2015 IEEE REPC

Engineering Analysis of

Possible Effects of 2017 NESC Change Proposal

To Modify or Remove 60’ Exemption

April 20, 2015

Robert W. Harris, PE and Shawn M. Higbe, PE

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Background

• Debate on validity of Rule 250B and 60’ Exclusion began nearly 20 years ago.

• After 2012 Code Cycle, some thought the issue settled.

• Hurricane Sandy breathed new life into the issue.

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2017 NESC Code Cycle

• Change Proposals submitted first half of 2013.

• Subcommittees met Fall 2013.• Two CPs submitted on these Rules:

– 250B Combined Ice & Wind District– 250C Extreme Wind– 250D Extreme Ice & Wind

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NESC Change Proposals

• CP 4611 Proposed Elimination of:– Rule 250B– 60’ Exemption for Rule 250C– 60’ Exemption for Rule 250D

• Unanimously Rejected by SC 5

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NESC Change Proposals

• CP 4610 Originally Proposed:– 15.5 psf for Grade C– 18 psf for Grade B– Only if structure <= 60’– Only for Rule 250C– Rule 250D?

• Rejected by SC 5

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NESC Change Proposals

• CP 4610 (Modified) Proposed:– 15 psf regardless of Grade– Only if structure <= 60’– Only for Rule 250C– Eliminating 60’ Exclusion for Rule 250D

• Tie Vote!

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NRECA’s Role

• Keep up with developments which affect our members.

• Inform our members.• Seek guidance and support, if

necessary, to determine further action.• T&D Engineering Committee.

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NRECA T&D Committee

• 74 Co-Op Engineers, RUS Representatives & Consultants.

• Six different Subcommittees.• Overhead Lines Subcommittee

– Kevin Jordan is a member from Horry Electric Cooperative in Conway, South Carolina.

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Why South Carolina?

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Study Group

• Ten South Carolina Distribution Co-Ops• Two North Carolina Distribution Co-Ops• One Distribution Co-Op Each from

Florida & Georgia• Two G&T Co-Ops

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Shawn M. Higbe, PE

McCall-Thomas Engineering Co., Inc.

Orangeburg, SC

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Project Details

• Bid Proposal from McCall-Thomas Engineering– Model recently built Distribution Lines.– Analyze using SpidaCalc and Partner

Staking.– Evaluate modification and elimination of

the 60’ Exclusion.– Analyze effect of Joint Use Attachments.

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Line Designs

• 1 - #2 ACSR• 1 - #1/0 ACSR• 3 - #336 ACSR• 3 - #477 ACSR• All built to Rule 250B- Medium Load

District- Grade C

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Rule 250C- Extreme Wind• Extreme Wind at 15 psf Grade C• Extreme Wind at 15.5 psf Grade C• Existing Grade B• Extreme Wind at 15 psf Grade B• Extreme wind at 18 psf Grade B• Extreme Wind at 90 mph• Extreme Wind at 130 mph

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Additional Loading

• Joint Use– One cooperative fiber, 1’ below neutral– One telephone joint user– One telephone and one cable joint user– One cooperative fiber, one telephone and

one cable joint user

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Basic Design Data(As-Built for Rule 250B)

• Standard RUS 25 kV construction • Southern Pine CCA Poles• 40’ Class 5 for 1 - 2 ACSR• 40’ Class 4 for 1 - 1/0 ACSR• 40’ Class 4 for all 3 base cases• 45’ Class 3 for 3 lines with taps• 50’ Class 3 for 3 vertical construction• 55’ Class 3 for 3 vertical construction with taps

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Cost Analysis

• Pole Height Class and Cost Data– Material and installation cost of poles only.

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Grade C Analysis1 - #2 ACSR - Power19 Poles

Case Description Change-Out Requirement Cost Increase

Extreme Wind, 15 psf None NA

Extreme Wind, 15.5 psf None NA

Extreme Wind, 90 mph None NA

Extreme Wind, 130 mph 2 poles 1.78%

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Grade C Analysis3 - #336 ACSR - Power22 Poles

Case Description Change-Out Requirement Cost Increase

Extreme Wind, 15 psf None NA

Extreme Wind, 15.5 psf 1 pole 0.17%

Extreme Wind, 90 mph 4 poles 0.94%

Extreme Wind, 130 mph 19 poles 14.15%

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Grade C Analysis1 - #1/0 ACSR - Power/JU10 Poles

Case Description Change-Out Requirement

Cost Increase

Extreme Wind, 15 psf – Power Only None NA

Extreme Wind, 15.5 psf – Power Only None NA

Extreme Wind, 90 mph – Power Only None NA

Extreme Wind, 130 mph – Power Only 4 poles 8.17%

Extreme Wind, 15 psf – Power/JU 0 / 1 / 2 / 4 0 / 0.38 / 1.2 / 3.42%

Exreme Wind, 15.5 psf – Power/JU 0 / 1 / 3 / 4 0 / 0.38 / 1.58 / 3.42%

Extreme Wind, 90 mph – Power/JU 2 / 2 / 4 / 5 0.98 / 1.39 / 3.42 / 10.98%

Extreme Wind, 130 mph – Power/JU 6 / 7 / 9 / 9 20.42 / 25.27 / 40.8 / 58.69%

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Grade C Analysis3 - #477 ACSR - Power/JU27 Poles

Case Description Change-Out Requirement

Cost Increase

Extreme Wind, 15 psf – Power Only 1 pole 0.8%

Extreme Wind, 15.5 psf – Power Only 1 pole 0.8%

Extreme Wind, 90 mph – Power Only 3 poles 1.63%

Extreme Wind, 130 mph – Power Only 23 poles 10.75%

Extreme Wind, 15 psf – Power/JU 2 / 4 / 5 / 5 1.3 / 2.21 / 2.54 / 5.23%

Exreme Wind, 15.5 psf – Power/JU 3 / 4 / 5 / 6 1.63 / 2.21 / 3.72 / 5.56%

Extreme Wind, 90 mph – Power/JU 3 / 7 / 13 / 17 3.1 / 5.21 / 8.4 / 9.62%

Extreme Wind, 130 mph – Power/JU 24 / 25 / 25 / 25 33.6 / 44.9 / 51.2 / 60.8%

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Grade B Analysis1 - #2 ACSR - Power19 Poles

Case Description Change-Out Requirement Cost Increase

Medium B 2 poles 0.95%

Extreme Wind, 15 psf None NA

Extreme Wind, 18 psf None NA

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Grade B Analysis3 - #336 ACSR - Power22 Poles

Case Description Change-Out Requirement Cost Increase

Medium B 1 pole 2.27%

Extreme Wind, 15 psf 1 pole 0.16%

Extreme Wind, 18 psf 1 pole 0.16%

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Grade B Analysis1 - #1/0 ACSR - Power/JU10 Poles

Case Description Change-Out Requirement

Cost Increase

Medium B – Power Only 1 pole 0.83%

Extreme Wind, 15 psf – Power Only None NA

Extreme Wind, 18 psf – Power Only None NA

Medium B – Power/JU 0 / 2 / 3 / 5 0 / 2.02 / 3.27 / 2.54%

Exreme Wind, 15 psf – Power/JU 0 / 1 / 3 / 5 0 / 0 / 0 / 1.97%

Extreme Wind, 18 psf – Power/JU 0 / 1 / 3 / 3 0 / 0 / 0 / 4.2%

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Grade B Analysis3 - #477 ACSR - Power/JU27 Poles

Case Description Change-Out Requirement

Cost Increase

Medium B – Power Only 2 poles 0.8%

Extreme Wind, 15 psf – Power Only 1 pole 0.46%

Extreme Wind, 18 psf – Power Only 3 poles 1.61%

Medium B – Power/JU 3 / 2 / 5 / 14 2.66 / 0.67 / 1.47 / 4.14%

Exreme Wind, 15 psf – Power/JU 2 / 4 / 3 / 6 1.39 / 2.19 / 3.81 / 4.7%

Extreme Wind, 18 psf – Power/JU 5 / 5 / 5 / 6 3.23 / 4.02 / 4.82 / 7.16%

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Conclusion

• Current Change Proposal- minimal cost increases, but increases design complexity for no apparent gains.

• 15.5 psf and 18 psf cause more significant cost increases.

• Elimination of 60’ Exclusion would bring major cost increases, especially in joint use situations.

Questions?Robert W. Harris, PE

Principal, Transmission & Distribution EngineeringOffice 703-907-5753Cell 571-205-3189

robert.harris@nreca.coop

Shawn M. Higbe, PE

VP, Director of Electrical Engineering Division

www.McCall-Thomas.com

Office 803-534-1040, ext. 1218

shigbe@mcteng.com