FIELD OF INVENTION
The invention relates to a method for in-situ repair of damaged hollow copper
conductors and water boxes of water-cooled stator winding of electrical
machines.
BACKGROUND OF INVENTION
The stator winding bar of water-cooled turbogenerators contain typically a
combination of Hollow and Solid copper conductors. Cooling water flows inside
Hollow copper conductors. All the solid and hollow copper conductors are brazed
to contact sleeve which provides electrical connection to the other winding bar.
The solid conductors are terminated at the contact sleeve while the hollow
copper conductors are brought out and brazed into the water box which is made
in two parts. The hollow conductors are brazed to it as well as to one another.

Water box top part also contains nipple for water hose connection to the water
header. The two parts are brazed together and the water chamber is formed. In
the typical design, the hollow copper conductors between contact sleeve and
water box are not covered with outer insulation and are exposed to the
surrounding gas environment. The gap so created between contact sleeve and
water box is required to pass the clamping studs.
In the water-cooled stator winding of electrical machines, the coolant is supplied
from circular water headers via insulating hoses to these water boxes at end of
winding bars.
In-situ repair of the contact sleeve and water box / conductors requires
development of special process and toolings because of the space limitation and
special brazing requirements of different components to one another. The
process should take care that the brazing material of already brazed component
does not flow out while replacing the damaged part by subsequent in-situ
brazing. The insulation of the winding bar under repair and all others nearby is
also to be saved from getting damaged due to heat / fire. There is no space
available for fixing the conventional brazing tools. Therefore, conventional
methods could not be employed so far.

WO2005039021 discloses a method of repairing water-cooled stator windings in
generators, the stator windings comprising stator bars including hollow
conductors sealed into a respective water box at each end thereof, the water box
being a single part element or a multi part element, comprising a connecting
device and a front cover, the method comprising opening the water box by
cutting a single part water box or by removing the front cover from a multi part
water box; grinding and/or cleaning the entire exposed copper conductor surface
of the opened water box; applying over the back end of the exposed interior
surface of the opened water box a coating of a filler metal; closing the water box
by means of brazing of a front cover of the original geometry.
Dl provides a method of repairing generator stator windings to improve the
reliability and service life of the repaired components. The cited invention
provides a repair method for in situ repair to avoid costs caused by
disassembling the whole generator. Furthermore, a fluid-cooled stator bar for a
generator, comprising at each end thereof a water box with extended life cycle is
provided.
US 5659944 teaches a method of repairing a joint between conductor elements
of a stator winding bar of an electrical machine and a connecting device
connected to an end of the stator winding bar for providing electrical connection
and coolant flow for the conductor elements includes the steps of removing an

existing connecting device from the end of the stator winding bar; aligning the
conductors of the end of the stator winding bar by heating the bar end to above
the flow point of the braze holding the conductors in position while
simultaneously holding the conductors of the end of the stator winding bar under
compression in two orthogonal directions perpendicular to the length of the
stator winding bar; forming slots in the end of the stator winding bar and at
locations such that the slots extend to locations where the conductor elements
abut one another; applying an electrically conductive first connecting part onto
the end of the stator winding bar such that the first connecting part substantially
surrounds the end of the stator winding bar and sealing the gaps and slots.
OBJECT OF THE INVENTION
It is therefore, an object of the invention to propose a method for uniform
heating all-around the water-box damaged part during in-situ brazing of
damaged stator bars to produce a leak proof joint of the replaced water box
part.

SUMMARY OF THE INVENTION
Accordingly, there is provided an improved method for in-situ repair of hollow
conductor elements of a stator winding of turbogenerators, the stator winding
bar comprises a plurality of stator bars and hollow copper conductor elements
being brazed to atleast one contact sleeve with a spacer disposed in between,
the contact sleeve allowing the conductor elements to remain partially overhung
to form a water box having two parts brazed together, the hollow conductors
being terminated and brazed in the bottom part of the waterbox, the overhang
part of the stator bars (TB, BB) clamped by clamping studs are supported on a
support ring thereby leaving a limited space between the water/electrical
connections and the support ring , the method comprising the steps of removing
the top part of the water box ; cleaning the hollow conductors fitted to the
bottom part of water box ; placing a water jacket around the damaged hollow
conductors , and between the contact sleeve and the water box bottom part;
carrying out in-situ brazing of copper conductors and the water box connection
by leaving space for taking out the clamping studs ; and carrying-out hydraulic
and electrical testing procedures to check healthiness of the repaired
components, wherein disposing a plurality of gas nozzles in an inverted U-
shape configuration between the assembled stator bars (TB, BB) and hollow
copper conductor elements of the stator winding to maintain an uniform heating
of the copper conductor elements for brazing with the contact sleeve , and to
protect the already brazed components from any damage.
A metal jacketing around the damaged water carrying conductors, including a
plurality of inverted gas nozzles maintain a uniform heating during the brazing
between electrical contact sleeve and water box bottom part and thereby making
a leak-proof water path upto the water box.

damaged hollow conductors between electrical contact sleeve and water box
bottom part by suitable process; ensuring a space for taking out electrical
connection studs; and checking the individual water flow from all hollow
conductors of the thus repaired bar.
The invention further provides a special device that takes care of uniform heating
all-around while holding the water box part to be replaced within the limited
space as well as hydraulic/ pneumatic testing of the resulting joints to ensure
healthiness of the repaired bar.
Exemplary embodiments of the invention and further advantages which can be
achieved thereby are explained in more detail in the following text, with
reference to the drawing.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
A more complete appreciation of the invention and many of the attendant
advantages thereof will be readily obtained as the same becomes better
understood by reference to the following explicit description when considered in
connection with the drawings, wherein :
Fig. 1 Shows a general arrangement of Electrical contact sleeve, Copper
Conductors and Water box in a turbogenerator.

Fig. 2 Shows a general arrangement of Stator winding bar overhang support and
Electrical contact sleeve, Water box, Supply hoses and Water header in a
turbogenerator.
Fig. 3 Shows a general arrangement of Electrical contact sleeve, spacer and
Clamping studs in a turbo generator.
Fig. 4 Shows the damages to the hollow copper conductors, water box and
nipple in a turbogenerator.
Fig. 5 Shows a device adaptable to uniformly heat the water box top part while
holding it simultaneously within the limited space according to the invention.
Fig. 6 Shows the water jacket employed to repair the damage and removal of
water box top part, according to the invention.
DETAIL DESCRIPTION OF PREFERRED EMBODIMENTS OF
THE INVENTION
Referring now to the drawings, wherein reference numeral legends designate the
corresponding parts throughout the several figures, the objective used is the
repair method which can repair the localized faults in the hollow conductors and

water boxes of the stator winding bars of an electrical machine, without
necessitating replacement of the complete winding bar as is illustrated above in
discussion and also schematically in FIGS. 1 to 6.
The stator winding bar of water-cooled turbogenerator contain typically a
combination of Solid and Hollow copper conductors (2,3). Cooling water flows
inside Hollow copper conductors (3) to dissipate heat generated in the winding
bar. All solid/ hollow copper conductors (2,3) are brazed to at least one contact
sleeve (1) which provides electrical connection of one bar (TB, BB) to the other
bar with the help of a copper spacer (10) disposed in between. Only hollow
copper conductors (3) are brought out and these are terminated at the water
box (4,5). The water box is made in two parts (4,5). The two parts (4,5) of the
water box are brazed together. All the hollow conductors (3) are brazed into its
bottom part (4) as well as to one another (3). This arrangement is explained in
Fig. 1. General arrangement of overhang support structure is shown in Fig. 2.
There are two bars in each slot of the stator core. The bar towards the air gap is
called "Top bar" (TB) and the bar towards the slot bottom is called "Bottom bar"
(BB). The overhang part of these bars (TB, BB) is supported on an insulating
cone called "support Ring" (11). The contact sleeve (1) and water connection
water box (4,5) are disposed after this support cone (11). The water boxes (4,5)
are connected to the water header (12) through water supply hoses (13). Thus
there is very limited space available between the support ring (11) and the

electrical and water connections. Accordingly innovative tools have been
designed to carry out the in-situ repair work. Fig. 3 shows the arrangement of
clamping studs (7) used to make electrical connection from one bar (TB, BB) to
the other. A copper spacer (10) is placed between the contact sleeves (1) of the
lower and upper bars (BB, TB) and the two bars are clamped together using at
least four number of said steel clamping studs (7). Two clamping studs (7) pass
through a limited space (14) available between the contact sleeve (1) and the
water box (4,5). A water jacket (9) is fitted in this space for in-situ repair which
takes care of the clamping studs assembly (7,8). Fig. 4 shows the typical
locations of localized damages (Dl, D2) in water carrying hollow copper
conductors (3), water boxes (4,5) and connection nipples (6). Fig. 5 shows the
device (18) invented for replacement (RPWB) of water box top part (5) at site.
The device (18) comprises a plurality of gas nozzles (15) and is able to be fitted
in the limited space and ensures uniform heating all around under pressed
condition. Fig. 6 shows the invented water jacket (9) employed to repair the
damages in hollow copper conductors (3). The device (10) is provided with LPG
supply via a rubber hose (19). A new brazing joint is done at a location (L). Both
the top and bottom bars (TB, BB) having insulations (16,17).

ADVANTAGES OF THE INVENTION
A. TIME SAVING
• So far in-situ repair of such faults in stator winding bars was not
feasible.
• Hence damaged winding bar had to be replaced. In may cases fault
occurs in lower bars at more than one locations.
• The replacement of lower bars require removal of upper bars also.
Thus earlier repair method amounted to partial or complete
rewinding depending upon the extent of fault.
• Adequate crane facility to handle larger sets at site may not be
available in many cases. Hence generator had to be brought to
works for repair & rewinding.
• The total time required for restoration of the faulty unit was much
longer due to time taken in removal of the stator, its transportation
to works, repair/rewinding transportation back to site and
recommissioning.

• The in-situ repair method invented now has solved the problem
and the machine is repaired at site in much shorter time without
replacement of winding bars.
• Thus the invention has resulted in huge Time saving to the
generation utility.
B. COST SAVING DUE TO EARLY RESTORATION
• Thus this invention will result in extra power generation.
• For a 500 MW set, a huge Cost saving will thus be achieved due to extra
power generation on account of early restoration of the generator.
B. COST SAVING DUE TO LESSER REPAIR COST
• The new invented In-situ repair is completed in much shorter time and
without replacing any winding bar.
• This will amount to lesser man hour cost, lesser material cost and lesser
technological / induction brazing machine hours cost.
• Therefore Repair Cost saving of substantial amount is achievable by this
invention.

WE CLAIM
1. An improved method for in-situ repair of hollow conductor elements of a
stator winding of turbogenerators, the stator winding bar comprises a plurality of
stator bars and hollow copper conductor elements (2,3) being brazed to atleast
one contact sleeve (1) with a spacer (10) disposed in between, the contact
sleeve allowing the conductor elements to remain partially overhung to form a
water box having two parts (4,5) brazed together, the hollow conductors (3)
being terminated and brazed in the bottom part (4) of the waterbox, the
overhang part of the stator bars (TB, BB) clamped by clamping studs (7) are
supported on a support ring (11) thereby leaving a limited space between the
water/electrical connections and the support ring (11), the method comprising
the steps of:
- removing the top part of the water box (5);
- cleaning the hollow conductors (3) fitted to the
bottom part of water box (4);
- placing a water jacket (9) around the damaged hollow
conductors (3), and between the contact sleeve (1)
and the water box bottom part (4);
- carrying out in-situ brazing of copper conductors and
the water box connection by leaving space for taking
out the clamping studs (7); and

- carrying-out hydraulic and electrical testing
procedures to check healthiness of the repaired
components,
wherein disposing a plurality of gas nozzles (15) in an inverted U-shape
configuration between the assembled stator bars (TB, BB) and hollow copper
conductor elements (2,3) of the stator winding to maintain an uniform heating of
the copper conductor elements (2,3) for brazing with the contact sleeve (1), and
to protect the already brazed components from any damage.
2. An improved method for in-situ repair of hollow conductor elements of a
stator winding of turbogenerators, the stator winding bar as substantially
described and illustrated herein with reference to the accompanying drawings

ASBTRACT

TITLE: An improved method for in-situ repair of hollow conductor elements of a
stator winding of turbogenerators
The invention relates to an improved method for in-situ repair of hollow
conductor elements of a stator winding of turbogenerators, the stator winding
bar comprises a plurality of stator bars and hollow copper conductor elements
(2,3) being brazed to atleast one contact sleeve (1) with a spacer (10) disposed
in between, the contact sleeve allowing the conductor elements to remain
partially overhung to form a water box having two parts (4,5) brazed together,
the hollow conductors (3) being terminated and brazed in the bottom part (4) of
the waterbox, the overhang part of the stator bars (TB, BB) clamped by clamping
studs (7) are supported on a support ring (11) thereby leaving a limited space
between the water/electrical connections and the support ring (11), the method
comprising the steps of removing the top part of the water box (5); cleaning the
hollow conductors (3) fitted to the bottom part of water box (4); placing a water
jacket (9) around the damaged hollow conductors (3), and between the contact
sleeve (1) and the water box bottom part (4); carrying out in-situ brazing of
copper conductors and the water box connection by leaving space for taking out
the clamping studs (7); and carrying-out hydraulic and electrical testing
procedures to check healthiness of the repaired components, wherein disposing
a plurality of gas nozzles (15) in an inverted U-shape configuration between the
assembled stator bars (TB, BB) and hollow copper conductor elements (2,3) of
the stator winding to maintain an uniform heating of the copper conductor
elements (2,3) for brazing with the contact sleeve (1), and to protect the
already brazed components from any damage.