FIELD OF THE INVENTION
The present invention generally relates to a cooling process in air cooled Turbo-
Generators and in particular a cooling scheme to balance the substantially
congruent air flow distribution between the four quarters of the generators . The
invention intends to improve the generator performance through reducing the
maximum hot air temperature.
BACKGROUND OF THE INVENTION
During operation of a turbo-generator, heat is generated due to various losses,
which is continuously out-transmitted to keep the temperature of the machine
within a permissible limit corresponding to particular electrical insulation
materials employed. A cooling medium is circulated through the generator to
absorb the heat generated during its operation which is allowed to exit to the
atmosphere or to a separate heat exchanger. Axial flow fans are provided to the
generator rotor on either side of it to force cold air into the generator. This air,
flows past the internals of the machine and during its course, absorbs heat and
becomes hot. The hot air is then let out to the atmosphere or to a series of 'air
to water' heat exchangers and circulated back into the machine through said
fans.

Main sources of heat generation in a turbo-generator during its operation are
stator stampings (core), stator and rotor windings. The present inventors
recognized that once all the required components in stator and rotor of the
generator are cooled to an optimum extent through a cooling system, the
temperature of the generator can be restricted within permissible limits.
With the increase in Turbo-Generator capacity, the heat transferability of the
cooling system becomes more and more vital to the generator reliability. By
reasonably optimizing the flow paths inside the stator frame, utilization rate of
the coolant can be improved, and the maximum temperature of the turbo-
generator reduced. The generator stator construction is made such that it is
symmetric about its centre line. The fans are mounted on the rotor, symmetric to
the centerline. This symmetry in the stator and rotor constructions and the
symmetry in the fan location vis a vis the machine centerline make the mass flow
of the cooling medium too to be symmetric and temperature profile along the
length of one the generator theoretically should be a mirror image of the same
on the other half. However, it is observed that this is not the case in reality and a
substantial variation in temperatures is seen between a zone on one side and
corresponding zone on the other side. Some of the reasons for asymmetry in the
temperature contours inside the generator between both the drive end non-drive
end halves or between the left side and right side, are given below:

This phenomenon can be seen from the typical view of a stator
end winding, looking from its backside, pictorially shown in figures
1 and 2. In view of the manual process involved during laying and
joining of the end winding, there exists a minor non-uniformity in
the routing of the end winding, which inter alia affets uniform
cooling of the end winding which is dependent on the degree of
non-uniformity in the spacing between coils.
The stator frame is assembled to the air cooler duct or air filter
duct on one side. In view of the proximity of the duct to one side of
winding, temperatures on the proximal side of the stator are
relatively less than those at the distal side. In a typical medium
sized air cooled turbo-generators, the difference in the hot air is as
high as 5 to 7 deg C.
Constructions wise, a Turbo-Generator, is symmetric about its
longitudinal as well as transverse centerlines. However, the end
winding construction on non drive end is different from that on the
drive end, when considered in respect of the air flow path. This
difference is in view of connectivity requirement of the end winding
to the output terminals.

The above aspects give rise to differential air flow head losses for the cooling
medium leading to a differential mass flow rate. This in turn results in a
differential temperature distribution which is asymmetric with respect to the
longitudinal and transverse centerlines.
Impact of variations in the ventilation circuit: According to the conventional
techniques, prediction of accurate temperature rise is difficult due to various
reasons. First among them is the difficulty in arriving at the air flow quantity
through different flow paths. Accurate calculation of air flow distribution inside
the machine is difficult, time consuming and involves iterative approach. Again,
due to variation in physical dimensions of the core building, and winding with
respect to design calculations, a difference in mass flow rates between the
design and physical data exists. Other difficulties like determination of accurate
values of thermal conductivity of active parts and the coefficients of heat
emissivity of various heat dissipating surfaces of the machine act as an
impediment to bridge the gap between the actual temperature rise vis a vis the
calculated value.
According to prior art, air flow takes place through one of the four ducts,
depending on which quarter of the machine having the maximum temperature.
As per prior art, the cold chambers are supplied with air via 'through ducts;
provided between fan discharge side of the stator frame to the corresponding
cold compartment.

OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose a regulating device to
balance mass flow rate difference of cooling air between the stator quarters in
turbo-generators.
Another object of the invention is to propose a regulating device to balance mass
flow rate difference of cooling air between the stator quarters in turbo-
generators, which allows a uniform temperature distribution through reduction of
temperature at the stator quarter having the highest temperature.
A further object of the invention is to propose a regulating device to balance
mass flow rate difference of cooling air between the stator quarters in turbo-
generators, wherein one each additional conduit is rigidly connected to the
bottom of the stator quarters to carry and supply additional cooling air to the hot
chamber formed at the stator frame.
A still further object of the invention is to propose a regulating device to balance
mass flow rate difference of cooling air between the stator quarters in turbo-
generators, wherein the stator frame covering the entire length of the core, is
divided alternately into hot and cold chambers.

SUMMARY OF THE INVENTION
According to the invention, four additional ducts operable as conduits are
provided in the bottom of each stator quarter, and supplying regulated quantity
of cold air to the stator zone where the hot air temperature is maximum. As a
result, this zone becomes cooler in view of the increased mass flow and the hot
air temperature is reduced. Thus, the invention allows maintaining uniform
temperature distribution between the generator stator quarters and substantially
reduces the highest winding temperature through balancing of mass flow rates.
The invention further enables improved utilization of the cooling medium in a
Turbo-Generator stator through optimizing the flow distribution inside the stator.
It is known that one of the functions of the stator frame is to carry and
distribute the cooling medium to different parts of the generator. In order to
achieve improved cooling, the frame that covers the core length according to the
invention is divided into hot and cold chambers alternatively.
The present invention bridges the gap in the mass flow rate difference
generated at the stator quarters by introducing a separate' regulated air flow
paths', leading to an increased air flow to those zones where air flow is depleted.
This enables a reduction of 3 to 6 degrees temperature for the hottest air and 7
to 8 degrees for the stator winding.

According to the invention, additional flow paths are established inside the
generator, through provisions of flow regulating conduits. The flow regulation is
decided based on the temperatures recorded in different chambers.
Differential mass flow rate of air according to the invention through the non-
uniform flow give rise to differential heat absorption including the temperatures
contours in the end winding.
According to the invention, the prior art ducts that allow air to pass through, are
differently configured with additional conduits to carry and supply an additional
and regulated quantity of air. During the initial operation of the machine a its
rated load, the zone where the temperature rise is more, is supplied with an
additional quantity of air through the corresponding duct as per invention. A
smaller quantity of air is only supplied through one or two other ducts.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figures 1 & 2 - show a typical view of a stator end winding of a turbo-
Figure 3 - shows the arrangement of ducts in a turbo-generator stator winding
as per prior art.

Figure 4 - shows the arrangement of ducts in a turbo-generator stator winding
according to the invention.
Figure 5 - shows a regulating device to balance mass flow rate difference of
cooling air between different stator quarters in turbo-generator
according to the invention.
DETAIL DESCRIPTION OF THE INVENTION
Figures 1 and 2 show typical end winding assembly of a generator. The gaps
between the coils are non-uniform but these gaps become uniform in normal
course. In view of the manual process involved, this variation in gaps is noticed.
This makes the air flow rate and cooling effect different from the calculated
value. Figure 3 shows a generator ventilation circuit as per Prior art. Figure 4
shows the ventilation circuit as per the invention. Figure 5 shows a device of
controlling the airflow through the duct with he help of the sliding plate and
jacking screw. The plate is adjusted to have a suitable opening for the required
airflow to take place.
Figure 3 shows configuration of ducts as per prior art. Figure 4 shows a modified
configuration of the ducts as per Invention. The proposed ducts, fabricated one
each in the individual quarters of bottom half of the stator frame, draw a pool of
cold air from the fan discharge side. The flow through these ducts is either
restricted or completely blocked with aid of a sliding plate device shown in

figure 5. Such a configuration supplement the flow requirement of that
particular stator quarter and makes the temperature distribution uniform,
resulting in reduction of maximum hot air temperature.
Each of ducts starts on a delivery side of the fan and gets opened into the stator
middle chamber. The air flow through these ducts is regulated by means of the
sliding plate device. To have a positive movement of the sliding plate inside the
duct to have either a partial opening or complete closing of the ducts, the plate
is slided along a groove with the help of a jacking screw.

WE CLAIM:
1. A regulating device to balance mass flow rate difference of cooling air
between different stator quarters in turbo-generator, the generator having
at least a stator core covered with a stator frame, a plurality of stator and
rotor windings, a plurality of fans, and a plurality of air ducts preferably
insulated carrying and supplying cool air during operation of the generator
to absorb heat generated, the device comprising:
- a plurality of conduits corresponding to the number of stator quarter, a
first end of the conduit is rigidly fixed at the bottom of the stator frame, a
second end of the conduits extending to each of the stator quarter for
supplying additional cool air through the discharge-side fans;
- a regulating means each provided inside said conduits having grooves;
and
- an actuating means enabled to cause a positive movement of said
regulating means inside the conduits to allow one of a partial opening and
complete closure of the air flow through the conduits to the stator
quarters.

2. The device as claimed in claim 1, wherein the stator frame is divided into
alternately disposed hot chamber and cold chamber along the stator core.
3. The device as claimed in claim 1, wherein the regulating means is a
slidable plate.
4. The device as claimed in claim 1, wherein the actuating means is a jacking
screw.

ABSTRACT

The invention relates to a regulating device to balance mass flow rate difference
of cooling air between different stator quarters in turbo-generator, the generator
having at least a stator core covered with a stator frame, a plurality of stator and
rotor windings, a plurality of fans, and a plurality of air ducts preferably insulated
carrying and supplying cool air during operation of the generator to absorb heat
generated, the device comprising a plurality of conduits corresponding to the
number of stator quarter, a first end of the conduit is rigidly fixed at the bottom
of the stator frame, a second end of the conduits extending to each of the stator
quarter for supplying additional cool air through the discharge-side fans; a
regulating means each provided inside said conduits having grooves; and an
actuating means enabled to cause a positive movement of said regulating means
inside the conduits to allow one of a partial opening and complete closure of the
air flow through the conduits to the stator quarters.