Specifications

16
sensitive to impurities. 2) It is reddish-brown in colour. 3) It is malleable and ductile.
4) It can be welded at red heat. 5) It is highly resistant to corrosion. 6) Melting point is 1084
0
C
7) Specific gravity of copper is 8.9. 8) Electrical resistivity is 1.682 micro ohm cm. 9) Its tensile
strength varies from 3 to 4.7 tonnes/cm
2
. 10) It forms important alloys like bronze and
gun-metal.
Copper is very widely used in wires, cables, windings of generators and transformers,
overhead conductors, busbars. Hard (cold-drawn) copper conductor is mechanically strong
with tensile strength of 40 kg/mm
2
. It is obtained by drawing cold copper bars into conductor
length. It is used for overhead line conductors and busbars. Annealed copper(Soft Copper)
conductor is mechanically weak having a tensile strength of 20 kg/mm
2
. It can be easily shaped
into any form. Low-resistivity Hard Copper is used in power cables, windings, and coils as an
insulated conductor. It has high flexibility and high conductivity.
Aluminium : 1) Pure aluminium has silvery colour and polish. It offers high resistance to corrosion.
2) Its electrical conductivity is next only to that of copper. 3) It is ductile and malleable. 4) Its
electrical resistivity is 2.669 µ
ΩΩ
ΩΩ
Ω- cm (micro ohm- cm) at 20
0
C 5) It is good conductor of heat
and electricity. 6) Its specific gravity is 2.7. 7) Its melting point is 658
0
C. 8) It forms useful alloys
with iron, copper, zinc and other metals. 9) It cannot be soldered or welded easily.
Aluminium is most often used as overhead transmission conductors, busbars, ACRS
conductors. Well suited for cold climate.
Comparison of Copper and Aluminium as conductors for Power Transmission Lines:
Copper Aluminium
1. Metal is costly Metal is cheap
2. 100 per cent conductivity 75 per cent conductivity
3. Good resistance to corrosion Good resistance to corrosion
4. Heavier as compared to aluminium Lighter as compared to copper
5. Good ductility and malleability Good ductility and malleability
6. Excellent soldering and welding capacity Poor solderability and weldability
7. Less suited for low temperature Well suited to cold climate
8. Very small cross-section can carry heavy Cross-section should be 50 percent
current more to carry the same current as that of
copper.
9. Because of softness and flexibility, it can Due to brittleness, cannot be twisted.
easily be twisted repeatedly.
10. The wind pressure and weight of snow is The wind pressure and weight of snow is
less because of smaller cross-section. more because of higher cross-section.