Classification of Electrical Conducting Materials

Electrical conducting material are the basic requirement for electrical engineering products. The electrical conducting material can be classified as below-

Based on Resistivity or Conductivity

· Low resistivity or high conductivity conducting material

· High resistivity or Low conductivity conducting material

A classification chart of conducting materials based on resistivity or conductivity is shown in figure below-

Low Resistivity or High Conductivity Conducting Material

Material having low resistivity or high conductivity are very useful in electrical engineering products. These material used as conductors for all kind of windings required in electrical machines, apparatus and devices. These material are also used as conductor in transmission and distribution of electrical energy. Some of low resistivity or high conductivity materials and their resistivity are given in table below –

· Silver

· Copper

· Gold

· Aluminum

High Resistivity or Low Conductivity Conducting Material

Materials having High resistivity or Low conductivity conducting are very useful for electrical engineering products. These material are used to manufacture the filaments for incandescent lamp, heating elements for electric heaters, space heaters and electric irons etc. Some of materials having High resistivity or Low conductivity are listed below:

· Tungsten

· Carbon

· Nichrome or Brightray - B

· Nichrome - Vor Brightray - C

· Manganin

Based on Area of Application

· Materials used as conductor for coils of electrical machines

· Materials for heating elements

· Materials for lamp filaments

· Material used for transmission line

· Bimetals

· Electrical Contact Materials

· Electrical Carbon Materials

· Material for Brushes used in Electrical Machines

· Materials used for fuses

A classification chart of conducting materials based on their applications is shown in figure below-

Materials Used as Conductor for Coils of Electrical Machines

Materials having low resistivity or high conductivity such as copper, silver and aluminum can be used for making coils for electrical machines. However, looking to optimum conductivity, mechanical strength and cost, copper is much suitable for making coils for electrical machines.

Materials for Heating Elements

Materials having high resistivity or low conductivity such as Nichrome, Kanthal, Cupronickel and Platinum etc. are used for making heating elements. Materials used for heating elements must possess following properties-

· High melting point

· Free from oxidation in operating atmosphere

· High tensile strength

· Sufficient ductility to draw the metal or alloy in the form of wire

Materials for Lamp Filaments

Materials having high resistivity or low conductivity such as Carbon, Tantalum and Tungsten etc. are used for making incandescent lamp filament. Materials used for making incandescent lamp filament must possess following properties-

· High melting point

· Low vapour pressure

· Free from oxidation in inert gas (argon, nitrogen etc.) medium at operating temperature

· High resistivity

· Low thermal coefficient of expansion

· Low temperature coefficient of resistance

· Should have high young modulus and tensile strength

· Sufficient ductility so that can be drawn in the form of very thin wire

· Ability to be converted in the shape of filament

· High fatigue resistance against thermally induced fluctuating stresses

· Cost should minimum

Material Used for Transmission Line

Materials used for making conductor for transmission line must possess following properties –

· High conductivity

· High tensile strength

· Light weight

· High resistance to corrosion

· High thermal stability

· Low coefficient of thermal expansion

· Low cost

Materials use for transmission lines are listed below-

· Copper

· Aluminum

· Cadmium-Copper alloys

· Phosphor bronze

· Galvanized steel

· Steel core copper

· Steel core aluminum

Bimetals

Many combinations of metals with different “Coefficient of linear thermal expansion” can be used to form the bimetals. Some of the commonly used combinations for making bimetallic strips are listed below-

· Iron, nickel, constantan (high “Coefficient of linear thermal expansion”)

· Alloy of iron and nickel (low “Coefficient of linear thermal expansion”)

Electrical Contact Materials

The successful operation of electrical contacts is function of various factors. While selecting a suitable material for electrical contact, we have to consider the factors. Some of most important factors of these are listed below –

· Contact resistance

· Contact force

· Voltage and current

Electrical Carbon Materials

Carbon in widely used in electrical engineering. Electrical carbon materials are manufactured from graphite and other forms of carbon. Carbon is having following applications in electrical Engineering-

· For making filament of incandescent lamp

· For making electrical contacts

· For making resistors

· For making brushes for electrical machines such as DC machines, alternators.

· For making battery cell elements

· Carbon electrodes for electric furnaces

· Arc lighting and welding electrodes

· Component for vacuum valves and tubes

· For makings parts for telecommunication equipment’s

Material for Brushes Used in Electrical Machines

Before selecting the material for brushes, we should keep in our mind following requirements in a brush –

· Contact resistance

· Thermal stability

· Lubrication properties

· Mechanical strength

· Low brittleness

Material used for Brushes in electrical machines are listed below-

· Carbon

· Natural graphite

· Electro graphite

· Metal graphite

· Copper

Materials Used for Fuse Elements

Fuse element is primary requirement of a fuse unit. The fuse element should have following properties- Low resistance - to avoid the undesirable voltage drop across the fuse element, so that it should effects the normal functioning or performance of circuit or device or equipment Low melting point - the fuse element must have low melting point. So that it blow out due to heating by excess current during over load or short circuit. Different types of metals and alloys are used for fuse element. Some of these elements are listed below –

· Aluminum

· Lead and tin

· Copper

· Silver

· Rose’ Alloys

· Wood alloys