linda1'ppt

1
Design Effects of CP2372
IEEE
Wade Shultz Southern Company February 6, 2000
2
Design Effects of CP 2372

• Transmission
• Distribution
• Steel and Wood Structures
• Spans

3
CP 2372 Impacts

• Wind loading
• Ice loading
• Construction and maintenance loading
• Load factors
• Loaded wire tension limits

4
(Extreme) Wind Loading

• 3-Second Gust map (Figure 250-2)
• Wind speed adjustments
• Terrain obstructions
• Height above ground or water
• Span length
• Will result in multiple wind pressures

5
(Combined)Wind and Ice Loading

• New ASCE 74 wind/ice map (Figure 250-1)
• Adjustments
• Ice thickness
• Height above ground or water
• Span length
• Terrain obstructions
• Will result in multiple wind pressures

6
(Combined) Wind and Ice Loading

• Alternative to Light, Medium, and Heavy loading
  zones
• Wind speed of 30, 40 ,50, and 60 mph
• Radial ice of 0 to 1.5 in 0.25 increments
• 18 wind/ice combinations plus special zones

7
Construction and Maintenance

• New Rule 250D
• Vertical load at any or all wire attachment
  points of 1.5 times the weigh span
• 350-pound load at lineman-support points (if
  climbed)
• Consideration of stringing loads
• Conductor termination and snub structures covered

8
Load Factors Table 253-1
9
Load Factors Table 253-2
10
Tensions Limits

• Initial loaded tension limit increased to 80 RBT
  (versus 60)
• Initial unloaded (35 RBT) unchanged
• Final unloaded (25 RBT) unchanged

11
Design Significance

• Greater sags shorten span lengths or increase
  structure heights
• Increased loading limit (80 vs. 60) can
  increase tensile loads on structures

12
Conductor Sags Ibis
13
Conductor Sags Drake
14
Impacts

• Sag
• Ice thickness of 0.75 or greater
• Wind speeds of 40 to 60 mph
• Greater sag impact on small conductor
• Tension
• Where final loaded sag exceeds maximum
  temperature sag. (Loaded tension will normally
  govern.)

15

• Loading Calculations for Wind

16
Wind Speed-to-Force Conversion

• Force 0.00256 x V2 x GRF x Cd x A
• V Design wind velocity (mph)
• GRF Gust response factor
• Cd Shape factor
• A Exposure area (ft2)

17
Gust Response Factors

• For wires (span and height dependent)
• For structures (height dependent)
• Calculate from equations or use Table 250-1 values

18
Gust Response Equations
19
Gust Response Equations
20
Table 250-1
21
Determine Required Strength

• Wood poles - Required groundline diameter (pole
  class)
• Steel Poles - Required groundline moment capacity
  (section properties can vary)

22
DISTRIBUTION

• 3-Phase delta-top structure
• Southern pine wood pole (8,000 psi)
• 795,000 cm AAC conductor
• 397,500 cm 18/1 ACSR neutral
• 500 wind span
• Atlanta, Georgia (suburban)
• Grades B and C

23
3-Phase Delta Structure
24
Distribution

• Wind and Ice Design

25
Grade B

• Wind / Ice 30 mph wind, 0.75 radial ice
• Suburban location
• Maximum height 52.5
• Terrain factor 0.80
• Load factor 1.0
• Strength factor 0.65

26
Applied Loads

• Force 0.00256 x V2 x GRF x Cd x A
• Velocity reduction 30 x 0.8 24 mph
• GRF for pole 0.93
• GRF for wires 0.73
• Cd 1.0 for round surface
• A (Wire)
• A (Pole)

27
Exposure

• Conductor
• Neutral
• Pole

28
Wind on Wires

• Conductors
• Force 0.00256 x V2 x GRF x Cd x A
• 0.00256 x (24)2 x (0.73) x 1.0 x
  105.25
• 113.3 lb.
• Neutral
• Force 0.00256 x V2 x GRF x Cd x A
• 0.00256 x (24)2 x (0.73) x 1.0 x
  93.46
• 100.6 lb.

29
Wind on Pole

• Force 0.00256 x V2 x GRF x Cd x A
• 0.00256 x (24)2 x (0.93) x 1.0 x 43.3
• 59.4 lb.

30
Strength Requirement

• Strength x Strength Factor Load x Load Factor
• Strength
• Strength
• Required GL moment capacity 36,152 ft-lb

31
Required Groundline Diameter for Grade B Wind and
Ice

• Flexure formula
• Moment Stress x Section Modulus
• Moment
• Moment
• Required diameter for Grade B 8.19 in.

32
Grade C

• Wind / Ice 30 mph wind, 0.75 radial ice
• Suburban location
• Maximum height 52.5
• Terrain factor 0.80
• Load factor for Grade C 1.0
• Ice reduction factor for Grade C 0.80
• Strength factor for wood Grade C 0.85

33
Applied Loads

• Force 0.00256 x V2 x GRF x Cd x A
• Velocity reduction 30 x 0.8 24 mph
• GRF for pole 0.93 GRF for wires 0.73
• Cd 1.0 for round surface
• Radial ice 0.80 x 0.75 0.60
• A (Wire)
• A (Pole)

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Strength Requirement

• Strength x Strength Factor Load x Load Factor
• Strength
• Strength
• Required GL moment capacity 24,503 ft-lb

35
Required Groundline Diameter for Grade C Wind and
Ice

• Flexure formula
• Moment Stress x Section Modulus
• Moment
• Moment
• Required diameter 7.19 in.

36
Distribution

• Wind Design

37
Grade B

• Wind speed 90 mph wind (Fig. 250-2)
• Suburban location
• Maximum height 52.5
• Strength factor for wood Grade B is 0.65
• Load factor for Grade B is 1.0
• Terrain factor is 0.80

38
Wind Loading

• Force 0.00256 x V2 x GRF x Cd x A
• Velocity reduction 90 x 0.80 72 mph
• GRF for pole 0.93 GRF for wires 0.73
• Cd 1.0 for round surface
• A (Wire)
• A (Pole)

39
Required Groundline Diameter for Grade B Wind

• Strength x Strength Factor Load x Load Factor
• Strength
• Required GL moment capacity 142,347 ft-lb
• Required groundline diameter 12.96 in.

40
Grade C

• Wind speed 90 mph wind
• Suburban location
• Maximum height 52.5
• Strength factor for wood Grade C is 0.85
• Load factor for Grade C is 0.9
• Terrain factor 0.80

41
Required Groundline Diameter for Grade C Wind

• Strength x Strength Factor Load x Load Factor
• Strength
• Required GL moment capacity 97,968 ft-lb
• Required groundline diameter 11.44 in.

42
Different Locations

• How do requirements vary over different loading
  situations?

43
Loading Sites
44
Grade B, 60 Ft. Wood 3-Phase Distribution, 500,
Arbutus
45
Grade C, 60 Ft. Wood 3-Phase Distribution, 500,
Arbutus
46
Terrain Effect

• How does open terrain affect the required pole
  strength?
• Wind speeds are not reduced for open terrain
  without obstructions.

47
Terrain Effect
48
1997 NESC vs. 2002 NESC(w/o Obstructions)
49
TRANSMISSION

• Normally facilities higher than 60 above ground
  or water
• Will have a greater variety of span lengths
• Design process is similar to the distribution
  example with adjustments for ice and wind loads
• Metal structures more common (than distribution)
  for insulation and strength.

50
Gust Response Factor

• For wires (span and height variable)
• For structure (height variable)
• Calculate from formulas or use Table 250-1 values

51
Required Strength

• Wood poles - Required groundline diameter (pole
  class)
• Steel Poles - Required groundline moment capacity
  (section properties can vary)

52
Transmission Design

• 115 kV Single Pole Fiberglass Arm (FGA) Delta
  Structure
• Southern pine wood pole (8,000 psi)
• 795,000 cm 26/7 ACSR (Drake) conductor
• 3/8 H.S. steel groundwire
• 600 wind span
• Atlanta, Georgia
• Grades B and C

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FGA Structure
54
Gust Response Factors
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Transmission

• Wind and Ice Design

56
Grade B

• Wind / Ice 30 mph wind, 0.75 radial ice
• Suburban location
• Maximum height 79
• No terrain reduction
• Load factor for Grade B 1.0
• Strength factor for Grade B wood 0.65

57
Applied Loads

• Force 0.00256 x V2 x GRF x Cd x A
• Velocity reduction 30 mph (no adjustment)
• GRF for pole 1.01 (gt60)
• GRF for wires 0.89 (gt60) 0.73 (lt 60)
• Cd 1.0 for round surface
• A (Wire)
• A (Pole)

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Exposure

• OH Groundwire
• Conductor
• Pole

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Wind Loading

• OH Groundwire and Top Two Conductors
• Force 0.00256 x V2 x GRF x Cd x A
• 0.00256 x (30)2 x (0.89) x 1.0 x
  93.5
• 191.7 lb.
• Top Two Conductors (each)
• Force 0.00256 x V2 x GRF x Cd x A
• 0.00256 x (30)2 x (0.89) x 1.0 x
  130.4
• 267.4 lb.

60
Wind Loading

• Bottom Conductor
• Force 0.00256 x V2 x GRF x Cd x A
• 0.00256 x (30)2 x (0.73) x 1.0 x
  130.4
• 219.3 lb.
• Pole
• Force 0.00256 x V2 x GRF x Cd x A
• 0.00256 x (30)2 x (1.01) x 1.0 x
  43.3
• 59.4 lb.

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Strength Requirement

• Strength x Strength Factor Load x Load Factor
• Strength
• Strength
• Required GL moment capacity 115,470 ft-lb

62
Required Groundline Diameter for Grade B Wind and
Ice

• Flexure formula
• Moment Stress x Section Modulus
• Moment
• Moment
• Required diameter for Grade B 12.08 in.

63
Grade C

• Wind / Ice 30 mph wind, 0.75 radial ice
• Suburban location
• Maximum height 79
• No terrain reduction
• Load factor 1.0
• Strength factor 0.85
• Ice reduction factor 0.8

64
Applied Loads

• Force 0.00256 x V2 x GRF x Cd x A
• Velocity reduction 30 mph (no reduction)
• GRF for pole 1.01 (gt60)
• GRF for wires 0.89 (gt60) 0.73 (lt 60)
• Radial ice 0.8 x 0.75 0.60
• A (Wire)
• A (Pole)

65
Required Groundline Diameter for Grade C Wind and
Ice

• Strength x Strength Factor Load x Load Factor
• Strength
• Required GL moment capacity 81,318 ft-lb
• Required diameter 10.75 in.

66
Transmission

• Wind Loading Design

67
Grade B

• Wind velocity from Figure 250-2 for Atlanta is 90
  mph
• OH groundwire and top two phases higher than 60
  ground
• Bottom phase less than 60 above ground
• Load factor 1.0
• Strength factor 0.65

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Applied Loads

• Force 0.00256 x V2 x GRF x Cd x A
• Velocity reduction 90 mph (no reduction)
• GRF for pole 1.01 (gt60)
• GRF for wires 0.89 (gt60) 0.73 (lt 60)
• Cd 1.0 for round surface
• A (Wire)
• A (Pole)

69
Required Groundline Diameter for Grade B Wind

• Strength x Strength Factor Load x Load Factor
• Strength
• Required GL moment capacity 461,154 ft-lb
• Required groundline diameter 19.17 in.

70
Grade C

• Wind velocity from Figure 250-2 for Atlanta is 90
  mph
• OH groundwire and top two phases higher than 60
  ground
• Bottom phase less than 60 above ground
• Load factor 0.90
• Strength factor 0.85

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Applied Loads

• Force 0.00256 x V2 x GRF x Cd x A
• Velocity reduction 90 mph (no reduction)
• GRF for pole 1.01 (gt60)
• GRF for wires 0.89 (gt60) 0.73 (lt 60)
• Cd 1.0 for round surface
• A (Wire)
• A (Pole)

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Required Groundline Diameter for Grade C Wind

• Strength x Strength Factor Load x Load Factor
• Strength
• Required GL moment capacity 317,362 ft-lb
• Required groundline diameter 16.93 in.

73
1997 vs. 2002

• How do proposed strength requirements for wood
  structures compare for various loading cases and
  to current NESC?
• How do proposed strength requirements for steel
  structures compare for various loading cases and
  to current NESC?

74
Loading Sites
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Grade B, 90 Ft. Wood Transmission FGA, 600, Drake
76
Grade C, 90 Ft. Wood Transmission FGA, 600, Drake
77
Grade B, 90 Ft. Steel Transmission FGA, 600,
Drake
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Grade C, 90 Ft. Steel Transmission FGA, 600,
Drake
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Wood vs. Steel

• How do proposed strength requirements for wood
  and steel structures compare for various load
  cases?
• (For illustration, assume pole structure and
  express as required moment capacity since section
  designs can vary. Applied moment is independent
  of material and section.)

80
Grade B Wood vs. Steel
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Grade C Wood vs. Steel
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Conclusions

• Load factors and strength factors are simplified
• (Extreme) wind loads must be considered for
  distribution
• Load reduction for facilities below 60 with
  terrain obstructions
• No reduction for taller facilities or for no
  obstruction

83
Conclusions

• Mechanical loading changes will be mixed
• Wind loading will increase significantly in
  coastal areas
• Wind and ice loading generally decreases
• Greatest effect will be Grade C loading in
  coastal areas

84
Conclusions

• Greatest impact will be on small conductors in
  ice areas
• Stronger structures
• Taller structures
• Shorter spans

85
Conclusions

• Design methodology will be significantly more
  complex
• Span length specific
• Height specific