Electric Power Generation, Transmission, and Distribution

conductor should be sagged to the initial stringing sags listed in the sag tables. However, if the conductor
tension is excessively high during stringing, or the conductor is allowed to remain in the blocks for an
extended period of time, then the creep elongation may become significant and the sagging tables should
be corrected prior to sagging.
Creep is assumed exponential with time. Thus, conductor elongation during the first day under
tension is equal to elongation over the next week. Using creep estimation formulas, the creep strain can
be estimated and adjustments made to the stringing sag tables in terms of an equivalent temperature.
Also, should this become a concern, Southwire’s Wire and Cable Technology Group will be happy to
work with you to solve the problem.
Prestressing conductor: Prestressing is sometimes used to stabilize the elongation of a conductor for
some defined period of time. The prestressing tension is normally much higher than the unloaded
design tension for a conductor. The degree of stabilization is dependent upon the time maintained at the

Procedure

Determine from nomograph the control factor of

transit "setup" used in sagging the conductor

(see examples on the right).

For most accurate results in sagging the conductor

this value of control factor should not be below the

curve shown below.

In all cases a control factor of 1.00 is ideal (For T= t).

1000 Examples

B = 60.0

B=60.0 9

S=49.1 9 T + B

B.M

T

t = 59.12

T = 40.0 9

A = 1400.0

(T - t) = 19.12S = 49.1' 9

A = 1400.0 9

(T − t) = "B" for horizontal line of sight

S = 49.1'

1 2 3 4 5 6 7 8

(^910)
20
30
S = 49.1
Conductor Sag (S)
40
50
60
70
80
90
100
200
300
400
500
600
700
800
(^9001000)
Control factor = 0.99 (From nomograph)
Control factor = 0.91 (From nomograph)
B = 60.0
T = 40.0
S = 49.1^9
T = 59.12^9
A = 1400.0
(T − t) = A tan f (+_B)
f = Angle of sight.
+f = When angle is above horizontal.
−f = When angle is below horizontal.
B = Vertical distance between points of support
+B = When support ahead is higher.
−B = When support ahead is lower.
φ (Angle of sight)
Control factor = 0.99 (From nomograph)
Then (T− t) = 1400.0 (+0.02920) − (+60.0) =19.12
Example 1: When sagging by calculated target
setting. (See Fig. 2-17)
Example 2: When sagging by horizontal line of sight.
(See Fig. 2-18)
Example 3: When sagging by calculated angle of sight.
(See Fig. 2-18)
In example, f = +1 8 40' 21" or tan f = +0.02920
A = 1400.0'
B = + 60.0'
S = 49.1'
900
800
700
600
500
400
300
200
1.00
.90
.80
.70
200
(^4060)
80
Control Factor^95
99
B
T
A
T = Distance transit is set below conductor support.
S S^1
90
70
305010
0
Control Factor
0.1 0.2 0.3 0.4
Control Factor Should Not Liein Shaded Area
0.5 0.6 0.7
(^10090) B/A
80
70
60
50
40
30
± (T
− t)
20
10
9 8 7 6 5 4 3
2 Control Factor = = = 1 −
1
S 1
S
ΔS 1
ΔS
(T−t)^2
(4S)^2
= 60.0
t = Corresponding distance target is set below opposite support.
S = Conductor sag determined from stringing charts.
S 1 = Corresponding sag of point of tangency of conductor and line of sight.
ΔS = Change of sag "s"
Sag is based on parabolic functions. If sag exceeds 5% of span,
do not use this chart.
ΔS 1 = Change of sag "S 1 "
·
FIGURE 14.15 Nomograph for determining control factor for conductor sagging.