CONSIDERATIONS FOR HTLS CONDUCTORS · 2018-09-20 · AAAC developed to free up steel for the war effort ... Southwire Max Storm™ high -resiliency conductor (ZTAL high-temperature

SEPTEMBER 5 - 7, 2018

CONSIDERATIONS FOR HTLS CONDUCTORS

Barrett M. Kimball, Director of Engineering, SouthwireErik Ruggeri, Principal Engineer, POWER Engineers, INC


CIGRE (Conseil International des Grands Réseaux Électriques) : Who they are and their goals:

• Established in 1921• 59 National

Committees representing over 90 countries

• 15,000 members



Best Paths: A European Consortium whose goal is to facilitate renewable energy into the European market.


CONDUCTOR TESTING PROGRAM


HTLS CONDUCTORS STUDIED:• ACPR: Aluminum Conductor Polymer matrix Reinforced

Polymer

• (Z)TACSR: Thermal resistant and Super Thermal (ZT) resistant Aluminum alloy Conductor Steel Reinforced


HTLS CONDUCTORS STUDIED:• TACIR & ZTACIR: Thermal resistant Aluminum alloy Aluminum Clad

Invar


HTLS CONDUCTORS STUDIED:• G(Z)TACSR: Gap Type Super thermal resistant Aluminum alloy Steel

Reinforced


• ACSS: Aluminum Conductor Steel Supported

• ACCR: Aluminum Conductor Composite Reinforced• ACCC: Aluminum Conductor Composite Conductor

Carbon


HTLS CONDUCTORS STUDIED:• Lamifil’s ACCC ice+soft and ACCC ice+hard

• Soft: Designed for up to 2” ice• Hard: Coming soon – designed for very large ice loads


1907: ACSR was introduced. Over a century of experience exists for ACSR.

1917: AAAC developed to free up steel for the war effort

1973: Reynolds Aluminum introduced SSAC. Reynolds exited the conductor industry in 2000. ACSS became a commodity available from numerous suppliers.

2002: ACCR (3M) and ACCC® (CTC) composite core conductors

2004: Southwire ACSS/HS285® (comeback for steel core)

2014: Southwire C7® composite core conductor

2017: Southwire Max Storm™ high-resiliency conductor (ZTAL high-temperature aluminum over UHS steel)

Conductor Brief History


ACSS conductors, unlike ACSR conductors, are not capacity-limited by concerns over annealing the hard-drawn aluminum strands. ACSR annealing concerns include: Loss of strength (typical ACSR conductors get 60% of their strength from the

aluminum component) Sag increase due to increased creep

ACSS conductors have pre-annealed aluminum strands. There is no concern over in-service annealing

ACSS conductors have more predictable creep characteristics, because the everyday tension is supported by the steel core which has negligible creep relative to aluminum creep

ACSS conductors have less sag increase at high-temperature, because steel has only half of the thermal elongation of aluminum

ACSS conductors are naturally self-damping

ACSS and ACSS/HS285


Bobbin Annealing (Reynolds) Process

Aluminum strands are oven-annealed on the strander bobbins.

Stranding fully-annealed aluminum is challenging, because the bobbin brake and closing die settings need to respect the softness and low tensile strength of annealed aluminum strands

The stranding mills understandably take advantage of the allowable tensile range for O-temper aluminum – above 11 kpsi is typical

Ultimate stress does not predict the yield stress

Strain-hardening of the aluminum is unavoidable at the closing dies for each layer. Mechanical interference is needed to size the OD. The degree of strain hardening depends on the mechanical interference, which changes as the dies wear.


Batch Annealing (all Southwire ACSS)

In 1994 ACSS batch annealing was developed: hard-drawn aluminum is stranded using ACSR settings for bobbin brakes and closing dies

Annealing is done after stranding – the entire take-up reel is placed in the annealing oven

Due to the long soak times required for a massive reel, batch-annealing produces consistently dead soft aluminum strands

With batch-annealing, the aluminum temper is not affected by variation in the stranding process.


High-purity aluminum rod is required by the Southwire process to ensure consistent annealing. A side benefit is improved conductivity for lower line loss. ASTM minimum conductivity for 1350-O is 61.8% IACS. Southwire internal controls require a minimum of 63% IACS (implying 2% lower line loss).

Southwire’s Cofer Technology Center has tested both bobbin-annealed and batch-annealed ACSS, and has consistently found a significant difference.

Southwire SAG10® software shows a 6% to 10% decrease in high-temperature sag for Southwire ACSS compared to bobbin-annealed (Reynolds-process) ACSS. PLS-CADD software mirrors SAG10 results.

Southwire’s Cofer Technology Center has evaluated ACSS self-damping characteristics, and found that Southwire ACSS can be regarded as self-damping even in early life. The current engineering consensus is that bobbin-annealed ACSS may need dampers to prevent fatigue failures.

What is Special about Southwire ACSS?

Copyright © 2018 Southwire Company. All Rights Reserved


16

“Reynolds Legacy” (Same Data) Stress-Strain Chart – Type 16 ACSS


17

“Batch-Annealed” Stress-Strain Chart – Type 16 ACSS


11.3 kpsi ultimate @ >20%

10.2 kpsi ultimate @ >20%


19

Effect of Coefficients on Sag Prediction


20

Recent-Production ACSS vs. Reynolds Coefficients


Significance of Aluminum Temper in ACSS

• On first consideration, stronger is better – harder aluminum will increase the conductor breaking strength (but not the RBS, which is computed based on allowable aluminum tensile strength)

• However, follow that logic to its conclusion, and you are back at ACSR (fully hard-drawn aluminum)

• Batch-annealing advantages• Better consistency – no dependency on stranding parameters• Slightly higher conductivity due to deeper annealing• Significantly less contribution to thermal sag (more charts to follow)• Improved early-life self damping: no dampers are required for ACSS with dead-soft aluminum



Type 13 (medium steel fraction) ACSS/MA5 Comparison

22


Type 13 ACSS/MA3 Batch-Annealed vs. ACSS/MA5 Bobbin-Annealed

23


HS285 vs MA5

24

• ACSS/MA5 and ACSS/HS285 are not the same:o ACSS/HS285 steel core tensile properties are verified after heat-aging. ACSS/MA5 is sold

without regard for loss-of-strength due to future high-temperature ACSS operationo ASTM B958 (MA5/UHS core) specifications are based on Southwire’s proprietary HS285

specification, first published in 2004. ASTM B958 does not contain the heat aging requirement for the steel strand.

o Southwire has always required the finished ACSS and ACSS/HS285 meet the nominal strength requirements. This means we account for the loss-of-strength due to stress-relief annealing of the steel core during batch-annealing

• Southwire ACSS, including ACSS/HS285 is batch-annealed, resulting in:o Tighter strandingo Less high-temperature sag (be sure to use Southwire Certified data for design)o Self-dampingo More consistent properties. The mission-critical yield stress is not specified or even

measured. Southwire’s process is consistent (dead soft).



Questions??

CONSIDERATIONS FOR HTLS CONDUCTORS · 2018-09-20 · AAAC developed to free up steel for the war effort ... Southwire Max Storm™ high -resiliency conductor (ZTAL high-temperature

Documents