Title of Invention	A NOVEL DESIGN APPROACH TO OPTIMISE THE MACHINE VENTILATION OF AIR COOLED GENERATOR STATORS
Abstract	The invention relates to a modified air-cooled turbogenerator preferably of 110 MW capacity with an improved ventilation circuit, the modification is hot chamber (4), and the cold chambers (11) disposed in such a way that hot air comes out of the generator (3) all along the length of the stator (5); the coolers (1) are disposed on both sides of the generator (3), and in contact with the stator frame (2); and the stator frame (2) comprising an improved ventilation circuit comprising configuration of an internal flow path having radial ribs (6), ventilation spacers, flow dividers, the coolers (1) being further disposed adjacent to the stator casing (5).

Title of Invention

A NOVEL DESIGN APPROACH TO OPTIMISE THE MACHINE VENTILATION OF AIR COOLED GENERATOR STATORS

Abstract

The invention relates to a modified air-cooled turbogenerator preferably of 110 MW capacity with an improved ventilation circuit, the modification is hot chamber (4), and the cold chambers (11) disposed in such a way that hot air comes out of the generator (3) all along the length of the stator (5); the coolers (1) are disposed on both sides of the generator (3), and in contact with the stator frame (2); and the stator frame (2) comprising an improved ventilation circuit comprising configuration of an internal flow path having radial ribs (6), ventilation spacers, flow dividers, the coolers (1) being further disposed adjacent to the stator casing (5).

Full Text	2 FIELD OF INVENTION The invention generally relates to turbo-generators operated in a power plant for utility or industrial application. I^ore particularly, the invention relates to a modified air-cooled turbo generator with an improved ventilation circuit. BACKGROUND OF THE INVENTION During the operation of a Turbo-generator, heat is generated due to operational losses like eddy current loss, copper loss, windage loss etc. It is necessary to dissipate this heat continuously, to keep internal temperature in limits. To enable continuous heat dissipation, a cooling medium is chosen that circulates through the machine with the help of axial flow fans mounted on the generator rotor. For small rating turbo-generators, air is chosen as the cooling medium while larger (more than 120 MW) generators, hydrogen is preferred. This is because, in higher capacity generators, larger quantity of heat is to be dissipated and air cannot handle the same, beyond a certain generator size. Advantages of hydrogen gas like higher specific heat, higher thermal conductivity and lower density make it suitable to handle the higher heat loads in these generators. The hot hydrogen after absorbing heat is circulated across a water to hydrogen heat exchanger where it dissipates heat before it is circulated back into the machine flow paths. Use of hydrogen, however, is susceptible to explosion, if allowed to leak out from the machine and mixes with air. In order to prevent this, a separate seal oil 3 system has to be employed, apart from continuous monitoring of hydrogen as purity and reviewing the periodic hydrogen consumption. In view of these problems associated with hydrogen, it is the practice to assemble heat exchangers inside the stator frame itself. The explosive nature of hydrogen and an additional requirement to employ a separate seal oil system generally prevent its usage as a cooling medium. However the disadvantages associated with air for example, high density, lower thermal conductivity and specific heats do not allow air to be sued as a cooling medium for the machine rating above a certain limit however, replacement of hydrogen cooled generator with air cooled generator has the problem that the hydrogen cooled generator houses coolers inside the generator stator itself, and there is no external space available to mount coolers, when modify the generator into an air cooled machine. The integral coolers used in the hydrogen cooled generator are too small for air cooled generator application. It is hence imperative to look for an alternative location to mount the coolers. In a prior art turbo generator having a closed circuit hydrogen cooling system the cold hydrogen is circulated across a heat exchangers (coolers) mounted inside the stator frame itself. When the machine is in operation, hot hydrogen from the generator is forced on to the heat exchangers, arranged inside the stator frame for heat dissipation and the cold hydrogen is brought back to the generator active parts. The fans mounted on generators rotor give the head necessary for the above flow to take place. 4 OBJECTS OF THE INVENTION It is therefore an object of the invention to propose a modified air-cooled turbogenerator with an innproved ventilation circuit. Another object of the invention is to propose a modified air-cooled turbo generator with an improved ventilation circuit, which is modified from hydrogen- cooled turbo generator to air-cooled turbogenerator. A further object of the invention is to propose an improved ventilation circuit which is adaptable to the existing air cooled turbo generators to enhance their cooling systems. SUMMARY OF THE INVENTION Accordingly, there is provided a modified air-cooled trubogenerator preferably of 110 MW capacity with an improved ventilation circuit, the modification is characterized by hot chambers and the cold chambers disposed in such a way that hot air comes out of the generator all along the length of the stator, the coolers are disposed on both sides of the generator and in contact with the stator frame and the stator frame comprising an improved ventilation circuit comprising configuration of an internal flow path having radial ribs ventilation spacers, flow dividers the coolers being further disposed adjacent to the stator casing. One of the solutions could be that the stator frame is so designed that coolers are mounted external to the stator and on both sides of generator, along the 5 machine length. In that case, the flow paths inside the generator stator shall be selected such that the cooler along its entire length is exposed to the hot air coming out of stator frame. As per the prior art, the coolers in an air-cooled generator are mounted in a cooler rack, which is mounted on one of the sides of generator. There will be a considerable gap between the cooler rack and stator frame casing wall and this gap facilitates distribution of hot air across the total cooler length. According to the present invention the coolers are butted to stator frame and the frame is configured to allow the hot air to flow past the cooler. The advantage of the present invention is that it makes it possible to replace a hydrogen cooled generator with an air-cooled generator of matching capacity. Further, the invention allows up rating the existing of the existing air cooled generators by optimizing the generator ventilation system. The inventive cooling circuit enables the power plants to draw more power from the same machine size or improve the machine efficiency. In a second aspect of the invention, the coolers are mounted in both sides of generator, to cool hot air. The internal flow paths are made such that hot air is brought all along the length of the frame. Schematic of a typical air flow paths in stator section are shown in Figure 1. This arrangement makes it feasible to replace the hydrogen with air as cooling medium. 6 The inventive, arrangement when employed to improve the rating and efficiency of old generators, envisages supply of a stator frame with an optimized cooling circuit. The circuit consists of internal arrangement of radial ribs, ventilation spacers, flow dividers in the stator frame, apart from placing the coolers adjacent to the stator casing. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS Figure 1 - shows a cross sectional arrangement of a frame structure as per invention, to optimize the air flow paths inside the frame. Figure 2 - shows the arrangement of heat exchangers on both sides of generator as per the proposed invention. DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION One of the prime factors on which generator's efficiency depends is the ventilation system employed. When hydrogen is replaced with air as the cooling medium, the machine rating will fall as air is less efficient than hydrogen for cooling by virtue of its lower specific heat, higher density and lower thermal conductivity. The reduction in efficiency can be compensated partially through an improvised cooling circuit. The invention aims at improving the generator rating of existing air cooled generators or to replace the existing hydrogen cooled generators with an air cooled generator. 7 Figure - 2 shows an arrangement of directing the hot air on to the coolers (1). The coolers (1) are made to be in contact with the stator frame (2). As per the prior art, the generator stator is longitudinally divided into various compartments such that the cold and hot air chambers are obtained along the active length of the generator, ensuring cold and hot air paths coexist in the same chambers at the same time. This arrangement enables a better cooling circuit in terms of maximizing the heat absorption. The hot air coming out of hot chambers is allowed to flow past the coolers to give away the heat, while the outer periphery of the stator in the cold chambers is blocked to prevent escape of cold air. As per the present invention as shown in figure - 2, the chambers (4) and the chamber (11) are designed such that hot air comes out of the machine (3) all along the length of the stator (5). This makes the ventilation circuit better as the total length of the cooler (1) is exposed to hot air and improved cooling gets effected. As shown in figure - 1, the coolers (1) are mounted on both sides of the generators (3). The cooling circuit comprises radial ribs (6), ventilation spacers, flow dividers in the stator frame (2). The coolers (1) are placed adjacent to the stator casing (7). The cold air flow path (8), hot air flow path (9) in bottom half of the stator frame (2), hot air flow path (10) in top half of the stator frame (2) are configured such that the hot air is brought ail-along the length of the stator frame (2). 8 WE CLAIM 1. A modified air-cooled turbogenerator preferably of 110 MW capacity with an improved ventilation circuit, the modification is characterized by: - hot chamber (4), and the cold chambers (11) disposed in such a way that hot air comes out of the generator (3) all along the length of the stator (5); - the coolers (1) are disposed on both sides of the generator (3), and in contact with the stator frame (2); and - the stator frame (2) comprising an improved ventilation circuit comprising configuration of an internal flow path having radial ribs (6), ventilation spacers, flow dividers, the coolers (1) being further disposed adjacent to the stator casing (5). 2. A modified air-cooled turbogenerator preferably of 110 MW capacity with an improved ventilation circuit as substantially described and illustrated herein with reference to the accompanying drawings. The invention relates to a modified air-cooled turbogenerator preferably of 110 MW capacity with an improved ventilation circuit, the modification is hot chamber (4), and the cold chambers (11) disposed in such a way that hot air comes out of the generator (3) all along the length of the stator (5); the coolers (1) are disposed on both sides of the generator (3), and in contact with the stator frame (2); and the stator frame (2) comprising an improved ventilation circuit comprising configuration of an internal flow path having radial ribs (6), ventilation spacers, flow dividers, the coolers (1) being further disposed adjacent to the stator casing (5).

Full Text

2
FIELD OF INVENTION
The invention generally relates to turbo-generators operated in a power plant for
utility or industrial application. I^ore particularly, the invention relates to a
modified air-cooled turbo generator with an improved ventilation circuit.
BACKGROUND OF THE INVENTION
During the operation of a Turbo-generator, heat is generated due to operational
losses like eddy current loss, copper loss, windage loss etc. It is necessary to
dissipate this heat continuously, to keep internal temperature in limits. To enable
continuous heat dissipation, a cooling medium is chosen that circulates through
the machine with the help of axial flow fans mounted on the generator rotor. For
small rating turbo-generators, air is chosen as the cooling medium while larger
(more than 120 MW) generators, hydrogen is preferred. This is because, in
higher capacity generators, larger quantity of heat is to be dissipated and air
cannot handle the same, beyond a certain generator size. Advantages of
hydrogen gas like higher specific heat, higher thermal conductivity and lower
density make it suitable to handle the higher heat loads in these generators. The
hot hydrogen after absorbing heat is circulated across a water to hydrogen heat
exchanger where it dissipates heat before it is circulated back into the machine
flow paths.
Use of hydrogen, however, is susceptible to explosion, if allowed to leak out from
the machine and mixes with air. In order to prevent this, a separate seal oil

3
system has to be employed, apart from continuous monitoring of hydrogen as
purity and reviewing the periodic hydrogen consumption. In view of these
problems associated with hydrogen, it is the practice to assemble heat
exchangers inside the stator frame itself.
The explosive nature of hydrogen and an additional requirement to employ a
separate seal oil system generally prevent its usage as a cooling medium.
However the disadvantages associated with air for example, high density, lower
thermal conductivity and specific heats do not allow air to be sued as a cooling
medium for the machine rating above a certain limit however, replacement of
hydrogen cooled generator with air cooled generator has the problem that the
hydrogen cooled generator houses coolers inside the generator stator itself, and
there is no external space available to mount coolers, when modify the generator
into an air cooled machine. The integral coolers used in the hydrogen cooled
generator are too small for air cooled generator application. It is hence
imperative to look for an alternative location to mount the coolers.
In a prior art turbo generator having a closed circuit hydrogen cooling system
the cold hydrogen is circulated across a heat exchangers (coolers) mounted
inside the stator frame itself. When the machine is in operation, hot hydrogen
from the generator is forced on to the heat exchangers, arranged inside the
stator frame for heat dissipation and the cold hydrogen is brought back to the
generator active parts. The fans mounted on generators rotor give the head
necessary for the above flow to take place.

4
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose a modified air-cooled
turbogenerator with an innproved ventilation circuit.
Another object of the invention is to propose a modified air-cooled turbo
generator with an improved ventilation circuit, which is modified from hydrogen-
cooled turbo generator to air-cooled turbogenerator.
A further object of the invention is to propose an improved ventilation circuit
which is adaptable to the existing air cooled turbo generators to enhance their
cooling systems.
SUMMARY OF THE INVENTION
Accordingly, there is provided a modified air-cooled trubogenerator preferably of
110 MW capacity with an improved ventilation circuit, the modification is
characterized by hot chambers and the cold chambers disposed in such a way
that hot air comes out of the generator all along the length of the stator, the
coolers are disposed on both sides of the generator and in contact with the
stator frame and the stator frame comprising an improved ventilation circuit
comprising configuration of an internal flow path having radial ribs ventilation
spacers, flow dividers the coolers being further disposed adjacent to the stator
casing.
One of the solutions could be that the stator frame is so designed that coolers
are mounted external to the stator and on both sides of generator, along the

5
machine length. In that case, the flow paths inside the generator stator shall be
selected such that the cooler along its entire length is exposed to the hot air
coming out of stator frame. As per the prior art, the coolers in an air-cooled
generator are mounted in a cooler rack, which is mounted on one of the sides of
generator. There will be a considerable gap between the cooler rack and stator
frame casing wall and this gap facilitates distribution of hot air across the total
cooler length.
According to the present invention the coolers are butted to stator frame and the
frame is configured to allow the hot air to flow past the cooler. The advantage of
the present invention is that it makes it possible to replace a hydrogen cooled
generator with an air-cooled generator of matching capacity.
Further, the invention allows up rating the existing of the existing air cooled
generators by optimizing the generator ventilation system. The inventive cooling
circuit enables the power plants to draw more power from the same machine
size or improve the machine efficiency.
In a second aspect of the invention, the coolers are mounted in both sides of
generator, to cool hot air. The internal flow paths are made such that hot air is
brought all along the length of the frame. Schematic of a typical air flow paths in
stator section are shown in Figure 1. This arrangement makes it feasible to
replace the hydrogen with air as cooling medium.

6
The inventive, arrangement when employed to improve the rating and efficiency
of old generators, envisages supply of a stator frame with an optimized cooling
circuit. The circuit consists of internal arrangement of radial ribs, ventilation
spacers, flow dividers in the stator frame, apart from placing the coolers adjacent
to the stator casing.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 - shows a cross sectional arrangement of a frame structure as per
invention, to optimize the air flow paths inside the frame.
Figure 2 - shows the arrangement of heat exchangers on both sides of generator
as per the proposed invention.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION
One of the prime factors on which generator's efficiency depends is the
ventilation system employed. When hydrogen is replaced with air as the cooling
medium, the machine rating will fall as air is less efficient than hydrogen for
cooling by virtue of its lower specific heat, higher density and lower thermal
conductivity. The reduction in efficiency can be compensated partially through an
improvised cooling circuit. The invention aims at improving the generator rating
of existing air cooled generators or to replace the existing hydrogen cooled
generators with an air cooled generator.

7
Figure - 2 shows an arrangement of directing the hot air on to the coolers (1).
The coolers (1) are made to be in contact with the stator frame (2).
As per the prior art, the generator stator is longitudinally divided into various
compartments such that the cold and hot air chambers are obtained along the
active length of the generator, ensuring cold and hot air paths coexist in the
same chambers at the same time. This arrangement enables a better cooling
circuit in terms of maximizing the heat absorption. The hot air coming out of hot
chambers is allowed to flow past the coolers to give away the heat, while the
outer periphery of the stator in the cold chambers is blocked to prevent escape
of cold air.
As per the present invention as shown in figure - 2, the chambers (4) and the
chamber (11) are designed such that hot air comes out of the machine (3) all
along the length of the stator (5). This makes the ventilation circuit better as the
total length of the cooler (1) is exposed to hot air and improved cooling gets
effected.
As shown in figure - 1, the coolers (1) are mounted on both sides of the
generators (3). The cooling circuit comprises radial ribs (6), ventilation spacers,
flow dividers in the stator frame (2). The coolers (1) are placed adjacent to the
stator casing (7). The cold air flow path (8), hot air flow path (9) in bottom half
of the stator frame (2), hot air flow path (10) in top half of the stator frame (2)
are configured such that the hot air is brought ail-along the length of the stator
frame (2).

8
WE CLAIM
1. A modified air-cooled turbogenerator preferably of 110 MW capacity with
an improved ventilation circuit, the modification is characterized by:
- hot chamber (4), and the cold chambers (11) disposed in such a
way that hot air comes out of the generator (3) all along the length
of the stator (5);
- the coolers (1) are disposed on both sides of the generator (3), and
in contact with the stator frame (2); and
- the stator frame (2) comprising an improved ventilation circuit
comprising configuration of an internal flow path having radial ribs
(6), ventilation spacers, flow dividers, the coolers (1) being further
disposed adjacent to the stator casing (5).
2. A modified air-cooled turbogenerator preferably of 110 MW capacity with
an improved ventilation circuit as substantially described and illustrated
herein with reference to the accompanying drawings.

The invention relates to a modified air-cooled turbogenerator preferably of 110
MW capacity with an improved ventilation circuit, the modification is hot chamber
(4), and the cold chambers (11) disposed in such a way that hot air comes out of
the generator (3) all along the length of the stator (5); the coolers (1) are
disposed on both sides of the generator (3), and in contact with the stator frame
(2); and the stator frame (2) comprising an improved ventilation circuit
comprising configuration of an internal flow path having radial ribs (6),
ventilation spacers, flow dividers, the coolers (1) being further disposed adjacent
to the stator casing (5).

Documents:

00570-kol-2008-abstract.pdf

00570-kol-2008-claims.pdf

00570-kol-2008-correspondence others.pdf

00570-kol-2008-description complete.pdf

00570-kol-2008-drawings.pdf

00570-kol-2008-form 1.pdf

00570-kol-2008-form 2.pdf

00570-kol-2008-form 3.pdf

00570-kol-2008-gpa.pdf

570-KOL-2008-(07-01-2014)-ABSTRACT.pdf

570-KOL-2008-(07-01-2014)-CLAIMS.pdf

570-KOL-2008-(07-01-2014)-CORRESPONDENCE.pdf

570-KOL-2008-(07-01-2014)-DESCRIPTION (COMPLETE).pdf

570-KOL-2008-(07-01-2014)-DRAWINGS.pdf

570-KOL-2008-(07-01-2014)-FORM-1.pdf

570-KOL-2008-(07-01-2014)-FORM-13.pdf

570-KOL-2008-(07-01-2014)-FORM-2.pdf

570-KOL-2008-(07-01-2014)-FORM-5.pdf

570-KOL-2008-(07-01-2014)-PA.pdf

570-kol-2008-form 18.pdf

abstract-0570-kol-2008.jpg

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Patent Number

263545

Indian Patent Application Number

570/KOL/2008

PG Journal Number

45/2014

Publication Date

07-Nov-2014

Grant Date

31-Oct-2014

Date of Filing

20-Mar-2008

Name of Patentee

BHARAT HEAVY ELECTRICALS LIMITED

Applicant Address

REGIONAL OPERATIONS DIVISION (ROD), PLOT NO: 9/1 DJBLOCK, 3RD FLOOR, KARUNAMOYEE, SALT LAKE CITY, KOLKATA-700091 BHEL HOUSE, SIRI FORT, NEW DELHI- 110049

Inventors:

#	Inventor's Name	Inventor's Address
1	UPPULURI SRIDHAR	EM ENGINEERING, BHEL, HYDERABAD-502032 BHARAT HEAVY ELECTRICALS LIMITED RC PURAM, HYDERABAD-502032

PCT International Classification Number

H02K15/00; B23K1/008; B23K1/20;B23K31/00

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA