TECHNICAL FIELD OF THE INVENTION
The present invention deals with the operation of a turbo generator operated in a power
plant or industrial establishment and especially on improvising the performance through
modifications to the existing ventilation system.
BACKGROUND OF THE INVENTION
The ventilation system as per prior art consists of mounting of axial flow fans on either
end of the rotor to throw air onto its delivery side. The temperatures of the stator and
rotor depends on the heat generated due to various losses and air flow directed onto it.
There are several losses in the generator which includes iron losses, copper losses,
windage losses, mechanical losses etc. The heat generated is not uniform and varies as
per the relative location of the zone with respect to the other. Few zones nearer to the
end winding are hot from the point of view of heat generated while the middle zone in
the stator is hot from the point of view of lower quantity of air flow taking place. The
individual components including the fan blades, the windings etc. bear different
temperature profiles as per the heat generated and quantum of air flow taking place. In
view of the possible variations in the machine construction and fan blade profiles, it is
inevitable to have certain temperature difference between rotor and stator. In such an
event as per the prior art, the winding (stator or rotor) which is hotter will dictate the

amount of loading. Though the ventilation scheme is symmetric with respect to centre
line of the machine, there will be variation in temperatures between the stator and the
rotor. As per prior art, there is no method of balancing the ventilation scheme between
stator and rotor to have an increased rating. The present invention deals with an
improved method of ventilation system where the difference in temperatures between
rotor and stator is reduced which will increase the turbo generator performance/rating.
Different fan blades and flow paths are described in the patens US6250886,
EP0947704A2, US8851851, US4569362A, WO2002027191A1, US5221187,
CA2224204C etc.
In Patent no.US6250886, invention provides an axial flow fan and fan blade. A true
tapered, twisted airfoil section is constructed by cutting a flat piece of light alloy to a
unique shape to obtain a flat pattern representative of a selected airfoil design, forming
the airfoil section by making three simple bends in the pattern and joining the trailing
edge with rivets. A transition piece is provided to connect the airfoil section to the fan
hub. In Patent no. EP0947704A2, the fan comprises a central hub and a plurality of
blades extending radially from the hub and each having a root portion adjacent the hub,
a radially intermediate portion, and a radially outermost, tip portion. In Patent no.
US8851851, large diameter axial Super Low Noise flow fans and commercial air cooled
apparatuses incorporating such fans are provided. The large diameter axial flow fan is

mounted on the air cooled apparatus for generating an axial air flow in the air cooled
apparatus for accomplishing the cooling. In Patent no. US4569362A, a compact,
efficient axial flow fan with blades that are rearwardly (i.e., away from the direction of
fan rotation) skewed and which are oriented at a pitch ratio which continuously decreases
as a function of increasing blade radius are used. In Patent no. WO2002027191A1,
invention relates to a shank for axial fan blades, in particular for axial fans used in
industry in large heat exchangers, condensers, cooling towers and similar applications.
The shank for axial fan blades allows to reduce the weight of the shank-blade group and
at the same time it is more flexible. In Patent no. US5221187, axial fan has angle of
curvature of the median line of each blade in axial projection is nil at the hub and for
about one third of the radial extension of the blade from the hub. In Patent no.
CA2224204C, a high efficiency fan and stator arrangement for generating an airflow
through a heat exchanger is proposed. The fan is rotated about its rotational axis by an
electric motor, and includes eight blades extending radially from a hub to a circular band.
Each fan blade has a stagger angle and chord lengths which vary along the span of the
blades.
OBJECTIVE OF THE INVENTION
The objectives of the invention are:
1. An object of the invention is to propose a ventilation system which will improve
operational performance of the generator

2. Another object of the invention is to devise a ventilation system where the
difference between maximum temperatures experienced by stator and rotor is
minimized.
SUMMARY OF THE INVENTION
The invention involves study of the existing temperature profile of the generator and
minimizing the difference between the rotor and stator through siphoning of some
quantity of air entering the rotor and directing it to the end winding of stator and air gap.
The measurements will be taken on both drive end and non-drive end. The device that
directs the air onto the stator is made in the present invention as per the requirement on
each side.
From the thermal data collected during the operation of a generator, the additional flow
requirement onto the stator is worked out. Accordingly a fan arrangement is fabricated
using composite materials. This fan will be of radial blade construction and is mounted on
centering ring. Depending on the flow requirement, the vine height is decided. The flow
directed by the main fan onto the rotor gets influenced by the above designed fan. This
fan will divert part of the air onto the end winding of stator instead of allowing it to go
through the rotor. The additional influx of air will reduce the temperature rise on the
stator while the reduced influx of air increases the temperature rise on rotor. Thus in the
present invention, the difference in maximum temperatures between the rotor and stator
is minimized through a radial fan fabricated on the face of the hub.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The advantages of the present invention will become apparent from the following
detailed description of embodiments with reference to the accompanying drawings, in
which:
Fig.1 – is a cross section of a typical generator showing the axial fan and air flow.
Fig.2 – is a cross section of a typical generator showing the radial fan location and air
flow.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION
During the operation of a turbo generator, heat is generated from two major sources
which are generator field winding and generator armature winding. The ventilation circuit
during the design state is devised such that the air flow takes place at all the heat
sources to maintain a temperature below the permissible values. However, there will be a
certain temperature difference between stator and rotor depending on their relative
loadings and flow distribution of air. The one going to higher temperature will limit the
machine rating. In normal course it is observed that the stator winding is hotter and the
present work devises a method of addressing this issue. The objective is to contribute to
lowering the peak temperature or gives us a clue on how much more power can be
extracted from the generator.

Fig. 1 shows the ventilation arrangement as per prior art. The cold air drawn from the
outside or from the cooler cartridges is circulated through the fans onto the stator and
rotor. The air discharged by the fan gets divided into three flow paths to absorb the heat
generated inside the generator.
The first path 101 enters the retaining rings through the gap between the end retaining
rings and the rotor body, take the heat generated in the windings. The air will enter the
rotor sub-slots and travel towards the rotor centre line. Part of these streams of air
moving towards the centre of rotor is thrown out radially into the rotor/stator air gap.
From there, the air exits the machine to the atmosphere or to a cooling arrangement
where the heat carried by the outgoing air is given to the cooling system.
The second steam of air 102 enters the air gap and moves axially towards the rotor
centre. During its course of movement, air is let out of core through axial ducts and let
out of the generator. During this process it takes the heat from the stator winding.
The third part 103 goes to the core back through the end winding and enters the central
chamber. The air is drawn inwards into the air gap which moves axially and then radially
outwards to the core back. It then exits the stator out to the atmosphere or to a cooling
arrangement.

Fig.2 shows the ventilation arrangement as per the present invention. To regulate the
flow of air going into the retaining rings, a radial fan 201 is assembled to the centering
ring 202 to draw some of the air going in the axial direction through the retaining rings
and force the same air 203 onto the air gap and stator end winding 204. The radial fan is
quite a lighter assembly in view of the composite material chosen. As the pressure
developed by the radial fan is higher, the height of the vine shall be chosen through
calculations. This will be different on drive end and non-drive ends as they suit to the
individual flow requirements. The fastening is to be done with the centering ring and
there will be an arrestor which sits in the ID of the centering ring. The function of
fasteners is to keep the fan in contact with the centering ring and the function of the
arrestor is to secure the radial fan again the centrifugal forces.

WE CLAIM
1. A ventilation arrangement to uprate an air cooled turbo generator through
balancing of air flows comprising:
- a fabrication made out of composite metal or carbon fibre consisting a radial
fan (201) mounted on the centering ring (202) for drawing some of the air
(101) entering the rotor in the axial direction through the retaining ring (101)
and forcing the air (203) diverting onto the air gap and stator end windings
(204)
wherein the second steam of air (102) enters the air gap and moves axially
towards the rotor centre and let out of core through axial ducts and finally let
out of the generator taking heat from the stator winding; the third part (103)
of air goes to the core back through the end windings and enters the central
chamber which is drawn inwards into the air gap moving axially and then
radially outwards to the core back before exiting the stator to go to the
atmosphere thus cooling the central areas and stator end windings as well as
minimizing the temp gradient between the stator and rotor.
2. The ventilation arrangement as claimed in claim 1, wherein the radial fan is
anchored to centering ring and connected in the ventilation circuit midway
between the axial fan discharge and rotor.

3. The ventilation arrangement as claimed in claim 1, wherein the height of the blade
of radial fan is chosen as per the flow requirement.
4. The ventilation arrangement as claimed in claim 1, wherein the fan is fixed on the
hub by fasteners.
5. The ventilation arrangement as claimed in claim 1, wherein an arrestor is built at
its ID to secure the radial fan against centrifugal forces.