Transformer oil is a petrolium product like kirocene,petrol,diesel,etc .The chemical name of
transformer oil is "hydro treated light nepthanic distilate.". Insulating oil in an electrical power
transformer is commonly known as Transformer oil.It is normally obtained by fractional distilation and subsequent treatment of crude petrolium.That is why this oil is also
known as Mineral insulating oil.
This product is used mainly for three purposes in power field. One for cooling of electrical equipments like CT,PT,metering units etc. Second for prvention of flash over between their live and ground parts and the third for arc extinction.as in OCB. Being in service for a long time transformer oil comes in contact with atmospheric nitric and nitrous acid clearly proves that nitric acid and nitrous acid producing acid and slug in it. Such oil taste slightly bitter. The dust and dirt from atmosphere also contaminate the oil reducing its dielectric strength.Moisture absorbed by winding and other insulatin materials play much important role in decreasing the dielectric strength of T Oil.The isulation resitance between live and ground parts also reduce increasing the chance of Flash over.In practice it has been observed that when in transformers water leaks into them and settles in bottom the transformer does not hold but if water is drained through lower outlet valve and the transformers charged they hold and start working. The above observations clearly prove that impurities when combine with water reduce dielectric strength.Distilled water is insulator of electricity.This shows that impurities when combined with moisture reduce the insulation resistane.Polarisation factor used as a measure of cleanliness of electrical equpments is defined as 1 minute insulation resitance to 15 seconds insulation resistance..Its value shouls not be less than 1.2. In order to improve The electrical properties of any oil filled elecrical machine ,acidity,impurities,and the moisture of T oil must be removed.
From the above discussions we come to the conclusion that to reclaim the old and impure T oil we will have to remove dirt,sludge,water and acid from it. The convetional China clay method in which alkaline clay is churned with T oil and then left to settle the dirt with clay in the bottom of receptacle is not practically a successful method. Traces of clay and impurities remain in oil reducing the desired properties.It has also been found that in some cases the dielectric strength of original oil reduce from its original value before reclamation. In order to overcome the above shortcomings of reclaimatioon of T oil a simple economic but more effect method had been developed by me while posted at MRT Dalton Ganj in 1995. and was demostrated to Honarable G N Roy Yadav. Member Technical Bihar State Electricity Board . Its production model was developed at TRW Chandauti Gaya and the result was found unexpectadly encouraging. In the acute crisis of T oil about 10,000 liters of usable oil were reclaimed and used successfully. The demand of Transformers repaired at Gaya increased from the fields.By use of T oil reclaimed through this method the rate of failure of repaired transformer reduced drastically.
This product is used mainly for three purposes in power field. One for cooling of electrical equipments like CT,PT,metering units etc. Second for prvention of flash over between their live and ground parts and the third for arc extinction.as in OCB. Being in service for a long time transformer oil comes in contact with atmospheric nitric and nitrous acid clearly proves that nitric acid and nitrous acid producing acid and slug in it. Such oil taste slightly bitter. The dust and dirt from atmosphere also contaminate the oil reducing its dielectric strength.Moisture absorbed by winding and other insulatin materials play much important role in decreasing the dielectric strength of T Oil.The isulation resitance between live and ground parts also reduce increasing the chance of Flash over.In practice it has been observed that when in transformers water leaks into them and settles in bottom the transformer does not hold but if water is drained through lower outlet valve and the transformers charged they hold and start working. The above observations clearly prove that impurities when combine with water reduce dielectric strength.Distilled water is insulator of electricity.This shows that impurities when combined with moisture reduce the insulation resistane.Polarisation factor used as a measure of cleanliness of electrical equpments is defined as 1 minute insulation resitance to 15 seconds insulation resistance..Its value shouls not be less than 1.2. In order to improve The electrical properties of any oil filled elecrical machine ,acidity,impurities,and the moisture of T oil must be removed.
From the above discussions we come to the conclusion that to reclaim the old and impure T oil we will have to remove dirt,sludge,water and acid from it. The convetional China clay method in which alkaline clay is churned with T oil and then left to settle the dirt with clay in the bottom of receptacle is not practically a successful method. Traces of clay and impurities remain in oil reducing the desired properties.It has also been found that in some cases the dielectric strength of original oil reduce from its original value before reclamation. In order to overcome the above shortcomings of reclaimatioon of T oil a simple economic but more effect method had been developed by me while posted at MRT Dalton Ganj in 1995. and was demostrated to Honarable G N Roy Yadav. Member Technical Bihar State Electricity Board . Its production model was developed at TRW Chandauti Gaya and the result was found unexpectadly encouraging. In the acute crisis of T oil about 10,000 liters of usable oil were reclaimed and used successfully. The demand of Transformers repaired at Gaya increased from the fields.By use of T oil reclaimed through this method the rate of failure of repaired transformer reduced drastically.
The principle of this method is very simple. When a dirty clothe soaked with T oil is kept inside the bottom of a container filled with water ,clean oil will go up onto the
surface of water because the oil is lighter than water.If a filter is placed in the path,the oil will be more filtered and more clean. The main problem is how to put an oil
of less density (density of T oil is 0.89 at 29 deg C) below water.For this ,T oil is is kept at a heightof higher than water kept in main filter F2( at least 6 inches
higher than the water lavel in the main filter F2) and oil is injected in the bottom of water of F2 through a pipe.
In upward journy of T oil through water acid of water is dissolved in water and the sand prevents the other impurities from going up with water. By this process clean oil collects on the upper surface which goes to the top of next sand filter F3. Clean oil collects in tank provided with air finned heaters.The moisture evavorates giving a pure ,clean,acid free and dry oil ready for use.
In upward journy of T oil through water acid of water is dissolved in water and the sand prevents the other impurities from going up with water. By this process clean oil collects on the upper surface which goes to the top of next sand filter F3. Clean oil collects in tank provided with air finned heaters.The moisture evavorates giving a pure ,clean,acid free and dry oil ready for use.
Procedures
a) In this method an open tank made of steel sheet (shown in extreme right ) is kept on a height such that its outlet is about 6 inches above the outlet of main filter F2. A filter F1 is placed vertical inside this tank.Dirty and impure oil is filled in this tank. Dirty and impure oil is filled in this tank with the help of a of a motor. oil of this tank goes inside filter F1.which is connected to the lower outlet valve of the dirty tank.This outlet is connected to the lower inlet of filter of filter F2. On the outlet nipple of dirty tank a vertical transparent pipe is provided which works both as dirty oil level indicator and enclosed air release pipe for smooth flow of oil nto the main filter F2.Dirty oil is filled in this tank and left for 12 hours for settling water and slugs in bottom which is poured out from valve provided in its bottom.b)
On the pricple that water seeks its own level the impure oil connected to bottom of main filter (F2) passes through the sand kept in a cotton bag. Water is filled in this filter upto the level of sand.By feeding T oil from bottom we get rid of clogging of filter which is found when oil is fed from top side of sand.The body(box) of this filter is made of steel sheet of 4 mm thickness on the upper surface of this filter an air release pipe of 3/4 inch dia is fitted vertically. As soon as oil enters into F2 it being lighter than water makes an upward journey.through sand and water due to boyancy.Solid impurities are filtered by sand and the acid is diluted in water.The filtered oil collected on upper suface of sand is fed to a thired sand filter (F3). As such oil is filtered in three stages by filter F1,F2 and F3. Water acts as solvent of acidity.
c) Clean oil collected in bottom F3 is sent to aan open steel box provided with two numbers of air finned electric heaters2 kw each.The heaters should not be taken out of heating tank withot first disconnecting its electric supply supply else fire will catch in the oil. On heating T oil for 4 hours The yellow bubbles vanish giving an idication for complete removal of moisture and completion of heating process. Now the oil is ready for use. The di electric strength of reclaimed oil is found greater than 55KV/2.5mm gap or 32KV/2mm gap.required for use in transformers and switch gears. Neutralisation value original unclaimed sample was 0.4 mg of koh /gram which improved to 0.3mgkoh/gram a permisible limit for use.
A temperature meter is provided in heating chamber so that the temperature of T oil may be kept below 100 deg c.Hot oil when poured on hot jobs give higher IR(insulation resistance) In spite of its numerous advantages this method as with others is also ineffective in reclamation of oil contaminated with liquid impurities like diesel and kerocene oil etc. In T oil mixed with other petrolium products The IR(insulation resistance)of HT Winding of transformer becomes less than that of lt winding which is reverse of a normal case.None use of forced circulation ensures quality of purification and reclamation.