best ppt on conductive materials.

1. CONDUCTIVE
MATERIALS
Submitted by-Daksha Soumya
Bhuwan Singh
Ashish Akash
Devesh Kumar

2. Content
• Fuses
• RTD
• Superconductivity
• Applications

3. 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.

4. 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.

5. Types of fuses
• Low voltage type
• High voltage type

6. 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.

7. 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.

8. • 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.

9. 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).

10. • 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.

11. Common Resistance Materials for
RTDs:
• Platinum (most popular and accurate)
• Nickel
• Copper
• Balco (rare)
• Tungsten (rare 10/5/2014 11
`

12. 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.

13. 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.

14. SUPERCONDUCTING MATERIALS
Superconductivity - The phenomenon of losing resistivity
when sufficiently cooled to a very low temperature (below a certain critical
temperature).
 H. Kammerlingh Onnes – 1911 – Pure Mercury
Resistance
(Ω)
4.0 4.1 4.2 4.3 4.4
Temperature (K)
0.15
0.10
0.0
Tc

15. Transition Temperature or Critical Temperature (TC)
Temperature at which a normal conductor loses its resistivity
and becomes a superconductor.
• Definite for a material
• Superconducting transition reversible

16. 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

17. MEISSNER EFFECT
• When the superconducting material is placed in a magnetic field under the
condition 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

18. Effect of Magnetic Field
Critical magnetic field (HC) –
Minimum magnetic field required to
destroy the superconducting property at
any temperature
   
T
    
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
Normal
Superconducting
T (K) TC
H0
HC
2
0 1 C
C
H H
T
   

19. 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
Superconducting
Normal
HC H
Superconducting
-M
Normal
Mixed
HC1 HC
HC2
H

20. 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 – plasma
maintenance.

21. Medical Application
• NMR – Nuclear Magnetic Resonance – Scanning
• Brain wave activity – brain tumour, defective cells
• Separate damaged cells and healthy cells

22. 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 Meissner
effect)
• This phenomenon is nothing but losing the
resistivity absolutely when cooled to
sufficient low temperatures

23. 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.

24. 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

25. APPLICATIONS OF SUPERconductors

26. 1. Engineering
• Transmission of power
• Switching devices
• Sensitive electrical instruments
• Memory (or) storage element in computers.
• Manufacture of electrical generators and transformers

27. 2. Medical
• Nuclear Magnetic Resonance (NMR)
• Diagnosis of brain tumor
• Magneto – hydrodynamic power generation

28. Thank You