Claims:WE CLAIM:
1. A system for cooling oil of a transformer, the system comprising:
a first unit having a refrigerant-absorbent mixture at a first concentration, and a first pathway connected with the transformer for carrying hot oil from the transformer through the first unit, at-least a portion of the first pathway submerged in the mixture at the first concentration causing a heat transfer between the hot oil and the mixture at the first concentration, whereby temperature of the hot oil is reduced to a first cooled state and refrigerant vapors are formed resulting in a refrigerant-absorbent mixture at a second concentration inside the first unit;
a liquefier unit connected with the first unit for condensing the refrigerant vapors from the first unit to a liquid refrigerant; and
a second unit having a heat exchange section and an absorption section, the heat exchange section having a second pathway connected with the first pathway, and the heat exchange section connected with the liquefier unit for introducing/spraying the liquid refrigerant onto the second pathway causing a heat transfer between the oil at the first cooled state in the second pathway and the liquid refrigerant whereby temperature of the oil at the first cooled state is reduced to a second cooled state and the refrigerant evaporates forming refrigerant vapors, and the absorption section connected with the first unit for introducing/spraying the mixture at the second concentration from the first unit, the mixture at the second concentration absorbs the refrigerant vapours forming the refrigerant-absorbent mixture which is returned to the first unit, and the oil in the second cooled state in the heat exchange section is returned to the transformer.
2. The system as claimed in claim 1, wherein the first pathway and the second pathway is a pipe or a conduit.
3. The system as claimed in claim 1, wherein the refrigerant-absorbent can be selected from any of lithium bromide in water, ammonia-water, ammonia-sodiumthiocynate, ammonia-lithium nitrate, ammonia-calcium chloride, ammonia-isobutene, water-lithium chloride and methyl chloride-tetraethylene glycol dimethyl ether mixtures.
4. The system as claimed in claim 1 further comprises of a heat pipe connected between the first unit and the liquefier unit.
, Description:FIELD OF THE INVENTION
[001] The invention relates to transformers, more particularly to a system, for cooling oil of an oil immersed transformer.

BACKGROUND OF THE INVENTION
[001] Generally, oil immersed transformers are used for high voltage applications. It is well known that such transformers generate a lot of heat, and the oil inside the transformer acts as an insulator and a coolant allowing the transformer to function efficiently. Hence, it is essential to cool the oil so as to avoid damage or malfunction of the transformer and/or its parts.
[002] Figure 1 shows a system 110 for cooling oil of an oil-immersed transformer 120 as per prior-art. The system includes a radiator unit 112 connected with the transformer. Typically, such transformers as shown include a tank 122, a core 124 and transformer windings 126. The transformer winding dissipate heat which is absorbed by the transformer oil in the tank and conducts it to the radiator unit through an outlet 128, and the heat is dissipated to the outside air/atmosphere from the radiator unit. The heat dissipated from the oil to the atmosphere results in cooling of the oil which is then again fed back to the transformer through an inlet 130. Further as shown a fan 114 or plurality of fans may also be provided adjacent to the radiator to force air over the radiator unit, especially under heavy loads.
[003] While such system cools the oil, the system is bulky as significant amount of space is required owing to the size of the radiator and the number of fans. Also, as radiators and fans are directly mounted on the transformer tank, large thickness and/or stiffeners of tank is required to maintain structural rigidity, which not only adds to the bulk but also increases cost. Further, the fans also generate noise, which is undesirable, especially when the transformer is installed in public spaces. Furthermore, auxiliary losses with use of fans are also more and a separate electronic control system may be required for control/operation of fans.
[004] From an environment perspective, in addition to the noise pollution caused by such systems, it is pertinent to note that a relatively higher grade of heat energy is directly dumped into the atmosphere causing air pollution. Industry best practices and norms mandate compliance of standards such as ISO 14001 for conserving environment and/or energy.
[005] Therefore, there exists a need in the art for a transformer oil cooling systems which addresses at least the above-mentioned problems.

SUMMARY OF THE INVENTION
[006] Accordingly, the present invention in one aspect provides a system for cooling oil of a transformer comprising a first unit having a refrigerant-absorbent mixture at a first concentration, and a first pathway connected with the transformer for carrying hot oil from the transformer through the first unit, at-least a portion of the first pathway submerged in the mixture at the first concentration causing a heat transfer between the hot oil and the mixture at the first concentration, whereby temperature of the hot oil is reduced to a first cooled state and refrigerant vapours are formed resulting in a refrigerant-absorbent mixture at a second concentration inside the first unit; a liquefier unit connected with the first unit for condensing the refrigerant vapours from the first unit to liquid refrigerant; and a second unit having a heat exchange section and an absorption section, the heat exchange section having a second pathway connected with the first pathway, and the heat exchange section connected with the liquefier unit for introducing/spraying the liquid refrigerant onto the second pathway causing a heat transfer between the oil at the first cooled state in the second pathway and the liquid refrigerant whereby temperature of the oil at the first cooled state is reduced to a second cooled state and the refrigerant evaporates forming refrigerant vapours, and the absorption section connected with the first unit for introducing/spraying the mixture at the second concentration from the first unit, the mixture at the second concentration absorbs the refrigerant vapors forming the refrigerant-absorbent mixture which is returned to the first unit, and the oil in the second cooled state in the heat exchange section is returned to the transformer.

BRIEF DESCRIPTION OF THE DRAWINGS
[002] Reference will be made to embodiments of the invention, examples of which may be illustrated in accompanying figures. These figures are intended to be illustrative, not limiting. Although the invention is generally described in context of these embodiments, it should be understood that it is not intended to limit the scope of the invention to these particular embodiments.
Figure 1 shows a transformer as per prior-art.
Figure 2 shows a system for cooling oil of a transformer in accordance with an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION
[003] The present invention provides a system for cooling oil of a transformer. The present invention is designed to cool oil and also reduce impact to the environment by providing a system which reduces noise and also reduces amount of heat energy dissipated to the atmosphere as compared to available transformer oil cooling systems.
[004] Figure 2 shows a system 200 for cooling oil of a transformer 250. As shown, the system is connected with the transformer via a transformer outlet 252 and a transformer inlet 254. Hot oil from the transformer is provided or drawn to the system through the transformer outlet, and cooled oil is returned to the transformer through the transformer inlet.
[005] The system as shown comprises a first unit 210, a liquefier unit 220 and a second unit 230. The first unit is an enclosed vessel with a first pathway 212, a first unit inlet 214, a first outlet 216 and a second outlet 218. The first unit which is an enclosed vessel is made of a metallic material such as mild steel, and inlets and outlets are pipes which are made of a metallic material such as copper, brass etc. However, use of other materials is well within the scope of the invention. The first unit/enclosed vessel holds a refrigerant-absorbent mixture at a first concentration which is introduced in the vessel through the first unit inlet. The refrigerant-absorbent mixture at the first concentration has a low absorbent concentration. Further, the refrigerant-absorbent mixture changes its concentration to a second concentration. At the second concentration, the refrigerant-absorbent has a high absorbent concentration. The refrigerant-absorbent mixture is preferably a lithium salt such as lithium bromide in water. However, the refrigerant-absorbent mixture can be selected from any of ammonia-water, ammonia-sodiumthiocynate, ammonia-lithium nitrate, ammonia-calcium chloride, ammonia-isobutene, water-lithium chloride, methyl chloride-tetraethylene glycol dimethyl ether etc. As shown, the first pathway is connected with the transformer for carrying hot oil from the transformer through the first unit. The first pathway can be connected with the transformer via a flange arrangement comprising of a valve such as a gateway valve. In an embodiment, the first pathway extends within the vessel such that at-least a portion of the first pathway is submerged in the mixture at the first concentration. The first pathway can be a pipe or a conduit extending within the first unit. As the first pathway is carrying hot oil which is at a higher temperature compared to the mixture at the first concentration, heat is transferred between the hot oil and the mixture at the first concentration. The heat transfer causes the temperature of the hot oil to reduce to a first cooled state. Also, refrigerant vapors are released from the mixture at the first concentration resulting in a concentrated refrigerant-absorbent mixture at the second concentration inside the first unit. In a relative embodiment, the first pathway acts as a heat source for the first unit which causes the refrigerant-absorbent mixture at the first concentration to change to refrigerant-absorbent mixture at the second concentration. Advantageously, the first unit does not require an independent heat source for achieving the aforesaid. The refrigerant vapors formed inside the first unit are discharged though the first outlet, and the mixture at the second concentration is discharged through the second outlet. In this regard, the first outlet is provided towards top of the first unit and the second outlet is provided at bottom of the first unit. As the refrigerant vapors find path of least resistance towards the top of the unit, the refrigerant vapors flow out through the first outlet towards the liquefier via a pipe/conduit. The second outlet being at the bottom of the first unit allows the mixture at the second concentration to discharge under gravity. The liquefier unit as shown is connected with the first outlet of the first unit through which refrigerant vapors from the first unit are sent to the liquefier unit via an inlet 222. The liquefier condenses/liquefies the refrigerant vapor forming liquid refrigerant which is discharged out of an outlet 224. The condensation of refrigerant vapor in the liquefier is achieved through circulating a condensing liquid in the liquefier. The condensing liquid can be water or any other cooling medium.
[006] Further, as shown the second unit has a heat exchange section 232 and an absorption section 242. The second unit is an enclosed vessel which is operated in vacuum. The heat exchange section has a second pathway 234 and a first inlet 236. The second pathway is connected with the first pathway through a pipe/conduit, and the second pathway extends within the heat exchange section, and is eventually connected with the transformer inlet to return cooled oil. The second pathway can be a pipe or a conduit extending within the heat exchange unit. The first inlet, as shown in the figure is connected with the liquefier unit and is positioned adjacent to the second pathway for introducing/spraying the liquid refrigerant onto the second pathway causing a heat transfer between the oil at the first cooled state in the second pathway and the liquid refrigerant. The first inlet can include a jet or plurality of jets positioned such that refrigerant sprayed is directed on the second pathway so as to cover most area of the second pathway. In this regard, as the second pathway is carrying hot oil (at first cooled state) which is at a higher temperature compared to the liquid refrigerant, heat is transferred to the liquid refrigerant causing the oil contained in the second pathway to cool down to the second cooled state and forming refrigerant vapors. The absorption section has a second inlet 244 connected with the second outlet of the first unit, and a second unit outlet 246 connected with the first unit inlet of the first unit. The second inlet introduces/sprays the absorbent-refrigerant mixture at the second concentration in the absorption section. The mixture at the second concentration absorbs the refrigerant vapors from the heat exchange section forming the refrigerant- absorbent mixture at the first concentration. The refrigerant- absorbent mixture at the first concentration is thereafter returned to the first unit via the second unit outlet where the refrigerant- absorbent mixture at the first concentration is re-concentrated or converted into the refrigerant- absorbent mixture at the second concentration by the first pathway carrying hot oil. In this regard, the second unit outlet is connected with the first unit inlet, and a pump 248 is provided there between for directing the refrigerant- absorbent mixture at the first concentration to the first unit. The hot oil from the transformer is thus cooled internally within various units – first unit and second unit of the system which reduces amount of heat energy dissipated to the atmosphere. Also, the cooling system does not employ any fans, and hence reduces noise generated by the system.
[007] Further, as shown a heat pipe 260 is provided between the first unit and the liquefier unit. A working fluid is circulated in the heat pipe between a hot side and a cold side of the heat pipe. The hot side of the heat pipe is towards the first unit, and the cold side towards the liquefier. At the hot side, the working fluid vaporizes by absorbing heat from the first unit which creates a pressure gradient inside the heat pipe. The pressure gradient forces the vapors of the working fluid to flow along the pipe to the cold side. As the cold side is provided towards the liquefier, the vapor condenses and gives up its latent heat of vaporization thereby transferring the heat from the first unit to the liquefier and increasing /enhancing thermal efficiency of the system. The working fluid again flows back towards the cold side of the heat pipe because of the capillary forces developed in a porous wick structure or by gravity and the cycle is repeated.
[008] Furthermore, one or more valves may be provided in the inlets and/or the outlets interconnecting the first unit, liquefier unit and the second unit for controlling flow/discharge of the oil or the refrigerant-absorbent mixture, as the case may be.
[009] While the present invention has been described with respect to certain embodiments, it will be apparent to those skilled in the art that various changes and modification may be made without departing from the scope of the invention as defined in the following claims.