loss (%) - 15 37
Table 3.3: Percentage of wire strength loss
Figure 3.6: Tensile strength in aluminium strands
A thorough inspection of three Hydro-Québec–TransÉnergie transmission lines built in 1987, 1999 and 2006
equipped with type 2 conductors has shown some looseness on the outer layer of the conductors in some areas, as
shown in Figure 3.9. There was no bird caging even if the two older lines experienced some ice rain episodes. This
small deformation of the outer layer does not affect the performance of the conductors.
In geographical areas which experience severe ice loadings, HTLS conductors which employ annealed aluminium
may yield sags under heavy loading conditions which are comparable or even larger than the sag at high
temperature i.e. weather load sags dominate over electrical sags in line design [EPRI, 2008].
No information could be found on the other conductor types.

37
Figure 3.7: Looseness on the outer layer of a Linnet ACSS cable after simulated ice rain
Figure 3.8: Artificial wet snow accretion on the ACSS TW 883R cable
Figure 3.9: Wires looseness on the Hydro-Québec transmission line
RECYCLING
Types 1 and 2 conductors
Aluminium, aluminium alloy, steel and invar steel are easily recycled.
Type 3 conductors
Type 3 conductors can be recycled like all aluminium alloy conductors. The outer strands are not separated from
the core. The fibres will be an alumina by-product in the smelting process and can be put into landfill or could be
treated as alumina in a secondary recycling process.

38
Type 4 conductors
Type 4 conductors envelope is made of aluminium or aluminium alloy and so is easily recycled. The polymer matrix
can be made with thermoplastic composite, which is easily recyclable, or thermosetting composite, which may be
more difficult to re-cycle.
For thermosetting, the core can be burnt off (the resin component may be dissolved from the core if it is an
environmental concern to burn or use environmentally unfriendly chemicals).

39
4. INSTALLATION OF NON-CONVENTIONAL
CONDUCTORS AND MAINTENANCE
EFFECT OF ERECTION TENSION AND STRINGING
Conductor tension changes as a function of time, temperature and environmental conditions. Generally speaking,
conductors are installed at an initial (erection) tension necessary to accommodate metallurgical changes that will
affect the conductor's behaviour later. Consideration is given to the mechanical limits of the conductor and
structures, anticipated ice loads, wind loads, conductor creep, and thermal loads associated with ambient
conditions and conductor temperature based on anticipated electrical loading. In addition to these design
parameters, substantial consideration is also given to conductor tension as it relates to aeolian vibration-induced
fatigue failure.
As a conductor is pulled from its shipping reel through a bull wheel tensioner and through a number of installation
sheaves installed at each support structure, the conductor undergoes a certain amount of stress. Depending upon
the pulling tension, the number of sheaves, and the angles (both vertical and horizontal), the core strand(s) and
outer strands will encounter mechanical forces they generally will not see after the installation has been
completed. While composite core conductors (types 3 and 4) may have bending limitations and require the use of
properly sized sheaves, particularly at the first and last structures (some manufacturers may recommend roller
array assemblies), following proper installation procedures such as IEEE 524 Installation Guidelines [2003] and the
manufacturer’s recommendations can ensure full conductor integrity. This is true not only for composite core
conductors, but for all other conductor types, as well.
After a conductor travels through numerous sheaves, and as the conductor’s tension is increased to the initial
stringing tension, some degree of strand settling will occur. Strand settling is essentially the result of the individual
conductor strands in each layer seating themselves into the layer below as tension is applied. Each layer of strands
is wound around the layer beneath the wire in opposing directions causing each layer to cross the other at an
angle of twice the lay length angle. Only the central ‘king’ strand wire at the centre of the conductor is straight.
Each point of strand-to-strand crossing becomes a point of compression between the strands as each helically
shaped strand tries to straighten out and force its way towards the centre of the conductor. Such compression can
effectively restrain tensile stretching of the aluminium strands during loading, and lengthen the strand’s helical
path/length after loading. Strand settling generally occurs relatively quickly. For conductors that use fully annealed
aluminium strands such as type 2 and 4 conductors, this typically happens in less than an hour. Due to the
substantial differences in the conductors discussed in this document, it is advisable to contact the manufacturer for
specifics.
After a conductor is pulled into place, in some cases, there can be substantial differences in time that the
conductor stays in the air before dead-ends are installed. In some cases, particularly with bundled conductors, it
can be advisable to temporarily increase the pulling tension to above the initial tension to equalize the
core/aluminium load sharing. This is known as pre-tensioning. In addition to helping equalize the core/aluminium
load sharing, pre-tensioning is also an effective way to lower the conductor’s knee-point.
The advantage of lowering the conductor’s knee-point is that the core strands of a non-homogeneous conductor
have a lower coefficient of thermal expansion (CTE). As a conductor’s temperature rises (as a function of its
electrical resistance and electrical load), the outer strands begin to ‘relax’ as they transfer tensile load to the lower
CTE core. Once the conductor passes through its thermal knee-point and the weight of the conductor is supported
only by its core, the core strand’s CTE then establishes the conductor’s thermal sag characteristic (discussed in
Chapter 3). Once they reach the knee-point, non-annealed conductive strands tend to go into compression.
When conditions and equipment allow, pre-tensioning can be a very effective means of improving a conductor’s
thermal sag profile.
The fittings and installation methods for (Z)TACIR (type 1 conductor) are essentially identical to those for ACSR,
the only exception being slightly longer current-carrying joints to accommodate higher load currents.

EXPERIENCE WITH THE MECHANICAL PERFORMANCE OF NON-CONVENTIONAL CONDUCTORS

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Similar to EXPERIENCE WITH THE MECHANICAL PERFORMANCE OF NON-CONVENTIONAL CONDUCTORS

Similar to EXPERIENCE WITH THE MECHANICAL PERFORMANCE OF NON-CONVENTIONAL CONDUCTORS (20)

More from Power System Operation

More from Power System Operation (20)

Recently uploaded

Recently uploaded (20)

EXPERIENCE WITH THE MECHANICAL PERFORMANCE OF NON-CONVENTIONAL CONDUCTORS