Effect of antioxidants on the performance of vegetable oils as liquid

International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –
6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 2, March – April (2013), © IAEME
393
EFFECT OF ANTIOXIDANTS ON THE PERFORMANCE OF
VEGETABLE OILS AS LIQUID DIELECTRICS
V.Champa1
, A.N.Nagashree1
, S.Vasudevamurthy2
, B.V.Sumangala2
,
G.R.Nagabhushana3
1
Department of Electrical & Electronics, BMS College of Engineering, Bangalore
2
Department of Electrical & Electronics, Dr.Ambedkar Institute of Technology, Bangalore
3
Former Chairman,IISc,Bangalore
ABSTRACT
Mineral oil and silicone fluids are in extensive use as liquid dielectric coolants in
transformers for over hundred years because of their relatively good thermal, physical and
dielectric properties. But the poor biodegradability of mineral oil and sensitivity of silicone
fluid to corona, results in contamination of soil and water in the event of an accidental spill.
Natural ester based vegetable oils are better due to their renewability, biodegradability, high
flash point and bio-compatible nature, are gaining importance for use as dielectric coolants in
transformers. A systematic study of vegetable oils such as Envirotemp and Biotemp based on
Sunflower and Soya bean oils respectively have been carried out in the recent past, which has
revealed the possibility of using them for dielectric applications. The most important
parameters of the oil for this application are Breakdown Strength, Dissipation factor,
Oxidation Stability and Permittivity. In the present work, two indigenously available natural
esters codenamed IO-18 and IO-19 are selected and various dielectric parameters like
Dissipation Factor, Relative Permittivity and Breakdown Voltage are studied. Here an effort
is made to obtain improved values of dissipation factor and permittivity by adding
antioxidants. The effect of food grade additives /antioxidants such as BHT, TBHQ and
Propyl Gallate added in different concentrations to the selected natural esters IO-18 and IO-
19 is investigated. The Dissipation Factor and Relative Permittivity is analysed for the
temperature range from room temperature to 90˚C before and after chemical treatment. The
oxidation stability of the samples was also studied and their suitability to be used as liquid
dielectric coolants is assessed.
INTERNATIONAL JOURNAL OF ELECTRICAL ENGINEERING
& TECHNOLOGY (IJEET)
ISSN 0976 – 6545(Print)
ISSN 0976 – 6553(Online)
Volume 4, Issue 2, March – April (2013), pp. 393-404
© IAEME: www.iaeme.com/ijeet.asp
Journal Impact Factor (2013): 5.5028 (Calculated by GISI)
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IJEET
© I A E M E

394
Keywords: Antioxidants, Breakdown Voltage, Dissipation Factor, Liquid dielectrics,
Relative Permittivity
1. INTRODUCTION
Dielectric fluid used in electrical power transformers and switchgear plays a dual role.
It acts as an insulating medium between the energized parts of the electrical equipment and
also acts as a coolant in the windings and core of a transformer. The important electrical
properties of a liquid dielectric are Breakdown Strength, Relative Permittivity and
Dissipation Factor. The physical properties are viscosity, flash point, thermal conductivity
and oxidative stability. Other desirable important properties include high bio-degradability,
material compatibility, eco-friendliness and non toxic nature and also easy availability with a
reasonable cost.
The most commonly used fluids have been petroleum oils, silicone fluids. These
materials have certain drawbacks particularly with respect to environmental impact and
biodegradability. Mineral oil is derived from petroleum and hence non-renewable and has
been in wide use as dielectric liquid in power transformers [1]. This can be hazardous to the
surrounding environment in case of an accidental spill as it is not bio-degradable.
In some applications such as in air-borne and defence applications silicone fluids are used in
transformers to utilize their higher working temperatures. Silicone fluids are biocompatible
but not completely bio-degradable in case of any spill. Also they are very sensitive to corona
and hence degrade faster and are expensive too. These have prompted the search for a better
environmental friendly liquid. Though the drawback of the seed based dielectric fluids was
their poor oxidation and high pour point [2] relative to mineral oil, recently there has been
renewed interest in ester based dielectric fluids to overcome the disadvantages of those used
earlier.
Natural esters (Vegetable oils) belong to a group of organic compounds. They are
derived from plants and have renewable sources with supply as per consumer demand [3].
They are finding growing acceptance and application as a dielectric fluid in electrical
equipments. Natural esters are renewable and require simple apparatus for their extraction.
Other main advantages of natural esters are [2], [4].
(i) Excellent fire safety characteristics: High flash point, which ensures better safety
in operation, handling, storage and transportation of natural esters.
(ii) Higher relative permittivity (approximately 3) and thus dielectric mismatch with
paper is lower.
(iii) High bio-degradability (97%), whereas Mineral oil has only 30% bio-
degradability and high temperature mineral oils have much poorer bio-degradability about
20% [5]
(iv) Reduced fire safety hazards, high flash point (above 300˚C) are comparable to or
possibly better than silicone fluids and are environmental friendly.
1.1 Properties of concern to use vegetable oil as a liquid dielectric
• Higher Dissipation factor
• Lower oxidative stability [5].
The dielectric loss for insulating materials used in electrical equipment are constituted
by two different components: the losses related to conduction processes which are
contributed mainly by electronic and atomic polarization and those related to the polarization

395
phenomena mainly due to oriental polarization. Natural esters being polar liquids have a
permanent dipole moment resulting in oriental polarization on the application external field
and contribute largely to dielectric losses though electronic and atomic polarization are also
present[6].
2. NATURAL ESTERS
Oils are the triesters of glycerol with long chain fatty acids. Hence these are also
called triglycerides. Fatty acids are formed by the hydrolysis of oils and they are long chain
aliphatic monocarboxylic acids. They are classified as saturated and unsaturated. Saturated
fatty acids have only carbon-carbon single bonds while the unsaturated fatty acids contain
either one or more double or triple bonds in their molecules [7].
Fig1. Formula for a triglyceride
All these ester oils have a triglyceride component of which many of the properties of
the oil are based on the fatty acid content of the oil. Fig 1 shows the formula for a
triglyceride. The R, R̕, and R̕̕ are organic groups (carbon, hydrogen, oxygen) consisting of
chains of eight to 22 carbons and are the fatty acid component. The unsaturated fatty acids
are Oleic acid, Linoleic acid and Linolenic acids. Table1 below shows the details.
Table1: Unsaturated Fatty acids in oils
More the number of double bonds in these fatty acids more will be the unsaturation
and hence they are more prone to oxidation. Oils from vegetable origin undergo oxidation at
the position of unsaturation during use and polymerise to a plastic like consistency. Oxidation
in oils occurs when heat, metals or other catalysts cause unsaturated oil molecules to convert
to free radicals. These free radicals are easily oxidized to yield hydroperoxides and organic
compounds such as aldehydes, ketones or acids. Oxidation can be prevented by the addition
of antioxidants or food grade additives. They are added in very small concentrations 0.01-
1.5% to suppress oxidation. Phenolic derivatives like Butylated Hydroxyanisole (BHA),
TertButylHydroQuinone (TBHQ) and Propylgallate are used as antioxidants.
Name Formula Structural formula No.of
double
bonds
Oleic
acid
C17H33COOH CH3(CH2)7CH=CH(CH2)7COOH One
Linoleic
acid
C17H31COOH CH3(CH2)4CH=CHCH2CH=CH(CH2)7COOH Two
Linolenic
acid
C17H29COOH CH3CH2CH=CHCH2CH=CHCH2CH=CH(CH2)7COOH Three

396
2.1 Antioxidant and its operation
Antioxidant is a chemical agent which inhibits attack by oxygen. Antioxidants are
compounds which interrupt the oxidation process by preferentially reacting with the fat
radical to form a stable radical which does not quickly react with oxygen. Antioxidants
function either by inhibiting the formation of free alkyl radicals in the initiation step or by
interrupting the propagation of the free radical chain [8]. Antioxidant activity involves the
donation of hydrogen to free radicals followed by the formation of a complex between a lipid
radical and the antioxidant radical formed as a result of the hydrogen loss. Here the
antioxidant radical functions as a free radical acceptor. The current accepted theory of the
role of antioxidants as radical scavengers or hydro peroxide decomposers can be explained as
oxidation taking place through a radical-initiated chain mechanism involving: initiation,
propagation, branching, chain inhibition, and peroxide decomposition as shown in Table 2.
Table 2: Radical Initiated Chain Mechanism
In the case of vegetable oils, the RH represents an unsaturated fatty acid arm of
triacylglycerol with H attached to a carbon atom. At high temperatures, thermal initiation is
possible to give rise to free radicals in the first step. The free radicals thus generated react
with oxygen to form peroxy free radicals and hydro-peroxides in the chain propagation step.
As the oxidation proceeds, the oxygenated compounds polymerize to form viscous material
that, at a particular point, becomes oil insoluble leading to oil thickening and deposits. This
sequence of reactions is affected by pro-oxidants like metals and antioxidants [9].
Natural antioxidants include polyphenols (for instance flavonoids), ascorbic acid
(vitamin C) and tocopherols (vitamin E). Synthetic antioxidants include butylated
hydroxyanisole (BHA), butylated hydroxytoluene (BHT), TBHQ and propyl gallate.The
natural antioxidants tend to be short-lived, so synthetic antioxidants are used when a longer
shelf-life is preferred. Antioxidants commonly used in foods with one exception have two
hydroxyl groups or one hydroxyl and one substituted hydroxyl group in ortho or para
positions. These compounds are effective at extremely low concentrations. Some lose
effectiveness as their concentration is increased [10].

397
3.0 DISSIPATION FACTOR AND RELATIVE PERMITTIVITY
The losses in a dielectric are characterized at a certain frequency and temperature by
the “loss tangent” given by, tanδ = ε r ″/ ε r ′. In each second the material absorbs an amount
of energy per m3
given by ω/2(ε 0 ε r″ E0
2
). The absorption of energy is proportional to the
imaginary part of the complex dielectric constant and hence results in dielectric losses [11].
3.1 Polarisation and its effect on Dissipation Factor
The relative permittivity is directly related to the electronic, ionic and oriental
polarization of the material. The electronic and ionic polarizations are induced by the applied
field. The electronic polarization is caused due to the shifting of electron clouds relative to
respective nuclei. The rearrangement of electrons when a molecule is formed from the
combination of atoms cause an imbalance in charge distribution and this results in a
permanent dipole moment. In the absence of external field these dipole moments exist in a
random manner and hence no ploarisation exists. The ionic polarisation is caused when atoms
in a molecule have an excess of positive or negative charge and the applied field tending to
shift positive ions relative to negative ions. This leads to an induced moment of different
origin. When an external field is applied to the molecule carrying a permanent dipole, it will
tend to align the permanent dipole along the field since it exerts a torque on the dipole and it
rotates. The direction of torque depends on the direction the field. The contribution of this
process of orientation of the permanent dipoles to the polarisation is called oriental
polarisation. Electronic and atomic polarization are temperature independent, but oriental
polarisation, depending on the extent to which the applied field can orient the permanent
dipoles against the disordering effect of the thermal energy of their environment, varies
inversely with absolute temperature. This results in energy loss in the dielectric which is
nothing but dielectric loss and dissipation factor is a measure of dielectric loss.
4. SAMPLE DETAILS
Indigenously available oils codenamed as IO-18 and IO-19 are selected based on
preliminary experiments carried out on a number of indigenously available oils. The fatty
acid composition of the samples considered for study is shown in the following Table3.
Table 3. Fatty acid composition
Sample Stearic Acid
–C18H36O2
(%)
Linoleic
acid-
C18H32O2(%)
Linolenic
acid-
C18H30O2(%)
IO-18 1.83 5.92 26.36
IO-19 5.49 2.4 37.5
The composition of these fatty acids plays an important role on the dielectric
properties of the samples and hence the concentration of antioxidants to be added to the
samples under consideration. The presence of a higher linoleic and linolenic concentrations
result in poor oxidation. But higher concentration of stearic acid results in a better oxidative
stability.

398
5. EXPERIMENTAL DETAILS
Dielectric properties such as Dissipation Factor, Relative Permittivity and
Breakdown Voltage and Oxidative stability are studied for the selected samples IO-18 and
IO-19 in ‘as received’ condition. The samples are subjected to chemical treatment like
neutralisation and addition of antioxidants such as BHT (Butylated Hydroxy Toluene),
TBHQ (Tetra butyl hydro Quinine) and Propyl Gallate in different concentrations. The results
thus obtained are compared with those of Mineral oil and Silicone fluid.
5.1 Neutralisation of the sample
The free fatty acids present in the ‘as received’ samples also contribute to higher loss
factor. This aspect is addressed by neutralizing the samples using NaOH and following the
standard procedures.
RCOOH + NaOH → RCOONa + H2 O -------- (1)
The antioxidants BHT, TBHQ and PG were added to the sample with 0.02%, 0.2% , 1% and
2% by weight to study the effect of concentration on the dielectric properties of the sample
[12].
5.2 Measurement of Dissipation Factor and Permittivity
Dissipation factor and Permittivity were measured as per IS6262, IEC-60247 and
ASTM D-1169 standards using Eltel model-ADTR-2K Capacitance - Tan Delta Bridge. Tan
Delta and Relative Permittivity were measured when the temperature of the liquid dielectric
was varied from room temperature through 90˚C. Experiments were conducted to find the
dissipation factor of both the samples in ‘as received’ condition. The experiments were
repeated after chemical treatment.
5.3 Measurement of Oxidative Stability
Oxidation Stability measurements were made by considering the sample under ‘as received’
condition and after chemical treatment at a temperatures of120˚C.The Oxidation Stability of
the samples was determined using Rancimat 743. The measuring standards were as per
Active Oxygen Method, AOCS Cd 12B-92 and ISO 6886.
5.4 Measurement of Viscosity–Viscosity was measured using Redwood Viscometer at
different temperatures from room temperature to 90˚C
5.5 Measurement of Breakdown voltage: As per the standard IS 6792.
6. RESULTS AND DISCUSSIONS
6.1 Dissipation Factor
It is seen that the dissipation factor of both samples IO-18 and IO-19 increases with
temperature for all concentrations of the three additives. This is because the viscosity of the
oil reduces which in turn increases the conductive losses and losses due to oriental
polarization.

399
It is observed from the results that with 1% concentrations of the additive TBHQ,
dissipation factor of IO-18 (Fig 2a, 2b and 2c) has remarkably reduced and very much in
comparison to that of mineral oil but slightly higher values compared to silicone fluid
particularly at higher temperatures. This is due to the fact that natural esters are polar liquids
and have higher values of dissipation factor compared to mineral oil and silicone oil. This can
be attributed to the disordering effect of the thermal energy on the dipoles. However, with an
increase in the TBHQ concentration to 2%, it is seen that the dissipation factor is increased
when compared to those for 1% concentration. It appears that TBHQ is showing improved
results compared to BHT and Propyl Gallate for IO-18 particularly at higher temperatures.
The operating temperature being much higher compared to the room temperature, all
the dielectric parameters like Dissipation Factor, Breakdown Voltage, Relative Permittivity
and Oxidation Stability are studied at 60˚C. Therefore, the study of Dissipation Factor at
60˚C is very significant to understand the dielectric behaviour. The values for both the
samples for different additive concentrations are shown in Table 4.
20 30 40 50 60 70 80 90 100
0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
0.16
0.18
IO-18 with TBHQ
DissipationnFactor
Temperature(degC)
IO-18(As recvd)
IO-18+TBHQ0.02
IO-18+TBHQ0.2
IO-18+TBHQ1
IO-18+TBHQ2
Min Oil
Sil Fld
20 30 40 50 60 70 80 90 100
0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
0.16
0.18
IO-18 with BHTDissipationFactor
Temperature(degC)
IO-18(As recvd)
IO-18+BHT0.02
IO-18+BHT0.2
IO-18+BHT1
IO-18+BHT2
Min Oil
Sil Fld
Fig 2a. Dissipation Factor –IO-18 Fig2b. Dissipation Factor–IO-18
with TBHQ with BHT
20 30 40 50 60 70 80 90 100
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
IO-18 with Propyl Gallate
DissipationFactor
Temperature(degC)
IO-18(As recvd)
IO-18+PG0.02
IO-18+PG0.2
IO-18+PG1
Min Oil
Sil Fld
Fig 2c. Dissipation Factor –IO-18 with PG

400
IO-19 has shown (Fig 3a, 3b and 3c) values comparable to or even better than those of
mineral oil with the additive TBHQ at all temperatures, though slightly higher when
compared to silicone oil particularly at higher temperatures. TBHQ has a more prominent
effect in reducing the value of dissipation factor in IO-19 than in the case of IO-18. From
Table 3 it seen that the stearic acid component which is a monounsaturated fatty acid is
higher in IO-19 than in IO-18 which contributes less to dissipation at higher temperatures.
The additive BHT has given better values of dissipation factor for all concentrations.
However, Propyl Gallate has not contributed much to reduction of dissipation factor for both
the oils though it has shown slight improvement at very low concentrations. With TBHQ,
both the oils are showing very good results and further encouraging to investigate the effect
of antioxidants (for different concentrations) on the selected samples.
20 30 40 50 60 70 80 90 100
0.00
0.05
0.10
0.15
0.20
0.25
0.30 IO-19withTBHQ
DissipationFactor
Temperature(degC)
IO-19(Asrecvd)
IO-19+TBHQ0.02
IO-19+TBHQ0.2
IO-19+TBHQ1
IO-19+TBHQ2
MinOil
SilFld
20 30 40 50 60 70 80 90 100
0.00
0.05
0.10
0.15
0.20
0.25
0.30
IO-19(Asrecvd)
IO-19+BHT0.02
IO-19+BHT0.2
IO-19+BHT1
IO-19+BHT2
MinOil
Sil Fld
IO-19withBHT
DissipationFactor
Temperature(degC)
Fig 3a. Dissipation Factor IO-19 Fig3b. Dissipation Factor IO-19
with TBHQ with BHT
20 30 40 50 60 70 80 90 100
0.00
0.05
0.10
0.15
0.20
0.25
0.30 IO-19with Propyl Gallate
DissipationFactor
Temperature(degC)
IO-19(As recvd)
IO-19+PG0.02
IO-19+PG0.2
IO-19+PG1
Min Oil
Sil Fld
Fig 3c. Dissipation Factor IO-19 with PG

401
Table 4. Dissipation Factor at 60˚C
From the Table 4, it is observed that the dissipation factor of IO-18 is minimum with 1%
BHT concentration and 1% TBHQ concentration. There is a continuous improvement with an
increase in concentration of BHT. IO-19 has a minimum value of dissipation factor with 2%
BHT concentration and 0.02% TBHQ. But when compared to the as received sample, there is
a significant improvement in the values. Both the samples have shown dissipation values
slightly increased with Propyl Gallate and it does not seem to have any effect for all
concentrations.
6.2 Relative Permittivity
Relative Permittivity value close to that of paper which ranges from 5 to 5.5 would be
an added advantage. It is seen from the Fig4a and 4b that the relative permittivity of both the
samples IO-18 and IO-19 in the as received condition is in the range 3.1 to 2.85.
20 30 40 50 60 70 80 90 100
0.0
0.5
1.0
1.5
2.0
2.5
3.0
IO-18 with TBHQ
RelativePermittivity
Temperature(degC)
IO-18 (As recvd)
IO-18+TBHQ1
IO-18+TBHQ2
Min Oil
Sil Oil
20 30 40 50 60 70 80 90 100
0.0
0.5
1.0
1.5
2.0
2.5
3.0
IO-19 with TBHQ
RelativePermittivity
Temperature(degC)
IO-19(As recvd)
IO-19+TBHQ1
IO-19+TBHQ2
Min Oil
Sil Fld
Fig 4a. Relative Permittivity–IO-18 Fig 4b.Relative Permittivity–IO-19
with TBHQ with TBHQ
Sl.no Samples with additive
concentrations
Range of DF
At 60˚C
1. Mineral oil 0.0038
2. Silicone fluid 0.01436
3. IO-18
i)‘as received’
ii)BHT (0.02% - 1% - 2%)
iii)TBHQ (0.02% - 1% - 2%)
iv)PG (0.02% - 1%)
0.024
0.067- 0.035 - 0.078
0.0557 - 0.027 - 0.0421
0.0339 - 0.1376
4. IO-19
i)‘as received’
ii)BHT (0.02% - 1% - 2%)
iii)TBHQ (0.02% - 1% - 2%)
iv)PG (0.02% - 1%)
0.1107
0.0028 - 0.00313 - 0.0024
0.004 - 0.01256 - 0.00986
0.0076 - 0.0763

402
From the results already discussed, it is seen that the additive TBHQ has given an
enhanced effect on the dielectric properties earlier discussed for the samples IO-18 and IO-19
when compared to other additives. With reference to this, the permittivity values of both samples
with TBHQ in different concentrations is analysed below, though the measurements are carried
out for all additives in all concentrations.
The increase in temperature has caused a slight reduction yet acceptable limits in the
value of relative permittivity for both the samples because of reduction in viscosity which in turn
increases the oriental polarisation thus reducing the value of relative permittivity.
6.3 Viscosity
Viscosity is the parameter indicating liquid flow and thereby heat conduction. The
viscosities have also been measured as a function of temperature. It is obvious that as temperature
increases the viscosity reduces and at higher temperatures values are comparable to those of
mineral oil which ranges from 5centistokes to 0.01 centistokes.
20 30 40 50 60 70 80 90 100
-5
0
5
10
15
20
25
30
Viscosity-IO-18
Viscosity(cSt)
Temperature(degC)
IO-18(As recvd)
IO-18+BHT
IO-18+TBHQ
30 40 50 60 70 80 90
-10
-5
0
5
10
15
20
25
Viscosity -IO-19
Viscosity(cSt)
Temperature(degC)
I0-19(As recvd)
IO-19+BHT
IO-19+TBHQ
Fig 5a. Viscosity IO-18 Fig 5b. Viscosity IO-19
However, it is seen from figure 5a and 5b that the viscosities of both oils have reduced
slightly with the addition of TBHQ though it is negligible. But it is to be noted that the
antioxidants have not adversely affected the viscosity which is an important parameter as it
contributes to heat convection within the loaded transformer.
6.4 Oxidation Stability
Oxidation Stability, expressed in hours for ‘as received’ sample is around 6.5 to 6.9 hours
only, whereas for mineral oil it is about 170 hours,. But with additives, there is a significant
increase in the Oxidation stability of IO-18 which has improved from 6.5 to 45.6 hours for an
additive concentration of TBHQ of 1% by weight. When the concentration is increased to 2%, it
was seen that oxidation stability increased to 100 hours which is very encouraging. Even though
the increase in concentration of the antioxidant BHT in the range of 0.02%, 0.2%, 1% and 2%
each by weight do not have much effect, there is an increasing trend seen in the oxidation
stability, hence calls for further investigations.
For the sample IO-19, the additives seem to have a significant impact on the oxidative
stability which has increased from about 6.93 hours for the ‘as received’ sample to about 70 hours
with both 1% and 2% addition of TBHQ. But with the additive BHT, the stability does not seem
to improve significantly for any of the concentrations though there is an increasing trend with a
maximum of 20 hours. Evidently, there is a lot of scope for improvement in the oxidative stability
with the addition of antioxidants.

403
6.5 Breakdown Voltage
With investigations carried out on the dissipation factor, relative permittivity,
viscosity and oxidative stability, the additive TBHQ has given encouraging values of all the
above parameters when compared to those with the additives BHT and Propyl Gallate. Hence
the breakdown voltage of IO-18 and IO-19 was measured using standard procedure for all the
concentrations of TBHQ. It is observed from 6a that the sample IO-18 has shown
improvement in breakdown values for varying TBHQ concentration from 0.02% to 1%.
10 20 30 40 50 60 70 80 90
0
10
20
30
40
50
60
70
80
90
100
IO-18 with TBHQ
BreakdownVoltage(kV)
Temperature(degC)
IO-18(As recvd)
IO-18+TBHQ0.02
IO-18+TBHQ0.2
IO-18+TBHQ1
IO-18+TBHQ2
Min Oil
Sil Fld
20 30 40 50 60 70 80 90 100
0
10
20
30
40
50
60
70
80
90
100
110
120
IO-19 with TBHQ
BreakdownVoltage(kV)
Temperature(degC)
O-19(As recvd)
IO-19+TBHQ0.02
IO-19+TBHQ0.2
IO-19+TBHQ1
IO-19+TBHQ2
Min Oil
Sil Fld
Fig 6a. Breakdown Voltage of IO-18 Fig6b.BreakdownVoltage of
with TBHQ IO-19 with TBHQ
From Fig 6b it seen that IO-19 has shown improved breakdown values when
compared to ‘as received’ sample. With an additive concentration of 1% of TBHQ in
particular, the sample has shown much improved values of breakdown voltages in the range
of 65kV which is very consistent from room temperature to 90˚C.
7. CONCLUSION
Chemical treatment by adding antioxidants as additives to the selected samplesIO-18
and IO-19 have shown improvement in the dielectric properties such as Dissipation Factor,
Breakdown Voltage and Oxidation Stability hence the conclusions are as follows:
• Variation in additive concentration has shown significant improvement in dissipation
Factor with reduced values. This is a prominent trend indicating further improvement
with other concentrations.
• The sample IO-18 has shown improved values of dissipation and also comparable to
that of mineral oil particularly for a 1% concentration of TBHQ
• With the 2% concentration of additive BHT, IO-19 has shown very good Dissipation
Factor by reducing from 0.028 to 0.0024 (comparable with mineral oil) whereas with
TBHQ, the sample has shown improved values except for a 1% concentration.
• Breakdown voltage of the sample IO-19 has shown improvement (about 65kV) with
1% TBHQ and is consistent for all the temperatures. Whereas IO-18 has shown
marginal improvement for higher concentrations.
• Both the samples have given very promising Oxidation Stability values ranging from
6 hours for as received condition to nearly 100 hours for varying concentrations.
On the whole, the results are encouraging and calls for further investigations in the
same direction.

404
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