17 February 2018

Compare Aluminum and Copper

The comparison between Aluminum and Copper is given below
Conductivity
  • The resistivity of copper to aluminum at constant temperature
                              = 0.021 × 10 – 6 / 0.034 × 10 – 6 

                              = 0.61
  • As the resistivity of copper is lower than the aluminum for same temperature, the conductivity of aluminum is 61% lower than the copper conductor.
Density
  • The density of aluminum is approximately 1 / 3.5 that of copper it means that it mass reduces 1/3.5 times than that of copper conductor.
  • The Aluminum is cheaper and light in weight than copper.
Losses
Copper loss in the conductor = I2R ….( 1 )
Current density δ = I / a 
Therefore I = δa………………….…..( 2 )
Resistance R = ρL / a ………………..( 3 )
Where ρ = Specific resistance
From equation ( 1 ) , ( 2 ) and ( 3 )
Copper loss in the conductor = ( δa )2 ( ρL / a )
                                               = δ2 ρL a
Copper loss per unit volume = δ2 ρL a / La
                                              = δ2 ρ
Copper loss per unit mass = δ2 ρ / g
Where g = mass density
  • Therefore we can say that copper loss per unit mass is directly proportional to resistivity and inversely proportional mass density.
The resistivity of Aluminum at 75 oC = 0.034 × 10 – 6 ohm meter
The resistivity of Copper at 75 oC = 0.021 × 10 – 6 ohm meter 
The ratio of resistivity of Aluminum to Copper at constant temperature = 1.62
  • Therefore the copper loss in the aluminum conductor is 1.62 times that of copper conductor for same volume of conducting material.
Rating
  • The rating of machine depends upon temperature rise. 
  • The current rating of aluminum conductor is 1 / √ 1.62 = 0.78 times that of copper conductor. 
  • Therefore the rating of machine is reduced by 100 – 78 = 22% if aluminum conductor is used.
Conductor space
  • If we consider equal length and equal loss in the aluminum and copper conductor, the area occupies by the aluminum conductor is 1.62 times that of copper conductor. 
  • Therefore the slot depth has to be increased by amount 60% for aluminum conductor we slot width is considered to be fixed.
Weight
Effect of atmosphere
  • The aluminum quickly reacts with atmosphere and oxidation start very rapidly. 
  • The oxide layer on aluminum increases its resistivity. 
  • The copper conductor offers high resistance to corrosion.
Soldering
  • The aluminum wire is hard to sold. It is soldered by special ultrasonic soldering iron.
Mechanical strength
  • The mechanical strength of hard drawn copper is much higher than the aluminum conductor. 
  • The aluminum is soft material but when alloyed with iron or silicon, its mechanical strength increases which can be used for overhead transmission line.
Contact resistance
  • The copper offers low contact resistance at joints as compared to aluminum.
Application
  • The aluminum is used for flexible wire, bus bar, moulded case rotor and in the overhead transmission line. 
  • Die cast aluminum winding is used for squirrel cage induction motor.
You may also like :