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Journal of Emerging Trends in Engineering and Applied Sciences (JETEAS) 3(1):33-37(ISSN: 2141-7016)

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A Comparative Study of Soya Bean Oil and Palm Kernel Oil as

Alternatives to Transformer Oil

M. A. Usman; O. O. Olanipekun; and U. T. Henshaw Department of Chemical Engineering,

University of Lagos, Nigeria

Corresponding Author: M. A. Usman ___________________________________________________________________________ Abstract This study investigated the use of soya bean oil and palm kernel oil as alternatives to mineral oil in a transformer system. Crude samples of these oils and their blend in varied proportions were tested for dielectric strength, pour point, flash point, kinematic viscosity, density and moisture content. The results showed that soya bean oil and palm kernel oil have good properties to act as insulating and cooling liquid in a transformer. These properties could be further improved when the oils are refined and purified. Soya bean oil and palm kernel oil have dielectric strengths of 39 kV and 25 kV respectively in their crude states compared with transformer (mineral) oil which has a maximum dielectric strength of 50 kV. Blend of soya bean oil and palm kernel oil showed synergy only in pour point and viscosity. The results of the study further showed that soya bean oil and palm kernel oil and their blends have very high flash points of 234°C and 242°C respectively. In terms of economic costs and environmental considerations, soya bean oil and palm kernel oil appear to be viable alternatives to transformer oils __________________________________________________________________________________________ Keywords: transformer oil, palm kernel oil, soya bean oil, dielectric strength, pour point, flash point __________________________________________________________________________________________ INTRODUCTION Transformers oil acts as an insulating and cooling medium in transformers. The insulating oil fills up pores in fibrous insulation and also the gaps between the coil conductors and the spacing between the windings and the tank, and thus increases the dielectric strength of the insulation. Transformers in operation generate heat in the winding, and that heat is transferred to the oil. Heated oil then flows to the radiators by convection. Oil supplied from the radiators, being relatively cool, in turn cools the winding. There are several important properties such as dielectric strength, flash point, viscosity, specific gravity and pour point that have to be considered when qualifying certain oil as transformer oil (Abeysundara et al., 2001). The quality of the oil is very important. A high voltage, highly loaded transformers demand better quality oil than a low voltage, lightly loaded transformer. Often, the loading on a transfer is increased as this will defer purchasing additional plant capacity. Thus the stress on the transformer increases (El-Sayed et al., 2009). The transformer oil must be of good quality to cope with the total effect of the thermal, electrical and mechanical stress brought on by increased service needs. Transformer dielectric fluid, also referred to as transformer oil, has undergone various significant changes over recent decades. At one time, polychlorinated biphenyls (PCBs) were used extensively. The fire retardant nature of this chemical was thought to be a highly desirable property. The disadvantage was its toxic

nature and the lack of biodegradability. Any spills of the product dictated an extensive and expensive clean-up process to remove all traces of the material from the soil. In the 1970s, PCBs were banned due to their health and environmental hazards. PCBs were used as dielectric liquids or insulator in capacitors and transformers, but these uses are supposed to be permanent because the material is not supposed to find its way into the environment; it is water insoluble and not readily leached out of discarded plastic materials, and capacitors and transformers are sealed. However, PCB's have been detected in rainwater, in human tissue, and in many species of birds and fish and so the problem of environmental pollution had still not been solved. New transformer oils were developed. They included naphthenic mineral oil which was the major product in early 2000 when the total U.S. consumption was about 45 million gallons per year according to a Cargill report. More specialty type products were also developed and marketed including high molecular weight hydrocarbons, synthetic esters and silicone fluid manufactured by Dow Corning (Wikipedia, April 2011). The basic raw material for the production of mineral oil is a low-viscosity lube termed as transformer oil base stock (TOBS), which is normally obtained by fractional distillation and subsequent treatment of crude petroleum. TOBS is further refined by acid treatment process to yield transformer oil (Mineral oil). Transformer oils consist of four major generic classes of organic compounds namely; paraffins,

Journal of Emerging Trends in Engineering and Applied Sciences (JETEAS) 3 (1): 33-37 © Scholarlink Research Institute Journals, 2012 (ISSN: 2141-7016) jeteas.scholarlinkresearch.org


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naphthenes, aromatics and olefines. However, these classes of transformer oils have low stability on usage. Paraffinic base oils have shown deterioration of electrical properties during use, at a rate which is a little bit faster than of naphthenic base oils (Singh & Ganguli, 2000), naphthenic based oils were also preferred due to their low cost but their relatively low flash points of 145-150°C makes them unsuitable for locations where flammability is a concern. Moreover the process of production is taking its toll on the environment as this requires further fractional distillation of crude petroleum which causes the release of harmful substances such as carbon monoxide gas, toxic gases, particulates e.t.c into the atmosphere thereby polluting the air. Silicone oils and synthetic esters and high molecular weight hydrocarbons have been used where the need for low flammability offsets their significantly higher costs, therefore since the early eighties, synthetic polyol esters have been used as substitutes for PCBs and mineral oil in specialty transformer applications. They are formed by processing fatty acids and alcohols. Use of natural ester oils began to receive serious attention in the 1990s due to the poor biodegradability and associated cleanup costs of mineral oil and significantly higher costs of silicone oils and synthetic esters (Erhan et al., 2009). Advantages of natural esters over mineral oil are renewable sources, much higher flash & fire points, environmentally friendlier, several performance improvements. The limitations thereof are; inferior oxidative property, poorer low temperature properties, higher viscosity and higher cost to produce. Hence the need to develop better transformer oils from natural esters arises (McShane et al, 2003). Attempts have been made with sunflower oil which is 100% environment friendly but unfortunately cost of sunflower oil is very high, an attempt was also made with coconut oil which is also environmental friendly and it possesses the necessary electrical, physical and chemical properties (Abeysundara et al, 2001). Further soya bean based oil have been successfully used in transformer systems (Bremmer et al., 2008; Biermann et al., 2007). Soya bean oil is predominantly composed of unsaturated fatty acid like sunflower oil. Palm kernel on the other hand is composed predominantly of saturated fatty acid like coconut oil. They are both readily available in Nigeria. This study is intended to compare the properties of soya bean oil and palm kernel oil as alternatives to transformer (mineral) oil. Also we investigated the properties of blends of the soya bean oil and palm kernel oil with the view to establishing possible synergy and their suitability as transformer oil. The justification for this work lies in finding a suitable replacement for mineral oil that is environmentally friendly.

EXPERIMENTALS Tests carried out on transformer oils and other related materials are usually carried out according to standard ASTM and IEC procedure (Gray, 2000; Hamrick, 2009). However for the purpose of this work tests will be carried out using basic laboratory procedure, only six parameters will be tested and they are; breakdown voltage, density, viscosity, moisture content, pour point and flash point. Five different samples of soya bean oil and palm kernel oil blended in various proportions namely; 100% soya bean oil, 30% palm kernel oil, 50% palm kernel oil, 70% palm kernel oil, and 100% palm kernel oil were subjected to the following tests. All experiments were performed in the Departments of Chemical and Electrical Engineering, University of Lagos, Nigeria. Moisture Content of the Oil This test was carried out by weighing oil samples initially and they were placed in an oven heating at 100°C (boiling point of water) to evaporate as much water as possible and then they were weighed again after evaporation. Actual moisture content was derived from calculations. Precautions were taken to ensure there was no spilling of oil samples as they were being moved to and from the oven. The Ohaus weighing balance was used to weigh the oil samples before and after heating (plate 2). Flash Point (Pensky‐Marten’s Closed Cup Method) This test was carried out in the laboratory using the Pensky-Marten flash point tester and a 0 - 400°C thermometer. The oil samples were placed in the cup of the flash point tester and then placed in the well or barrel of the tester as shown in the plate 2. A thermometer was inserted into the cup where the oil sample is to monitor temperature and so the oil is heated in the cup and at intervals of 10°C the fumes being released from the oil is tested with a lighted match stick, the temperature at which the fumes support the flame for about 2 seconds is determined as flash point.

Plate 1: A Pensky-Marten Flash Point Tester


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Pour Point This test was carried out in the laboratory using an ice bath, test tubes and a negative thermometer. The apparatus was set up such that the test tubes containing the oil samples were stuck in the ice bath and while being checked periodically (at intervals of 3°C) for flow characteristics, the negative thermometer was used to check for temperature and temperature at which oil sample starts to coagulate is determined as pour point. Density This test was carried out by weighing oil samples in fixed volume density bottles, the density bottles have a fixed volume of 50 ml and then density derived from calculation of mass per unit volume. The weighing balance used is an Ohaus brand, Pioneer model weighing balance (Plate 1).

Plate 2: An Ohaus Weighing Balance Kinematic Viscosity This was carried out using the NDJ-5S Digital Rotary Viscometer and the DBK MiniMag Stirrer/Heater (Plate 3). The oil samples were placed in beakers and the beaker placed on the heater and the piston of the viscometer placed inside the beaker. As the piston of the viscometer was rotating in the beaker and the heater was heating the oil, readings were taken from the viscometer over the range of temperatures, 45-60°C. A thermometer was placed at the side of the beaker and the viscometer to monitor temperature.

Plate 3: A Digital Rotary Viscometer

Dielectric Strength This test was carried out by placing oil samples in a constant fixed volume beaker to be placed in the Foster Transformer, current is passed through oil sample till circuit breaker goes off and flow of current is stopped, voltage at which this occurs is the breakdown voltage. This process is repeated twice for each sample and average result is taken. The transformer used is the Foster Transformer manufactured in London, model no; SW19 and serial no; 91ZA925 (Plate 4).

Plate 4: A Foster Transformer RESULTS AND DISCUSSION Figure 1 shows the moisture content of the five samples investigated. The standard value of moisture permissible in transformer oil is 1.5 mg/kg (Table 4). All the samples have moisture content higher than the permissible level except the 70% palm kernel oil with a slightly lower value of 1.4 mg/kg. The highest value of 3.6 mg/kg was obtained for 50% palm kernel oil blend. Moisture can react with the cellulose in paper insulators and result in paper degradation (Bhumiwat et al., 2010) in addition to reducing dielectric strength of the oil. The traditional transformer oil (mineral oil) is obtained from fractions of crude oil (petroleum) and so is more volatile with little water content compared to vegetable oils such as soya bean oil and palm kernel oil which contain unsaturated acids that can easily absorb moisture. However this does not disqualify the samples as good alternatives to mineral oil since the moisture content can be reduced by heating to enhance insulating property of oil sample. Figure 2 shows the dielectric strength of the five samples. The sample with 100% soya bean oil has the highest value of 39 kV while the 100% palm kernel oil has a value of 25 kV. The 50% palm kernel oil has the lowest value of 17 kV. This is a direct consequence of the level of moisture content present in each sample. The standard requirement for transformer oil is 50 kV (Table 4). Hence none of the samples are good enough for use in a high voltage


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transformer. However, both the 100% soya bean oil and 100 % palm kernel oil have a very high prospect when refined and purified. This is so considering the fact that crude coconut oil has a dielectric strength of 20 kV while upon refinement and purification it improved significantly to 60 kV. Furthermore, with these present breakdown voltages of palm kernel oil and soya bean oil, they can be used as insulating liquids in low-medium voltage transformers i.e. 69-288 kV transformers which require minimum dielectric breakdown voltage to be 20-30 kV (FIST 3-30, 2000).

Figure 1: Moisture Content of Oil Samples Table 1 shows the pour point of the five samples. It is observed that the pour point of 100% soya bean oil is the least with value of -1oC. The pour point increases as the proportion of palm kernel increases and is highest for 100% palm kernel oil with a value of 15o. This can be explained by the degree of unsaturation inherent in each sample. Pour point of unsaturated acids is very low compared to pour point of saturated acids. Pour point affects the insulating property of the oil when the transformer is used in cold weather conditions. The standard pour point value is -40oC (Table 4). This is to ensure that the oil does not solidify under cold weather conditions, if the power supply is disconnected for a long time. The transformer in operation generates heat which results in the temperature raise in oil. On pour point consideration, 100% soya bean oil is the best while 100% palm kernel oil is the least. However, unsaturated fatty acids contain double bonds. Inside the transformer, oil is subjected to heavy electro-magnetic fields. There is a possibility that double bonds may break due to polarization, so from this point of view 100% palm kernel oil is far better than 100% soya bean oil. Table 1: Pour Points of Oil Samples

Figure 2: Dielectric Strength of Oil Samples From Table 2 it is observed that flash point of the fivel samples are generally higher than that of mineral oil whose value is 154oC (table 4). This is because mineral oil is composed of more volatile substances that burn faster and at lower temperatures. This high flash point is very desirable because it helps the cooling property of the oil and reduces the risk of explosions of fire during operation of transformer. Hence based on flash point consideration all the samples are good candidates for transformer oil. Table 2: Flash Point of Oil Samples

Oil Samples (%) Flash Point (°C) Soya (100) 234 Palm Kernel (30) 266 Palm Kernel (50) 260 Palm Kernel (70) 268 Palm Kernel (100) 242

From Figure 3 it is observed that the viscosities of all five samples are very high when compared with mineral oil whose value is 0.895 kg/m3(table 4). Viscosity of the oil affects its cooling property; this is because cooling of a transformer is mainly governed by convection, so it is important to have a low viscosity to facilitate convection: the lower the viscosity, the better the cooling. Increase in temperature reduces viscosity. The viscosities of the five samples generally decrease with increasing temperature; the desired range of viscosity could be reached at some elevated temperature. At the highest temperature tested in the laboratory 60°C, viscosities of soya bean oil and palm kernel oil are 21.82 and 15.62 mPa.s respectively. There is decrease in viscosity as the proportion of palm kernel oil increases. This suggests that unsaturation increase viscosity while saturation reduces it. Palm kernel oil is therefore favoured on this count. Table 4 shows a comparison of the properties of the mineral oil (standard), coconut oil, soya bean oil and pam kernel oil. It should noted that the entries for coconut oil are the values obtained after purification and refinement. Considering the three most important properties namely dielectric strength, pour point and

Oil Samples (%) Pour Point (°C) Soya (100) -1 Palm kernel (30) 7 Palm kernel (50) 12 Palm kernel (70) 14 Palm kernel (100) 15


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flash point; soya bean oil appears better than palm kernel oil. However, both show good potential on refining.

Figure 3: Variation of Viscosities of Oil Samples with Temperature Table 4: Properties of Pure Oil Samples and Mineral oil Property Mineral

Oil Coconut Oil

Soya bean Oil

Palm Kernel Oil

Dielectric strength (kV)

50 60 39 25

Moisture content (mg/Kg)

1.5 1.0 2.0 1.9

Pour Point(°C)

-40 20 -1 15

Flash point(°C)

154 225 234 242

Density (Kg/dm3)

0.895 0.917 1.4642 1.4624

Viscosity (mpa.s) @ 40°C

1.3 29 34.5 29.2

CONCLUSION The two vegetable oils investigated in this study; soya bean oil and palm kernel oil are good alternatives for transformer oil. They can be used in their raw form for low voltage transformer but have to be refined and purified to improve on their properties for high voltage transformers. Blending of the oil does not show significant synergy except on the properties that are dependent on degree of saturation such as pour point and viscosity. REFERENCES Abeysundara D C, Weerakoon C and Lucas J R, Gunatunga K.A.I and Obadage K.C. (2001): Coconut Oil as an Alternative to Transformer Oil Bart J. Bremmer & Dr. Larry Plonsker. (2008): Bio-based Lubricants Market Study

Bhumiwat S, Lowe S, Nething P, Perera J, Wickramasuriya P, Kuansatit P (2010): Performance of Oil and Paper in Transformers Based on IEC 61620 and Dielectric Response Techniques, IEEE Electrical Insulation Magazine 0883-7554/07 Biermann Ursula & Metzger O. Jürgen (2007): Faculty of Mathematics and Natural Sciences, Carl Von Ossietzky University, Oldenburg. Application of Vegetable Oil Based- Fluids as Transformer Oils Doble Engineering Company, (1993): Reference Book on Insulating Liquids and Gases EL-Sayed M. M., EL-Refaie, Mohamed R. Salem, and Wael A. Ahmed. (2009): Prediction of the Characteristics of Transformer Oil under Different Operation Conditions Erhan, Sharma and Doll (2009): Opportunities for Industrial Use of Agricultural Products FIST 3-30 Hydroelectric Research and Technical Services Group (2000): United States Department of the Interior Bureau of Reclamation Denver, Colorado. Facilities Instructions, Standard and Techniques, Transformer Maintenance Gray I.A.R, Transformer Chemistry Services (2000): A Guide to Transformer Oil Analysis Hamrick Lynn, ESCO Energy Services, (2009): Dissolved Gas Analysis for Transformers McShane Patrick C, Cooper T.V. Oommen, ABB, Charles Tanger, Cargill. (2003): Ester Transformer Fluids Petrolab PT Services, (2011): Transformer Oil Analysis Singh M.P, Ganguli T.K. (2000): Materials Used in Transformers The Hindustan Times Online, (2001), New Delhi, "Coconut oil's in, auto lubricants are out"; http://www.hindustantimes.com/nonfram/220201/detSTA06.asp Wikipedia, the free encyclopedia, www.wikipedia.com

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