U.S. patent number 3,860,322 [Application Number 05/466,881] was granted by the patent office on 1975-01-14 for sealed electrical connector.
This patent grant is currently assigned to RTE Corporation. Invention is credited to Thomas J. Holtgrieve, Edward L. Sankey.
United States Patent |
3,860,322 |
Sankey , et al. |
January 14, 1975 |
SEALED ELECTRICAL CONNECTOR
Abstract
A load break electrical connector including a plug and a
bushing, the plug having an electrically conductive probe and an
arc-extinguishing follower mounted on the end of the probe, the
bushing having an electrically conductive tubular contact and an
arc-extinguishing sleeve positioned at the end of the tubular
contact, a first seal mounted on the arc follower and a second seal
positioned adjacent the end of the tubular contact, the seals being
positioned to respectively sealingly engage the inner surface of
the arc-extinguishing sleeve and the outer surface of the
arc-extinguishing follower.
Inventors: |
Sankey; Edward L. (New Berlin,
WI), Holtgrieve; Thomas J. (Warren, OH) |
Assignee: |
RTE Corporation (Waukesha,
WI)
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Family
ID: |
26909168 |
Appl.
No.: |
05/466,881 |
Filed: |
May 3, 1974 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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214603 |
Jan 3, 1972 |
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Current U.S.
Class: |
439/184;
439/592 |
Current CPC
Class: |
H01R
13/53 (20130101) |
Current International
Class: |
H01R
13/53 (20060101); H01r 013/52 () |
Field of
Search: |
;339/111,59R,6R,6C,61R,94R,94C |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Custer, Jr.; Granville Y.
Assistant Examiner: Jones; DeWalden W.
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATION
This application is a continuation of U.S. Ser. No. 214,603, filed
Jan. 3, 1972, entitled "Sealed Electrical Connector," now
abandoned.
Claims
We claim:
1. A high voltage load break plug for a bushing having an
electrically conductive contact and an arc extinguishing sleeve on
the end of the contact, said plug having an electrically conductive
probe and an arc-extinguishing follower on the end of the probe,
the improvement comprising,
a resilient seal ring mounted on the follower and having an outer
diameter equal to or greater than the inner diameter of the sleeve
to sealingly engage the sleeve, said seal ring being located at the
end of the follower remote from the probe so that the products of
decomposition produced upon interruption are confined in the space
between the follower and the sleeve and within the bushing.
2. The plug according to claim 1 wherein said seal ring comprises a
first O-ring seal on the end of the follower.
3. A high voltage load break bushing for a plug having an
electrically conductive probe and an arc-extinguishing follower on
the end of the probe, the bushing having an electrically conductive
contact and an arc-extinguishing sleeve on the end of the contact,
the improvement comprising,
a resilient seal ring mounted within and adjacent to the open end
of said sleeve to sealingly engage said follower upon interruption
and having an inner diameter equal to or smaller than the outer
diameter of the follower to confine the gases produced by the heat
of the arc upon interrupton in the space within the bushing.
4. The bushing according to claim 3 wherein said seal ring
comprises an elastomeric cylindrical sleeve on the inner surface of
said sleeve.
5. The bushing according to claim 3 wherein said seal ring
comprises an elastomeric material covering the inner surface of
said sleeve.
6. The bushing according to claim 3 wherein said seal ring
comprises an O-ring.
Description
BACKGROUND OF THE INVENTION
In a safe break or load break connector of the type shown in U.S.
Pat. No. 3,474,386, entitled "Electrical Connector," the arc
created on separation is interrupted by the cooperation of an
arc-interrupting follower with a cylindrical type arc-interrupting
sleeve which are provided on the ends of the electrically
conductive members. It has been found that due to the inability to
obtain the desired quality of arc-interrupting material for the
follower and sleeve, a restrike arc can occur on interruption.
Restrike is believed to be aided by the distillation of the
arc-extinguishing material due to the heat of the arc resulting in
the production of a pressurized gas between the follower and
sleeve. These gases when mixed with air are combustible and if
ignited by the heat of the arc produce a highly-ionized atmosphere
between the live parts of the connector and the adjacent
electrically conductive parts of the distribution system.
On close in, prestrike will occur when the electrically conductive
members are a predetermined distance apart, i.e.,1/2 to 3/4 inch
for 8.3 kv.; 3/4 to 1 inch for 15.2 kv.; 1 to 11/2 inches for 21.2
kv. and so on. On prestrike, the pressure of the gas in the bushing
increases rapidly and must be vented in order to prevent rupture of
the bushing.
SUMMARY OF THE INVENTION
The electrical connector of the present invention is provided with
a first seal to confine or isolate the combustible gases created by
the heat of the arc on interruption within the bushing. These gases
are confined within the busing until the heat from the arc has
dropped sufficiently to prevent ignition of the combustible mixture
released from the bushing or the mechanical separation of the
bushing and elbow is far enough to prevent restrike. To minimize
prestrike a second seal is positioned to engage the arc follower
either over its full length or is positioned in close proximity to
the electrically conductive sleeve to increase the dielectric
breakdown strength of the creep path and thus decrease the length
of the prestrike arc. Normally on close in the conductive members
see 0 to 1 cycle of current during the time it takes to move the
conductive members through the prestrike distance.
DRAWINGS
FIG. 1 is a side view, partly in section, of the electrical
connector of this invention showing the location of the seals when
the connector is disconnected. FIG. 2 is a side view, in section,
of a portion of an electrical connector, showing alternate
embodiments of the seals.
DESCRIPTION OF THE INVENTION
An electrical connector of the type contemplated herein is shown in
FIG. 1 and generally includes a plug 10 and a bushing 12. The plug
10 is connected to a high voltage, shielded cable 14 and is
normally provided with a semi-conductive coating 16 on the outer
surface which is electrically connected to the semi-conductor 18 of
the cable 14. The bushing 12 is generally mounted on a housing for
an electrical device, and is electrically connected to the device
by a conductive element 20 located within the housing. The
electrical device can be a transformer located within the housing
or any other type of electrical device. The bushing 12 is provided
with an electrically-conductive shield 22 that is grounded through
the housing as is generally understood in the art. Electrical
termination between the cable 14 and the electrically conductive
element 20 is achieved by positioning the plug on the bushing and
inserting an electrically conductive member 24 into an electrically
conductive contact 26 in the bushing.
More particularly, the plug 10 includes a housing 28 having a
tapered opening 30 being formed from a dielectric material such as
rubber. The electrically conductive probe or member 24 extends
axially outwardly through the tapered opening 30 and is connected
to the cable conductor of the shielded cable 14. An arc follower or
rod 32 is provided on the outer end of the conductive member 24 and
is formed of an arc-extinguishing material such as Nylon.
The bushing 12 includes a housing 34 having an outer tapered
surface 36 which matingly engages the taperd opening 30 in the plug
10. The bushing 12 has a central bore 38. The electrically
conductive sleeve or contact 26 is positioned within the bore 38
and is connected to the conductive element 20 through a conductive
tube 40. A cylindrical arc snuffer or tube 42 is provided at the
end of the bore 38 in a position to cooperate with the
arc-extinguishing probe 32 to confine the arc produced on
interruption or close in to the space between probe 32 and the
sleeve 42.
The operation of an electrical connector of this type is fully
described in U.S. Pat. No. 3,474,386. In regard to the present
invention it should be understood that the heat of the arc produced
on interruption decomposes the arc extinguishing material into the
space between the probe 32 and the sleeve 42. The intense heat
generated by high energy arcing causes decomposition of polymeric
materials in close proximity to the arc. Materials such as epoxy,
acetals (Delrin), polyesters, silicones and fluorocarbons (Teflon)
fall into the polymer category. Decomposition of such polymers
begins with breakdown of polymer chains into monomers and pendent
side groups of much lower molecular weight, some of which are
volatile in themselves others continue to break down until
combustible. Silicone functions well under high energy arcing
because a portion of its monomer converts to SiO.sub.2 --thus not
contributing 100 percent to a gaseous mixture. Due to the intense
energy present during high energy arcing many other atoms and
elements are present. Hydrogen though present does not contribute
to combustible condition of the evolved gas mixture (at least in
quantity) nearly as much as the volatile monomers and/or by
products of their decomposition.
It has been found that these volatile gases are under pressure and
are forced out of the bore 38 of the bushing into the recess 30 in
the plug where they mix with air. When these gases combine with
air, a combustible mixture is formed which if ignited will blow
back along the sides of the bushing due to the configuration of the
tapered opening 30 in the plug. If these gases are ignited, a
highly-ionized atmosphere will exist both within the bushing and
along the outer surfaces of the bushing. This ionized atmosphere
provides an electrically conductive path between the live parts of
the connector and the electrically conductive ground shields 16 and
22 on the plug and bushing.
In accordance with the invention, meanw are provided to confine the
gases created by the heat of the arc on interruption within the
bushing, until the arc temperature has been reduced or the distance
between the conductive members has been increased sufficiently to
eliminate the possibility of ignition of the combustible mixture
which forms on release of the gases from the bushing. Such means is
in the form of an O-ring seal 46 on the probe 32 (FIG. 1) or an
O-ring seal 44 in the arc snuffer 42. Each of these seals will seal
the interior of the bushing from the atmosphere and confine the
gases within the bushing until interruption has been completed.
The O-ring seal 46 has an outer diameter slightly larger than the
inner diameter of the arc snuffer or sleeve 42 to sealingly engage
the inner surface of the sleeve on close in or interruption. The
O-ring seal 44 has an inner diameter slightly smaller than the
outer diameter of the follower 32. These seals can be made from
silicon rubber or other similar elastomeric materials such as Buna
N or Neoprene rubber. All of these materials are known to have
sufficient heat resistance not to crack or disintegrate when
exposed to the heat of an arc.
The critical point on current interruption occurs when the
conductive probe 24 clears the end of the arc snuffer 42. If the
gases which have been produced by the arc on interruption within
the .pace between the arc follower 32 and arc snuffer 42 are
released, they will combine with the air to form a combustible
mixture in the tapered recess 30 in the plug. If these gases are
ignited by the heat of the arc, a highly ionized atmosphere will
exist around the end of the bushing. Restrike can occur not only
between the live parts 24 and 26 of the system but also between the
live parts and the ground shields 16 and 22 provided on the plug
and bushing.
The gases are confined within the bore 38 of the bushing on
interruption, by means of the O-ring seal 46 provided in groove 47
in the end of the arc follower 32 or by the O-ring seal 44 in the
groove 45 in the sleeve 42. The gases in the bore 38 of the bushing
will not be released until the probe clears the end of the sleeve
42. By this time, the distance between the probe 24 and the
conductive sleeve 26 will be great enough to eliminate any
possibility of restrike.
In the embodiment of the invention shown in FIG. 2 an alternate
form of seal 50 is shown on the probe 32. The seal 50 is provided
in a groove 52 at the end of the probe 32 and is in the form of a
sleeve having a diagonal cut 54 to allow for expansion and
contraction of the sleeve 50. The sleeve 50 can be formed of
Delrin, Nylon or Teflon.
On close in, the prestrike distance is reduced by means of the seal
48 (FIG. 1) or the seal 60 (FIG. 2). The seal 48 is provided within
the bore 38 of the bushing 12 in close proximity to the end of the
conductive contact 26. The seal 48 can be made of the same material
as the O-ring seals 44 and 46, such as silicon rubber, Buna N or
Neoprene rubber. It should be understood, however, that the sleeve
seal 48 can also be made of other dielectric materials such as
Delrin, Teflon or Nylon.
The seal 48 has an inner diameter slightly smaller than the outer
diameter of the arc follower 32 to provide sealing engagement with
the probe 32 as the probe is pushed into the bore 38 of the bushing
12. On close in, the seal 48 will increase the dielectric strength
of the creep path between the conductive members 24 and 26 thus
reducing the prestrike distance minimizing the gases. These gases
created from the high current (up to 10,000 amps.) can cause
rupture of the bushing and flying parts. By shortening the
prestrike distance, the amount of gas is minimized because of the
shorter time to which the arc extinguishing materials are exposed
to the current.
On interruption, the seal 48 will cooperate with the seals 44 and
46 to confine the gases in the bushing until the probe 32 clears
the sleeve 42. In this regard, it should be noted that the O-ring
seal 46 on the probe 32 or 50 on follower 32 will continue to
confine the gases within the arc snuffer 42 until the probe 32
clears the end of the snuffer 42.
The seal 60 is formed on the inner surface of the sleeve 42 and is
in the form of a coating or insert which extends the full length of
the sleeve 42. The coating is molded on the inner surface of the
arc snuffer 42 and is made of a silicon, Buna N or Neoprene rubber.
The seal 60 is retained in the sleeve 42 by means of outwardly
extending flanges 62 which are embedded in the sleeve 42. It should
be noted that the seal 60 provides protection from both restrike on
interruption and prestrike on close in.
The bushing 12 is sealed on the inner end by means of a diaphragm
60 to prevent contamination of the bushing by air in the
transformer housing. This oil can enter the housing through the
flexible valve sleeve 62 and ports 64. The diaphragm should have
sufficient strength to resist normal interruption and close in
pressure and to break when subjected to explosive pressure.
RESUME
An electrical connector having a seal arrangement as shown in this
invention, provides good interruption of load current without
subsequent restrike between the inner contacts or to the exterior
ground shields. Seals are also arranged to minimize the creation of
gases on close in by reducing the prestrike distance. The seals on
the arc follower and arc snuffer also cooperate to confine gases
within the bushing on interruption.
* * * * *