U.S. patent application number 13/786852 was filed with the patent office on 2014-09-11 for passivation of hollow copper strands in a stator water cooling system.
This patent application is currently assigned to GENERAL ELECTRIC COMPANY. The applicant listed for this patent is GENERAL ELECTRIC COMPANY. Invention is credited to Stephen Frank Francese, Raymond Grant Rowe, Leonard Paul Squillacioti, James Jun Xu, Weijun Yin, Ronald Joseph Zawoysky.
Application Number | 20140251504 13/786852 |
Document ID | / |
Family ID | 50235935 |
Filed Date | 2014-09-11 |
United States Patent
Application |
20140251504 |
Kind Code |
A1 |
Xu; James Jun ; et
al. |
September 11, 2014 |
PASSIVATION OF HOLLOW COPPER STRANDS IN A STATOR WATER COOLING
SYSTEM
Abstract
A system for passivating a plurality of hollow copper strands in
a stator water cooling system including; a first storage tank
containing a cleaning solution, a second storage tank containing
rinsing water; a third storage tank containing a passivation
solution; a plurality of conduits connecting the first, second, and
third storage tanks in a closed loop with the plurality of hollow
copper strands; and an alkaline pump for pumping the cleaning
solution, the rinsing water, and the passivation solution through
the closed loop.
Inventors: |
Xu; James Jun; (Niskayuna,
NY) ; Francese; Stephen Frank; (Ballston Spa, NY)
; Rowe; Raymond Grant; (Niskayuna, NY) ;
Squillacioti; Leonard Paul; (Saratoga Springs, NY) ;
Yin; Weijun; (Niskayuna, NY) ; Zawoysky; Ronald
Joseph; (Clifton Park, NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
GENERAL ELECTRIC COMPANY |
Schenectady |
NY |
US |
|
|
Assignee: |
GENERAL ELECTRIC COMPANY
Schenectady
NY
|
Family ID: |
50235935 |
Appl. No.: |
13/786852 |
Filed: |
March 6, 2013 |
Current U.S.
Class: |
148/254 ;
118/400; 118/58; 148/269 |
Current CPC
Class: |
H02K 15/00 20130101;
F28G 9/00 20130101; C23C 8/42 20130101; C23C 22/00 20130101; H02K
3/22 20130101 |
Class at
Publication: |
148/254 ;
118/400; 118/58; 148/269 |
International
Class: |
C23C 8/42 20060101
C23C008/42 |
Claims
1. A system for passivating a plurality of hollow copper strands in
a stator water cooling system, the system comprising: a first
storage tank containing a cleaning solution; a second storage tank
containing rinsing water; a third storage tank containing a
passivation solution; a plurality of conduits connecting the first,
second, and third storage tanks in a closed loop with the plurality
of hollow copper strands; and an alkaline pump for pumping the
cleaning solution, the rinsing water, and the passivation solution
through the closed loop.
2. The system of claim 1, further comprising: a flow control device
for controlling the flow of the cleaning solution, the rinsing
water, and the passivation solution through the closed loop; and a
temperature control device for controlling the temperature of the
cleaning solution, the rinsing water, and the passivation
solution.
3. The system of claim 1, wherein the passivation solution includes
one of sodium chlorite solution, sodium hydroxide solution,
trisodium phosphate solution, and deionized water.
4. The system of claim 1, wherein the plurality of conduits include
polytetrafluoroethylene (PTFE).
5. The system of claim 1, wherein the cleaning solution includes a
detergent and water, wherein the ratio of the detergent to the
water is about 1 part to about 3 parts.
6. The system of claim 1, further comprising: a hot air fan for
blowing hot air through the plurality of hollow copper strands.
7. The system of claim 1, further comprising: a drainage tank for
receiving a discharge from the plurality of hollow copper
strands.
8. A method for passivating at least one hollow copper strand,
comprising: cleaning an inner surface of the at least one hollow
copper strand with a cleaning solution; rinsing, after the
cleaning, the inner surface with a rinsing water; and passivating,
after the rinsing, the inner surface with a passivation
solution.
9. The method of claim 8, wherein the cleaning solution includes a
detergent and water.
10. The method of claim 9, wherein the ratio of the detergent to
the water is about 1 part to about 3 parts.
11. The method of claim 8, wherein the cleaning solution is at a
temperature of about 50.degree. C.
12. The method of claim 8, wherein the rinsing water has a
temperature of about 50.degree.-70.degree. C. and the rinsing
occurs for about 3 minutes.
13. The method of claim 8, wherein the passivation solution
includes one of sodium chlorite solution, sodium hydroxide
solution, trisodium phosphate solution, and deionized water.
14. The method of claim 13, wherein a temperature of the
passivation solution during the passivating is in a range of about
50.degree. C. to about 70.degree. C.
15. The method of claim 13, wherein the passivating is for a period
of time of about 2 to about 30 minutes.
16. The method of claim 8, wherein the passivating includes flowing
the passivation solution at a flow rate of about 1 cubic
foot/second.
17. A system for passivating at least one hollow copper strand, the
system comprising: a first storage tank containing a cleaning
solution; a second storage tank containing rinsing water; a third
storage tank containing a passivation solution; a plurality of
conduits connecting the first, second, and third storage tanks in a
closed loop with the at least one hollow copper strand; and an
alkaline pump for pumping the cleaning solution, the rinsing water,
and the passivation solution through the closed loop.
18. The system of claim 17, further comprising: a flow control
device for controlling the flow of the cleaning solution, the
rinsing water, and the passivation solution through the closed
loop; and a temperature control device for controlling the
temperature of the cleaning solution, the rinsing water, and the
passivation solution.
19. The system of claim 17, wherein the passivation solution
includes one of sodium chlorite solution, sodium hydroxide
solution, trisodium phosphate solution, and deionized water.
20. The system of claim 17, wherein the cleaning solution includes
a detergent and water, wherein the ratio of the detergent to the
water is about 1 part to about 3 parts.
Description
FIELD OF THE INVENTION
[0001] This invention relates generally to stator water cooling
systems for a generator and more particularly to passivation of
hollow copper strands in a stator water cooling system against
obstruction.
BACKGROUND OF THE INVENTION
[0002] High megawatt electrical power generators may have liquid
cooling systems for their stator windings. Such a liquid cooling
system may be known as a stator water cooling system (SWCS). Stator
cooling fluid, e.g., oxygenated water whose dissolved oxygen
content is recommended to be more than 2 ppm (parts per million,
weight based), circulates through the SWCS to cool the stator
windings. The cooling fluid removes heat from the stator windings
generated by the high energy electrical current flowing through the
stator windings. The SWCS includes a network of cooling passages
throughout the stator and that extend between the stator windings.
These cooling passages should remain open and free of obstructions
to ensure a high flow of coolant fluid to all sections of the
stator windings. The SWCS also includes several components external
to the stator including piping, pumps, filters, a reservoir tank
and a strainer. As known, an SWCS may include additional
components.
[0003] FIG. 1 shows schematically a stator water cooling system
(SWCS) 100 which circulates coolant, e.g., oxygenated water,
through a generator 104 that includes a plurality of stator
windings (not shown), each stator winding including a plurality of
copper strands 102. FIG. 2 shows a perspective cut-away view of a
known stator winding 101 and the plurality of copper strands 102.
Stator winding 101 includes a top stator bar 107 and a bottom
stator bar 109 both stator bars 107, 109 including the plurality of
copper strands 102. FIG. 3 shows a cross section view of the
plurality of copper strands 102 in the stator winding. FIG. 4 shows
a cross-sectional perspective view of a known copper strand 102.
The plurality of copper strands 102 is hollow to allow the passage
of the coolant through the plurality of copper strands 102.
Accordingly, each copper strand 102 has an inner surface 103 and an
outer surface 105. Referring again to FIG. 1, the SWCS 100 includes
piping 106 external to the generator 104 that carries the coolant
through a network including a reservoir tank 108, at least one pump
110, a deionizer bed 112, rectifier 114, at least one heat
exchanger 116, flow control valves 118, at least one filter 120,
and a strainer 122. The strainer 122 may include mesh (not shown)
capable of catching precipitate-able solute and particulate
impurities in the coolant. The strainer 122 is typically in the
piping 106 upstream (referring to the flow of the coolant) of the
generator 104 and in a cool (low) temperature portion of the SWCS
100.
[0004] Coolant continually circulates through the SWCS 100 network.
The coolant is drawn from the reservoir tank 108 by the at least
one pump 110, and flows into the at least one heat exchanger 116
which cools the fluid. The cooled fluid from the heat exchanger 116
flows through at least one filter 120 and the strainer 122 and into
the plurality of copper strands 102. As the coolant flows over the
plurality of copper strands 102, the coolant removes heat from the
stator windings and the plurality of copper strands 102. The heat
is carried by the coolant out of the generator 104 into the
reservoir tank 108.
[0005] Any electrical charge accumulated by the coolant as it flows
through the highly electrically charged passages in the stator is
discharged as the coolant is circulated through the rectifier 114.
The coolant is deionized in the deionizing bed 112 to reduce the
tendency of metal oxides to form in the coolant. The flow rate of
the coolant is controlled by flow control valves 118. The flow rate
may be monitored by flow meters (not shown) that provide a feedback
control for a controller (not shown) that operates the flow control
valves 118.
[0006] The plurality of copper strands 102 have a tendency to
accumulate copper oxides from the coolant of the SWCS 100 in the
form of cuprous oxide and cupric oxide. The oxides build up on the
inner surfaces of the copper strands 102 and reduce the flow of the
coolant. As the deposition of copper oxides in the copper strands
102 increases, the resistance of the plurality of copper strands
102 to the coolant flow similarly increases. Accumulated copper
oxide deposits in the plurality of copper strands 102 may
eventually obstruct the flow of the coolant, reducing the flow of
cool fluid through the stator, and disrupting proper cooling of the
stator winding assembly.
[0007] Among copper oxides, the formation of particulate-like
cuprous oxide (Cu.sub.2O) layer is of chief concern. Cuprous oxides
are reddish, loose, morphologically and chemically unstable, and
thus are lost into the coolant stream in particulate forms. Cuprous
oxide layers are formed on the inner surfaces 103 of the plurality
of copper strands 102, as well as on the strainer 122. Due to
insufficient exposure or insufficient oxygen content (such as 25
ppb-250 ppb (parts per billion, weight based)) in coolant flow,
they are found to be associated with the most rapid copper
corrosion rate because of its morphological instability and
constitute a large portion in the blockage deposit. Cupric oxides
(CuO), however, are morphologically and chemically stable. They
tend to form a firm layer having better resistance to coolant flow
and much slower development of thick blockage deposit on the inner
surfaces 103 of the plurality of copper strands 102. Loss of the
firm cupric oxide layer into coolant flow, when it would occur,
forms dissolvable cupric oxide, instead of undissolvable particles
such as cuprous oxide. These dissolvable cupric oxides tend to
deposit on the strainer 122 that is replaceable once a year or so
without discontinuing the operation.
[0008] The prevention of forming loose cuprous oxide on the inner
surfaces 103 of the plurality of copper strands 102 proves to be an
economic challenge and laborious effort. Complete depletion of
oxygen (e.g., below 25 ppb-250 ppb) in the SWCS 100 requires the
most stringent control and rigorous treatment of large quantities
of industrial coolant for daily usage such as deionized water. Rich
oxygen content present in the water presents another challenge as
oxidization of possibly fresh inner surfaces 103 of the plurality
of copper strands 102 would go deep without stopping. It eventually
erodes the plurality of copper strands 102 designed for
decades-long service life. Oxygenated cooling water within a
relatively narrow specification limit has been proposed and is
being practiced. It tends to render the high ratio of forming a
firm cupric oxide layer to a loose particulate cuprous oxide layer,
thus reduced rate of copper corrosion, and reduce the occurrence of
incidents of strand and strainer plugging. However, the level of
oxygenation of water requires stringent control and consistent
monitoring and adjustment during the generator operation where
other key operating parameter maintenance is taken with priority.
The observation of reddish or purplish layer deposited on inner
surfaces 103 of the plurality of copper strands 102 of those
decade-long serviced stator bars is often attributed to operational
deviation from water oxygenation specification.
[0009] Passivation of the inner surfaces 103 of the plurality of
copper strands 102 may be best performed either prior to or after
they are Roebelled for forming stator bare bars. However, it is
known that at that particular stage of the stator bar-making
process, the grease and other detergents may be present on the
inner surfaces 103 of the plurality of copper strands 102, which
was carried from wire drawing process. However, even the inner
surfaces 103 of the plurality of copper strands 102 have the clean
and fresh copper surfaces, it would take weeks, if not a month to
form desirable firm passivation layers with merely air exposure and
yet its homogeneity and controlled time and thickness of the layer
along axis of hollowed strands are not warranted.
BRIEF DESCRIPTION OF THE INVENTION
[0010] A first aspect of the invention provides a system for
passivating a plurality of hollow copper strands in a stator water
cooling system, the system comprising: a first storage tank
containing cleaning solution; a second storage tank containing
rinsing water; a third storage tank containing a passivation
solution; a plurality of conduits connecting the first, second, and
thirds storage tanks in a closed loop with the plurality of hollow
copper strands; and an alkaline pump for pumping the cleaning
solution, the rinsing water, and the passivation solution through
the closed loop.
[0011] A second aspect of the invention provides a method for
passivating at least one hollow copper strand, comprising: cleaning
an inner surface of the at least one hollow copper strand with a
cleaning solution; rinsing, after the cleaning, the inner surface
with a rinsing water; and passivating, after the cleaning, the
inner surface with a passivation solution.
[0012] A third aspect of the invention provides a system for
passivating at least one hollow copper strand, the system
comprising: a first storage tank containing a cleaning solution; a
second storage tank containing rinsing water; a third storage tank
containing a passivation solution; a plurality of conduits
connecting the first, second, and third storage tanks in a closed
loop with the hollow copper strand; and an alkaline pump for
pumping the cleaning solution, the rinsing water, and the
passivation solution through the closed loop.
[0013] These and other aspects, advantages and salient features of
the invention will become apparent from the following detailed
description, which, when taken in conjunction with the annexed
drawings, where like parts are designated by like reference
characters throughout the drawings, disclose embodiments of the
invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] The above and other aspects, features and advantages of the
invention will be better understood by reading the following more
particular description of the invention in conjunction with the
accompanying drawings.
[0015] FIG. 1 shows a schematic diagram of a known stator water
cooling system (SWCS).
[0016] FIG. 2 shows a shows a perspective cut-away view of a known
stator winding and the plurality of copper strands.
[0017] FIG. 3 shows a cross section view of the plurality of copper
strands in the stator winding.
[0018] FIG. 4 shows a cross-sectional perspective view of a known
copper strand.
[0019] FIG. 5 shows a schematic diagram of one embodiment of a
system for passivating a plurality of hollow copper strands in a
stator water cooling system in accordance with the present
invention.
[0020] FIG. 6 shows a flow diagram of one embodiment of a process
for passivating a plurality of hollow copper strands of stator
water cooling system for a stator winding assembly in accordance
with the present invention.
[0021] The drawings are not necessarily to scale. The drawings are
merely schematic representations, not intended to portray specific
parameters of the invention. The drawings are intended to depict
only typical embodiments of the invention, and therefore should not
be considered as limiting the scope of the invention. In the
drawings, like numbering represents like elements.
DETAILED DESCRIPTION OF THE INVENTION
[0022] Referring to FIG. 5, a schematic diagram of one embodiment
of the invention is shown. As shown in FIG. 5, a system 200 for
passivating a plurality of hollow copper strands 202 in a stator
water cooling system may be incorporated in a known SWCS (FIG. 1,
100) or may be a stand-alone system for passivating a plurality of
hollow copper strands 202. The system 200 may include a first
storage tank 204 containing a cleaning solution; a second storage
tank 206 containing rinsing water; a third storage tank 208
containing a passivation solution; a plurality of conduits 210
connecting the first storage tank 204, the second storage tank 206,
and the third storage tank 208 in a closed loop with the plurality
of hollow copper strands 202; and an alkaline pump 212 for pumping
the cleaning solution, the rinsing water, and the passivation
solution through the closed loop. A person skilled in the art will
readily recognize that the system 200 could be used to passivate at
least one hollow copper strand 202.
[0023] The system 200 may further include at least one flow control
valve 214 for controlling the flow of the cleaning solution, the
rinsing water, and the passivation solution through the closed
loop. Flow control valve 214 may be adjusted to various speeds and
flow may be stopped. A person skilled in the art will readily
recognize that flow control valve 214 may be placed anywhere in the
closed loop to control flow of the cleaning solution, the rinsing
water, and the passivation solution. At least one temperature
control device 216 may be included for controlling the temperature
of the cleaning solution, the rinsing water and/or the passivation
solution. A person skilled in the art will readily recognize that
more than one temperature control device 216 may be included. For
example, each of the first, second, and third storage tanks 206,
208, 209 may include a temperature control device 216. At least one
filter 218 may be included to filter debris and particles in the
cleaning solution, the rinsing solution, or the passivation
solution.
[0024] The passivation solution may include, for example, one of a
sodium chlorite solution, a sodium hydroxide solution, a trisodium
phosphate solution, deionized water, and any combination of the
foregoing. The sodium chlorite solution may have a concentration of
sodium chlorite in a liter of deionized water of about 30
grams/liter. The sodium hydroxide solution may have a concentration
of sodium hydroxide in a liter of deionized water of about 10
grams/liter. The trisodium phosphate solution may have a
concentration of trisodium phosphate in a liter of deionized water
of about 5 grams/liter. The plurality of conduits 210 may be
flexible or rigid and may include, for example, hoses and pipes.
The plurality of conduits 210 may include polytetrafluoroethylene
(PTFE) for resisting chemical reaction with the copper passivation
solution. Other materials may similarly be used.
[0025] The system 200 may further include a hot air fan 220 for
blowing hot air through the plurality of hollow copper strands 202
through liquid-cooled stator winding clips (not shown) after the
rinsing and a drainage tank 222 for draining the plurality of
hollow copper strands 202 after the cleaning, the rinsing, or the
passivating. A hot air fan control valve 224 and a drainage tank
valve 226 may be included to control the blowing and draining of
the closed loop.
[0026] Referring to FIG. 6, a flow diagram of one embodiment of a
method for passivating at least one hollow copper strand (FIG. 5,
202) is shown. As shown in FIG. 6, at S1, an inner surface of the
at least one hollow copper strand (FIG. 5, 202) may be cleaned with
a cleaning solution. Cleaning may remove oil, grease, dust, and
other contaminants from the at least one hollow copper strand (FIG.
5, 202). The cleaning solution may include a detergent and water.
The ratio of the detergent to the water may be about 1 part to
about 3 parts. The cleaning solution may be at a temperature of
about 50.degree. C.
[0027] At S2, after the cleaning, the inner surface may be rinsed
with a rinsing water. The rinsing includes rinsing with water. The
rinsing water may be a temperature of about 120.degree. C. and the
rinsing may be performed for about 3 minutes. At S3, optionally
after the rinsing, hot air may be blown through the at least one
hollow copper strand (FIG. 5, 202) for drying.
[0028] At S4, after the rinsing (or optionally after the blowing),
the inner surface may be passivated with a passivation solution.
The passivation solution may include one of sodium chlorite
solution, sodium hydroxide solution, trisodium phosphate solution,
and deionized water. A passivation temperature of the passivation
solution may be in a range of about 50.degree. C. to about
70.degree. C. A passivation duration may be a period of time of
about 2 to about 30 minutes. At the completion of the passivation
duration, the passivation solution may be drained from the at least
one hollow copper strand (FIG. 5, 202). The passivating may include
flowing the passivation solution at a flow rate of about 1 cubic
foot/second. Alternatively, after the at least one hollow copper
strand (FIG. 5, 202) are filled with passivation solution, the
passivating may include allowing the passivation solution to stand
in the at least one hollow copper strand (FIG. 5, 202) for the
passivation duration.
[0029] It will be appreciated by a person skilled in the art, that
the method and system presented herein may be used for passivating
a single hollow copper strand. For example, each of the plurality
of hollow copper strands (FIG. 5, 202) in the SWCS 100 could be
passivated before they are installed in the SWCS 100 either as a
new installation of equipment or as a service or repair of existing
equipment or for any other use for a hollow copper strand (FIG. 5,
202).
[0030] The terminology used herein is for the purpose of describing
particular embodiments only and is not intended to be limiting of
the disclosure. As used herein, the singular forms "a", "an" and
"the" are intended to include the plural forms as well, unless the
context clearly indicates otherwise. It will be further understood
that the terms "comprises" and/or "comprising," when used in this
specification, specify the presence of stated features, integers,
steps, operations, elements, and/or components, but do not preclude
the presence or addition of one or more other features, integers,
steps, operations, elements, components, and/or groups thereof
[0031] While various embodiments are described herein, it will be
appreciated from the specification that various combinations of
elements, variations or improvements therein may be made by those
skilled in the art, and are within the scope of the invention. In
addition, many modifications may be made to adapt a particular
situation or material to the teachings of the invention without
departing from essential scope thereof. Therefore, it is intended
that the invention not be limited to the particular embodiment
disclosed as the best mode contemplated for carrying out this
invention, but that the invention will include all embodiments
falling within the scope of the appended claims.
* * * * *