Information about Electrical Materials.

1. Electrical Materials
1. Conducting Material.
2. Magnetic Material
3. Insulating Material
• Electrically Conducting Material :- This materials carry current in an
electrical machine.
• Highly Conducting Material :- Copper, Aluminum, Gold, Silver.
• Highly resistive material:- Alloys (heating elements)
Now, R=Ro(1+αΔT)
Where α= temperature coefficient of resistance
ΔT= Change in temperature of per degree Celsius
R & Ro = Initial and final value of resistance

2. Properties of Highly Conducting material
• Highest Possible Conductivity
• Less temperature Coefficient of Resistance
• Adequate Mechanical Strength and absence of brittleness
• Rollability and Draw ability.
• Good weldability and solder ability to ensure the low resistance of
joints.
• Adequate resistance to corrosion.

3. Copper
• Machine Windings
Ϭau>Ϭag>Ϭcu>Ϭal
(Gold)> (Silver)> (Copper) >(Aluminum)
Ϭ= Conductivity of the material
• It is used to construct winding of an electrical machine because the cost is
not very high and it is highly conducting.
• Copper is resistance to oxidation and corrosion.
• Hard drawn copper wires are used in electrical machine because their
mechanical strength is high
αcu =0.00393 per degree Celsius
(high)

4. Aluminum
• Since copper is getting depleted aluminum is the next best choice for
conducting material it is abundantly available
• Aluminum cannot be drawn into thin wires but it can be used to form
thin sheets.

5. Parameter Copper (Cu) Aluminum (Al)
Cost 1 0.49
Cross Section Area 1 1.62
Diameter 1 1.27
Volume 1 2.04
Weight 1 0.49
Strength 1 0.64
Comparison of Aluminum(Al) and Copper(Cu)

6. Why cross sectional area of Aluminum(Al) is higher
then the cross sectional area of the copper(Cu) ?
• As we know that
• Ϭcu > Ϭal
• So, R=∫*l/A = l/Ϭ*A
• Since, Rcu = Ral
• Now, l/Ϭcu*Acu = l/Ϭal*Aal
• Therefore Aal = Ϭcu*Acu/Ϭal > Acu
Where∫ = resistivity of the material and Ϭ = conductivity of the material
and l=length of the material and A= cross sectional area of the material
Hence cross sectional area of Aluminum is higher then the cross sectional
area of Copper.

7. • For Al wire the size of slot required is higher as compared to Copper.
• For Induction motor above 100KW output Aluminum can be used for cage
rotor.
• Aluminum can be used to form foil type low voltage winding in a
transformer.
• Aluminum can be used to construct tank of a transformer to reduce stray
losses.
• Aluminum easily gets oxidized to form Al2O3 which prevent further
oxidation.