Electrical Materials Basic Theory:

Conducting Materials:

Conducting materials which must be good conductors of electricity, characterized by a large electrical conductivity and small electrical resistance  serve to carry current in electrical equipment. Conducting materials are further classified into two groups namely materials of high conductivity (or low resistivity) and materials of high resistivity.

High Conductivity Materials:

These materials usually will have low resistivity and therefore employed in making windings of electrical machines (windings of transformers, motors etc), conductors used for transmission and distribution of electrical power, materials required to make equipment or apparatus. Some of the important properties or characteristics possessed by high conductivity materials are:

• Least resistivity or good conductivity
• Very low temperature coefficient of resistance
• Good mechanical strength (high tensile strength and degree of flexibility)
• Good Weldabiltiy and Solderability helps in providing better reliabiltiy and low electrical resistance of the joints
• Reliability and drawability
• Good resistance against corrosion

Some of the commercially acceptable good conductivity materials are copper and aluminum. Steel with proper combination of copper and aluminum is also used as a conducting material. Silver has highest conductivity compared to copper and aluminum but because of the economical factor it is not feasible

High Resistivity materials:

These materials have the characteristics such as high resistivity, low temperature coefficient of resistance, good ductility, good mechanical strength, very high melting point and no tendency for oxidation. These materials are alloys of different metals. High resistivity materials are employed in precision electrical measuring instruments, making standard resistance, rheostats, high temperature elements for electrical furnace and other heating applications. Maganin. Constantan, Nichrome, Tungsten, Carbon etc are some of the examples of high resistivity materials.

Semi-Conductor Materials:

In terms of conductivity semi-conductors lies some where between good conductors and insulators. Because of the excellent properties of semi conductors they have wide applications in electrical and electronic applications.

The resistivity of the semi conductor material depends on:

• The temperature coefficient of semi conductors is negative.
• Semiconductors are basically non linear resistance materials. They do not follow Ohm’s law (Current is proportional to applied voltage)

The resistivity of semiconductors vary drastically even a minute impurity is added. Introduction of some impurities change the conductivity properties of semiconductor materials.

Germanium and silicon are the two best semiconductors available.

Insulating Materials:

Insulating materials are very poor conductors. Insulating materials are placed around the conducting materials to prevent leaking of current between two different potentials. The characteristic property of insulating materials is  poor conductivity. Insulators can be either solid like mica, glass etc, liquids like transformer oil, silicon liquids and vegetable oils and gases like SF6, air and nitrogen. Some of the ideal properties of insulating materials (dielectrics) are:

High dielectric strength, chemical inertness, good mechanical strength, very high resistivity, good fire proofing and water proofing properties, and high resistance to heat. Some of the insulating materials are: Wood, paper, mica, varnished or impregnated textiles, ceramics, asbestos, glass, enamels and varnishes etc.