This presentation describes the basics and technicalities of Dielectric Spectroscopy in both time and frequency domain. IT also includes the procedure and results involved in Dielectric Spectroscopy on different dielectrics.

1. Dielectric Spectroscopy in
Time and Frequency Domain
Term Paper Presentation
EE – 5232
High Voltage & Insulation Engineering

2. Presented by:
Girish Gupta
Roll no. 15082023
Power System
M. Tech
Vivek Kumar
Roll no. 15082020
Power System
M. Tech
Presented to:
Dr. J C Pandey,
Assistant Professor,
Department of Electrical Engineering,
IIT-BHU

3. CONTENTS
Need for Dielectric Spectroscopy
Why Dielectric Spectroscopy
Dielectric Response
What is Dielectric Spectroscopy
Frequency Domain Spectroscopy
Time Domain Spectroscopy
Results from Spectroscopy
Precautions

4.  Most dangerous breakdowns are caused by the aging
effects of HV insulation systems used within HV
components.
 Traditionally to avoid any damage to the equipments
Time Based Maintenance have been used which is
costly in nature.
 Now there is a move towards Condition Based
Maintenance which reduces the maintenance cost and
increases the life of the equipments.
 For CBM, the actual conditions of equipments must be
known.
 For knowing the actual conditions, Dielectric
Spectroscopy is used as a powerful tool.
1. NEED FOR DIELECTRIC SPECTROSCOPY

5.  Dielectric properties are dependent on many factors,
e.g. on frequency, time, temperature, chemical
composition of an individual dielectric, or on the
structure of an insulation system composed of
different dielectrics.
 Most of the above factors are measured and analyzed
using standardized test but they are performed at
power frequency only.
 The above quantities at single frequency is insufficient
to find changes is dielectric properties of materials.
 So Dielectric Spectroscopy is used.
2. WHY DIELECTRIC SPECTROSCOPY

6.  Every kind of insulation material consists, at an atomic
level, of negative and positive charges balancing each
other.
 When a material is exposed to an electric field the
positive and negative charges become oriented thus
forming different kinds of dipoles even on atomic
scales.
 These dipoles leads to Dipole Moment which can be
written as
P = α E
where α = Polarizability
E = applied Electric Field
P = Dipole Moment / Polarizability
3. DIELECTRIC RESPONSE

7.  Different types of Polarization are :-
a. Electron polarization - the displacement of nuclear and
electrons in the atom under the influence of external
electric field. It is effective up to optical frequencies and is
very fast.
b. Atomic polarization - the displacement of atoms or atom
groups in the molecule under the influence of external
electric field. It can be polarized up to Infra Red
frequencies.
c. Dipolar polarization – materials containing molecules
with permanent dipole moments with orientations
statistically distributed due to the action of thermal
energy. It follow frequency up to MHz or GHz.
d. Interfacial polarization – is effective in insulating
materials composed of different dielectric materials. It
occurs in Power frequency and below.

9.  In summary, the dielectric polarization is the result of
a relative shift of positive and negative charges in a
material.
 During all of these processes, the electric field is not
able to force the charges to escape from the material,
which would cause inherent electric conduction in
Dielectric or Insulator.
 For insulators Polarization P and electric field E is
related as
P = χ ε E
where χ = susceptibility ( relating to all process)
ε = permittivity of free space.

10.  Now usual sense says that when applied Electric field
should be made zero, Polarization should also become
zero i.e. Depolarization should happen.
 But in reality that do not happen. There is a delay in
the whole depolarization process which is known as
relaxation time.
 So longer the relaxation time, lesser the quality of
Insulator.
 Similarly there is polarization time also for a material.
 Dielectric Spectroscopy picks the above said points for
the analysis.
 Also as all dielectric quantities depends on
temperature also, it is also taken into account during
the process.

11.  Dielectric spectroscopy measures the dielectric
properties of a medium as a function of frequency
or time.
 It is also known as Impedance Spectroscopy or
Electrochemical Impedance Spectroscopy(EIS).
 It is based on the interaction of an external field with
the electric dipole moment of the sample, often
expressed by permittivity.
 This technique measures the impedance of a system
over a range of frequencies, and so the frequency
response of the system, including the energy storage
and dissipation properties, is revealed.
4. WHAT IS DIELECTRIC SPECTROSCOPY

12.  Often, data obtained by EIS is expressed
graphically in a Bode plot or a Nyquist plot. It can
also be expressed as logarithmic function of
frequency also.
 It is of two types:- Frequency Domain and Time
Domain.
 It is also an experimental method of characterizing
electrochemical systems.

13.  It includes the measurement of capacitance and
dissipation factor (tan delta) over a frequency range
of 0.1 mHz to 1 kHz.
 This technique can also be seen as the extension of
the measurement of the dissipation factor at the
power frequency.
 Also here Frequency response analyzers is used in
measuring dielectric permittivity's in the frequency
range 10-2 - 106 Hz.
5. FREQUENCY DOMAIN SPECTROSCOPY

14.  An a.c. voltage V1 is applied to the sample, and then
a resistor R, or alternatively a current-to-voltage
converter for low frequencies, converts the sample
current Is, into a voltage V2 .
 Taking an example of Transformer bushing, A
sinusoidal signal is applied to the high voltage
bushing and current is measured through the low
voltage terminal.

15.  If the applied voltage is an alternating signal at a
frequency w, then the measured capacitance is a
complex quantity and whose real and imaginary
parts correspond directly to the real and imaginary
components of the complex permittivity.
1 2 1 2
2
s
s
V V V V
Z R
I V
 
 

16.  Here the sample is represented by an equivalent
parallel plate capacitor.
 Here A is the plate area of the capacitance, C(w) is the
permittivity and w is the distance between two plates.
C’(w) corresponds to the ordinary capacitance,
while the imaginary component C’’(w) represents
the dielectric loss component.
 Now the dissipation factor from above eq. is
calculated as

17.  This factor is plotted as the function of frequencies
and the plotted over the Nyquist plot.
 On the basis of the readings taken, the graph is
plotted which can be seen here. Here is the plotting
of dissipation factor w.r.t. frequency for the samples.

18.  On the basis of the readings taken, the graph is
plotted which can be seen here. Here is the
plotting of capacitancew.r.t. frequency for the
samples.

19.  Here the measurement of polarization and
depolarization currents (PDC) following a dc voltage
step is done.
 It is made sure that voltage source free from any
ripple and noise is taken to measure the above
currents with sufficient accuracy.
 The procedure consists in applying a dc charging
voltage of certain magnitude to the test object for a
long time (e.g., 10,000 s).
 As each type of polarization have different time
periods from short to large, that’s why such a large
time is taken.
5. TIME DOMAIN SPECTROSCOPY

20.  As
P = χ ε E
and all the polarization are time dependent, the
susceptibility in the above eq. is treated as a function of
time to do the analysis.
 So for doing the analysis, a step voltage is applied to
the sample with the following arrangement:-

21.  Here DC supply upto 1000 volts can be used and
current is in picoamperes measured by
electrometers.
 In the above, Ipol is measured until it decays down to
zero or takes a steady state value of low magnitude
for considerable larger time.
 Now after the constant value of polarization current,
sample is short circuited to measure the
depolarization current.
 The same procedure is applied for the depolarization
current also so as to measure the time taken by the
sample to depolarize completely.

22.  The waveforms for the voltages and current is shown
as below: -
 The time period upto Tc and T is used to characterize
the dielectric properties of the material.
 Here the larger the value of the currents, the larger
the conductivity of the material so more worse it is.

23.  Many a times when the dielectric spectroscopy have
been used, certain conclusions have been found out
about the samples which are:-
 polarisation and depolarisation currents increase with
temperature increase.
 Both currents also increase with the moisture content
around the sample.
 temperature, ageing and water content caused a higher
increase of dissipation factor and capacitance at lower
frequencies.
5. RESULTS FROM SPECTROSCOPY

24.  The equipment in operation must be removed from
service before performing measurements using this
technique.
 Dielectric measurements require constant insulation
temperatures during application for accurateness, as
the polarization phenomena are temperature
dependent. So temperature must be kept constant
during the test.
 The charging time period should be large enough to
complete all the polarization and depolarization
technicques.
 Moisture content around sample should be controlled
and measured for getting precise data.
6. PRECAUTIONS

25.  Electromagnetic devices should be avoided at all cost
as it can disrupt the devices used.