This document summarizes key concepts related to conductive and dielectric materials. It discusses mechanically processed forms of conductive materials and commonly used materials like copper. It also discusses high and low resistivity materials, contact materials, fusible materials, and carbon as a filament. Additionally, it covers dielectric constants, dielectric strength, polarization mechanisms, and factors affecting dielectric properties. Dielectric materials are classified and their uses discussed.

1. Conductive Materials and Applications: Mechanically processed forms of electrical
materials, Types of conducting materials, Low resistivity materials, High resistivity
materials, Contact materials, Fusible materials, Filament materials, Carbon as filamentary
and brush material, Material for conductors, cables, wires, solder, sheathing and sealing.
Dielectrics: Introduction to dielectric materials, classification of dielectric materials,
Dielectric constant, Dielectric strength and Dielectric loss. Polarization, Mechanisms of
polarization, Comparison of different polarization process, Factors affecting polarization,
Spontaneous polarization, Behavior of polarization under impulse and frequency
switching, Decay and build-up of polarization under ac field, Complex dielectric constant.

2. Cladded Metals
Mechanically Processed Forms of Electrical Materials
Several electrical materials are processed mechanically before use to impart special qualities in
them. By doing so they perform better in their purpose. A brief explanation of such materials is
given below.
Bimetals
Sintered Materials Hot Rolled and Cold Rolled Metals

3. Hard Drawn and Soft Drawn Metals

4. Annealed Metals

5. Types of Conducting Materials

7. Low Resistivity Materials
• Low resistivity materials possess lower value of resistivity i.e. higher conductivity.
• Hence, they are suitable for those applications where the voltage drop and
power loss are to be kept to a minimum value.
• Used in the windings of alternators, motors, transformers; in domestic wiring,
and in electricity transmission from power stations to other places. Gold, silver,
copper and aluminum are the examples of low resistivity materials. Amongst
these materials, copper is commercially most acceptable.
Characteristics of Low Resistivity Materials
Low coefficient of temperature resistance .
The value of ά should be low to avoid the variation in voltage drop and power loss, with
change in temperature.
If the value of ά is high, the voltage drop and power loss will increase.
A low value of helps in reducing the heat in windings of electrical machines and in increasing
the resistance of transmission lines during hot season.

8. High resistance to corrosion. This is a desired requirement to prevent corrosion
due to environmental effects. The conducting material should not easily corrode,
particularly when used in atmospheric exposure without insulation.
Good solderability.
• Conductors are often required to be jointed.
• The joints should offer a minimum contact resistance.
• Joining is normally done by soldering because it offers minimum contact resistance.
• All materials do not possess good solderability.
• Hence, the solderability of conducting materials should be such as to develop
minimum resistance.
High mechanical strength.
• Overhead transmission and distribution lines are subjected to stresses and strains
under their self weight and also due to winds.
• The conductors used in the windings of electrical machines and transformers
develop mechanical and thermal stresses also when loaded.
• Therefore, the low resistivity materials should be mechanically strong enough to
resist these stresses.
Good ductility.
The conducting materials should be ductile enough to enable themselves to be drawn
into different shapes and sizes.

9. Copper and its Types
Due to its high conductivity and reasonable cost, copper is most widely used metal for
electrical purposes. It is a crystalline, non-ferrous, nonmagnetic (diamagnetic), reddish colou
red metal. • It is a ductile metal
• It can be easily drawn into thin bars and wires. Hence, it
is very useful for making cables, strands, and conductors.
• Its ultimate tensile strength is high enough (300–350
MPa) which makes it substantially strong to sustain
mechanical loads.
• Its melting point is sufficiently high (1083°C) that makes
it suitable for use at high temperatures also.
• When exposed to atmospheric environment, it forms a
protective layer of copper oxide (CuO). Thus, the
copper is highly resistant to corrosion which is a
desired property for bare/open overhead conductors.
• It can be easily brazed (a kind of welding) which is a
necessary requirement in electrical wiring and other
connections.
Types of copper.

13. High Resistivity Materials
• High resistivity materials possess a high value of resistivity i.e. lower conductivity.
• When used as conductors, they require a higher potential difference to set-up the
movement of electrons.
• More heat is also generated in them due to heating effect of current.
• Such materials are used to make resistors, filament of lamps, heating elements,
and in energy conversion (electrical energy into heat energy) appliances e.g.
heaters, hot plates, ovens and furnaces etc.

14. Characteristics of High Resistivity Materials
Lower coefficient of temperature resistance α
• It is an essential requirement for precision applications where a high degree of accuracy in
measurements is desired.
• A lower value of α minimizes the heating effect of current and increases the accuracy of
measurement.
Ability to withstand higher temperature without oxidation.
• Since a high resistivity material has to sustain high temperatures for longer duration in use,
the oxide layer should not form on the heating element.
High melting point.
• It is required for the purpose of minimizing heating effect of current.
• This is an essential requirement in resistance elements that are subjected to high
temperatures for long durations.
• They are required to withstand these temperatures without melting
High mechanical strength.
• High resistivity materials are used as thin wires also in several applications such as precision
wire-wound resistors etc.
Adequate ductility.
• High resistivity materials are also used in the form of wires and coils as elements of heaters,
ovens, and starters etc.

15. Salient Applications of High Resistivity Material

16. Contact Materials
• Contact materials are used as ‘contact points’ and ‘contact surfaces’ in electrical
equipment's, appliances, devices and instruments.
• They operate under severe conditions and under frequent reversal of mechanical
rubbing while ‘making and breaking’ the electrical circuits.
• They are also subjected to arcing and sparking due to ionization of surrounding
medium between the contacts, when the contacts are separated.
Requirements of a Good Contact Material

17. Types of Contact Materials

20. Salient Applications of Contact Materials

21. Fusible (or Fuse) Materials
• A fuse (or fusible cutout) is a wire conductor connected to an electrical circuit
or electrical device for the purpose of its protection against excessive current.
• It is designed to carry a pre-determined amount of current, and melts if more
than the stipulated current passes through it.
• When it melts, the circuit breaks and damage to the connected device by
excessive current is avoided
Requirements of Fuse Materials

22. Fusible Metals and Alloys
i. Lead. It can carry about 67% of its fusing current continuously without damage. Its
melting point is 327°C.
ii. Tin. Its melting point is 232°C.
iii. Lead-tin alloys such as Tinman solder (66% Sn + 34% Pb).
iv. Tinned copper. The copper wire is tinned (coated with Sn), reduces the tendency of
oxidation at high temperatures. It can carry about 53% of its fusing current without
deterioration. Its melting point is less than the melting point of copper which is 1083°C.
v. Silver. It can carry more than 90% of its fusing current. It is least affected by oxidation. Its
melting point is 961°C.
vi. Bismuth based alloys such as Wood’s metal (50% Bi + 25% Pb + 12% Sn + 13% Cd), Rose
metal (50% Bi + 28% Pb + 22% Sn), Newton metal etc. Their melting point varies from
60°C to 95°C.

23. Carbon As Filamentary and Brush Material
Electrical carbon materials are basically available in raw carbon forms, which are
processed to obtain carbon products.
The processing involves the following operations.
i. Grinding of raw carbon materials into powder form.
ii. Mixing the binding agent (binder) to the powder.
iii. Moulding the powder-binder paste to a desired shape.
iv. Baking the moulded shape.
Commonly used electrical carbon materials are the following.
1. Raw graphite 2. Carbon graphite 3. Copper graphite 4. Electrographite

24. Conductors, Cables, and Wires: Types and Materials

25. Solder Materials for Joining Wires and Joints in Power Apparatuses
Sheathing Materials

26. Introduction to Dielectric Materials
i. Dielectrics are characterized by their
• high specific resistance
• negative temperature coefficient of resistance
• large insulation resistance.
ii. The insulation resistance is affected by
• moisture
• temperature
• applied electric field and age of dielectrics.
iii. Dielectric materials may be
• solid,
• liquid
• gas
Uses. Dielectric materials are used in
• electrical insulation
• capacitors
• in strain gauges and
• sonar devices etc.

27. Classification of Dielectric (or Insulating) Materials

31. Main Properties
The main properties of dielectric materials are the following.
1. Dielectric constant,
2. Dielectric strength,
3. Dielectric losses, and
4. Surface and volume resistivity
Dielectric Constant

33. Factors Affecting Dielectric Constant Dielectric constant is influenced by the
following main factors. 1. Frequency f of applied field, and 2. Temperature T

34. Dielectric Strength
• The voltage per unit thickness that can be sustained by an insulating material
before its breakdown is called as dielectric strength.
• A good insulating material possesses high dielectric strength
Types of Dielectric Breakdown Dielectric breakdown occurs on account of the
following factors. These are called as
1. Intrinsic breakdown.
2. Thermal breakdown.
3. Electrochemical breakdown.
4. Discharge breakdown, and
5. Defect breakdown.
Intrinsic breakdown occurs when
electrons in the valence band cross the
forbidden gap under the influence of
applied voltage, and enter into the
conduction band.
Thermal breakdown occurs at high
temperatures due to poor dissipation, and
hence accumulation of non-dissipated
heat produced by electrical energy. This
breakdown is more severe in d.c. field
than in a.c. field
Electrochemical breakdown takes place
when the leakage current increases due
to larger mobility of ions at raised
temperatures. The dielectrics convert
into their oxides, and insulation
resistance decreases due to this
chemical action. Breakdown

35. Discharge breakdown occurs due to the presence of gas bubbles in the solid and
their bombardment on application of applied field.
Gaseous atoms get ionized at lower potential than the solid atoms, and hence
causing deterioration
Defect breakdown occurs on the surface of dielectric materials due to detrimental effects of
moisture on the cracks and pores.
Glazing of the surface may eliminate this breakdown. Fireproof silica, high strength mica, and
other chemically inert materials are used to provide good surface finish.
Dielectric Loss
Duration t of the applied voltage V as compared to relaxation time affects the
behavior of dielectric materials. It may result into loss of electrical energy under
certain conditions. There can be three possible conditions.

37. Factors Affecting Dielectric Loss :
The dielectric loss is influenced by following main factors.
• Temperature • Frequency • Applied voltage • Humidity
i. A low value of is desired for electrical capacitors to be used at high frequency The
electrical loss is least in transformer oil.
ii. Dielectric losses increase with an increase in temperature, humidity, applied voltage and its
frequency.

38. Calculation of Loss Factor The loss factor for a dielectric is expressed as the ratio
given as

40. Polarization
1. The polarization is the sum of total dipole moments produced within the solid on
application of electric field.
2. It occurs because, on application of an electric field to a dielectric, the positive
charges are displaced towards negative end of the field while the negative charges
are displaced towards the positive end.
3. Hence, local dipoles are produced in the dielectric due to this displacement.
4. These dipoles keep their moments and are called dipole moments. Total dipole
moments within the volume of a solid is called polarization P