This document discusses the electrical properties and factors affecting the resistance of conducting materials. It describes how resistance increases with temperature, thickness, and certain alloys. Common conducting materials like copper, brass, and bronze are discussed due to their high conductivity. Materials with higher resistivity like nickel and alloys are also summarized for applications requiring greater resistance like heating elements. Classification of materials into low and high resistivity types is covered along with their suitable applications based on properties.
Generation of High D.C. Voltage (HVDC generation)RP6997
Generation of high dc voltage using different methods like half wave and full wave rectifier, voltage doubler circuits, voltage multiplier circuits, cockcroft-walton circuits and van de graaff generators.
Fundamentals of learn how to Semiconductors can easily be mani pulated to become conducting or insulating materials and can change their conductive properties
The project is based on electric heating and its method. This project is a college project done by students. So the project might have some mistakes. Use this project as any source is restricted. The project is uploaded only because of the benefits of the students who want to get the basic idea of the powerpoint presentation of a project.
Generation of High D.C. Voltage (HVDC generation)RP6997
Generation of high dc voltage using different methods like half wave and full wave rectifier, voltage doubler circuits, voltage multiplier circuits, cockcroft-walton circuits and van de graaff generators.
Fundamentals of learn how to Semiconductors can easily be mani pulated to become conducting or insulating materials and can change their conductive properties
The project is based on electric heating and its method. This project is a college project done by students. So the project might have some mistakes. Use this project as any source is restricted. The project is uploaded only because of the benefits of the students who want to get the basic idea of the powerpoint presentation of a project.
basic electrical and electronics engg. components of LT switch gear, switch fuse unit, MCB, MCCB, ELCB, TYPES OF WIRES AND CABLES, ELECTRICAL EARTHING, TYPES OF BATTERIES,
Energy bands consisting of a large number of closely spaced energy levels exist in crystalline materials. The bands can be thought of as the collection of the individual energy levels of electrons surrounding each atom. The wavefunctions of the individual electrons, however, overlap with those of electrons confined to neighboring atoms. The Pauli exclusion principle does not allow the electron energy levels to be the same so that one obtains a set of closely spaced energy levels, forming an energy band. The energy band model is crucial to any detailed treatment of semiconductor devices. It provides the framework needed to understand the concept of an energy bandgap and that of conduction in an almost filled band as described by the empty states.
Current Transformer and Potential TransformerRidwanul Hoque
One of the major difference between them is that the current transformer converts the high value of current into low value whereas the potential or voltage transformer converts the high value of voltages into low voltage.
Topics of the Presentation
1.Semiconductor
2.Intrinsic and Extrinsic semiconductor
3.Difference between Intrinsic and Extrinsic semiconductor
4.Superconductor
5.Application of Superconductor
basic electrical and electronics engg. components of LT switch gear, switch fuse unit, MCB, MCCB, ELCB, TYPES OF WIRES AND CABLES, ELECTRICAL EARTHING, TYPES OF BATTERIES,
Energy bands consisting of a large number of closely spaced energy levels exist in crystalline materials. The bands can be thought of as the collection of the individual energy levels of electrons surrounding each atom. The wavefunctions of the individual electrons, however, overlap with those of electrons confined to neighboring atoms. The Pauli exclusion principle does not allow the electron energy levels to be the same so that one obtains a set of closely spaced energy levels, forming an energy band. The energy band model is crucial to any detailed treatment of semiconductor devices. It provides the framework needed to understand the concept of an energy bandgap and that of conduction in an almost filled band as described by the empty states.
Current Transformer and Potential TransformerRidwanul Hoque
One of the major difference between them is that the current transformer converts the high value of current into low value whereas the potential or voltage transformer converts the high value of voltages into low voltage.
Topics of the Presentation
1.Semiconductor
2.Intrinsic and Extrinsic semiconductor
3.Difference between Intrinsic and Extrinsic semiconductor
4.Superconductor
5.Application of Superconductor
Spot welding (or resistance spot welding[1]) is a type of electric resistance welding used to weld various sheet metal products, through a process in which contacting metal surface points are joined by the heat obtained from resistance to electric current.
The process uses two shaped copper alloy electrodes to concentrate welding current into a small "spot" and to simultaneously clamp the sheets together. Work-pieces are held together under pressure exerted by electrodes.
Seam welding is a welding technique in which two similar or dissimilar metals are connected by supplying an electric current and in this process a nugget formation takes place. Mostly, these nuggets are formed in the form of a butt or overlapping welding components. Do you know the meaning of these nuggets? Well, the nuggets are nothing but small pools of molten metal which are formed at the location with high electrical resistance. Seam welding is one of the types of Resistance welding.
Seam welding is a welding technique in which two similar or dissimilar metals are connected by supplying an electric current and in this process a nugget formation takes place. Mostly, these nuggets are formed in the form of a butt or overlapping welding components. Do you know the meaning of these nuggets? Well, the nuggets are nothing but small pools of molten metal which are formed at the location with high electrical resistance. Seam welding is one of the types of Resistance welding. Spot welding and seam welding are two of the most commonly used welding processes in the manufacturing industry. Spot welding is a process that uses heat and pressure to join two metal pieces together. It applies an electric current between two electrodes, creating an electrical arc that melts the metal at the point of contact. Seam welding is a similar process. But instead of using two electrodes, it involves running a continuous wire along the seam of two metal pieces to join them together. Both are used in automotive and aerospace manufacturing for joining sheet metal components.Spot welding is better utilized for welding materials that’re smaller and are overlapping. Spot welding has a manual mode while seam welding does not. Seam welding is great for welds that need an air-tight seal (remember that spot welds tend to not be the best overall. It’s also great for welds that must be continually done such as for placing strings of spot welds. What are the best uses for spot vs. seam welding? Spot welding is ideal for joining thin sheets of metal. Making it ideal for light duty applications including electronics and battery manufacturing. It is also widely used in the automotive sector, due to it’s ease of automation in high-volume production lines.
While seam welding is best suited for joining thicker materials, or creating a continuous weld along a seam. Thus making it ideal for the fabrication of tanks and vessels, as well other pipe and tube welding applications.
Spot and seam welding are both important met
High-frequency welding is included in a group of resistance welding process variations that use high-frequency welding current (1kHz to 800kHz) to concentrate the welding heat at the desired location.
The heat produces the coalescence of metals, and an upsetting force usually is applied to produce a forged weld.
High-frequency resistance welding is an automated process and is not adaptable to manual welding.
High-frequency resistance welding was developed during the late 1940s and early 1950s to fill the need for high-integrity butt joints and seam welds in pipe and tubing.
But today the process is also used in the manufacture of products such as spiral-fin boiler tubes, closed roll form shapes, and welded structural beams.
A wide range of commonly used metals can be welded, including low-carbon and alloy steels, ferritic and austenitic stainless steels, and many aluminum, copper, titanium, and nickel alloys.
HFW is based on two main electrical phenomena
Skin effect
Proximity effect
Stainless steel is one of the most widely used materials in dentistry for the production of dental instruments, e.g. scalpel blades and forceps, orthodontic wires, denture bases and partial denture clasps, endodontic posts and as stainless steel crowns for the treatment of severely decayed primary molars.
power systems ppt on Arc welding and Electric welding equipment and compariso...sanjay kumar pediredla
this ppt is mainly based on the power systems related topic and in this ppt mainly consists of ac and dc weldings and which welding is used mainly and the importance of arc welding and electric welding and the techniques are also discussed in this and it is so helpful .and the safety requirements and the equipment used is also discussed in this topic
Overview of the fundamental roles in Hydropower generation and the components involved in wider Electrical Engineering.
This paper presents the design and construction of hydroelectric dams from the hydrologist’s survey of the valley before construction, all aspects and involved disciplines, fluid dynamics, structural engineering, generation and mains frequency regulation to the very transmission of power through the network in the United Kingdom.
Author: Robbie Edward Sayers
Collaborators and co editors: Charlie Sims and Connor Healey.
(C) 2024 Robbie E. Sayers
Explore the innovative world of trenchless pipe repair with our comprehensive guide, "The Benefits and Techniques of Trenchless Pipe Repair." This document delves into the modern methods of repairing underground pipes without the need for extensive excavation, highlighting the numerous advantages and the latest techniques used in the industry.
Learn about the cost savings, reduced environmental impact, and minimal disruption associated with trenchless technology. Discover detailed explanations of popular techniques such as pipe bursting, cured-in-place pipe (CIPP) lining, and directional drilling. Understand how these methods can be applied to various types of infrastructure, from residential plumbing to large-scale municipal systems.
Ideal for homeowners, contractors, engineers, and anyone interested in modern plumbing solutions, this guide provides valuable insights into why trenchless pipe repair is becoming the preferred choice for pipe rehabilitation. Stay informed about the latest advancements and best practices in the field.
Cosmetic shop management system project report.pdfKamal Acharya
Buying new cosmetic products is difficult. It can even be scary for those who have sensitive skin and are prone to skin trouble. The information needed to alleviate this problem is on the back of each product, but it's thought to interpret those ingredient lists unless you have a background in chemistry.
Instead of buying and hoping for the best, we can use data science to help us predict which products may be good fits for us. It includes various function programs to do the above mentioned tasks.
Data file handling has been effectively used in the program.
The automated cosmetic shop management system should deal with the automation of general workflow and administration process of the shop. The main processes of the system focus on customer's request where the system is able to search the most appropriate products and deliver it to the customers. It should help the employees to quickly identify the list of cosmetic product that have reached the minimum quantity and also keep a track of expired date for each cosmetic product. It should help the employees to find the rack number in which the product is placed.It is also Faster and more efficient way.
Sachpazis:Terzaghi Bearing Capacity Estimation in simple terms with Calculati...Dr.Costas Sachpazis
Terzaghi's soil bearing capacity theory, developed by Karl Terzaghi, is a fundamental principle in geotechnical engineering used to determine the bearing capacity of shallow foundations. This theory provides a method to calculate the ultimate bearing capacity of soil, which is the maximum load per unit area that the soil can support without undergoing shear failure. The Calculation HTML Code included.
CFD Simulation of By-pass Flow in a HRSG module by R&R Consult.pptxR&R Consult
CFD analysis is incredibly effective at solving mysteries and improving the performance of complex systems!
Here's a great example: At a large natural gas-fired power plant, where they use waste heat to generate steam and energy, they were puzzled that their boiler wasn't producing as much steam as expected.
R&R and Tetra Engineering Group Inc. were asked to solve the issue with reduced steam production.
An inspection had shown that a significant amount of hot flue gas was bypassing the boiler tubes, where the heat was supposed to be transferred.
R&R Consult conducted a CFD analysis, which revealed that 6.3% of the flue gas was bypassing the boiler tubes without transferring heat. The analysis also showed that the flue gas was instead being directed along the sides of the boiler and between the modules that were supposed to capture the heat. This was the cause of the reduced performance.
Based on our results, Tetra Engineering installed covering plates to reduce the bypass flow. This improved the boiler's performance and increased electricity production.
It is always satisfying when we can help solve complex challenges like this. Do your systems also need a check-up or optimization? Give us a call!
Work done in cooperation with James Malloy and David Moelling from Tetra Engineering.
More examples of our work https://www.r-r-consult.dk/en/cases-en/
Final project report on grocery store management system..pdfKamal Acharya
In today’s fast-changing business environment, it’s extremely important to be able to respond to client needs in the most effective and timely manner. If your customers wish to see your business online and have instant access to your products or services.
Online Grocery Store is an e-commerce website, which retails various grocery products. This project allows viewing various products available enables registered users to purchase desired products instantly using Paytm, UPI payment processor (Instant Pay) and also can place order by using Cash on Delivery (Pay Later) option. This project provides an easy access to Administrators and Managers to view orders placed using Pay Later and Instant Pay options.
In order to develop an e-commerce website, a number of Technologies must be studied and understood. These include multi-tiered architecture, server and client-side scripting techniques, implementation technologies, programming language (such as PHP, HTML, CSS, JavaScript) and MySQL relational databases. This is a project with the objective to develop a basic website where a consumer is provided with a shopping cart website and also to know about the technologies used to develop such a website.
This document will discuss each of the underlying technologies to create and implement an e- commerce website.
Saudi Arabia stands as a titan in the global energy landscape, renowned for its abundant oil and gas resources. It's the largest exporter of petroleum and holds some of the world's most significant reserves. Let's delve into the top 10 oil and gas projects shaping Saudi Arabia's energy future in 2024.
Industrial Training at Shahjalal Fertilizer Company Limited (SFCL)MdTanvirMahtab2
This presentation is about the working procedure of Shahjalal Fertilizer Company Limited (SFCL). A Govt. owned Company of Bangladesh Chemical Industries Corporation under Ministry of Industries.
2. • Resistance: It is the property of the material that oppose the flow of
electric current.
• Effect of material dimensions
• Effect of temperature
• Effect of Material
• Why thick wires are used for greater current capacity?
Electrical Properties of Conducting materials
𝑅 = 𝜌
𝐿
𝐴
3. Electrical Properties of Conducting materials
• Conductivity (σ) : The conductivity (σ) is the reciprocal of electrical
resistivity of the material.
• Units: mhos/cm
• It is the property of a material due to which the electric current flows
easily through the material. In other words it provides ability to the
material to flow electric current through the material.
𝜎 =
1
𝜌
4. • Temperature
The effect of heat on the atomic structure of a material is to make the atoms vibrate, and the higher
the temperature the more violently the atoms vibrate. The vibration of the atom due to the collision
of electrons produces heat. The collision hinders the path of electron flow and thus the resistance
of the conductor increase with an increase in the temperature. It has Positive temperature
coefficient.
α is the temperature coefficient of resistance.
Q: The resistance of a platinum resistance
thermometer at 0 C temperature is 3Ω and at
100 C it is 3.75Ω. Find the resistance at 20 0C.
Factors affecting resistance
𝑅1 = 𝑅0(1 + 𝛼∆𝑇)
At Room Temp
At elevated Temp
5. Alloying
• Alloying is the process of combining more than two material by heating and formation of
another material.
• By adding some impurities (a small percentage of some other material) to a metal its
resistivity/resistance can be increased.
• The increase in resistance can be due to formation of irregular arrangement of atoms due
to diffusion of material.
• Alloys have higher resistivity than the pure base metal.
• By alloying copper with zinc its resistivity is increased i.e. conductivity is decreased by about
4 times.
• But the strength of brass is much more than that of copper and therefore may be used for
making structural products such as rods, shafts, heavy plates, plug points, socket outlets,
knife switches etc. where high strength and hardness are usually desirable
Factors affecting resistance
6. Effect of mechanical stressing on resistance:
The resistivity of a material changes also under the influence of mechanical treatment.
The fabrication of conductor to the final stage comprises initially hot working and finally cold
drawing. Cold working operation (stressing)distorts the crystal structure of the metal.
This generally tends to harden the material, increase its tensile strength and increase slightly
its resistivity.
The increase in tensile strength is very useful for many purposes such as overhead conductor. T
hat is why many types of conductors are finally drawn in cold stage in which case they are
identified as hard drawn.
Although mechanical stressing increase the resistivity i.e. decreases the conductivity, annealing
(heat treatment process) restores the electrical conductivity by establishing regularity in crystal
structure.
Factors affecting resistance
7. Classification of Conducting materials
Conducting materials
High resistivity Materials
• Heating element
• Starters
• Resistances
• Filaments
Low resistivity Materials
• House Wiring
• Power transmission
• Windings
All application where power loss and
voltage drop should be low.
Eg: Transmission of power from bhakhra
to Bathinda
Materials: Copper, Aluminum, Silver
All such applications where a large
value of resistance is required .
• if low resistivity materials were used:
the length of the wire would be too
large. Eg: Manganin, Nichrome etc.
8. Classification of Conducting materials
Low Resistivity Materials:
Apart form low resistivity, the materials should also have following properties:
• Low temperature coefficient: The change of resistance with change in temperature should be low. This is necessary
to avoid variation in voltage drop and power loss with changes in temperature.
• Eg: the resistance of transmission lines which are very long will increase when exposed to hot summer sun. this
will cause increase in voltage drop and power loss in the transmission line.
• The windings of electrical machines andapparatus become hot when loaded. This causes temperature rise and if
theconducting material of the winding has high temperature coefficient of resistance, the voltage drop and
power loss in the winding will be high
• Mechanical Strength: To bear the mechanical loadings eg. Overhead wires: wind loading; windings
• Ductility:The conducting material should be ductile enough to enable itself being drawn into different sizes and
shapes
• Solderability: The joint should offer minimum contact resistance. A simple joint would be to twist the conductors with
the material to which it is to be jointed. But this gives high contact resistance. Minimum contact resistance results if
the joint is soldered. All materials do not lend themselves to proper soldering. So while selecting a conducting
material, this point should be kept in view.
• Resistance to corrosion: the conducting material should be such that it is not corroded when used in out door
atmosphere.
9. Classification of Conducting materials
High Resistivity Materials:
Apart form low resistivity, the materials should also have following properties:
• Low temperature coefficient: high resistivity materials are often used as shunts in electrical measuring instruments,
in making wire wound precision resistance and resistance boxes. For such precision applications an important
requirement is that the material of the element should have negligible temperature coefficient of resistance as
otherwise the accuracy of measurements will be reduced.
• High melting point: in application like loading rheostats and starters for electrical motors the material of the resistance
element should be able to withstand high temperature for a long time without melting.
• No tendency for oxidation: materials used as high resistance elements in heating appliances should be able to
withstand high temperatures for a long time without oxidation.
• Ductility: The conducting material should be ductile enough to enable itself being drawn into different sizes and
shapes
• Mechanical Strength: used for applications where the wire must be very thin are required to have high tensile
strength as otherwise they may break during the drawing of the wire or during the assembly and subsequent
operation.
10. Low resistivity Material: copper alloys
Copper
• 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 colored metal.
Advantages:
• It is a ductile metal having a ductility of more than 15%. By virtue of this property, 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:
1. Annealed copper, and
2. Hard drawn copper.
11. Annealed copper is more ductile than the hard drawn copper. It can withstand severe bending and forging stresses
without failure. It is used as power cables, winding wires for electrical machines and transformers, and in making coils.
Hard drawn copper possesses high mechanical strength. It is suitable for overhead transmission wires etc.
Description Annealed Copper Hard drawn Copper
Conductivity Higher Lower
Tensile strength Less More
Hardness Less More
Resistivity 1.72x10-8 1.77x10-8
Applications Low voltage Power cables,
Insulated conductors, coils,
flexible wires, transformers
Overhead conductors,
high-voltage cables, under
ground cables
Low resistivity Material: copper alloys
12. 1. Brass = Cu + Zn
2. Bronze = Cu+Sn
Both are available with different compositions so have different properties.
Brass:
• It is an alloy of copper containing 40% Zn.
• Its conductivity is lower than that of copper.
• It has a high tensile strength and is fairly resistant to corrosion.
• It can be easily pressed into a desired shape and size, can be drawn into wires, and can be easily brazed.
• Brasses are widely used in the following applications: plug-points • socket-outlets • lamp holders • fuse holders •
switches • knife switches • sliding contacts for rheostats and starters, etc.
Low resistivity Material: copper alloys
13. Low resistivity materials: copper alloys
Bronze:
• It has a composition of 10% Sn in 90% Cu.
• Its conductivity is lower than that of pure copper.
• Bronze components are generally made by forging process.
• It is corrosion resistant and possesses high strength.
• Different types of bronze are generally used in the following applications.
• Beryllium bronze for making current carrying springs, sliding contacts, knife-switch blades etc.
• Phosphor bronze for making springs, bushings etc.
• Cadmium bronze for making commutator segments.
14. High resistivity materials: Nickel
• It is a crystalline, non-ferrous, ferromagnetic metal of silvery-white colour.
• Its hardness matches with the hardness of soft steel but ductility is less than that.
• It is capable of high quality polishing, thereby provides luster to the products on which it is polished.
• It is reasonably malleable and can also be rolled provided the carbon content is in small amount (upto 0.05% or less).
• It is resistant to acidic attacks, but dissolves readily in nitric acid.
• Its electrical resistivity at 20°C is 1.05 10–7 ohm-m and thermal conductivity is 54 W/m-K.
Applications:
Nickel is extensively used for nickel-plating of metals to provide protective coating against corrosion. Carbonized nickel is
used to make anodes of power tubes for rapid conduction of heat.
15. High resistivity materials: Alloys
• Nichrome, a nickel-chromium alloy, having a composition of about 79-80% Ni + 19-20% Cr + 1-1.5% Mn + some Fe.
• Constantan, a copper-nickel alloy, having a composition of about 60% Cu + 40% Ni.
• Manganin., a copper-manganese alloy, having a composition of about 86% Cu + 12% Mn + 2% Ni.
Applications:
• Shunts in electrical measuring instruments
• Wire-wound precision resistances
• Filaments for incandescent lamps.
• Starters for electric motors
• Loading rheostats
• Heating elements for heaters, ovens, starters etc
Parameter Nichrome Constantan Manganin
Resistivity 110 x 10-8 52 x 10-8 48 x 10-8
Melting Pt. 1540 oC 1300 oC 1020 oC
Permissible
working
temperature
1100°C 850°C 700°C
Important
applications
Heating
elements for
electric furnaces
and ovens,
room heaters,
electric Iron
Resistance
elements for
rheostats,
starters of
electric
motors
Wire-wound
shunts and
precision
resistances, coils
for precision
measuring
instruments
16. SuperConductivity
• The phenomenon of superconductivity, in which the electrical resistance of
certain materials completely vanishes at low temperatures.
• In 1911 Kamerlingh Onnes and one of his assistants discovered the
phenomenon of superconductivity while studying the resistance of metals at
low temperatures. They studied mercury because very pure samples could
easily be prepared by distillation.
• As in many other metals, the electrical resistance of mercury decreased
steadily upon cooling, but dropped suddenly at 4.2 K, and became
undetectably small. Soon after this discovery, many other elemental metals
were found to exhibit zero resistance when their temperatures were
lowered below a certain characteristic temperature of the material, called
the critical temperature, Tc.
17. The Meissner effect
• In 1933, Walter Meissner and Robert Ochsenfeld discovered a
magnetic phenomenon that showed that superconductors are not
just perfect conductors.
• Imagine that both the ideal conductor and superconductor are above
their critical temperature, Tc.
• It is found that the superconductor expels the magnetic field from
inside it, while the ideal conductor maintains its interior field. Note
that energy is needed by the superconductor to expel the magnetic
field. This energy comes from the exothermic superconducting
transition.
• Switching off the field induces currents in the ideal conductor that
prevent changes in the magnetic field inside it – by Lenz’s law.
However, the superconductor returns to its initial state, i.e. no
magnetic field inside or outside it.
18. Type-I and Type-II Superconductors
• High magnetic fields destroy superconductivity and restore the normal conducting
state.
• Depending on the character of this transition, we may distinguish between type I
and II superconductors.
• It is found that the internal field is zero (as expected from the Meissner effect) until
a critical magnetic field, Bc, is reached where a sudden transition to the normal
state occurs. This results in the penetration of the applied field into the interior.
Superconductors that undergo this abrupt transition to the normal state above a
critical magnetic field are known as type I superconductors.
• Type II superconductors, on the other hand, respond differently to an applied
magnetic field, as shown in Figure 5. An increasing field from zero results in two
critical fields, Bc1 and Bc2.
• At Bc1 the applied field begins to partially penetrate the interior of the
superconductor. However, the superconductivity is maintained at this point. The
superconductivity vanishes above the second, much higher, critical field, Bc2.
19. Applications of superconductors
• The first large scale commercial application of superconductivity was in magnetic resonance imaging (MRI).
• This is a non-intrusive medical imaging technique that creates a two-dimensional picture of say tumors and other
abnormalities within the body or brain. This requires a person to be placed inside a large and uniform electromagnet
with a high magnetic field.
• Although normal electromagnets can be used for this purpose, because of resistance they would dissipate a great deal
of heat and have large power requirements.
• Superconducting magnets on the other hand have almost no power requirements apart from operating the cooling.
• Once electrical current flows in the superconducting wire, the power supply can be
switched off because the wires can be formed into a loop and the current will persist indefinitely as long as the
temperature is kept below the transition temperature of the superconductor.
20. Insulating materials
• Electrical insulators are materials with a high resistivity (resistivity is a property of the material) so they can make
objects with a high resistance. This allows insulators to prevent electric current from flowing where it's not wanted.
Insulators are useful for coating wires, or acting as dielectrics in capacitors.
Electrical Properties: Volume resistivity, Surface resistance, Dielectric loss, Dielectric strength (breakdown voltage),
Dielectric constant
21. Volume Resistivity
• The volume resistivity of a polymer material is its ability to oppose the flow of electric current through a volume of the
cubic specimen. The SI unit of volume resistivity is ohm-meter (Ohm-m).
• Volume resistivity is also known as:
• electrical resistivity,
• bulk resistivity,
• specific electrical resistance, or
• specific volume resistance.
22. Factors affecting Restivity
• Temperature: The insulation resistance falls off with an increase in temperature. For example, PS has high insulation
resistance. It becomes unsatisfactory above 80°C (176°F). Under these conditions, polymers like PTFE and PCTFE are
more suitable.
• Relative humidity: The insulation resistance falls off with an increase in humidity. Plastics with high water resistance
are less affected by high humidities.
• Voltage: The longer the application of voltage the higher the volume resistivity.
• Presence of fillers: The presence of fillers in the polymer affects the volume resistivity. The type and amount of filler
change the volume resistivity.