CONDUCTIVE MATERIALS

Submitted by-Daksha Soumya

Bhuwan Singh

Ashish Akash

Devesh Kumar

Content

• Fuses

• RTD

• Superconductivity

• Applications

Fuses:

• Fuse is essentially a sort piece of a metal which melts when a excessive current flows through it. The circuit is then interrupted and so the damage due to the fault is prevented at the expense of the fuse.

• These are designed to operate upto 115kv.

History

• In 1847, Breguet recommended use of reduced-section conductors to protect telegraph stations from lightning strikes by melting, the smaller wires would protect apparatus and wiring inside the building. A variety of wire or foil fusible elements were in use to protect telegraph cables and lighting installations as early as 1864.

• A fuse was patented by Thomas Edison in 1890 as part of his successful electric distribution system.

Types of fuses

•Low voltage type

•High voltage type

Low voltage fuses(upto 33kv)

• Semi enclosed rewirable fuse : It has one or more strands of fuse wire stretched between terminal blocks. Used where low value of fault current are to be handled.

• Cartridge fuses : It consists of a ceramic body having metal end caps to which are welded fusible silver current carrying elements. The space within the body surrounding the elements is completely packed with filling powder.

High voltage fuses

• High voltage high power fuses are protective switching devices used to operate upto 115 kV.

• Large power fuses use fusible elements made of silver, copper or tin.

• They are used in power supply networks ,transformer circuits, motor circuits and capacitor banks.

• High voltage expulsion fuses surround the fusible link with gas-evolving substances, such as boric acid. When the fuse blows, heat from the arc causes the boric acid to evolve large volumes of gases. The associated high pressure (often greater than 100 atmospheres) and cooling gases rapidly extinguish the resulting arc. The hot gases are then explosively expelled out of the end(s) of the fuse.

RTD

• RTD stands for Resistance Temperature Detector.

• The change in temperature is detected by the change in resistance of the wire.

• There are two types of RTD, viz. having positive and negative thermal coefficients of resistivity (resistance increases or decreases with the increase in temperature respectively).

• RTDs are used for temperature measurements by using them in bridge circuits.

• The change in temperature causes considerable resistance change which gives a voltage drop in accordance with the thermal coefficient of resistance of the wire.

• This voltage is further amplified and the temperature is read thus. This is how the RTDs are used in circuits assisting in automatic control and measurement with high accuracy.

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Common Resistance Materials for

RTDs:

•Platinum (most popular and accurate)

•Nickel

•Copper

•Balco (rare)

•Tungsten (rare 10/5/2014 11

Advantages

• Due to no fluid present absolute temperature is recorded.

• It is highly sensitive and gives accurate results.

• It has a good range of temperature measurement. It can thus measure from very low to very high

temperature.

• Due to electrical output (resistance change) complete automation can be achieved.

Applications of RTD

• It is widely used in furnaces for automatic temperature measurement.

• Due to its compactness, it replaces conventional thermometers as well as thermocouples thus

eliminating the use of lots of wires.

• Used in medical and chemical laboratories to detect very low temperatures (like dry ice and

liquid nitrogen).

• Due to electrical output it is used wherever feedback system is required and corrective action is

thus taken in an automated system.

SUPERCONDUCTING MATERIALS

Superconductivity - The phenomenon of losing resistivitywhen sufficiently cooled to a very low temperature (below a certain criticaltemperature).

H. Kammerlingh Onnes – 1911 – Pure Mercury

Resistance

(Ω)

4.0 4.1 4.2 4.3 4.4

Temperature (K)

0.15

0.10

0.0Tc

Transition Temperature or Critical Temperature (TC)

Temperature at which a normal conductor loses its resistivityand becomes a superconductor.

• Definite for a material

• Superconducting transition reversible

Occurrence of Superconductivity

Superconducting Elements TC (K)

Sn (Tin) 3.72

Hg (Mercury) 4.15

Pb (Lead) 7.19

Superconducting Compounds

NbTi (Niobium Titanium) 10

Nb3Sn (Niobium Tin) 18.1

MEISSNER EFFECT

• When the superconducting material is placed in a magnetic field under thecondition when T≤TC and H ≤ HC, the flux lines are excluded from the material.

• Material exhibits perfect diamagnetism or flux exclusion.

• χ = I/H = -1

• Reversible (flux lines penetrate when T ↑ from TC)

• Conditions for a material to be a superconductor

i. Resistivity ρ = 0

ii. Magnetic Induction B = 0 when in an uniform magnetic field

• Simultaneous existence of conditions

Effect of Magnetic Field

Critical magnetic field (HC) –

Minimum magnetic field required to destroy the superconducting property at any temperature

H0 – Critical field at 0K

T - Temperature below TC

TC - Transition Temperature

Element HC at 0K(mT)

Nb 198

Pb 80.3

Sn 30.9

Superconducting

Normal

T (K) TC

H0

HC

2

0 1C

C

TH H

T

Types of Superconductors

Type I

• Sudden loss of magnetisation

• Exhibit Meissner Effect

• One HC = 0.1 tesla

• No mixed state

• Soft superconductor

• Eg – Pb, Sn, Hg

Type II

• Gradual loss of magnetisation

• Does not exhibit complete Meissner Effect

• Two HCs – HC1 & HC2 (≈30 tesla)

• Mixed state present

• Hard superconductor

• Eg – Nb-Sn, Nb-Ti

-M

HHC

Superconducting

Normal

Superconducting

-M

Normal

Mixed

HC1 HCHC2

H

Application

• Large distance power transmission (ρ = 0)

• Switching device (easy destruction of superconductivity)

• Sensitive electrical equipment (small V variation large constant current)

• Memory / Storage element (persistent current)

• Highly efficient small sized electrical generator and transformer

• Superconducting solenoids – magneto hydrodynamic power generation – plasmamaintenance.

Medical Application

• NMR – Nuclear Magnetic Resonance – Scanning

• Brain wave activity – brain tumour, defective cells

• Separate damaged cells and healthy cells

SUPERCONDUCTORS

• Superconductivity is a phenomenon in certain materials at extremely low temperatures ,characterized by exactly zero electrical resistance and exclusion of the interior magnetic field (i.e. the Meissnereffect)

• This phenomenon is nothing but losing the resistivity absolutely when cooled to sufficient low temperatures

WHY WAS IT FORMED ?

• Before the discovery of the superconductors it was thought that the electrical resistance of a conductor becomes zero only at absolute zero

• But it was found that in some materials electrical resistance becomes zero when cooled to very low temperatures

• These materials are nothing but the SUPER CONDUTORS.

WHO FOUND IT?

• Superconductivity was discovered in 1911 by Heike Kammerlingh Onnes , who studied the resistance of solid mercury at cryogenic temperatures using the recently discovered liquid helium as ‘refrigerant’.

• At the temperature of 4.2 K , he observed that the resistance abruptly disappears.

• For this discovery he got the NOBEL PRIZE in PHYSICS in 1913.

• In 1913 lead was found to super conduct at 7K.

• In 1941 niobium nitride was found to super conduct at 16K

APPLICATIONS OF SUPERconductors

1. Engineering

• Transmission of power

• Switching devices

• Sensitive electrical instruments

• Memory (or) storage element in computers.

• Manufacture of electrical generators and transformers

2. Medical

• Nuclear Magnetic Resonance (NMR)

• Diagnosis of brain tumor

• Magneto – hydrodynamic power generation

Thank You