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

• The aluminum is used for making transformer tank because of light weight and it will reduce stray load loss.

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.

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