Electrical Conductor - Conductor and Insulator - Types of Conductor - Semiconductors - Coulomb's Law - Examples of Conductors & Insulators - Energy Bands - Conductor Sizes - Standard Wire Gauge (SWG)

Conductor

An Electric Conductor is a material from which the electric charge transfers freely without any interruption such as copper, aluminum, steel, silver, iron etc. There are many types of conductors with respect to material like aluminum, silver, copper etc. These materials are free from resistance and free electrons move easily without any interruption in it. Some conductive materials are minor resistive so the amount of current is increased in it to move free electrons in it and these conductors produce heat in it.

Coulomb’s Law

Charles Augustin de Coulomb studied the relational forces of charged particles in detail in 1784. He used the torsion balance to study the very pathetic gravitational force. Coulomb discovered that the electric force is proportional to 1/r² . This happens when the distance r doubles then the force decreases to one quarter of its initial value and when the distance r is halved the force increases to four times to its initial value.

The electric force between the two point charges also depends on the quantity of charge on each form which is denoted by q or Q. To explore more, Coulomb divided a charge into two equal parts by placing a small charged spherical conductor into contact with an identical but uncharged sphere and by symmetry the charge is shared equally between the two spheres and thus he obtained the one-half, one-quarter and so on of any initial stage. He found that the forces that two point charges q₁ and q₂ exert on each other are proportional to each charge and are proportional to the product q₁q₂ of the two charges.

Thus The Coulomb established the following that we call as Coulomb’s Law and the Coulomb’s Law states that:

“The magnitude of the electric force between two point charges is directly proportional to the product of the charges and inversely proportional to the square of the distance between them.”

Mathematically the magnitude F of the force of two point charges q₁ and q₂ a distance r exerts on the other is expressed as:

Equation of Coulomb's Law, Coulomb's Law

Where k is a proportionality constant whose numerical value depends upon the system of units used. The charges q₁ and q₂ can be either positive or negative while the force F is always positive.

The direction of the force and the two charges exert on each other are always along the line joining them. When the charges q₁ and q₂ have the same sign then the forces are repulsive and when the charges have opposite sign then the forces are attractive. The two forces obey Newton’s Third Law that these are always equal in magnitude and opposite in direction even the charges are not equal in magnitude.

Conductors and Insulators

Conductors are the materials in which electrons flow rapidly and continuously and these are used to transmit electricity into it like copper, aluminum and steel etc. While the insulators are the materials from which electrons cannot move freely and provides large amount of resistance that electric current cannot pass from it and these are used to protect from electricity and the examples of insulators are glass, porcelain, rubber, paper, polyethylene, fiberglass etc.

Examples of Conductor

Examples of Conductors are:

Silver, Gold, Copper, Aluminum, Mercury, Steel, Iron, Seawater, Concrete Platinum, Brass, Bronze, Graphite, Dirty water, Lemon juice

Examples of Insulators

Examples of Insulators are:

Rubber, Glass, Pure water, Oil, Air, Diamond, Dry wood, Dry cotton, Plastic, Asphalt, Fiberglass, Dry paper, Porcelain, Ceramics, Quartz, Yarn, Fabric, cotton

Semiconductors

A semiconductor is an intermediate material between good conductors and good insulators. These materials are most commonly used in electronic components due to the electrical properties in it with its sensitivity due to impurities in them. The most common and the basic examples of semiconductor materials are silicon and germanium. These two materials are present in group 4 of the periodic table. Both materials have four electrons in their valance shells. At a very low temperature, electrons present in their outermost shells cannot move or jump from valence band to the conduction band so in this state these materials become good insulators while at a room temperature, the energy gap between the valence band and the conduction band is small as compared to the energy gap at low temperature thus at this state these materials become good conductors. The room temperature value for silicon is 1.12 cV and 0.67 cV for germanium.

Energy Bands

The concept of the Energy bands is very useful for us to understand the various properties of solids. We can determine from the nature of the energy bands that the material is an electrical, insulator or a semiconductor.

In an insulator at zero temperature, the highest band that is filled completely called the valence band and it is also the highest band that has electrons in it. The next higher band is the conduction band and it is completely empty and there are no electrons in it.

A semiconductor at zero temperature, the conduction band is empty above the valence band the main difference between the insulator and a semiconductor is that the energy gap between these two bands is very small and electrons can move very easily to the conduction band. At the increase of the temperature, the electrons move rapidly to the conduction band and the electrons are increased in the conduction band and it becomes the electrical conductor and starts conductivity.

In a conductor there are electrons present in the conduction band at a zero temperature. The atoms are so close to each other that the bands spread out and overlap into a single band and we call this a conduction band because it is only partially occupied

Types of conductors

§ In physics

Spherical conductors

The spherical conductors are the materials from which current passes only through the outer shell of the conductor.

Super conductors

Super conductors are the materials from which electric charges move without any interruption.

§ With Respect to Material

There are so many conductor materials such as gold, silver, platinum etc and these materials are expensive so these are not used as conductor so the following are the materials which are most commonly used as a conductor:

Copper

Copper is a most commonly used line conductor and it conducts electric current very readily as compared to silver. It is rich in nature so that its cost is low and it can be easily merged. There are three types of copper wires which are hard-drawn copper, medium hard-drawn copper and annealed copper also known as soft drawn-copper wire.

Hard-drawn copper wires are used for overhead line purposes because of its greater strength while medium hard-drawn copper wires are used for distribution purposes specially for wire sizes which are smaller than American Wire Gauge (AWG) and the soft drawn-copper wires are used for ground wires and other applications where it is necessary to bend and shape the conductor.

Aluminum

Aluminum is widely used for transmission and distribution line conductors. Its conductivity is two third as compared to copper. The aluminum wire must be 100/66 = 1.60 larger than the copper wire in cross section area to have the same conductivity. An aluminum wire of this size 75 % of tensile strength and 55 % of the weight of the equivalent copper conductor.

Steel

Steel wire is used to a limited range where minimum construction is desired. Steel wire has high tensile strength of 160,000 lb/inch² therefore requires support. Bare steel wire rusts rapidly and is very short lived. Steel is also a poor conductor as compared to copper and it is only 10 % to 15 % good. Galvanized steel conductors are used for shield in transmission and sub-transmission lines.

§ With Respect to Transmission

Solid Conductor

Solid conductors are the single conductor of a solid circular section and these are used for low distances for electricity transmission and on Earthing because they have less flexibility.

Stranded Conductor

Stranded conductors are the sum of solid conductors of small diameters and these solid conductors are stranded with each other. These conductors are used as transmission lines for high flexibility and overall diameter. These conductors normally have a central wire around which there are successive layers of 6, 8, 12 etc. In the process of construction, adjacent layers are soared in opposite direction, so that the layers are bound together. This type of construction is called concentric lay. Another type of construction used for conductors of large cross-section is rope lay.

Hollow Conductor

Hollow conductors have large diameter as compared to the solid conductors. Corona loss is reduced due to larger diameter and skin effect is also reduced as compared to stranded conductors. These conductors have low inductance and low voltage gradient as compared to solid conductors. This type of conductor is generally used for bay extension in 400KV Substations.

All Aluminum Conductor (AAC)

All Aluminum Conductor (AAC) belong to overhead conductors and used as transmission conductors and power distribution conductors in power transmission and distribution lines. AAC consists of one aluminum strand which is present in middle of the cable and the other aluminum strands are wrapped helically around it. It offers easy handling during installation and lighter in weight.

All Alloy Aluminum Conductors /All Aluminum Alloy Conductor (AAAC)

All Alloy Aluminum Conductor /All Aluminum Alloy Conductor (AAAC) is a concentric lay stranded consisting of aluminum alloy wires wrapped helically around a central aluminum alloy wire. It is similar in construction and appearance to AAC conductor. It has higher strength to weight ratio, better rust resistance, low power losses as compared to ACSR. It is suitable for long spans network.

Aluminum Conductor Steel Reinforced (ACSR)

Aluminum Conductor Steel Reinforced (ACSR) consists of one steel strand conductor covered with a welded layer of aluminum and the other conductors are aluminum strands. The layer of aluminum increases the conductivity of the steel strand and it also prevents it from rusting. All the strands of the cable, the steel strand welded with aluminum layer and the aluminum strands have same life. These conductors are also called Alumoweld conductors.

Aluminum Conductor Alloy Reinforced (ACAR)

Aluminum Conductor Alloy Reinforced (ACAR) is made by concentrically stranded wires of aluminum on high strength of Aluminum Magnesium Silicon (AlMgSi) Alloy core. It provides high current carrying capacity and higher strength with lower conductor weight. It is used where the high current capacity, higher strength and lower conductor weight is required to design the line. These conductors are used for overhead distribution and transmission which requires all aluminum conductors with higher strength and longer spans and is capable with AAC conductors.

All Alloy Aluminum Conductor Steel Reinforced (AACSR)

All Alloy Aluminum Conductor Steel Reinforced (AACSR) conductor are composed of one or more layers of aluminum alloy wire stranded with high strength coated steel core. The core may be a single wire or stranded with respect to size. The quantities of alloy aluminum and steel can be varied to obtain the relation between the current carrying capacity and mechanical strength. These are used as overhead transmission cable and as primary and secondary distribution cable because it offers optimal strength for line design. Variable steel core enables required strength without sacrificing Ampacity.

AACSR are used in transmission towers, extra high voltage transmission lines like ACSR. It has been using for long time because of its strength to weight ratio. The combined light weight and high conductivity of aluminum and steel cores strength enables high tension, less sag and longer spans. These are ideal for extra-long spans with heavy load.

Aluminum Conductor Steel Supported (ACSS)

Aluminum Conductor Steel Supported (ACSS) consists of steel strands from the central core of the conductor with one or more layers of aluminum wire stranded around it. The steel cores carry mechanical load of the conductor. Steel core wires are protected from rust by galvanizing with alloy coating. These conductors are used for the lines which transfer very high or fluctuating loads.

Aluminum Conductor Composite Reinforced (ACCR)

Aluminum Conductor Composite Reinforced (ACCR) conductors consist of high temperature aluminum zirconium (Al-Zr) strands covering a stranded core of aluminum oxide fiber reinforced composite wires. Both the composite core and the outer strands contribute to the overall conductor strength and conductivity. The core wires have the strength and stiffness of steel with lower weight and higher conductivity.

Aluminum Conductor Composite Core (ACCC)

Aluminum Conductor Composite Core (ACCC) is coaxially stranded conductor with one or more layers of trapezoidal shaped hard drawn and annealed aluminum wires on a central core of light weight carbon glass fiber composite. ACCC conductor uses a carbon fiber core that is 25% stronger and 60% lighter a steel core. These conductors are designed to operate continuously at higher temperatures and has good sag characteristics.

Sizes of Conductor

Conductor sizes are expressed by numbers. There are many numbering methods to specify a conductor size by its number and it is also compulsory to state which wire gauge or numbering method is used. There are two types of wire gauge which are used in the whole world. The first one is American Wire Gauge (AWG) which is used in United States only while the other one is named as Standard Wire Gauge (SWG) which is used in all other countries except United States.

American Wire Gauge (AWG)