Effect of antioxidants on the performance of vegetable oils as liquid


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Effect of antioxidants on the performance of vegetable oils as liquid

  1. 1. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 2, March – April (2013), © IAEME393EFFECT OF ANTIOXIDANTS ON THE PERFORMANCE OFVEGETABLE OILS AS LIQUID DIELECTRICSV.Champa1, A.N.Nagashree1, S.Vasudevamurthy2, B.V.Sumangala2,G.R.Nagabhushana31Department of Electrical & Electronics, BMS College of Engineering, Bangalore2Department of Electrical & Electronics, Dr.Ambedkar Institute of Technology, Bangalore3Former Chairman,IISc,BangaloreABSTRACTMineral oil and silicone fluids are in extensive use as liquid dielectric coolants intransformers for over hundred years because of their relatively good thermal, physical anddielectric properties. But the poor biodegradability of mineral oil and sensitivity of siliconefluid 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, highflash point and bio-compatible nature, are gaining importance for use as dielectric coolants intransformers. A systematic study of vegetable oils such as Envirotemp and Biotemp based onSunflower and Soya bean oils respectively have been carried out in the recent past, which hasrevealed the possibility of using them for dielectric applications. The most importantparameters of the oil for this application are Breakdown Strength, Dissipation factor,Oxidation Stability and Permittivity. In the present work, two indigenously available naturalesters codenamed IO-18 and IO-19 are selected and various dielectric parameters likeDissipation Factor, Relative Permittivity and Breakdown Voltage are studied. Here an effortis made to obtain improved values of dissipation factor and permittivity by addingantioxidants. The effect of food grade additives /antioxidants such as BHT, TBHQ andPropyl 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 thetemperature range from room temperature to 90˚C before and after chemical treatment. Theoxidation stability of the samples was also studied and their suitability to be used as liquiddielectric 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.aspJournal Impact Factor (2013): 5.5028 (Calculated by GISI)www.jifactor.comIJEET© I A E M E
  2. 2. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 2, March – April (2013), © IAEME394Keywords: Antioxidants, Breakdown Voltage, Dissipation Factor, Liquid dielectrics,Relative Permittivity1. INTRODUCTIONDielectric 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 andalso acts as a coolant in the windings and core of a transformer. The important electricalproperties of a liquid dielectric are Breakdown Strength, Relative Permittivity andDissipation Factor. The physical properties are viscosity, flash point, thermal conductivityand oxidative stability. Other desirable important properties include high bio-degradability,material compatibility, eco-friendliness and non toxic nature and also easy availability with areasonable cost.The most commonly used fluids have been petroleum oils, silicone fluids. Thesematerials have certain drawbacks particularly with respect to environmental impact andbiodegradability. Mineral oil is derived from petroleum and hence non-renewable and hasbeen in wide use as dielectric liquid in power transformers [1]. This can be hazardous to thesurrounding 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 intransformers to utilize their higher working temperatures. Silicone fluids are biocompatiblebut not completely bio-degradable in case of any spill. Also they are very sensitive to coronaand hence degrade faster and are expensive too. These have prompted the search for a betterenvironmental friendly liquid. Though the drawback of the seed based dielectric fluids wastheir poor oxidation and high pour point [2] relative to mineral oil, recently there has beenrenewed interest in ester based dielectric fluids to overcome the disadvantages of those usedearlier.Natural esters (Vegetable oils) belong to a group of organic compounds. They arederived 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 electricalequipments. 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 safetyin operation, handling, storage and transportation of natural esters.(ii) Higher relative permittivity (approximately 3) and thus dielectric mismatch withpaper 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 about20% [5](iv) Reduced fire safety hazards, high flash point (above 300˚C) are comparable to orpossibly 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 constitutedby two different components: the losses related to conduction processes which arecontributed mainly by electronic and atomic polarization and those related to the polarization
  3. 3. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 2, March – April (2013), © IAEME395phenomena mainly due to oriental polarization. Natural esters being polar liquids have apermanent dipole moment resulting in oriental polarization on the application external fieldand contribute largely to dielectric losses though electronic and atomic polarization are alsopresent[6].2. NATURAL ESTERSOils are the triesters of glycerol with long chain fatty acids. Hence these are alsocalled triglycerides. Fatty acids are formed by the hydrolysis of oils and they are long chainaliphatic monocarboxylic acids. They are classified as saturated and unsaturated. Saturatedfatty acids have only carbon-carbon single bonds while the unsaturated fatty acids containeither one or more double or triple bonds in their molecules [7].Fig1. Formula for a triglycerideAll these ester oils have a triglyceride component of which many of the properties ofthe oil are based on the fatty acid content of the oil. Fig 1 shows the formula for atriglyceride. The R, R̕, and R̕̕ are organic groups (carbon, hydrogen, oxygen) consisting ofchains of eight to 22 carbons and are the fatty acid component. The unsaturated fatty acidsare Oleic acid, Linoleic acid and Linolenic acids. Table1 below shows the details.Table1: Unsaturated Fatty acids in oilsMore the number of double bonds in these fatty acids more will be the unsaturationand hence they are more prone to oxidation. Oils from vegetable origin undergo oxidation atthe position of unsaturation during use and polymerise to a plastic like consistency. Oxidationin oils occurs when heat, metals or other catalysts cause unsaturated oil molecules to convertto free radicals. These free radicals are easily oxidized to yield hydroperoxides and organiccompounds such as aldehydes, ketones or acids. Oxidation can be prevented by the additionof 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.ofdoublebondsOleicacidC17H33COOH CH3(CH2)7CH=CH(CH2)7COOH OneLinoleicacidC17H31COOH CH3(CH2)4CH=CHCH2CH=CH(CH2)7COOH TwoLinolenicacidC17H29COOH CH3CH2CH=CHCH2CH=CHCH2CH=CH(CH2)7COOH Three
  4. 4. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 2, March – April (2013), © IAEME3962.1 Antioxidant and its operationAntioxidant is a chemical agent which inhibits attack by oxygen. Antioxidants arecompounds which interrupt the oxidation process by preferentially reacting with the fatradical to form a stable radical which does not quickly react with oxygen. Antioxidantsfunction either by inhibiting the formation of free alkyl radicals in the initiation step or byinterrupting the propagation of the free radical chain [8]. Antioxidant activity involves thedonation of hydrogen to free radicals followed by the formation of a complex between a lipidradical and the antioxidant radical formed as a result of the hydrogen loss. Here theantioxidant radical functions as a free radical acceptor. The current accepted theory of therole of antioxidants as radical scavengers or hydro peroxide decomposers can be explained asoxidation 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 MechanismIn the case of vegetable oils, the RH represents an unsaturated fatty acid arm oftriacylglycerol with H attached to a carbon atom. At high temperatures, thermal initiation ispossible to give rise to free radicals in the first step. The free radicals thus generated reactwith 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 materialthat, at a particular point, becomes oil insoluble leading to oil thickening and deposits. Thissequence 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 butylatedhydroxyanisole (BHA), butylated hydroxytoluene (BHT), TBHQ and propyl gallate.Thenatural antioxidants tend to be short-lived, so synthetic antioxidants are used when a longershelf-life is preferred. Antioxidants commonly used in foods with one exception have twohydroxyl groups or one hydroxyl and one substituted hydroxyl group in ortho or parapositions. These compounds are effective at extremely low concentrations. Some loseeffectiveness as their concentration is increased [10].
  5. 5. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 2, March – April (2013), © IAEME3973.0 DISSIPATION FACTOR AND RELATIVE PERMITTIVITYThe losses in a dielectric are characterized at a certain frequency and temperature bythe “loss tangent” given by, tanδ = ε r ″/ ε r ′. In each second the material absorbs an amountof energy per m3given by ω/2(ε 0 ε r″ E02). The absorption of energy is proportional to theimaginary part of the complex dielectric constant and hence results in dielectric losses [11].3.1 Polarisation and its effect on Dissipation FactorThe relative permittivity is directly related to the electronic, ionic and orientalpolarization of the material. The electronic and ionic polarizations are induced by the appliedfield. The electronic polarization is caused due to the shifting of electron clouds relative torespective nuclei. The rearrangement of electrons when a molecule is formed from thecombination of atoms cause an imbalance in charge distribution and this results in apermanent dipole moment. In the absence of external field these dipole moments exist in arandom manner and hence no ploarisation exists. The ionic polarisation is caused when atomsin a molecule have an excess of positive or negative charge and the applied field tending toshift positive ions relative to negative ions. This leads to an induced moment of differentorigin. When an external field is applied to the molecule carrying a permanent dipole, it willtend to align the permanent dipole along the field since it exerts a torque on the dipole and itrotates. The direction of torque depends on the direction the field. The contribution of thisprocess of orientation of the permanent dipoles to the polarisation is called orientalpolarisation. Electronic and atomic polarization are temperature independent, but orientalpolarisation, depending on the extent to which the applied field can orient the permanentdipoles against the disordering effect of the thermal energy of their environment, variesinversely with absolute temperature. This results in energy loss in the dielectric which isnothing but dielectric loss and dissipation factor is a measure of dielectric loss.4. SAMPLE DETAILSIndigenously available oils codenamed as IO-18 and IO-19 are selected based onpreliminary experiments carried out on a number of indigenously available oils. The fattyacid composition of the samples considered for study is shown in the following Table3.Table 3. Fatty acid compositionSample Stearic Acid–C18H36O2(%)Linoleicacid-C18H32O2(%)Linolenicacid-C18H30O2(%)IO-18 1.83 5.92 26.36IO-19 5.49 2.4 37.5The composition of these fatty acids plays an important role on the dielectricproperties of the samples and hence the concentration of antioxidants to be added to thesamples under consideration. The presence of a higher linoleic and linolenic concentrationsresult in poor oxidation. But higher concentration of stearic acid results in a better oxidativestability.
  6. 6. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 2, March – April (2013), © IAEME3985. EXPERIMENTAL DETAILSDielectric properties such as Dissipation Factor, Relative Permittivity andBreakdown Voltage and Oxidative stability are studied for the selected samples IO-18 andIO-19 in ‘as received’ condition. The samples are subjected to chemical treatment likeneutralisation and addition of antioxidants such as BHT (Butylated Hydroxy Toluene),TBHQ (Tetra butyl hydro Quinine) and Propyl Gallate in different concentrations. The resultsthus obtained are compared with those of Mineral oil and Silicone fluid.5.1 Neutralisation of the sampleThe free fatty acids present in the ‘as received’ samples also contribute to higher lossfactor. This aspect is addressed by neutralizing the samples using NaOH and following thestandard procedures.RCOOH + NaOH → RCOONa + H2 O -------- (1)The antioxidants BHT, TBHQ and PG were added to the sample with 0.02%, 0.2% , 1% and2% by weight to study the effect of concentration on the dielectric properties of the sample[12].5.2 Measurement of Dissipation Factor and PermittivityDissipation factor and Permittivity were measured as per IS6262, IEC-60247 andASTM D-1169 standards using Eltel model-ADTR-2K Capacitance - Tan Delta Bridge. TanDelta and Relative Permittivity were measured when the temperature of the liquid dielectricwas varied from room temperature through 90˚C. Experiments were conducted to find thedissipation factor of both the samples in ‘as received’ condition. The experiments wererepeated after chemical treatment.5.3 Measurement of Oxidative StabilityOxidation Stability measurements were made by considering the sample under ‘as received’condition and after chemical treatment at a temperatures of120˚C.The Oxidation Stability ofthe samples was determined using Rancimat 743. The measuring standards were as perActive Oxygen Method, AOCS Cd 12B-92 and ISO 6886.5.4 Measurement of Viscosity–Viscosity was measured using Redwood Viscometer atdifferent temperatures from room temperature to 90˚C5.5 Measurement of Breakdown voltage: As per the standard IS 6792.6. RESULTS AND DISCUSSIONS6.1 Dissipation FactorIt is seen that the dissipation factor of both samples IO-18 and IO-19 increases withtemperature for all concentrations of the three additives. This is because the viscosity of theoil reduces which in turn increases the conductive losses and losses due to orientalpolarization.
  7. 7. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 2, March – April (2013), © IAEME399It 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 incomparison to that of mineral oil but slightly higher values compared to silicone fluidparticularly at higher temperatures. This is due to the fact that natural esters are polar liquidsand have higher values of dissipation factor compared to mineral oil and silicone oil. This canbe attributed to the disordering effect of the thermal energy on the dipoles. However, with anincrease in the TBHQ concentration to 2%, it is seen that the dissipation factor is increasedwhen compared to those for 1% concentration. It appears that TBHQ is showing improvedresults compared to BHT and Propyl Gallate for IO-18 particularly at higher temperatures.The operating temperature being much higher compared to the room temperature, allthe dielectric parameters like Dissipation Factor, Breakdown Voltage, Relative Permittivityand Oxidation Stability are studied at 60˚C. Therefore, the study of Dissipation Factor at60˚C is very significant to understand the dielectric behaviour. The values for both thesamples for different additive concentrations are shown in Table 4.20 30 40 50 60 70 80 90 1000. with TBHQDissipationnFactorTemperature(degC)IO-18(As recvd)IO-18+TBHQ0.02IO-18+TBHQ0.2IO-18+TBHQ1IO-18+TBHQ2Min OilSil Fld20 30 40 50 60 70 80 90 1000. with BHTDissipationFactorTemperature(degC)IO-18(As recvd)IO-18+BHT0.02IO-18+BHT0.2IO-18+BHT1IO-18+BHT2Min OilSil FldFig 2a. Dissipation Factor –IO-18 Fig2b. Dissipation Factor–IO-18with TBHQ with BHT20 30 40 50 60 70 80 90 1000. with Propyl GallateDissipationFactorTemperature(degC)IO-18(As recvd)IO-18+PG0.02IO-18+PG0.2IO-18+PG1Min OilSil FldFig 2c. Dissipation Factor –IO-18 with PG
  8. 8. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 2, March – April (2013), © IAEME400IO-19 has shown (Fig 3a, 3b and 3c) values comparable to or even better than those ofmineral oil with the additive TBHQ at all temperatures, though slightly higher whencompared to silicone oil particularly at higher temperatures. TBHQ has a more prominenteffect in reducing the value of dissipation factor in IO-19 than in the case of IO-18. FromTable 3 it seen that the stearic acid component which is a monounsaturated fatty acid ishigher 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 boththe 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 effectof antioxidants (for different concentrations) on the selected samples.20 30 40 50 60 70 80 90 1000. IO-19withTBHQDissipationFactorTemperature(degC)IO-19(Asrecvd)IO-19+TBHQ0.02IO-19+TBHQ0.2IO-19+TBHQ1IO-19+TBHQ2MinOilSilFld20 30 40 50 60 70 80 90 1000. FldIO-19withBHTDissipationFactorTemperature(degC)Fig 3a. Dissipation Factor IO-19 Fig3b. Dissipation Factor IO-19with TBHQ with BHT20 30 40 50 60 70 80 90 1000. IO-19with Propyl GallateDissipationFactorTemperature(degC)IO-19(As recvd)IO-19+PG0.02IO-19+PG0.2IO-19+PG1Min OilSil FldFig 3c. Dissipation Factor IO-19 with PG
  9. 9. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 2, March – April (2013), © IAEME401Table 4. Dissipation Factor at 60˚CFrom 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 anincrease 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 isa significant improvement in the values. Both the samples have shown dissipation valuesslightly increased with Propyl Gallate and it does not seem to have any effect for allconcentrations.6.2 Relative PermittivityRelative Permittivity value close to that of paper which ranges from 5 to 5.5 would bean added advantage. It is seen from the Fig4a and 4b that the relative permittivity of both thesamples 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 1000. with TBHQRelativePermittivityTemperature(degC)IO-18 (As recvd)IO-18+TBHQ1IO-18+TBHQ2Min OilSil Oil20 30 40 50 60 70 80 90 1000. with TBHQRelativePermittivityTemperature(degC)IO-19(As recvd)IO-19+TBHQ1IO-19+TBHQ2Min OilSil FldFig 4a. Relative Permittivity–IO-18 Fig 4b.Relative Permittivity–IO-19with TBHQ with TBHQSl.no Samples with additiveconcentrationsRange of DFAt 60˚C1. Mineral oil 0.00382. Silicone fluid 0.014363. IO-18i)‘as received’ii)BHT (0.02% - 1% - 2%)iii)TBHQ (0.02% - 1% - 2%)iv)PG (0.02% - 1%)0.0240.067- 0.035 - 0.0780.0557 - 0.027 - 0.04210.0339 - 0.13764. IO-19i)‘as received’ii)BHT (0.02% - 1% - 2%)iii)TBHQ (0.02% - 1% - 2%)iv)PG (0.02% - 1%)0.11070.0028 - 0.00313 - 0.00240.004 - 0.01256 - 0.009860.0076 - 0.0763
  10. 10. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 2, March – April (2013), © IAEME402From the results already discussed, it is seen that the additive TBHQ has given anenhanced effect on the dielectric properties earlier discussed for the samples IO-18 and IO-19when compared to other additives. With reference to this, the permittivity values of both sampleswith TBHQ in different concentrations is analysed below, though the measurements are carriedout for all additives in all concentrations.The increase in temperature has caused a slight reduction yet acceptable limits in thevalue of relative permittivity for both the samples because of reduction in viscosity which in turnincreases the oriental polarisation thus reducing the value of relative permittivity.6.3 ViscosityViscosity is the parameter indicating liquid flow and thereby heat conduction. Theviscosities have also been measured as a function of temperature. It is obvious that as temperatureincreases the viscosity reduces and at higher temperatures values are comparable to those ofmineral oil which ranges from 5centistokes to 0.01 centistokes.20 30 40 50 60 70 80 90 100-5051015202530Viscosity-IO-18Viscosity(cSt)Temperature(degC)IO-18(As recvd)IO-18+BHTIO-18+TBHQ30 40 50 60 70 80 90-10-50510152025Viscosity -IO-19Viscosity(cSt)Temperature(degC)I0-19(As recvd)IO-19+BHTIO-19+TBHQFig 5a. Viscosity IO-18 Fig 5b. Viscosity IO-19However, it is seen from figure 5a and 5b that the viscosities of both oils have reducedslightly with the addition of TBHQ though it is negligible. But it is to be noted that theantioxidants have not adversely affected the viscosity which is an important parameter as itcontributes to heat convection within the loaded transformer.6.4 Oxidation StabilityOxidation Stability, expressed in hours for ‘as received’ sample is around 6.5 to 6.9 hoursonly, whereas for mineral oil it is about 170 hours,. But with additives, there is a significantincrease in the Oxidation stability of IO-18 which has improved from 6.5 to 45.6 hours for anadditive concentration of TBHQ of 1% by weight. When the concentration is increased to 2%, itwas seen that oxidation stability increased to 100 hours which is very encouraging. Even thoughthe 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 oxidationstability, hence calls for further investigations.For the sample IO-19, the additives seem to have a significant impact on the oxidativestability which has increased from about 6.93 hours for the ‘as received’ sample to about 70 hourswith both 1% and 2% addition of TBHQ. But with the additive BHT, the stability does not seemto improve significantly for any of the concentrations though there is an increasing trend with amaximum of 20 hours. Evidently, there is a lot of scope for improvement in the oxidative stabilitywith the addition of antioxidants.
  11. 11. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 2, March – April (2013), © IAEME4036.5 Breakdown VoltageWith investigations carried out on the dissipation factor, relative permittivity,viscosity and oxidative stability, the additive TBHQ has given encouraging values of all theabove parameters when compared to those with the additives BHT and Propyl Gallate. Hencethe breakdown voltage of IO-18 and IO-19 was measured using standard procedure for all theconcentrations of TBHQ. It is observed from 6a that the sample IO-18 has shownimprovement in breakdown values for varying TBHQ concentration from 0.02% to 1%.10 20 30 40 50 60 70 80 900102030405060708090100IO-18 with TBHQBreakdownVoltage(kV)Temperature(degC)IO-18(As recvd)IO-18+TBHQ0.02IO-18+TBHQ0.2IO-18+TBHQ1IO-18+TBHQ2Min OilSil Fld20 30 40 50 60 70 80 90 1000102030405060708090100110120IO-19 with TBHQBreakdownVoltage(kV)Temperature(degC)O-19(As recvd)IO-19+TBHQ0.02IO-19+TBHQ0.2IO-19+TBHQ1IO-19+TBHQ2Min OilSil FldFig 6a. Breakdown Voltage of IO-18 Fig6b.BreakdownVoltage ofwith TBHQ IO-19 with TBHQFrom Fig 6b it seen that IO-19 has shown improved breakdown values whencompared to ‘as received’ sample. With an additive concentration of 1% of TBHQ inparticular, the sample has shown much improved values of breakdown voltages in the rangeof 65kV which is very consistent from room temperature to 90˚C.7. CONCLUSIONChemical treatment by adding antioxidants as additives to the selected samplesIO-18and 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 dissipationFactor with reduced values. This is a prominent trend indicating further improvementwith other concentrations.• The sample IO-18 has shown improved values of dissipation and also comparable tothat of mineral oil particularly for a 1% concentration of TBHQ• With the 2% concentration of additive BHT, IO-19 has shown very good DissipationFactor by reducing from 0.028 to 0.0024 (comparable with mineral oil) whereas withTBHQ, the sample has shown improved values except for a 1% concentration.• Breakdown voltage of the sample IO-19 has shown improvement (about 65kV) with1% TBHQ and is consistent for all the temperatures. Whereas IO-18 has shownmarginal improvement for higher concentrations.• Both the samples have given very promising Oxidation Stability values ranging from6 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 thesame direction.
  12. 12. International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 2, March – April (2013), © IAEME404REFERENCES[1] Oomen.T.V, “Vegetable Oil for Liquid Filled Transformers”, IEEE ElectricalInsulation Magazine, Vol. 18, No.1, 2002, pp. 6-11[2] C Patric Mc Shane “Vegetable Oil Based Dielectric Coolants”, IEEE industryapplications magazine, May-June 2002.[3] Stefan Tenbohlen, Member, IEEE, and Maik Koch “Aging Performance and MoistureSolubility of Vegetable Oils for Power Transformers”, IEEE transactions on PowerDelivery, Vol. 25, NO. 2, April 2010, pp 825-830[4] D. Martin, I. Khan, J. Dai & Z.D. Wang, “An Overview of the Suitability of VegetableOil Dielectrics for Use in Large Power Transformers”, Euro Tech Con 2006 pp 5-23[5] Md Amanullah, Syed M Islam, Samer Chami, S. Gary Ienco, “Analyses of electro-chemical characteristics of vegetable oils as an alternative source to mineral oil-baseddielectric fluid” Dielectric liquids.ICDL2005.IEEE International Conference on 26June-1 July 2005, pp 365 – 368[6] Z. H. Shah*and Q. A. Tahir, “ Dielectric Properties of Vegetable Oils”,Journal ofScientific Research,19thMay 2011[7] Endah yuliastuti , “Analysis of dielectric properties comparison between mineral oiland synthetic ester oil” ,MTech Thesis[8] Emmanuel.O.Aluyor et al.., “The Use of Antioxidants in Vegetable Oils-A Review”African Journal of Biotechnology Vol. 7 (25), ISSN 1684–5315, 29 December, 2008,pp 4836-4842[9] Brajendra.K.Sharma et al.., “Soybean Oil Based Lubricants: A search for SynergisticAntioxidants” Conference on Energy & Fuels Journal, American Chemical Society2007, pp 2408-2414[10] Rubalya Valantina .S. “Antioxidant Potential in Vegetable Oil”, Research Journal ofChemistry & Environment, Vol.16 (2) June 2012[11] A.J.Dekker, “Electrical Engineering Materials”, PHI Edition,2007[12] Ursula Biermann and Jürgen O. Metzger “Application of Vegetable Oil-Based Fluidsas Transformer Oil” Oleochemicals under Changing Global Conditiones,Hamburg, 25-27 February 2007[13] Ahmed Thabet and Youssef A. Mobarak, “Experimental Study for Dielectric Strengthof New Nanocomposite Polyethylene Industrial Materials”, International Journal ofElectrical Engineering & Technology (IJEET), Volume 3, Issue 1, 2012, pp. 353 - 364,ISSN Print : 0976-6545, ISSN Online: 0976-6553[14] Ahmed Thabet, “Experimental Investigation on Thermal Electric and DielectricCharacterization for Polypropylene Nanocomposites using Cost-Fewer Nanoparticles”,International Journal of Electrical Engineering & Technology (IJEET), Volume 4,Issue 2, 2012, pp. 1 - 12, ISSN Print : 0976-6545, ISSN Online: 0976-6553[15] Kailas M. Talkit and D.T.Mahajan, “Studies on Physicochemical Properties ofSoybean Oil and its Blends with Petroleum Oils”, International Journal of MechanicalEngineering & Technology (IJMET), Volume 3, Issue 2, 2012, pp. 511 - 517,ISSN Print: 0976 – 6340, ISSN Online: 0976 – 6359