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CONDUCTING MATERIALS

CONDUCTING MATERIALS. Prepared By: Prof. Samyak S. Shah & Prof. Nisarg P. Dave Assistant Professor Electrical Engg . Dept., IT-NU. Topics Covered. Conducting Material Types of it Low Resistivity material High Resistivity material Low Resistivity Material Copper Aluminium.

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CONDUCTING MATERIALS

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  1. CONDUCTING MATERIALS Prepared By: Prof. Samyak S. Shah & Prof. Nisarg P. Dave Assistant Professor Electrical Engg. Dept., IT-NU

  2. Topics Covered • Conducting Material • Types of it • Low Resistivity material • High Resistivity material • Low Resistivity Material • Copper • Aluminium

  3. ACSR Conductors • Abbreviation for Aluminium Conductor Steel Reinforced • Layer of harddrawn aluminium over galvanized steel core • Aluminium  Bulk of current Steel Core  Mechanical Strength • Good Strength/Weight Ratio • It provides higher tension, less sag & longer span lengths

  4. Aluminium Conductors • AAC – All Aluminium Conductors • AAAC – All Aluminium Alloy Conductors • ACAR – Aluminium Conductor Aluminium-Alloy ReinforcedS

  5. Steel • It is an alloy of Iron and other elements but primarily it carbon (Iron + Carbon) • Carbon is added to improve Mechanical Strength. • Properties • Resistivity  8 to 9 times of Cu • Good mechanical strength • Corroded by moisture and heat • Galvanized Steel for O/H lines • Less flexible • Applications • Overhead telecommunication lines & earth wires • To transfer small amount of power

  6. Alloys of Cu • Brass  60% of Cu + 40% of Zn • Bronze  86% of Cu + 12% of Tin + 2% of phosphorous, scilicet • Cadmium Copper  Cu + Cadmium of 1-2%

  7. Brass • High tensile strength but low conductivity • Can be welded and soldered by lead tin alloy • No oxidisation • Less costly • Easily moulded • Applications • Widely used in current carrying & structural material in socket, fuse holder, lamp holder, switches, knife switches, sliding contacts for starters & rheostats • Electrical fixtures & decoration parts for indoor purposes • Welding rods and springs

  8. High Resistivity Materials & their Applications

  9. Tungsten • Properties • Grey in colour & is one of the standard resistance materials • Melting Point  3300 • Ductile  Which is able to deformed without losing its physical properties • Resistivity is twice that of aluminium • High Tensile Strength • Pure material is non-magnetic material but tungsten steel is good magnetic material • Applications • Filament for incandescent lamp • Heater coil in electron tube to heat cathode • For making PM (Permanent Magnet) as alloy of tungsten steel

  10. Nichrome • Properties: • Silver white in colour • Ductile • Good mechanical strength • Maximum permissible temp. is 1100 • High Resistivity () Ωm at 20 • Temperature Coefficient of resistance is 0.0001 • Applications: • Electric ovens • Electric irons** other application to be submitted on google drive

  11. Manganin • Manganin  76% Cu + 12% Mn + 12% Ni • Properties: • Melting Point  102 • Ductile • High resistance but low temperature coefficient of resistance • Applications: • Wire wound precision resistances for measuring instruments* • * other application to be submitted on google drive

  12. Constantan/Eureka • Manganin  40% Cu + 40% Ni • Properties: • Max. permissible temperature  500 • Maximum Point  1300 • Ductile • Applications: • Making resistance elements like loading rheostats and starters for machine* • * other application to be submitted on google drive

  13. Fuse • A short piece of metal which melts when an excessive current flows through it • The fuse is a protective device which consists of a thin wire which is called fuse wire and is placed in series with the circuit/phase wire need to be protected • Fuse wire is placed in a fuse holder of porcelain • Functions of Fuse Wire • Carry normal working current safely without heating • Break the circuit when current exceeds limiting value • Properties of Fuse Material • Low resistivity • Low melting point • Low ohmic loss • Free from deterioration • Cu  1084 • Al  659 • Lead  328 • Tin  232 • Silver  960

  14. Fusing Material • Silver: • Silver is considered to be the best material for fuse wire because of following reasons: • High conductivity • Free from oxidation • Low specific heat • Non deteriorating properties • For current up to 30 A Tin, Lead, Lead-Tin Alloy • For current above 30 A  Copper

  15. Terms related to Fusing • Rated carrying current/ Current rating of fuse element: It is the max. value of current which can be safely carried without any undue heating and melting. • Min. fusing element: Min. value of current due to which fuse melts. • Fusing Factor: Fusing factor:> 1

  16. Continue… • Fusing Time: • Characteristic  inverse current time relationship • Time taken for blowing out depend upon magnitude of excessive current • I = Fusing current in A • K = fuse constant depending upon type of material • n 1.5 • d = diameter of fuse wire • Min. fusing current of a fuse wire depends upon the following factors: • Length of fuse wire • Material around fuse wire • Cooling effect of contacts to which fuse wire is attached Aluminium  59 Copper  80 Iron  24.6 Lead  10.8

  17. Types of Fuse Fuse Carrier or Cutout • Low Voltage Type • Semi Enclosed rewire-able Fuse • Cartridge Type Fuse • High Voltage Type Fuse Base

  18. Bimetals & Thermostats • It provides automatic temperature control of system, used in electric furnace, oven, geyser, electric iron, air-conditioner to keep temp. constant. • Function: • To switch on the supply automatically when temperature is raised above limit of its setting point and switch off in reverse case. • Working principle: • It works on the principle of heating due to current and linear expansion. • Construction: • It consist of 2 strips of different metal or alloy with different co-efficient of thermal expansion. The strip are fixed together length wise.

  19. Bimetals & Thermostats • Working: • When element is heated, it bends in such a way that metal with higher co-efficient of expansion is on outside of arc formed and metal with smaller co-efficient is inside. • When element is cooled, it bends in other direction. • When bi-metallic strip is heated enough due to passage of current which is more than set value, it will bend and break the circuit directly or through the relay. • Material: • Alloy of iron+nickelwith lower co-efficient of thermal expansion are used as one-element. • The other element consist of material having high value of thermal expansion like, iron, nickel, constantant, brass etc.

  20. Contact Materials • Purpose of the contact materials. • Contact deteriorate, reason? • Mechanical wear • Corrosion resulting from oxidation and chemical reaction • Erosion from fusing, evaporation etc. • Successful operation of contact materials depends on: • Low contact resistance. • Good contact force: in close position for longer time. • Voltage and current. • Speed of contact separation • Type of load • Operating medium • Frequency of operation

  21. Contact Materials • Common Contact Materials: • Copper: • High electrical and thermal conductivity, but poor resistance to oxidation which lowers the efficiency. • Silver: • Low contact resistance, good current carrying capacity. • High resistance to oxidation. • Cost is high and not suitable for arcing contacts. • Cadmium sliver can be used. (20% cadmium) • Used upto 600V, 200A

  22. Seeback Effect • The conversion of temperature difference to electric current and vice-versa is termed as thermos electric effect. • In 1981, Thomas Johann Seeback found that a circuit with two dissimilar metals with different temperature junction would deflect a compass magnet. • It was electric potential or voltage which was driving electric current in closed circuit. • V=α(Th-Tc) ; Where α = Seeback co-efficient

  23. Thermocouple • Thermocouple is a temperature measuring device consisting of two dissimilar conductors that contact each other at one or more spots, where a temperature difference is experienced by different conductors. • It is a sensor used to measure temperature. • At junction temperature is measured. • When junction experience change in temperature voltage is generated. • Thermocouple are often enclosed in protective sheet to isolate from the local atmosphere. It drastically reduce the effect of corrosion.

  24. Solder • Solder:It is an alloy of two or more metals used to join together metal workpiece and having a melting point below that of work piece • Soldering:Soldering is a process in which two or more metal items are joined together by melting and flowing a filler metal into the joint, the filler metal having a lower melting point than the adjoining metal. • Difference between soldering and welding?

  25. Materials used for Solder • Soft Solder: Tin/Lead solder are commercially available. • Higher the content of tin, greater the solder tensile and shear strength. • For electrical work 60/40 Tin/Lead are used which melts at 183*C and 63/37 Tin/Lead are used for electronic works. • Solder paste are available for PCB. Lead is toxic so lead free solders may contains tin, copper, silver, bismuth, indium, zinc or antimony. • Tin-Silver-Copper solders are used in 75% of companies in Japan, Tin-Silver-Copper-Zinc is the recent material in soldering. • Flux(Zinc Chloride) is used to remove oxides from the surface. • Soft solder has melting point less than 400*C.

  26. Materials used for Solder • Hard Solder: Alloy of Copper+Zinc is used. • Melting point is greater than 400*C, melts at very high temperature. • Used for making permanent connection for joining. Copper, Silver, Gold and alloys such as brass and gunmetal is used. • It is also called as brazing solder. • Alloy of copper with zinc or copper are most common for hard solder.

  27. Some more Conducting Materials • Lead:Obtained from lead sulfied. • Properties: It is softest and heaviest of all metals • Blueish grey colour, can be scratched easily. • Less conductivity 7.8% of copper. • Melting point 327.4*C. • Mechanically weak and cannot withstand vibration at high temperature. • Malleable and ductile, easily castable. • Applications: • Electrodes for batteries. • Cable sheath • Fuse materials • Used as solderand cable joints.

  28. Some more Conducting Materials • Carbon:Made from amorphous carbon i.e. coal, coke etc. • Properties:Pure carbon is good semiconductor • It has negative temperature co-efficient. • Low conductivity, melting point 3400*C. • Low surface friction, not affected by moistures, acids. • Resistivity 1000-7000 μΩ-cm. Temperature co-efficient -0.0022 to -0.0008 • Good thermal conductivity. Good arc withstanding capability.

  29. Some more Conducting Materials • Carbon: • Applications: • Film type carbon resistor consists of thin layer of carbon deposited on the surface of ceramic rod. • Carbon rod also can work as resistor, carbon composite resistor • Carbon brushes in electrical machines because of smooth surface, adequate conductivity and sufficient strength. • As electrodes of electric arc furnace and arc welding. • Battery cell element. • Arcing tips in circuit breaker. • Carbon arc lamp and carbon filament lamp.

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