Patented Dec. 8, 1942
2,304,334
UNITED STATESX PATENT OFFICE
2,304,334
RUSHING
Charles Philippe Boucher and Bertrand H. ll.
Noble, Paterson, N. I., aulgnors to Boucher In
l ventions, Ltd., Washington, D. C., a corporation
of Delaware
Application July 29, 1939, Serial No. 287,410
8 Claims. V(Cl. 174-153)
Our invention relates to high potential bush
breakage has been encountered. In some cases
ings and more particularly concerns such bush
the bushings are chipped in handling the equip
ings as may be used in connection with high po
tential electrical equipment, such as neon sign
ment.
transformers.
ment, as by being struck with a wrench. Break
age in such cases requires costly repairs because
the transformer must be torn down to remove
the broken part from the casing of the equip
ment, and then rebuilt with a new bushing in
One object of our invention, therefore, is the
provision of a simple, economical and eillcient
bushing assembly which is capable of withstand
ing high electrical potentials, which has great
mechanical strength, and which is well adapted
In others, they are chipped or broken
completely during the installation of theequip
place. Accordingly, an outstanding object of
to withstand the varying conditions of actual
our invention is the production of a highpoten
practical use.
tial bushing assembly which is sturdy and not
Another object is the provision of a compact
readily broken and in which external parts sub
ject to mistreatment readily may be replaced
which combines high internal dielectric strength 15 when broken-all at small cost and without the
with high resistance to external surface leakage,
necessity for tearing down the transformer.
which affords protection of parts expensive to
In heretofore known bushing assemblies em
replace, and which permits ready replacement
ploying a plurality of parts, it has been cus
of parts likely to be damaged in handling or in
tomary to employ a clip to secure the several
stalling the associated equipment.
20 parts of the assembly together. This construc
Another object is the provision of a high po
tion has been found to be not entirely satisfac
tential bushing assembly for electrical equip
tory, however, for the reason that no adequate
ment in which detrimental flash-over, and pos
and lasting seal between the bushing and the
sible destruction of insulation and damage to the
casing of the electrical equipment, upon which
equipment upon appearance of voltages in ex
the bushing is mounted, has been obtained. We
cess of rated voltages„is avoided in a simple,
attribute this to insuilicient pressure being ob
direct and fully reliable manner.
tained on the sealing gasket employed. An im
Other objects of our invention in part will
portant object of our invention, therefore, is to
be apparent and in part pointed out hereinafter.
‘ eliminate this disadvantage of known multi-part
The invention accordingly consists in the com
v bushing assemblies, and to provide a bushing as
bination of elements, features of construction,
sembly which is tightly and positively sealed to
and rugged high potential Abushing assembly
and arrangement of parts, all as described here
in, the scope of the application of which is in
dicated in the following claims.
In the drawing, the single figure is a longitudi
nal sectional view of a bushing assembly in ac
cordance with`our invention,
As conducive to a clearer understanding of cer
tain features of our invention, it may be noted at
the equipment casing on which it is mounted.
Referring now more particularly to the prac
tice of our invention, attention is directed to the
36 drawing illustrating one embodiment of our in
vention. An inner bushing member l is provided
which is formed of suitable material of high di
electric strength such as wet process porcelain.
'I'his possesses high mechanical strength. More
this point that in handling high potential elec
40 over, such wet process porcelain is found to have
trical equipment such as neon sign transformers,
an internal electrical resistance which is about
and especially in the installation and repair of
seventeen times that of, say, the comparatively
the same, a considerable breakage of bushings
inexpensive dry process porcelain. Thus, despite
has been encountered.
l
the greater cost of the wet process porcelain, we
It is customary practice to assemble neon sign 45 prefer to employ this material in the production
transformers, with their attendant enclosures
of the inner bushing member I, because it is so
and bushings, at. the place of manufacture, plac
located that it must withstand the greatest elec
ing the transformers in their enclosures, mount
trical stress, as well as the various mechanical
ing the bushings, and thereafter filling the en
stresses encountered in use. Of course it is with
closure with whatever insulated ñller or com 50 in the purview of our invention to substitute for
pound it is desired to employ. Thus theì trans
the wet process porcelain from which the inner
formers are shipped with their bushings in situ,
bushing member l is fashioned, some other suit
and upon delivery, it is necessary only to con
able insulating material, either plastic or other
nect the high tension terminal leads to the load.
wise, having the desired high dielectric qualities
The bushings are of porcelain and considerable 65 and required mechanical strength,
2
2,304,334
Bushing member I is so shaped as to have a
body portion 2 and a protruding extension 3.
of reducedv section, extending to the right as
seen in the drawing. While body portion 2 and
the protruding extension I may be formed of
any desired cross sectional shape, it is always
desirable in high potential practice to eliminate
wherever possible the occurrence of sharp bends
or corners, in order to avoid local concentration
the wall 4 and beyond the projecting extension
I, in a threaded portion I1. This bolt is con
nected at its head 1 to a conductor I3 from the
transformer or other high potential electrical
equipment housed within casing 4. Conductor Il
is secured to the head 1 in any suitable manner,
as by soldering, or by looping it under the head.
Bolt l is thus seen to conduct the high potential
current either into or out of the enclosure, as
of electro-static forces and attendant discharge. 10 desired, and at the same time, as will be more
Accordingly, we prefer to shape the cross-section
fully pointed out hereinafter, it is used to hold
of parts 2 and 3 along some continuous curve,
tightly together the several parts oi' the bushing
preferably making them circular. A 'I'he circular
cross-section, and hence cylindrical elongated
assembly to give a strong and rugged construc
tion suited to the varying conditions of actual
shape facilitates low manufacturing costs of 15 use.
these bushing assemblies. Ordinarily, in its
In order to protect bushing member I from
manufacture, the bushing member is turned to
breakage
and from weathering and the forma
desired size and shape.
tion of a conductive film along its surface, a cov
The bushing member I‘ is mounted interiorly
ering body I9 is provided. The body or outer
of the casing of the associated electrical equip 20 bushing member is recessed axially at 2l to re
ment with body part 2 abutting the inner surface
ceive the projecting extension of bushing mem
of casing wall 4. A shoulder 3 is provided at the
ber I with a fair degree of snugness. Convenient
junction of body portion 2 and extension I, and
ly, this recess 20 is continued as a bore 2I of
in practice, the bushing I passes by its extension
smaller diameter, to receive the bolt 5, the thread
I from the interior of the enclosure through an 25 ed end I‘I of which protrudes to the exterior
therebeyond. It will thus be seen that the cov
erably is of such size as to loosely receive the
ering body I9, when in its assembled position,
extension 3i Moreover, shoulder 9 is nicely ñtted,
lies axially with respect to the bushing member
to ensure intimate contact with the interior face
I. Moreover, it will be seen that it lies on the
of wall 4, and thereby effectively seal against 30 opposite side of the casing wall 4 from the body
leakage of the insulating compound with which
portion 2, and completely encloses the projecting
the casing may be filled.
`
extension 3.
A conducting bolt 5 passes centrally through
While the outer bushing member or covering
bushing member I, by way of the longitudinal
body I9 may be formed of any desired insulating
bore Ii provided in parts 2 and 3 of the said
material, it advantageously is shaped from an
bushing I for this purpose. Bolt 5 is provided
inexpensive material of low dielectric and me
with a head portion -I which is adapted to seat
chanical strength as compared with the wet proc
in a recess 8 in the bushing member body por
ess porcelain from which we prefer to form the
tion I. Bolt head and recess may be shaped to
inner bushing member. For example, as pointed
prevent twisting of the bolt within the bushing
out hereinbefore, it is desired that the inner
opening I0 in the wall 4. This opening pref
member.
.
y
The inner bushing member I serves to insulate
the casing against the high potential of the con
ducting bolt 5, and to this end, it is formed of the
bushing member of high dielectric strength be
protected from breaking and chipping in handling
and installation of the equipment by an outer
bushing member which lies entirely outside of the
material of high dielectric qualities previously 46 equipment casing and which is formed of inex
described. Moreover, it is formed of a material
having high mechanical strength because in ac
pensive material and of a shape which is con
ducive to low production costs. Moreover, it is
tual practical use it may be desired to lift or
unnecessary that this element have the high di
otherwise handle the transformer or other equip
electric strength of the inner bushing member I
ment by the bushing. The fit between the open 50 because the region of the conducting bolt 5 pass
ing ID and the projecting extension 3 is made
ing through the covering body I9 is so much
snug, to prevent dynamic shear resulting from
more remote from the casing wall 4 than in the
play between these two parts when the equipment
case of the inner bushing member. All that is
is lifted by means of the bushing.
required of the covering body I9 is that its sur
To ensure that bushing member I properly in 55 face be glazed, vitrifled, or in general, non-mois
sulates against the rated voltage of the equip
ture absorbing, and that its effective surface
ment, the surface path II, I2, I3, I4 is of such
length be suflicient to prevent surface leakage
length as to prevent high potential current leak
from bolt 5 to wall 4. In order to increase the
age from bolt 5 to the wall 4. That is to say,
effective length of surface, to the aforementioned
the recess 8 of bushing I is of such depth as to
end, the covering body is provided with suitable
ensure a leakage path of desired length. Fur
profile irregularities, such as the skirted por
thermore, the thickness through the body por
tion 22.
tion 2 is suiiicient to prevent rupture across the
Outer bushing member or covering body Il
bushing under the electrical stresses maintaining.
is recessed centrally as at 23, the recess termi
The length I5, I6 of the projecting extension 65 nating in a shoulder 24. This shoulder is pro
of the bushing member is designed so that at
vided to receive a washer 25, and a nut 25,
rated voltage no sparking occurs between bolt 5
threadedly engaging the threaded extension I'I
and the wall 4, either through the air or over
of bolt 5. Thus, when the nut is turned down on
the surface of the projecting extension. The an
bolt 5, the outer bushing member I9 is drawn
nular section of the projecting extension 3 is of 70 tightly against the wall 4 thru the action of wash
sufficient thickness to ensure against rupture
er 25. Interposed between the wall 4 and the
thereacross, either from electrical stresses, or
inner face of the outer bushing member, we pre
rough mechanical handling.
fer to insert a sealing gasket 21 of any suitable
The conducting bolt 5 extends axially through
material. This gasket is compressed when the
the bushing member I to the exterior, beyond 76 outer bushing member is drawn into place, and
3
2,304,334.
serves to prevent any moisture from entering
of our invention is directed to the utilization, if
the transformer enclosure, through breathing.
Moreover, this gasket also cushions the outer
bushing member I9 to prevent the latter from
cracking under local compressive strains.
The space 28 sealed off by the washer 25 and
gasket 21 and defined by bolt 5, outer bushing
member I9 and the projecting portion of inner
bushing 3, may be conveniently iilled with a vis
desired, of what we call a set-gap corona dis
is provided with a notch 29 in which is received,
when the bushing is assembled, one face of a
and so long as the excessive potential is present
charger. As shown in the drawing, this corona
discharger comprises opposed washers 38 and 39`
of conducting material mounted axially in the
assembly. Washer 38A is disposed about the base
of the projecting extension 3_ of the inner bushing
member and against the shoulder 9 of body por
tion 2. This washer has an outwardly extending
cous insulating material, such as a thick insu
flange 40 in electrical contact` with casing wall 4,
and an axially extending rim or ñange 4 I. Facing
lating varnish or wax, or an` insulating oil, to
make the bushing assembly air- and moisture
the washer 38 there is the washer 39 mounted about
tight. Whenever this insulating material is use_d
bolt 5, in electrical contact therewith, and seated
washer 25 is in the form of a steel lock-washer
on the extreme end of the projecting extension
which allows for the expansion and contraction là 3 of the inner bushing member. Washer 39 is
of the bushing assembly in use. In another em
provided with an axially turned peripheral flange
bodiment of our invention We fashion Washer 25
42. 'I'he iiange 4I of washer 38 and ilange 42 of
of senil-hard, pliable material, such as lead, which
washer 39 are directed towards each other, andyields and compresses under the pressure of the
together comprise the operating part of the corona
nut 26 and obstructs the space 28, so that the 20 discharger. The space between those two rims
insulating filler may be omitted, if desired.
constitutes the spark-gap of the discharger, and
To prevent the outer bushing member I9 from
this space will break down uniformly, in a brush
moving relative to casing wall 4, one of these ele
discharge, upon critical voltages being impressed
ments is provided with a notch and the other with
upon the equipment. The brush, or corona, dis
a cooperating protuberance. Conveniently, the 25 charge takes place between the washer 39, at high
wall contacting face of outer bushing member I9
potential, and the washer 38 at ground potential,
this uniform, tuft-like discharge continues, there
by precluding a disruptive spark discharge within
from the wall 4, a protuberance 30 conforms to 30 the equipment.
struck portion 21A in the gasket 2l. Extending
the other face of the struck portion 21A of the
gasket 21. In this simple manner the outer bush
ing member is protected against axial rotation.
A high-potential conductor (not shown) is con»
nected to our bushing assembly by way of bolt 5
and a second nut 3I threadedly engaging the bolt.
When desired, a washer 32 is used to separate nuts
25 and 3I in order to prevent a loosening of the
former in backing off the latter while changing
the high-potential conductor.
40
To facilitate corona discharge action, and for
general purposes of safety, the wall 4 or other part
of the transformer casing may be grounded, in
conventional manner, as shown at 43.
'
When a corona discharger is employed, it may
be desirable t'o normalize pressure conditions with
in the bushing assembly, and to this end, gases
stressed as by increased pressure resulting from
corona discharge may be vented, if desiredf'
through opening's 44 formed in the outer bushing
member I9. Where this expedient is adoptedfit of
object contacting the bolt 5 or the high-potential
course is necessary either to omit the’use of the
connection to the bolt, or Where there is possibility
seal of viscous insulating material for the space
of damage thereto, it is desirable to protect the
28, or `to confine the seal to the space between
end of the bolt, and the connecting end of the 4. Washers 25 and 39, and bolt 5 and outer bushing
member I9.
high-potential conductor, in some suitable man
ner. To this end, we provide a cover 33 of soft,
It will readily be seen, from a consideration of
the foregoing, that there is provided in our in
pliable material, such as rubber or a suitable plas
tic having the elastic qualities or characteristics
vention a bushing assembly in which the various
of rubber. One end, 34, of this cover protrudes ci C objects hereinbefore noted, together with many
Where there is any likelihood of a person or
in the manner of a cap, and this end is illustrated
as provided with a blind hole 35 which fits over
the end of bolt 5. We prefer to form the cover so
practical advantages,are fully achieved. Our new
bushing assembly is much more dependable than
the assemblies hitherto employed by those work
that it engages the bolt by tight friction fit. Once
ing in the art. 'I'he bushing assembly enjoys a
pressed into position, the cover 33 will remain in 55 combination of high dielectric strength with high
place. A notch 36 is provided near the inner end
resistance »to external surface leakage. It is
of the cover 33, to house snugly, and to permit the
strong and rugged in construction. 'I'he outer
passage therethrough, of the high potential cable.
bushing member, or covering body, protects the
projecting extension of the inner bushing member
It will be noted that at its inner end, the cover
member has outwardly ñaring or tapered, thinned 00 _from breakage or damage. Where the outer bush
knife-edges 31, also formed of the soft, pliable
ing member is chipped or otherwise damaged in
rubber or the like, to adapt the cover sensitively to
handling the equipment with which the bush
the contours of the outermost edge of the outer
ing is associated, it can be readily replaced with
out any necessity for opening the equipment clo
bushing member I9. Thus, when the cover 33 is
pressed onto the end of bolt 5, the knife-edges 65 sure, or impairing in any way the function of the
31 spread on the surface of the covering body' I9
same.
and provide a perfectly dust-proof and bug~proof
As many possible embodiments may be made of
seal. Moreover, this seal to a large extent pre
our invention, and as many changes may be made
vents corrosion or other deterioration of or dam
in the embodiment hereinbefore set forth, it will
70 be understood that all matter described herein, or
age to the bolt itself, or to the connection.
In many instances, it is desirable to prevent oc
shown in the accompanying drawing, is to be
currence of over-voltages, transient or otherwise,
interpreted as illustrative, and not in a limiting
from locally overstraining any part of the electri
sense.
We claim:
cal equipment or system with which our bush
ing assembly is associated. To this end, one phase Ans
1. A high potential bushing assembly, com
4
2,304,884
bining high internal dielectric strength with high
resistance to external surface leakage, and
adapted to be mounted on the casing of high
potential electrical equipment, said bushing as
sembly comprising, in combination, an elongated,
Wet process porcelain bushing member, having
a shoulder portion thereof and an axial bore ex
same substantially completely against the ex
terior, the open ene` of said cap having outwardly
haring edges which engage against the outermost
edge oi' said second bushing member, thus pro
viding a dust-prooi’ and bug-proof seal for the
cable connection.
4. A high potential bushing assembly, com
bining high internal dielectric strength with
tending therethrough and being adapted to bear
snugly against an inner surface ofthe casing of
high resistance to external surface leakage, and
the equipment and protrude exteriorly there 10 adapted to be mounted on the casing of high
through; a conducting terminal bolt for said
potential electrical equipment, said bushing as
equipment extending through said bushing mem
sembly comprising, in combination, an elongated
ber and protruding exteriorly in a threaded ex
bushing member of high dielectric and mechani
tension beyond the same; a dry, molded process
cal strengths having a shoulder portion thereof
porcelain second bushing member skirted to in 15 and an axial bore extending therethrough and
crease the effective path of surface leakage, hav
being adapted to bear snugly against an inner
ing an axial bore receiving said bolt and en
closing the protruding portion of said hrst
mentioned bushing member and adapted to bear
surface of the casing of the equipment and pro
trude exteriorly therethrough; a conducting ter
minal bolt for said equipment extending through
against an outer surface of said casing; and 20 said bushing member and protruding exteriorly
means engaging the threaded portion of said
in a threaded extension beyond the same; a sec
terminal bolt for maintaining said bushing mem
ond bushing member of high resistance to ex
bers in proper abutting relation to said equip
ternal surface leakage, having an axial bore re
ment casing.
ceiving said bolt and enclosing the protruding
2. A high potential bushing assembly, com 25 portion of said hrst-mentioned casing; means
bining high internal dielectric strength with
engaging the threaded portion of said terminal
high resistance to external surface leakage, said
bolt for maintaining said bushing members in
bushing assembly comprising, in combination, a
proper abutting relation to said equipment cas
wet process porcelain bushing member of high
ing; and corona discharge means for said equip
dielectric and mechanical strengths having an
ment comprising two opposed hanged washers,
elongated portion and having an axial bore ex
disposed coaxially on the protruding extension
tending therethrough, a conducting terminal bolt
of said mst-mentioned bushing member, with
extending through said bushing member and
hanged portions facing each other to determine
protruding exteriorly in an extension beyond the
the maximum potential for the equipment, one
same, a dry process porcelain bushing mem $5 said hanged washer being seated at the base oi'
ber of high resistance to external surface leak
the protruding extension of said member and in
age having an axial bore receiving said bolt and
electrical contact with the equipment casing, and
enclosing the Wet process porcelain bushing
the other being seated at the free end of the pro
member, means engaging the extending portion
truding extension and in electrical contact with
of said terminal bolt and maintaining said bush 40 said terminal bolt.
ing members in assembled relationship; means
5. A high potential bushing assembly, com
for securing a high-tension cable to the extension
bining high internal dielectric strength with high
of said bolt; and an insulating cover engaging
the free end of the bolt to close the same sub
resistance to external surface leakage, and
stantially completely against the exterior.
potential electrical equipment, said bushing as
sembly comprising, in combination, an elongated
bushing member of high dielectric and mechani
cal strengths having a shoulder portion thereof
and an axial bore extending therethrough and
being adapted to bear snugly against an inner
3. A high potential bushing assembly, com
bining high internal dielectric strength with high
resistance to external surface leakage,- and
adapted to be mounted on -the casing of high
potential electrical equipment, said bushing as
sembly comprising, in combination, an elongated,
wet process porcelain bushing member, having
a shoulder portion thereof and an axial bore ex
tending therethrough and being adapted to bear
adapted to be mounted on the casing of high
surface of the casing of the equipment and pro
trude exteriorly therethrough; a conducting ter
minal bolt for said equipment extending through
said bushing member and protruding exteriorly
snugly against an inner surface of the casing of 55 in a threaded extension beyond the same; a sec
ond bushing member of high resistance to ex
through; a conducting terminal bolt for said
ternal surface leakage, having an axial bore re
the equipment and protrude exteriorly there
equipment extending through said bushing mem
ceiving said bolt and enclosing the protruding
ber and protruding exteriorly in a threaded ex
tension beyond the same; a dry, molded process
porcelain second bushing member skirted to in
crease the effective path of surface leakage, hav
ing a recessed end-portion and an axial bore re
portion of said hrst-mentioned casing; means
engaging the threaded portion of said terminal
bolt for maintaining said bushing members in
proper abutting relation to said equipment cas
ing; corona discharge means for said equipment
ceiving said bolt and enclosing the protruding
comprising two opposed flanged washers, dis
portion of said first-mentioned bushing member 65 posed coaxially on the protruding extension of
and adapted to bear against an outer surface of
said first-mentioned bushing, with hanged por
said casing; means seated in the recessed end
tions facing each other to determine the maxi
portion of said second bushing member and en
mum potential for the equipment. one said
gaging the threaded portion of said terminal bolt
hanged washer being seated at the base oi' the
for maintaining said bushing members in proper 70 protruding extension of said member 'and in
abutting relation to said equipment casing;
electrical contact with the equipment casing,
means for securing a high tension cable to the
and the other being seated at the free end of
threaded extension of said bolt; and a cap of
the protruding extension and in electrical contact
soft, pliable insulating material engaging the free
with said terminal bolt; and means comprising
end of the bolt by tight frictional ht to close the 75 breathing holes in said second bushing member
2,304,334.
for relieving the pressure of expanding atmos
phere between the space of said first and second
bushing members during operation of said
corona discharge means.
~
6. A high potential bushing assembly, com
5
electric and mechanical strengths having a
shoulder portion thereof and an axial bore ex
tending therethrough and being adapted to bear
snugly against an inner surface of the casing
of the equipment with a portion protruding ex
teriorly therethrough; a conducting terminal bolt
bining high internal dielectric strength with
high resistance to external surface leakage, and
for said equipment extending through said bush
adapted to be mounted on the casing of high
ing member and protruding exteriorly in an ex
potential electrical equipment, said bushing as'
tension beyond the same; a dry process porce
sembly comprising, in combination, a Wet process y10 lain bushing member of high resistance to ex
porcelain bushing member of high internal di
ternal surface leakage, having an axial bore
electric and mechanical strengths having a
shoulder portion thereof and an axial bore ex
tending therethrough and being adapted to bear
snugly against an inner surface of the casing of
the equipment with a portion protruding ex
teriorly therethrough; a conducting terminal
bolt for said equipment extending through said
bushing member and protruding exteriorly be
yond the same; a dry process porcelain bushing 20
member of high resistance to external surface
sealed from the exterior receiving said bolt and
enclosing the protruding portion of said wet
process porcelain bushing member; means main
taining the said bushing members in assembled
relation, with the dry bushing member in locked
engagement with said equipment casing; and
an insulating cap engaging the free end of the
bolt to close the same substantially completely
against the exterior.
8. A high potential bushing assembly, com
leakage, having an axial bore sealed from the
bining high internal dielectric strength with high
exterior receiving said bolt and enclosing the
resistance to external surface leakage, compris
protruding portion of said wet process porcelain
ing, in combination, a Wet process porcelain
bushing member having an elongated portion
bushing lmember, and being in locked engage
ment with an outer portion of said equipment
and having an axial bore extending there
casing; and tightening means on said bolt for
through, a dry process porcelain bushing mem
maintaining said bushing members and casing
ber having an axial bore and receiving said
in abutting relationship.
elongated portion of said wet process porcelain
7. A high potential bushing assembly, com 30 bushing member, and axial conductor means
bining high internal dielectric strength with high
positioned within the bores of said bushing mem
resistance ,to external surface leakage, and
bers and maintaining the same in assembled
adapted to be mounted on the casing of high
relationship.
'
potential electrical equipment, said bushing as
sembly comprising in combination, a wet process
CHARLES PHILIPPE BOUCHER.
porcelain bushing member o1' high internal di
BERTRAND H. H. NOBLE.