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2009 International Conference on Electrical Engineering and Informatics5-7 August 2009, Selangor, Malaysia
978-1-4244-4913-2/09/$25.00 ©2009 IEEE
EE-07
Properties of RBDPO Oleum as A Candidate of
Palm Based-Transformer Insulating Liquid
Abdul Rajab
(1), Suwarno
(2), Aminuddin S.
(3)(1)
Doctoral Student of STEI-ITB, Educational Staff of Electrical Engineering Andalas Univ., Padang.
(2)
Educational Staff of Elektrical Engineering, STEI-ITB, Bandung.
(3)
Educational Staff of Chemical Department, FMIPA-ITB, Bandung. Jl. Ganesa No 10 Bandung 40132, Indonesia
[email protected] [email protected]
Abstract-This paper presents properties of RBDPO Oleum to be used as an insulating liquid. RBDPO stand for Refined, Bleached and Deodorized Palm Oil. Electrical properties like breakdwon voltage, dielectric dissipation factor and relative permitivity of RBDPO Oleum were measured for three different temperature and compared to that of ASTM D-6871 standard. Physical and chemical properties like viscosity, acid number and water content are also investigated. Experimental results show that RBDPO oleum can be considered as an initial material for developing palm oil based-transformer insulating liquid. Breakdwon voltage of sample at room temperature, 25oC, is 57kV. The relative permtivity is 3.1, very closed to that of strandard, 3.2, while the dissipation factor is 0.03. Viscosity and water content of oil are significantly lower then those of ASTM D-6871 standard value. The remaining problems are reducing acid number wich are stil slightly above standard value.
Key words-palm oil, insulating liquid, electrical properties, chemical properties, physical properties.
I. INTRODUCTION
Up to now, mineral oils derived from crude petroleum were widely used as insulating and cooling liquids in electrical equipment. Though such oils possess a satisfactory dielectric strength and are compatible with equipment materials, they are not considered nonflammable, and because they are petroleum based, they are considered to cause a negative effect to environment [1].
In the early 1990s, while the increasing concern on environment issues, vegetable oils, that have been considered unsuitable for use in transformer, were revisited. Their susceptibility to oxidation was the primary reason of resistance of their application as an insulating liquid. However, oil modifications and the use of suitable additive can compensate this characteristic.
Vegetable oils (natural esters) which be considered for potential transformer application are fatty acid ester triglyceride. The fatty acid components are linier chains 14-22 carbons long containing zero to three double bonds. Fig.1 show the triglyceride structure of vegetable oil, where the R, R’ and R” are fatty acid chains [2].
Fig.1 Structure of vegetable oil (natural ester) triglyceride
Material Selection
Palm oil, like others vegetable oils, is mixes of fatty acid triglycerides. Oils with high percentage of unsaturated fatty acids, especially three-unsaturated, result lower viscosity, but more susceptible to oxidation. In the other side, high percentage of saturated fatty acids oils result higher resistance to oxidation, but have a higher viscosity and pour point. The best choice is monounsaturated [3,4].
By searching on palm oil and it’s by product, it is found that RBDPO Olein has a highest content of monounsaturated fatty acids, especially oleic. Table I shows fatty acids content of palm oil and it’s by product. The oils are CPO (crude palm oil), PKO (palm kernel oil), RBDPO, RBDPO Olein, RBDPO Stearin and PFAD (palm fatty acid distillate). Palmatoleic (16:1) mean it’s fatty acid chain containing 16 carbons atom, one of carbon-carbon bond is a double bond. The same way, oleic (18:1) meaning the fatty acid chain consist of 18 carbons atom, one of carbon-carbon bond is double bond. Therefore, oleic and palmatoleic are monounsaturated fatty acids.
CH2
CH
CH2
R
R’
R”
O C
O
O C
O
O C
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TABLEI
FATTYACIDSCONTENTOFPALMOILANDIT’SBYPRODUCT[5]
Fatty Acid Percentage (wt)
CPO PKO RBD Oleum RBD Stearum PFAD
Lauric (12:0) Miristic (14:0) Palmitic (16:0) Stearic (18:0) Pamitoleic (16:1) Oleic (18:1) Linoleic (18:2)
0.2 1.1 44 4.5 - 39.2 10.1
47 - 53 15 - 19 8 - 11
1 - 3 - 12 - 19
2-4
0.1 – 0.5 0.9 – 1.4 37.9 – 41.7
4.0 – 4.8 0.1 – 0.4 40.7 – 43.9 10.4 – 13.4
0.1 – 0.6 1.1 – 1.9 47.2 – 73.8
4.4 – 5.6 0.05 – 0.2 15.6 – 37.0
3.2 – 9.8
0.1 – 0.3 0.9 – 1.5 42.9 – 51.0
4.1 – 4.9 - 32.8 – 39.8
8.6 – 11.3
II. EXPERIMENT
A. Sample
Electrical properties, especially breakdown voltage and dissipation factor can be adversely affected by the presence of contaminant, especially polar and/or conductive contaminant. Therefore, the presence of impurity must be minimized in sample selection.
Some of RBDPO Olein oils in market have been surveyed their content. Two samples from different producers have been selected. Table 2 shows content of those samples, exclude RBDPO Olein in triglyceride form as the main content.
TABLE II.
CONTENT OF TWO OIL SAMPLE EXCLUDE RBDPO OLEIN AS THE MAIN CONTENT
Sample
Content (g/Kg)
Free Fatty Acid Vitamin
Saturated Unsaturated A E
S-1 2 3 - -
S-2 2 2 2.2 0.37
B. Electrical Properties Measurement
B.1. Breakdown Voltage
Breakdown voltage measurement was performed using Liquid Dielectric Test Set, Model LD60, produced by Phenix Technologies as depicted in fig.2. For measurement purpose, rate of rise of voltage, 2 kV/s and electrode gap 2.5 mm have been chosen according to IEC 156 [6]. The measurement was performed at three different temperature, 25 0C, 40 0C and 60 0C.
B.2. Relative Permittivity and Dissipation Factor
Relative permittivity and dissipation factor were measured using Schering circuit test and null indicator oscilloscope. Measurement were performed at three different temperatures, 25 0C, 40 0C and 60 0C. The Test Cell, made from stainless steel, is a two terminals test cell that form
capacitance system where liquids or gases as its dielectric. The cell is depicted in fig.3.
Fig. 2 Liquid Dielectric Test Set, Model LD60 for breakdown measurement
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dissipation factor measurement[7]C. Physical and chemical Properties Measurement
In addition to electrical properties, physical and chemical properties like viscosity, density, acid number and water content, were also measured.
The viscosity of oil is very important property as the oil is used as a cooling medium. And acid number, as well as water content effect on the susceptibility of the oil to oxidation. In addition, water content that higher then
saturation limit of the oil will adversely effect on breakdown voltage.
III. EXPERIMENTAL RESULTS
A. Electrical properties
Results of electrical properties measurement can be seen in table III. The last three columns of Table 3 are electrical properties of vegetable oil based insulating liquid required by ASTM D-6871 standard, was given for comparison.
TABLE III.
ELECTRICAL PROPERTIES OF OIL SAMPLE S-1, SAMPLE S-2 AND STANDARD SPESIFICATION OF VEGETABLE OIL ACCORDING TO ASTM D-6871
No. Electrical Properties
Temperature
Sample-1 Sample-2 ASTM D-6871
250C 400C 600C 250C 400C 600C 250C 400C 600C
1 2 3
Breakdown voltage (kV) Dissipation factor (%) Relative Permittivity
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are 0,2% and 4% respectively.
A.1. Breakdown Voltage
It can be seen from table III, that breakdown voltage of sample S-1 at temperature 250C, is above ASTM D-6871 standard value (see table III). Heating of oil to 400C, cause only once breakdown occurrence of five times trial, 58 kV. Therefore, the breakdown measurements were not carried out at temperature 600C. Maximum capacity of equipment is 60 kV.
Table III also shows that breakdown voltage of oil sample S-2 at temperature 250C is slightly above ASTM D-6871 standard value, 35 kV. Rising up the temperature to 600C effect on the increasing of breakdown voltage of sample S-2 significantly from 36,2 kV at temperature 250C to 52,8 kV.
Facts that breakdown voltage of sample S-2 is significantly lower then that of sample S-1 clarify the presence of Vitamin A and/or Vitamin E as impurities (table II). The presence of impurities in insulating liquid which are able to lower its breakdown voltage value can be explained by suspended particle breakdown theory[8].
According to suspended particle breakdown theory, under an applied electric field, and because of relative permittivity of particles εrf is higher than that of oil εro, the
particles are polarized and directed by the field as shown in fig. 4.
Assuming hemispherical tips for the particles with radius r, the charges ±q at either of its ends would be :
±q = ±πr2(εrf - εro)ε0 E
where εo is the permittivity of free space and E is the field
strength at either end of the particle, assumed equal. Under
nonuniform field, as usually the case, the resultant force will move the particle toward the electrode (Fig. 4). When the particle reaches either electrode, its outward tip will act as an extension to the electrode and attract more particles.
For a short particle of length equal to radius r and with εrf >> εro, another force will work on particle.
F = r3εoE grad E
This force will drive the particle toward the higher field between electrodes. When particles bridging the gap, conducting path are built which would short circuit the gap, resulting in breakdown.
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Fig. 4 Particles are polarized and directed by fieldThese explanation we propose to explain the evidence of breakdown voltage of oil sample S-2 are lower then that of oil sample S-1. As we can see from table II, unlike the oil sample S-1, both vitamin A and vitamin E are present in oil sample S-2.
A.2. Relative Permittivity
Relative permittivity of sample S-1 is 3.1. This value is much better then that of mineral oil, the most widely used insulating liquid in transformer. Relative permittivity’s of mineral oils are in range 2.2 to 2.6. Relative permittivity of oil sample 2 is around 2.5, worst then that of sample S-1. The higher value of relative permittivity is an advantage for more uniformly electric field. Electric field for two dielectric materials connected in series is inversely proportional to their relative permittivity’s.
The dependence of electric field E on their relative permittivity’s (ε1 and ε2) of two dielectrics connected in
series expressed by equation :
ࡱൌ ࢂ
of dielectric 1 and dielectric 2 respectively.
In the case of transformer application, insulating liquids can be considered to be connected in series with insulating paper. For the relative permittivity of insulating paper 5,6 [9], and relative permittivity’s of oils sample S-1 and sample S-2 are 3.1 and 2.5 respectively, the electric field suffered by oil sample S-2 would be 1.24 times higher then that of oil sample S-1.
A.3. Dissipation Factor
For three different temperatures, all of three dissipation factor values of sample S-1 are higher then that of sample S-2 (see table III). Generally, dissipation factor of both of sample S-1 and sample S-2 are significantly lower compared to that of ASTM standard.
These results complete two other properties showing the suitability of sample to be candidate of transformer insulating fluid from electrical properties viewed.
B. Physical and chemical properties
Results of the physical and chemical properties measurement are given in table IV. Table IV also shows the physical and chemical properties of vegetable oil based insulating liquid according to ASTM D-6871 standard.
TABLE IV.
PHYSICAL AND CHEMICAL PROPERTIES OF SAMPLE S-1 AND STANDARD SPESIFICATION OF VEGETABLE OILS ACCORDING TO ASTM D-6871
No. Properties
Temperature
Sample-S1 ASTM D-6871
25oC 40oC 60oC 100oC 25oC 40oC 60oC 100oC
1 2
3
Viscosity, cSt, max
Acid number, mg KOH/g sample, max
Water content, ppm, max
0.074
Table IV shows that the RBDPO Olein can be consider as an alternative insulating liquid to replace mineral oil. The viscosity’s of oil at two different temperatures, 40oC and 100oC, are significantly lower then that of ASTM D 6871 standard. It’s water content also considerably below the ASTM standard value.
C. Comparison of Properties of RBDPO and Biotemp and Envirotemp and Standards
As can be seen from table IV, acid number of RBDPO Olein is slightly above the ASTM D 6871 standard. The higher acid number of RBDPO Olein caused by the presence of free fatty acid in form of 2 g/kg saturated fatty acid and 3 g/kg unsaturated fatty acid (table II). For comparison, the acid number of Biotemp is 0.075 (table V).
TABLE V PROPERTIES OF SEVERAL OILS AND CORRESPONDING VALUES FROM ASTM STANDARD
Properties RBDPO Olein Biotemp[10] Envirotemp[11] ASTM D6871
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Acid Number, mg KOH/g sampleWater Content, ppm
0.074 60
0.075 150
0.01-0.03 20-30
≤ 0.06
≤ 200 Table V shows the comparison of several
properties of RBDPO Olein and Biotemp and Envirotemp, two vegetable-based insulating liquid that has been in market and corresponding values from ASTM standard.
IV. CONCLUTION
Breakdown voltage of oil sample S-1 is much better then that sample S-2. At room temperature 250C, breakdown voltage of sample S-1 and sample S-2 are 57 KV and 36.2 kV respectively. Relative permittivity of sample 1, 3.1, is also much better then that of sample S-2. Generally, from electrical properties viewed, oil sample S-1 is more suitable to be a candidate for developing palm oil based- transformer insulating liquid.
Further investigation on oil sample S-1 show that physical and chemical properties like viscosity and water content are considerable to be a candidate of transformer insulating liquid. Whereas the acid number need to be reduced slightly form 0.074 to 0.06 mg KOH/g sample.
REFERENCES
[1] C.P. McShane, et al., “Food Grade Vegetable Oil Based Dielectric Fluid and Method of Using Same” US Patent No. 6,398,986 B1, Jun 4, 2002
[2] C. Patrick McShane, “Vegetable-Oil-Based Dielectric Coolant”, IEEE Industry Applications Magazine, May/June 2002.
[3] P. Boss and T.V. Oommen, “New Insulating Fluid for Transformers Based on Biodegradable High Oleic Vegetable Oil and Ester Fluid”, The Institution of Electrical Engineers, London, 1999. [4] T.V. Oommen, et al., “A New Vegetable Oil Based Transformer
Fluid : Development and Verification”, Proceedings of Conference on Electrical Insulation and Dielectric Phenomena, 2000.
[5] Erliza Hambali, dkk., “Teknologi Bioenergi”, ArgoMedia Pustaka, Jakarta, 2007.
[6] IEC 156, Insulating Liquids – Determination of the Breakdown Voltage at Power Frequency – Test Method, 1995.
[7] IEC 60247, Insulating Liquids – Measurement of Relative Permittivity, Dielectric Dissipation Factor and DC Resistivity, 2004.
[8] Mazen Abdel Salam, et al., High Voltage Engineering, Theory and Practice, Marcel Dekker, Inc., New York, 2000.
[9] B. Dolata, et al., “Comparison of Electric and Dielectric Properties of Ester Fluids with Mineral Based Transformer Oil”, Proceedings of XVth International Symposium on High Voltage Engineering,
Ljubljana, Slovenia, August 27-31, 2007.
[10] T.V. Oommen, C.C. Claiborne, and E.J. Walsh, “Introduction of a New Fully Biodegradable Dielectric Fluid”, IEEE, 1998.
