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
Current density
δ = I / a
Therefore I =
δa………………….…..( 2 )
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.
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