Electrical Power Systems

382 Electrical Power Systems
Therefore,
Tmin = H ...(15.47)
But H = wc,
\ Tmin = wc
rom eqns. (15.48) and (15.44),
... (15.48)
T min = w
HG
2 2
s - d
2d
I
KJ
rom ig. 15.3,
c = y – d ...(15.49)
The conductor length is
l = 2s ...(15.50)
rom eqns. (15.50) and (15.35),
l = 2c sinh x
c
I
HG KJ ...(15.51)
rom eqns. (15.45) and (15.48), we get,
T max = T min + wd ...(15.52)
15.3.2 Parabolic Method
In the case of short span between supports, the sag is small and the curve can be considered as
parabola. or the sake of simplicity, the following assumptions are made:
1. Throughout the span, tension is considered uniform
2. The change in conductor length due to elastic stretch or temperature expansion is equal
to the change of length of conductor equal in length to the horizontal distance between
the supports.
Let P be any point on the parabolic curve as shown in ig. 15.4, such that are OP is equal
to x. The portion OP is in equilibrium.
ig. 15.4: Parameters of parabola.