Electric Power Generation, Transmission, and Distribution

14.6.3.2 Sagging by Transit Methods

IEEE Guide Std. 524–1993 lists three methods of sagging conductor with a transit: ‘‘Calculated Angle of
Sight,’’ ‘‘Calculated Target Method,’’ and ‘‘Horizontal Line of Sight.’’ The method best suited to a
particular line sagging situation may vary with terrain and line design.

B

T

S

B.M

(Level Sight)

A

T + B

T = S (1 − B/4S)^2 = SK

T = Vertical distance of transit below lower support for taking level sight.

A = Horizontal distance between points of support - obtained from structure list of plan & profile.

B = Vertical distance between points of support - obtained from plan & profile, tower site data

sheets or field measurement.

S = Sag.

K = (1−B/4s)^2 –Determined from curve below.

EXAMPLE

A = 1400.0'

B = 60.0'

S = 49.1' @ 60 8 F

S = 51.2' @ 90 8 F

B/S = 60.0/49.1 = 1.22 @60 8 F B/S = 60.0 / 51.2 = 1.17 @ 90 8 F

K = 0.482 @ 60 8 F K = 0.501 @ 90 8 F

T = (49.1) (0.482) = 23.66' @ 60 8 F T = (51.2) (0.501) = 25.65' @ 90 8 F

Change in "T" for 5 8 F = (25.65−23.66) = 0.33' ( ) 305

1.0

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0.0

0.0 0.5 1.0 1.5 2.0

Ratio (B/S)

"K" Factor

2.5 3.0 3.5 4.0

Sag is based on parabolic functions. If sag exceeds 5% of span, do not use this chart.

For most accurate results, use that

part of curve drawn in solid line.

FIGURE 14.18 Conductor sagging by horizontal line of sight.