What is the maximum sag of an overhead transmission line having a
A. 1.52 m
B. 0.75 m
C. 1.25 m
D. 1.6 m
Please scroll down to see the correct answer and solution guide.
Right Answer is: A
SOLUTION
Concept:
Sag s:
The distance between the highest point of electric poles or towers and the lowest point of a conductor connected between two poles or towers.
Span length:
It is the shortest distance between two towers or poles.
Sag \(s = \frac{{W{l^2}}}{{8T}}\)
Where,
S is the sag of the conductor
W is the weight of the conductor
l is the span length of the conductor
T is the working tension on the conductor
Calculation:
Span length = 240m
Weight of conductor = 727 kg/km
Breaking strength (Ultimate strength) = 6880kg
Weight of conductor W = 727 kg/km
= 727kg/1000m (1km = 1000m)
w = 0.727 kg/m
working tension T
T = U / S
Where,
U is the ultimate strength
S is the safety factor
\( = \frac{{6880}}{2}\)
T = 3440 kg
Sag \(s = \frac{{W{l^2}}}{{8T}}\)
= \(\frac{{\left( {0.727 \times {{240}^2}} \right)}}{{8 \times 3440}}\)
= 1.52m
The maximum sag of an overhead transmission line is 1.52m
