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
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.
2
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
3
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
4
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
5
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!
6
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.
7
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.
8
Why South Carolina?
9
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
10
Shawn M. Higbe, PE
McCall-Thomas Engineering Co., Inc.
Orangeburg, SC
11
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.
12
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
13
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
14
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
15
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
16
Cost Analysis
• Pole Height Class and Cost Data
– Material and installation cost of poles only.
17
Grade C Analysis
1 - #2 ACSR - Power
19 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%
18
Grade C Analysis
3 - #336 ACSR - Power
22 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%
19
Grade C Analysis
1 - #1/0 ACSR - Power/JU
10 Poles
Case Description
Change-Out Cost Increase
Requirement
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%
20
Grade C Analysis
3 - #477 ACSR - Power/JU
27 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%
21
Grade B Analysis
1 - #2 ACSR - Power
19 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
22
Grade B Analysis
3 - #336 ACSR - Power
22 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%
23
Grade B Analysis
1 - #1/0 ACSR - Power/JU
10 Poles
Case Description
Change-Out Cost Increase
Requirement
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%
24
Grade B Analysis
3 - #477 ACSR - Power/JU
27 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%
25
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.
26
Questions?
Robert W. Harris, PE
Principal, Transmission & Distribution Engineering
Office 703-907-5753
Cell 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