Pole Guying More Complicated Than Meets the Eye. NRECA TechAdvantage 2014 Presented by Jason Settle, P.E.

Transcription

1 Pole Guying More Complicated Than Meets the Eye NRECA TechAdvantage 2014 Presented by Jason Settle, P.E.

2 Pole Guying Strength of components NESC vs. RUS Guy Factor Grounding 2

3 Pole Guying Purpose Support fully loaded design tension of conductors Applied wind and ice load 3

4 The Components of a Guyed Structure Guy Attachment Guy Attachment Height Guy Pole Anchor Guy Lead 4

5 The strength of the guy-anchor assembly is dependent on: Strength of the guy wire de-rated to 90% of the RBS (NESC Table 261-1) Strength of the guy attachment including the bolt and washer Strength of the anchor and rod Holding power of the soil in which the anchor is installed Only as Strong as the Weakest component 5

6 Guy Hardware 6

7 Thimble-eye Bolt 7

8 Johnny Ball & Guy Strain Insulator 8

9 Guy Wire Strength Data 9

10 RUS Guy Assemblies & Strength Assembly Item Material E1.1 E1.1L E1.2 b Bolt, machine 5/8 (12,400 lbs) 3/4 (18,350 lbs) None d Washer, curved 3 square (7,800 lbs) v Guy attachment Standard (6,600 lbs) y Guy wire 3/8 SM (6,255 lbs) 4 square (14,200 lbs) Heavy Duty (8,500 lbs) 3/8 HS steel (9,720 lbs) None 90% of guy wire 7/16 SM (8,415 lbs) Total Guy Strength 6,255 lbs 8,500 lbs 8,415 lbs 10

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12 RUS Standard Washer Allowed Load RUS standards allow no more than 910 pounds per square inch of compression for washers on wood poles and crossarms. 12

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15 RUS Standard Distribution Anchor Assemblies Anchor Type Expanding Screw (Power Installed) RUS Designation Maximum Holding Power (lbs)* F1.8 8,000 F ,000 F ,000 F2.8 8,000 F ,000 F ,000 *Maximum Holding Power based on installation in Class 5 Soil 15

16 Types of Soils for Anchor Placement Class Description Soil Class Descriptions 1 Solid rock 2 Dense sand, hard silts, course gravel 3 Compact clay & gravel mixed, shale, hardpan 4 Compacted sand, clay-pan, compacted gravel 5 Loose sand, gravel & clay, compacted course sand 6 Clay loam, damp clay, compacted fine sand, loose course sand 7 Silt loam, loose sand fines, wet clay, miscellaneous fill 8 Swamp, saturated loam, marshland 16

17 Expansion Anchors Rating (pounds) 6,000 8,000 10,000 12,000 Item Anchor Rod F1.6 F1.8 F1.10 F1.4 x Anchor Rod 5/8 x 7 5/8 x 7 N/A N/A Thimble Eye x Anchor Rod N/A N/A 3/4 x 8 3/4 x 8 Twin Eye z Anchor (sq. in.)

18 Expansion (Bust) Anchors Un-expanded Anchor Expansion Tool Illustration courtesy of Hubble Power Systems (Chance) 18

19 Screw Anchors Single Helix Double Helix Illustration courtesy of Hubble Power Systems (Chance) 19

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21 Spacing of Anchors 5 feet 5-ft for standard duty 8-ft for heavy duty 21

22 Guying Situations Change in conductor size New wire sagged against old wire Line angles Dead-ends Grade B Crossings Spans that exceed the ruling span by 150% Long crossings 22

23 Guy & Anchor Selection Depend on: Horizontal pull at the guy attachment Guy resultant tension in the down guy Soil type in which the anchor is installed Available materials and assemblies 23

24 Standard Guy and Anchor Assemblies Guys Anchors E1.1 ( 6,255 lbs) F1.6 (6,000 lbs) E1.1L (8,500 lbs)* F1.8 (8,000 lbs) E1.2 (9,720 lbs)* F1.10 (10,000 lbs) * 3/8 HS steel 24

25 Guy & Anchor Grade of Construction RUS requires Minimum Grade C on distribution Must match highest Grade of construction on pole Transmission underbuild Grade B Railroad, Limited Access Hwy Grade B 25

26 Type of Guy Loads Transverse Forces acting perpendicular to the line Wind blowing on ice loaded conductors Tension in the wire Longitudinal Forces acting parallel to the line Maximum loaded design tension 26

27 Deadend Guying Calculations Tension A,B,CΦ Height Neutral Height Guy Height (Hg) Guy Lead (Lg) 27

28 Dead-end guying Gh = Mt/Hg Gh = Horizontal pull at guy attachment Mt = Sum of moments due to tension in the wire Hg = Average guy attachment height NESC construction grade = C NESC loading district = Light Primary cond. = 1/0 ACSR 6/1, Neutral cond. = 2 ACSR 7/1 Pole height and class = 40 ft, Class 4, SYP Pole-top assembly = C5.71L (RUS Assembly) 28

29 *NESC Load factors for deadend guyed structures defined in Rule 250B Type of Loading Grade B Grade C Crossing Elsewhere Transverse wind Transverse wire tension Longitudinal load at dead-ends *Adapted from NESC Table 253-1, 2012 Edition 29

30 *NESC Load factors for Extreme Weather when applicable Type Loading Rule 250 C Extreme Wind Grade B Crossing Grade C Elsewhere Wind Loads All other loads Rule 250D Extreme ice with concurrent wind *Adapted from NESC Table 253-1, 2012 Edition Applied to NESC 250B load if a structure or its supported facilities exceed 60 feet above ground or water. 30

31 Transverse Wind Load for 1-ft of Conductor Conductor Physical Data Transverse Wind Name Size/Strand Dia. (in) RBS (lb) Light (lb/ft) Medium (lb/ft) Heavy (lb/ft) Sparate Raven Penguin Merlin 2 ACSR 7/1 1/0 ACSR 6/1 4/0 ACSR 6/1 336 ACSR 18/

32 Step 1: Moment Due to Tension (Mt) Mt = Σ(Dt Hc Ft) Mt = Moment due to tension in the wire DT = Fully loaded design tension DT = 50% RBS 1/0 ACSR = 0.50(4,380 lbs) = 2,190 lbs 2 ACSR = 0.50(3,640 lbs) = 1,820 lbs Hc = Height of conductor above grade (RUS C5.71L) Ft = NESC wire tension load factor = 1.10 (grade C) 32

33 Step 1: Moment due to tension (Mt) Wire DT(lb) x Hc (ft) x Ft (ft) = Mt(ft-lb) A-phase 2190 x 32.5 x 1.10 = 78,293 B-phase 2190 x 32.5 x 1.10 = 78,293 C-phase 2190 x 32.5 x 1.10 = 78,293 Neutral 1,820 x 28.5 x 1.10 = 57,057 Σ(Dt Hc Ft) = 291,936 Mt = 291,936 ft-lbs 33

34 Step 2: Horizontal Pull (Gh) Gh Mt Hg Hg = Height of guy attachment = ft (RUS drawing C5.71L) Mt = 291,936 ft-lbs Gh = 291,936/31.75 = 9,195 Gh = 9,195 lbs 34

35 Guy Resultant or Total Guy Load (Gr) Gr Gh Lg 2 Lg Hg 2 Gr = Guy resultant tension (lbs) Gh = Horizontal pull at guy attachment (lbs) Hg = Height of guy attachment (ft) Lg = Guy lead length (ft) 35

36 Guy Resultant for Example 1 (Equation Method for 1:1 Guy Lead) Gr Gh Lg 2 Lg Hg 2 Gr 9, lbs Total Guy Load (Gr) = 13,004 lbs 36

37 Guy Factors Gf Lg2Hg2 Lg Hg Gf = Guy Factor Lg = Guy lead length Hg = Guy attachment height Lg 37

38 Guy Factors Gf Gf Gf 15 1 to 1 2 to 3 1 to

39 Guy Resultant for Example 1 (Guy Factor Method) Gr Gh * Gf 1:1 Guy Lead Gr 9,195* ,001lbs 2:3 Guy Lead Gr 9,195* ,579 lbs 1:2 Guy Lead Gr 9,195* ,560 lbs 39

40 Guy Leads Specify and stake adequate guy leads Not based on truck setup Short guy leads can cause Significant increase in total guy load Pole buckling due to the vertical component of guy tension Buckling Guy Lead 40

41 Pole Buckling Short Guy Leads Small Pole Class Heavy Wire Tension Specify a larger class pole 41

42 Guy Factors Guy Lead (ft) Guy Attachment Height (ft) # # # # # # # #

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44 Clearance from Guys to Other Conductors Adapted from NESC Table Bare Guy Wire Insulator Link Secondary and Neutral 6 inches 4.5 inches 12 kv Primary 6 inches 4.5 inches 25 kv Primary 10 inches 7.5 inches 44

45 Code Violation! 45

46 Grounding Anchor Guys and Span Guys Rule 215C2 All anchor guys and span guys shall be effectively grounded. Only EXCEPTION is to use a guy insulator Fiberglass guy strain insulators Johnny Balls used in the past Eliminated EXCEPTION for triplex service conductors Guys on secondary poles must be grounded Big change for many utilities Per Bulletin 1724E-153 RUS considers it to be nonstandard construction when guy wires are not effectively grounded. 46

47 RUS Use of Insulator Links RUS calls for insulator links on 12 kv systems when there is less than 15 inches of wood separating guy attachment and phase associated hardware. RUS also calls for the lower portion of the guy to be grounded. Thus it meets the requirements of 215C2 Insulator link used for two reasons 1. Increase BIL on the structure 2. Provide for increased spacing between phase conductors and ground conductors as one means of providing safety to lineman. 47

48 Guy on secondary pole must be grounded Guy must be grounded or have guy strain insulator 48

49 Grounded Guy Grounded guy near to phase associated hardware Susceptible to flashover from lightning Solution 1. Lower guy RUS says 18 inches 2. Install guy insulator Still ground the lower part of the guy Guy Attachment 49

50 Guy Insulator Link Common mistake is to assume the guy insulator link must extend past lower conductors Not a NESC requirement To achieve BIL goals 18 inches is long enough To achieve working space Some use 36 inches 50

51 Span Guys Span guy is grounded at structure At stub pole Grounding jumper from span guy to down guy RUS requires grounding nut in anchor eye 51

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53 Pole Guying Verify/Know your material/inventory. Be careful of short guy leads RUS - insulate and ground Questions? 53