Factor affecting sag in the transmission line

The equation of the sag is

S = WC L2 / 8T


    S = Sag

   WC = Weight of conductor per meter

    L = Length of conductor

    T = Tension on conductor

Weight of conductor

  • As the weight of conductor increases, the sag also increases. 
  • The ice formation on the conductor also increases the sag on the transmission line.

        S α ( WC )

Span ( length of conductor )

  • The sag is directly proportional to square of length of conductor. 
  • If the length of conductor double, the sag increases four times.

        S α ( L2 )


  • The sag and tension are inversely proportional. 
  • As the tension on the conductor increases, the sag decreases. 
  • The tension on the conductor increases by wind pressure, ice loading and natural disasters.

       S α ( 1 / T )


  • As the temperature increases, the length of conductor expand and vice versa therefore the sag increases as the temperature increases.

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