Materials used for Busbar, Winding Wires
Materials used for Bus-bars :
The most common material for Busbar is an aluminium alloy with a composition of 4.22 % copper, 0.65 % Mn, 0.54 % Mg, 0.22 % Si, 0.42 % Fe, and the remaining is aluminium. The alloy is suitable for casting and is utilised in the production of bus bars. It has low inertia, good electrical conductivity, and strong mechanical properties. Duraluminium is the brand name for this. Bus bars and overhead transmission lines are sometimes made of an alloy having 0.3 to 0.5 % magnesium, 0.4 to 0.7 % silicon, 0.2 to 0.3 % iron, and the rest aluminium. Aldrey is the brand name for this material, which has a melting point of 1100°C. It has a specific gravity of 2.7 gm/cm2 and a tensile strength of 32-37 kgf/mm2. Aluminium Bronze, which contains 85 to 90% copper, 6 to 8% aluminium, 3% iron, and 0.5% tin, is occasionally used for bus bars where low contact resistance is required.
Materials used for Winding Wires :
The conductors should be
in the shape of wires for winding. Copper and aluminium are the most popular
materials used to wound wire. The requirements of the materials are:
(a) Mechanical Properties: It should be flexible without cracking or breaking over the temperature range in which it will be used, and it should be resistant to hard handling. It should also have a homogeneous composition and be vibration and shock-resistant. Under normal conditions of use, it should not change shape or size.
(b) Physical Conditions: It should have a wide operating temperature range and not cause the material to brittle or soften. The insulation should be non-combustible, have a long operational life, and be resistant to all types of radiation.
(c) Chemical Conditions: The conductor and
insulation should be non-corrosive and unaffected by atmospheric oxygen.
Other than the electrical properties of the conductor, all of the preceding parameters must be satisfied. The most common winding material is copper. The cross-section of 99.99 % pure electrolytic copper is first hot-rolled to make it suitable for cold drawing. It is then pickled in sulfuric acid to remove oxide scale, neutralised, and water washed. The ends of the cleaned wire rod are now pointed for insertion into the drawing dies, which can number up to thirteen and each reduce the diameter of the wire progressively. After each significant drawing, the wires must be annealed. Tungsten carbide is commonly used for dies. Pierced precious stones, such as diamonds, are commonly used for tiny wire gauges. Wire and dies are lubricated with an aqueous solution of soluble oil or soap during the actual drawing operation. The conductivity of aluminium is 61 % that of copper, but it has the added benefits of exceptional softness and lightweight. Apart from their electrical qualities, the only issue with aluminium wires is jointing them satisfactorily in terminals.
Materials used for Commutator Segments:
The V-shaped notch on the commutator segments generates a cylindrical shape when assembled. Cadmium is most frequently used. Corrosion resistance is achieved by using a copper alloy containing 0.55 % to 1.04 % Cadmium. The cadmium presence enhances the alloy's fatigue strength almost proportionally, but without increasing brittleness. It is more expensive than copper and is utilised in commutator section manufacturing.