U.S. patent application number 12/032146 was filed with the patent office on 2008-06-05 for method of sealing a generator stator bar and a stator bar end fitting.
This patent application is currently assigned to GENERAL ELECTRIC COMPANY. Invention is credited to Jeffrey Michael Breznak, Lawrence Lee Sowers, Yu Wang.
Application Number | 20080129127 12/032146 |
Document ID | / |
Family ID | 34941823 |
Filed Date | 2008-06-05 |
United States Patent
Application |
20080129127 |
Kind Code |
A1 |
Wang; Yu ; et al. |
June 5, 2008 |
METHOD OF SEALING A GENERATOR STATOR BAR AND A STATOR BAR END
FITTING
Abstract
A method of sealing a generator stator bar and a stator bar end
fitting receiving the end including the steps of: brazing the
fitting to the end of the stator bar with a braze material;
applying a metallic barrier coating material to the end of the
stator bar in the fitting; heating the fitting at a temperature at
least as hot as a liquidus temperature of the metallic coating
material and cooler than a solidus temperature of the braze
material; coating the end of the stator bar in the fitting with
liquid metallic barrier coating material, and solidifying the
liquefied metallic coating material to form a metallic barrier
coating on the end of the stator bar in the fitting.
Inventors: |
Wang; Yu; (Clifton Park,
NY) ; Breznak; Jeffrey Michael; (Waterford, NY)
; Sowers; Lawrence Lee; (Ballston Lake, NY) |
Correspondence
Address: |
NIXON & VANDERHYE P.C.
901 NORTH GLEBE ROAD, 11TH FLOOR
ARLINGTON
VA
22203
US
|
Assignee: |
GENERAL ELECTRIC COMPANY
Schenectady
NY
|
Family ID: |
34941823 |
Appl. No.: |
12/032146 |
Filed: |
February 15, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10900184 |
Jul 28, 2004 |
7334316 |
|
|
12032146 |
|
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|
|
Current U.S.
Class: |
310/52 ; 29/525;
310/66 |
Current CPC
Class: |
Y10T 29/49721 20150115;
Y10T 29/4973 20150115; Y10T 29/49012 20150115; Y10T 29/49009
20150115; Y10T 29/49064 20150115; Y10T 29/49742 20150115; H02K 3/22
20130101; Y10T 29/49945 20150115; H02K 15/0093 20130101 |
Class at
Publication: |
310/52 ; 310/66;
29/525 |
International
Class: |
H02K 15/00 20060101
H02K015/00; H02K 9/00 20060101 H02K009/00; B23P 19/02 20060101
B23P019/02; H02K 5/124 20060101 H02K005/124 |
Claims
1. A method of sealing a generator stator bar and a stator bar end
fitting receiving the end comprising: attaching the fitting to the
end of the stator bar with a braze material; applying a metallic
barrier coating material to the end of the stator bar attached to
the fitting; heating the fitting at a temperature at least as hot
as a liquidus temperature of the metallic coating material and
cooler than a solidus temperature of the braze material to liquefy
the metallic coating material; coating the end of the stator bar in
the fitting with the liquid metallic barrier coating material, and
cooling the fitting to solidify the liquefied metallic coating
material to form a metallic barrier coating on the end of the
stator bar in the fitting.
2. The method as in claim 1 wherein the end of the stator bar is
horizontal as the liquid metallic barrier coating coats the end of
the stator bar.
3. The method as in claim 1 wherein attaching the fitting comprises
brazing the fitting and stator bar with the braze material that
includes a phosphorous copper braze alloy, and the metallic coating
material comprises a tin-silver-copper alloy.
4. The method as in claim 3 wherein brazing the fitting comprises
brazing with at least one of a BCuP-5 and a BCuP-1 phosphorous
copper braze alloy, and the metallic coating comprises a
Sn/3.8Ag/0.7Cu solder material.
5. The method as in claim 3 wherein the fitting is brazed with the
braze alloy having a solidus temperature of no cooler than 600
degrees Celsius and the metallic coating material has a liquidus
temperature no hotter than 600 degrees Celsius.
6. The method as in claim 1 wherein the fitting is oriented
vertically during the step of coating the end of the stator bar
with liquid metallic coating material.
7. The method as in claim 1 wherein the end of the stator bar
comprises ends of hollow strands extending beyond ends of solid
strands of the bar, and the liquid metallic coating covers the ends
of the solid strands and said ends of the hollow strands extends
above the liquid metallic coating.
8. The method as in claim 1 wherein the end of the stator bar
comprises ends of hollow strands, and the method further comprises
inserting hollow inserts into open ends of the hollow strands such
that the inserts extend beyond ends of solid strands of the bar,
and the liquid metallic coating covers the ends of the solid
strands and flows around the hollow inserts.
9. The method as in claim 8 wherein the inserts are ceramic.
10. The method as in claim 1 wherein the coating material is
applied to the end of the stator bar through a chamber in the
fitting.
11. The method as in claim 1 wherein the coating material is
applied to the end of the stator bar as a solid.
12. The method as in claim 1 wherein the coating material comprises
a group consisting of a paste, a powder, metallic chips and
metallic shavings.
13. A fitting for a stator bar of a generator comprising: a fitting
housing having a collar at a first end and a cooling fluid coupling
at an opposite end, wherein said collar is brazed with a braze
material to an end of the stator bar; a chamber extending from the
first end to the opposite end of the fitting, and a metallic
barrier coating on an end of the stator bar in said chamber and
forming a seal between the end and a remaining portion of the
chamber, wherein said metallic barrier coating has a liquidus
temperature lower than a solidus temperature of the braze material
applied to braze the stator bar to the fitting.
14. A fitting as in claim 13 wherein the metallic barrier coating
is a tin-silver copper alloy.
15. A fitting as in claim 13 wherein said stator bar comprises
solid copper strands and hollow copper strands, wherein the end of
the stator bar further comprises ends of the solid copper strands
and ends of the hollow copper strands extending beyond the ends of
the solid copper strands, and wherein the coating covers the ends
of the solid copper strands and the ends of the hollow copper
strands extend through the coating.
16. A fitting as in claim 13 wherein said stator bar comprises
solid copper strands and hollow copper strands, wherein the end of
the stator bar further comprises inserts in open of the hollow
copper strands, and wherein the coating covers ends of the solid
copper strands and the inserts extend through the coating.
17. A fitting as in claim 16 wherein the inserts are ceramic.
18. A fitting as in claim 13 wherein a thickness of the coating is
in a range of 10 to 500 mils.
Description
RELATED APPLICATION
[0001] This application is a divisional of application Ser. No.
10/900,184, filed Jul. 28, 2004, which application is incorporated
in its entirety by reference herein.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to seals between generator
stator bars and their end fitting connections, and to a method for
sealing a stator bar end fitting to prevent or reduce corrosion due
to coolant water flowing through the fitting and the stator
bar.
[0003] Water-cooled stator bars for electrical generators are
comprised of a plurality of small rectangular solid and hollow
copper strands brazed to one another to form a bar. The ends of the
strands are brazed to an end fitting, typically referred to as
stator bar clip. The end fitting serves as both an electrical and a
cooling flow connection for the stator bar.
[0004] The hollow end fitting typically includes an enclosed
chamber for ingress or egress of stator bar cooling liquid,
typically deionized water. At one open end, the end fitting
receives the ends of the strands of the stator bar. The fitting and
the peripherally outermost copper strands of the stator bar are
brazed to one another. The opposite end of the fitting is connected
to a stator cooling conduit, e.g., a house.
[0005] Over time, leaks can developed about the connection between
the stator bar ends and the stator bar fitting as well as between
adjacent strands. It is believed that the leak mechanism is due to
a two-part corrosion process which initiates in the braze alloy at
the interior surface of the braze joint. Stagnant water in the
chamber of the fitting has in the past been in contact with the
braze alloy and the copper strands. This coolant contact with the
braze joint and cooper strands is believed to cause corrosion and
consequent leakage.
[0006] Field repair of coolant leaks through the stator bar end
connections has been moderately successful. A leak site is
identified by external visual examination of where the strands
enter the end fitting. External visual leak detection indirectly
identifies the leak site because the visible external leak on the
outside of the bar and/or fitting may be a considerable distance
away from a point within the fitting where the leak begins. This is
particularly true if the leak is occurring between the strands of
the stator bar.
[0007] Once a leak is identified by visible inspection, a vacuum is
drawn inside the fitting and stator bar. An anaerobic cement is
applied externally or reflow the braze material around the
suspected leak sites. The vacuum suction draws the cement inwardly
towards the leak path. However, it has been found that this cement
repair method is not 100% effective in repairing the leak and is
therefore considered only a temporary repair.
[0008] As an alternative to applying cement to seal a leak, an
epoxy barrier coating has been applied to provide protection
against water initiated corrosion mechanisms along the brazed
length of the strand package. The epoxy barrier coating technique
is disclosed in U.S. Pat. No. 5,605,590. The epoxy barrier coating
has been an improvement over earlier corrosion protection
techniques. However, the epoxy barrier coating may deteriorate when
exposed to extreme temperatures and can be difficult to inspect in
certain stator clip designs.
[0009] There is a need for an improved barrier coating for stator
bar clips. In particular there is a need for corrosion protection
between the stator bars and their clips. The corrosion protection
should be robust and be applicable to various stator bar clip
designs, including clips for raised hollow strand stator
designs.
BRIEF DESCRIPTION OF THE INVENTION
[0010] The invention may be embodied as a method of sealing a
generator stator bar and a stator bar end fitting receiving the end
including the steps of: attaching the fitting to the end of the
stator bar with a braze material; applying a metallic barrier
coating material to the end of the stator bar in the fitting;
heating the fitting at a temperature at least as hot as a liquidus
temperature of the metallic coating material and cooler than a
solidus temperature of the braze material; coating the end of the
stator bar in the fitting with liquid metallic barrier coating
material, and solidifying the liquefied metallic coating material
to form a metallic barrier coating on the end of the stator bar in
the fitting.
[0011] The invention may also be embodied as a method of sealing a
stator bar end to a stator bar end fitting, the fitting having a
chamber for receiving a liquid through an opening and in
communication with hollow strands in said stator bar to enable
coolant liquid flow through the hollow strands, said method
comprising: brazing the fitting to the end of the stator bar;
inserting a metallic barrier coating material into the chamber of
the fitting; liquefying the metallic barrier coating material by
heating the material to a temperature at least as hot as a liquidus
temperature of the coating material; coating the end of the stator
bar in the fitting with the liquefied metallic barrier coating
material, and solidifying the liquefied metallic barrier coating
material to form a barrier over the end of the stator bar in the
fitting, wherein said hollow end strands comprise end openings
extending through the barrier.
[0012] The invention may also be embodied as a fitting for a stator
bar of a generator comprising: a fitting housing having a collar at
a first end and a cooling fluid coupling at an opposite end,
wherein said collar is configured to be brazed to an end of the
stator bar; a chamber extending from the first end to the opposite
end of the fitting, and a metallic barrier coating on an end of the
stator bar in said chamber and forming a seal between the end and a
remaining portion of the chamber, wherein said metallic barrier
coating has a liquidus temperature lower than a solidus temperature
of a braze material applied to braze the stator bar to the
fitting.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a schematic illustration of a liquid-cooled stator
winding arrangement illustrating the stator bars and end fittings
coupled to inlet and outlet coolant headers;
[0014] FIG. 2 is a representative end cross-sectional view of the
strands of a stator bar within an end fitting, and
[0015] FIG. 3 is an enlarged cross-sectional view of a stator bar
end fitting taken along line 3-3 in FIG. 2. FIG. 3 illustrates a
barrier coating that has been applied to the end of the bar within
the fitting such that hollow strands of the bar extend through the
coating, and that the coating otherwise seals the bar end and braze
from the coolant.
[0016] FIG. 4 is an enlarged cross-sectional view of a stator bar
end and a fitting, wherein inserts are in the open ends of hollow
end strands and the inserts extend through the metallic barrier
coating in the fitting.
DETAILED DESCRIPTION OF THE INVENTION
[0017] FIG. 1 illustrates a liquid-cooled stator winding
arrangement used in a typical liquid-cooled generator. A stator
core 10 having stator core flanges 12 and core ribs 14. Stator bars
16 pass through radially extending slots and terminate at opposite
ends in end fittings 18 and 20. Inlet hoses 22 connect the inlet
fitting 18 to an inlet coolant header 24. Outlet hoses 26 connect
the outlet fitting 20 to an outlet coolant header 28.
[0018] FIG. 2 is an end view of a stator bar and one of the stator
bar fittings 18, 20. FIG. 3 is a cross-sectional side view of the
end of the stator bar and its end fitting. Each stator bar includes
a plurality of solid and hollow copper strands 30 and 32,
respectively, disposed in side-by-side and superposed relation one
to the other along the length of the bar. The strands are brazed to
one another. The ends of the strands form the end 31 of the stator
bar. The inlet fitting 18 and an outlet fitting 20 are brazed to
opposite ends of the stator bar 16.
[0019] The strands 30, 32 are brazed to one another, as well as to
the inside walls of the end fitting. The brazing material 44 is for
example BCuP-5 and/or BCuP-1. The strands are also brazed to one
another within the stator bar. It is believed that the initiation
of the leakage paths is caused by stagnant coolant liquid in the
sub-chamber 40 of the fitting which corrodes the end of the stator
bar.
[0020] The end fittings 18, 20 are each formed of an electrically
conductive material, such as copper. The fitting (also referred to
here as a "stator bar clip") is hollow and includes a collar 34
that slides over the outer side surfaces of the end 31 of the
stator bar 16. Opposite to the collar, the fitting includes a
coupling end 36 that is configured to connect to one of the cooling
hoses 22, 26.
[0021] The coupling end 36 of the end fitting is normally connected
to and closed by a copper hose tube 22, 26 which serves as both an
electrical connection and as a hydraulic conduit. Liquid coolant,
e.g., deionized water, flows through the tubes 22, 26 into or from
the internal chamber 38 defined by the fitting 20 and the exposed
ends 39 of the hollow copper strands 32. The liquid in the chamber
38 flows into a first fitting, through the hollow strands 32 and
out an opposite fitting. The opposite end fittings 18, 20 comprise
an inlet fitting or receives the liquid coolant from the hollow
strands 32 for egress when the fitting is employed as an outlet
fitting.
[0022] Each end fitting 18, 20 includes an internal chamber 38
generally coaxial with the fitting and extending the length of the
fitting. The chamber 38 includes an expanded sub-chamber 40
adjacent to the end 31 of the stator bar, a necked down section and
a second expanded sub-chamber configured to receive an end of a
hose. The external and internal shapes of a fitting may vary to
suit different stator bar configurations.
[0023] To install an end fitting 18, 20 on a stator bar end, the
bar ends are solidified and brazed to the collar of the fitting. A
conventional high-temperature phosphorous copper braze alloy, e.g.,
BCuP-1, may be applied to the braze the end of the bar to the
fitting when the bar is held horizontally or vertically. A BCuP-5
braze alloy may be applied to the joint between the end fitting and
stator bar to seal the fitting to the strand ends. A conventional
high temperature phosphorous copper braze material, e.g., BCuP-5,
may be used to seal the collar of the clip to the strand ends of
the stator bar.
[0024] Typically, a BCuP-5 braze alloy has a solidus temperature of
1190.degree. Fahrenheit-F. (643.degree. Celcius-C.), a liquidus
temperature of 1475.degree. F. (802.degree. C.) and a brazing range
of 1300.degree. F. to 1500.degree. F. (704.degree. C. to
816.degree. C.). Typically, a BCuP-1 braze alloy has a solidus
temperature of 1310.degree. Fahrenheit-F. (710.degree. Celcius-C.),
a liquidus temperature of 1688.degree. F. (920.degree. C.) and a
brazing range of 1454.degree. F. to 1724.degree. F. (790.degree. C.
to 940.degree. C.). A solidus is a temperature below which the
braze is solid and a liquidus is a temperature above which the
braze is entirely liquid.
[0025] When the bar is brazed to the end fitting, the ends of the
solid cooper strands 32 are generally flush with a back wall of the
expanded sub-chamber 40. The ends 39 of the hollow cooper strands
extend partially into the sub-chamber 40. The ends 39 of the hollow
cooper strands 32 may extend about 10 to 500 mils beyond the ends
of solid strands 30 and into the sub-chamber 40.
[0026] The end 31 of the stator bar is sealed with a metallic
barrier coating 46 to prevent coolant corrosion. The coating is
applied after the fitting is brazed to the stator bar and a braze
seal is applied to the joint between the fitting and bar. The
metallic barrier coating seals the end of the stator bar without
blocking the openings 39 to the hollow strands and thereby allows
coolant to flow through the fitting and the hollow strands. The
coating material 46 forms a barrier across the sub-chamber 40 that
prevents the coolant from corroding the end of the stator bar.
[0027] The metallic barrier coating material 46 may be a
low-liquidus, corrosion resistant braze alloy or solder material. A
tin-silver-copper alloy solder, and in particular Sn/3.8Ag/0.7Cu,
is suitable as a coating material. The coating material 46 is
selected such that its liquidus temperature is lower than the
solidus temperature of the braze alloy(s) used to both braze the
copper strands together and to braze the fitting to the end of the
stator bar. For example, the liquidus of the coating material may
be in a range between 150.degree. C. to 600.degree. C., which is
below the 643.degree. C. solidus of a BCuP-5 braze alloy applied to
bond the end fitting to the stator bar. The coating material when
applied to the fitting and bar end may be in the form of a paste,
powder, chips or other small size form.
[0028] After being brazed together, the stator bar fitting and
stator bar are oriented vertically. This orientation places the end
surface of stator bar and the ends of the strands are horizontal
and the coupling end 36 of the fitting is upright. The metallic
barrier coating material 46 is initially inserted in a solid or
liquid form through the coupling end 36 of the fitting, into the
sub-chamber 40 and on the end of the stator bar. The coating
material is applied over the solid strands 30 end surfaces and
around the ends 31 of the hollow strands 32 to form a coating over
the end of the stator bar in the clip.
[0029] A bore scope or other inspection instrument may be inserted
into the chamber 40 so that a technician may view the end of the
stator bar and the coating material to confirm that the coating
material is at the bottom of the sub-chamber 40 and on the stator
bar, and that the ends of the hollow strands extend up through the
coating. This inspection may be accomplished when the coating
material is initially inserted into the fitting and/or after the
coating material has been liquefied and solidified on the end of
the bar.
[0030] Heating the coating material, end of stator bar and fitting
to a temperature above the liquidus temperature of the coating
material, e.g., 5 degrees Celsius higher, causes the coating
material 46 to liquefy and form a barrier coating over the end
surface 31 of the bar in the fitting. Because the stator bar end 31
is horizontal, the liquefied coating material forms a pool over the
end of the bar and at the bottom of the sub-chamber 40. The depth
of the pool is less than the height of the ends of the hollow
strands, e.g., the coating material pool is less than 10 to 500
mils. The hollow end strands protrude above the surface of the pool
of the coating material. When the coating cools, the liquid coating
material solidifies as a metallic barrier coating over the end of
the stator bar.
[0031] The coating 46 forms a metallic barrier 46 over the end of
the stator and within the sub-chamber 40 of the fitting. The
coating 46 seals potential leakage paths within the fitting. The
coating serves as a seal between the liquid coolant and the cooper
strands and brazing alloy applied to the strands.
[0032] While the invention has been described in connection with
what is presently considered to be the most practical and preferred
embodiment, it is to be understood that the invention is not to be
limited to the disclosed embodiment, but on the contrary, is
intended to cover various modifications and equivalent arrangements
included within the spirit and scope of the appended claims.
* * * * *