Low resistivity materials: The conducting materials having resistivity between 10-8 to 10-6 ohm-m come under this category and are used in house wiring, as conductors for power transmission and distribution, in the winding of transformer and machines like motors and generators. In fact low resistivity materials are used in all such applications where power loss and voltage drop should be low. Copper and aluminium are examples of commercially acceptable low resistivity than copper but because of its prohibitive cost it uses commercially as a conductor is not feasible. A low resistivity material should have the following additional applications properties:
1. Low temperature coefficient: This means that the change of resistance with change in temperature should be low. This is necessary to avoid variation in voltage drop and power loss with change in temperature. For example, the resistance of transmission lines which are very long with increase with when exposed with to hot summer sun. This will increase in voltage drop and power loss in the transmission line. The windings of electrical machines and apparatus become hot when the winding has high loaded. This cause temperature rise and if the conducting material of the winding has high-temperature coefficient of resistance, the voltage drop and power loss in the winding will be high.
2. Sufficient mechanical strength: These materials must withstand with the mechanical stresses developed during its use for particular applications. For examples, the overhead line conductors used for transmission and distribution of electrical power and are subjected to stresses due to wind and their own weight. The conducting materials used for the windings of transformers, motors and generators develop mechanical forces when loaded. These forces can become very large if a high current flows due to a short circuit. Therefore, to withstand the mechanical stresses, developed in the above mentioned application, the conducting material should possess sufficient mechanical strength.
3. Ductility: Ductility is that property of a material which allows it to be drawn out into a wire. Conductors are required into different sizes and shapes. In some applications round wire section is used, while in other rectangular wire section is used. The conducting material should be ductile enough to enable itself being drawn into different sizes and shapes.
4. Solderability: The conducting materials are often required to be jointed and the joint must have a minimum contact resistance, which is minimum, if a solder joint is used. Thus, these materials must have good solder ability.
5. Resistance to corrosion: The material should have a high resistance to corrosion so that it should not be corroded when used in actual or practical environment conditions.