US 3860322 A
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.
Description (OCR text may contain errors)
United States Patent [1 Sankey et al.
[ Jan. 14, 1975 SEALED ELECTRICAL CONNECTOR  Inventors: Edward L. Sankey, New Berlin,
Wis; Thomas J. Holtgrieve, Warren,
 Assignee: RTE Corporation, Waukesha, Wis.
 Filed: May 3, 1974  Appl. No.: 466,881
Related U.S. Application Data  Continuation of Ser. No, 214,603, Jan. 3, 1972,
 U.S. Cl 339/111, 339/60 R, 339/61 R, 339/94 R  Int. Cl HOlr 13/52  Field of Search 339/111, 59 R, 60 R, 60 C, 339/61 R, 94 R, 94 C  References Cited UNITED STATES PATENTS 2,809,360 10/1957 Cobbett 339/111 3,277,424 10/1966 Nelson 339/94 R 3,376,541 4/1968 Link... 339/61 R 3,474,386 10/1969 Link 339/60 R Primary Examiner-Granville Y. Custer, Jr. Assistant Examiner-DeWalden W. Jones  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 arcextinguishing 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 arcextinguishing sleeve and the outer surface of the arcextinguishing follower.
6 Claims, 2 Drawing Figures SEALED ELECTRICAL CONNECTOR 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.
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., /z to inch for 8.3 kv.; to 1 inch for 15.2 kv.; 1 to 1% 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 to 1 cycle of current during the time it takes to move the conductive members through the prestrike distance.
DRA WINGS 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 conncctor, 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 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 arcextinguishing 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 are 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 US. Pat. No. 3,474,386. In regard to the present invention it should be understood that the heat of the are 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 poly mer 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 thus not contributing percent to a gaseous mixture. Due to the intense energy present during high energy arcing many other atoms and elements are present. Hydrogen though presentdoes 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 l6 and 22 on the plug and bushing.
In accordance with the invention, means are provided to confine the gases created by the heat of the are 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 are on interruption within the .pace between the arc follower 32 and are snuffer 42 are released, they will combine with the air to form a combustible mixture in the tapered recess in the plug. If these gases are ignited by the heat of the are, 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 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 5 in, the seal 48 will increase the dielectric strength ofthe 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 I0 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 IS 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 ofa 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 35 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 are snuffer also cooperate to confine gases within the bushing on interruption.
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 arcextinguishing 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 65 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 arcwithin 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.