Why Aluminum conductor is used in Transmission instead of copper conductors.
Material used in Transmission lines should have following properties:-
1. Low cost of construction
2. Resistivity should be lower
3. Material should have high conductivity
4. Material should have Low temperature coefficient
5. Material should have High current carrying capacity
6. Material should have High mechanical strength
7. Weather resistance properties of material
8. There should have good elasticity of material
The metals which partially fulfill the above requirements are copper, aluminum and steel. These are used alone or in combination.
Aluminum conductors are having conductivity closer to conductivity of copper conductors. Aluminum conductors have conductivity 61% of copper conductors. For Same resistance of that of copper conductor, aluminum conductor weight will be half of that copper conductor. Although when we compare conductivity we should consider copper conductors for transmission instead of aluminum conductor. But Aluminum conductors have resistance 1.6 times as much resistance/foot of that equivalent gauge of copper conductor. This means for equivalent conductor size aluminum conductor will have more power losses (I²R). These losses will be 60% higher when compared to copper conductors. The above stated reason will justify that we should use copper conductor in transmission instead of copper conductors.
Aluminum conductors are used for transmission of electricity instead of copper conductors is due to below stated reasons:-
(i) Lower cost
(ii) Lower density
Now let’s above two factors will be considered while designing Transmission system and why we use aluminum conductors instead of copper conductors:-
(i) Lower cost:-
Weight of Aluminum conductor is around 30% of Copper conductor for per meter length this means that we required more material which leads to very higher cost of Transmission , also copper is costlier about 5-6 times that of aluminum conductor. Higher weight means transmission towers to be strong enough to bear the load of conductor which means higher cost of designing the transmission towers. Since Transmission system is in multiple Kilometers so it is always beneficial to use aluminum conductors considering higher cost associated with copper conductors.
(ii) Lower density.
Aluminum conductors have lower density of conductor. Density of conductor is about 1/3rd the weight of copper conductor for same volume , so aluminum conductor will be lighter than copper conductor. So mechanically we can increase cross-section of aluminum conductor. With increase in cross-sectional area I²R loss will get reduced as Resistance is inversely proportional to cross-sectional area of conductor. By increasing cross-sectional area to double , this will increase diameter of conductor to 1.414 times. With increase in cross-sectional area I²R loss will get reduced to 0.8 times the I²R loss in copper conductor which earlier were 60%. Now increase in cross-sectional area weight of conductor will increase but still weight will be 2/3 times the total weight of copper conductor so constructing towers will become cheaper as they don’t need to be as strong by a factor of .66
Weight of Aluminum conductor is around 30% of Copper conductor. That means even though we used 2/3 the weight above we are still at a 10% cost (.66 x 1/6) for the wire itself, not to mention the tower costs savings as mentioned above.
So there are following advantages associated while using Aluminum conductor instead of copper conductors:-
1. With increase in Conductor size by double resistance will get reduced by 20% and I²R power losses will be reduced from 6% to 5%.
2. Very lower construction cost as due to lower weight and lower cost of aluminum conductor , cost of construction is 33% , tower strength required is less.
3. Huge saving approx. 90% of the cost of the wire itself due to difference in material costs between aluminum and copper conductor.
4. Aluminum conductors are easy to bend and easy to handle as aluminum has more elasticity then copper.
Although transmission losses are higher in aluminum conductors but while due consideration of above factors we must consider aluminum conductors for transmission.
There is another question arise why not we use Steel conductors for transmission as cost is very low for Steel conductors?
Steel conductors are not used for Transmission as these have very lower skin depth as they have large permeability at 50/60 HZ in comparison to copper and aluminum conductors, this will leads to very high huge power losses due to high resistance.