Comparison of Physical Characteristics between Vegetable

Comparison of Physical Characteristics between Vegetable and Mineral Oils

Punyavee Chaisiri1, Anantawat Kunakorn1, Thanakorn Penthong2, Peerawut Yutthagowith1, Bunloet Mekloy1

1 Electrical Engineering Department, Faculty of Engineering, King Mongkut’s Institute of Technology Ladkrabang, Bangkok, Thailand.

2 Power System Control Division, Provincial Electricity Authority, Ngamwongwarn, Bangkok, Thailand.

Abstract This paper presents physical characteristics of vegetable oils which are commercial products. The vegetable oils under consideration in this work are comprised of sunflower oil and rice bran oil. The characteristics of the vegetable oils are found by testing and they are compared with that of the mineral oil according to IEC and ASTM standard. The results show that physical characteristics of the two vegetable oil types, it is found that the vegetable oils under test have satisfactory characteristics comparable with the mineral oil. Therefore, it has high possibility that those vegetable oils can be used for electrical insulation of electrical machines.

1 INTRODUCTION

The coming of global oil crisis also affects the price of the mineral oil which is refined from petroleum oil. Mineral oil is well known as an insulating materials and arc quenching medium in electrical power equipment [1, 2]. Liquid dielectrics are mainly employed as impregnates in high voltage equipment. The petroleum based oils are commonly used in the transformers are electric insulation and a coolant for heat dissipation. These materials can be mineral oils, synthetic hydrocarbon, silicone and ester. All of these liquid materials have been proved as an efficient medium in the transformer insulating system. However due to environment concern, there have been plenty of attempts to develop products from the nature, in particle vegetables, in order to be the electrical insulating materials [2-6] In addition, it has been found that the distribution transformer with vegetable oils has benefits in the longer useful life and lower failure rates due to overload condition [7].

Especially in Thailand, we have a little resource of natural gas and almost no oil resource but we have a lot of agriculture products. Therefore, the study of oil produced from vegetable for replacing the mineral oil is one of the best solutions in Thailand. The main propose of the vegetable oils in Thailand is for cooking, and some applications in bio-fuels.

In the past of research [8], it was presented dielectric characteristics of vegetable oils. Two types of vegetable oils are sunflower oil and rice bran oil to be a good trend to study of other properties.

This paper provides a comparison of physical characteristics between commercial vegetable oils and insulated mineral oil.

2 VEGETABLE OILS

Vegetable oils are the natural products. The vegetable oils are mostly produced by the fatty acid in vegetable seed [1-7]. In Thailand, there are two types of popular oils, which are sunflower oil and rice bran oil. These oils contain unsaturated fatty acid. The samples of these two commercial vegetable oils are show in figure 1.

(a) (b)Figure 1: Sample of vegetable oils used in experiments, (a) the sunflower oil and b) rice bran oil).

3. EXPERIMENTS AND TEST RESULTS

Experiments in this paper are carried out according to international standards and can be separated in two parts. The first part is experiments for evaluation of physical characteristics and the second part is an aged test by simulated PD.

3.1 Physical Characteristics3.1.1 AC Dielectric Breakdown Voltage Test

The purpose of the AC dielectric breakdown voltage test is to determine the breakdown voltage of the insulating material. The AC dielectric breakdown voltage test of the two vegetable oils samples were performed according to IEC 156 [9]. The automatic tester for liquid insulating material was employed. The equipments are shown in Figure 2 and 3.

XVII International Symposium on High Voltage Engineering, Hannover, Germany, August 22-26, 2011

Figure 2: Dielectric breakdown voltage test unit

Figure 3: Electrodes and test cell

The results shown in Figure 4 are the dielectric breakdown voltage of the two compared with a mineral oil. The breakdown voltages were recorded automatically from the tester unit. It is found that the sunflower oil gives the highest AC withstand voltage more than others.

Figure 4: AC dielectric breakdown voltages of the vegetable oils compared with of the insulated mineral oil.

3.1.2 Dielectric loss test (Tan)Dielectric loss factor or dielectric dissipation

loss factor is an important indicator for the quality of the electrical insulation since the factor represents the level of loss in the insulation. For liquid insulating materials, the dielectric loss factor is also relevant to the contaminants quantity such as water in the insulation [1, 2]. It is well know that the dielectric loss factor is measured in the term of tan delta. The dielectric loss tests of the two vegetables oil samples were performed according to ASTM D924-03A [10]. During the tests, the temperature of the oils was controlled at 30 100 oc. The equipments used in the experiments are shown in Figure 5. Figure 6 shows the test results of the tan delta of the oils. The dielectric loss of the insulating materials is caused by the

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Mineral oil Sunflower oil Rice bran oil

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Dielectric breakdown voltage test unit

The results shown in Figure 4 are the two oil samples

compared with a mineral oil. The breakdown voltages were recorded automatically from the tester unit. It is found that the sunflower oil gives the highest AC withstand voltage more than

: AC dielectric breakdown voltages of the the insulated

factor or dielectric dissipation loss factor is an important indicator for the quality

l insulation since the factor represents the level of loss in the insulation. For liquid insulating materials, the dielectric loss factor is also relevant to the contaminants quantity such as water in the insulation [1, 2]. It is well know that

ric loss factor is measured in the term of tan delta. The dielectric loss tests of the two vegetables oil samples were performed according

. During the tests, the temperature of the oils was controlled at 30 oc and

The equipments used in the experiments are shown in Figure 5. Figure 6 shows the test results of the tan delta of the oils. The dielectric loss of the insulating materials is caused by the

presence on conductive current, and regarded to be proportional with the tan delta value. Hence, the sunflower oil has the lowest dielectric loss among the vegetable oils used in the experiments. It is found that the sunflower oil has the same value of tan delta as that of mineral oil.

Figure 5: Equipments for loss factor test

Figure 6: Tan delta result.

3.1.3 Permittivity measurementThe result shown in Figure

permittivity of the vegetable oils. All vegetable oils have similar relative permittivity.

Figure 7: Relative permittivity of the vegetable oils compared with of the insulated mineral oil.

3.1.4 Impulse Voltage Withstand TestsDuring the operation of the transformer,

there are possibilities for the transformer to be under the electric stress caused by tvoltages, which are generated by switching operations of switchgears and lightning. the electrical insulation material in the transformer, must withstand the over voltages at the

Rice bran oil

25.8 kV -

0.005

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Mineral oil Sunflower oil

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presence on conductive current, and regarded to h the tan delta value. Hence, the

sunflower oil has the lowest dielectric loss among the vegetable oils used in the experiments. It is found that the sunflower oil has the same value of

factor test.

shown in Figure 7 is the relative permittivity of the vegetable oils. All vegetable oils

Relative permittivity of the vegetable oils compared with of the insulated mineral oil.

Impulse Voltage Withstand TestsDuring the operation of the transformer,

there are possibilities for the transformer to be under the electric stress caused by transient over-

are generated by switching operations of switchgears and lightning. Therefore,

in the transformer, must withstand the over voltages at the suggested

Rice bran oil

0.003

0.015

0.025 100 oC

Rice bran oil

3.14


level. The overvoltage withstand of electrical power equipments are tested by subjecting impulse voltages. The impulse voltage withstands tests of the two vegetable oil samples were performed according to ASTM D3300-00 [11]. The impulsevoltages with negative polarity were applied to the test cell, and the breakdown voltage wasThe testing arrangement and a test cell in Figure 8 and 9

Figure 8: Impulse voltage test arrangement

Figure 9: Test cell for oil insulating materials

The results of the breakdown voltages shown in Figure 10 are the average values, and it is found that the polarities of the impulse waveforms have an effect on the breakdown voltage of the vegetable oils. The sun flower oil has the highest impulse voltage withstandComparing with the standard impulse breakdown voltage of the transformer oil, the vegetable oils reveal inferior properties in withstanding voltage. It should be noted that all experiments were conducted with the surrounding temperatures of 27oc-30oc, the humidity of 73-77 pressure of 763 mm.Hg.

Figure 10: Impulse breakdown voltage of the oils under test.

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110.3 kV 107.4 kV

overvoltage withstand of electrical power by subjecting impulse

. The impulse voltage withstands tests of the two vegetable oil samples were performed

The impulseapplied to the

voltage was recorded. The testing arrangement and a test cell are shown

Impulse voltage test arrangement

Test cell for oil insulating materials

breakdown voltages are the average values, and it

is found that the polarities of the impulse waveforms have an effect on the breakdown

The sun flower oil ghest impulse voltage withstand.

paring with the standard impulse breakdown voltage of the transformer oil, the vegetable oils

perties in withstanding voltage. It should be noted that all experiments were conducted with the surrounding temperatures of

and the air

Impulse breakdown voltage of the oils

3.1.5 Acid Number TestThe purpose of the acid number test is to

determine the acid number of the liquid insulating material. High acidities accelerate the degradation of the paper insulation and causes corrosion of the steel tanks. The acid number of the oil samples was measured by titration with a KOH solution in according to ASTM D974(Molarity, M = 0.03). The automatic tester for liquid insulating material was employed. The equipments are show in Figure 11.

Figure 11: Acid number test unit

The results shown in Figure 12number of two types of oils compared with a mineral oil. The acid numberautomatically from the tester unit. It is found that the vegetable oils are gives the acid number less than the mineral oil.

Figure 12: Acid numbers of the oils under test.

3.1.6 Interfacial Tension Test (IFT)Interfacial tension test (IFT)

evaluate the property of liquid insulation. The interfacial tension of the liquid insulation should be keep low for preventing sludgeinsulation. The interfacial tension tesvegetable oil samples were performed according to ASTM D971 [13]. The automatic tester for liquid insulating material was employed. The equipments are show in Figure 13.

Rice bran oil

107.4 kV

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0.06 mgKOH/g

0.036 mgKOH/g

acid number test is to determine the acid number of the liquid insulating

acidities accelerate the degradation of the paper insulation and causes corrosion of the

of the two vegetable measured by titration with a KOH

ASTM D974-04 [12]The automatic tester for liquid

insulating material was employed. The equipments

The results shown in Figure 12 are the acid compared with a

umber was recorded automatically from the tester unit. It is found that the vegetable oils are gives the acid number less

the oils under test.

(IFT)(IFT) is a tool to

evaluate the property of liquid insulation. The interfacial tension of the liquid insulation should be

sludge on the soild The interfacial tension tests of the two

ormed according to The automatic tester for liquid

insulating material was employed. The equipments

Rice bran oil

0.039 mgKOH/g


Figure 13: Interfacial tension test unit

The results shown in Figure interfacial tension of two types of oilswith a mineral oil. The interfacial tension wasrecorded from the tester unit. It is found that the rice bran oil has the lowest interfacial tensionthe both of vegetable oils have the interfacial tension less than the mineral oil.

Figure 14: Interfacial tension test results

3.1.7 Moisture ContentThe moisture content is used t

the water in the liquid insulating material.may be introduced to the oil by leaking gaskets, poor handling techniques or from thenatural insulating paper and oil degradation. Water is a polar liquid having a high permittivity or dielectric constant. It is therefore attracted to areas of strong electric fields. Thus, the internal moistureis not uniformly distributed, but in fact potentially concentrating in the most dangerous parts of the system. If oil is oxidized to any extent, any water coming into the transformer will partially beabsorbed into the oil decay productsmoisture content tests of the two vegetable oil samples were performed according to ASTM D1533 [15]. The moisture content of an oil samples is measured using an automatic Karl Fischer Coulometric Titration. The equipments are showin Figure 15.

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30 mN/m28.3 mN/m

12.2 mN/m

The results shown in Figure 14 are the of oils compared

The interfacial tension wasrecorded from the tester unit. It is found that the

lowest interfacial tension and the both of vegetable oils have the interfacial

Interfacial tension test results

o determine the water in the liquid insulating material. Water may be introduced to the oil by leaking gaskets,

the product of egradation. Water

is a polar liquid having a high permittivity or attracted to areas

the internal moisturein fact potentially

concentrating in the most dangerous parts of the If oil is oxidized to any extent, any water

coming into the transformer will partially beabsorbed into the oil decay products [14]. The

vegetable oil samples were performed according to ASTM

The moisture content of an oil samples is measured using an automatic Karl Fischer

The equipments are shown

Figure 15: Moisture content test unit

The results shown in Figure 16 are the moisture content of two samples compared with a mineral oil. The moisture content from the tester unit. It is found that the sunflower oil and rice bran oil gives the highest content more than the mineral oil.

Figure 16: Moisture content test results

3.2 Aged Test by Simulated PD

3.2.1 The preliminary testThe preliminary test is a

voltage test with varied temperaturesamples from 20 to 90 degree Celsius. The test cell is according to IEC 156 distance varied from 2.5 to 10 mm.arrangement and test cell in the testFigure 16.

Figure 17: Breakdown voltage test arrangement

Rice bran oil

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20.25 ppm.

546.5 ppm.

Moisture content test unit

The results shown in Figure 16 are the of two samples compared with a moisture content was recorded

from the tester unit. It is found that the sunflower oil and rice bran oil gives the highest moisture

he mineral oil.

Moisture content test results

3.2 Aged Test by Simulated PD

The preliminary test is an AC breakdown voltage test with varied temperature of the two oil

from 20 to 90 degree Celsius. The test 156 [9] but the gap

10 mm. The test t and test cell in the tests are shown in

Breakdown voltage test arrangement

Rice bran oil

668.7 ppm.


Figure 18: Test cell for breakdown voltage test

The results of breakdown voltage under gap spacing and temperature differencemineral oil, sunflower oil and rice bran oil shown in Figure 19, 20 and 21. The voltages are increased when gap spacing and temperature are increased.

Figure 19: The result of breakdown voltage under gap spacing and temperature differencesmineral oil



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of breakdown voltage under gap spacing and temperature differences of the mineral oil, sunflower oil and rice bran oil are

. The breakdown when gap spacing and

reakdown voltage under temperature differences of



3.2.2 Partial Discharge TestThe simulated partial discharges are

generated by applying to the rodenclosed by the test cell filled by the oil, which is either sunflower oil or rice bran oil. measurement is carried out according to the IEC standard [16].The applied voltage is fixeand the gap distance is set to beperiods of the tests are 10 to 30 minutes. arrangement and the test cell used in the experiments are shown in Figure of the results of simulated partial discharge in vegetable oil samples are shown in figure 23 to

Figure 22: Partial discharge test arrangement

Figure 23: Simulated partial dischargeoil for 30 minutes.

Figure 24: Simulated partial dischargesunflower oil for 30 minutes.

Figure 25: Simulated partial dischargeoil for 30 minutes.

10 12.5

Temp. 25 - 30

Temp. 40 - 45

Temp. 85 - 90

10 12.5

Temp. 25 - 30

Temp. 40 - 45

Temp. 85 - 90

10 12.5

Temp. 25 - 30

Temp. 40 - 45

Temp. 85 - 90

he simulated partial discharges are generated by applying to the rod-plane gap enclosed by the test cell filled by the oil, which is either sunflower oil or rice bran oil. The PD measurement is carried out according to the IEC

tage is fixed at 20 kV set to be 2 cm. The time

periods of the tests are 10 to 30 minutes. The test test cell used in the

s are shown in Figure 22. The examples partial discharge in

are shown in figure 23 to 25.

Partial discharge test arrangement

artial discharge in mineral

artial discharge in

artial discharge in rice bran


The results shown in Figure 26 are the breakdown voltage of the two vegetable oil samples and mineral oil aged by simulated PD with various time periods of the experiments. The vegetable oil under test show better performance than that of mineral oil when aged test by simulated partial discharge is performed.

Figure 26: Breakdown voltages of the oils after the aged test.

4. CONCLUTIONSThe physical characteristics of the two

types of vegetable oils, rice bran and sunflower,are investigated in this paper. It is found that the two vegetable oils have satisfactory characteristics comparable with the mineral oil. Therefore, it has high possibility that those vegetable oils can be used for electrical insulation of electrical machines.

AcknowledgementThe authors would like to thank Energy

Conservation Promotion Fund from Energy Policy and Planning Office, Ministry of Energy, Thailand,and faculty of engineering, King Mongkut’s Institute of Technology Ladkrabang for financial support. The contribution of Electric Generator Authority of Thailand (EGAT) for providing equipments used in experiments is acknowledged.

References[1] M.S. Naidu and V.Kamaraju: “High Voltage

Engineering” 2nd edition, McGraw-Hill, 1996[2] R. Arora and W.Mosch: “High Voltage

Insulation Engineering” 1st edition, New Age International Publishers, 2007 (Reprint)

[3] T.V. Oommen, C.C. Claiborne, E.J. Walsh and J.P. Beker: “A new vegetable oil based transformer fluid: development and verification” IEEE Conference on Electrical Insulation and Dielectric Phenomena, British Columbia, Canada, 2000

[4] C.P. Mcshane: “vegetable-oil-based dielectric coolant” IEEE Industry Applications Magazine, pp. 32-41, June 2002

[5] Suwarno, F.Sitinja, I.Suhariadi and L.Imsak:“Study on the characteristics of palm oil and it’s derivatives as liquid insulating material” 7th

International Conference on Properties and Applications of Dielectric Materials, Nagoya, Japan, 2003

[6] U.U. Abdullahi, S.M. Bashi, R. Yunus, Mohibullah and H.A. Nurdin: “The potentials of palm oil as a dielectric fluid” National Power and Energy Conference (PECon), Kuala Lumpur, Malaysia, 2004

[7] A.R. Marulanda, M.A. Artigas, A. Gavidia, F.Lanarca and N. Paz: “Study of the vegetal oil as a substitute for mineral oil in distribution transformer” IEEE Transmission and Distribution Conference and Exposition Latin American, Bagota, 2008

[8] P.Thongkiew, A.Kunakorn: “Dielectric Characteristics of Vegetable Oils in Thailand for Transformer Insulating Systems”International Conference on Electrical Engineering (ICEE), Hunghom Kowloon, Hong Kong, 2011

[9] IEC 156 “Insulating liquids-Determination of the breakdown voltage at power frequency-test method”

[10] ASTM D924-03a “Standard test method for dissipation factor (or power factor) and relative permittivity (dielectric constant) of electrical insulating liquids”.

[11] ASTM D3300-00 “Standard test method for dielectric breakdown voltage of insulating oils of petroleum origin under impulse comditions”

[12] ASTM D974-04 [13] ASTM D971-99a “Standard test method for

interfacial tension of oil against water by the ring method”

[14] P. M. Mitchinson1, P. L. Lewin1, I. L. Hosier1, G. Chen1 and P. Jarman “Oil reclamation –just a question of moisture?” Annual Report Conference on Electrical Insulation and Dielectric Phenomena, 2006

[15] ASTM D1533-00 “Standard test method for water in insulating liquids by Coulometric Karl Fischer Titration”

[16] IEC 60270 “High-voltage test techniques -Partial discharge measurements”

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Comparison of Physical Characteristics between Vegetable