The transmission line is a significant part of the power system. The cost and life of transmission lines chiefly depend on the material used for assembling conductors for the transmission line. The most important and much appropriate material for the conductor of the transmission line is copper as it has high conduction and high tensile strength. More ever it is having good ductileness. The only restraint is its cost. The most widely used material in a transmission line is Aluminum.
What is a stringing pulley?
Stringing Pulley is a rotation roller, which is always made of high-strength MC nylon, alum, or super quality steel, outer diameter ranges from 508 to 916mm, with several sheaves from a single to 9 pulleys to couple with a steel frame to work overhead the power line. According to its sheave number, it can be applied for different split conductors. For these characteristics, It is widely and efficiently used in various LV and HV electric power line transmission construction.
Why Aluminum is not used?
Aluminum is having adequate conductivity. More ever it is light in mass. The only limitation is the low tensile strength. To overcome this restraint strength is used in steel core for increasing the tensile strength of aluminum conductors such as in Aluminum conductor steel reinforced conductor. This conductor is very much general for high voltage overhead transmission lines. The choice of appropriate material for the Transmission line depends upon
- Mandatory electrical properties
- Mandatory mechanical strength
- Local condition
- Cost of the material
Properties in Materials Used in Transmission Line
- High conduction
- High stretchable strength
- High confrontation to corrosion in whether conditions
- Great thermal stability
- Very low coefficient of thermal expansion
- Very low cost
Materials Use for Transmission Lines
The Materials used for transmission lines are
- Cadmium–Copper alloys
- Galvanized steel
- Steel core aluminum
- Phosphor bronze
- Steel core copper
The widely used, high conductivity material as a conductor for electrical machines, is copper. Malleability, weldability, and solderability are the most significant properties of copper. Copper in unadulterated form is having good conductivity. But the conductivity of normal grade copper is reduced due presence of impurities.
Properties of Copper
- The Resistivity is 1.68 µΩ -cm.
- Its Melting point: 1085oC.
- The Specific gravity: 8.96gm /cm3.
Uses of Copper
Copper is the most significant and much suitable material for the conductor of the Transmission line as it has high conductivity and high ductile strength. The only restraint is its cost.
Aluminum is an element that is a silver-white, lightweight, soft, non-magnetic, and spongy metal. Aluminum is having a very low density, high ductility as in stringing pulley, corrosion resistance, and good conductivity, which makes it appropriate to use as an electric conductor for transmission and delivery of electricity.
Properties of Aluminum
- Its Resistivity: 2.65 µΩ -cm.
- The Temperature coefficient of resistance at 20oC.
- Its Melting point: 660oC.
- The Specific gravity: 2.70 gm /cm3.
Uses of Aluminum
The most lengthily used material in a transmission line is Aluminum. Aluminum is having adequate conductivity. The only restraint is its low tensile strength. To overcome the limitation steel core is used for growing the tensile strength of aluminum conductors such as in Aluminum conductor steel reinforced conductor. ACSR conductor is very much general for high voltage overhead transmission lines.
Cadmium – Copper Alloy
The cadmium copper alloys contain cadmium from 0.6%. This small addition of cadmium increases the tensile strength and erosion resistance of copper. The conductivity of cadmium copper alloys is 90% of pure copper.
Use of Cadmium – Copper alloy
- For making conductors for High tensile strength communication line.
- For making trolley car wire.
- In Heating pads.
- In Electrical blanket elements.
Phosphor bronze is an alloy of copper with 3.5 tin and 1% phosphorus. Occasionally, it is also is called “Phos-Bronze”. Phosphorus is often added as a deoxidizing agent during the melting process. Phosphor bronze is having moral strength, toughness, low coefficient of friction, and fine grains. The addition of phosphorous increases the fluidity of molten which grades in improved castability of alloy, and cleans up the grain boundaries which improves the mechanical properties of the alloy.
Uses of Phosphor Bronze
- For making conductor for transmission line passing through the marine atmosphere.
- For the creation of spring and bolts where high resistance to tiredness is required.
- Ships propeller where high corrosion resistance is required in the marine environment.
- For making all electrical contacts.
In cryogenics, where the fair electrical conductivity and low thermal conductivity allow the making of electrical connections to the device at low temperature without adding excessive heat in stringing pulley.
Pure Iron gets rusted or corroded in open weather conditions. To avoid corrosion, sheet, wire, etc. made of these metals are covered with Zinc. For this Hot-dip galvanization is used. In this process, the iron is dipped in molten Zinc at a temperature of around 449oC. When exposed to the atmosphere, the zinc reacts with oxygen and forms the substance zinc oxide, which then reacts with carbon dioxide and then forms zinc carbonate. This zinc carbonate is typically dull and fairly strong material, which defends the iron or steel beneath from corrosion in open weather conditions.
Use of Galvanized Steel
- Galvanized steel wire is used for making conductors which are used in transmission lines where the resistance to corrosion to obligatory.
- Galvanized steel sheets and pipes are also used for making poles of transmission.
Steel Core Copper
This is also called a copper-clad steel conductor. For high tensile strength applications to upsurge the strength of wire, the steel is used as a core of conductor and copper for collecting the conductivity of the conductor. Here, copper not only provides conductivity but also works as a protective layer to stop the corrosion of steel by atmospheric weather conditions.
Use of Steel Core Copper
- Steel core copper wire is used for earthing electrical installations.
- In drop wire of telephone cables.
Steel Core Aluminum
Aluminum is light in weight and is having very good conductivity. But it is having low tensile strength. To make it suitable for the transmission line, we should upsurge its tensile strength. To raise the tensile strength, steel is used as the core of the conductor. A good instance of steel core aluminum is an Aluminum Conductor Steel Reinforced conductor. As it has high tensile strength, good conductivity, and is economical.
Use of Steel Core Aluminum
- Steel core Aluminum wire is used as a conductor for a transmission line.
- It is used as the inner conductor of coaxial cable.