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Патент USA US2127232

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Aug- 15, 1938-
L. c. NICHOLS
2,127,232
RECTIFIER TRANSFORMER
Filed July 25, 1936
3 Sheets-Sheet l
Aug. 16, 1938.
L. c. NICHOLS. v‘ .
>
- f
2,127,232
RECTIFIER TRANSFORMER
Filed July 25, 1936
I
3 Sheets-Sheet 2
Aug. 16, 1938.
L. C. NICHOLS
2,127,232
RECTIFIER TRANSFORMER
Filed July 25, 1936
5 Sheets-Sheet 3
2,127,232
Patented Aug. 16, 1938
UNITED STATES PATENT OFFiCE
2,127,232
RE GTIFIER» TRANSFORMER.
Louis C. Nichols, Wauwatosa, Wis., assignor _to
Allis-Chalmers Manufacturing Company, Mil
waukee, Wis., a corporation of Delaware
Application July 25, 1936, Serial No. 92,472
10 Claims.
(Cl. 1'75—363)
This invention relates in general to improve
ments in recti?er transformers, and more par
ticularly to transformers adapted to supply cur
rent to groups of electric valves operating in
5 parallel circuits.
It is well known that electric valve converting
systems are occasionally subject to disturbances,
such as the so-called back?res resulting from
momentary failure of the valve action of a valve
10 utilized as part of the system. In systems uti
lizing a transformer connecting one or more
valves with an alternating current circuit, such
failure particularly results in effectively short cir
cuiting the alternating current circuit through
15 the transformer, and the latter is then caused to
carry an excessive current which may damage
the windings thereof by overheating and by the
electromagnetic action thereon of the magnetic
leakage ?elds thereof. It is therefore desirable
20 to so design the transformer as to reduce the
magnitude of any back?re currents ?owing
through the windings thereof. In particular,
when the system presents a plurality of parallel
circuits, the transformer is preferably provided
25 with a secondary winding divided into parallel
sections each connected in one of such circuits
through a separate valve, such sections being
severally associated with serially connected sec
tions of the transformer primary winding. Dur
30 ing a back?re some of the sections of the primary
winding are thus associated with secondary wind
ing sections which are without current, and such
primary winding sections then are linked with
02 01
extensive magnetic leakage ?elds which mate
rially reduce the flow of current through the
transformer. With such arrangement, current
?ow if also forcibly initiated simultaneously
through all parallel secondary winding sections,
during normal operation of the transformer, and
40 such sections are forced to carry equal amounts
of current at every instant.
It is, therefore, one of the objects of the
present invention to provide a, transformer for an
electric valve converting system having windings
45 so arranged that the flow of back?re current
therethrough is reduced to a relatively low value.
Another object of the present invention is to
provide a transformer for an electric valve con
verting system having a secondary winding form
50 ing parallel circuits and so- arranged that the ?ow
of current is forcibly initiated simultaneously
through the several circuits.
Another object of the present invention is to
provide a transformer for an electric valve con
55 verting system having a secondary Winding form
ing parallel circuits and so arranged that such
circuits are forced to carry equal currents at
every instant.
Objects and advantages other than those above
set forth will be apparent from the following de- 5
scription when read in connection with the ac
companying drawings in which:
Fig. l diagrammatically illustrates the arrange
ment of the windings and the connections of a
transformer of the shell type forming an embodi- 10
ment of the present invention and comprising a
three-phase primary winding and a six-phase
secondary winding divided into three parallel sec
tions supplying a group of eighteen valves of an
alternating current rectifying system;
15
Fig. 2 diagrammatically illustrates another
embodiment of the present invention differing
from the embodiment illustrated in Fig. l in be
ing provided with two parallel primary windings
and with a six-phase secondary winding divided 20
into four parallel sections;
Fig. 3 diagrammatically illustrates a further
embodiment of the present invention consisting
of a transformer of the core type having a three
phase primary winding and a six-phase second- 25
ary winding divided into two parallel sections.
It will be understood that some of the features
of any one of the embodiments illustrated may
also be utilized in combination with features of
the other embodimens to form further embodi- 30
ments of the present invention.
Referring more particularly to the drawings by
characters of reference, reference numeral 6 in
Fig. 1 generally designates a transformer of the
so-called shell type adapted to be utilized in con- 35
junction with a plurality of electric valves l to
form a converting system such as the system
illustrated by way of‘ example, which is adapted
to rectify alternating current supplied thereto
from a three~phase supply line 8 and to deliver 40
the recti?ed current to a direct current output
line 9. Valves l each comprise an anode Hi, the
anodes being either each associated with a sepa
rate cathode, or being associated with a lesser
number of cathodes or even with a single cathode 45
connected with one conductor of line 9. It will
be understood that by providing valves ‘I with
suitable control electrodes and with a suitable
control system therefor, the transformer and the
valves may also be caused to transmit energy from 50
line 9 to line 8, or to transmit energy between
line 8 and another alternating current line suit
ably connected with the transformer and with
the valves.
Transformer 6 is provided with a three-phase 55,
2
2,127,232
core I I on which are arranged the phase portions
I2, I3, Id of a three-phase primary winding, each
portion consisting of a plurality of sections such
as I211, I22), I20, I2cl serially connected across a
pair of conductors of line 8. Means are provided
for varying the connections between the sections
of each primary winding phase portion to thereby
adjust the secondary voltages of the transformer.
Although such result could be obtained by chang
II) ing taps of only one or of less than all the sections
of each phase portion, it is generally preferred
to provide all such sections with taps connected
to no load tap changers equal in number to the
number of interconnections between primary:
winding sections. In the present embodiment,
each primary winding portion comprises four sec
tions and therefore presents three connections
between sections, which connections may be
changed by means of three tap changers. Only
tap changers I6, I1, I8 associated with winding
portion I2 are illustrated in detail, the tap chang
ers associated with winding portions I3 and I5
being similarly arranged and connected. Tap
changer I6, for example, is provided with a plu
rality of contacts I9, of which alternate contacts
are severally connected with the taps and with
one terminal of winding section I2a, the remain
ing segments being severally connected with the
taps and with one terminal of winding section
I2b. Each pair of adjacent taps may be bridged
by a brush 2|, the brushes of the several tap
changers being mounted on a common shaft 22
in order that they may be moved simultaneously
over the same number of steps of the respective
tap changers.
The polyphase secondary winding of trans
former 6 comprises a plurality of phase portions
23, 24, 25 each divided into a plurality of inter
connected parallel sections such as 23a, 23b, 23c
40 interleaved with the sections of the associated
primary winding phase portion I2. Both the pri
mary and secondary winding sections consist of
stacks of disk shaped coils, also called pancake
coils, of which only the coils of winding portions
I2 and 23 are shown in cross section, the support
ing means therefor being omitted to clarify the
drawings.
Winding portions I3, I4, 24, 25 are
shown in elevation and are represented as being
insulated from each other and from core II by
means of insulating spacers 26. Such spacers also
serve to brace the windings against each other
and against core II for preventing displacement
of the winding sections by the electromagnetic
action thereon of the magnetic leakage ?elds
thereof during flow of back?re or short circuit
current through the transformer. In addition,
it is generally preferable to arrange the taps of
each primary winding end section, such as I id,
at the end of such section remote from the ad
jacent secondary winding section such as 23a,
and to arrange the terminals and the taps of each
intermediate primary winding section, such as
I21), near the center of such section to thereby re
move the taps, which constitute weak points of
the winding, from the magnetic leakage ?elds
present in the gaps between adjacent primary
and secondary winding sections.
In order to obtain six-phase current from the
transformer secondary winding, each section
thereof, such as 23a, is divided into two portions
which are symmetrically arranged with respect to
the adjacent primary winding sections, such as
I2a, I2b, and which may also be interleaved to
reduce the leakage reactance thereof with respect
75 to the associated primary winding portion. Each
primary winding section is thus arranged ad
jacent both portions of at least one of the second
ary winding sections and has a relatively low
leakage reactance with respect thereto, and is
also arranged remote from the remainder of the
primary and secondary winding sections and,
therefore, has a relatively high leakage reactance
with respect thereto.
The two portions of a sec»
ondary winding section, such as 23a, are adapted
to alternately transmit unidirectional current im 10
pulses to the associated anodes, such as Hm, I 0d,
of valves 1 in the course of alternate half cycles
of the voltage of line 8. The operation of the
secondary winding sections is preferably con
trolled by means of an-interphase transformer 27
connected therewith and forming therewith, in
effect, a unitary transformer structure, as is well
known in the art.
In operation, line 8 being energized, current
is drawn from line 8 sequentially through wind 20
ing portions I2, 13 and I4, and the currents in
duced thereby in winding portions 23, 24 and 25
are converted, by the action of valves 1, into suc
cessive unidirectional impulses which combine at
the common cathode of valves ‘I to form a flow
of direct current supplied to line 9. At every in
stant, three valves receive current from the as
sociated parallel'sections of one of winding por
tions 23, 24 and 25, the action of interphase trans
former 21 causing the flows of current which are 30
successively initiated in the different groups of
valves to overlap by one-half of their duration,
so that current is carried at every instant by at
least six valves. Considering such operation in
greater detail, at a particular moment of the
voltage cycle of line 8, the voltage conditions of
such line are such that three valves 1 cease carry
ing current, and a flow of current is then estab
lished simultaneously through three valves ‘I such,
for example, as the valves comprising anodes Illa, 40
I fig and Him respectively associated with parallel
portions of winding sections 23a, 23b and 230.
The three parallel circuits established through
such winding portions are similar to one another
and receive equal voltages, so that normally the 45
flow of current is established therethrough simul
taneously.
If one of the circuits, such as the circuit includ
ing anode Illa and the associated winding portion
23a, fails to carry current for any reason such as 50
non-uniform conditions of pressure and tempera
ture in the valves, the primary winding portions
I2a and I2b adjacent to section 23a cause the
establishment of a magnetic leakage ?ux there
through, such leakage flux closing itself about
winding section I2a through a. portion only of
core II and through winding section 23a. Wind
ing section In accordingly takes an increased
fraction of the voltage of line 8 and, as a result
of the series connection of winding portion I2, 60
winding sections I22), I2c, I2d thereof receive a
lesser fraction of the voltage of line 8 and link
with a reduced magnetic flux, whereby the volt
ages induced in adjacent winding sections 23b and
230 decrease while the ‘voltage induced in section
23a rises to a value sufficient to overcome the
cause of the failure of section 2311 to carry cur
rent, thus forcing the substantially simultaneous
initiation of the flow of current through all three
parallel sections. Such action would also take 70
place in a similar manner, if two of the three
parallel circuits tended to remain without cur
rent, to increase the voltages impressed on the
two momentarily inoperative circuits and thus re
store normal operating condition.
2,127,232
By a process similar to that above described, if
the currents in the parallel circuits become un
balanced, the voltage impressed on the circuit
carrying the smallest current is increased by an
increase of the magnetic flux linking therewith,
while the voltage impressed on the circuit carry
ing the highest current is decreased by a decrease
of the magnetic flux linking therewith; such ad
justment of the magnetic ?uxes being obtained
automatically by the distribution of the leakage
fluxes produced by the serially connected primary
winding sections.
3
maximum value being determined by the resist
ance of the circuit traversed thereby. The flow
of back?re current caused by failure of the valve
action of anodes other than anode lOa would be
reduced in the manner above set forth as a result
of the serial connection of the sections of winding
portions l2, l3 and Ill. The heating and stressing
of the conductors of the transformer windings are
thus considerably reduced, and the thrusts im
pressed on the winding sections by the electro 10
magnetic action of the magnetic leakage ?elds
The occurrence of a back?re in valves 1 would
result from the loss of the valve action of one
thereof are reduced to values such that the sec
tions may be held in place by means of spacers 26.
In the embodiment illustrated in Fig. 2 core H
of the valves, of which the anode may then become
a cathode. Assuming that anode l?a, for ex
ample, becomes a; cathode, current may flow
thereto from all other anodes except the anodes
is provided with a three-phase primary winding, 15
of which each phase portion such as 28 comprises
four sections such as 28a, 28b, 28c, 28d connected
in series parallel connection through tap changers
normally operating in parallel therewith whereby
such as 29 and 3|. The tap changers are illus
trated as being each provided with an odd number 20
of segments to obtain an even number of steps,
20 line 8 is short circuited through the transformer.
As is well known, a back?ring anode may receive
current simultaneously from several of the sec
ondary phase circuits of the transformer at every
instant. For example, at a particular moment of
25 the voltage cycle of line 8, current may ?ow from
the upper terminal of interphase transformer 21
through one portion of each of the parallel sec
tions of winding portion 24 and the associated
anodes to anode Illa and the associated portion
30 of winding section 23a back to the upper terminal
of interphase transformer 21 and also from the
lower terminal of the interphase transformer
through one portion of each of the parallel sec
tions of winding portion 25 and the associated
35 anodes through anode Illa, the associated portion
of winding section 2311, and through the interphase
transformer. As is usual in the operation of
transformers, such currents are induced in the
_ secondary winding portions by the associated pri
40 mary winding portions.
During such operation,
winding sections 231) and 230 are without current.
Primary winding sections I20 and lZd may thus
establish extensive magnetic leakage ?elds about
themselves and through secondary winding sec
45 tions 23d and 230 and, as the result of the serial
connection of winding sections Her and I21)‘ with
sections I20 and l2d, the latter function in the
same manner as windings of independent reactors
connected in series with winding sections l2a,
50 I221. The flow of current through winding por
tion [2 is thereby considerably reduced, and the
magnitude of the ?ow of back?re current between
winding portions 23, 24 and 25 is thus reduced
to a material extent.
If generators or converting systems other than
the systems shown are connected to supply cur
rent to line 8, the occurrence of a back?re at
anode l 0a also causes direct current to ?ow from
line 9 through the common cathode of valves 1,
60 then functioning as an anode, through anode Illa,
55
the associated portion of winding section 2311 and
one winding of interphase transformer 21 to the
other conductor of line 9. Such current is not
established instantly at a constant value and,
65 during the rise of the value thereof, the flow of
such current through winding section 23a tends
to induce a similar rising ?ow of current through
winding portion I2. The magnetic leakage ?elds
established about winding sections [20 and [2d,
70 however, oppose the establishment of such current
in winding portion I2, thereby also reducing the
rate of increase of the current in winding section
23a. Such current may therefore be interrupted
by means of suitable switching means before hav75 ing reached the maximum value thereof, such
the two winding sections being connected with
one tap changer which is then provided with num
bers of taps differing by one. In the present em
bodiment, each secondary phase portion such as 25
32 is divided into four sections such as 32a, 32b,
32c, 3201 each divided into two portions supplying
two valves 1, there being accordingly twenty-four
valves which are preferably divided into two equal
groups each provided with a separate cathode to 30
form a separate structure or recti?er. It is gen
erally preferable to control the operation of the
winding sections associated with different recti
?ers by means of separate interphase transform
ers such as transformers 33 and 34.
The opera
tion of the serially connected primary winding
sections in causing the currents through the asso
ciated parallel secondary winding sections to be
initiated simultaneously and to be maintained at
equal values, and in limiting the flow of back?re 40
current through the transformer, is similar to that
set forth with respect to the embodiment illus
trated in Fig. 1.
In the embodiment illustrated in Fig. 3, the
transformer is assumed to be provided with a 45
core 36 adapted to receive coextensive phase
winding portions arranged side by side about
different legs of the core to form a transformer
of the so-called core type. Each primary wind
ing phase portion, such as 31, is divided into a 50
plurality of sections such as 31a, 31b‘ each Wound
about one of the sections such as 38a, 38b of a
secondary phase winding portion 38. Each wind
ing phase portion is shown as being divided into
only two sections whereby the transformer is op 55
erable to supply current to a group of twelve
valves operating in parallel in pairs, but it will
be understood that a greater number of sections
may also be utilized as in the embodiments illus
trated in Figs. 1 and 2. The two sections of each 60
primary winding phase portion may be connected
through a single tap changer such as at 39. The
operation of the serially connected primary wind
ing sections in causing the currents in the asso
ciated parallel secondary winding section to be 65
initiated simultaneously and to be maintained at
equal values and in limiting the flow of back?re
current through the transformer, is similar to
that above set forth with respect to the embodi
ment illustrated in Fig. 1.
70
It will be observed that, in the present embodi
ment, the two winding sections such .as 31a, 31b of
a primary winding phase portion as well as the
two sections such as 38a and 38b of the associ
ated secondary winding phase portion are alined 75
4
2,127,232
end to end on a core leg and each consists of a
plurality of nested cylindrical coils. It is well
known that such coils cannot be braced satisfac
torily against the core to withstand axial thrusts
resulting from the action of the magnetic leak
age ?eld established thereabout during a back
?re. For example, if an anode connected with
winding section 38a loses its valve action, during
a part of the cycle of the voltage of line 8 a large
10 current ?ows from at least one of the secondary
winding portions other than portion 38 and
through the associated anode or anodes of valves
1 through anode Illa and the associated portion
of section 38a, while section 3% remains with~
15 out current. Both portions of primary winding
portion 3'! necessarily carry equal currents at
such time and, section 38a being arranged dis
symmetrically with respect to the entire winding
portion 31, the magnetic leakage ?eld of winding
20 portion 31 tends to exert a large axial thrust on
winding section 38a which would displace such
section bodily on core 36. To avoid such result,
means are arranged between the winding sections
respect thereto to thereby limit the ?oW of back
?re current between said secondary phase p0r~
tions.
3. A transformer structure for an electric valve
converting system comprising a polyphase pri
mary winding having each phase portion thereof
divided into a plurality of serially connected sec
tions, a polyphase secondary winding having each
phase portion thereof divided into a plurality of
parallel sections, each primary winding section 10
being arranged adjacent at least one of said sec
ondary winding sections and having a relatively
low leakage reactance with respect thereto and
being arranged remote from the remainder of
said primary and secondary winding sections
and having a relatively high leakage reactance
with respect thereto to thereby limit the flow of
back?re current between said secondary phase
portions, and interphase windings connected with
said secondary winding for controlling the opera
tion thereof.
ii. A transformer for an electric valve convert
ing system comprising a primary winding hav
for diverting the magnetic leakage ?eld of each
primary winding section and of the adjacent sec
ondary winding section from all other winding
ing having a plurality of interconnected parallel
sections.
sections arranged on said core and each divided
Such means are thus essentially mag
netic shields which may consist of additional
yokes 4| of core 36 separating the top and bottom
winding sections or of other equivalent means
such as disks of magnetic material inserted be
tween the top and bottom winding sections Each
ing a plurality of serially connected sections
arranged on a common core, a secondary wind
into two portions adapted to alternately transmit
unidirectional current impulses, each said pri
mary winding section being arranged adjacent 30
both portions of one of said seconary winding
winding section is thus subject to only magnetic
leakage ?elds which are symmetrical with respect
thereto and which do not exert .any axial thrust
thereon.
Although but a few embodiments of the pres
ent invention have been illustrated and described,
it will be apparent to those skilled in the art that
various modi?cations and changes may be made
therein without departing from the spirit of the
sections and having a relatively low leakage
reactance with respect thereto and being ar
ranged remote from the remainder of said pri
mary and secondary winding sections and having
a relatively high leakage reactance with respect
thereto, and means arranged between said wind
ing sections for diverting the magnetic leakage
?elds of each said primary winding section and
of the adjacent said secondary winding section
from all other said winding sections.
invention or from the scope of the appended
claims.
It is claimed and desired to secure by Letters
ing system comprising a primary winding having
45 Patent:
1. A transformer for an electric valve convert
ing system comprising a primary winding having
a phase portion thereof divided into a plurality
of serially connected sections arranged on a com
50 mon core, and a secondary winding having a plu
rality of interconnected parallel sections ar~
ranged on said core and each divided into two
portions adapted to alternately ‘transmit unidi~
rectional current impulses, each said primary
55 winding section being arranged adjacent both
portions of at least one of said secondary wind~
ing sections and having a relatively low leakage
reactance with respect thereto and being ar
ranged remote from the remainder of said pri
60 mary and secondary winding sections and having
a relatively high leakage reactance with respect
thereto.
2. A transformer for an electric valve convert
5. A transformer for an electric valve convert
a plurality of serially connected sections ar
ranged on a common core, a secondary winding _.1~
having a plurality of interconnected parallel sec
tions arranged on said core and each divided into
two portions adapted to alternately transmit
unidirectional current impulses, each said pri
mary winding section being arranged adjacent
both portions of at least one of said secondary
winding sections and having a relatively low
leakage reactance with respect thereto and being
arranged remote from the remainder of said pri
mary and secondary winding sections and having
a relatively high leakage reactance with respect
thereto, said primary and secondary winding
sections being interleaved, and means for bracing
said winding sections against each other and
against said core for preventing displacement of
said winding sections by electromagnetic action
thereon of the magnetic leakage ?elds thereof
during flow of back?re current through the
ing system comprising a polyphase primary wind
ing having each phase portion thereof divided
transformer.
6. A transformer for an electric valve convert
into a plurality of serially connected sections, and
ing system comprising a primary winding having
a polyphase secondary winding having each phase
a phase portion thereof divided into a plLu'ality
of sections arranged in series parallel connection
portion thereof divided into a plurality of par
allel sections, each primary winding section be
70 ing arranged adjacent at least one of said sec
ondary winding sections and having a relatively
low leakage reactance with respect thereto and
being arranged remote from the remainder of
said primary and secondary winding sections and
having .a relatively high leakage reactance with
51)
and arranged on a common core, and a secondary
winding having a plurality of interconnected
parallel sections arranged on said core and each
divided into two portions adapted to alternately
transmit unidirectional current impulses, each
0
said primary winding section being arranged ad
jacent both portions of one of said secondary 75
2,127,232
winding sections and having a relatively low
leakage reactance with respect thereto and being
arranged remote from the remainder of said pri—
mary and secondary winding sections and having
a relatively high leakage reactance with respect
5
the combination with a source of electric current,
and electric valve means comprising a plurality
of anodes, of means for causing the flow of cur
thereto.
'7. A transformer for an electric valve convert
ing system comprising a primary winding having
a plurality of serially connected sections ar
10 ranged on a common core, a secondary winding
having a plurality of interconnected parallel sec
tions arranged on said core and each divided into
rents supplied from said source of predetermined
relative magnitudes simultaneously through said
anodes and for opposing changes in the magni
tude of the flow of current through any one of
said anodes relative to the magnitude of the flow
of current through another of said anodes com
prising a transformer winding phase portion 10
divided into a plurality of interconnected parallel
sections severally connected with said anodes
two portions adapted to alternately transmit
‘unidirectional current impulses, each said pri
15 mary winding section being arranged adjacent
and positioned on a common core, and another
transformer Winding phase portion connected
with said source of current and divided into a 15
plurality of serially connected sections severally
both portions of at least one of said secondary positioned on said core adjacent at least one of
winding sections and having a relatively low said interconnected parallel sections and having
leakage reactance with respect thereto and being relatively low leakage reactance with respect
arranged remote from the remainder of said pri
thereto and being positioned remote from the 20
20 mary and secondary winding sections and having remainder of the ?rst and second said winding
a relatively high leakage reactance with respect sections and having a relative high leakage reac
thereto, and means for adjusting the voltages of tance with respect thereto.
said secondary winding comprising means for
10. In an electric current converting system,
varying the connections between said primary the combination with a source of electric cur 25
winding sections.
rent, and electric valve means comprising a plu
8. In an electric current converting system, rality of anodes, of means for causing the flow
the combination with a source of electric current, of currents supplied from said source of prede
and electric valve means comprising a plurality termined relative magnitudes simultaneously
of anodes, of means for causing the flow of cur
through said anodes and for opposing changes in 30
80 rents supplied from said source of predetermined magnitude of the flow of current through any
relative magnitudes simultaneously through said one of said anodes relative to the magnitude of
anodes and for opposing changes in magnitude the ?ow of current through another thereof com
of the flow of current through any one of said prising a transformer winding phase portion di
anodes relative to the magnitude of the flow of vided into a plurality of interconnected parallel 35
current through another thereof comprising a sections severally connected with said anodes,
transformer winding phase portion divided into
a plurality of interconnected parallel sections
severally connected with said anodes, and an
other transformer winding portion connected
with said source of current and divided into a
plurality of serially connected sections severally
closely inductively coupled with at least one of
said interconnected parallel sections and rela
tively loosely coupled with the remainder of the
winding sections.
46 said
9. In an electric current converting system,
and another transformer winding connected
with said source of current having a phase por
tion thereof divided into a plurality of sections, 40
in series parallel connection severally relatively
closely inductively coupled with at least one of
said interconnected parallel sections and rela
tively loosely coupled with the remainder of said
winding sections.
LOUIS C. NICHOLS. 45
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