FIELD OF INVENTION
The present invention relates to a method of sealing bearing oil leakage by providing a hollow designed fan.
BACKGROUND OF THE INVENTION
Enough work has been done to make an air cooled turbo generator more compact through employing improved insulation and devising optimized ventilation system. This has resulted in extended threshold mega-watt level of a turbo generator using air as ventilation medium. The above will reduce the active parts of the generator. An approach is followed to minimize the length of the generator through improvising the bearing seal design. This will reduce the overall length of the machine. The method followed will also ensure positive oil sealing in the bearings which is one of the prime requirements sought by today’s customer. Bearing oil leakage is one issue that makes the turbine environment shabbier and power plant operator spends time and resources to minimize the oil leaks from the bearings. To identify the source of the oil leakage problem it is necessary to stop the machine and examine all the issues responsible for oil leakage. This takes considerable time and efforts at the cost of power

loss. In the present invention, an approach is chosen to achieve a positive leak free oil scraping system using modified fan design.
It is the endeavour of any power equipment manufacturer to supply compact machines which in many a case are cheaper and at the same time occupy less space and weight. A turbo generator is supported on two oil fed journal bearings on either end of the rotor. Lubricating oil at pressure is supplied to the bearings to carry the static and dynamic loads of the rotor. The oil after absorbing the heat is let out to the bearing pedestal. This pedestal carries the bearing shell, inlet and outlet oil ports. The bearing shell is provided with a set of seals (type-1) on its either side in the same way the bearing pedestal too is provided with one set of seals (type-2) on its either side. The seals are provided with scrapper fins made out of brass which will maintain very low clearance between fin and shaft. Type-1 seal is provided with one number of scrappers and type-2 seal is provided with multiple number of scrappers (typically six to eight). The lubricating oil supplied to the bearing shell through inlet port will contribute to the hydrodynamic lubrication and during the process it picks up heat due to fictional losses. This oil will then be continuously let out to the outlet port. The type-1 seal is provided to prevent oil from leaking out and ensure collection into the pedestals from where it is discharged to the outlet port. As the set of seals (type-1) are in the vicinity of the oil discharging out of the bearing, only one number of scrapper fin is provided to ensure that the flow from bearing is not stopped due to a high degree of resistance

offered by the seal immediate to the oil outlet. The purpose of the seal also to maintain certain pool of oil inside the bearing shell which gives a better damping and oil film characteristics. The type-2 seal which is wider due to a number of scrappers assembled, occupies larger length and there is no other method of reducing it and at the same time ensures positive sealing. A compact bearing housing will reduce the overall machine length by the same length obtained through seal length savings. To meet the above objective, a method is chosen in a present invention to ensure leak proof bearing and at the same time reduce the length of the bearing. Different sealing systems are described in the patents US3976165, US20140286599, US7025356, WO2001031235A2, US3413008, US7287384, EP0035891A1, US4856794 etc.
Patent No. US3976165 discloses, a high speed centrifugal compressor which is closely directly coupled to the power turbine of a two-shaft gas turbine having a gas generator section separate from its power turbine. Through the direct close coupling and center-line mounting of the gas turbine exhaust casing for free and uniform heat expansion, alignment between stationary and rotating parts of the power turbine and compressor is maintained free from mechanical problems. Bearings and oil seals are fed by an integrated lubrication and a sealing oil system utilizing a compact oil distribution manifold assembly incorporating a quick filter change structure. The gas turbine-compressor finds particularly useful application in areas where high power, compact,

relatively maintenance-free units are required, as, for example, on offshore platforms in the natural gas industry.
Patent No. US20140286599, in order to effect a seal a porous material which comprises one side of two opposing surfaces is used to restrict and evenly distribute externally pressurized gas, liquid, steam, etc. between the two surfaces, exerting a force which is opposite the forces from pressure differences or springs trying to close the two faces together and so may create a non-contact seal that is more stable and reliable than hydrodynamic seals currently in use. A non-contact bearing is also disclosed having opposing surfaces with relative motion and one surface issuing higher than ambient pressure through a porous restriction, wherein the porous restriction is part of a monolithic porous body, or a porous layer, attached to lands containing a labyrinth, the porous restriction and lands configured to not distort more than 10% of a gap created from differential pressure between each side of the porous restriction.
Patent No. WO2001031235A2 discloses, a buffer seal arrangement which is provided for improved buffer sealing of oil sump seals in gas turbine engines. The buffer seal arrangement includes a three section labyrinth seal. Disposed between the first and second section is a buffer air supply annulus for delivering pressurized air from the

engine to said first and second sections of the seal. Oil drains are disposed between said second and third sections and adjacent the third section. The first section has four knife seals, and the second and third sections have three knife seals. Rig testing has shown that this buffer seal arrangement can prevent the leakage of oil into the gas path of the gas turbine engine.
OBJECTS OF THE INVENTION
Therefore, it is an object of the invention to propose a method of sealing bearing oil leakage by providing a hollow designed fan, which is capable of providing necessary sealing and arresting complete oil leakage.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig. 1 : Shows sectional view of type-1 seal. Fig. 2 : Shows sectional view of type-2 seal. Fig. 3 : Shows sealing arrangement by provision of seal air connection.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION
Turbo generator is a rotating electrical equipment converting mechanical energy to electrical energy. The rotating part called the rotor is supported on two oil fed

journal bearings, one on each side. Lubricating oil at pressure is supplied to the bearings to carry the static and dynamic loads of the rotor. The oil after absorbing the heat is let out to the bearing pedestal. During operation of turbo generator, lot of heat is produced at different zones of the machine due to air friction losses, copper losses, iron losses and bearing losses etc. To keep the machine operation within temperature limits acceptable to the insulation, air is circulated inside the machine through several flow paths. After collecting the above heat from different heat sources, the air becomes hot and the hot air is circulated through a heat exchanger where it gives away heat and becomes cool. The cold air is drawn back into the machine and the circulation of air takes place in a closed circuit.
Fans are provided on either end of the machine and each fan assembly consists of a number of fan blades, size and number of which are dependent upon the flow parameters. The fan, if designed hollow, works as a pump to throw out air radially due to centrifugal action. The pressure and velocity of air discharged out of the fan tip depend on peripheral velocity of the blade and frictional loss during its passage through the blade. A pool of air can be collected in a container for using it against several applications. One such application is sealing of bearing oil. As per prior art, the shaft bearing system is provided with several stages of scrappers mounted on the shaft with a clearance in between. Type-1 seal (101) provided in the bearing shell (102) has only

one scrapper fin (103) with low clearance between fin and shaft (104) as shown in Fig. 1 and the purpose of seal is to seal majority of oil and at the same time act as a barrier to maintain a healthy oil film having required dynamic properties. The bearing pedestal (201) carrying the bearing shell (202) is also provided with one set of type-2 seals
(203) on its either side as shown in Fig. 2. The seals are provided with scrapper fins
(204) made out of brass which will maintain very low clearance between fin and shaft (205). The type-2 seal which is wider due to a number of scrappers assembled, occupies larger length and there is no other method of reducing it and at the same time ensures positive sealing.
A system is devised in the present invention where the number of scrapper stages can be minimized through introduction of a different sealing arrangement. The difference in the new arrangement includes provision of seal air connection and utilization of hollow fan blades. A hollow fan blade can be made out of composite materials or carbon fibre which are lighter and stronger. The hollow fan blades serve the purpose of circulating air in the radial direction also in addition to circulating air in the axial direction. The air thrown out radially due to centrifugal action is collected through a groove (301) provided in the air guide ring (302) made out of aluminium casting as shown in Fig. 3. Air collected from the tip (303) of the blade (304) is taken through a flexible or copper tube (305) to the bearing seals (306) as shown in Fig. 3.

The pressurised air connection given to the type-2 seal from the pool of pressurised air will affect the necessary sealing and arrest complete oil leakage.
Important features:
In the context of present invention, the important features are as follows:
1. The fan blade of a generator can be made hollow.
2. The material chosen for the fan blade is a composite material.
3. The fan blade discharges out air in radial and axial directions.
4. The air forced out of the hollow opening and through tip of the blade is collected in a container or directly into the shaft and seal assembly.
5. The pressurised air collected to the bearing seals forms as a air curtain which prevents oil leakage.
6. The pressure film is continuous in the annular space and there will not be any oil leak.
7. As long as rotor is in rotation, the seal continues to prevent oil from leaking out. This is as opposed to a possible leakage of oil through the scrapper fins a minimum clearance should be maintained.

WE CLAIM
1. A method of sealing bearing oil leakage by providing a hollow designed fan on
either side of a turbo-generator, comprising;
providing fans on either end of a turbo-generator;
making the fans hollow in design to work similar to a pump for throwing out an radially due to centrifugal action in addition to circulating air in the axial direction, when the rotor being in rotation;
wherein air thrown out radially is collected through a groove (301) provided in a air guide ring (302) and also the air collected from tip (303) of blade (304) is taken through a flexible tube (305) to bearing seals (306) wherein the pressurised air connection given to a type-2 seal from the pool of pressurised air provides necessary sealing arresting complete oil leakage.
2. The method as claimed in claim 1, wherein the hollow fan blade is made out of
composite materials or lighter and stronger carbon fibre.

3. The method as claimed in claim 1, wherein the air is collected through a flexible copper tube (305) to the bearing seals.
4. The method as claimed in claim 1, wherein the air guiding ring is made of aluminium casting.