Why HTLS (High temperature, low sag) conductor is not used in transmission lines?

  1. What is HTLS Conductors in Transmission Lines? HTLS stands for High-Temperature Low-Sag conductors, and they are used in transmission lines. However, they are only one of the choices for some situations. In India there is lot of issues of RoW for strengthening of new transmission lines. That is why reconductoring of old lines is done with HTLS conductors. It has almost same weight as old conductors so the same towers only can be used but the advantage is that it has the more ampacity.


As with ACSR, HTLS conductors typically consist of aluminum wires helically stranded over a reinforcing core. Most of the electrical current flows in the high conductivity, low- density aluminum strand layers. Most of the tension load is in the reinforcing core at high temperature and under high loads.

  1. Cost Consideration: HTLS conductors are more expensive than traditional conductors. Cheaper options among HTLS also have higher power loss, making them less economical. So, they are used selectively in places where the need for high power justifies the cost.


  2. Equipment Capacity Limitation: The amount of current a conductor can carry is limited by the capacity of the other equipment in the system. If the equipment can't handle a higher current, using a conductor capable of carrying more would be pointless.


  3. Surge Impedance Load (SIL) Limit: Transmission lines have a design limit called Surge Impedance Load (SIL). This limit is crucial for long lines, typically those longer than 150/160 km. Even if an HTLS conductor can handle more current, the SIL limit puts a cap on the amount of power it can effectively transmit. This is a design consideration to ensure the stability of the transmission system.

In simple terms, using HTLS conductors depends on a careful balance between the need for higher power, the cost of the conductor, and the limitations set by the capacity of the existing equipment and the design constraints like SIL limits for long transmission lines. It's like choosing the right tool for the job, taking into account both capability and cost.

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