CONDUCTORS The role of conductive materials in power electronics
Did you know that the world's very first power electronics devices were made from mercury - an excellent conductor of electricity? Conductive materials have high conductivity which allows them to serve a variety of household and industrial applications in power electronics.
What are conductive materials and what are they used for?
Whenever an input voltage is applied across a conductive material, an electric current flows through it. A conductor is defined as a material that allows electric current to pass through it without offering resistance.
σconductor= (104 - 108) S/m
According to Valence Bond Theory, the low-energy valence band and high-energy conduction band should overlap in a conductor. There should be no forbidden energy gap (Eg= 0) between the low-energy valence band and the high-energy conduction band. It implies that the electrons in the low-energy valence band can easily jump into the high-energy-conduction band. The Fermi Level is the highest state an electron can occupy at absolute zero. In conductors, the fermi level lies in the conduction band.
Conductive materials in the periodic table
In periodic table trends, the electrical conductivity of elements decreases across a period and varies down a group.
See electrical conductivity of all the elements in the image on the left.
- The electrical conductivity of metals depends upon their delocalization of electrons. In short, it depends upon the ability of electrons to participate in a bond. Metals, alkali metals, alkaline earth metals, and post-transition metals have electrical conductivity in the order of 105 - 107 S/m.
- Nonmetals, halogens, and noble gases have low conductivity, with some of them being insulators.
- Metalloids are the most interesting materials with varying electrical conductivity. Boron has one of the lowest electrical conductivity of 10-4 S/m in the periodic table. Silicon, Germanium, and Tellurium are semiconductors with moderate electrical conductivity. However, some metalloids like Arsenic, Antimony, and Polonium have good electrical conductivity in order of 106 S/m.
- We must not consider Lanthanides because they are scarcely found in the earth’s crust, and Actinides as they are radioactive.
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Conductive materials and their applications in power electronics
Industrial applications of conductive materials do not depend solely on electrical conductivity. Many other factors like the conductive material’s cost of manufacturing, presence in nature, chemical reactivity, mechanical strength, longevity, etc, decide its household and commercial application. The importance of conductive materials in power electronics is huge because they are used in power generators, transmission lines, distribution systems, and devices.
Underground transmission lines
Conductive materials like Copper are used to make underground transmission lines, operating at high voltage. These are the most common conductive materials in power electronics to make transmission lines. It is because of exceptional properties like high electrical conductivity (5.9 x 107S/m), high tensile strength, and resistance to corrosion.
Technically, Silver, Copper, and Gold are the top 3 conductive materials in power electronics. Silver is the best conductor of electricity (6.2 x 107S/m) in the periodic table, followed by copper (5.9 x 107S/m), and gold (4.5 x 107S/m). However, Silver and Gold are rarely used because the cost of manufacturing is extremely high, making them unsuitable for commercial use. Moreover, Silver is a highly reactive element that would result in the formation of oxide and sulfides to degrade the quality of wires.
Solid conductive wires covered with insulators are used in homes. These solid conductors are applicable in short distances where wires do not have to be twisted. Solid cables are made of copper with insulation protection because the current is persistent across its surface. Examples include home wiring, speaker wires, kitchen connections, etc..
Alloys of Copper
Copper is a widely used conductor due to its exceptional conductivity and physical properties. Even alloys of copper like Brass and Bronze are good conductors of electricity. Brass is used in sockets, and pins at homes while Bronze is a costly conductor. However, bronze is used in musical instruments, medals, and aesthetically-pleasing equipment. Phos-Bronze is another alloy of Phosphorus and Bronze to make transmission lines in marine areas, electronic products, springs, bolts, etc..
Aluminum conductors in transmission lines
- All Aluminum Conductors (AAC): AAC is used in overhead lines.
- All Aluminium Alloy Conductors (AAAC): AAAC transmission lines are used over short distances in coastal areas.
- Aluminium Conductor Alloy Reinforced (ACAR): ACAR makes up distribution lines.
- Aluminum Conductor Steel Reinforced (ACSR): ACSRs are used in long-distance high-voltage transmission lines.