Electrical and electronics Unit 1_gk.pptx

Utilization of Electrical Energy
SUBJECT CODE: EE417
Department of Electrical and Electronics Engineering
National Institute of Technology Puducherry, Karaikal-
609 609

Syllabus
Unit 1: Illumination -lighting calculations - Design of lighting schemes - factory
lighting - flood lighting - electric lamps.
Unit 2: Electric Heating-Electric furnaces and welding - Resistance, inductance and
Arc Furnaces -Construction and fields of application – Induction heating.
Unit 3: Electric drives and control - Group drive - Individual drive - selection of motors
- starting characteristics - Running characteristics.
Unit 4: Traction system – tractive effort calculations - electric braking - recent trend
in electric traction.
Unit 5: Refrigeration and Air-Conditioning -Various types of air conditioning system,
domestic refrigerator and wiring system.

Syllabus
Reference Books
1. Uppal, S.L., 'Electrical Power', Khanna publishers, New Delhi, 1992.
2. Gupta, J.B., 'Utilisation of Electrical Energy and Electric Traction', S.K.Kataria and
sons, 1990.
3. Partab, . H., 'Art and Science of Utilisation of Electrical Energy', Dhanpat Rai and
Sons, New Delhi, 1998.

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Unit 1

Lighting
Light
 Light is a form of radiant energy radiated from a various form of incandescent
bodies. It is expressed in lumen-hours.
 The Illuminating Engineering Society of North America (IESNA) defines light as
“radiant energy that is capable of exciting the retina and producing a visual
sensation.”
 Incandescence is the emission of light from "hot" matter (T 800 K).
≳

Lighting
Light
 Light can be of different colours, which depend on the wave length of the radiation
causing it.

Lighting
Sensitivity of eye
 The eye has greatest sensitivity for wavelengths of about 550 nm

Lighting
Luminous flux
 It is defined as the total quantity of light energy emitted per second from a
luminous body.
 It is represented by symbol F and is measured in lumens.
 The concept of luminous flux helps us to specify the output and efficiency of a
given light source.

Lighting
Luminous Intensity
 Luminous intensity in any particular direction is the luminous flux emitted by the
source per unit solid angle in that direction.
 It is denoted by I and its unit is candela or candle power (CP).
 Luminous intensity of source in a particular direction,
I = φ or F / ω

Lighting
Lumen
 The lumen is the unit of luminous flux and is defined as the luminous flux emitted
per second in one unit of solid angle by a source having an intensity of one candle
power in all direction.
 Lumens = candle power × solid angle = cp × 𝜔
Candle power
 The light radiating capacity of a source is called its candle power.
 The number of lumens given out by a source per unit solid angle in a given
direction is called its candle power.
 It is denoted by CP

Lighting
Illumination
 When light falls on a surface, it becomes visible, the phenomenon is called as
illumination.
 It is defined as luminous flux falling on a surface per unit area.
 It is denoted by E and measured in lumen per square meter or meter- candle.
 E = Ф / A lux

Lighting
Requirement of Good Lighting Scheme
 Illumination Level
 Glare
 Shadows
 Color Rendering
 Lamp Fittings
 Maintenance

Lighting
Illumination Level
 Illumination level is the amount of light measured in a plane surface.
 Illumination level depends on size of the object and its distance from the observer.
 If the object is moving one, then the greater level of illumination is necessary than
the stationary object.

Lighting
Illumination Level
Condition Illumination (lux)
Sunlight 107527
Full Daylight 10752
Overcast Day 1075
Very Dark Day 107
Twilight 10.8
Deep Twilight 1.08
Full Moon 0.108
Quarter Moon 0.0108
Starlight 0.0011
Overcast Night 0.0001

Lighting
Illumination Level
Activity Illuminance
(Lux)
Public areas with dark
surroundings
20 - 50
Simple orientation for short
visits
50 - 100
Areas with traffic and
corridors - stairways,
escalators and travelators -
lifts - storage spaces
100
Working areas where visual
tasks are only occasionally
performed
100 - 150
Warehouses, homes,
theaters, archives, loading
bays
150
Activity Illuminan
ce (Lux)
Easy office work 250
Class rooms 300
Normal office work, PC work,
study library, groceries, show
rooms, laboratories, check-out
areas, kitchens, auditoriums
500
Supermarkets, mechanical
workshops, office landscapes
750
Normal drawing work, detailed
mechanical workshops,
operation theaters
1000

Lighting
Illumination Level
Activity Illuminance
(Lux)
Detailed drawing work, very
detailed mechanical works,
electronic workshops, testing
and adjustments
1500 - 2000
Performance of visual tasks of
low contrast and very small
size for prolonged periods of
time
2000 - 5000
Performance of very prolonged
and exacting visual tasks
5000 - 10000
Performance of very special
visual tasks of extremely low
contrast and small size
10000 -
20000

Lighting
Glare
 Glare is a visual sensation caused by excessive and uncontrolled brightness.
 Glare causes unnecessary eye fatigue.
 It can be prevented by using diffusing glass screens, suitable reflectors and proper
mounting heights.

Lighting
Shadows
 Shadow is a dark area or shape produced by a body coming between rays of light
and a surface.
 The formation of long and hard shadows must be avoided. The hard and long
shadows often cause accidents. Such long shadows can be avoided by :
Using proper mounting heights of lamp.
Using more number of lamps and providing indirect lighting
Employing wide surface source of light

Lighting
Color Rendering
 Color rendering describes how well the light renders colors in objects.
 Color Rendering Index (CRI) measures the ability of a light source to reveal colors
of objects in contrast to a natural light source.
 CRI is a scale from 0 to 100 percent.

Lighting
Lamp Fittings
 A lamp fitting is an electronic device of a luminaire that holds the lamps, serves as
a protective enclosure, or housing, delivers electric power to the lamps, and
incorporates devices for control of emitted light.

Lighting
Maintanence
 A large part of reducing energy use is proper lighting maintenance.
Cleaning dust off fixtures, lamps, and lenses every 6 to 24 months.
Replace lenses if they appear yellow.
Clean or repaint small rooms every year and larger rooms every 2-3 years
because the dirt collected on these surfaces could reduce the amount of light
they reflect.
Consider group light replacement.

Lighting
Plane angle
 An angle formed by two
intersecting straight lines.
 Angle is measured in 2 dimension.
 Plane angle is measured in radian.
 Plane angle,
Solid angle
 An angle formed by two intersecting
planes.
 Angle is measured in 3 dimension.
 Solid angle is measured in steradian.
 Solid angle, dA
dA / r2

Lighting
Utilization factor
 Utilization factor =Lumens received on the working plane/Lumens emitted by the
lamp
 Utilization factor depends on the type of light, light fitting, Colour surface of walls
and ceiling, mounting height of lamps and area to be illuminated.
 Its value lies between 0.4 and 0.6 for direct fittings it varies from 0.1 to 0.35 for
indirect fittings.
Depreciation or Maintenance factor
 D.F = Illumination under normal working conditions / Illumination when everything
is clean.
 Good = 0.70, Medium = 0.65 and Poor = 0.55

Lighting
Waste light factor
 When a surface is illuminated by a number of lamps, there is certain amount of
wastage due to overlapping of light waves.
 Waste light factor =Total lumens emitted by source / Total lumens available after
waste of light.
 Its value will be between 1.2 to 1.5.
Reflection factor
 Reflection factor = Luminous flux leaving the surface / Luminous flux incident.
 It’s value will be always less than 1.

Lighting
Absorption factor
 Absorption factor=Net lumens available on the working plane after absorption /
Total lumens emitted by the lamp.
 When the atmosphere is full of snow or smoke fumes, it absorbs some light.
 It’s value varies from 0.5 to 1.
Luminous efficiency or specific out put
 Luminous efficiency = Number of lumens emitted / Electric power consumed by the
source.
 It’s unit is lumen/watt (lm/W).

Lighting
Spacing to mounting height ratio (SHR)
 Spacing between luminaires divided by their height above the horizontal reference
plane.
Room index
 L is the length of the room, W is its width and H is the mounting height above the
work plane.

Lighting
Mean horizontal candle power (MHCP)
 MHCP is defined as the mean of the candle power of source in all directions
in horizontal plane.
Mean spherical candle power (MSCP)
 MSCP is defined as the mean of the candle power of source in all directions
in all planes.
Mean hemispherical candle power (MHSCP)
 MHSCP is defined as the mean of the candle power of source in all directions
above or below the horizontal plane.

Lighting
Reduction factor
Reduction factor of the source of light is defined as the ratio of its mean
spherical candle power to its mean horizontal candle power.

DRILL PROBLEMS
A 200-V lamp takes a current of 1.2 A, it produces a total flux of 2,860
lumens. Calculate:
a) the MSCP of the lamp and
b) the efficiency of the lamp.
Solution:

DRILL PROBLEMS
A room with an area of 6 × 9 m is illustrated by ten 80-W lamps. The luminous
efficiency of the lamp is 80 lumens/W and the coefficient of utilization is 0.65.
Find the average illumination.
Solution:

DRILL PROBLEMS
The flux emitted by 100-W lamp is 1,400 lumens placed in a frosted globe of 40 cm
diameter and gives uniform brightness of 250 milli-lumens/m2
in all directions.
Calculate the candle power of the globe and the percentage of light absorbed by the
globe.
Solution:
Flux emitted by the globe = brightness × globe area
= 1,256.63 lumens
Flux absorbed by the globe = flux emitted by source – flux emitted by globe
= 1,400 – 1,256.63 = 143.36 lumens.

Lighting
LAWS OF ILLUMINATION
Mainly there are two laws of illumination.
 Inverse square law.
 Lambert's cosine law.
Inverse square law
This law states that ‘the illumination of a surface is inversely proportional
to the square of distance between the surface and a point source’.

Lighting
Inverse square law
Proof
Let, ‘S’ be a point source of luminous intensity
‘I’ candela, the luminous flux emitting from
source crossing the three parallel plates
having areas A1 A2, and A3 square meters,
which are separated by a distances of d, 2d,
and 3d from the point source respectively as
shown in Fig.
Luminous flux reaching the area A1
= luminous intensity × solid angle

Lighting
Inverse square law
∴ Illumination 'E1' on the surface area 'A1' is:
Similarly, illumination 'E2' on the surface
area A2 is:
and illumination ‘E3’ on the surface area
A3 is:
From above Equations

Lighting
Lambert's cosine law
This law states that ‘illumination, E at any point on a surface is directly proportional
to the cosine of the angle between the normal at that point and the line of flux’.
While discussing, the Lambert's cosine
law, let us assume that the surface is
inclined at an angle ‘θ’ to the lines of flux
as shown in Fig
PQ = The surface area normal to the source and inclined at ‘θ’ to
the vertical axis.
RS = The surface area normal to the vertical axis and inclined at
an angle θ to the source ‘O’.

Lighting
Lambert's cosine law
This law states that ‘illumination, E at any point on a surface is directly proportional
to the cosine of the angle between the normal at that point and the line of flux’.

Lighting
Calculation of number of light points for interior illumination
 The number of lamps required in a particular place can be designed by following
three methods
Watt per square meter:
 This is a rough method. Watts per square meter are calculated on the basis of
efficiency of lamp (lm/watt).
Inverse square law:
 This method is used in street light calculations. In this method law of illumination
is used. For this candle power of the lamps should be known.
Lumen per square meter method:
 This method is used for design of general lighting. In this method, lamp efficiency,
Depreciation factor, utilization factor etc. are used.

Lighting
Lumen method steps
1. Find required lux level
2. Select luminaire
3. Determine room index
4. Determine Number of Fixtures
N =number of lamps required, E=illumination level required (lux), A = area at
working plane height (m2
), F = average luminous flux from each lamp (lm),
UF=Utilization factor and MF=Maintenance factor

Lighting
Lumen method steps
5. Determine Minimum spacing between luminaire
 Minimum spacing = SHR * H
H= Mounting height
SHR= Space to height ratio.
6. Determine Number of required rows of luminaire along width of the room
 Number of required rows= Width of the room/ Minimum spacing
7. Determine Number of luminaire in each row
 Number of luminaire in each row= Total luminaire / Number of rows

Lighting
Lumen method steps
8. Axial spacing along luminaire
 Axial spacing= Length of the room/ Number of luminaire in each row
9. Transverse spacing between luminaire
 Transverse spacing = Width of the room/ Number of luminaire in each row

Lighting
Flood Lighting
 Flood light means flooding of large surfaces with light from powerful projectors.
 Aesthetic Flood Lighting- For increasing the beauty of ancient buildings and
monuments during night

Lighting
Flood Lighting
 Industrial and commercial flood lighting- Illumination of airports, dockyards,
railway yards, sports stadiums and so on.

Lighting
Flood Lighting
 Industrial and commercial flood lighting

Lighting
Flood Lighting
 Advertising

Lighting
Flood Lighting
Projectors
 In order to have a good flood lighting, it is necessary to direct the light from a lamp
into a beam. The reflector and the housing used with the lamp is called flood light
projector.
 It should be robust and weather proof.
 To have the maximum amount of light falling on an object, the projector is provided
with silvered glass, stainless steel or chromium plate surface for the projector.
Narrow beam projectors
 Beam spread between 120
to 250
.
 Used for distance beyond 70 m.

Lighting
Flood Lighting
Projectors
Medium angle projectors
to 400
.
 Used for distance between 30 to 70 m.
Wide angle projectors
to 900
.
 Used for distance below 30 m.

Lighting
Factory / Industrial Lighting
A good industrial lighting should take into account
 Adequate quantity of illumination
 Good quality of illumination.
Adequate quantity of illumination
 A general lighting system should be designed to provide a uniform
distribution of light over the entire work area. Where work areas are close
to walls, such as work benches, the first row of luminaires should be located
closer to wall or additional lighting should be provided over the particular
work space.

Lighting
Factory Lighting
Adequate quantity of illumination
 To ensure that a given illumination level will be maintained, it is
necessary to design a system to give initially more light than the required
minimum.
 In locations where dirt will collect very rapidly on luminaire surfaces
and where adequate maintenance is not available, the initial value should be
still higher.
 Higher initial values shall be provided for the absorption of the
light while designing lighting requirements.

Lighting
Factory Lighting
Good quality of illumination
 Quality of illumination pertains to the distribution of brightness in the visual
environment.
 Brightness should contribute favorably to visual performance, visual comfort, ease
of seeing, safety and aesthetics for the specific visual task involved.
 Factors which has effect on visibility and the ability to see easily, accurately and
quickly.
Direct Glare

Lighting
Factory Lighting
Luminance and Luminance Ratios
 The ability to see detail depends upon the contrast between the detail
and its background. The greater the contrast, difference in luminance,
the more readily the seeing task is performed.
Reflected Glare

Lighting
Factory Lighting
Distribution, Diffusion and Shadows
 The general lighting system for a factory should be designed for
uniformly distributed illumination.
 Diffuse reflection is the reflection of light from a surface such that an
incident ray is reflected at many angles, rather than at just one angle as
in the case of specular reflection. The visibility of objects, excluding
light-emitting ones, is primarily caused by diffuse reflection of light.
Colour quality of light
 The light source should have the good colour rendering index.

Lighting
Factory Lighting
Selection of light for industries
 For industrial lighting the sources of light generally available at present are
tungsten filament lamps, tubular fluorescent lamps, high pressure mercury vapour
(HPMV) discharge lamps and LEDs.
 The selection of any one of these or a combination of these depends on
• Type of application
• Atmospheric conditions of
industrial interiors and/or
exteriors
• Structural features
• Initial outlay
• Running cost
• Ease of maintenance

Lighting EXAMPLE PROBLEMS
The Illumination at a point on a working plane directly below the lamp is to be 80
lumens/m2
. The lamp gives 180 C.P. uniformly below the horizontal plane. Determine:
(i) The height at which the light is suspended.
(ii) The illumination at a point on the working plane 1.5 m away from the vertical axis
of the lamp.

Lighting
Types of lamps
 Thermal light sources (Thermal radiation)
Incandescent lamps
Halogen lamps
 Discharge lamps (Gas discharge)
Low-intensity discharge lamps
Fluorescent lamp
Compact fluorescent lamp
High-intensity discharge lamps
Metal halide lamp
Sodium discharge lamp
Mercury discharge lamp

Lighting
Types of lamps
 Semiconductor light sources (Electroluminescence)
Light Emitting Diode (LED) lamp
Organic Light Emitting Diode (OLED) lamp

Lighting
Types of lamps
Incandescent lamps
Features
Tungsten filament yields light
Electric wire delivers power
Glass bulb protects filament
Inert gas fill prolongs life
Working
 When current is passed through the wire, both heat and light are produced.

Lighting
Types of lamps
Incandescent lamps
Working
 When wire is red hot it emits more heat as compared to light.
 At white hot position, the amount of light radiation being much more than heat
energy.
 Material used for filament is tungsten, carbon, osmium or tantalum.
 Glass blub is filled with a chemical inert gas as nitrogen or argon.

Lighting
Types of lamps
Incandescent lamps
Working
 Lamps below 40watts are not filled with gas to avoid waste of heat.
 Type and color used for the glass cover produce a vital effect on the quality of light
emitted.
 Efficiency of coiled lamp is high as compared to single coil lamps.
 If operating voltage increases, the life of the lamp reduces.

Lighting
Types of lamps
Halogen lamps
 Features
Service life and luminous efficiency
better than incandescent lamps
Dimmable
Brilliant light
Excellent colour rendering

Lighting
Types of lamps
Halogen lamps
Working
 In a typical incandescent lamp, tungsten slowly evaporates from the burning
filament. This causes blackening of the lamp, which decreases light output and
reduces life.
 Halogen lamps are largely able to eliminate this problem because the halogen gas
reacts chemically with the evaporated tungsten to prevent it from affixing to the
glass.
 The halogen light bulb or lamp is a type of incandescent lamp which uses a halogen
gas in order to increase both light output and rated life.
 Current flows through a filament and heats it up in exactly the same way as in an
incandescent lamp.

Lighting
Types of lamps
Fluorescent lamp
 Features
High to very high luminous efficiency
Very good colour rendering
Long service life
Dimmable

Lighting
Types of lamps
Fluorescent lamp
Working
 An alternating electrical field between two electrodes in the discharge tube
produces invisible UV radiation.
 The tube’s white fluorescent coating converts this radiation into high-quality,
visible light.
 These lamps need ignitors and current limiting; these functions are combined in an
electronic ballast.

Lighting
Types of lamps
 Features
Compact designs
High luminous efficiency
Excellent colour rendering
Dimmable

Lighting
Types of lamps
Working
 An alternating electrical field between two electrodes in the discharge tube
produces invisible UV radiation.
 The tube’s white fluorescent coating converts this radiation into high-quality,
visible light.
 These lamps need ignitors and current limiting; these functions are combined in an
electronic ballast.

Lighting
Types of lamps
Home work:
Metal halide lamp
Sodium discharge lamp
Mercury discharge lamp
LED and OLED

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Unit 2

Electric Heating
Introduction
 Electric heating is a process in which the electrical energy is converted into heat
energy.
 When current is passed through a conductor, the conductor becomes hot
(resistance heating)
 When a magnetic material is brought in the vicinity of an alternating magnetic
field, heat is produced in the magnetic material (induction heating).
 When an electrically insulating material was subjected to electrical stresses, heat
is produced in the material (dielectric heating).

Electric Heating
Introduction
 Domestic applications
room heaters
immersion heaters for water heating
hot plates for cooking
Electric kettles
electric irons
pop-corn plants
electric ovens for bakeries
electric toasters
melting of metals
heat treatment of metals like
annealing, tempering, soldering and
brazing etc.
moulding of glass
baking of insulators
enameling of copper wires
 Industrial applications

Electric Heating
Advantages of electric heating
 Cleanliness
 Absence of flue gases
 Ease of control
 Low maintenance requirement
 Special heating requirement
 Higher efficiency

Electric Heating
Different Methods of Heat Transfer
Conduction
 In this mode of heat transfer, one molecule of the body gets heated and transfers
some of the heat to the adjacent molecule and so on.
 There is a temperature gradient between the two ends of the body being heated.
Convection
 Convection is the transfer of heat by the movement of a fluid (liquid or gas) between
areas of different temperature.
Radiation
 Heat transfer due to emission of electromagnetic waves is known as thermal
radiation

Electric Heating
Classification of electric heating methods
Power frequency heating
 Resistance heating
Direct resistance heating
Indirect resistance heating
 Arc heating
Direct arc heating
Indirect arc heating
High frequency heating
 Induction heating
Direct core type induction heating
Coreless type induction heating
 Dielectric heating
 Infrared heating

Electric Heating
Resistance Heating
Requirements of a good heating material
 High specific resistance
 High melting point
 Free from oxidation
 Low temperature coefficient
 Some commercial materials-Ni-Cr, Ni-Cr-Fe, Ni-Cu and Fe-Cr-Al

Electric Heating
Resistance Heating
Direct Resistance Heating
 In this method the material (or charge) to be heated is
treated as a resistance and current is passed through it.
 Two electrodes are inserted in the material or charge to
be heated. Electrodes can be connected to either a.c. or
d.c. supply.
 The material or charge may be in the form of powder,
small solid pieces or liquid.
 Two electrodes will be required in the case of d.c. or
single-phase a.c. supply but there would be three
electrodes in the case of 3-phase supply.

Electric Heating
Resistance Heating
Direct Resistance Heating
 When the charge is in the form of small pieces, a
powder of high resistivity material is sprinkled over the
surface of the charge to avoid direct short circuit.
 This method of heating is employed in salt bath
furnace and electrode boiler for heating water.

Electric Heating
Resistance Heating
Indirect Resistance Heating
 In this method of heating, electric current is passed
through a resistance element which is placed in an
electric oven (Heating Chamber).
 The heat so produced is delivered to the charge either by
radiation or convection or by a combination of the two.
 Sometimes, resistance is placed in a cylinder.
 This arrangement provides uniform temperature.

Electric Heating
Arc Heating
 The heating of matter by an electric arc. The matter may be gas, liquid or solid.
 An electric arc is a phenomenon in which an electric current (a flow of electrons)
is caused to flow between two electrodes separated by a gas.
 Direct arc heating-Electric arc is formed between the electrodes and the charge
(Material to be heated).
 Indirect arc heating- Radiation contributes for the heating of material.
 Electrodes used are, Carbo / graphite / self-braking electrodes.

Electric Heating
Arc Heating
Direct Arc Heating
 Since the arc is formed between electrodes and the
charge, heat is produced by flow of current through the
charge which offers very low resistance.
 Three phase supply is generally employed for large
capacity furnaces. These three phase supply is connected
to these electrodes spaced at the corners of an equilateral
triangle; the material forms the star point.
 The arc is controlled by either applying variable voltage or
by adjusting the arc length and the arc resistance.

Electric Heating
Arc Heating
Direct Arc Heating
 The most important feature of the direct arc furnace is
that the stirring action is inherent due to the
electromagnetic force setup by the current. This results in
uniform heating of material.
 The most common application is to produce steel.

Electric Heating
Arc Heating
Indirect Arc Heating
 The arc is struck by short circuiting the electrodes
manually or automatically for a moment and then,
withdrawing them apart. The heat from the arc and the hot
refractory lining is transferred to the top layer of the charge
by radiation.
 The heat from the hot top layer of the charge is further
transferred to other parts of the charge by conduction.
 Since no current passes through the body of the charge,
there is no inherent stirring action due to electro-magnetic
forces set up by the current.

Electric Heating
Arc Heating
 Hence, such furnaces have to be rocked (moved)
continuously in order to distribute heat uniformly by
exposing different layers of the charge to the heat of the
arc.
 An electric motor is used to operate suitable grinders and
rollers to impart rocking motion to the furnace.
 Rocking action (Movement) provides not only thorough
mixing of the charge.

Electric Heating
Arc Heating
 Since in this furnace, charge is heated by radiation only, its
temperature is lower than that obtainable in a direct arc
furnace.
 Such furnaces are mainly used for melting nonferrous
metals although they can be used in iron foundries where
small quantities of iron are required frequently.

Electric Heating
Induction Heating
 Induction heating is based on the principle of
electromagnetic induction.
 The current flows on the outer surface of metallic
disc.
 The current flow is restricted axially to that
surface of the metal with the turns of the heating
coil.
 The heat energy is transferred to the metal at an
extremely rapid rate, much faster that any
conventional method of heating metal.

Electric Heating
Induction Heating
 The heat is generated within the metal without any
physical contact between the source of electrical
energy.
 If the current continues to flow in the disc, the
surface would attain extremely higher temperature.
 The heat in the disc can be controlled by,
High coil current
Larger number of coil turns
High frequency supply
Closing spacing between the coil and work
Magnetic material disc-High permeabillity
Higher electrical resistivity of the disc

Electric Heating
Induction Heating
Core type induction heating
 The furnace consists of hearth (Base of furnace)
in the form of a trough which contains the
material to be melted in the form an annular
ring.
 This metal ring quite large in diameter is
magnetically inter-linked with an electrical
winding which is energized from an AC source.
 The furnace is therefore a transformer in which
the material to be heated forms a single turn
short circuited secondary and is magnetically
coupled to the primary by an iron core.

Electric Heating
Induction Heating
Core type induction heating
 The magnetic coupling between primary and
secondary is poor. This results in high leakage
current and low PF.
 The melting rapid and clean.
 The inherent stirring action of the melt insures a
uniform temperature in the furnance.

Electric Heating
Induction Heating
Core-less type induction heating
 The furnace consists of a ceramic crucible
(vessel in which metals or other substances are
heated) cylindrical in shape enclosed within a
coil which forms the primary of transformer and
the charge in the crucible, the secondary of
transformer.
 The flux produced by the primary winding sets
up eddy-current in the charge which flow
concentrically with those in the primary winding.
 These current heat up the charge to the melting
point and provide stirring action to the charge.

Electric Heating
Induction Heating
Core-less type induction heating
 The crucible and coil are relatively light in
construction and could be conveniently tilted for
pouring.
 These furnaces are used for steel production.

Electric Heating
Dielectric heating
 It is also called high-frequency capacitive heating
and is used for heating insulators like wood, plastics
and ceramics etc. which cannot be heated easily and
uniformly by other methods.
 This method of heating is based on dielectric loss
and this dielectric loss can be expresses as,
Conducting
Plates
V-applied voltage magnitude
F-Frequency of applied voltage
D-distance between plates
εr-Relative permittivity of the medium
A-Area of the plate
d-Thickness of the material to be heated
Δ-Loss angle
Material to
be heated.

Electric Heating
Dielectric heating
 The supply frequency required for dielectric heating is between 10-50 MHz.
 The applied voltage is upto 20 kV.
 The overall efficiency of dielectric heating is about 50%.

Electric Heating
Dielectric heating
Applications
 For gluing of multilayer plywood boards.
 For baking of sand cores which are used in the moulding process.
 For preheating of plastic compounds before sending them to the moulding section.
 For drying of tobacco after glycerine has been mixed with it.
 For baking of biscuits and cakes etc. in bakeries with the help of automatic
machines.
 For electronic sewing of plastic garments like raincoats etc. with the help of cold
rollers fed with highfrequency supply.

Electric Heating
Dielectric heating
Applications
 For dehydration of food which is then sealed in air-tight containers.
 For removal of moistures from oil emulsions.
 In diathermy for relieving pain in different parts of the human body.
 For quick drying of glue used for book binding purposes.
HW: Infrared heating

Electric Heating
Electric welding
 It is defined as the process of joining two metal pieces, in which the electrical
energy is used to generate heat at the point of welding in order to melt the joint.
 Resistance Welding
Spot Welding
Seam Welding
Projection Welding
Butt Welding
Flash Butt Welding and Percussion Welding
 Arc Welding
Carbon Arc Welding
Shielded Metal Arc Welding
Gas Metal Arc Welding
Submerged Arc Welding

Electric Heating
Electric welding
Resistance Welding
The term ‘resistance welding’ denotes a process in which welding heat is produced
by the resistance offered to the passage of electric current through the two metal
pieces being welded.
Spot Welding
 It consists of two electrodes which are mounted on
two arms.
 The lower arm is fixed whereas the upper one is
movable.

Electric Heating
Electric welding
Spot Welding
 The electrodes are made of low resistance, hard-
copper alloy and are either air cooled or water
cooled.
 Mechanical pressure is applied by the tips of the two
electrodes.
 These electrodes are used not only for providing the
pressure but also to carry the welding current and
concentrate the welding heat on the weld spot
directly below them.

Electric Heating
Electric welding
Spot Welding
 As the movable electrode comes down and presses
the two work pieces together, current is passed
through the assembly.
 The metals under the pressure zone get heated upto
about 950°C and fuse together.
 As they fuse, their resistance is reduced to zero,
hence there is a surge of current. This surge is made
to switch off the welding current automatically.
 Spot welding is used for galvanized, tinned and lead
coated sheets and mild steel sheet work.

Electric Heating
Electric welding
Seam Welding
 Seam welding is the series of continuous spot
welding.
 If number of spots obtained by spot welding are
placed very closely that they can overlap, it gives rise
to seam welding.
 It consists of two wheel type or roller electrodes.
 These electrodes are placed over metal pieces to be
joined.

Electrical and electronics Unit 1_gk.pptx

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