AU2021100929A4

AU2021100929A4 - Method for evaluating liquid dielectric characteristics and feasibility of pongamia pinnata oil as liquid dielectrics

Info

Publication number: AU2021100929A4
Application number: AU2021100929A
Authority: AU
Inventors: V. Kirubakaran; T. Mariprasath
Original assignee: Kirubakaran V Dr; Mariprasath T Dr
Current assignee: Kirubakaran V Dr; Mariprasath T Dr
Priority date: 2021-02-18
Filing date: 2021-02-18
Publication date: 2021-05-13
Anticipated expiration: 2029-02-18

Abstract

The present disclosure relates to a method for evaluating liquid dielectric characteristics and feasibility of Pongamia Pinnata oil as liquid dielectrics. The method been proposed for feasibility study on non-edible Pongamia Pinnata oil as an alternate liquid dielectric which can be used in Distribution Transformers. The method reviews the alternate insulating oil, electrical, physical and chemical properties. Subsequently, Pongamia Pinnata Oil's electrical properties (Dielectric Strength, Dielectric Constant, Dielectric Dissipation Factor and Specific Resistance), chemical properties (Water content, Acidity) and physical properties (Viscosity, Flash Point, Interfacial Tension) have been estimated according ASTM and IEC for comparing the Pongamia Pinnata oil with conventional mineral oil. Alongside, solid insulating material deterioration, both in Pongamia Pinnata oil and mineral oil, using XRD and SEM is carried out. If oil suited for these characteristics the value addition has been made from this oil which leads to waste land utilization and rural development. 45 CJ co a) LcN a)0 a) L~ c_ E a) a) w 2 Eo C 0 0 r 0.- 0 ~ -m m 4 CL ~ acu a)m _ L U U E 7-5~ JiCo a) ) :E C- 0 a) 0L _ .0 a)C 16 l a)-5 C 0 a) , C C w) c -0 Sa) 0 cu a) - i-0 -jc 0- 0 u -- 0 - =2 0 LQL ; 0.- a)~ Ca) aC C4- c _ 0 ) C: L a) 0 Ca) 0ao Li4 C: a)m L V ) a W a) 2 baD a) w t aL ci Ei~ EOc E t 2~3f 0 2 .2o Li Lic L C ) 0i 0 2- E 2 ) 4-a) 2 a)fC a Z Liba) CU mt 0 a) C D CL oE3 c~ ~i WC7A U u a ow C C CL a) 0 0 In> c 2 0: b ) W)(a) a) CL 0 aa) 04 CD EC~ 0- OCU bD~~~>-- a)a o0 D M L cC - _ n 2Db 00 0 - 0-fEInb 0~ a . s a)) a) =i 0- a) c Cj 0a Cu c bfl m jcu E L S a)0 0n m 3c 2~C 0-0a 0 2D 0 0 -

Description

CJ co a) LcN

a)0 a) L~

c_ E

a) a) 2 w

Eo C 0 0 0.- 0 ~ r -m m 4 CL ~ acu a)m

_ L U U E 7-5~ JiCo a) ) :E C- 0 a) 0L _ .0 a)C 16 l a)-5 0 C a) , C C

w) c -0 Sa) 0 cu a) - i-0 -jc

- 0 u 0 - -- =2 0 LQL ; 0.- a)~ Ca) aC C4- c _ 0 ) C: L

a) 0 Ca) 0ao Li 4 C: a)m L V ) a W a) 2 baD a) w Ei~ t aL ci EOc E t 2 2~3f 0 .2o Li Lic L C )

0 0i 2- E 2 )

4-a) 2 a)fC a Z Liba) CU mt C 0 DCL oE3 a) c~ ~i U WC7Au a ow

C C CL a) 0 In> c 2 0: b )W)(a) a) CL 0 aa)

04 CD EC~ 0- OCU bD~~~>-- o0 D a)a M L cC - _n 2Db 00 - 0 0~ 0-fEInb a. s a)) a) =i 0- a) c

0a Cj c Cu bfl m jcu

E L S a)0 m 0n 3c 2~C 0-0a 0 0 2D 0 -

METHOD FOR EVALUATING LIQUID DIELECTRIC CHARACTERISTICS AND FEASIBILITY OF PONGAMIA PINNATA OIL AS LIQUID DIELECTRICS FIELD OF THE INVENTION

The present disclosure relates to a method for evaluating liquid dielectric characteristics and feasibility of Pongamia Pinnata oil as liquid dielectrics.

BACKGROUND OF THE INVENTION

Distribution Transformer is the most significant component in power system. The lifetime of transformer strongly depends on life time of the insulation to be used. Commonly, oil-impregnated distribution transformer is used in power system since its lifecycle is higher than that of others. Transformer operating condition and mechanical-, electrical-and thermal stresses are occurring during routine service; it accelerates the ageing rate of the insulation system. The deterioration of insulation is strongly dependent on its operating temperature. In transformers, 70% of the failures are due to liquid insulation, whereas 50% of them are due to tensile strength of solid insulation.

The liquid dielectrics used in distribution Transformers perform two important functions. That is, it acts as an insulation medium and maintains the transformer operating temperature within limits. Over100 years, mineral oils are used as the liquid di-electrics in transformers, since its physiochemical and electrical properties are suitable for the transformer; also, it is said to be of low cost. However, the negative aspects of mineral oils are low flashpoint, fire point and dielectric strength. Adding all these aspects with mineral oils are extracts from fossil fuel, nowadays fossil fuels are being rapidly decreased. As the mineral oil is less biodegradable, it doesn't satisfy new environmental laws.

The low fire and flash point and breakdown strength can be rectified by using a Higher Molecular Weight of Hydrocarbon, but its viscosity is high and so the capacity of heat transfer is low. In Later years, biodegradable synthetic ester, developed by organic components, is synthesized from organic acids and alcohols. But it has higher viscosity and cost wise higher. In 1970's, silicone oil is developed which has high fire point, very low pourpoint and not affected by oxidation. But it has higher viscosity at low temperature. Also,

Silicone oil contains methyl polysiloxanes which can generate formaldehyde at around 300 °F, which causes cancer to living organisms.

Since 1990's, the vegetable oils are the commonly used liquid dielectrics in Distribution transformers, as its physical, chemical and electrical properties satisfy the required standard. The vegetable oils are band triglyceride structures, which can be classified according to their fatty acid composition like saturated and un-saturated (mono, Di and Tri). These fatty acids are the deciding factors of physiochemical and electrical properties of the oil. The saturated fatty acid oils are having higher viscosity, higher freezing point and pourpoint; but they have low oxidation stability and low dielectric strength. The Triple unsaturated fatty acids exhibit a lower viscosity, and consequently, it has an unstable property, while the polyunsaturated fatty acids oils have good oxidation stability.

In recent years, highly biodegradable insulation fluids, such as EnvirontempFR3 and Biotemp, are developed and successfully used in distribution transformers in USA. Apart from these oils, several researchers are investigating sunflower oil, coconut oil, canola oil, palm oil, rape seed oil, soybean oil and olive oil properties according international standards. Results show that, except for viscosity, sunflower, soybean, rapeseed and canola oil perfectly satisfies the liquid dielectric standards. These oils are obtained from edible oil. This increases the competitions between food and insulating oil. This research work has been proposed for feasibility study on non-edible Pongamia Pinnata Oil as an alternate liquid dielectric which can be used in Distribution Transformers. Furthermore, deteriorations of solid insulating materials are investigated using XRD and SEM.

However, green insulating fluids are playing a vital role in insulation design of the distribution transformers, but traditionally used mineral oil has lesser biodegradable and low fire resistant characteristics. Hence, it does not satisfy the new environmental regulation. Besides that, the availability of fossil fuels is also going to run out. In the view of the forgoing discussion, it is clearly portrayed that there is a need to have a method for evaluating liquid dielectric characteristics and feasibility of Pongamia Pinnata oil as liquid dielectrics.

SUMMARY OF THE INVENTION

The present disclosure seeks to prepare a method for evaluating characteristics of alternating liquid dielectrics and feasibility study on Pongamia Pinnata oil as liquid dielectrics.

In an embodiment, a method for evaluating liquid dielectric characteristics and feasibility of Pongamia Pinnata oil as liquid dielectrics is disclosed. The method comprises:

inserting electrodes inside the insulating oil for calculating dielectric strength of the insulating oil by upon testing withstand voltage stress without failure, which depends on physical chemical properties of the insulating oil, impurities present in the oil; measuring breakdown strength of oil sample using Neutronics oil test kit consists of two hemispherical electrodes with 2.5 mm gap spacing and measuring dielectric dissipation factor using Schering circuit test and null indicator oscilloscope; pouring oil sample into three terminal test cells to from a capacitance where oil acts as a dielectric medium for calculating dielectric constant of oil and evaluating specific resistivity from the ratio between the direct potential gradient in volts/centimeter (V/cm) paralleling the current flow within the sample to the current density in amperes/square centimeter (A/cm2) at a given instant of time and under prescribed conditions; measuring acidity by pouring required KOH into one gram of oil to neutralize acids and measuring water content of oil sample using coulometrically generated Karl Fischer reagent; measuring viscosity of oil sample using red wood Viscometer and measuring flash point of oil sample using Pensky Martens Closed cup Test Method and measuring interfacial tension of the oil sample by calculating molecular attractive force (oil and water) between their unlike molecules at the interface using Ring Method and measuring density of oil sample using digital density meter; and performing thermal degree of degradation studies on solid insulating materials like Press board and Kraft paper by XRD and SEM using PW3040/60 X'pert PROinstrument.

In an embodiment, the breakdown strength of oil sample is measured according to IEC 60156 and the dielectric dissipation factor is measured according to ASTMD-924 and the specific resistance of oil samples is measured according to IEC 60247 and the acidity of oil sample is measured ac- cording to ASTM-D 974, and the water content of oil sample is measured according to ASTM-D 1533, and viscosity of oil sample is measured according to ASTM-D 445, and the flash point of oil sample is measured according to ASTM-D 93, and the interfacial number is measured according to ASTM D-971, the density of oil sample is measured according to ASTM-D 4052.

In an embodiment, a process for performing XRD analysis comprises:

cutting solid insulating materials into the dimensions of 180x120mm with the thickness 0.5 mm for Kraft paper and 1I mm for pressboard, wherein the solid insulating materials satisfy IEC 60641-2 standards; keeping the insulating materials in an oven at 90degree Celsius for 48 hours, to reduce the moisture content of test samples; pouring Pongamia Pinnata and mineral oil samples into a separate vacuum box and immersing solid insulating materials in oil samples, wherein the ratio between solid and liquid insulating materials is 10:1; and keeping samples in an oven at 110degree Celsius for one week and thereafter selecting a sample for analysis, wherein Powder XRD analysis is performed using PW3040/60 X'pert PRO instrument.

In an embodiment, the average dielectric strength for Pongamia Pinnata oil is 64 kV, which is much higher than that for mineral oil. In an embodiment, the Pongamia Pinnata oil has a higher amount of unsaturated fatty acids due to this, the viscosity of Pongamia Pinnata oil is high when compared to mineral oil, this viscosity limits the particle movement inside the oil.

In an embodiment, movement of dissociation of oil molecules in the oil is low, due that the conductivity of the oil becomes low; consequently, dielectric dissipation factor of oil also becomes low, wherein the Pongamia Pinnata oil has a polar nature, whereas mineral oil has a polar alkane molecule, which influences the dielectric constant of the oil.

In an embodiment, the dielectric constant of Pongamia Pinnata oil is higher than that of mineral oil and the dielectric constants of both the oil samples decrease with aging that results in reducing the density and viscosity of the oil, which leads an increase samples, and also reducing the dipole orientation of the oil samples, resulting in a low di- electric constant.

In an embodiment, the Pongamia Pinnata oil has a much higher resistivity than the mineral oil, which infers that Pongamia Pinnata oil contamination rate is low when compared to the mineral oil for same sampling temperature.

In an embodiment, the Pongamia Pinnata oil does not influence the cellulose insulation, since the acid generation phenomenal in Pongamia Pinnata oil is in a different manner than mineral oil, wherein in contrast to Pongamia Pinnata oil, acid formation in mineral oil follows chain off, chain continuity and chain breaking out.

In an embodiment, the mineral oil has lower molecular acids such as formic, acetic and levulinic acids, whereas in Pongamia Pinnata oil, it has higher amount of oleic acid and linoleic acid, which are higher molecular fatty acids and these acids do not accelerate the aging rate of the paper, but the lower molecular acids react with paper, so it influences the paper aging.

An object of the present disclosure is to study feasibility on non - edible Pongamia Pinnata oil as an alternate liquid di- electric which can be used in Distribution Transformers.

Another object of the present disclosure is to review the alternate insulating oil, electrical, physical and chemical properties.

Another object of the present disclosure is to carry out solid insulating material deterioration, both in Pongamia Pinnata oil and mineral oil, using XRD and SEM.

Yet another object of the present invention is to deliver an expeditious and cost effective method for evaluating liquid dielectric characteristics and feasibility of Pongamia Pinnata oil as liquid dielectrics.

To further clarify advantages and features of the present disclosure, a more particular description of the invention will be rendered by reference to specific embodiments thereof, which is illustrated in the appended drawings. It is appreciated that these drawings depict only typical embodiments of the invention and are therefore not to be considered limiting of its scope. The invention will be described and explained with additional specificity and detail with the accompanying drawings.

BRIEF DESCRIPTION OF FIGURES

These and other features, aspects, and advantages of the present disclosure will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:

Figure 1 illustrates a flow chart of a method for evaluating liquid dielectric characteristics and feasibility of Pongamia Pinnata oil as liquid dielectrics in accordance with an embodiment of the present disclosure; Figure 2 illustrates a XRD pattern of solid insulating material in accordance with an embodiment of the present invention; Figures 3A and 3B illustrate an SEM image of fresh Kraft paper at x200 magnifications and x400 magnifications, respectively in accordance with an embodiment of the present invention; Figures 4A and 4B illustrate SEM images of aging Kraft paper in mineral oil at x200 magnification in accordance with an embodiment of the present invention; Figures 5A and 5B illustrate SEM images of aging Kraft paper in Pongamia Pinnata oil at x200 magnification in accordance with an embodiment of the present invention; Figures 6A and 6B illustrate SEM images of fresh press board at x200 and x400 magnifications, respectively in accordance with an embodiment of the present invention; Figures 7A and 7B illustrate SEM images of mineral oil aged press board with x200 and x400 magnifications, respectively in accordance with an embodiment of the present invention; and Figures 8A and 8B illustrate SEM images of Pongamia Pinnata oil aged press board with x200 and x400 magnifications in accordance with an embodiment of the present invention.

Further, skilled artisans will appreciate that elements in the drawings are illustrated for simplicity and may not have been necessarily been drawn to scale. For example, the flow charts illustrate the method in terms of the most prominent steps involved to help to improve understanding of aspects of the present disclosure. Furthermore, in terms of the construction of the device, one or more components of the device may have been represented in the drawings by conventional symbols, and the drawings may show only those specific details that are pertinent to understanding the embodiments of the present disclosure so as not to obscure the drawings with details that will be readily apparent to those of ordinary skill in the art having benefit of the description herein.

DETAILED DESCRIPTION

For the purpose of promoting an understanding of the principles of the invention, reference will now be made to the embodiment illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated system, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates.

It will be understood by those skilled in the art that the foregoing general description and the following detailed description are exemplary and explanatory of the invention and are not intended to be restrictive thereof.

Reference throughout this specification to "an aspect", "another aspect" or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present disclosure. Thus, appearances of the phrase "in an embodiment", "in another embodiment" and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment.

The terms "comprises", "comprising", or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a process or method that comprises a list of steps does not include only those steps but may include other steps not expressly listed or inherent to such process or method. Similarly, one or more devices or sub-systems or elements or structures or components proceeded by "comprises...a" does not, without more constraints, preclude the existence of other devices or other sub-systems or other elements or other structures or other components or additional devices or additional sub-systems or additional elements or additional structures or additional components.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The system, methods, and examples provided herein are illustrative only and not intended to be limiting.

Embodiments of the present disclosure will be described below in detail with reference to the accompanying drawings.

Referring to Figure 1, a flow chart of a method for evaluating liquid dielectric characteristics and feasibility of Pongamia Pinnata oil as liquid dielectrics is illustrated in accordance with an embodiment of the present disclosure. At step 102, the method 100 includes inserting electrodes inside the insulating oil for calculating dielectric strength of the insulating oil by upon testing withstand voltage stress without failure, which depends on physical chemical properties of the insulating oil, impurities present in the oil.

At step 104, the method 100 includes measuring breakdown strength of oil sample using Neutronics oil test kit consists of two hemispherical electrodes with 2.5 mm gap spacing and measuring dielectric dissipation factor using Schering circuit test and null indicator oscilloscope.

At step 106, the method 100 includes pouring oil sample into three terminal test cells to from a capacitance where oil acts as a dielectric medium for calculating dielectric constant of oil and evaluating specific resistivity from the ratio between the direct potential gradient in volts/centimeter (V/cm) paralleling the current flow within the sample to the current density in amperes/square centimeter (A/cm2) at a given instant of time and under prescribed conditions.

At step 108, the method 100 includes measuring acidity by pouring required KOH into one gram of oil to neutralize acids and measuring water content of oil sample using coulometrically generated Karl Fischer reagent.

At step 110, the method 100 includes measuring viscosity of oil sample using red wood Viscometer and measuring flash point of oil sample using Pensky Martens Closed cup Test Method and measuring interfacial tension of the oil sample by calculating molecular attractive force (oil and water) between their unlike molecules at the interface using Ring Method and measuring density of oil sample using digital density meter.

At step 112, the method 100 includes performing thermal degree of degradation studies on solid insulating materials like Press board and Kraft paper by XRD and SEM using PW3040/60 X'pert PROinstrument.

In an embodiment, a process for performing XRD analysis comprises:

cutting solid insulating materials into the dimensions of 180x120mm with the thickness 0.5 mm for Kraft paper and 1 mm for pressboard, wherein the solid insulating materials satisfy IEC 60641-2 standards; keeping the insulating materials in an oven at 90degree Celsius for 48 hours, to reduce the moisture content of test samples; pouring Pongamia Pinnata and mineral oil samples into a separate vacuum box and immersing solid insulating materials in oil samples, wherein the ratio between solid and liquid insulating materials is 10:1; and keeping samples in an oven at 110degree Celsius for one week and thereafter selecting a sample for analysis, wherein Powder XRD analysis is performed using PW3040/60 X'pert PRO instrument.

For breakdown strength, Abdi et al. conducted accelerated thermal aging teston andl40 transformer oil at temperature ranges of 80 °C, 100 °C, 120 °C °C for 5000 h of the aging period. For every 500 h of sampling interval, Breakdown strength of oil sample is measured as per IEC 60156 for accessing the electrical characteristics of transformer oil under elevated temperature. Initially, the breakdown strength of oil is 80kV, which is reduced % at the temperature ranges 80 °C and 100 °C for end of aging periods, where it is reduced to 80% when thermally aged at 120 °C. Further raise in temperature dropped the BDV of transformer oil to a critical value after 3000h of sampling periods. Because of overheating of oil, water molecule is developed, which motivates the formation of gas bubbles in the oil. Due to these impurities, a streamer phenomenon occurs in the gas bubbles. It is propagating during application of voltage. This process expands, consequently leading to breakdown. Al E shaikh et al. analyzed corn's oil electrical property and its viability as a liquid dielectric. The breakdown strength of the oil samples is measured as per IEC-60156 by using Foster type 60A automatic oil tester. The mean BDV of mineral oil is 33.9kV with a standard deviation of 3.96, whereas for corn oil, BDV is 46.lkV, with a standard deviation of 4.7kV. However, mineral oil sample has a moisture content of 15ppm, and corn oil is having moisture content of127ppm. It is inferred that the breakdown strength of corn oil is not affected by moisture content because corn oil has more than 70% unsaturated fatty acids. Liao et al. conducted accelerated thermal aging test for catalytic added vegetable (BIOTEMP) oil at 170 °C for 216h which measures BDV of oil samples as per ASTMD 1816. The BDV of oil sample depends on the moisture furfural concentration at the initial stage and acid content at the later stage. The acid content is higher in natural ester oil when compared to mineral oil, but it does not affect the break down strength of Natural Ester oil, because, during thermal aging of natural ester oils, mild long chain fatty acids are generated, which are not corrosive. Furthermore, it generates peroxide, which has a high affinity to hydrogen gas and reduces formation of bubbles in the oil. Singh et al. investigated 10 different transformer oil's BDV for evaluating the influence of the aging factor into oil electrical property. The oil sample's BDV has been measured as per IS335 using a 12.5 mm sphere electrode with 2.5 mm gap spacing. From the experimental results, the BDV of transformer oil decreases gradually, and it bears a nonlinear relationship with aging. During transformer operating condition, an electrochemical stress occurs inside transformer, which degrades the transformer insulation.

These effectively increase the number of conducting particles, which are rapidly increased with aging. Hence, the BDV of oil samples is strongly affected by these impurities. Abderrazzaq et al. evaluated the breakdown strength of olive oil as per the IEC 60156 standard, and the test results are compared with mineral oil. The breakdown strength is performed at 25 °C with a 2.5mm sphere gap electrode. Asper ASTMD877, the average value of unused mineral oil's breakdown strength is 59.2 kV, which is 13.8% higher than the acceptable value. In case of used mineral oil, the breakdown strength is reduced to 24kV, which is 49% of the acceptable value as per IEEE Std C57.106-2002. Due to the operating condition, transformer mineral oil involves an electrometrical stress which contaminates the oil. The unfiltered fresh olive oil breakdown strength is 14.5kV whereas that of the old oil is 10.9kV. The breakdown strength of filtered new olive is 36kV, while it is 19kV for old oil. The naturally grown and irrigated olive oils are filtered by using a multi filtration process.

Due to this process, the average breakdown strength of naturally grown olive oil is significantly increased to 37.5kV while it is 57.75kV for irrigated olive oil, which is best suitable for power transformer applications, because the filtration process effectively removes carbon, free water, sludge, other suspended particles and acidity of oil. Liu and Wang evaluated the breakdown and with standing strength of natural ester (FR3), synthetic ester (Mide17131) and mineral oil (Gemini X) as per the IEC standard. The breakdown voltage is applied to oil samples with the help of 10 stage Haefely impulse generator using sphere to sphere electrode configuration. It can generate 1.2/50 ms Lightning impulse and 250/2500 ms switching impulse. Initially, the negative lightning impulse voltage is applied to oil samples. Gemini X oil sample has higher mean break down strength (243.9kV), followed by Midel 7131 (208.8kV) and for FR3 (202.8kV). Furthermore, Gemini X has higher breakdown strength at the instant of switching impulse voltage, which is followed by 169.7kV for FR3 and 169.2kV for Midel 7131. When the positive lightning impulse is applied to oil samples, the withstand-strength is 236.0kV for Gemini X, which is the highest, followed by 214.5kV for FR3 and 205.7kV for Midel 7131. The lightning impulse voltage is applied to oil sample by the following methods: Rising-voltage (1shot/step), Rising-voltage (3shots/step) Up-and down, Multiple level. Here, breakdown strength is also obtained in the same order. Only the voltage value has to be changed, which infers that the polarity of voltage and test methods do not affect the order of breakdown strength and only change the value of voltage. Arazoe et al. evaluated the breakdown strength of mineral oil, silicone oil (dimethyl), natural ester (FR3) and synthetic ester oil (Midel 7131) at the temperature ranges of 30 °C, 50 °C, 100 °C and

130 °C and evaluated the surface breakdown strength of the composite insulating materials. The Positive impulse voltage (1.2/50 ms) is applied to oil samples, using a sphere plane electrode with the configuration of the 3mm gap. Initially, the breakdown strength of the natural ester (FR3) oil is higher followed by mineral oil (Gemini X), synthetic ester oil (Midel7l3l) and Silicone oil. Up to 100 °C, breakdown strength of the natural ester oil rapidly increases, followed by silicone oil. In contrast, the breakdown strength of mineral oil will get saturated at 70 °C itself. The surface breakdown strength of the composite insulating medium is tested using a sphere plane electrode configuration. The composite insulation material is made by oil with press board and Kraft paper (with the thickness of 3mm and 6mm respectively). The average breakdown strength of FR3 oil composite with a solid insulation system has higher breakdown strength followed by silicone oil, synthetic ester and mineral oil. Since the difference between relative permittivity of Kraft paper with mineral oil insulation medium is more, higher electrical stress will occur, which intern reduces the breakdown strength.

Wang and Wang conducted the breakdown strength for mineral oil (Gemini x), synthetic ester (Midel7l3l), Natural ester (FR3) asper ASTMD 1816. The influence of breakdown strength by using cellulosic materials, copper and water content is investigated. The breakdown voltage is applied to the oil samples; the experiment is carried out with Baur automatic breakdown tester with the 36mm diameter spherical electrode and 1mm gap. From the experimental results, the average breakdown strength of filtered and dehydrated mineral oil sample is 47.7kV, whereas for FR3, it is 44.5kV and 45.1kV for Midel 1713. This breakdown strength is higher than the unprocessed samples. The cellulosic material is added to the clean oil samples. Due to this, particle content of oil is increased.

When its value exceeds 200,000, the breakdown strength of mineral oil sample has to be reduced to 50% of clean oil samples, which is lower than synthetic ester and FR3 oil. When number of the copper particles reached 3000, the breakdown strength of Gemini x oil is reduced to 40% that of clean oil, whereas it is 70% for Synthetic ester and 73% for FR3. This infers that FR3 oil had superior breakdown strength than mineral oil even if it is contaminated by transformer's metallic parts and cellulosic materials. Due to following phenomena, viscosity of mineral oil is low; this allows moving particles more easily than ester oil. The relative moisture content of the oil is low; these water molecules combine with polar molecules of hydrocarbon molecules by weak H-H bonds. In contrast, the relative moisture content of the mineral is high; some of the water molecules which escape from the oil act as a charge carrier. It reduces breakdown strength of oil samples.

Singha et al. conducted the breakdown strength test on HONE and mineral oil as per ASTMD 1816. The oil samples are aged using hot air oven at 150 °C for 3000h. At regular sampling interval, the breakdown strength of oil has been measured. The breakdown strength of the oil HONE sample is not stable before the sampling period of 1176h, but after the sampling period, the HONE oil breakdown is retained but mineral oil breakdown strength has to be reduced. The HONE oil had low water content during the whole ageing period because the water molecules are consumed by the hydrolysis reaction with triglyceride molecules. During ageing periods, the HONE oils emit higher molecular acids, which are easily soluble and miscible in high oleic natural ester oil.

In contrast, the mineral oil has low molecular acids; these lower molecular acids' polarity and structures are different so that the inter molecular force between mineral oil molecules and the acids molecules is different. It will form a separate phase in oil. Due to these phenomena, breakdown strength of mineral oil is effectively reduced. Liao et al. investigated the influence of ageing factor on breakdown strength of Bio temp, Kara may 25# naphthenic based oil with and without the presence of press board. During the first 30 days of sampling period Bio temp oil has higher breakdown strength than that of mineral oil. After days of sampling period, the breakdown strength of Bio temp decreased due to the increase of relative moisture content and acidity of oil. However, in mineral oil, the breakdown strength gets reduced to about 20days of sampling periods. It infers that the contaminated rate of mineral oil is faster than the natural ester oil. The permittivity ratio between the natural ester oil impregnated press boards into natural ester oil is lower than the mineral oil impregnated press board into mineral oil. Due to this, less stress will occur on oil duct which prevents the occurrence of creep discharge on natural ester oil with paper impregnated insulation system. Also, natural ester oil acts as a proactive layer for cellulosic insulating materials, so its degradation rate is low. During operation, the rise in temperature will support the formation of peroxide; it having an affinity to hydrogen gas and reduces the formation of bubbles.

Jeong et al. checked the breakdown strength of aged vegetable and mineral oil samples. The vegetable oil and mineral oil sample 1 have to be sampled at 30 °C for nearly

1674h of aging period, whereas mineral oil sample 2h as to be tested at 30 °C for 756h of aging period. During the aging period, using appropriate lab setup, the top-level-oil temperature is maintained at 120 °C while lowest oil temperature is 30 °C. The breakdown voltage is applied to oil sample using two copper wires with a diameter of 12.5mm with 2.5mm spacing. Throughout, whole aging period vegetable oil has higher acidity and water content than mineral oil samples. But, the breakdown strength of vegetable oil is much higher than mineral oil samples. Because the vegetable oils are composed of carbon and hydrocarbon molecules, they react with oxygen, but it generates a very little quantity of sludge, wherein mineral oil generates huge sludge. Due to this sludge, breakdown will occur earlier in mineral oil samples.

Saruhashi et al. conducted the breakdown strength of thermally aged (1000h at 130 °C and180 °C) natural ester, synthetic ester and mineral oil samples using 2.5mm rod electrode. A negative lightning impulse voltage is applied to the oil samples. Initially, the breakdown strength of the natural ester oil is high, followed by silicone, synthetic ester oil. When thermal ageing increases, it gradually reduces the breakdown strength of oil samples. The mean breakdown value of fresh natural ester oil is 172kV, while that of silicone oil is 153kV and of synthetic ester oil is 121kV. In contrast, the mean breakdown strength of aged natural ester oil is 138kV and that of silicone oil is143kV. The break down strength of aged oil is reduced to 10% for silicone oil, 20% for synthetic ester oil and 30% for natural ester oil, which infers that silicone oil breakdown strength reduction is low because, during ageing process, the total acid number of natural ester oil is higher than that of others. Matharage et al. measured the breakdown strength of the wet mineral oil, Dry mineral oil and coconut oil using rod plain electrode withl5mm gap spacing. The breakdown voltage is applied to oil samples using kVA, 60kV, 50Hz transformer. Initially, the breakdown strength of wet and dry mineral oil is the same (18.6kV), whereas it is 34kV for coconut oil. After's even weeks, wet and dry mineral oils' breakdown strengths get significantly increased to 31.7kV and 31.3kV, respectively. This is because the ageing process effectively removes the moisture content of mineral oil samples, where the breakdown strength of coconut oil is 77.9kV. For all ageing periods, coconut oil has higher breakdown strength; also, the ageing phenome non doesn't affect the breakdown strength of oil, because coconut oil contains higher percentage of lauric and myristic fatty acids which are saturated fatty acids. Due to this, coconut oil is stable even when in contact with oxygen.

Naranpanawe eta 1. evaluated the breakdown strength of virgin coconut oil, Refined Bleached coconut oil, sesame oil and castor oil using two spheres of 2.5mm radius with 2.5mm gap. The di-electric strength of the virgin mineral oil is 10.5kV, whereas breakdown strength of the aged mineral oil is 8.8k V because, during the operation of the transformer, electrometrical stresses occur inside the transformer, which contaminate the liquid and solid insulation. The breakdown strength is 25.7kV for castor oil, 26.9 kV for sesame oil, 10.2kV for raw coconut oil and 18.6kV for RBD coconut oil, Because RBD process reduces the moisture content of coconut oil. Except raw coconut oil, all vegetable oils have much higher breakdown strength than that of mineral oil, because castor oil has mainly 85-95% unsaturated fatty acids while sesame oil contains 70% of mono unsaturated fatty acids. Due to this, the viscosity of oil is much higher than mineral oil, wherein refined, bleached and deodorized coconut oil has saturated fatty oil. Hence, it is said to have higher viscosity than mineral oil, lower viscosity than castor and sesame oils.

Dielectric dissipation factor Sifeddine Abdi et al. conducted accelerated thermal aging test into transformer oil at the temperature ranges of 80 °C, 100 °C, 120 °C and 140 °C for 5000 h of aging period. For every 500h of sampling interval, DDF of the oil sample is measured as per IEC60247 using Automatic Dissipation Factor and Resistivity Test Equipment Diel test DTL system to access the electrical characteristics of transformer oil under elevated temperature. From the experimental results,belowl00 °C operating temperature, DDF of oil sample is 0.0025. It is an acceptable limit, whereas beyond 100 °C the DDF of oil sample is 0.0165, which is much higher than the measured value at 80 °C and 100 °C. Because of an elevated temperature, the ionic mobility is increased, which leads to higher conduction loss. Since viscosity of oil decreases, the oxidation reactions are occurring inside the oil.

Al-E shaikh et al. measures the corn oil using Tettex precision Schering bridge system. At room temperature, DDF of corn oil is almost double that of mineral oil, which increases the neutralization number to great extant when compared to mineral oil at 80 °C DDF of corn oil increases from 0.2% to 2.7%, which increases greatly that of mineral oil. Due to this solid insulating, material does not degrade. Also, DDF of the sample aged at 110 °C for 600h has been measured with catalytic added. At the initial aging process, DDF of corn oil sample is slightly higher than mineral oil because it is composed of glycerol and corporeal groups.

However, after 300h of sampling period, mineral oil DDF is rapidly increasing with temperature rises, because it is mainly composed of hydrocarbon components. This infers that corn oil is more stable than the mineral oil. Liao et al. conducted accelerated thermal aging test on catalytic added vegetable oil at 170 °C for 216h which measures the DDF of oil samples as per ASTMD924. During the first 150h of aging period, the DDF of oil has to be slowly increased. Furthermore, DDF of oil sample is rapidly increased due to the increase of charged particles per volume of oil. Initially moisture and furfural contents are increased, which is significantly reduced at the later stages of aging. Hence, beyond 150h of sampling period, DDF of oil depends on higher molecular weight acids.

Singh et al. investigated the DLF of 10 transformer oils in order to evaluate the influence of the aging factor in oil's electrical property, which is measured as per IS6262-71 using Eltel. The DLF of oil samples is increased with aging. Due to the transformer's operating condition, electrical and chemical stresses occur on Power Transformer. These increase the number of conducting particles in the oil, which effectively increases the possibility of dielectric loss of transformer oil. Liao et al. measured the relative permittivity of natural ester oil, natural ester oil impregnated press board and mineral oil, and mineral oil impregnated press board at a wide frequency range of 20-90 °C using Navo Control Concept broad band dielectric spectroscopy. For all temperature range, relative permittivity of natural ester oil is higher than mineral oil. It is closer to relative permittivity of oil Impregnated press board. The ratio of oil impregnated press board to oil is lower than that of others. Due to this, lower stress will bed is tributed in oil duct or oil wedge.

Hence, it limits the initiation of creepage discharge on natural ester Impregnated insulation system. Rajab et al. measured the dissipation factor of palm oil sample at the temperature ranges of 20-100 °C using the Schering Bridge circuit and a null indicator oscilloscope as per IEC 60247. Results are compared with Silicone oil and traditionally used mineral oil. The dissipation factor of palm oil is more or less equal to Silicone oil for the temperature ranges of 20-60 °C. For further temperature rises, DDF of palm oil is low as compared to silicone oil and mineral oil, Because DDF strongly depends on oil conductivity. The conductivity of oil sample depends on dissociated molecules present in the oil samples. In contrast, the viscosity of palm oil is high, which restricts the mobility of ionized molecules; hence, DDF of oil sample is low.

Shah et al. measured the Dielectric Loss Factor of corn oil and cotton seed oil as per IEC 60296, and the results are compared with PCB free mineral oil. The measurement is performed between 25 and 70 °C temperature ranges, frequency 30-3 MH, using the dielectric loss measurement system. From 330 to 1kHz, the dielectric loss factor of vegetable oil is significantly decreased due to the polarization effect. After 10kHz, the dielectric loss factor of oil will be increased due to conduction with arise in frequency. It is inferred that DLF of vegetable oil is strongly dependent on conductivity and polarization phenomena, wherein transformer oil is a non-polar liquid who's a capacitance changing very little with frequency. Furthermore, it has conductivity; which increases at high-frequency ranges. Hence, DLF of transformer oil depends on conductance only. For all frequency ranges, the DLF of transformer oil is higher than vegetable oils, which infers that it has more stability than that of mineral oil. Xu et al. conducted accelerated thermal aging test on oil samples at 100 °C for 2500h of sampling period under opened and sealed conditions. At regular intervals, the DDF of oil sample is measured using Tettex2821 bridge. Initially, both oils' DDF drops down due to some catalytic oxidation, which could neutralize some ions responsible for high conductance. The DDF of sealed oil sample fluctuates between 0.015 and 0.03 for the whole aging period. After 1000 h of sampling periods, DDF of the open cup thermally aged oil is higher than others because oxidation process of vegetable under open cup condition is more than that of the hydrolysis condition.

Dumitran et al. studied the effect to f accelerated thermal aging on electrical properties of VO and MO with and without catalysts added, using Novo control impedance Analyzer. The accelerated thermal aging test is performed at three temperature ranges (135 °C, 155 °C and 175 °C) for 1600h. The measurement is performed every 200h. At the low temperature range, loss factor did not significantly vary, but at high temperature range (175 °C), it is strongly influenced by the temperature, because of the thermal degradation of insulating materials. The catalyst-added oil sample's dielectric loss is higher than that of another due to thermal degradation of paper, increasing the charge carrier, which reduces the quality of oil. Along with polarization, a conduction phenomenon also increases the dielectric loss of oil.

Ten Bohlen and Koch measured the DDF of with catalytic added Sunflower SHO, Environ temp FR3 Fluid, MideleN, Midel7131and Nynas Nytro300X as per the standards. The oil samples are aging with and without catalyst and presence of air. The DDF of Midele

N oil with catalyst is much higher than that of others because thermal degradation of paper is higher than that of other samples. The DDF of HOSO is low for all testing conditions because it has more than 90% of oleic acids; this increases oxidation stability of the oil. Furthermore, FR3 oil has saturated and unsaturated fatty acids with chain lengths between 14 and 24 carbon atoms, which limit the thermal degradation of FR3 oil during the thermal aging; hence, DDF of oil sample is low. Hosier et al. conducted accelerated thermal aging test into food grade (Green olive oil, Corn oil, yellow, olive oil, Rape seed oil) vegetable oil samples at 105-135 °C using a fan oven for measuring dielectric loss factor. The experimental results are carried out using Dielectric spectroscopy. Thermally aged green olive oil and corn oil exhibit higher dielectric loss irrespective of the presence of catalyst, since these oil samples contains chlorophyll, carotene and its degradation products. Although rape seed oil exhibits higher dielectric loss, its oxidation stability is poor; In contrast, Environ temp FR3 and yellow olive oil exhibit low dielectric loss, since they have good oxidation behavior than that of others.

Pei Guo et al. measured the Dielectric Dissipation Factor of VO and MO at 50Hz using Concept 80 broadband dielectric spectrometer. For all the temperature ranges, DDF of mineral oil is lower than vegetable oil as its polarization is mostly in the form of electronic polarization, so that at 50Hz the DDF of mineral oil is primarily caused by conductivity. It is rapidly increasing with temperature rises. In contrast, vegetable oil polarization is in the form of electronic displacement polarization. Consequently, dipole relaxation of vegetable oil is very small one compared to conductivity loss at 50 Hz. Hence, the DDF of vegetable oil depends on conductivity and is higher than that of mineral oil. Hinduja et al. measure the loss factor of 13 varieties viz. virgin, treated and three different coconut oils using the Insulation Dielectric Analyzer. The experiment is performed at room temperature and high temperature at 65 °C. The heated oil loss factor is reduced to 70% than unheated oil because this process effectively reduced moisture content of oil. As compared to the natural cooling process, the vacuum cooling process has only 25% lower loss. By adding NaOH into oil samples, this effectively reduces FFAs in oil samples. Due to this process, the losses are reduced by 20% when compared to others. Consequently, accelerated thermal ageing process significantly increases the loss factor.

Santanu Singha et al. conducted accelerated thermal aging test into HONE, mineral oil at 150 °C for 3000 hours to assess the electrical property of oil as per international standard. For all ageing periods, DC of HONE is higher than mineral oil. Before 1000 hours of ageing period, the DC of oil samples is not stable due to the presence of ageing by-product of cellulose insulation and oil. Beyond 1000 hours of ageing period, the DC of oil samples is stable. Abdul Rajab et al. measured the Dielectric Constant of palm oil sample at the temperature ranges of 20 °C to 100 °C using the Schering Bridge circuit and a null indicator oscilloscope as per IEC 60247, and the results are compared with Silicone oil and traditionally used mineral oil. The DC of palm oil is 3.26 at 25 °C and 3.23 at 100 °C whereas DC of mineral oil and silicone oil varied from 2.21 to 2.14 and 2.56 to 2.49, respectively. From the experimental analysis, DC of palm oil is significantly higher than that of others. Since the formation of the dipole on palm molecules is very easy when compared to mineral oil and silicone oil it is more prone to polarize under the influence of an electric field and silicone oil it is more prone to polarize under the influence of an electric field.

Z. H. Shah et al. measured the corn oil, cottonseed oil DC, as per IEC 60296, and the results are compared with PCB free mineral oil. The measurement is performed between 25 °C to 70 °C temperature ranges, frequency 30Hz to 3MHz using the dielectric loss measurement system. At room temperature, the DC of vegetable oil is significantly higher than transformer oil. Vegetable oils are having a polar nature; whereas transformer oils are refined oil and so they contain non polar alkaline molecules. If the temperature is raised further, the DC of oil samples is decreased due to the decrease in the density of oil, which is directly related to the dipole orientation. The dipole orientation of oil samples depends on the temperature, which is rising; it increases the kinetic energy of moving particles inside the oil sample; due to this, dipole orientation of oil decreases. Suwarno et al. conducted accelerated thermal aging tests into silicone oil, natural ester Oil and Mineral Oil which measures the Dielectric constant as per IEC 60247 using Tettex standard liquid test measurement cell. The DC is 3.3 for ester oil and 2.9 for silicone oil, 2.5 for mineral oil. Among the oil samples, ester oil has higher water content as compared to others; during ageing process there exists higher water content which promotes liquid as more polar. Due to this, the DC of Natural Ester oil sample is high.

Pei Guo et al. measured the Dielectric constant of VO, MO at 50Hz using Concept8O brad band dielectric spectrometer. The DC of oil samples is decreased at 50 Hz with an increase in temperature. For further temperature rises, it attains a steady state, because when the volume of insulating oil is significantly increased, the density is decreased. Hence, the number of polar molecules' unit volume is decreased as well as the thermal molecules' motion is strengthened. This is limiting dipole turning-direction polarization rate. For all the temperature ranges, vegetable oil has higher DC than that of mineral oil, since it is made up of hydrocarbon molecules whereas; vegetable oil consists of fatty acid triglyceride.

In acidity, Sifeddine abdi et al. conduct accelerated thermal aging test for measuring the acidity of transformer oil at an elevated temperature for 5000 hours of aging periods. The entire ageing period at low temperature range such as 80 °C and 100 °C, 120 °C, the acidity of transformer oil is increased, which is within the acceptable limits because the stability of oil is not affected. Where acidity of oil exceeded the acceptable limits at 140 °C for 2000 hours of sampling periods, the measured acidity of oil is 1.2 mg Cu/g. This infers thermal degradation of insulating oil because the higher temperature promotes oxidation; it leads to acid formation within the oil. Ruijin Liao et al. conducts an accelerated thermal aging test on vegetable oil with NOMEX paper and press board for analyzing acid contents of oil samples as per IEC 60296. This test is performed at 170 °C for 216 hours of sampling periods. The acid content of vegetable oil increases with ageing period; particularly, beyond 192 hours of sampling period, it rises exponentially, because vegetable oil generates acids of higher molecular weight. It is dissolved more in oil and not in paper; hence, these reacting to the cellulosic insulating material is low so that acceleration rate of paper is low.

Santanu Singha et al. conducted an accelerated single thermal aging test into HONE, mineral oil samples at 150 °C for 300 hours for evaluating the acidity of oil samples. The measurement is carried out as per ASTM D974. For first 500 hours of sampling period, mineral oil's acidity content increases with ageing due to the Kraft paper degradation which generates LMWA into oil samples. Furthermore, with the rise in ageing periods, the acidity of oil samples saturates; hence, LMWA doesn't diffuse into the oil and it remained in Kraft paper, which is accelerating the ageing rate of paper. This degradation severely reduces the tensile strength of paper after 500 hours of the sampling period, which is measured according to ASTM D828 using DuPont TM 0659-98. In contrast, HONE oil's acidity is slightly increased up to 336 hours. Furthermore, it hugely increases with ageing periods, because, after 500 hours of sampling periods, the LMA acid gets extracted from cellulose insulation and diffused in the oil samples. Therefore, the tensile strength reduction rate of paper will be saturated after 500 hours of sampling periods.

RuijinLiao et al. conducted an accelerated thermal aging test into with and without Kraft paper, copper wire added biotemp, Karamay 25 naphthenic mineral oil samples at 110 °C for 120 days to evaluating acidity of oil sample per ASTM D974. During an accelerated thermal ageing process, BIOTEMP oil generates HMWA where mineral oil generates LMWA. The HMWA does not react with paper so that the acidity of Natural ester oil sample without paper is higher than the mineral oil. The LMWA easily reacts with a paper due to it is easily absorbed by cellulose insulating materials than that of others. Consequently, press board agreed with mineral oil generates more soluble carboxylic, which is infers that deterioration rate is higher than that of others. For all sampling periods, the acidity of natural ester oil without catalyst is higher than mineral oil.

Daisuke Saruhashi et al. conducted thermal aging test into with catalyst added oil samples at the temperature ranges of 130 °C, 180 °C for 1000 hours to evaluating acidity content of oil samples in terms of TAN according to JIS K2501. From the measurement natural ester oil, Synthetic ester oil TAN value is significantly increased with the rise in temperature; it is much higher than that of silicone oil, since silicone oil has excellent oxidation stability characteristics than that of others. This infers that thermal degradation on Natural Ester and Synthetic ester is higher during the long-time thermal ageing process. B. S. H. M. S. Y. Matharage et al. conducted thermal and electric test on coconut oil and mineral oil. When the oil samples are aging at 120 °C for 7 weeks, the dissolved gases are measured using Myrko faults gas Analyzer. From the analysis, coconut oil exhibits slightly higher amount of H2, CO and C02 than that of mineral oil. Twenty consecutive breakdown tests are conducted to coconut oil; it generates a slightly higher amount of H2 but exhibits a huge amount of CO than mineral oil. Partial discharge fault simulated time coconut oil exhibits a significant amount of CO and C02, but in mineral oil the emission of CO is very less but C02 emission only significant quantity. Thermal and electrical faulty time coconut oil exhibits higher amount of CO and C02 that of mineral oil. Higher the amount of CO and CO2, more will be the solubility. Hence, coconut oil had a higher solubility than mineral oil. The Pressboard and Metal substances are added in oil sample, so that both oil samples emit significant amount of CO and C02.

Yang Xu, Sen Qian et al conducted accelerated thermal aging test into oil sample at 110 °C for 2500 hours of sampling periods under the condition of open, sealed for evaluating vegetable oil acidity as per IEC 62021-1 using Metrohm. 848 titrino plus. The acid content of both oil samples increased with aging time. When compared to closed cup oil samples, acidity of open cup oil is higher since open cup oil samples are in contact with air, which oxidizes the oil sample. It is more pronounced than the hydrolysis reactions on sealed-cup oil samples. H. M. Wilhelm et al. conducted an accelerated thermal aging test into RSO, RRO and SRO at 95 °C for 102 hours an oxygen flow rate llh-1 to measure the acid number of oil samples according to ASTM D974. For the whole ageing period, the acid number of Biovolt A refined soya oil remained within the limits, according to IEEE recommendations (0.3 mg KOH/g). In contrast, acid number of refined rice oil exceeded its threshold limit value before hours of sampling periods, whereas sunflower refined oil takes 80 hours. This infers that Biovolt A, refined soya oil's degradation rate; as well as, its reaction with oxygen is less when compared with other oil samples.

C. Perrier et al. conducted accelerated thermal aging test into vegetable oil (VOl blend of mono- and tri-ester without additive, V02,VO3- Tri-ester), synthetic ester (Tetra ester), mineral oil and silicone oil (Polydimethyl siloxane) at 120 °C for 164 hours to measure the acidity as per IEC 61125C. Before ageing, the acidity of vegetable oill (blend of mono and tri-ester without additive) is higher than that of others. After the ageing period, acidity of Vegetable oill is above 4.5mg KOH/g followed by vegetable oil 3 (Tri-ester) and vegetable oil2 (Tri- ester). While the acidity of Synthetic ester is low when compared to vegetable oil under both the conditions, the acid generation in vegetable oil depends on additive and types of seeds.

In Water Content Analysis, Sifeddine abdi et al. conduct accelerated thermal aging test on transformer oil at the temperature ranges of 80 °C, 100 °C, 120°C and 140 °C for 5000 hours of the aging period. For Every 500 hours of sampling interval, water content of oil sample is measured as per IEC 60814 using automatic Kal Ficher titration method. The water content of oil is within the limits for the whole aging period at 80 °C and 100 °C sampling temperature, whereas it significantly increased at the temperature range of 120 °C and 140 °C, which reaches a critical value after 3000 hours of sampling periods due to the reduced stability of oil; hence, it decomposed and oxidized after overheating at elevated temperature. M. H. Abderrazzaq et al. measured the water content of various type Olive oils as per IEC 60814 standard. The water content of filter new (old) olive oil is 446 (520) ppm while that of unfiltered new (old) oil is 861 (918) ppm. Also, the water content of naturally grown and irrigated olive oil is 1127/1796 ppm. The maximum permissible water content of transformer oil is 50 ppm. This is achieved by reclamation process. The moisture content of olive oil is reduced by heating and filtering process. Heating process has significantly reduced water content of olive oil, but cooling process will increase water content. By filtration process, the moisture of new oil which lesser than unfiltered oil by 93% whereas the reductions are only 76% for old olive oil. Hence, filtration method is an effective method for reduction of water in oil. Santanu signgha et al. compared the absolute and relative moisture content of mineral oil with HONE. The absolute and relative moisture content of mineral oil is increased by at least 250% for 3000 hours of ageing, while the relative moisture content of HONE is increased between 336 to 672 hours of ageing period. After 672 hours of operation, the number of water molecules in HONE decreased, because it involves hydrolysis reaction with water molecule present in the oil, which consumes water molecules. Between 1500 to 2500 hours, the relative moisture content of high oleic oil is slightly increased.

Ruijin Liao et al. compared the relative and absolute moisture content of mineral oil with ester oil under various aging periods. The absolute moisture content of ester oil is much higher than mineral oil for the entire ageing period. The relative moisture content of mineral oil is high except for first 30 days. After 58 days of sampling time, the moisture content of ester oil is 1.25weight%. This is because, moisture reacts with ester oil by a hydrolysis reaction which consumes dissolved water content of natural ester oil. Stefan and Maik Koch analyzed the water solubility of FR3 fluid, Midel eN, Midel 7131, synthetic ester, HOSO and mineral oil. From this analysis, for all the temperature ranges, the water solubility of synthetic ester is higher than all-natural esters, since hydrogen bonds of the polar OH group attract water contents in synthetic ester oil. The water solubility of FR3, model en, mineral oil has increased about 30%, while synthetic ester oil, moisture content decreased 20% under the presence of oxygen at 1440 hours of operation. Daniel martin et al. measure the water solubility of vegetable oil and mineral oil using visala probes and Karl Fishcher titration method. The solubility of mineral oil and vegetable oil is 50 and 1100 ppm at room temperature. It's measured by Vaisala probes. It infers that vegetable oil has higher water solubility than mineral oil. As per ASTM D 1533, water content of vegetable oil on energizing transformer is 30 ppm, which is measured by Karl Fischer titration method. After six months of operation, it gets reduced to 22 ppm. After 26 months of operation, it gets reduced to 7 ppm. During operating condition, the measurement of water solubility of oil follows IEC 60814 Standard. Maikoch et al investigated the water solubility of mineral oil, ester oil and synthetic ester oil. The vegetable oils have fatty acids, which dissolve 20-50 times more hydrocarbon than mineral oil. Also, vegetable oils have a polar group of esters which causes much higher moisture solubility of vegetable oil. During the operation, the water molecule of mineral oil is increased because of lower molecular acids such as formic and acetic acids of mineral oil. The synthetic ester has four ester groups which influence higher water solubility than mineral oil. M-L. Coulibaly et al. measured the moisture content of mineral, vegetable and synthetic ester oils with press board with and without catalysts during the first 15 days of sampling period, vegetable oil samples alone have higher moisture content (above 150 ppm) than that of others. Whereas, after 40 days of sampling period, synthetic ester oil (above 100 ppm) has higher amount of moisture content, followed by mineral oil (above 90 ppm) and vegetable oil (below 30 ppm). This is inferring that vegetable oil's moisture content gradually decreases with increasing ageing time. After 15 days of sampling period vegetable oil with air samples has higher amount of moisture content (above 150 ppm), followed by mineral oil (above 150 ppm) and synthetic ester oil (above 60 ppm). After 40 days of sampling period, it reflects same results for samples without catalysts, with change in quantity. Mineral oil with paper has much higher amounts (above, near 5%) of water content than that of vegetable oil (below 0.5%) and synthetic ester oil with paper samples.

Daniel Martin et al. measured the moisture content of paper impregnated with FR3 liquid samples and Mineral oil impregnated oil samples as per the Standards and compared the results. The samples are dried over a CA-06 Mitsubishi Karl Fischer (KF), and then the water content is measured. Initially, water content of FR3 and mineral oil impregnated oil sample are measured over a dry paper mass and found to be 1.3 and 1.4%, respectively. Before 20 hours of sampling period, the water content of mineral oil impregnated paper sample had a slightly higher amount of water content than the other one. During the ageing period, non-impregnated samples are having higher moisture than oil impregnated samples. After 45 hours of sampling periods, the water content absorption rate of FR3 oil impregnated paper sample is 1% higher than the other, Because FR3 oil is having a higher hygroscopic nature compared to mineral oil. M.A. Usman et al. prepared various propositions of blended vegetable oil samples for measuring the moisture content of oil samples. The oil samples are heated up to 100 °C in the oven. The oil samples' weights are measured before and after sample heating. From this measurement, for 100% soya bean oil, moisture is 2mg/kg, whereas for 100% palmkemal oil, it is 1.9 mg/kg. Consequently, in 50% palm kernel oil, moisture content is above 3.5 mg/kg. Among the samples, 70% blended palm kernel oil has the lowest moisture content, which is 1.5 mg/kg. N.A Muhamad et al. measured the water content of soybean oil and mineral oil as per ASTM D1533 under different conditions (normal dried and wet). Normal mineral oil and FR3 oil samples are having water content of 31 ppm and 170 ppm, respectively. The dried oil samples' moisture contents are 14ppm for mineral oil and 22 ppm for FR3 oil. The wet mineral oil and FR3 oil samples' moisture contents are 40 ppm and 380 ppm, respectively. It is inferred that drying process significantly reduces moisture content of Fr3 oil by 80%, which is 30% higher than that of mineral oil.

In Viscosity, Sifeddine abdi et al. conduct accelerated thermal aging test on transformer oil at the temperature ranges of 80 °C, 100 °C, 120 °C and 140 °C for 5000 hours of aging period. For every 500 hours of sampling interval, viscosity of oil sample is measured according to ISO 3104. Initially measured oil viscosity is 6.998 cSt at 40 °C. However, the viscosity of oil sample is not constant for all sampling temperature and time interval. The reduction rate is high at aging temperature 80 °C for 2500 hours sampling period. Whereas, the viscosity of oil sample reached too high value at 120 °C for 5000 hours of sampling periods. M. A. Al-Eshaikh et al. measured the viscosity of corn oil and mineral oil sample using Oswald Viscometer with an accuracy of 0.1 according to ASTM D-455. Here, the viscosity of oil sample is measured as the ratio of dynamic viscosity to the density of the sample. Kinematic viscosity refers to the capacity of specific oil to move at a given temperature. At room temperature viscosity of cornoil is higher than mineral oil, so that cooling capability oil is low. On the contrary, mineral, which forms sludge inside the transformer when oxidized, reduced the heat transformer's ability of the oil. Whereas, vegetable oil dose not form sludge while oxidation. RuijinLiao et al. Conducted accelerated thermal aging test on catalytic (NOMEX) added vegetable (BIOTEMP) oil sample at 170 °C for 216 hours for measuring viscosity as per ASTM D445. The viscosity of oil sample has to be measured in every 50 hours of sampling time intervals. The viscosity of oil sample satisfies the standard limit at 80 0C, which lies between 11 and 13 cSt, respectively. But, viscosity of oil is much higher at 40°C under flowing dry air. Since the solid and liquid insulation is gradually oxidized, it increases furfural contents and acid in the oil. Furthermore, polymerizations also take place so that the viscosity of oil is high. Hence, at low voltage application, the heat transfer ability of oil is low. But, viscosity of oil is much higher at 40°C under flowing dry air. Since the solid and liquid insulation is gradually oxidized, it increases furfural contents and acid in the oil. Furthermore, polymerizations also take place so that the viscosity of oil is high. Hence, at low voltage application, the heat transfer ability of oil is low. M.H Abderarazzaq et al. measured various types of olive oil viscosity. The viscosity of new and old olive oils is 9.9 and 11.6 cSt, respectively. Also, the viscosity of naturally grown tree oil is 8.43 cSt and irrigated olive oil tree is 8.5 cSt, respectively. If temperature of oil increases, it reduces the oil viscosity and increases the pressure inside the transformer. Hence, viscosity of oil depends on temperature and pressure. Santanu Singha et al. investigate viscosity of mineral oil as per ASTM D445 at 40 °C and compared with High Oleic Natural Ester. During the first 1500 hours of operation, the viscosity of mineral oil and HONE oil is not stable. Up to 3500 hours of operation, the viscosity of HONE and mineral oil almost didn't change, because the test is conducted under nitrogen atmosphere which limits the influences of oxygen with ester oil, so that high oleic natural ester oil is highly suitable for hermetically sealed transformer applications. Yang Xu, Sen Qian measured vegetable oil's dynamic viscosity using Brookfield LV-I pro viscometer at the temperature ranges of 25 to °C with 5 °C intervals. Then, this is converted to kinematic viscosity by using the formula Okinematics = Odynamic/density. In this investigation, density of oil is 0.91 g/cm3; the kinematic viscosity of the open cup oil sample is gradually increased with ageing time while sealed oil viscosity levels off at initial value, which infers that the viscosity of oil is severely affected by oxidation more than hydrolysis. Stefan Ten Bohlen et al. studied the effects of oxygen on viscosity of oil. Natural ester oil's viscosity is strongly increased with the influence of oxygen present in the air. The molecules of ester oils are divided into small elements due to oxidation process where remaining molecules of ester oils involve a polymerization process; it strongly increases the viscosity of oil, so as to maintain ester filled transformer without contact with air. Mineral oil's viscosity is less affected by oxidation as compared with ester oil. IL Hosier et al. measured the viscosity of oil using physical reolabmcl at room temperature with and without catalysts. Sunflower oil's viscosity is significantly increased for all sampling periods; whereas DDB, environment temp and olive oil have no significant change in their viscosities after ageing. Corn oil and rapeseed oil's viscosity is slightly increased when catalyst is added in these oils. Here, a copper wire acted as a catalyst. R karthic et al. evaluated the viscosity of mixed insulating liquids at 60 °C. The viscosities of ester oil, mineral oil and synthetic ester oils are 17.2 cSt, 5.72 cSt and 289.74 cSt, respectively. It infers that mineral oil has lower viscosity than natural and synthetic ester oils, while synthetic ester oil's viscosity is much higher than mineral oil and ester oil. The viscosity of 80% mineral oil mixed with 20% synthetic ester oil is 16.92 cSt while viscosity of 80%mineral oil is mixed with 20% ester oil is 6.82 cSt. Hence, the viscosity of synthetic ester, natural ester oil has to be significantly reduced by mixing it with mineral oil. A

Raymon et al. studied the effect of antioxidants mixing with vegetable oil. The viscosity of sunflower oil, Rice Bran oil, Soya bean oil and corn oils are 132,154,164, and 134 cSt, respectively; this higher viscosity of oils is reduced by adding different quantities of antioxidants. After adding antioxidants, Viscosity of Rice bran oil reduced to a very little amount. In soya bean oil, the viscosity considerably decreased; expect for the 5 g butylated Hydroxyl and 5g acidic acids. Kailas M. Talkit et al. measured the viscosity of soybean, sesame, coconut and sunflower oil using Redwood Viscometer No.1. Also, the author measures the viscosity of the soybean oil mixed together with various proportions of sesame oil, coconut oil and sunflower oil. Up to 30 °C of operation, the viscosity of vegetable oils is very high. While beyond 80 °C operating temperature, the viscosity of vegetable oils significantly decreased. The mixing ratio of 10% soya bean oil with coconut oil had 18.18 cst, which is the minimum value as compared to all other combinations. The mixing of 90% soya bean with 10% coconut oil had a higher viscosity than all other combinations of oil mixing. H. M. Wilhelm, L. Thalia et al. measured the viscosity of Environtemp FR3 and Biotemp liquid at the temperature ranges of 20 °C, 40 °Cand 100 °C as per ASTM D445 standard. In general, viscosity of vegetable oil is 4 times higher than mineral oil. The 20 °C operating temperature viscosity of Environtemp FR3 oil is 77 cSt, which is lower than bitmap (82 cSt). Initially, vegetable oil's viscosity is very high, which gradually decreased after 100 °C of operating temperature. C perrior et al. measures the three types of vegetable oils (VOl blend of mono- and tri-ester without additive, V02, V03- Tri-ester), Synthetic Ester(Tetra ester), Mineral Oil (Polydimethylsiloxane) and Silicone Oil according to ISO 3014 specifications. The viscosity of natural ester oils is higher than the mineral oil and lower than silicone oil. Hence, heat transfer ability of natural ester oil filled transformer is less efficient but better than that of silicone oil. To overcome this cooling tube of transformer should be effectively designed. H.M Wilhelm et al. conducted an accelerated thermal aging test under an oxygen flow rate of 1 Lh-1 in athermo-stabilized bath. The viscosity of Biovolt A and Refined vegetable oils is measured with and without adding antioxidants. At 40 °C, the viscosity of Biovolt A is36.1 x10-6 m2/s, which is rapidly decreasing at 100 °C. At 40 °C, Sunflower oil has higher viscosity than refined soya oil and rice oil, where at 100 °C rice bran oil has a lower viscosity than others. Before adding antioxidants, refined soya oil and rice oil require 2 hours to reach a viscosity limit while sunflower oil requires 10 hours of aging. After adding antioxidant refined soya oil, Sunflower oil reaches a limited value after 69 hours, Whereas Refined rice oil takes 64 hours to reach it; it infers that AD-4 antioxidants could maintain the viscosity of vegetable oil within the limits during the aging process.

In Fire Resistant Characteristics, Sifeddine abdi et al. conducted an accelerated thermal aging test into transformer oil at the temperature ranges of 80 °C, 100 °C, 120 °C and 140 °C for 5000 hours of the aging period. For every 500 hours of sampling interval, flash point of oil sample is measured as per ISO 2719 standard using pensky-Martens Closed-cup method. At low temperature ranges (80 °C,100 °C, 120 °C), the flash point of oil is reduced beyond 3000 hours of sampling periods. It is significantly reduced at 140 °C; the range of reduction is 40 °C. Due to thermal degradation of oil which increases volatile components within the oil, lower molecular acids are generated at higher temperature range. M. H. Abderrazzaq and F. Hijazi measured the flash points of new and old olive oil as per ASTM D92. The flash point of an old olive oil is 300 °C and 330 °C for new olive oil, which infers that ageing factor influences the flash point of insulating oil. After the filtration process, it reflects the same because filtration process does not improve the fire-resistant characteristics of olive oil. Daisuke Saruhashi et al. studied the burning characteristics of dimethyl silicone oil, natural ester oil (Envirotemp FR3) and synthetic ester oil (Midel 7131). Then the results are compared with mineral oil. The flash point of silicone oil is higher than 240 °C, whereas it is 316 °C for soybean oil, 260 °C for synthetic ester oil and 148 °C for mineral oil. The burning characteristic of oil has been performed using a stainless-steel open cup at atmospheric condition. Among the oil samples, natural ester oil has a higher burning temperature, which is followed by 300 °C for silicone oil, 320 °C for synthetic ester oil and 180 °C for mineral oil. But the flame extinguishing characteristics of silicone oil are faster than others due to white oxide film formed on the surface of the oil, inhibiting oxygen supply to the flame. Hence, the burning area is decreased, and the flame gradually disappeared. A. Raymon et al. measured the flash point and fire point of vegetable oil with and without antioxidants using Pensky Martin Flash point apparatus according to ASTM D93. From the measurement, soybean oil had higher flash point (310 °C) and fire point (320 °C) than others. Among the oil samples, sunflower oil has lower flash (260 °C) and fire (270 °C) points where rice bran oil (280 °C) has intermediate characteristics between Sunflower oil and Soya Bean Oil. When Butylated Hydroxyl Toluene is added as an anti-oxidant to oil samples, it reduced the fire resistance characteristics of sunflower oil, rice Brand oil and Corn oil, due to huge ignitable mixtures formed during experiment; as well as citric acid effectively reduces fire resistant characteristics of sunflower oil. S. Senthil Kumar et al. measured the flash point and fire point of Mustard oil, Olive oil, Gingelly oil, Groundnut oil, Sunflower oil, Palm olein oil and Rice bran oil using Pensky Martin Flash point apparatus according to ASTM D93. The flash and fire points of mustard oil is higher than others, since it has high monounsaturated fatty acid and high saturated fatty acid. But the flash point, fire point of rice bran oil is lower than others. Vegetable oils are having higher fire-resistant characteristics than mineral oil. The critical properties of various vegetable oil, refined vegetable oil, natural and synthetic ester oil is shown in Table 1, Table 2, Table 3 and Table 4 respectively.

Table 1: Critical Properties of Vegetable oil

Soya Sunflower Canola Olive HONE Coconut HOS Rice Corn Rapeseed Camellia bean Property oil oil oil oil oil oil oil Bran Oil oil oil oil

27 38-45 45 42 49 60 39.8 37.8 24.3 0.88 trenghikv Dissipation factor 0.59 0.09 0.07 0.11 17.3 0.88 in %at90 'C Dielectric 3.1 2.93 3.19 constant at 25 °C

cStty°n 140 41.4-45 92 37 40 29 40 84 56 44.2 39.9 Moisture <80 110 Content in ppm

Flash point in °C 310 <330 321 280 314 170-225 274 258 320 322

Fire point in °C 320 <360 341 300 280 282 272

Pour point in °C -12 tO -25 -12 -15 23 -17 -28

Acidity in mg KOH/g 0.02 0.05 0.2 0.0241 0.0297 0.6 0.04 Density in kg/dm3 at 0.919 0.92 0.91 0.9 0.9 °C

Referred By 4 9 14 17 22 28 47 48 49

Table 2: Critical Properties of Refined oil

Property RSO RRO RSF RBD

Breakdown strength in kV 42 37 37 73

Dissipation factor in % at 90°C 0.16 0.15 0.36 2

Dielectric constant at 25°C 2.9

Viscosity in cSt at 40°C 33.1 32.4 37.5 43

Moisture Content in ppm 100 99 10

Flash point in °C 318 318 312

Fire point in °C 352 357 350 325

Pour point in °C -12 -15 -6 -18

Acidity inmg KOH/g 0.08 0.04 0.06 0.03

Density in kg/dm3 0.92 0.92 0.92 0.9

Referred By 46 50

Table 3: Critical Properties of Synthetic oil

Property Silicone oil Midel eN Midel 7131 pentaethryol NYCODIEL 1233

Breakdown strength in kV 50 75 75 < 75 65

Dissipation factor in % at 90 °C <0.008 0.01

Dielectric constant at 25°C 2.7 3.1

Viscosity in cSt at 40°C 50 37 28 28 16.1

Moisture Content in ppm 30 50 55

Flash point in °C >300 327 275 260 241

Fire point in °C 370 356 322 284

Pour point in °C -60 -66

Acidity in mg KOH/g 0.0001 <.03 <.03 <0.03 0.02

Density in kg/dm3 0.96 0.92 0.97 0.953

Referred By 9 28 46 51

Table 4: Critical Properties of Natural ester oils

Property Biotemp FR3 Bio Volt A

Breakdown strength kV 45 45 55

Dissipation factor in % at 90°C 0.16 0.05 0.15

Dielectric constant at 25°C

Viscosity in cst at 40°C 40 36 36.1

Moisture Content in ppm 81 68 64

Flash point in °C 322 317 312

Fire point in °C 356 352 346

Pour point in °C -18 -21 -21

Acidity in mg KOH/g 0.01 0.03 0.05

Density in kg/dm3 0.9159 0.9197 0.92

Referred By 42 46

Pongamia Pinnata is a medium sized evergreen tree, which belongs to the family Fabaceae and subfamily Papilionaceae. Its origin is India and in its subcontinents; also, it is successfully introduced in the humid tropical regions of the world such as Australia, Newlands, China and USA. A single tree can produce about 9-90 kg seeds per year, and the yield potential of tree is about (900-9000 kg/ha). The oil content of the tree ranges between - 40 wt%. As it is a nitrogen fixing plant; it improves the fertility of the soil. It is also drought resistant (500-2500 mm rainfall per year), heat resistant (-1-50 °C), synchronizes flowering and har- vesting, tolerates saline conditions and alkaline soils. In an environmental point of view, the C02 sequestrating the perennial tree is estimated at the rate of 30 t/ha/a. Historically, this plant is used in India as a medicine, especially in Ayurveda and Siddha system, and the crude oil is used for curing tumors', piles, skin diseases, abscess, etc., and also used as animal fodder, green manure, timber, water-paint binder, pesticide, fish poison, etc. Recently, Pongamia Pinnata oil has been recognized as a viable source of oil in the biofuel industry. The PPO Fatty acid profile is shown in Table 5.

Table 5: Fatty Acid Profile of PPO

Fatty Acid Molecular Formula Percentage Types Palmitic acid CH 3(CH 2) 14COOH 3.7-7.9 Saturated Fatty Acids Stearic acid CH3(CH 2) 1 1COOH 2.4-8.9 Saturated Fatty Acids

Oleic CH3(CH 2) 14 (CH=CH)COOH 44.5-71.3 Unsaturated Fatty Acids

Poly Unsaturated Fatty Linoleic acid CH3(CH 2) 12(CH=CH)2COOH 10.8-18.3 Acids

Eicosenoic CH3(CH2)18COOH 2.4 Mono Unsaturated Fatty Acids Arachidic C 2 aH 4 0 0 2 5.3 Saturated Fatty Acids Lignoceric acid CH3 (CH 2 ) 2 2 COOH 1.1-3.5 Saturated Fatty Acids

The dielectric strength of insulating oil refers to its ability to withstand voltage stress without failure, which depends on physical chemical properties of the insulating oil, impurities present in the oil and also the arrangement of electrodes. The breakdown strength of oil sample is measured according to IEC 60156. It is conducted by using Neutronics oil test kit, which consists of two hemispherical electrodes with 2.5 mm gap spacing. Dielectric dissipation factor is the measure of dielectric loss of an insulating fluid due to the application of alternating electric field. It is measured according to ASTMD-924 using Schering circuit test and null indicator oscilloscope. The oil sample is poured into three terminal test cells; it is from a capacitance where oil acts as a dielectric medium, this is also used to dielectric constant of oil. The specific resistivity is the ratio between the direct potential gradient in volts/centimeter (V/cm) paralleling the current flow within the sample to the current density in amperes/square centimeter (A/cm2), at a given instant of time and under prescribed conditions. Specific resistance of oil samples is measured according to IEC 60247.

Acidity is the measure of amount of KOH required to neutralize the acids in one gram of oil. This is the best indicator to measure the condition of the oil. The acidity of oil sample is measured ac- cording to ASTM-D 974. The water content has a highly influenced factor for electrical characteristics of insulating oil; also, it deteriorates cellulosic materials, copper and transformer metal parts. The water content of oil sample is measured according to ASTM-D 1533 using coulometrically generated Karl Fischer reagent.

The cooling capacity of oil is highly dependent on oil viscosity. If the oil has a high viscosity, it reduces the fluid flow and heat transfer ability of the oil. The viscosity of oil sample is measured according to ASTM-D 445 using red wood Viscometer. Flash point is the lowest temperature at which the vapor pressure is sufficient to from a flammable mixture with air near the surface of the liquids. The Flash point of oil sample is measured according to ASTM-D 93 using Pensky Martens Closed cup Test Method. Interfacial tension is the measure of the molecular attractive force (oil and water) between their unlike molecules at the interface. It is used to detect the soluble polar contaminations, oil deterioration and oxidation products. The interfacial number is measured according to ASTM D-971 using Ring Method. Density is the ratio between the equal volume of oil and water. This is used to infer the chemical composition of substances in insulating oil. Besides, the quality of oil can be evaluated by density. The Density of oil sample is measured according to ASTM-D 4052 using digital density meter.

Table 6: Comparison of Critical Properties of Pongamia Pinnata oil and Mineral oil

Property Standard Limit PPO MO

Break Down strength in kV IEC 60156 45 64 57 0 Dielectric Dissipation Factor at 25 C 0.05 0.0012 0.05 ASTMD-924 at 90 °C 0.3 0.013 0.16 Dielectric Constant at 25 °C ASTMD-924 2.7 3.5 2.5 at 90 °C 3.1 2.3

Specific Resistivity in Um at 900 C IEC 60247 Min 2x1012 12x10 1 102 Acidity in mgKOH/g ASTM-D 974 Max. 0.015 0.03 0.008 Water Content in ppm ASTM-D 1533 Max. 35 105 45 0 Kinematic Viscosity in cSt at 40 C Max. 12 26 12 ASTM-D 445 at1O00C Max. 3 18 6 Flash Point in °C ASTM-D 93 Min. 145 258 186 Inter Facial Tension mN/m at 25°C ASTM D-971 Min. 40 15 28 Pour Point in °C ASTM-D 97 Max. -40 -10 -40 Density in g/cm3 at 15 0 C 0.924 0.85 at 40 °C ASTM-D 4052 Max.0.910 0.872 0.76 at 90°C 0.65 0.432

The average dielectric strength for Pongamia Pinnata oil is 64 kV, which is much higher than that for mineral oil as shown in Table 6, because mineral oil consists of hydrocarbon component with different compositions. This oil reacts with oxygen and pro duces carbon mono oxide, carbon dioxide, hydrogen and sludge which have effectively reduced breakdown strength. In contrast, Pongamia Pinnata oil has a higher amount of unsaturated fatty acids due to this, the viscosity of Pongamia Pinnata oil is high when compared to mineral oil this viscosity limits the particle movement inside the oil. For all sampling temperatures, the dielectric dissipation factor of mineral oil is higher than that of Pongamia Pinnata oil, because mineral oil are mainly composed of hydrocarbon molecules with 15-40 carbon atoms per molecule and also these molecules are composed of C-C and C-H bonds. Due to thermal stress, the chemical bonds between the atoms get broken. Whereas, in Pongamia Pinnata oil, it has of triglyceride structure. It has more than 70% of unsaturated fatty acids as shown in Table 5, and so the viscosity of Pongamia Pinnata oil is high when compared to mineral oil. So that movement of dissociation of oil molecules in the oil is low, due that the conductivity of the oil becomes low; consequently, dielectric dissipation factor of oil also becomes low.

The Pongamia Pinnata oil has a polar nature, whereas mineral oil has a polar alkane molecule, which influences the dielectric constant of the oil. From the experimental analysis, the dielectric constant of Pongamia Pinnata oil is higher than that of mineral oil as shown in Table 6. The Dielectric constants of both the oil samples decrease with aging. Since it reduces the density and viscosity of the oil, it leads an increase samples, and also it reduces the dipole orientation of the oil samples, resulting in a low di- electric constant. The specific resistivity of the oil gradually decreases when the temperature rises. It has a direct relationship with the interfacial tension and the dielectric loss factor. When the oil has low resistivity, it increases the conductivity and reduces the breakdown strength of the oil. Here, Pongamia Pinnata oil has a much higher resistivity than the mineral oil as shown in Table 6, which infers that Pongamia Pinnata oil contamination rate is low when compared to the mineral oil for same sampling temperature.

In Chemical properties of Investigated oils, acid generation in Pongamia Pinnata oil is higher than that of mineral oil as shown in Table 6. It does not influence the cellulose insulation, since the acid generation phenomenal in Pongamia Pinnata oil is in a different manner than mineral oil. In contrast to Pongamia Pinnata oil, acid formation in mineral oil follows chain off, chain continuity and chain breaking out. Thus, mineral oil has lower molecular acids such as formic, acetic and levulinic acids, whereas in Pongamia Pinnata oil, it has higher amount of oleic acid and linoleic acid, which are higher molecular fatty acids. These acids do not accelerate the aging rate of the paper, but the lower molecular acids react with paper, so it influences the paper aging. The water content of Pongamia Pinnata oil is much higher than that of the mineral oil as shown in Table 6. Because of moisture, saturation limit Pongamia Pinnata oil is much higher than that of mineral oil. Even though, the investigated electrical characteristics of Pongamia Pinnata oil is better than mineral oil, since mineral oil had high relative moisture content than Pongamia Pinnata oil. According to the Mark-Houwink-Sakurada equation, viscosity of oil is related to the average molecular weight. It is much higher in Pongamia Pinnata oil than in mineral oil. Aging factor and severe oxidation are highly influencing the oil's viscosity. The viscosity of Pongamia Pinnata oil is higher for all sampling temperature than mineral oil.

In Physical Properties of Investigated oils, a flash point is the best indicator that determines the quantity of volatile contamination present in the insulating oil. If the flash point is low, it contains a higher amount of volatile contamination. The flash point of mineral oil is much higher than that of mineral oil, so that it is suitable for fire sensitive areas. Interfacial tension is used to detect the soluble polar contamination, oil deterioration and oxidation products. The Pongamia Pinnata oil has higher acid content than the mineral oil. Also, the polar content is more than the mineral oil. Hence, interfacial tension of Pongamia Pinnata oil is lower than that of mineral oil in the same sampling temperature. The density of Pongamia Pinnata oil is higher than the mineral oil. However, the density of oil samples is gradually increased with temperature raise.

In Sample Preparation for XRD, SEM, the thermal degree of degradation studies on solid insulating materials like Press board and Kraft paper has been performed by XRD, SEM. At first, the solid insulating materials are cut to the dimensions of 180x120mm with the thickness 0.5 mm for Kraft paper and 1 mm for pressboard, respectively. These solid insulating materials satisfy IEC 60641-2 standards. Subsequently, these insulating materials are kept placed in an oven at 90 °C for 48 hours, which has significantly reduced the moisture content of test samples. Then, Pongamia Pinnata and mineral oil samples are poured into a separate vacuum box. Then, the solid insulating materials are immersed in oil samples. The ratio between solid and liquid insulating materials is 10:1. Then, samples are kept placed in an oven at 110 °C for one week. After that, a sample is taken for further analysis. The Powder XRD analysis is performed using PW3040/60 X'pert PROinstrument. The instrument specifications are enclosed in annexure.

Figure 2 illustrates a XRD pattern of solid insulating material in accordance with an embodiment of the present invention. Figure 2 includes 6 patterns i.e., a, b, c, d, e, and f, wherein (a) Fresh Mineral oil (b) Aged Kraft paper with Mineral oil (c) Aged press board with Pongamia Pinnata oil (d) Fresh Pongamia pinnata oil (e) Aged Pongamia Pinnata oil with Kraft paper (f) Aged Pongamia Pinnata oil with press board. The electrical properties of cellulosic insulating materials are depending on its crystal structure and crystalline. The XRD analysis is one of the effective methods for investigating the crystal structure of the cellulosic fiber in transformer solid insulation. It analyses the length, width, height, diffraction angle and crystal structure identification as well as chemical phase angle that could be presented. A typical XRD pattern of solid insulating material is shown in Figure 2. It shows two types of segment presents in the pattern. One is sharp diffraction peaks with high relative intensity related to crystalline character since paper consists of higher amount of cellulose. Consequently, smooth diffraction peaks with low intensity is appeared on spectrum. Since paper contains small amount of hemi cellulose and lignin, XRD spectrum is evidence of crystalline and amorphous regions exiting in the solid insulation. However, the crystalline regions are compact whereas, amorphous regions are disordered, irregular and easily deteriorate. The change in insulating materials is assessed by the crystallite size, relative crystallinity and relative intensity, respectively.

The crystal size of insulating material is calculated by Scherrer equations:

X- X-ray wave length P- Full width at half maximum of the reflectance surface, hkl measured in 20 (0 is the corresponding Bragg angle) The relative crystalline of cellulosic insulating materials is calculated using the following formula.

%Cr1= X 100........

where CrI-relative Crystallinity 1002- diffraction intensity of crystalline region lam- diffraction intensity of amorphous region

Table 7: Degradation Studies on solid insulating Materials Sample Type Crystallite Size in nm % Crystallinity Fresh Kraft paper 4.335 44.17 Aged Kraft paper with Miner oil 4.286 41.1255 Aged Kraft paper with Pongamia Pinnata oil 5.009 54.48 Fresh Press Board 6.676 76.69 Aged Press Board with Mineral oil 6.776 76.57 Aged Press Board with Pongamia Pinnata oil 5.226 83

The crystallite size of the sample aged with mineral oil immersed cellulosic insulating materials is slightly decreased when compared to new cellulosic insulating materials, since chain scission is very low in crystalline region than that of amorphous, these regions have more free energy when compared to crystal region. Hence, influence of temperature is more in amorphous than that of crystalline region. On the Contrary, the Kraft paper crystallite size slightly increases whereas pressboard crystallite size is slightly decreased when solid insulating materials are immersed in Pongamia Pinnata oil that of others.

However, the percentage of crystallinity index of mineral oil immersed solid insulating materials is slightly decreased when compared to fresh sample as shown in Table 7 Whereas, the percentage of crystallinity Pongamia Pinnata oil is much higher than that of others. It infers that degradation rate of solid insulating materials is low when they are immersed in Pongamia Pinnata oil than that of others. Our results are in a good agreement with the results of M. Ali et al.

Figures 3A and 3B illustrate an SEM image of fresh Kraft paper at x200 magnifications and x400 magnifications, respectively in accordance with an embodiment of the present invention. It shows cellulose fibres joined mutually and packed in order. As well as, there is no bond breaking between the cellulose fibres. Furthermore, cellulose fibres are forming a chain structure.

Figures 4A and 4B illustrate SEM images of aging Kraft paper in mineral oil at x200 magnification in accordance with an embodiment of the present invention. It showed that cellulose fibers' order is not drastically changed. But the same spot appears as white; it is clearly shown in Figure 4B. This is indicating fiber order displacement and rough surface on samples. The change of surface from smooth to rough is an indication of deterioration of the samples. It is caused by thermal stress.

Figures 5A and 5B illustrate SEM images of aging Kraft paper in Pongamia Pinnata oil at x200 magnification in accordance with an embodiment of the present invention. It demonstrates that when the of fibers are tightly packed together, there is no band breaking. When magnification increased, it is clearly indicating that the fibers are packed-in tightly. Hence, influencing thermal stress on solid insulating material is lower than that of mineral oil immersed Kraft paper.

Figures 6A and 6B illustrate SEM images of fresh press board at x200 and x400 magnifications, respectively in accordance with an embodiment of the present invention. Both images are clearly indicating a fresh press board cellulose fiber, which is in order as well as connected mutually. In addition, there is no band breaking.

Figures 7A and 7B illustrate SEM images of mineral oil aged press board with x200 and x400 magnifications, respectively in accordance with an embodiment of the present invention. Aged cellulosic insulation fibers' order is hugely changed than that of the fresh press board, and middle layer of fibers is exposed. This is indicating that there is bond breaking. It is inferred that thermal aging process significantly deteriorates the press board.

Figures 8A and 8B illustrate SEM images of Pongamia Pinnata oil aged press board with x200 and x400 magnifications in accordance with an embodiment of the present invention. It indicates that cellulose fibers' orders are not significantly changed. As well as, the changes of structure in cellulosic fibers is not significant. Figure 4.13 clearly shows that no bond breaking takes place. From the SEM analysis, it is found that cellulose insulation degradation is low in the presence of Pongamia Pinnata oil than that of mineral oil.

In an embodiment it is concluded that, a broad review about the critical properties of alternating insulating fluid has been made. The main conclusions are summarized as follows. The breakdown strength of corn oil, filtered type irrigated olive oil, coconut oil has satisfies the minimum requirement as a liquid dielectric for Transformers. Also, natural ester oil like an Environtemp FR3, BIOTEMP has higher breakdown strength than that of mineral oil. Among them, Environtemp FR3 has higher with- stood strength under impulse condition. The Dielectric Dissipation Factor of corn oil, palm oil, cottonseed oil, yellow olive oil and FR3 oil is lower than that of mineral oil but rapeseed oil has high. The dielectric constant of palm oil, corn oil, cottonseed oils are higher than that of mineral oil. Also, the specific resistivity of vegetable oil is much higher than that of conventionally used mineral oil. Furthermore, the fire resistant characteristics vegetable oil is comparable than mineral oil since it has higher flash point and fire point temperature, respectively. Moreover, the absolute moisture content in the ester fluids is much higher than that of mineral oil while the relative water content in mineral oil is high. However, the silicone oil and synthetic ester oil has higher oxidation stability than ester oils. But silicone oil has low bio degradable characteristics than the vegetable oil. Consequently, vegetable oil is best alternative liquid dielectrics for transformer application due to it has better electrical, fire safety and bio degradable characteristics than the mineral oil. Experimental analysis shows that, Pongamia Pinnata oil, electrical properties such as breakdown strength, dielectric dissipation factor, dielectric constant and specific resistivity is higher than that of mineral oil. Whereas, in mineral oil has lower absolute moisture content that of mineral oil. Also, acidity is lower than that of Pongamia Pinnata oil. But these are dose not influencing critical characteristics of Pongamia Pinnata oil, since its acid generation is beneficial that of mineral oil and so relative water con- tent is low. Furthermore, viscosity of Pongamia Pinnata oil more than two times higher than the Pongamia Pinnata oil for same sampling temperature so that care must to be needed for cooling tube design of transformers. From the physical property point of view it has higher fire resistance characteristics hence it is suitable for fire sensitive areas. Degradation studies of solid insulating materials immersed in Pongamia Pinnata oil and mineral oil have been successfully investigated using XRD and SEM analysis. XRD analysis shows that the relative crystallinity of Pongamia Pinnata oil impregnated solid insulation is higher when compared to mineral oil impregnated solid insulation. On the Contrary, crystallite size reduction in Pongamia Pinnata oil immersed solid insulating material is low as compared to others. From the SEM analysis, it has been inferred that the degradation of solid insulating material immersed in mineral oil is high compared to Pongamia Pinnata oil immersed solid insulating materials. All the above studies show positive results for using Pongamia Pinnata oil as an alternative fluid for distribution transformers.

The drawings and the forgoing description give examples of embodiments. Those skilled in the art will appreciate that one or more of the described elements may well be combined into a single functional element. Alternatively, certain elements may be split into multiple functional elements. Elements from one embodiment may be added to another embodiment. For example, orders of processes described herein may be changed and are not limited to the manner described herein. Moreover, the actions of any flow diagram need not be implemented in the order shown; nor do all of the acts necessarily need to be performed. Also, those acts that are not dependent on other acts may be performed in parallel with the other acts. The scope of embodiments is by no means limited by these specific examples. Numerous variations, whether explicitly given in the specification or not, such as differences in structure, dimension, and use of material, are possible. The scope of embodiments is at least as broad as given by the following claims.

Benefits, other advantages, and solutions to problems have been described above with regard to specific embodiments. However, the benefits, advantages, solutions to problems, and any component(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential feature or component of any or all the claims.

Claims

WE CLAIM

1. A method for evaluating liquid dielectric characteristics and feasibility of Pongamia Pinnata oil as liquid dielectrics, the method comprises:

inserting electrodes inside the insulating oil for calculating dielectric strength of the insulating oil by upon testing withstand voltage stress without failure, which depends on physical chemical properties of the insulating oil, impurities present in the oil; measuring breakdown strength of oil sample using Neutronics oil test kit consists of two hemispherical electrodes with 2.5 mm gap spacing and measuring dielectric dissipation factor using Schering circuit test and null indicator oscilloscope; pouring oil sample into three terminal test cells to from a capacitance where oil acts as a dielectric medium for calculating dielectric constant of oil and evaluating specific resistivity from the ratio between the direct potential gradient in volts/centimetre (V/cm) paralleling the current flow within the sample to the current density in amperes/square centimetre (A/cm2) at a given instant of time and under prescribed conditions; measuring acidity by pouring required KOH into one gram of oil to neutralize acids and measuring water content of oil sample using coulometrically generated Karl Fischer reagent; measuring viscosity of oil sample using red wood Viscometer and measuring flash point of oil sample using Pensky Martens Closed cup Test Method and measuring interfacial tension of the oil sample by calculating molecular attractive force (oil and water) between their unlike molecules at the interface using Ring Method and measuring density of oil sample using digital density meter; and performing thermal degree of degradation studies on solid insulating materials like Press board and Kraft paper by XRD and SEM using PW3040/60 X'pert PROinstrument.

2. The method as claimed in claim 1, wherein the breakdown strength of oil sample is measured according to IEC 60156 and the dielectric dissipation factor is measured according to ASTMD-924 and the specific resistance of oil samples is measured according to IEC 60247 and the acidity of oil sample is measured ac- cording to ASTM-D 974, and the water content of oil sample is measured according to ASTM D 1533, and viscosity of oil sample is measured according to ASTM-D 445, and the flash point of oil sample is measured according to ASTM-D 93, and the interfacial number is measured according to ASTM D-971, the density of oil sample is measured according to ASTM-D 4052.

3. The method as claimed in claim 1, wherein a process for performing XRD analysis comprises:

4. The method as claimed in claim 1, wherein the average dielectric strength for Pongamia Pinnata oil is 64 kV, which is much higher than that for mineral oil.

5. The method as claimed in claim 1, wherein the Pongamia Pinnata oil has a higher amount of unsaturated fatty acids due to this, the viscosity of Pongamia Pinnata oil is high when compared to mineral oil, this viscosity limits the particle movement inside the oil.

6. The method as claimed in claim 1, wherein movement of dissociation of oil molecules in the oil is low, due that the conductivity of the oil becomes low; consequently, dielectric dissipation factor of oil also becomes low, wherein the Pongamia Pinnata oil has a polar nature, whereas mineral oil has a polar alkane molecule, which influences the dielectric constant of the oil.

7. The method as claimed in claim 1, wherein the dielectric constant of Pongamia Pinnata oil is higher than that of mineral oil and the dielectric constants of both the oil samples decrease with aging that results in reducing the density and viscosity of the oil, which leads an increase samples, and also reducing the dipole orientation of the oil samples, resulting in a low di- electric constant.

8. The method as claimed in claim 1, wherein the Pongamia Pinnata oil has a much higher resistivity than the mineral oil, which infers that Pongamia Pinnata oil contamination rate is low when compared to the mineral oil for same sampling temperature.

9. The method as claimed in claim 1, wherein the Pongamia Pinnata oil does not influence the cellulose insulation, since the acid generation phenomenal in Pongamia Pinnata oil is in a different manner than mineral oil, wherein in contrast to Pongamia Pinnata oil, acid formation in mineral oil follows chain off, chain continuity and chain breaking out.

10. The method as claimed in claim 1, wherein the mineral oil has lower molecular acids such as formic, acetic and levulinic acids, whereas in Pongamia Pinnata oil, it has higher amount of oleic acid and linoleic acid, which are higher molecular fatty acids and these acids do not accelerate the aging rate of the paper, but the lower molecular acids react with paper, so it influences the paper aging.

inserting electrodes inside the insulating oil for calculating dielectric strength of the insulating oil by upon testing withstand 102 voltage stress without failure, which depends on physical chemical properties of the insulating oil, impurities present in the oil

measuring breakdown strength of oil sample using Neutronics oil test kit consists of two hemispherical electrodes with 2.5 mm gap spacing and measuring dielectric dissipation factor using Schering circuit test and null indicator oscilloscope 104

pouring oil sample into three terminal test cells to from a capacitance where oil acts as a dielectric medium for calculating dielectric constant of oil and evaluating speciﬁc resistivity from the ratio between the direct potential gradient in volts/centimeter (V/cm) paralleling the current ﬂow within the sample to the current density in amperes/square centimeter 106 (A/cm2) at a given instant of time and under prescribed conditions

measuring acidity by pouring required KOH into one gram of oil to neutralize acids and measuring water content of oil sample 108 using coulometrically generated Karl Fischer reagent

measuring viscosity of oil sample using red wood Viscometer and measuring flash point of oil sample using Pensky Martens Closed cup Test Method and measuring interfacial tension of the oil sample by calculating molecular attractive force (oil and 110 water) between their unlike molecules at the interface using Ring Method and measuring density of oil sample using digital density meter

performing thermal degree of degradation studies on solid insulating materials like Press board and Kraft paper by XRD and 112 SEM using PW3040/60 X’pert PROinstrument

Figure 1

Figure 2 Figure 3A Figure 3B

Figure 4A Figure 4B Figure 5A

Figure 5B Figure 6A Figure 6B

Figure 7A Figure 7B Figure 8A

Figure 8B