Materials used for conducting electricity are known as Conducting materials. These materials play a vital role in Electrical Engineering. It is interesting to know the applications of these materials in the field of Electrical Engineering, like the type of materials used in Transmission lines, Electrical Machines, Starters, and Rheostats, etc., along with different conducting materials, we will also go through their alloys.
Conducting materials can be classified into Low resistivity materials and High resistivity materials.
Before going into details, first of all, will see what resistivity here is
What is the resistivity of conducting materials?
Every material opposes the flow of electrons through it. The resistivity of a material is the resistance between opposite faces of a portion of a material having unit length and unit cross-sectional area.
Factors affecting resistivity:
Metals in their pure form possess the lowest resistivity when they are alloyed with other metals their resistivity increases.
Alloying decreases the rate of increase of resistance.
Resistivity of a metallic conductor increases with the rise in temperature and vice versa
- Mechanical stress:
Stresses are developed in metals due to mechanical forces and their crystal structure gets distorted. Due to these mechanical stresses metals conductivity decreases hence resistivity increases.
Low Resistivity Conducting Materials:
They should have a low voltage drop, small power loss. Also, these materials have a low-temperature coefficient of resistance and high mechanical strength.
Applications of Low resistivity Materials:
- House wiring
- Transmission and Distribution
- Knife switches
- Current carrying springs
- Sliding contacts
- ACSR conductor is used for transmission and distribution purpose as it has less sag.
Low resistivity conducting materials are as following.
- Copper and its alloys like Cadmium copper, Chromium copper, Brass, Bronze, and its alloys like Phosphorus Bronze, Berrilium Bronze, etc.
- Aluminium and its alloys like Duraluminium, Hindaluminium, Magnaluminium.
Copper is available in 2 forms
1. The Annealed Copper:
Annealed copper is obtained by heating at a specific temperature and then cooling.
This is chemically the same as hard drawn copper but has different mechanical strength due to the different processes used for making them.
Applications: This is used at places where flexibility is required e.g. Wiring of binding, Winding wires of electrical machines, and transformers. Braided copper flexible links used in spot welding machines and busbars.
2. Hard Drawn Copper:
This is obtained by drawing copper bars or rods in cold conditions. Hard drawn copper is chemically the same as annealed copper but has different mechanical strength due to the heat treatment process used in making them.
Applications: This is used at places where high tensile strength is required even though the conductivity is less e.g. transmission and distribution lines.
2. Alloys of Copper:
- Cadmium Copper:
Cadmium of 0.55-1.04% is added to Copper to increase the tensile strength. It appears in white color. It is a corrosion-resistant material. With an increase in cadmium content, the conductivity decreases.
Applications: Used for flexible telephone cords, trolley wires, electrodes, switchgear contacts, commutator segments, etc.
- Chromium Copper:
Chromium is mixed with Copper to increase hardness. It has excellent conductivity and hardness also.
Applications: Used for resistance welding electrodes, seam welding wheels, switchgear, cable connectors, circuit breaker parts, and electrical and thermal conductors that require strength.
Brass is an alloy of Copper-60% and Zinc-40%. It does not get oxidized when exposed to the atmosphere. It is fairly resistant to corrosion. And it has high tensile strength but conductivity is lower than Copper.
Applications: Used in current-carrying and structural material in socket outlets, fuse holders, lamp holders, switches, knife switches, sliding contacts for starters, and rheostats.
- Muntz Metal:
When alloy contains 57 to 63% Cu and 43 to 37% of Zinc it is called as Muntz metal. This metal is malleable, ductile, and anti-corrosive.
Applications: It is used for bolts, nuts, rods and tubes, welding rods, condensers, springs, bases, and caps of valves.
It is an alloy of Copper-90% and Tin-10%. It is chemically very stable and does not react with most of the gases and liquids. Its corrosion resistance is better than Brass. It has good conductivity but less than Copper.
5. Alloys of Bronze:
- Phosphorus Bronze:
It contains 10 to 15% Tin and up to 0.5% Phosphorous.
Phosphorus bronze has high tensile strength, elasticity, and low conductivity and is used for making current-carrying springs, brush holders, knife switches, blades, etc.
- Berrilium Bronze:
It consists of Copper, Tin and Berrilium.
Berrilium bronze’s mechanical strength is higher than Cadmium bronze. It is used to making sliding contacts, knife switches, blades, etc.
- Silicon Bronze:
It contains 90 to 96% Copper, 3 to 5% Silicon, 0.5 to 2% Manganese or Zinc.
Silicon Bronze is a restraint to corrosion and certain chemicals also. It has more electrical conductivity and has good tensile strength. It is used for boiler parts, aerial wires, and spring materials.
- Aluminium Bronze:
It is an alloy of 80-90% Copper, 6-7% Aluminium, 2% Iron, and 0.5% Tin.
Aluminium bronze is light in weight, strong, and resistant to oxygen and chemical actions. It is tough, ductile, and shockproof. It is used for gear drives, sliding parts, brush holder frames, die-castings, parts coming in touch with saline water.
Aluminium’s electrical conductivity is next to Copper. It is malleable and ductile and can be drawn into wires. Al offers high resistance to corrosion due to the oxide layer formed on its surface when exposed to the atmosphere. It is a good conductor of heat and electricity. It is much lighter than copper for the same mass.
Applications: It is used in overhead transmission lines, domestic wiring, flexible wires, busbars, and rotor bars of squirrel cage induction motor.
7. Alloys of Aluminium:
Pure aluminium does not have good machining properties and has poor strength and is mechanically weak. It is alloyed to improve these properties while retaining its corrosion resistance.
It is an alloy of 4.22% Cu, 0.65% Mg, 0.22% Si, 0.42% Fe and rest of it Al.
It has better tensile strength and good machinability than Al and is most suitable for making sheets, tubes, and bars in the automobile and aeronautical industry.
It is an alloy of Al, Hg, Mn, Cr and Si.
Components made from Hindaluminium are strong, hard and are low in cost.
It is an alloy of consisting of 0 to 2.5% Cu, 1 to 55% Mg, 0 to 1.2% Li, 0 to 3% Si, 0 to 0.9% Fe, 0 to 0.03% Mn, and 85 to 95% Al.
Magnaluminium is a brittle alloy with poor castability and has lightweight. It can be welded and machined. It is mostly used in the aircraft and automobile industries. E.g. Vehicle door handles.
High Resistivity Conducting Materials:
High resistivity materials are the materials used in such applications where a high value of resistance is required. These materials have properties like the low-temperature coefficient of resistance, high melting point, and no tendency for oxidation. They must be ductile and should have high mechanical strength.
Applications of High resistivity Materials:
- Starter resistance
- Heating elements
- Precision resistance
- Loading resistance
- Incandescent Lamp filament
High resistivity conducting materials are as following.
- High resistivity materials consist of Manganin, Constantan or Eureka, Platinum, Nichrome, Tungsten, Carbon, and Mercury.
Manganin is an alloy of 86% copper, 12% manganese, and 2% nickel. It can be easily drawn into thin wires. It possesses a very low value of the temperature coefficient of resistance.
Applications: It is used in making wire-wound precision resistance for measuring instruments, Shunts for electrical measuring instruments, and Resistance boxes.
2. Constantan or Eureka:
Constantan or Eureka is an alloy of 60% copper and 40% nickel. It is a very stable alloy with very high working temperatures. It does not corrode due to air, heat, and moisture.
- It is used in making resistance elements in resistance boxes and thermo-couples for temperature measurements.
- Used for resistance elements in field regulators used for regulating the generated voltage of a generator.
- Used as supporting wires for electric filaments.
Platinum has a high melting point of 1770oC, it is rustproof and chemically inert. And it is a malleable and ductile metal.
Applications: It is used as heating elements in laboratory ovens and furnaces. Platinum Rhodium thermocouples are used for measurement for temperature up to 1600oC.
Nichrome is an alloy of nickel 75-78%, chromium 20-30%, manganese 1.5%, and balance is iron. It can withstand high temperatures up to 1100oC for a long time without melting and oxidizing.
Applications: Used in making heating elements for electric heaters, electric irons, and furnaces.
Tungsten is a hard metal and does not become brittle at high temperatures. It has a very high tensile strength. It oxidizes very quickly in the presence of oxygen even at temperatures of a few hundred degrees centigrade. In the atmosphere of inert gasses like Argon or in a vacuum it can easily work up to 2000oC.
It does not exhibit magnetic properties when pure but when alloyed with steel called Tungsten Steel it becomes magnetic material of top quality.
Applications: It is commonly used as filaments in incandescent lamps and in heaters in electron tubes. In the form of an alloy of Tungsten steel, it is used for making permanent magnets.
Carbon is mostly available as graphite which contains about 90% of carbon. To increase the conductivity of carbon products, different kinds of additives like copper as bronze powder are mixed with the carbon moulding compounds.
Carbon is resistant to moisture and it does not get oxide. It has low surface friction, it can withstand arcing and it is not affected by moisture, acids, and bases.
Applications: Used extensively as brushes as it possesses mirror-smooth surface. Used as an electrode in arc lamps and arc welding. Carbon also finds application in carbon resistors.
Mercury is the only metal that is liquid at room temperature. Its expansion and contraction is uniform over a wide range of temperature changes.
Applications: It is used in mercury vapor lamps. Used in arc rectifiers to convert AC to DC. It is used for making and breaking contact in Bucchholz relay and thermometers.