FIELD OF INVENTION
The present invention relates to a new interpad cooling device for thrust bearing of Hydro Generator. Interpad cooling is needed in case of bearings designed with high bearing load capacity and high specific pressure. Purpose of this interpad cooling is to provide adequate cold oil for the lubrication and cooling of thrust bearing of Hydro Generators.
BACKGROUND OF THE INVENTION
The Bharat Heavy Electricals Limited has designed, manufactured and commissioned large number of Hydro Generators. Hydro generators are large electrical machines, tailor made to customer's specifications. The generator design is largely based on the characteristics of the prime mover that is Hydro turbine. With ever increasing competition there has been a continual effort in evolving new design of components of Hydro generators requiring low cost technology to manufacture with improved performance. Variety of changes has been made in the design philosophy of large thrust bearing based on operating

experience of machines. BHEL has adopted the spring mattress type of thrust bearing for the most satisfactory application of Hydro Generators.
The working principle of the thrust bearing is based on the Hydro Dynamic principle of lubrication. The thrust bearing is housed in a large housing which forms oil chamber. Oil enters at the leading edge of thrust pad and leaves out at the trailing edge continuously. The rotating part continuously churns on thrust bearing pad surface where the heat generated between the runner surface and the thrust pad surface is taken out by the oil which is entering at the leading edge. The hot oil which is coming out of the thrust pad mixes with the oil in the bearing housing chamber. Thus the heat generated in the thrust bearing is continuously transferred to the oil. The hot oil is then cooled by the oil/water heat exchanger known as oil cooler. The complete assembly is shown in fig.l. Two types of heat exchangers are used. One method is to mount oil cooler in the housing itself and connected to the cooling water circuit. In the second method, the hot oil is taken out from the bearing housing and fed to a external oil/water heat exchanger and the cold oil is pumped back to the bearing housing near thrust bearing.

In case of large capacity thrust bearing it has been found that sufficient quantity of cold oil does not enter into thrust pad leading edge resulting in high pad temperature. Further more, it has been observed that cold oil gets trapped in the pockets of the bearing housing because of its constructional restrictions. Various other methods were adopted to improve the entry of cold oil to thrust pad leading edge.
Different manufacturers have adopted different methods of introducing cold oil to thrust pad so that thrust bearing can operate below allowable temperature. One of the manufacturers have used PTFE lined oil scrapper which is fixed between two thrust pad known as inter pad gap and pressed against the thrust runner surface to break the hot oil film on the runner surface and a lesser temperature oil can enter at the leading edge of thrust pad.
Another method is to spray cold oil to thrust runner surface directly between inter pad gap of thrust pads with the help of pipe having number of holes like flute by pumping cold oil. The complete assembly is shown in fig. 2(a) and 2(b). In this design it was not possible to ensure the flow of oil between the thrust pads due to clogging of flute holes leading to no benefit to hinder higher temperature of thrust bearing beyond permissible operating temperature. Also in this arrangement, method of fixing the pipe is complicated and needs more

time for assembly and dismantling for maintenance purpose, causing prolonged shut down of generator.
OBJECTS OF THE INVENTION
It is therefore, an object of the present invention to propose a new interpad cooling device for thrust bearing of Hydro Generator which eliminates the disadvantages of the existing state of art.
Another object of the present invention is to propose a new interpad cooling device for thrust bearing of Hydro Generator which imparts cold oil directly to the leading edge of thrust pad.
A further object of the present invention is to propose a new interpad cooling device for thrust bearing of Hydro Generator which makes maintenance easy.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig.l - shows a diagram of thrust bearing mechanism as per prior art.
Fig. 2(A) & 2(B) - shows a diagram of interpad cooling arrangement in prior art.
Fig. 3A - shows a diagram of interpad cooling device as per instruction.
Fig. 3B - shows a diagram of an assembly of flexible hoses as per invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION
As shown in fig.3(A), an interpad cooling device to cool trust bearing has been developed. The cooling device comprises a vertical fixed pipe (13) disposed at the thrust pad (1) and spring plate (12) and one flexible hose pipe (4) is connected to one end of a fixed pipe (13) and a second end of the flexible hose pipe (4) is connected to pipe bus ring (14) placed in the bearing housing in which cold oil taken from cold oil zone (5) is pumped back. The second end of fixed pipe is vertically open end for oil flow. The cold oil inside the bearing housing (8) beneath the oil cooler cold zone (5) or from the external oil coolers (6) is pumped and distributed in the inner gap of thrust pad (1) through the flexible hose (4) and fixed pipe (13) such that cold oil gets flooded at the loading edge of thrust pad (1) to reduce thrust runner surface temperature thus ensuring proper cooling of thrust bearing. The cold oil beneath coolers (3) is pumped back (6) to pipe ring which is fixed inside the bearing housing (8).

WE CLAIM
1. An interpad cooling device for thrust bearing of Hydro Generator comprising:
- a vertically fixed pipe (13) having an upper open end and a second
bottom open end is connected to a spring plate (12) and first end
of a flexible hose pipe (4) is connected to spring plate (12) and the
second end of the flexible hose (4) is connected to a cold oil bus
ring pipe (14);
- the fixed pipe (13) is disposed vertically at the thrust pad (1) via a
spring plate.(12);
characterised in that oil is pumped from cold oil zone (5) or from external oil coolers (6) and distributed in the inner gap of thrust pad (1) via the said flexible hose (4) and fixed pipe (13) such that cold oil get flooded at the leading edge of thrust pad (1) below thrust runner surface, thus ensuring proper cooling of thrust bearing.

The present invention relates to an interpad cooling device for thrust bearing of Hydro Generator comprising a vertically fixed pipe (13) having an upper open end and a second bottom open end is connected to a spring plate (12) and first end of a flexible hose pipe (4) is connected to spring plate (12) and the second end of the flexible hose (4) is connected to a cold oil bus ring pipe (14) and the fixed pipe (13) is disposed vertically at the thrust pad (1) via a spring plate (12) characterised in that oil is pumped from cold oil zone (5) or from external oil coolers (6) and distributed in the inner gap of thrust pad (1) via the said flexible hose (4) and fixed pipe (13) such that cold oil get flooded at the leading edge of thrust pad (1) below thrust runner surface, thus ensuring proper cooling of thrust bearing.