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Which of the following materials are not used for the bus-bar or transmission and distribution of electrical power?
Copper
Aluminium
Tungsten
Steel
Tungsten
Tungsten is not used for bus-bars because it has a very high electrical resistivity compared to copper or aluminium and is extremely brittle, making it difficult to manufacture into long, flexible conductors. Bus-bar materials are selected based on high electrical conductivity, low cost, and mechanical ductility to handle thermal expansion and installation stresses.
Tungsten is not used for bus-bars because it has a very high electrical resistivity compared to copper or aluminium and is extremely brittle, making it difficult to manufacture into long, flexible conductors. Bus-bar materials are selected based on high electrical conductivity, low cost, and mechanical ductility to handle thermal expansion and installation stresses.
R=╧БAlтАЛ тАФ Resistance formula where ╧Б is resistivity, l is length, and A is area.
PlossтАЛ=I2R тАФ Power loss calculation showing why low R is essential.
The efficiency of power transmission is inversely proportional to the resistance of the conductor, governed by R=╧БAlтАЛ. Since tungsten's resistivity (╧Б) is significantly higher than that of copper or aluminium, using it would result in excessive I2R power losses and high voltage drops across the transmission network. Furthermore, its high melting point (used for lamp filaments) is unnecessary for transmission and adds to processing costs.
Copper and Aluminium are the industry standards due to high conductivity and low cost.
Steel is primarily used in ACSR (Aluminium Conductor Steel Reinforced) cables for mechanical strength, not for primary current carrying.
Tungsten's high resistivity leads to massive thermal dissipation and inefficiency in power systems.
Bus-bar selection is a balance of conductivity, weight, tensile strength, and corrosion resistance.
Copper: Excellent conductivity and corrosion resistance.
Aluminium: Lightweight and cost-efficient for overhead transmission.
Tungsten: High cost, high resistivity, and extreme brittleness.
Steel: High resistivity compared to Copper/Aluminium.
Copper: Indoor wiring and transformer windings.
Aluminium: Long-distance transmission lines (ACSR).
| Feature | Copper | Aluminium |
|---|---|---|
Conductivity | High (100% IACS) | High (61% IACS) |
IACS stands for International Annealed Copper Standard.
Option D (Steel) is frequently used as a core in conductors to provide tensile strength, unlike Tungsten which has no utility in this domain.
C is correct тАФ Tungsten is unsuitable for bus-bars due to its high electrical resistivity, brittleness, and exorbitant cost compared to copper or aluminium.
Always remember that in transmission line design, the material selection is a trade-off between electrical performance (R) and mechanical performance (Tensile strength/Ductility).