Post on 08-Mar-2018
High Performance Conductors
An International viewpoint
Brian Wareing
Brian Wareing.Tech Ltd
Chester, UK Overhead Lines & Lightning Protection Consultancy
Phone +44 1244 550578
Mobile +44 7976 123 738
jbwareing@btinternet.com
bwareing@theiet.org
Brian Wareing.tech
High Performance Conductors - An International viewpoint 2
Introducing myself
Worked in the electricity industry for 48 years
Vibration measurements on OHL since 1995
Author of book on „Wood pole Overhead Lines‟
Deliver OHL courses in UK, Middle East, SE Asia and Australia
Member of Cigré International committees on OHL design, weather loads on OHLs and electrical and mechanical aspects of OHLs – WG29 anti-icing for OHLs
– WG16 weather loads for OHLs
– AG06 Mechanical aspects of OHL design
– WG25 Fittings for OHLs
– WG11/WG46 Vibration of OHLs
– Convenor Cigre AG06 WG48 „Field experience with new conductor types‟
– Secretary Cigre SCB2 WG28 „Meteorological data for assessing climatic loads‟
– SCB2 WG44 „Coatings for protecting power network equipment in winter conditions‟
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High Performance Conductors - An International viewpoint 3
Topics
General overview of high performance conductors (HPC)
– Standard conductor materials and choice
– The HPC range of conductors available today
– HPC and the „knee point‟
– Handling of HPC with composite cores
International perspective on the various technologies
available on HPC
International experience and economics
Line Losses - How HPC could help bring down
Transmission losses
Vibration management on HPC
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Basic Aluminium Conductors
ACSR Combination of high strength galvanised steel and aluminium Can suffer from internal corrosion due to dissimilar metals Suffers from salt pollution in coastal areas AAC
Good conductivity but Low strength conductor so uses are limited
Not good in coastal areas due to salt pollution
AAAC
High strength/weight ratio conductors with Good conductivity
Doesn‟t suffer from galvanic corrosion
Differing grades of alloy available (e.g. Al59)
ACAR
High strength/weight ratio conductors
Aluminium core heat treated to give higher strength but lower conductivity than external aluminium strands
Doesn‟t suffer from galvanic corrosion but still suffers from salt corrosion in coastal areas.
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5
AAAC Al59 Introduced over 40 years ago in Sweden as an
improvement to the conductivity of standard AAAC.
Previous AAAC conductivity was ~54%IACS whereas AL-59 is 59%IACS (hence it‟s name).
Higher conductivity (~20% more ampacity) is associated with lower strength (15% lower UTS) and hence greater sags (~11% lower sag at 80°C on 350m span at same tension as standard AAAC)
So can have same current carrying capacity
with smaller OD than standard AAAC and
ACSR.
Leads to lower power loss and higher power
transfer capacity.
Note: Al6201 has far better corrosion
resistance than Al59 IEEMA Seminar High Performance Conductors - An International viewpoint
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6
New Conductor Types
Gap
ACCR
CCC
Invar type
ACSS
IEEMA Seminar High Performance Conductors - An International viewpoint
Multi-strand
Polymer matrix (C7)
Brian Wareing.tech Issues with Gap conductor
IEEMA Seminar High Performance Conductors - An International viewpoint 7
Difficult to use mid-span connectors
– If Gap breaks then the internal steel core immediately
contracts down the conductor core and so a mid-span joint
cannot be made.
– The only alternative is re-conductoring the section
Gap relies on the grease staying put – Oman, Ireland, UK have all experienced Gap losing its grease
– Sometimes dripping onto people‟s roofs and cars
– Commonly burning off on the surface and causing black marks
– The steel is then not protected.
Brian Wareing.tech Issues with Gap conductor
Gap „knee point‟ is at erection temperature, so if
sections are erected at different temperatures (on
different days) then their sag/temperature behaviour will
be different in the different sections and this can put
stresses on tension towers.
Because the aluminium is not connected with the steel
core, the whole conductor can be twisted easily by hand
This means that wet snow can also twist the conductor
and hence Gap accretes higher snow loads than, for
example, CCC.
It is filthy and very slow to erect as the steel core has to
be stripped bare and pre-tensioned for 12 hours
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Brian Wareing.tech
High Temperature Conductors
With the ever growing need for more power to be
transmitted along existing lines new types of
conductors have been developed to run at higher
temperatures than traditional materials
According to Cigré, these conductors can be put into 4
basic clarifications
Type 1. Conductors composed of a steel core and
an envelope for which the high temperature
effects are controlled by means of thermal-
resistant aluminium alloys (e.g. GAP, Thermal)
Type 2. Conductors composed of a steel core and
an envelope for which the high temperature
effects are controlled by means of annealed
aluminium or aluminium alloy (e.g. ACSS)
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Brian Wareing.tech
High Temperature Conductors
New conductor types
Type 3. Conductors composed of a non-metallic
core, and an envelope for which the high
temperature effects are controlled by means of
thermal resistant aluminium alloys (e.g. ACCR)
Type 4. Conductors composed of a non-metallic
core, and an envelope for which the high
temperature effects are controlled by means of
annealed aluminium or aluminium alloys (e.g.
CCC)
10
Brian Wareing.tech Aluminium – how hot?
Standard Aluminium and Aluminium Alloys can only operate continuously at temperatures up to 93ºC without causing metallurgical decay resulting in lifetime reduction
TAL and ZTAL aluminium have a lower conductivity but essentially the same tensile strength as ordinary electrical conductor grade aluminium but can operate continuously at temperatures up to 150ºC and 210ºC, respectively, without any loss of tensile strength over time.
Fully annealed aluminium is chemically identical to ordinary hard drawn aluminium and can operate indefinitely at temperatures at 250ºC (and higher) without any change in mechanical or electrical properties but has a much reduced tensile strength.
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12 High Performance Conductors - An International viewpoint IEEMA Seminar
Brian Wareing.tech Core Material
Galvanised steel is the normal core material for standard
ACSR conductors.
This is subject to corrosion and potential failure when the
galvanising has disappeared due to corrosion – a big
problem in corrosive or coastal areas.
High Tensile steel is used when stronger conductors with
less sag are required but this is still subject to corrosion.
Invar steel is used for low sag because of its very low
thermal expansion coefficient but it is very expensive.
High strength, low conductivity aluminium alloy can be
used as a core material to give improved strength to AAAC
conductors.
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Core Materials Description ASTM
Spec
MOE (Gpa) TS (Mpa) Cf(x10-6
/°C Unit wght
(mg/mm³)
HS Steel B498 200 1379-1448 11.5 7.778
EHS Steel B606 200 1517 11.5 7.778
EXHS Steel
galvanised
200 1965 11.5 7.778
Aluminium clad
20.3% IACS
B502 162 1103-1345 13 6.588
Galvanised Invar
alloy
B388
B753
162 1034-1069 1.5-3.0 7.778
Mischmetal Std
HS
A856
A857
200(I)-
186(F)
1379-1448
1517-1620
11.5 7.778
Aluminium Oxide
matrix
B976 210 1380 6.3 3.337
Carbon fibre B987 112.3 2158 1.61 1.88
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ACS ~4
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15
Knee Point
To take advantage of the high temperatures (and so Ampacities) for „redundancy‟, low sag is also required and this uses the technique of the „Knee point‟
The knee point occurs for all ACSR type conductors when the tensile load is transferred from the (high expansion coefficient) aluminium to the (low expansion coefficient) core
This produces a change of angle in a sag/temperature graph
The region over which this occurs is known as the „Knee point‟ although in practice it is not a specific point.
It has always been there but at too high a temperature for „standard‟ ACSRs
The following graph is schematic but shows how the different expansion coefficients affect sag.
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8
9
10
11
12
13
14
15
0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200
Sa
g o
f 3
66
m S
tan
da
rd L
2 S
pa
n, m
Conductor Temperature, 0C
620 mm2 Matthew GZTACSR38 kN @ 10 0C
Original 400 mm2 Zebra ACSR26.5 kN @10 0C
570 mm2 Sorbus AAAC36.9 kN @ 10 0C
560 mm2 ZTACIR38 kN @ 10 0C
Original design maximum sag,
1950s
620 mm2 Matthew GZTACSR38 kN @ 10 0C
Knee points
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ACCC Drake 30 kN @ 10 0C
Brian Wareing.tech
17
Fittings
Most new conductor types require special fittings
An exception is the ZTAL/Thermal ACSR which
can use existing conventional fittings
These fittings may run hotter than normal and so
may incur some overheating unless specifically
designed for high temperature operation
But commonly many HT conductors are run at
<100ºC in normal operation so fittings only have
to withstand high temperatures for short periods
More information in Cigré Technical Brochure (in
course of publication)
IEEMA Seminar High Performance Conductors - An International viewpoint
Brian Wareing.tech Cigré WG 48 TB
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Brian Wareing.tech
Proposed new WG
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Brian Wareing.tech
International perspective on
the various technologies
available on HPC
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Brian Wareing.tech
Cigré Survey of
experience with HPC
As part of the Cigré WG48 TB, a survey
was made of suppliers and utilities and
their experience with HPC.
The following slides are a brief summary
of the utilities‟ views.
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Brian Wareing.tech
High Performance Conductors - An International viewpoint
Dealing with new conductor types
These are the views of 35 utilities world-wide
Why choose new conductor types?
Types of Installations
Installation
Fittings
Are utilities still putting them up?
Are they economic?
Did they perform?
Is training given?
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High Performance Conductors - An International viewpoint
Why choose new conductor types?
• Reasons for new conductor use
• 75% said increased ampacity (average 85% increase required)
• 40% said ground clearance problems
• Only 2 utilities mentioned voltage drop
• However 22 utilities (63%) said it was an economic choice
• Two said limited corridor
• Other reasons:
• optimise (n-1) criteria
• Reduce visual impact (replacing bundle)
• Insufficient outage time to rebuild
• Planning permits and outages
• Minimise line losses. Reliable corridor
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High Performance Conductors - An International viewpoint
Type of installations of new
conductors
• Reconductor upgrade: 48%
• Replacing aged conductor: 12%
• New line: 15%
• Special application (e.g. long crossings,
heavy ice loads, high ambient
temperatures): 10%
• Trial/pilot: 15%
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High Performance Conductors - An International viewpoint
Installation • 77% said special requirements were needed (2
mentioned CCC)
• 70% said special training was required (one mentioned
Gap)
• 40% installed in-house; 67% by contractor (7% did both)
• 100% found following installation instructions easy!
• 35% installed with one circuit live
• 35% said some changes to utilities'
equipment/procedures necessary
• 100% said no problem with different conductor types on
same line
•
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High Performance Conductors - An International viewpoint
Installation
86% said special conductor hardware fittings
were necessary
87% said these fittings were easy to install
Conductors with composite cores (CCC, ACCR)
should not be bent round small wheels – normally
a 1 metre diameter bull wheel is fine
Most conductors can be pulled up as a complete
conductor but Gap requires the steel core to be
pulled separately and tensioned for 12 hours
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High Performance Conductors - An International viewpoint
Fittings Most new conductor types require special fittings
Extensive testing has shown that an HTLS conductor
dead-end operates at about ½ the temperature of the
conductor (Slightly higher at the nose, cooler at the
jumper pad).
The dead-ends and splices were designed with
reliability as paramount
When CCC conductor is operated at temperatures up
to 215°C the temperature of jumper pads (at dead-
ends) and suspension clamp bolts only reach
temperatures of 60° to 70°C.
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High Performance Conductors - An International viewpoint
Fittings
The added mass of the dead-ends, splices, and
suspension clamps serve to reduce operating
temperatures of these components.
During EPRI-ANSI testing degradation of the
conductivity between the dead-ends and conductor
did not occur until an CCC conductor was operated
at temperatures to 330°C
But commonly many HT conductors are run at
<100ºC in normal operation so fittings only have to
withstand high temperatures for short periods
70% used Stockbridge dampers; 30% no dampers at
all: 90% said no vibration problems
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High Performance Conductors - An International viewpoint
Are utilities still putting them up?
12 utilities are currently planning new
conductor use
• Planned installations: • 68 route km<100kV (all single)
• 704 route km 100<200kV (all single)
• 2 route km single, 115 route km bundled at 200<300kV
• 100 route km single, 2761 route km bundled at >300kV
No concerns expressed about use in bundled
formation
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Brian Wareing.tech Are they economic?
Economic justification
• Commonly 20-50% cheaper than a new line
• Benefits 80% (up to 200%) better than new line
• Time advantage 1 to 5 years compared with new line
• 50% of utilities said lack of need for regulatory approval
was a major economic justification
• Tower modifications including change to foundations
require a building licence which means additional project
time and risk; HTLS conductors offered a quick (and so -
economic) solution
High Performance Conductors - An International viewpoint IEEMA Seminar 30
Brian Wareing.tech Did they perform?
• Performance compared with expectation • Performance as expected with 100% normal operation levels and
x2 for emergency. Highest noted as 240MVA for CCC
• Reliability given as 100% (but not many answered the question)
• Recorded faults were due to poor
installation or excessive weather loads
High Performance Conductors - An International viewpoint IEEMA Seminar 31
Brian Wareing.tech Training
Training up to 3 days provided by
suppliers
Fittings available from at least 20
manufacturers.
High Performance Conductors - An International viewpoint IEEMA Seminar 32
Brian Wareing.tech Summary of the survey
Reasons for new conductor use
75% said increased ampacity (average 85% increase required)
40% said ground clearance problems
Types of installation:
Reconductor upgrade: 48%
Replacing aged conductor: 12%
New line: 15%
Fittings:
– 86% said special conductor hardware fittings were necessary
– 87% said these fittings were easy to install
No utility expressed any regrets in their use
All users said they were an economic choice
Performed up to expectation
No problems with installation or fittings
Adequate training is given
High Performance Conductors - An International viewpoint IEEMA Seminar 33
Brian Wareing.tech
Westnetz
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HTLS Re-conductoring for upgrade of
an OHL in Hunsrück area near Koblenz
Brian Wareing.tech
Grid problems
From 2011 to 2012 the energy generated by wind energy
converters (WEC) in Hunsrück area multiplied by nearly six.
Particularly in times of poor load for example on Sundays with a
lot of wind and little consumption, more energy has to be
transported into the transmission grid.
Wind farm in Hunsrück near Bl. 0738
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Increase of the transmission capacity to 200 MVA Model 1:
Reconductoring using high temperature conductors
2x3x 264-AT1/34-A20SA (TAL/Stalum 265/35) (ACS core)
150° design temperature
In order to fulfill the requirements regarding ground clearances a
reconstruction of 16 of the 36 towers is required.
Costs:
Conductors: 220.000 €
Insulator strings: 125.000 €
Steel: 260.000 €
Tower installation + foundation: 840.000 €
Circuit installation: 490.000 €
Permission process: 100.000 €
Total: 2.035.000 €
Reconductoring 110-kV-Overhead line Anschluss Simmern, Bl 0738
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Brian Wareing.tech
Increase of the transmission capacity to 200 MVA Model 2:
Reconstruction of the whole OHL using 110 kV-towers capable to carry twin
bundle circuits and a conductor configuration of
2x3x2x 264-AL1/34-ST1A
80° design temperature
Costs: ca. 6.500.000 €
Long lasting permission procedure has to be considered
Costs were determined within following requirements: 12,3 km line length
Conductor: 264-AL1/34-ST1A, 2er-Bundle
Earth wire: 264-AL1/34-ST1A, Einfachseil
26 Suspension towers, 10 WA, 4 WE Tension tower
Insulator strings: 210 double tension strings, 156 double suspension strings
Temporary road construction: overall 150 m per tower
crossings: federal motorway, 13 other streets
Dismounting existing overhead line: 40 towers and foundation without sump pumping
Permission process
supervision
Reconductoring 110-kV-Overhead line Anschluss Simmern, Bl 0738
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Brian Wareing.tech
Increase of the transmission capacity to 200 MVA Model 3:
Reconductoring using HTLS-conductors CCC 317/60 (Oslo)
130° design temperature (1050 A)
In order to fulfill the requirements regarding ground clearances a
reconstruction of only one of the 36 towers is required. Verifications of
the distance calculations were done with the programme “FM-Profil“
(EPE-Model)
Costs:
Conductors: 1.032.000 €
Insulator strings : 260.000 €
Steel: 19.850 €
Tower installation +foundation: 50.500 €
Circuit installation : 731.250 €
Total: 2.093.600 €
Reconductoring 110-kV-Overhead line Anschluss Simmern, Bl 0738
Costs 264-AT1/34A20SA
Conductors: 220.000 €
Insulator strings : 125.000 €
Steel: 260.000 €
Tower installation + foundation: 840.000 €
Curcuit installation : 490.000 €
Permission process: 100.000 €
Total: 2.035.000 €
IEEMA Seminar 38 High Performance Conductors - An International viewpoint
Brian Wareing.tech
Line losses - how HPC could help
bring down Transmission losses
Radiative losses
Thermal losses
Corona losses
Reactive power gains and losses
Optimising SIL
BUT – all the time the sag requirements
and power capacity (including n-1) should
be kept in mind
IEEMA Seminar High Performance Conductors - An International viewpoint 39
Brian Wareing.tech
Network Requirements
Affordable re-conductoring or new-build
Efficient (low loss) conductor
High capacity
Low Sag
– The carbon fibre composite core has lowest electrical sag of all HT
conductors
– Invar steel has a much lower coefficient of thermal expansion than
other steels
Running cooler – a conductor that delivers high
ampacity at a lower temperature has
– Lower line losses
– Longer fitting life
– Less chance of breaking regulatory clearances
40 IEEMA Seminar High Performance Conductors - An International viewpoint
Brian Wareing.tech
Real power losses - radiative and thermal losses
All conductors gain and lose real power
(excluding reactive power) by I²R, solar
gain, radiation and convection.
Heat Balance Equation:
Where – PS = Solar Heat gain
– PC = Convective Heat Loss
– PR = Radiative Heat Loss
IEEMA Seminar High Performance Conductors - An International viewpoint 41
Brian Wareing.tech
How does conductor choice help?
- Standard aluminium alloys (54-59%IACS)
Main input/output power
– Wind speed
– Radiation losses (emissivity)
– Solar gain
– Current
Typically the largest power input is due to the
current.
Current limited by keeping the aluminium below
93°C or the electrical sag.
Higher current may therefore require larger
diameter which may result in sag or structure
problems.
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Brian Wareing.tech
How does conductor choice help? - Zirconium aluminium alloys (58-60%IACS)
The limitation on temperature is not as severe
with Zirconium alloys as they can reach between
150 and 210°C.
Sag limitations are dictated by the core material if
they can be operated above the knee point.
The generally higher conductivity means that for
increasing currents, the diameter can be kept low
depending on the core size
However, the higher temperature mean increased
thermal radiation losses
IEEMA Seminar High Performance Conductors - An International viewpoint 43
Brian Wareing.tech
How does conductor choice help?
- Annealed aluminium alloys (63%IACS)
The limitation on temperature is generally even better
than Zirconium alloys as annealed aluminium can
reach between 250°C.
Sag limitations are dictated by the core material if
they can be operated above the knee point – this is a
limitation for ACSS but generally not for CCC.
The significantly higher conductivity means that for
similar currents, the conductor temperature will be
lower than the equivalent ACSR and so thermal power
losses will be smaller.
The savings can compensate for the more expensive
conductor within a few years.
IEEMA Seminar High Performance Conductors - An International viewpoint 44
Brian Wareing.tech Explanation!
Using annealed aluminium generally means that, compared with
AAAC, the conductor will operate at a lower temperature for the
same ampacity and so have lower thermal losses.
It is quite common for high temperature conductors to operate at
similar ampacities to standard conductors and to use their high
temperature capability only for n-1 situations.
In the tables in the next few slides it can be seen that operating an
ACSR Panther (21mm OD) will have a thermal power loss (at 75°C)
of 5231MWh per 10km at the rated current of 473A.
Switching to AL-59 241 (20.1mm OD) at 473A operates at a lower
temperature and so lower losses of 4488MWh, a saving of
743MWHr/10km of line.
However, using CCC (21.8mm OD) has a loss of just 3222MWh – a
saving of over 2000MWh/pa/10km.
IEEMA Seminar High Performance Conductors - An International viewpoint 45
Brian Wareing.tech Conductor comparisons
Consider a 350m span with ACSR Panther
(201mm² aluminium area) and 21mm OD.
At 75°C this has current carrying capacity of 473A
and a sag of 10.06m (tension of 3.8kN at 32°C at
25%UTS).
Assumptions:
– Ambient temp: 40°C, Wind 0.6m/s, Sun Radiation 1045 W/m²,
Elevation 350 m; Solar/Emissivity 0.5.
Compare CCC , AL59, ACCR, ACSS, Invar and
Gap (all Hawk equivalent).
Look at 473A and doubling capacity to 946A
IEEMA Seminar High Performance Conductors - An International viewpoint 46
Brian Wareing.tech Power losses (Thermal)
IEEMA Seminar High Performance Conductors - An International viewpoint 47
Conductor
Name
Units CCC
Casablanca
CCC Lisbon ACSR
PANTHER
AL59 241 ACCR/TW -
HAWK
ACSS/TW-
HAWK
INVAR
HAWK
GAP 240
HAWK
Max DC
Resistance @
20°C
ohm/km 0.1024 0.0887 0.132 0.123 0.1153 0.1136 0.111 0.119
Overall
Diameter of
Conductor
mm 20.5 21.79 20.98 20.1 21.64 21.79 19.66 20.60
Rated Tensile
Strength of
Conductor
kg 10,312 10,554 9,708 5,659 8,708 7,077 8,515 8,851
Maximum
Working
Current @ 75°C
A 548 598 473 503 518 517 477 515
Line Losses
per 10 km line
length @ 473
Amps
MWh 3756 3,222 5,231 4,488 4,197 4,214 4,979 4,323
Line Losses
per 10 km line
length @ 946
Amps
MWh 18,613 15,390 N/A N/A 21,432 21,641 26,507 21,532
Conductor
Temperatures
@ 946 Amps
°C 139°C 122°C N/A N/A 153°C 154°C 176°C 152°C
Brian Wareing.tech
But what about sags at high
ampacity levels?
IEEMA Seminar High Performance Conductors - An International viewpoint 48
The two Invar conductors and ACSS
cannot make the sag if >90°C
ACCR is OK up to 130°C
CCC and Gap are OK throughout their range
Brian Wareing.tech And ampacity?
IEEMA Seminar High Performance Conductors - An International viewpoint 49
The two INVAR need 162 and 176°C
to reach 946A but break sag at <90°C
ACSS needs 154°C but breaks sag at <90°C
ACCR needs 153°C but breaks sag at 130°C
GAP needs 152°C and can make the sag
CCC Lisbon needs just 122°C
and can make the sag
CCC Casablanca needs 139°C
And can make the sag
Brian Wareing.tech Conductor capability
It can be seen that the sag limitation reduces the
capability of INVAR, ACSS and ACCR by restricting
their temperature and hence ampacity.
Both CCC and Gap can make the full capability (946A)
and maintain sag but Gap loses 21,532MWh/10km
compared with 15,390MWh for CCC Lisbon and
18,613MWh for CCC Casablanca due to their lower
temperatures and hence lower thermal power losses.
Whilst these conductors are more expensive than, say,
AL59, the savings in power losses can pay back these
higher capital costs in just a few years.
IEEMA Seminar High Performance Conductors - An International viewpoint 50
Brian Wareing.tech Corona losses
Corona occurs when the electric field at the conductor surface is
strong enough to break down the air.
It is very noticeable in damp weather and is often associated with
audible crackling or fizzing.
Although sometimes occurring at voltages down to 33kV it is
more of a problem at EHV voltages.
However, it is generally a fairly small component of the losses
overall.
Surface electric fields are related to conductor and sub-conductor
diameter and bundling but not conductor type, as they are a
surface area, surface condition, voltage and weather related
phenomenon.
Corona losses should not normally be a factor in selecting the
type of conductor
IEEMA Seminar High Performance Conductors - An International viewpoint 51
Brian Wareing.tech
Re-conductoring and
increasing power transfer For this it is necessary also to look at reactive power losses and
the ability to achieve a high SIL - Is this conductor dependent?
Replacing conductors such as ACSR or AAAC with an HPC such
as CCC or ACSS of the same diameter can be a cost effective way
to increase the transfer capacity of transmission lines.
Maintaining the same conductor diameter/weight/tension makes it
likely that existing structures can be used and with proper
conductor selection and application ground clearances can
normally be maintained.
But increasing power transfer will impact reactive power
consumption, and therefore voltage, as well as real power losses.
Voltage drop and reactive power flow are related and
interdependent and to understand how these are affected by
conductor choice, a brief explanation is required.
IEEMA Seminar High Performance Conductors - An International viewpoint 52
Brian Wareing.tech Reactive power
Reactive power is either trapped in the capacitive (electric field) or
inductive (magnetic field) elements of an AC system, or is in transit
between the capacitive and inductive elements of the system.
Reactive power flow does affect system voltage and can be
managed by application of equipment which will offset or
supplement reactive power flow occurring in the electrical system.
Reactive power is normally described as being:
– “consumed” or “lost” in inductive circuit elements, typically the series
inductive impedance in electric transmission lines or shunt connected inductors
(shunt reactors). Inductive elements store energy in magnetic fields.
– “supplied” by capacitive circuit elements, typically the shunt capacitive
impedance in electric transmission lines or shunt connected capacitors.
Capacitive elements store energy in electric fields.
IEEMA Seminar High Performance Conductors - An International viewpoint 53
Brian Wareing.tech
Reactive power consumed (energy
loss) and supplied (energy gain)
The reactive power consumed in an inductor every cycle, Q=
V²/XL= I². XL, where XL the inductive reactance (in Ω).
So if the power capacity is increased by doubling the current, I,
the real power, P, will double but the reactive power loss, Q, will
quadruple.
The reactive power supplied by a capacitor and released every
cycle, Q = I². XC = V²/XC where XC the capacitive reactance (in Ω).
1/ XC is known as susceptance (BC).
So the reactive power supplied, Q, varies as the square of the
voltage across the capacitance or the square of the current
through the capacitance.
IEEMA Seminar High Performance Conductors - An International viewpoint 54
Brian Wareing.tech Reactive power loss
Reactive power loss is dependent on the inductive
reactance of the circuit which varies with conductor
diameter for single conductor designs
Larger diameter conductors reduce inductive reactance of
the line e.g. for example going from single conductor
170mm² ACSR to 800mm² (large change) will reduce
reactive power loss by ~10% (relatively low).
But going from 800mm² single ACSR to 2x400mm² bundle
will reduce reactive power loss by ~25% - so geometric
conductor spacing is more important than conductor
choice.
IEEMA Seminar High Performance Conductors - An International viewpoint 55
Brian Wareing.tech Reactive power gain
Reactive power gain is dependent on the shunt capacitance of the
circuit
Larger diameter conductors increase the susceptance of the line
e.g. for example going from single conductor 170mm² ACSR to
800mm² will increase reactive power gain by ~13%.
But going from 800mm² single ACSR to 2x400mm² bundle will
increase reactive power gain by ~30% - so again geometric
conductor spacing is more important.
Both reactive power gains and losses vary with line length.
IEEMA Seminar High Performance Conductors - An International viewpoint 56
Brian Wareing.tech SIL
Surge Impedance Loading (SIL) is the point at which the Q supplied
by the shunt capacitance of the line equals the Q lost in the series
inductance of the line.
Changes in line design that increase susceptance (BC) and
consequently increase the Q supplied (more sub-conductors, larger
bundle spacing, and closer phase spacing) move the red “Q
Supplied” curve up.
These same changes in line design also reduce series inductive
reactance (XL) and the Q losses moving the blue “Q Lost” curve to
the right.
The net effect is to increase the SIL point, located at the intersection
of these two curves, thereby allowing increased power levels whilst
maintaining the line voltage within acceptable levels.
IEEMA Seminar High Performance Conductors - An International viewpoint 57
Brian Wareing.tech What effect do conductors have?
IEEMA Seminar High Performance Conductors - An International viewpoint 58
It can be seen that conductor diameter makes very little difference.
The biggest effect is the reduced SIL from the INVAR conductor.
This is due to the increase inductive losses due to the smaller diameter and
the magnetic core of this conductor but the effect is still minor.
As loading increases above the SIL reactive power losses quickly increase and
so larger amounts of reactive power compensation (typically shunt capacitors)
will need to be applied to maintain system voltage (at a cost).
Data for 150kV 100km line.
Brian Wareing.tech
Power losses overall
IEEMA Seminar High Performance Conductors - An International viewpoint 59
Lower resistance means lower electrical
losses whilst higher power flow
increases reactive losses. For a single
conductor line at:
100MW power flow: reactive losses are
12MVAR whilst electrical losses vary
from 8.5MW (CCC) to 12MW (INVAR)
150MW power flow: reactive losses are
37MVAR whilst electrical losses vary
from 12.8MW (CCC) to 18MW (INVAR)
Brian Wareing.tech Conductor type
The previous slides illustrate that real power
losses are dependent upon internal conductor
construction, and that conductors with smaller
cores and trapezoidal stranding, such the
CCC/TW Amsterdam, can provide more
aluminium cross sectional area in the same
diameter significantly reducing resistance and
real power losses.
However, reactive losses show very little change
with conductor diameter or type
IEEMA Seminar High Performance Conductors - An International viewpoint 60
Brian Wareing.tech
61
Aeolian vibration
In standard conductors, line design is influenced by
the erection tension and maintaining an Every Day
Stress (EDS) so that Aeolian vibration does not cause
vibration fatigue and shorten the conductor life.
Such failures are caused by dynamic stresses
resulting from reverse bending by wind-induced
conductor motions such as wake-induced oscillations
IEEMA Seminar High Performance Conductors - An International viewpoint
Brian Wareing.tech New and Old
Vibration damage occurs when the energy input (from
wind) is not matched by self-damping (from the
conductor)
It is accepted that, for conventional ACSR and AAAC,
vibration levels are higher as the conductors age due
to long term geometrical compaction which stop the
strands sliding (and hence self-damping decreases and
damage potential increases).
In contrast, HTLS conductors, when operated above
the knee point, have much slacker strands which can
move and so increase self-damping and reduce
damage potential.
IEEMA Seminar High Performance Conductors - An International viewpoint 62
Brian Wareing.tech Self damping
The self damping characteristics of a conductor are basically
related to the freedom of movement or “looseness” between the
individual strands or layers of the overall construction.
In standard conductors the freedom of movement (self damping)
will be reduced as the conductor ages or tension is increased.
It is for this reason that vibration activity is most severe in the
coldest months of the year when the tensions are the highest.
Conductors with trapezoidal shaped outer strands have higher
self damping performance due to the gaps between layers.
Conductors, such as ACSS and CCC, utilise fully annealed
aluminium strands that become inherently looser when the
conductor progresses from initial to final operating tension.
So the best self-damping HTLS conductors are those that use fully
annealed aluminium with trapezoidal strands.
IEEMA Seminar High Performance Conductors - An International viewpoint 63
Brian Wareing.tech
Vibration Monitor installations
64
Deadwater Fell tests
UK IEEMA Seminar High Performance Conductors - An International viewpoint
Brian Wareing.tech Load shifting
Conductors such as CCC exhibit load
shifting after a tension is applied.
This tension can occur naturally (e.g. after
a snow/ice incident) or be applied on
erection (pre-tensioning).
The load shift moves (permanently)
tension from the aluminium to the core,
thereby reducing aluminium stress levels.
It also reduces the knee point temperature
IEEMA Seminar High Performance Conductors - An International viewpoint 65
Brian Wareing.tech Effect of Load shifting
Lisbon CCC with no pre-tension was tested at the
Deadwater in comparison with a load-shifted version
(load share ~80% core ~20% on the aluminium) to see
how load shifting affected the vibration level.
The data showed that new HT conductor types which
depend on the core above their knee point do not follow
the same vibration pattern as standard conductors where
the load is mainly on the aluminium
With little load on the aluminium, it is only there for the
ride and the data indicates that vibration levels are
reduced significantly above the knee point
So – are there benefits to pre-tensioning?
IEEMA Seminar 66 High Performance Conductors - An International viewpoint
Brian Wareing.tech
67
Comparison of load-
shifted and new Lisbon
ACCC at the same tension
The vibration level is
reduced substantially as
the conductor goes
through load shift.
Load shifting can be
achieved at erection by
pre-tensioning.
This may require the use
of back stays on the
crossarms
„Load shifted‟ Lisbon
„New‟ Lisbon
IEEMA Seminar High Performance Conductors - An International viewpoint
Brian Wareing.tech Summary
Brief description of HPC including the
component materials
Showed how power losses can be reduced
by the use of HTLS conductors
International perspective: – Results of world-wide survey
– Specific example of economic choice from Germany
Bit about vibration levels on new
conductor types.
IEEMA Seminar High Performance Conductors - An International viewpoint 68
Brian Wareing.tech That‟s it!
Thank you!
IEEMA Seminar 69 High Performance Conductors - An International viewpoint