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 L1 & L3 and crossing span L2, the equivalent span for river crossing portion is determined by the following formula :
Eq. Span = ÖL13 + L23 + L33 / L1   + L2   + L3 (Refer Figure 10-II)

Sag and tension calculation for conductor/earth wire for above equivalent span is done from the following formula :

T2 (T - K + aEa (q2-q1)) = W2 L2 aE / 24 x q2
where,
T = Tension at temperature q2 (kg)
K= Constant
a = Area of conductor/Earth wire (mm2)
E = Modulus of Elasticity kg/mm2
a = Linear Coeft. of expansion (per degree celcius)
W = weight of conductor (kg/m)
L = Equivalent span (m)
q = Wind load factor = P2 + W2 / W2 = 1 (At no wind condition)
q1 = Initial condition temperature

Calculation for conductor

• Initial condition for conductor is taken as 32°C and No wind and T0 tension under these conditions is taken as 22% of ultimate tensile strength of conductor.
• From the above value of T0, we calculate the constant 'K which is fixed for all further sag-tension calculations.
• Considering the calculated value of K, the tension at 0°C under No-wind & full wind and 32°C full wind and 75°C No-wind is determined from the above formula by hit & trial method.
• Sag at various tension :
  = WLA2 / 8T  where LA is actual span

Calculation for Earth wire

• The earth wire sag at 0°C and no-wind should be 90% of the Conductor sag at 0°C and No-wind. Value of tension at 0° and no wind is determined by the following formula
  T = {WL2 / 0.9 x Sag of Conductor at 00N/W}
  for equivalent span
  where L = Equivalent span in meters.
• As in the case of conductor, the tensions at 0°C (No-wind & full wind Condition), 32"C full wind conditions and 75°C no-wind condition are determined.
• Sag = [WLA2 / 8TA] where LA = Actual span.

Fig. 10-II