FIELD OF INVENTION
This invention is related to an improved rim ducts for floating rim of
hydrogenerators to generate adequate air for ventilation of hydrogenerators.
BACKGROUND OF THE INVENTION
In hydrogenerator, two types of rims are used and categorised as shrink fitted and
floating type. The shrink fitted rim is expanded by heating and assembled on to
spider. This rim has interference between spider and inner diameter of rim. The
provision of rim ducts in shrink fitted rim is very easy and are being provided by
many manufacturers. The rim is built by thin laminations of high tensile sheet steel
around the periphery of spider.
The floating type rim has clearances between spider and inner diameter of rim.
This type of rim is free to expand during running of the machine. The provision of
rim ducts is very difficult in floating type rim.
In prior art, the rim ducts for ventilation were not provided in floating type rim.
The air was generated fully by the rotor mounted fans on top & bottom of rotor for
cooling the generator a shown in figure: 1. The hot air is cooled by number of air
coolers and approx. 50% air returns to bottom side of rotor through number of
foundation ducts and remaining air returns from top side of rotor through the
space available between top bracket arms. The complete cooling circuit of
hydrogenerator is also shown in figure: 1. In existing design, it was also not
possible to control the flow due to fixed fans and resulting higher churning &
windage losses. These higher losses were leading to lower efficiency of generator
which was national loss.

OBJECTS OF THE INVENTION
It is therefore, an object of the present invention to propose an improved rim duct
for floating rim of hydrogenerators which eliminates the disadvantages of existing
art.
Another object of the present invention is to propose an improved rim duct for
floating rim of hydrogenerators which controls the quantity of airflow for achieving
best performance of generator.
A further object of the present invention is to propose an improved rim duct for
floating rim of hydrogenerators which reduces the windage losses by reducing the
churning.
A still further object of the present invention is to propose an improved rim duct
for floating rim of hydrogenerators which increases the efficiency of the
generators.
An yet further object of the present invention is to propose an improved rim duct
for floating rim of hydrogenerators which saves cost due to reduction in weight.
BRIED DESCRIPTION OF ACCOMPANYING DRAWINGS
FIGURE 1: Cooling circuit of hydrogenerators in existing design.
FIGURE 2(A): Assembly of invented rim ducts-section AA.
FIGURE 2(B): Assembly of invented rim ducts-section BB.
FIGURE 3(A): Rim ducts segment.
FIGURE 3(B): Rim ducts segment.
FIGURE 4: Cooling circuit of hydrogenerators with invented design.

BRIEF DESCRIPTION OF A PREFERRED EMBODIEMENT OF THE
INVENTION
In the improved rim duct for floating type rim is comprising a number of ducts are
which provided in axial direction and each duct covers complete circle. The
complete assembly of rim ducts are shown in figure: 2(A) & B. The ducts are made
in segments (1) as shown in figure: 3 and assembled as shown in figure: 2(A&B).
The rim punching segment (1) itself has been used to make the ducts. Number of
bushes (2) having specific height are welded onto the punching segment to create
axial gap for generating air. A baffle (3) is welded around the outer bushes to
make a canal for air and to reduce the churning & windage losses. The
construction of rim ducts is shown in figure: 3. In this invented design, the flow is
optimised by adjusting the opening provided on to top (4) & bottom plate (5) of
spider (6). The cover (7) having various sizes of opening are provided to regulate
the air for achieving best performance of generator, See figure 2(a) & (b). These
covers are fitted with the screws (8) on to spider. In improved system, the fans of
lower capacity are designed and rest quantity of air is being generated by the
improved rim ducts for floating type rim. The complete circuit of cooling is shown
in figure: 4 as per new invention.

KEY FEATURES
Reference Character Figure
Numerals
1 RIN PUNCHING 3(A) &(B)
SEGMENT
2 Bushes 3(A) &(B)
3 Baffle 3(A) &(B)
4 Top plate of spider 2(B)
5 Bottom plate of spider 2(B)
6 Spider 2(B)
7 Cover 2(A)
8 Screw 2(A)
9 Number of openings 2(A)
for adjusting air in Top
(4) & Bottom (5) plate
of spider
10 Number of RIM ducts 2(A)
11 Opening for adjusting 2(B)
air in bottom plate
12 Opening for adjusting 2(B)
air in top plate
13 Thin Laminations of high 2(B)
tensile sheet steel
14 RIM DUCT 2(B)
15 Canal for air 3(A)

WE CLAIM
1. An improved rim ducts for floating rim of hydrogenerator to generate
adequate air for ventilation of hydrogenerator comprising
- a rim punching segment (1) on which a plurality of bushes
(20) having specific height are welded to create axial gap for
generating air;
- a baffle (3) is welded around the outer bushes to make a
canal for air and to reduce the churning and windage losses;
- a regulating cover (7) provided for opening on top (4) and
bottom plate (5) of spider (6) to optimise air flow;
- fixing up the cover (7) on to top (4) and bottom (5) plate by
the screw (8),
2. The rim duct for floating rim as claimed in claim 1 is made of high
tensile sheet steel.

An improved rim ducts for floating rim of hydrogenerator to generate adequate air for ventilation of hydrogenerator comprising
- a rim punching segment (1) on which a plurality of bushes (20) having specific height are welded to create axial gap for generating air;
- a baffle (3) is welded around the outer bushes to make a canal for air and to reduce the churning and windage losses;
- a regulating cover (7) provided for opening on top (4) and bottom plate (5) of spider (6) to optimise air flow;
- fixing up the cover (7) on to top (4) and bottom (5) plate by the screw (8),