R Satish Kumar: Presented by

RGMCET- NANDYAL.
Presented by :
R SATISH KUMAR
EE502.21 1
OBJECTIVES
Upon completion of this topic you would be able

to know
• Application and Advantages of Dielectric heating
EE502.21 2
DIELECTRIC HEATING.
• When an insulating material is subjected to an alternating
electric field, the atoms get stressed and due to inter-atomic
friction caused by repeated deformation and rotation of
atomic structure heat is produced.
• This loss is known as dielectric loss.
EE502.21 3
• The dielectric loss is dependent upon the frequency
and high voltage.
• High voltage at above 20KV and frequencies range of
order 10 to 30 Mega cycles per second are employed.
EE502.21 4
• The hysteresis loss is due to the reversal of magnetism or
magnetic molecular friction which appears as heat.
• Electrically every atom is neutral, since the central positive
charge equals the surrounding negative charge.
• The centers of positive charge and negative charge are co-
incident as long as there is no external electrical field.
EE502.21 5
NEUTAL ATOM
Fig.1
EE502.21 6
• When atom is subjected to some external electric fields.
• The positive charge of nucleus is acted upon by some
force in the direction of the field.
• And negative charge in the opposite direction.
• The effective centers of positive and negative
charges are no longer coincident i.e., POLARIZED.
EE502.21 7
POLARIZED
Fig.2
EE502.21 8
•This is known as electric dipole moment.
Fig.3
p = q d.
where q = charge on the nucleus (coulomb)
d = distance between the two centres (m)

EE502.21 9
• The atom in this state as said to be polarized.
• The electric field strength is increased, the degree of
polarizalation also increases. After attaining a
certain value of electric field, all the electric dipoles of
a dielectric material will align themselves.
EE502.21 10
A.C. supply
Fig.4
• The orientation of electric dipole will try to change
according to the electric field applied.
• Some of the energy applied direction of the will be waster

towards the inter atomic friction and is called the dielectric
loss. EE502.21 11
• The loss increases with increase in frequency and
strength of the electric field.
• Dielectric loss taking place in insulting material is
analogous to hysteresis loss.
• This loss takes place in a ferro magnetic material.
• Hence it is also known as dielectric hysteresis.
EE502.21 12
• As far as possible no air-gap should be left over
between the electrode and material to be heated.
• The dielectric strength of air is smaller than any dielectric
material.
• If voltage applied across the electrodes with air-gap
and dielectric, air gets ionized first and result into the break
EE502.21 13
down.
• Therefore, it is desirable in dielectric heating not to
apply high voltage but to use high frequencies.
Fig.5
EE502.21 14
• All dielectric materials can be represented by a
parallel combination of a leakage resistor ‘R’ and a
capacitor ‘C’.
Fig.6 EE502.21 15
• The total current I can be supposed to be made up of
two components IR and IC.
• The capacitive current IC leads V by 900.
• The leakage current IR is in phase with applied
voltage.
EE502.21 16
Derivation of electric loss
Dielectric loss = V I CosΦ
= VIR
= V Ic Tan 
= V [ V / xc ] Tan 
= V 2  c Tan  ( Tan   )
= 2πf x o r A x  / d watt.
VEE502.21
2 17
Where v = Applied voltage (Volt.)
f = Supply frequency (Hz).
o = Absolute permittivity
8.854 x 10-2 F/m.
r = Relative permittivity of the medium
= one for free – space.

EE502.21 18
A = Area of the plate or electrode (m2)
d = Thickness of dielectric medium or
distance between electrode (m).
 = Loss angle (radian).
r  = Loss factor.
The dielectric loss p = of equation can be written as
p α V2 and p α f.
EE502.21 19
• The use of high voltage is also limited due to break
down voltage of the thin dielectric which is to be
heated, safety conditions and corona.
• Under normal conditions, voltage gradient used is
limited to 18 KV/cm.
• The choice of frequency depends on the loss factor of
the dielectric.
EE502.21 20
• Higher frequencies are used for low loss factor
dielectric and vice-versa.
• Dielectrics having loss factor less than 0.05 are not
economical to be heated by this method.
• Usual frequency used for dielectric heating is the
range of 1 to 40 MHZ.
EE502.21 21
Applications of dielectric heating:
1. Drying tobacco, paper, wood and rayon.
2. Welding of PVC.
3. Stress annealing textile fibers.
4. Heating of bones and tissues.
5. Gluing and bonding of woods.
6. Sterilization of cereals and medical equipment.
7. Processing of rubber synthetic materials and

chemicals during manufacture.
EE502.21 22
Contd…
8. Heat-sealing of plastic resins.
9. Preparation of thermo plastic resins.
10.Sewing of rain coats, umbrellas made of plastic film

materials.
11.Diathermy treatment of certain body pains and

diseases etc.
EE502.21 23
Advantages of dielectric heating:
1. Heat is produced in the whole mass of the material.
2. Heating non-conducting materials is very speedy.
3. Uniform heating.
4. Materials heated by this method are combustible
which cannot be heated by flame.
EE502.21 24
SUMMARY
• We have discussed about dielectric heating
EE502.21 25
QUIZ
1.Dielectric loss is ____ proportional to tan 

a. Directly
b. Inversely
c. None of the above.
EE502.21 26
QUIZ
2.Loss factor is ______
a.  
b.  / 
c.  / 
EE502.21 27
FREQUENTLY ASKED QUESTIONS
1) What is dielectric heating ?
2) What are the ranges of voltage and frequencies used for

dielectric heating ?
3) Explain the process of dielectric heating.
4) List the applications of dielectric heating.
5) State the advantages of dielectric heating.

EE502.21 28

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RGMCET- NANDYAL.

Upon completion of this topic you would be able

• Application and Advantages of Dielectric heating

• When an insulating material is subjected to an alternating

electric field, the atoms get stressed and due to inter-atomic

friction caused by repeated deformation and rotation of

atomic structure heat is produced.

• This loss is known as dielectric loss.

and high voltage.

• High voltage at above 20KV and frequencies range of

order 10 to 30 Mega cycles per second are employed.

magnetic molecular friction which appears as heat.

• Electrically every atom is neutral, since the central positive

charge equals the surrounding negative charge.

• The centers of positive charge and negative charge are co-

incident as long as there is no external electrical field.

• The positive charge of nucleus is acted upon by some

force in the direction of the field.

• And negative charge in the opposite direction.

• The effective centers of positive and negative

charges are no longer coincident i.e., POLARIZED.

where q = charge on the nucleus (coulomb)

d = distance between the two centres (m)

• The electric field strength is increased, the degree of

polarizalation also increases. After attaining a

certain value of electric field, all the electric dipoles of

a dielectric material will align themselves.

• Some of the energy applied direction of the will be waster

strength of the electric field.

• Dielectric loss taking place in insulting material is

analogous to hysteresis loss.

• This loss takes place in a ferro magnetic material.

• Hence it is also known as dielectric hysteresis.

between the electrode and material to be heated.

• The dielectric strength of air is smaller than any dielectric

• If voltage applied across the electrodes with air-gap

apply high voltage but to use high frequencies.

parallel combination of a leakage resistor ‘R’ and a

two components IR and IC.

• The capacitive current IC leads V by 900.

• The leakage current IR is in phase with applied

Dielectric loss = V I CosΦ

f = Supply frequency (Hz).

8.854 x 10-2 F/m.

r = Relative permittivity of the medium

= one for free – space.

d = Thickness of dielectric medium or

distance between electrode (m).

 = Loss angle (radian).

The dielectric loss p = of equation can be written as

down voltage of the thin dielectric which is to be

heated, safety conditions and corona.

• Under normal conditions, voltage gradient used is

• The choice of frequency depends on the loss factor of

dielectric and vice-versa.

• Dielectrics having loss factor less than 0.05 are not

economical to be heated by this method.

• Usual frequency used for dielectric heating is the

1. Drying tobacco, paper, wood and rayon.