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Патент USA US2411656

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Nov- 26, 1946.
K. L. HENDERSON ET AL
2,411,856
COAXIAL BUSHING
Filed Feb. 7, 1944
JNVENTQRS
Patented Nov. 26_, 1946
2,411,656
UNITED_'STATES PATENT OFFICE
2,411,656
COAXIAL BUSHING
Kenneth IL. Henderson and Edward F. lDe Mers,
Irondequoit, N. Y., assignors to Stromberg
Carlson Company, Rochester, N. Y., a corpora
tion of New York
Application February 7, l91f4, Serial No. 521,463
3 Claims.
1
(Cl. 174-73)
2
This invention relates to insulating bushings
nected to the other conductor B3 of the bushing
especially adapted for use in connection with
as will appear later.
high voltage apparatus.
The bushing 5 has the central metal conductor
or stem l3 (just mentioned) which is provided
at its lower end with a threaded portion and is
provided at its upper end with a mushroom-like
metal cap M having a screw terminal l?. As il
lustrated, the upper end portion of the stem is
In certain high voltage devices such as in an
oil-immersed transformer, it is essential that
two output conductors thereof be extended
through the wall of the transformer to suitable
terminals, in a way that will prevent oil leak
age and yet will insure that there Will be no volt
knurled so that when it is forced into the open
age breakdown or corona effects between the 10 ing in the cap, a close ?t results and the joint
several parts.
v
The present invention has for its main purpose
the production of a coaxial bushing which will
satisfy the mentioned requirements and in ad
dition will be sturdy in construction as well as 15
especially compact in design.
The various features and advantages of the
between these parts can be sealed by soldering or
brazing. The stem is enclosed by a paper or
other insulating sleeve lt extending from the
inner surface of the cap M to the threaded lower
portion of the stem. The other conductor lt
(previously mentioned) of the bushing comprises
a brass tube which surrounds the paper sleeve
invention will appear from the detailed descrip
E6, with the stem l3 enclosed therein. Thus, the
two conductors iS and BB are concentrically ar
tion and claims when takenV with the drawing
in which:
,_
20 ranged with respect to each other. The tube lß
Fig. l illustrates a side elevation of the coaxial
has its upper end fusibly joined in concentric
bushing of the present invention, together with
relation to the inner border of an annular disc
a fragment of an oil-?lled transformer on which
20, so that the disc extends perpendicular to the
axis of the tube. This disc is provided With an
it is mounted, the transformer units being di
agrammatically illustrated;
25 integral ferrule fi having a screw terminal 22.
Fig. 2 is a longitudinal section through the
This ferrule tapers in the direction of the cap, >
bushing; and
the outer edge of the disc being connected to an
intermediate portion of the inner surface of the
Fig. 3 is a cross-sectional view of the bushing
ferrule, to provide a recess at each surface of the
taken on the line 3-3 of Fig. 2.
Referring especially to Fig. 1, the numeral ä 30 disc.
generally designates the coaxial insulating bush
The cap M and the ferrule ?l are insulated
from each other by a porcelain sleeve or insulator
ing of the present invention, having its lower
portion extending through an opening in the
24. This insulator, With asbestos washers 25 and
top of an oil-?lled metal transformer case li.
26 engaging its respective ends, surrounds the
Within this case there are mounted the oil-im 35 stem l3 and the enclosing paper tube M3. It will
mersed transformer units 8 and 9. The primary
be seen that the upper end of the insulator ex
windings of these transformers are connected in
tends into the recess at the under side of the cap,
multiple to the conductors ll and |2 which re
while the lower end thereof extends into the re
spectively lead to a low voltage supply, such as
cess at the upper part of the ferrule. Since hot
a hundred ten volt alternating current source. 40 oil tends to seep through any mechanical joint,
These conductors pass through spaced openings
it is essential that such a joint be avoided at any
part of the bushing. On the other hand, solder
or other fused metal will not adhere to glazed
?bre and screw terminals having a suitable ad
porcelain when untreated. In this construction,
hesive such as *'Glyptal" applied to the joints be 45 however, bands 28 and 29 of the porcelain glaze
tween the several parts. The secondary Wind
at the respective ends of this insulator are
ing of the high voltage transformer unit 8 has
metallized by having a thin ñlm of metal fused
one terminal conductively connected to the case
or sputtered into the glaze at these portions. The
6 as by means of solder and has its other termi
unoccupied portion of the recess in the cap is
nal conductively connected through terminal 44, 50 fllled with molten solder 3| while the unit is held
to one conductor 18 of the bushing 5. This con
inverted from the position illustrated. This
ductor of the bushing is also connected in mul
solder becomes fused to the cap and to the metal
tiple to one terminal of the secondary winding
lized band 28 of the insulator 24, thereby provid
of the low voltage transformer 9. The remain
ing an oil-proof seal at this joint. Similarly, the
ing terminal of this winding is conductively con 55 un?lled portion of the recess in the top of the
in the bottom of the transformer case where
they aresealed against oil leakage by well-known
2,4i1,858
ferrule 2| is ?lled with molten solder 82, while
the unit is held in theA upright position shown.
This solder likewise becomes fused to the ferrule
and to the metallized band 29 on the insulator
thereby affording an oil-proof seal at this sec
ond location. It should be noted that the ?llets
4
in a position to encircle the insulator. The diam
eters of these rings are such that they project
beyond the adjacent sharp edges 42 and 56 (Fig.
2) of the mentioned ?llets.
The coaxial bushing is pai'ticularly applicable
where two conductors, such as |3 and |8, both
3| and 32 of solder taper to sharp edges at 33
at high potential with respect to a case but at
and 34 at the boundaries between the metallized
low potential with respect to each other, .are to
bands and the adjacent insulator portion, i. e.,
be brought through the case.
where they merge with the outer surface of the 10
While the invention has been illustrated with
insulator. The thin edges of solder at the men
two conductors extending from within the case
tioned points tend to reduce the strain and there
6, through the insulator 38, it also includes an
_by reduce the danger of fracture of the porcelain
arrangement wherein but a single conductor ex
v insulator resulting from the unequal rate of ex
tends through the mentioned insulator. Also, the
pansion and contraction of porcelain and solder. 15 invention has been particularly described with
The part of the hollow conducting tube |8
reference to an oil-sealed device but it is equally
which extends from the ferrule to almost the
applicable to any fluid-sealed electrical device
lower end of the assembly, is enclosed by a sec
where the the lfluid may be air at any predeter
ond porcelain sleeve or insulator 3B, an asbestos
mined pressure, nitrogen or the like.
washer 31 being placed between .the upper end 20
The terms porcelain and ceramic, as used here
of the insulator and the under surface of the disc
in, are intended to include those materials pos
20. A band-like portion at the upper .part of the
sessing good insulating properties and having a
outer surface of the insulator as well as the top
vitreous surface.
edge and the entire inner surface of the insulator
What we claim is:
are provided with a continuous metallized ?lm of 25
1. A coaxial bushing for use with a ?uid-?lled
the character mentioned, as indicated at 38, 39
and 40. Molten solder 4| is used to ?ll the re
receptacle of an electricaldevice, said bushing
cess in the under 'part of the ferrule and to make
a fused joint between the ferrule and the metal
ductor extending through said hollow conductor
comprising a hollow conductor, a second con
in insulated relation thereto, each conductor ter
lized band 38. In this instance also, the solder 30 minating in an annular terminal, a hollow ce
is caused to thin out to a sharp edge 42 at its
ramic insulator enclosing one of said conductors
junction with porcelain insulator, for the reason
and spacing said terminals, band-like surface
given above. It should be mentioned that the
areas of said insulator encircling both end por
metallized layer at 39 and 40, which covers the
tions thereof being metallized, fused metal con-g
end and the inner surface of the insulator 36, 35 nections sealing each terminal to an adjacent
is conductively connected to the ferrule 2|
metallized band, a second ceramic insulator en
through the layer at 38 and' through the solder
closing said conductors, spaced band-like surface
in contact therewith. The construction `just de
areas of said second insulator encircling the same
scribed substantially eliminates any corona effect
being metallized, a fused metal connection seal
between the inner surface of the insulator 36 and 40 ing one of said metallized areas to the terminal
the adjacent parts.
›
of the hollow conductor, a metal ring encircling
The lower end of the insulator is engaged by
said last-mentioned insulator and adapted to 'be
an asbestos washer 43 through which the con
metal sealed to the margin of the wall of the
ductor tube |8 is inserted. An annular, metal ter
receptacle de?nin'g an opening therein, and a
minal 44 which snugly contacts 'the lower surface 45 fused metal connection sealing said ring to the
of .the asbestos washer 43, is soldered on the tube
remaining band-like metallized area of said sec
|8 as indicated at 45. An insulating collar 4B
ond in-sulator, certain of said metal connections
is next assembled over the lower end of the tube
having relatively thick portions tapering to thin
|8 as well as over the threaded portion of the
edges at the boundaries between the several met
stem |3 where a lock washer 41 and a nut 48 50
allized hands and the adjacent insulator portion.
tightly hold the .parts in assembled relation as
2|. A coaxial bushing for use with a ?uid-?lled
indicated. The washer 41| and nut 48 are dipped
into molten solder to provide soldered joints as
indicated at points 49 and 50.
Since .the bushing must make an oil-.tight seal
receptacle of an electrical device, said bushing
comprising a hollow conductor, a second con
ductor extending through said hollow conductor
in insulated relation thereto, each conductor ter
with the transformer casing, fprovision must be
minating in an annular terminal, a hollow ce
made to solder these parts together. To this end,
ramic insulator enclosing one of said conductors
the outer surface of the insulator sleeve is pro
and spacing said terminals, band-like surface
vided with a metallized band 52 at an interme
diate point thereon. To this band there is sealed 60 areas of said insulator encircling both end por
tions thereof being metallized, fused metal con
as by solder 53, the inner part of an inverted
nections sealing each terminal to an adjacent
channel-shaped ring or apron 54 which encircles
metallized band, a second' ceramic insulator en
the insulator. The outer edge of this apron is
closing said conductors, spaced band-like sur
soldered, as indicated at 55, to that portion of the
face areas of said second insulator encircling the
top of the transformer case 8 surroundingthe
same being metallized, a fused metal connection
opening therein.
sealing one of said metallized areas to the ter
It will be noted that the ?llet of solder 53 tapers
minal of the hollow conductor, a metal ring en
to a thin edge 58. This sharp edge is directed
circling said last-mentioned insulator and adapt
toward the sharp edge 42 of the ?llet of solder ß i.
to be metal sealed to the margin of the wall
With a great difference in potential lbetween the 70 ed
of the receptacle de?ning an opening therein, a
apron 54 and the ferrule 2 |, |the respective sharp
fused metal connection sealing said ring to the
edges 5B and 42 thereof would promotecorona
remaining band-like metallized area of said sec
discharge effects. In order to avoid such effects,
ond insulator, the fused connections related to
the ?llets of solder 4| and 53 have metal ríngs
said second insulator having relatively thick por
51, 51, of circular cross section, soldered thereto 75 tions tapering to thin edges directed toward each
2,411,e5e
5
other, and a ring of curved cross section individual
to each of said last-mentioned connections and
minal of the hollow conductor, a substantial por
tion of the inner surface of said second in
conductively connected thereto, said rings en
sulator being provided with an electrically con
circling said second insulator and projecting .'e
ducting coating conductively connected to the
yond the thin edges of their related connections. UI terminal of the hollow conductor, a metal ring
3. A coaxial bushing for use with a fluid-?lled
encircling said last-mentioned insulator and
receptacle of an electrical device, said bushing
adapted to be metal sealed to the margín of the
comprising a hollow conductor, a second con
wall of the receptacle de?ning an opening there
ductor extending through said hollow conductor
in, a fused metal connection sealing said ring to
in insulated relation thereto, each conductor ter 10 the remaining band-like metallized area of said
minating in an annular terminal, a hollow ce
second insulator, the fused connections related to
ramic insulator enclosing one of said conductors
said second insulator having relatively thick por
and spacing said terminals, band-like surface
tions tapering to thin edges directed toward each
areas of said insulator encircling both end por
other, and a ring of curved cross section in
tions thereof being metallized, fused metal con 15 dividual to each of said last-mentioned connec
nections sealing each terminal to an adjacent
tions and conductively connected thereto, said
metallized band, a second ceramic insulator en
rings encircling said second insulator and pro
closing said conductors, spaced band-like surface
jecting beyond the thín edges of their related con
areas of said second insulator encircling the
nections.
same being metallized, a fused metal connection 20
KENNE'I'H L. HENDERSON.
sealing one of said metallized areas to the ter
EDWARD F. DE MERS.
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