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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
2
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.
3
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
4
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
5
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
6
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!
7
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.
8
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
11
Shawn M. Higbe, PE
McCall-Thomas Engineering Co., Inc.
Orangeburg, SC
12
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.
13
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
15
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
17
Cost Analysis
• Pole Height Class and Cost Data– Material and installation cost of poles only.
18
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%
20
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%
21
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
23
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%
24
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%
25
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%
26
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
Shawn M. Higbe, PE
VP, Director of Electrical Engineering Division
www.McCall-Thomas.com
Office 803-534-1040, ext. 1218