Different types of conductors are used in transmission lines. They vary in number and size, depending on the type of circuit and the transmission voltage. Steel, aluminum and copper are the most common conducting materials used in transmission lines.
In the design and construction of transmission lines, the selection of conductor size shall be governed by two factors:
1. Electrical Requirements
2. Mechanical Requirements
Electrical requirements
The size of conductor will be determined based on following parameters:
1 Installed capacity of the plant, P in kW
2 Operating voltage of the line V in kV
3 Total length of the line to calculate the losses
4 Cost of construction
When load growth is considered, the selection of conductor shall be carried out by optimizing the system planning based on costs and benefits for the total benefits for the total system with projected load growth and generation expansion plan.While in the case of load growth, the selection of conductor shall be carried out by optimizing the system planning based on costs and benefits for the total benefits for the total system with projected load growth and generation expansion plan.
Mechanical strength
The mechanical strength of the conductor is one of the major parameter during the selection of the conductor of the line. Three limits on conductor tension are set by “The National Electrical Safety Code (NESC)” to keep normal tensions within reasonable limits and to prevent conductor stresses above the elastic limit when the conductor is fully loaded.
When the conductor is loaded to the assumed climatic load, the tension shall not exceed 60% of the ultimate strength. This is referred to as the “loaded condition”.
When the conductor is initially strung and is carrying no climatic load, the tension shall not exceed 35% of ultimate strength at a temperature of 15.60 C (60o F). This is referred to as the “initial unloaded condition”. After the conductor has been subjected to the assumed climatic load, it receives a permanent or inelastic stretch. When the conductor reaches this condition, the tension without climatic load at a temperature of 15.60 C (600 F) shall not exceed 25% of ultimate strength. This is referred to as the ”final unloaded condition”. For a given ruling span only one of these conditions will control the selection of conductor size and the other two may have relatively little significance in so far the maximum allowable tensions are concerned.
Deregulation and competition have changed power flows across transmission networks significantly. Meanwhile, demand for electricity continues to grow, as do the increasing challenges of building new transmission circuits. As a result, utilities need innovative ways to increase circuit capacities to reduce congestion and maintain reliability. Read more...
A conductor is a material that facilitates the flow of electricity (or electric current) through a transmission line. Different types of conductors are used in transmission lines. They vary in number and size, depending on the type of circuit and the transmission voltage. Steel, aluminum and copper are the most common conducting materials used in transmission lines. Read more...
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