III.A.2.a.1.d. ICPADM 2015 Makalah

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Comparison of Low Thermal Fault Gases of

Various Fatty Acid Mono Esters

Abdul Rajab

*

, M. Tsuchie, M. Kozako, M. Hikita

Dept. of Electrical and Electronics Engineering Kyushu Institute of Technology, *Andalas University 1-1 Sensui-cho, Tobata-ku, Kitakyushu 804-8550, Japan

n589503r@mail.kyutech.jp

Satoshi Hatada, Takashi Suzuki, Akinori Kanetani

Chemical Research Laboratories

Lion Corporation, Ltd.

2-1 Hirai 7-Chome, Edogawa-ku, Tokyo 132-0035, Japan

Abstract—Proven to be a good substitute for mineral oil as insulation in distribution transformer, natural ester oils have been implemented in higher voltage of power transformer since 2002. Gases generated by such oils need to be examined to diagnose the presence of faults in natural ester immersed transformer in service, based on dissolved gas analysis (DGA) method. In this paper, the gas generations of chemically modified natural esters which are palm fatty acid monoesters under low temperature overheating ranging from 200 to 300 oC were analyzed. Localized thermal faults were conducted to simulate the real condition in transformer operation. Experiment on several kinds of fatty acid monoesters with similar and different molecular structure as well as mineral oil were also performed for comparison. Types of gases, concentrations and their trend against temperature variation were investigated. The differences of generated gases between the fatty acid monoesters having C-C double bond in their molecular structure and those without C-C double bond are discussed. Comparison of the gas generation trend between tested oils and commercially available natural ester insulation oil reported in the previous literature, as well as mineral oil are also elaborated. The possibility of generating gas ratio method to expect the overheating temperature is also evaluated.

Keywords—dissolved gas analysis; gas ratio; insulating oil; low thermal fault; chemically modified natural ester; transformer.

I. INTRODUCTION

Gaining a successful application in middle voltage of distribution transformer, natural ester oils were then implemented in higher voltage of power transformers since 2002 [1]. As the power transformers play a vital role in transmission and distribution and are one of the most expensive units in electrical power system, then the need for monitoring and diagnosis of natural ester oils filled transformer becomes inevitable. Dissolved gas analysis (DGA) is one of the most common method which was used to diagnose the presence of thermal or electrical faults in mineral oil immersed transformer. Gases generated by natural ester oils need to be examined to anticipate the use of DGA method to diagnose the presence of faults in natural ester immersed transformer in service.

Some investigation results on gases generated by natural esters have been reported [2-6]. Reference [2] stated that ethane is more likely to be produced in higher amount by the natural ester compared to that of the mineral oil under thermal fault. The similar observations are reported in [3]. Ethane

accompanied by hydrogen, are also found in higher amount in the natural ester immersed transformer in service [4, 5]. The ethane was then suggested to be the key gas of natural ester for thermal fault, as reported in [6].

However, most of the previous results were obtained from the investigation on natural esters of triglyceride form. The results on gas generation of chemically modified natural ester which is monoester type were still rare. In our previous work [7, 8], we have studied the gases generated by palm fatty acid esters (PFAE) in the temperatures ranging from 200 to 300 oC and compared the results with that of mineral oil. The PFAE is a chemically modified natural ester of monoester type synthesized from palm oil which is expected to become an alternative to mineral oil due to its high fluidity and strong dielectric characteristics [9].

This paper presents gas generation under low thermal fault of PFAE and other fatty acid monoesters as well as mineral oil. The differences of generated gases between fatty acid mono esters having C-C double bond in their molecular structure and those without C-C double bond are discussed. Comparison of the gas generation trend between tested oils and commercially available natural ester insulation oil reported in the previous literature, as well as mineral oil are also elaborated. The possibility of generating gas ratio method to expect the overheating temperature is also evaluated.

II. EXPERIMENT

A. Samples

Samples used in the experiment were fatty acids monoester synthesized from palm oil (PFAE, M12, and 2H-08), soybean methyl ester, and rice bran methyl ester oils. PFAE is a chemically modified natural ester fluids which was developed to be used for oil immersed transformer, M12 and 2H-08 consist of methyl laurate and caprylic acid ester, respectively. All monoester oils were manufactured and supplied by Lion Co., Ltd. Japan. Mineral oil (MO) was also used for comparison. Some properties of the oils are listed in table I. Iodine value is often used to determine the amount of unsaturation in fatty acids and their derivatives. The higher the iodine value, the more C-C double bonds are present in the fats and their derivatives. Accordingly, soybean and rice bran methyl ester oils contain significant number of C-C double bond, whereas PFAE, M12, and 2H-08 do not.

ISBN: 978-1-4799-8903-4 2015 IEEE 11th International Conference on the Properties and Applications of Dielectric Materials (ICPADM)

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TABLE I. SOME PROPERTIES OF

Oil Type Iodine Value

(g/100g)

Kinematic Viscosity (mm2_{/s, 40 ºC)}

PFAE 0 5.1

2H-08 0 2.8

M12 0 2.4

Soybean 120 4.3

Rice bran 107 4.3

Mineral oil - 8.7

The chamber was firstly vacuumed to before the oil sample was inserted into the sample was filtered while being inserted into the filling process was stopped when the vo 1000 ml. Then, degassing the oil and argon g into the chamber to occupy the space above the oil system to the ambient pressure. operations, contamination by surroundi minimized.

Low thermal fault was performed to simu which is usually the case in transformer. The of the procedure can be found in [10].

III. RESULTS AND DISDUSSIO

A. Distribution of Generated Gases

The gases of concern for the experiment gases, i.e. hydrogen, methane, ethane, ethyle carbon monoxide, and the typical graph combustible gases generated by fatty acid mineral oil, taken at the temperature of 250 oC 2. Under low thermal fault within the temp 300 oC, ethylene and acetylene were not foun Carbon monoxide was found to be generat

DC Power Supply

F OILS

Breakdown Voltage (kV/2.5 mm)

81

83

84

89

75

B. Experimental Arangement a

Fig. 1 shows photographi equipment used in the experim supply, temperature and time c recorder. The DC power sup current for ceramic heater i controller worked to maintain t value and to stop the heat temperature reaches at 84 oC, heating time comes. The g continuously monitor and recor This experiment was carrie temperature at 21 ºC.

Fig. 1. Experimental Arrangement

evacuate the air chamber. The oil o the chamber, and olume of oil reach gas was introduced e the oil and bring Based on these ng air can be

ulate local heating detail explanation

N

were combustible ene, acetylene, and of distribution of d monoesters and C, is shown in Fig. perature of 200 to nd in all tested oils.

ted in the highest

amount by all tested oils, and exception was found in soybean where the second highest amou A small, but distinguishable, found in soybean and rice generation rate of hydrogen by in Fig. 3.

Fig. 2. Generation rate of combustib mineral oils under low thermal fa Temperature & Time

Controller

Oil Chamber

and Procedure

c and schematic views of the ment. They consist of DC power

ontroller, oil chamber and graph pply was used to provide DC

immersed in oil sample. The the heater temperature at a given

ting process, when the oil’s or when the setting duration of graph recorder was used to rd heater and oil’s temperatures. ed out under constant room

then followed by methane. An n and rice bran methyl ester oils, unt of generated gas was ethane. amount of hydrogen was also

bran methyl ester oils. The y oils can be seen in more detail

ble gases of fatty acid monoester and ault.

Graph Recorder

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B. Comparison of Gases Generation betwee Monoesters and Mineral Oil

Carbon monoxide was the most dominan all tested oils (Fig. 2). The presence of carbon can be due to the oxidation of oil molecule, by surrounding air [11]. And in case of ester natural ester, synthetic ester and fatty acid possibility of carbon monoxide gas genera COO- bond cleavage. That is why carb generated in higher amount in fatty acid m that of mineral oil (Fig. 4). Methane, on the to be produced by mineral oil in higher am fatty acid monoesters (Fig. 5). These results previous report. [12].

The thermal energy inserted into the oil weakest bond of oil molecules, namely -CO acid monoester oils. The existence of oxy have higher electronegativity than carbon depletion of electrons around -COO- bond surrounding it weakened, and hence, the -CO to be cut than C-C bond in oil molecule. O mineral oil composed of hydrocarbon s alicyclic and aromatic hydrocarbon. And th point where the hydrocarbon would be cut carbon chain in the oil molecule. Then, CH combining with H2 after cleavage at the end o

Fig. 3. Generation rate of hydrogen of fatty acid mono under low thermal fault.

Fig. 4. Generation rate of carbon monoxide of fatty mineral oil under low thermal fault.

en Fatty Acid

nt gas generated by n monoxide in oils , and/or ingression r type oils, such as monoester have a ation because of

-bon monoxide is monoester oils than

e other side, seems mount than that of correspond to the

l firstly breaks the OO- bond in fatty ygen atom, which atom, cause the and get the bond OO- bond are easier

On the other hand, such as aliphatic, he most vulnerable

t is at the end of H4 is produced by of carbon chain.

oesters and mineral oil

y acid monoesters and

C. The Effect of C-C Double B

In our previous works rega thermal fault below 200 oC, we natural ester oil of fatty acid m bond in their molecular structur amount of ethane, whereas the did not, or in some cases prod ethane [7]. PFAE, as well as mi although the oils were heated u is fatty acid monoester oil w structure, and the mineral oil us the results partly confirmed the

Additional data was obtain works provide more detail infor under low thermal faults in the from 200 to 300 oC. Soybean both are known to have C-C d generate ethane in remarka temperature levels, as can be s 2H-08, which do not have C-C and mineral oil, do not generat be in line with the claim ma ethane generation phenomenon about the difference between oi bond in their molecular structu with the difference in oil type, e

Fig. 5. Generation rate of methane o under low thermal fault.

Fig. 6. Generation rate of ethane of under low thermal fault.

Bond

arding the gas generation of low e found that chemically modified monoester containing C-C double res tended to produce noticeable e oils without C-C double bond duced no significant amount of ineral oil did not produce ethane up to 300 oC [8]. Since the PFAE without C-C double bond in its

sed was of naphthenic type, then claim made in earlier work.

ned from our latest experimental rmation of gas generation of oils e temperature is set to the range and rice bran methyl ester oils, double bond in their structures, able amount at all heating seen in Fig. 6. PFAE, M12, and C double bond in their structures, te ethane. These results seem to ade in our previous report that

n under low thermal faults was ils with and without C-C double ures, and that has nothing to do ester oil or mineral oil [8].

f fatty acid monoesters and mineral oil

fatty acid monoesters and mineral oil

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The ethane generation from oils und according to the previous reports [6, 11], is the oxidation. They proved this by their expe where the change in ethane generation, as w gassing phenomena, coincide with the chang oxygen in oil in reverse way which me consumed during the process [3]. They s ethane is developed according to the pero which is commonly taken place in omega-3 acids [11]. The process is not uniquely ow because some mineral oils was also repo significant amount of ethane, either from thermal fault in laboratory experiment [3], or in service [13]. However, ethane gen pronounced in natural esters than in observation results reveal that ethane was us for thermal fault of natural esters [6, 11]. Th from our results where no ethane gen chemically modified natural esters such as 2H-08 which do not have C-C double bond It should be noticed that the natural esters th in the previous studies were FR3 or Biotemp to be in triglyceride form. In triglyceride st chains occupying three branches of triglyce combination of saturated and unsaturated hyd

D. Fault Temperature Estimation from CO/C

Under low thermal faults, where the am gases are very low, gas ratio methods such a Rogers ratio, and Doernenberg ratio cannot b alternative gas ratio is sometimes used to e temperatures. For instance, the ratio of C2H6 the previous report [14] to estimate temperature within the range of 100 t experimental results (Fig. 7), show the decre CO/CH4 as the heating temperature increas indicated that the ratio of CO/CH4 could po estimate the temperature of low thermal fa when the ratio of CO/CH4 of Soybean meth bran methyl ester is over 100, overheatin estimated below 200 ºC. When the ratio is be overheating temperature is estimated from 20 case of 2H-08, when the ratio of CO/CH4 is overheating temperature is estimated over 2 further investigations are required in order t comprehensive understanding on how the varies to the change in overheating temperatu

Fig. 7. The variation of CO/CH4 ratio of fatty aci

temperature change.

der thermal fault, strongly related to erimental evidence well as others stray ge in the amount of eans oxygen was suggested that the oxidation of lipids 3 unsaturated fatty wned by ester oils, orted generating m simulated low r from transformer neration is more

mineral oil, the sed as the key gas

his slightly differs neration found in

PFAE, M12 and in their structures. hat commonly used p which are known tructure, fatty acid ride are a random drocarbon.

CH4 Ratio

mount of generated as IEC 60599 ratio, be applied. Instead, expect the heating 6/CH4 was used in the overheating to 200 oC. Our ease in the ratio of

sed. These results ossibly be used to aults. For instance, hyl ester and Rice ng temperature is etween 10 and 100, 00 to 300 ºC. In the s less than 10, the 250 ºC. However, to obtain the more ratio of CO/CH4 ure.

id monoesters against

IV. CONC

1. Fatty acid monoesters ten carbon monoxide, but less of mineral oil.

2. Fatty acid monoesters hav generate noticeable amoun

3. It is indicative that ethane low thermal faults in oils h structure.

4. It seems that the ratio of C to estimate the temperature

ACKNOWL

Authors would like to thank samples. Abdul Rajab also Republic of Indonesia for provi

REFER [1] WG A2.35, “Experiences in S

CIGRE, 2010.

[2] Zhongdong Wang, Xioao Yi, J “Fault Gas Generation in Natur Localized Thermal Faults”, IEE 28, No.6, Nov./Dec. 2012. [3] I. Atanasova-Höhlein, “Stray

Manifestation and Influence Conference on Liquid Dielectrics [4] M. Duval and R. Baldyga, “Stra in Service”, The 76th Annual Intl [5] Daniel Martin, Nick Lelekakis “Further Studies of a Vegetable Electrical Insulation Magazine, V [6] I. Atanasova Hohlein, C. Reho Oxidation Behaviour of Insulatin the 6th Southern Africa Regional [7] Abdul Rajab, et. al., : “Study o

Thermal Properties of Natural E on Insulating Oil Section, JPI, Ju [8] Abdul Rajab et. al. : “Gas Gene Levels of Low Temperature Ov Static Apparatus, IEE Japan, Dec [9] T. Kano, et. al., “Analyses of El Fatty Acid Esters as Insulating O [10] M. Tsuchie, M. Tien and M

Advancement of Dissolved Gas by LTOH” The 8th International W on Electrical Discharge and High [11] I. Atanasova Hohlein and Rain Interpretation of Dissolved Ga Changers”, IEEE Electrical In November/December, 2010. [12] Pierre, M. Marugan, and A. Bero

and Mineral Oils” IEEE Tran Insulation, Vol. 19, No. 5, Octob [13] I. Atanasova Hohlein, “Unusual Service”, IEEE Electrical Ins January/February, 2006. [14] M. Tsuchie, Masahiro Kozako

“Modelling of Early Stage Degradation of Paper-oil Insula and Electrical Insulation, Vol. 21

CLUSIONS

nd to generate higher amount of s amount of methane than those

ving C-C double bond tend to nt of ethane.

e could be used as key gas for having C-C double bond in their

CO/CH4 could possibly be used e of low thermal faults.

LEDGMENT

k Lion Co. Ltd. for providing oil would like to thank DGHE, iding doctoral scholarship.

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