Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to an improved pressure sensitive
lnterrupter for electrical capacitors and is an improvement
over the invention as disclosed in U.S. Patent No. 3,377,510
dated April 9, 1968, Rayno, assigned to the same assignee
as -the present invention.
In a typical capacitor, a capacitor roll section is
assembled .in a metal can having a metal cover sealed thereto.
Electrical capacitor leads pass from the capacitor roll
section in the can through the cover. In such a capacitor,
failures result from internal arcing and thermal runaway
cause a pressure build-up in the capacitor can. This
pressure build-up causes an outward bulging of the cover
to such an e~tent that the case or can rupture with the
result of fluid spillage Erom the can. Where the fluicl
in the capacitor is flammable, a potential fire hazard
results.
In the Rayno patent, there is disclosed a pressure
sensistive electrical circuit interrupter device combined
with an electrical capacitor. The Rayno device utilizes
the bulging action of the cover to flex a bridge member
which is supported independently of the cover under the
cover. The bridge member served as a local connection
for a terminal stud extending through the cover and
hridge member, and a -tab rising from the capacitor section
to join to the stud at the bridge member. Accordingly,
during the bulging of the cover the flexible bridge member,
by means of the terminal and tab connection, flexes the
bridge member until it is under sufficient flexing tension
to break the connection which connects the capacitor tab
to the terminal thereby interrupting the capacitor circuit
through the tab.
It is now desirable to have maximum assurance that the
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capacitor is electrically removed from the circuit. Since .
the Rayno device served only to break one capacitor tab
connection, the other tab remained connected to the
electrical circuit. Under these conditions it is possible
to have a short circuit from the capacitor tabs to the ~ :~
can with the attendant danger of remaking the capacitor
circuit through the can. On the other hand once the
capacitor has been removed from the circuit and begins to
cool the internal pressure in the capacitor can subsides
and the bulging cover may return towards its initial position.
Under these conditions an arc may be struck between the in-
terrupred connection in the capacitor tab and the capacitor
reenergized with attendant danger of arcing and fire hazards.
Accordingly, it is a principle object of this invention
to adapt the bulging cover concept of the Rayno device
to provide separation of a plurality o tabs or leads of
an electrical capacitor.
In the practice of one form of this invention, each
of a pai.r of spaced terminals of a two terminal capacitor
has an electrical stud which projects through an insulat- ,~
ing bridge member positioned at the underside of a cap-
acitor cover. The bridge member spans a pair of in-
dentations in the cover which serve as fulcrum points or
spaced supports for the bridge member. The pair of capacitor
terminal studs extend through the cover member and through
a pair of spaced apart apertures in the bridge member :
between the fulcrum points. The terminals are positioned
along a straight line joining the indentations and are
spaced on opposite sides of the center of the capacitor :~
cover. Tab leads from the capacitor section projection
upwardly to the underside of the bridge member adjacent
the apertures through which the terminal studs project.
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The tabs are joined by welding to -the terminals at the under-
side of the bridge member in such a manner that the tabs
are not free to pass through the aperture. When the cover
bulges due to an internal pressure build-up condition, the
terminals follows the movement of the cover and take up a
position significantly axially spaced from the capacitor
section in the can and slightly rotated with respect to the
capacitor can since they are on the slope of the cover.
At the same time a weld connection of the tab to the ter-
minal causes the bulging cover to flex the bridge memberin a direction to approximate the curve of the capacitor
cover. The stresses in the weld connection are greatly
increased because they must not only withstand the bu:Lg-
ing of the cover but also the rocking or the rotation oE
the terminals. At a predetermined point in the operation
this combined tension and rocking stress in the weld is
sufficient to cause the weld to rupture and the bridge
member then springs back into essentially a level position.
Consequently as the bridge springs back into its level or
unstressed position the space between -the tabs and the
studs are maintained in a wide position to provide safety
agains-t a remake of the circuit or a striking of an
arc. at the broken connection. At the same time both tabs
of the capacitor are broken and the capacitor is wholly
removed from the electrical circuit.
This invention will be better understood when taken
in connection wi-th the following description and the
drawings in which:
FIG. 1 is a prior art illustration of a single
terminal circuit interrupter of the Rayno patent.
Fig. 2 is a prior art illustratlon of a two terminal
capacitor of the Rayno paten-t in which only one terminal
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circuit is broken.
Fig. 3 is a side elevational view of a two terminal
circuit interrupter device of the present invention.
Fig. 4 is a plan view of a bridge member of the two
terminal interrupter device of Fig. 3.
Fig. 5 is an elevational view of a capacitor showing
the circuit interrupter device of Fig. 3 after it has
functioned.
Fig. 6 is a side elevational view of a three terminal
circuit interrupter device of the present invention.
Referring now to Figs. 1 through 3 there is shown an
electrical capacitor 1 which may be any of the various
types of capacitors utilized for fluorescent lighting
ballasts, motor start, motor run, and other such capacitors.
These capacitors may be either in a cvclindrical can con-
figuration, or as is more common at the moment, in an oval
or flattened can 2 configuration. A capacitor roll section !
3 is positioned within the can 2 and submerged in a die
electric liquid impregnant. A cover member 4 having ter-
minal assemblies 5 and 6 therein is sealed -to the casing 1. ~;
The terminals 5 and 6 are similar and a description of one
suffices for both. Each terminal assembly comprises a
bushing member 7 made of a resilient material such as
silicone rubber through which passes a conductive terminal
stud 8 electrically connected at its inner end to a cap-
acitor tab or lead such as tab 9. Prong connectors are
joined to the external extremity of the stud 8 for external
connec-tion to the capaci-tor.
In Fig. 1 the Rayno device was disclosed in connection
with the breaking of an electrical circuit at only one
terminal. Even with a two terminal design of Fig. 2 only
one terminal circuit was broken. A three terminal design
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would still retain the single circuit breaker concept. ~ne
problem was that the underside of the terminals were used as
supports on fulcrums, or, in a two terminal design, a dimple
support at the location of the absent terminal was used as
the fulcrum. Under these conditions the brea]cing of two
or three terminal circuits was not feasible. The present
invention involves the breaking of at least -two terminal
circuits because of the predetermined location of the ter-
minals and the use of an improved support of the bridge
member.
Referring now to Figs. 3 and 4 a bridge member 11 is
positioned adjacent the underside of the cover 4 and rests
against a pair of oppositely positioned inwardly projecting
supports oE fulcrum memhers 12. In addition each terminal
assembly is equidistently spaced from the center of the
capacitor or cover.
Referring now to Fig. 4 there is illustrated a plan ;
view of the bridge member 11 of the present invention.
Bridge member 11 is made up of an insulating material
for example a plastic material such as a phenolic resin
or a resin paper laminate. As illustrated, the bridge
member 11 is provided with a pair of spaced apertures 13
which lie directly under the terminals 5 and 6. Terminal
studs 8 project through the bridge member in a close but
loose fitting relationship with the apertures 13.
Referring again to Fig. 3 the tabs 9 from the capacitor
roll section 2 project upwardly and lie underside the
apertures 13 in the bridge member 11. At this point the
studs 8 which have hemispherical shaped ends are welded to
the tabs 9. The hemispherical ends provide a correct and
constant weld connection with minimal variation between
welds. As illustrated, the tabs 9 overlie the apertures
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13 and are thus prevented from being drawn through the
apertures 13 in conjunction with the ordinary tensions
which are expected to take place.
The operation of this device progresses from Figs. 3
to Fig. 5. Starting from the Fig. 3 device, upon over-pressure
conditions in Can 2 there is a pressure build--up which
causes -the cover 4 to commence bulging outwardly. As cover
4 commences bulging, the fulcrums 12 which engage the bridge
11 also begin to move outwardly but at a much lower rate
and over less distance than the terminal assemblies 5 and 6.
Consequently the bridge member 11 is being pulled or flexed
upwardly by the terminal members 5 and 6 while the ends
thereof are being restrained by the fulcrums 12. As the
cover member 11 continues to move outwardly, the termlnals
5 and 6 which are spaced from the center of the capacitor .
can also begin to rotate or rock slightly to follow the
curvature of the cover. The attachment of the terminal
studs 8 to the tabs 9 take place through a narrowly con-
fining aperture 13. Accordingly the rocking action of
the terminal may also add a bending or shear stress in the
weld connect.ion to accentuate the breaking of the con-
nection. The rapid separation o~ breaking of the connection
is facilitated by the use of a weld connection instead of
a soldered connection.
The flexibility of the bridge member 11 also con-
tributes to the rapid separation of the con-tacts. For
exampler a very stiff bridge member may lend sufficient
restraining support to the cover so that a breaking of
each of the contacts may not take place. Also, a low
flexibility bridge member may provide a separation of the
contacts so quickly -that there will be no maximum separation
of the contact members after the breakage occurs. In the
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alternative i the bridge member is too flexible, the contacts
will remain unbroken at the maximum bulging of the cover or so
n~ar that point that the capacitor can may still rupture. With
the terminals placed off center as in this in~ention, the distance
of travel of a terminal on a bulging cover is limited, compared
with the distance of travel of a terminal in the center of a
bulging cover. By placing the terminals equicListantly off center
and correlating the ~eld connections with the flexibility of the
bridge, a quick break and maximum separation at both connection~
L0 can be provided.
It has also been discovered that this invention is
applicable to break the leads for three terminals as well as for
two terminals without any additional design criteria. With the
three terminal conEiguration as illustrated in Fig~ 6, terminal
1~ is positioned in the center o the cover, and terminals 5 and
6 are positioned equidistantly on opposite sides of the center.
Under these conditions, when the co~er 4 bulges, the central
terminal 14 is the one that rises first and progresses through
the greatest distance. The central terminal 14 will then have
flexed the bridge sufficiently to break the center tab connection
before the tab connections break at the outer terminals. However,
when the tab connection of the central terminal 14 breaks, the
entire flexing stress must then be carried by the tab connections
of the two outer terminals 5 and 6. This additional stress placed
on the two outer tab connections causes them to break substantially
simultaneously. Accordingly, it can be seen that the same design
criteria and thé same flexing s~resses involved, in the two
terminal capacitor can be utilized to break the connections in a
three terminal capacitor. In the breakage sequence for the
three terminal capacitor, however, breaking of the tab for
the central terminal occurs first, followed by nearly
simultaneous breaking of the tabs for the two outer terminals.
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36CA-3432
In one preferred form of this invention~ the capacitor
has an oval cross-section, with the length of the cover being
about 2.75 inches and the width of the cover being about 1.75
inches. The cover and the case may be made of either steel or
aluminum. With steel the thickness is from about 0.012 to
about 0.016 inch, and with aluminum it is frorn about 0~020 to
about 0.025 inch. The bridge member is a phenolic resin strip
about 2.5 inches in length, about 0.8 inch in width and from
about 0.060 to about 0.064 inch thick. The fulcrum mer~ers
are located close to the outer extremity of the cover and project
downwardly about 0.08 inch. ;
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