Sag and tension calculations for conductor earth
wire are done for the river crossing by following steps :

Determination of Equivalent Span :
Based on anchor spans L_{1} & L_{3} and
crossing span L_{2}, the equivalent span for river crossing portion is
determined by the following formula :
Eq. Span = ÖL_{1}^{3
}+ L_{2}^{3} + L_{3}^{3 }/ L_{1}^{ }
+ L_{2}^{ } + L_{3} (Refer Figure 10II)^{
}

Sag and tension calculation for conductor/earth wire for above equivalent span
is done from the following formula :
T^{2 }(T  K + aEa (q_{2}q_{1}))
= W^{2 }L^{2 }aE / 24 x q^{2
}where,
T = Tension at temperature q_{2} (kg)
K= Constant
a = Area of conductor/Earth wire (mm^{2})
E = Modulus of Elasticity kg/mm^{2
}a = Linear Coeft. of expansion (per degree celcius)
W = weight of conductor (kg/m)
L = Equivalent span (m)
q = Wind load factor = P^{2 }+ W^{2 }/ W^{2 }= 1 (At
no wind condition)
q_{1} = Initial condition temperature

Calculation for conductor

Initial condition for conductor is taken as 32°C and No wind and T_{0}
tension under these conditions is taken as 22% of ultimate tensile strength
of conductor.

From the above value of T_{0}, we calculate the constant 'K
which is fixed for all further sagtension calculations.

Considering the calculated value of K, the tension at 0°C under Nowind &
full wind and 32°C full wind and 75°C Nowind is determined from the above
formula by hit & trial method.

Sag
at various tension :
= WL_{A}^{2 }/ 8T where L_{A }is actual span

Calculation for Earth wire

The
earth wire sag at 0°C and nowind should be 90% of the Conductor sag at 0°C
and Nowind. Value of tension at 0° and no wind is determined by the
following formula
T = {WL^{2 }/ 0.9 x Sag of Conductor at 0^{0}N/W}
for equivalent span
where L = Equivalent span in meters.

As
in the case of conductor, the tensions at 0°C (Nowind & full wind
Condition), 32"C full wind conditions and 75°C nowind condition are
determined.

Sag
= [WL_{A}^{2
}/ 8T_{A}] where L_{A }= Actual span.
Fig. 10II 