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.

Alloys of Copper and their Uses

Alloys of Copper and their Uses

Copper alloys mainly include the following 4 types:

(a) Cadmium copper alloy

(b) Chromium copper alloy

(c) Brass         

(d) Bronze

Cadmium Copper Alloy : 

Cadmium is whitish in colour and similar to tin in appearance. It is present in traces with zinc ore. It is corrosion resistance. When maximum electrical conductivity in conjunction with high tensile strength is required, the alloy of cadmium copper with 0.55% to 1.04% of cadmium is used. The tensile strength of this type of alloy is about 65 kgf / sq. mm with 1% cadmium, the conductivity falls only to 94% to that of pure copper. For most purposes the alloy containing about 0.8% of cadmium is found to have most favourable combination of tensile and fatigue strength with good conductivity. The fatigue strength of alloy increases which is almost proportional to the cadmium content, but without the increase of brittleness. This is suitable for flexible telephone cords and trolley wires. This is also used as electrodes due to its hardness and high annealing temperature. This alloy is also used for switchgear contacts, commutator segments and conductor for overhead transmission lines. It is costlier than copper.

Chromium Copper Alloy : Chromium is a hard and white metal. Where optimum conditions of a conductivity, strength and hardness in a casting are required, the chromium copper alloy is ideal. By simple heat treatment of alloy, the hardness can be increased to 100, tensile strength more than 40 kgf / sq.mm and conductivity 80% that of pure copper can be achieved. At higher temperatures, chromium copper alloys are far superior to any other copper alloys.

Brass : Brass is an alloy of copper (Cu 60% to 80%) and zinc (40% to 20%). It has greater mechanical strength and wear resistant than copper but has considerably lower conductivity. It is malleable and ductile, can be casted, and is resistant to corrosion. It is used as current carrying structural material in plug points, socket outlets, switches, lamp holders, fuse holders, knife switches, sliding contacts for starters and rheostats etc. Its melting point is lower than copper. Some of the physical constants of Brass is shown in Table 2.1. The amount of copper in brass varies its properties.

	Percentage Composition
Specific Gravity	Cu 60 + Zn 38 + Pb 1 + Sn 1	Cu 67 + Zn 29 + Pb 3 + Sn 1	Yellow Brass Cu 66 + Zn 34
Young’s Modulus (kg/sq mm)	8.3	8.3	8.3
Ultimate tensile strength  (kg/sq mm)	9800	9500	7300
Hardness	56	48	54
Resistivity at 20o C in micro ohm-cm	65	50	62.7
Melting point (0o C)	7.5	6.78	6.29
	890	840	930

When the alloy has 70% copper, it bears a clear golden yellow colour and is known as yellow brass or high brass, 80% of copper changes the colour to reddish and the metal becomes softer with more copper characteristics. Addition of zinc makes metal tougher and stronger.

When the alloy contains 57 to 63% of copper and 43 to 37% of zinc, it is called MUNITZ metal. The metal is malleable, ductile, hard and corrosion resistant and is used for bolts, nuts, rods and tubes. Lead is added for better machinability. Tin or nickel improves the resistance to corrosion or wear. Welding rods, condensers, springs, bases and caps of valves are some of the application of brass.

Bronze : Bronze is an alloy of copper and tin. Other materials like phosphorous, silicon, aluminium, berilium are alloyed with copper and is also called Bronze. The physical constants of a typical Bronze is shown in Table.

TABLE - Physical Constants of a Typical Bronze

	Cu 88 + Sn 10 + P 2
Temperature Co-efficient of resistance at 0o C	0.0005
Resistivity at 0o C	17.8 micro ohm-cm
Specific gravity	8.89
Ultimate tensile strength	70 kg/sq mm
Young’s Modulus	9400 – 11000  kg/sq mm
Melting point (0o C)	950o C

Phosphorous Bronze: It contains 10 to 15% of tin and upto 0.5% phosphorous. It has high tensile strength and elasticity but fairly low conductivity. Its resistivity is 6 to 12 micro ohms-cm and temperature co-efficient at 0°C is 10 x 10^-4 /degree centigrade. This resistance to corrosion is due to dissimilar metals. Although the impurities of metals in copper decreases the conductivity, the conductivity of bronze containing 2% iron and 0.5% phosphorous can be increased to more than 90% by correct heat treatment. This is used for making current carrying springs, brush holders, knife switch blades etc.

Berilium Bronze: It is another alloy whose mechanical strength is higher than cadmium bronze and is also used for making current carrying springs, sliding contacts, knife switch blades etc.

Silicon Bronze: It contains 90 to 96% of copper, 3 to 5% silicon, 0.5 to 2% manganese or zinc. It is resistant to corrosion and contains chemicals also. Soldering and brazing are not possible on this. This has more electrical conductivity than phosphorous bronze. This has very good tensile strength. It is used for boiler parts, aerial wires and spring materials.

Aluminium Bronze: It contains 85 to 90% of copper, 6 to 8% aluminium, 3% iron and 0.5% tin. It has beautiful golden colour. It is light, strong and resistant to oxygen and chemical actions. It is brittle, strong, ductile and shock proof. It is used for gear drives, sliding parts, springs, brush holder frames, die castings, parts coming in touch with saline or sea water.

Atomic Structure of Elements

Atomic Structure of Element

The atomic structure of a material must be studied in order to understand its behaviour as a conductor, insulator, or semi-conductor. Every material is assumed to be made up of the tiniest and tiniest indivisible particles that cannot be further divided, which are referred to as Atoms. A number of atoms make up each element. An atom of any element consists of:

(a) electrons which are negatively charged, light in weight and movable.

(b) protons which are immovable

(c) neutrons have no charge but heavy and immovable.

 

The negative electrical charge of each electron is 1.602 x 10^-19. Coulombs and protons in the nucleus have the same positive charge. A force of attraction exists between the oppositely charged electrons and the nucleus because opposite charges attract. The centrifugal force generated by the migration of electrons around the nucleus balances the attraction force. Electrons are extremely small particles with minimal mass, and hence can be said to have no mass when compared to the mass of the nucleus. A cluster of protons and neutrons makes up the nucleus of an atom. The charge of a neutron is 0 (zero). The number of protons in the nucleus of an atom equals the number of orbiting electrons for that atom.

Energy Level and Energy Band

ENERGY LEVELS

Near the nucleus, electrons are bound more strongly than those further away from the nucleus. The energy required to pull an electron out of its orbit is higher in the inner orbit than in the outer orbit. As a result, energy levels are used to refer to orbits. The number of electrons that can be received or sent away from an element's outermost orbit to another element in a reaction determines its valency. The valence electrons of elements with three or fewer valence electrons are given away, but elements with five or more valence electrons receive the balance electrons to make up the total of eight for stability. Valence electrons are electrons in the outermost orbit that are weakly connected to the nucleus. In the outermost orbit of a stable atom, there are 8 valence electrons, while in the outermost orbit of an unstable atom, there are less than 8 valence electrons.

 

The energy of Electron:

Consider the hydrogen atom, which has only one electron in its orbit. When the nucleus' electrostatic force equals the electron's centrifugal force, the system is stable. The energy level grows in inverse proportion to the square of the orbit number as the orbit number increases. The greater the forces that attach an electron to the nucleus get as it gets closer. The energy level indicates how much energy would be required to remove an electron from its orbit or shell.

 

The amount of energy required to carry one electron via a potential difference of one volt (1 eV = 1.60 x 10^-19 J) is defined as an electron volt (eV). The energy levels that electrons may occupy appear as hands. Within any given substance, there are two separate bands in which electrons can exist. The valence band and the conduction hand are the two. The energy gap that separates these two bands is known as the forbidden gap, because no electrons may exist within it. The identical energy band diagram is shown in Figure.

Energy Level of an electron in Hydrogen Atom

 

Energy Band Diagram

The forbidden gap is wide when the number of electrons in the outermost orbit exceeds four, and the material is categorized as an insulator. The amount of additional energy necessary for the electrons to escape the orbit in an insulator must be considered for them to go to the conduction band. When the number of electrons in the outermost orbit is less than four, detaching the electrons from the orbit with a modest amount of energy is easy, and the material is designated as a conductor. The number of electrons in the outermost orbit of a semi-conductor is equal to four, therefore it can behave either as a conductor or as an insulator. In general, the total energy required to remove an electron is proportional to the material's resistivity. The resistivity increases as the energy required to detach the outermost electron increases, and vice versa.

Classification of Materials based on Energy Band Diagram

Classification of Materials:

Any electrical device must use materials that will serve the function under extreme conditions without sacrificing reliability. As a result, a thorough understanding of materials and their characteristic amounts in relation to their role is required. Temperature, pressure, frequency, response to the atmosphere, ageing, tension, and fatigue are some of the material's parameters. The variable parameters are determined by experimental results, and only those that are relevant are reflected in the specific topics.

It is possible that materials used in electrical engineering applications are also used in mechanical, civil, and other applications. However, when it comes to electrical engineering materials, the properties and behaviour of the material in relation to its role in electrical engineering takes priority. For example,  Copper is utilised in refrigeration and air conditioning as well as electrical applications. Copper's electrical characteristics are important in electrical engineering materials, even though they're not as important in refrigeration and air conditioning.

When designing electrical machines and equipment, a designer must take all precautions to choose the appropriate material for each component of his product. He must have a thorough knowledge and grasp of the characteristics and behaviours of electrical engineering materials to meet this criteria. Materials used in electrical applications may have restrictions, and it would be dangerous if their suitability for the conditions of needs was not thoroughly investigated. For example, the maximum working temperature of a material is determined by experimental results, and if it is exceeded in its role in electrical equipment, it will fail, causing severe damage to the equipment.

Before selecting any material to serve a purpose or role in the equipment, focus on aspects such as cost, availability, feasibility of manufacture without involving complicated processes, and its peripheral characteristics.

Classification of Materials based on Energy Band Diagram:

The energy band diagram of a conductor, semiconductor, and insulator is shown in the figure. Since the forbidden zone between the valence band and the conduction band is so large in an insulator, it requires additional extra energy for electrons to become free and migrate towards the conduction band. Because there is no prohibited gap between the valence and conduction bands in a conductor, electrons from the valence band can easily pass into the conduction band even with low applied energy.

Energy Band Diagram for Conductor, Insulator, and Semi-Conductor

Comparison of Conducting Materials :

A conductive material containing less than four electrons in its last orbit and has a negligible or zero forbidden band. Consider three distinct elements, each with a different number of orbits. Consider the case of gold. Copper and silver. The configurations of respective shells are listed in the table.

Shell configuration of Gold, Silver, and Copper

	Shell
	K	L	M	N	O	P
Gold	2	8	18	32	18	1
Silver	2	8	18	18	1
Copper	2	8	18	1

 

Since there is just one electron in the last orbit, Gold has a lower energy level to detach the electrons from the last orbit than silver or copper because the bondage decreases as the orbit level increases. As a result, gold is a superior conductor to silver. Similarly, because the valence electron occupies the 'O' shell in silver and the 'N' shell in copper, the energy required to remove the electron from the final orbit in silver is less than in copper. The higher the energy level required to remove the electron from the final orbit, the lower the conductivity and the higher the resistivity. Any conducting material is graded on this basis.

 

Free electrons flow at a random velocity in conducting materials. The temperature affects the magnitude of velocity. Electrons in a conductor acquire a regular velocity when an electric field is applied. The resultant drift current is 0 when there is no electric field.

 

General Classification of Electrical Engineering Materials :

 

The materials are divided into three basic categories based on the energy level principle. Conductor, insulator, and semi-conductor are the three types of materials. Some of the conducting materials can also operate as magnets. In the same way, insulators can be employed as dielectric materials. Materials can be categorized into five categories based on their applications. They are:

 

(a) Conducting material: There are less than four valence electrons in the outermost orbit. The total energy required to detach one electron is directly proportional to the material's resistance. The more the energy required to detach, the higher the resistivity, and vice versa. Conductive materials include silver, copper, aluminum, brass, carbon, and others.

 

(b) Magnetic material: Some conducting materials can be magnetized or attracted to a magnet. Magnetic materials, such as Iron, Cobalt, Steel, and others, provide a channel for magnetic flux. Many alloys have significant magnetic characteristics, such as Cobalt steel and Cadmium steel. They are used to make magnetic circuits in relays and transformers, among other things, in addition to forming a medium for energy conversion in static and dynamic equipment.

(c) Insulators: These materials have more than four valence electrons in their outermost orbit and have significant resistance to current flow. Solids, liquids, and gases have resistivities ranging from 10¹² to 10¹⁸ ohm meter. They're utilized in situations when a charged conductor needs to be separated, such as in an electric iron element where nichrome wire is isolated using mica. Some of these substances can also be utilized as dielectrics.

 

(d) Dielectric material: Dielectric materials are used to store electric energy and are made of insulating materials. They are characterized as insulating materials that can sustain an electric field with minimal power dissipation. Mica, oil, and paper are examples of dielectric materials.

 

(e) Semi-conducting material: Semiconducting materials are neither conducting nor insulating because they have four valence electrons in the outermost orbit. However, act unusually. It is a crystalline solid with a modest resistivity ranging from 1 to 100 Ω – m. Over a portion of the temperature range, these materials have a negative temperature coefficient. Germanium, Silicon, and other materials that fail this test are employed in electronic circuits as capacitors, rectifiers, and other components.