Increasing the capacity of existing

transmission lines by re-conductoring

using ACSS HTLS conductors

Thomas Wilki

Director, International Sales & Development

Southwire Company

• Intro: Performance map

• What is ACSS compared to ACSR?

• Strength, conductivity, temperature

• Misch metal coating of steel

• Batch annealed vs bobbin annealed

ACSS

• Re-conductor examples

• Installation of ACSS

• ACSS hardware

ACSS CONDUCTORS - TOPICS

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500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900

Ma

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Line Rating (Amperes)

Performance Map Example - NESC Medium, 244 m Span, "Drake" ACSR Tension Limit (48.4 kN)

100 C

250 C

75 C

250 C

Assumptions:NESC 261.H.1.b Medium Load ZoneNESC 261.H.1.b tension limits0.5 emissivity and absorptivity0.6 m/sec windJune 10 Sun @30° N Lat48.4 kN max structure load

225 C180 C

Sag Limit (ACSR max sag + 0.6 m)

* ZTACCR/C7 sag improves by 0.85 m @ NESC tension limits vs. 48.4 kN structure limit used here

WHAT IS ACSS COMPARED TO ACSR

• ACSR (Aluminum Conductor Steel Reinforced)

• ACSS (Aluminum Conductor Steel Supported)

• ACSS is considered to be part of the HTLS conductor

family

• They look the same and have similar strand

configuration and code names

• But there are significant differences in how they operate:

• ACSR relies on aluminum strength

• The aluminum is hard

• ACSR is typically rated for 75°C

continuous operating

• 100 °C limited emergency

• Steel core options include Class A

Zinc (GA), Al Clad (AW or AC),

Mischmetal (MA)

• Moderate coefficient of Thermal

Expansion (CTE)

• Known steel performance

• Most used conductor for

transmission

1350-H19

Aluminum

Zinc-Galvanized

Class A (GA)

TRADITIONAL ACSR

ACSS CONDUCTOR

1350-O

Aluminum

Zinc-5% Aluminum-Mischmetal Alloy

Coated Steel or AW Core

• ACSS does not rely on aluminum

strength

• The aluminum is soft

• ACSS is typically rated 250 °C

continuous with MA or AW steel

• Some use a galvanized core,

which must be rated below 200°C

• Available in standard, high (HS),

Extra high (EHS) and ultra-high

(UHS) strengths.

• Corresponding to standard rating

2, 3, 4 & 5.

• Same known steel performance

ACSS COMPARED TO ACSR

Two Major Differences:

• Response to Thermal Loading

• Elongation

• Response to Physical Loading

• Strength

• Loaded and unloaded tensions

• Creep

• Self damping

COEFFICIENT OF THERMAL EXPANSION

ACSS sags less because steel elongates at half the rate of aluminum

per °C x 10-6

1350 Aluminum (all tempers) 23.0

Aluminum Alloys (all) 23.0

Steel 11.5

Metal Matrix Composite 6.3

Polymer Composites 1.7

COMPARING BREAKING STRENGTH

• ACSR’s have a high RBS due to the strength contribution from the

hard drawn aluminum 1350-H19

• Higher steel strength is often needed for ACSS

• UHS results in ACSS strengths similar to ACSR strengths without

adding steel

• This means same weight and strength as ACSR with lower thermal

elongation rates

RBS in kN ACSR ACSS HS

ACSS

UHS

ACSS

242 mm2 477 HAWK 86.7 69.4 76.1 88.1

403 mm2 795 DRAKE 140 115 125 145

483 mm2 995 CARDINAL 150 116 125 144

MATERIAL STRENGTH (N/mm2)

1350 - O (soft) Aluminum ~ 60

1350 - H19 (hard) Aluminum 162 – 200

AL3, AL5, AL7 Alloy 255 – 300

6201 Aluminum Alloy 317 – 331

Aluminum Zirconium Alloy 155 – 166

Standard core steel 1379 – 1448

High Strength (HS) Steel 1517 – 1620

Ultra High Strength (UHS) steel 1827 – 1965

Composites (depends on fiber and fiber %) 1720 – 2550 +

ELECTRIC CONDUCTIVITY (% IACS)

Copper (SD) 100.0% IACS

Aluminum (O) 63.0

Aluminum (H19) 61.2

Aluminum Zirconium (ZT) 60.0

Aluminum Alloy AL3-AL7 53.0 - 57.5

Aluminum Alloy – 6201 52.5

Steel - Al. Clad 20.3

Steel - Galvanized or MA 8 – 9

Metal Matrix Composite 20

Polymer Composites 0

OPERATING TEMPERATURE LIMITS

1350 – H19 Aluminum 75 C/100 C

Aluminum Alloy (AL1-AL7 etc.) 75 C/100 C

Aluminum Zirconium 210 C/240 C

1350 – O-temper 250 C +

Steel (zinc galvanized coating) < 200 C

Steel (Misch Metal coating, AW) 250 C +

Composite cores will depend on materials

MISCH METAL COATING

• Misch Metal coatings are well-proven in overhead

conductor – in USA there are no known coating

failures to date in ACSR or ACSS conductors

• Lab testing suggests 2X to 3X improvement in

corrosion life, compared to hot-dip zinc. MM protection

is comparable to AW, but with the advantage of greater

damage tolerance

• Higher strength, including available MA5 (UHS)

provides options for high-strength conductors, or for

same-strength conductor at lower core fraction

compared to AW core

• Misch Metal (or AW) is required for the batch annealed

ACSS process but recommended for all ACSS

conductors to ensure heat-tolerance and acceptable

corrosion life

ACSS DEVELOPMENT: BATCH ANNEALING

• ACSS conductors were developed in the early 1970s.

• ACSS was traditionally bobbin annealed which result in both a harder

aluminum and a looser stranding more prone to birdcages.

• In 1994 the batch annealed ACSS was developed to remedy the

issues: The hard-drawn aluminum is annealed after stranding. The

complete take-up reel is annealed in a large oven.

• Batch annealing has improved the quality and performance of ACSS:

• Less installation issues

• Lower sag due to softer aluminum (lower knee-point)

• Better self-damping properties (faster)

• Better conductivity (>63% vs 61.8% required)

CHARTS: BOBBIN VS. BATCH ANNEALING

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0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0 3.2 3.4 3.6 3.8 4.0

Stre

ss (

MP

a)

Strain (%)

Single-Strand Stress-Strain Data - Bobbin (Pre)-Annealed vs. Batch (Post)-Annealed ACSS

Pre B-1 Pre B-1 IQR Pre .2% Offset Post B-1 Post B-1 IQR

Yield = 64.5 MPa

Yield = 31.1 MPa

TYPE 16 MA5: BOBBIN VS BATCH ANNEALING

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Conductor Temperature (°C)

Sag vs. Temperature: Batch-Annealed ACSS/MA5 Sags 10% Less than Bobbin-Annealed ACSS/MA5

Per NESC, tension limit is 25% RBS at conductor temperature of 15 °F (-9.4 °C). Sag and tension are identical at the reference temperature, but the lower knee point for the batch-annealed conductor results in a 10% sag reduction at temperatures above the knee point

TYPE 16 MA5/MA3: BOBBIN VS BATCH ANNEAL.

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-25 0 25 50 75 100 125 150 175 200 225 250

Sa

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Conductor Temperature (°C)

Sag vs. Temperature: Batch-Annealed ACSS/MA3 is Equivalant to Bobbin-Annealed ACSS/MA5

Per NESC, tension limit is 25% RBS at conductor temperature of 15 °F (-9.4 °C). MA3 sag is 0.53 m greater due to lower tension, but essentially equal above 30 °C due to lower knee point temperature

TYPE 7 MA5: BOBBIN VS BATCH ANNEALING

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@ N

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Conductor Temperature (°C)

Sag vs. Temperature: Type 7 Conductors

795.0 kcmil "Tern/ACSS/MA5" (Bobbin-Annealed)

795.0 kcmil "Tern/ACSS/MA5" (Batch-Annealed)

Per NESC, tension limit is 25% RBS at conductor temperature of 15 °F (-9.4 °C). Sag is identical at -9.4 °C but 2.0 ft less above 70 °C due to lower knee point temperature

TYPE 7 MA5/MA3: BOBBIN VS BATCH ANNEAL.

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@ N

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Conductor Temperature (°C)

Sag vs. Temperature: Type 7 Conductors

795.0 kcmil "Tern/ACSS/MA5" (Bobbin-Annealed)

795.0 kcmil "Tern/ACSS/MA3" (Batch-Annealed)

Per NESC, tension limit is 25% RBS at conductor temperature of 15 °F (-9.4 °C). MA3 sag is 2.5 ft greater due to lower tension, but is within 0.5 ft above 60 °C due to lower knee point temperature

ACSS DEVELOPMENT: BATCH ANNEALING

• In NESC Medium, and 244 m (relatively short) span, the sag

improvement for batch-annealed ACSS/MA5 is 0.6 m (~10%),

compared to bobbin-annealed ACSS/MA5.

• ACSS/MA3/batch-annealed has high-temperature sag comparable

to ACSS/MA5/ bobbin-annealed, despite lower allowable stringing

tension for ACSS/MA3

• 10% is enough to differentiate a new class of HTLS conductors –

line designs using structure optimization will see, on average,

shorter structures or fewer structures

• Note that when using PLS-CADD for ACSS: While the final sags

and tensions (final condition) are often determined by normal creep

for ACSR designs, the final condition in ACSS designs is always

determined by load creep from high tension events, such as ice

and/or wind loading

EXAMPLE: RE-CONDUCTOR ACSR

Assumes•400 m ruling span •NESC Medium Loading •55,000 Newton tower limit

Max loaded Sag: 10.3 m

ACSR

403 mm2 26/7 “DRAKE”

Max thermal sag: 13.8 m (100°C)Max rating: 993 Amps(75°C : 731 Amps)

EXAMPLE: RE-CONDUCTOR ACSR

Assumes•400 m ruling span •NESC Medium Loading •55,000 Newton tower limit

ACSS Solution Examples

403 mm2 DRAKE ACSS-HS: 1308 A (143 °C)403 mm2 DRAKE ACSS-UHS: 1668 A (216 °C)486 mm2 SUWANNEE ACSS/TW-UHS: 1758 (201 °C)

ROUND WIRE & TRAPEZOIDAL WIRE

Round Wire

Diameter EquivalentArea

Equivalent

- More Aluminum

- Heavier

- Higher Ampacity, Same ice and wind

- App. 10% OD

- App. Equal Wt.

- Reduced Ice & Wind Loading

EXAMPLE: NEW LINE WITH ACSS

New ACSR Line:

483 mm2 45/7 ACSR “Rail”

152 m ruling span

41 kN tower limit

NESC heavy loading

New ACSS/TW Line:

587 mm2 Type 7 ACSS/TW

“Genesee”

152 m ruling span

41 kN tower limit

NESC heavy loading

Temperature Amps Sag AC

Resistance

‘Rail’ ACSR 75°C 800 4.2 m 0.074 Ω/km

‘Genesee’

ACSS/TW

71°C 800 3.8 m 0.060 Ω/km

Using an ACSS/TW conductor reduces I2R by approx. 20%

Emergency availability of 1375 amps at 4.2 m of sag

Decrease resistance, decrease your line losses

Increase mm2 area and use fully annealed aluminum

INSTALLATION OF ACSS

• ACSS installs in a similar manner to ACSR.

• Due to the softness of AL, ACSS is more susceptible to

damage and less forgiving of improper sized or damaged

equipment and “shortcuts”.

• In general IEEE 524 “Guide to the Installation of Overhead

Transmission Line Conductors” can be used.

INSTALLATION OF ACSS

• Bottom grove diameter should be at

least 20x conductor OD, preferably

lined (i.e. Neoprene, Polypropylene).

• Blocks must be free wheeling, clean.

Blocks that skip or hang may cause

birdcaging.

• Depending on entry angle, entrance

and angle blocks may need to be

larger

• Dual-drum, multi-grove, lined

bullwheel tensioner is required

• Bottom groove diameter: min. 35 x

Conductor OD

• A detailed ACSS installation guide

should provide further details

ACSS HARDWARE

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Dead End

Full tension two piece

compression

Full tension pre-formed rods

Splices

Full tension two piece

compression

Full tension pre-formed rod

Must be specified for use with

ACSS (high temperature rating)

EXAMPLE

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• Suspension Clamps

• AGS with armor rods

• Other types may be used

• Dampers

• With or without armor rods

• Repairing aluminum is simple

• Repair sleeve

• Rods